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FACULTY OF SCIENCE
THESIS
SUBMITTED
TO THE SCHOOL OF GRADUATE STUDIES
OF LAVAL UNIVERSITY
for the
DEGREE OF DOCTOR OF SCIENCE
by
JOSE DOMINGO MEDINA', L.Ch.
ALKALOIDS OF VENEZUELAN APOCYNACEAE
June, 1968
To my wife
Ill
TABLE OF CONTENTS
CONTENTS . .
ACKNOWLEDGEMENTS
LIST OF FIGURES
INTRODUCTION .
Page
iii
iv
v
1
Chapter I : A. Alkaloids of A. excelsum ....
B. Alkaloids of A. cuspa ......
Chapter II : Alkaloids of A. fendleri ......
Chapter III : Alkaloids of T. psychotrifolia . . .
EXPERIMENTAL ..................
General remarks ..............
Chapter I : A. Alkaloids of A. excelsum .
B. Alkaloids of A. cuspa . . .
Chapter II : Alkaloids of A. fendleri . . .
Chapter III : Alkaloids of T. psychotrifolia
9
17
. 46
. 60
. 91
. 92
94
. 98
. Ill
. 118
. 133
REFERENCES 137
IV
■ 'ACKNOWTVBUGEMENTS
I wish to express my profound gratitude to Professor R.H. Burnell for
his continuous encouragement through the duration of this investigation. His
role as scientific tutor was always most important for the achievement of
this work.
I am very much indebted to the Instituto de Investigacion.es Cientificas
CIVIC) of Caracas, Venezuela, who provided the necessary financial help in
the form of an Overseas Scholarship.
I sincerely thank Dr. W.A. Ayer of the Chemistry Department of the
University of Alberta for his cooperation in the performance of HR-100 nuclear
magnetic resonance and mass spectra in the early stages of this work.
I like to express my appreciation to my colleagues of the Organic
Chemistry Laboratories for their cooperation and helpful attitude during the
period spent on this investigation.
I wish to thank Mme M. Veilleux for accepting to undertake the task
of typing this thesis and for the excellent performance of it.
Thanks are due to the National Research Council of Canada for the help
provided in the form of Research Grants.
V
Figure
Figure
Figure
Figure
Figure
Figure
Figure
Figure
Figure
Figure
Figure
Figure
Figure
Figure
Figure
Figure
Figure
Figure
Figure
Figure
Figure
Figure
Figure
Figure
1 = "
2.-
3. -
4. -
5. -
6. -
7. -
8. -
9. -
10. -
11.-
12.-
13. -
14. -
15. -
16. -
17. -
18. -
19. -
20. -
21.-
22.-23. -
24. -
LIST OF FIGURES
Page
Nuclear magnetic resonance spectrum of yohimbine ...... 11
Mass spectrum of yohimbine ................ 13
Nuclear magnetic resonance spectrum of 0-acetylyohimbine . . 15
Interconversions of aspidodasycarpine derivatives ..... 24
Mass spectrum of des-O-methylaspidocarpine ......... 31
Nuclear magnetic resonance spectrum of diacetyl-des-O-methyl- asp ldo carp me 33
Mass spectrometric fragmentation of des-O-methylaspido-carp me .......................... 36
Mass spectrum of pyridine XXIX ............... 38
Mass spectrometric fragmentation of pyridine XXIX ..... 44
Nuclear magnetic resonance spectrum of fendleridine .... 48
Mass spectrum of fendleridine ............... 50
Nuclear magnetic resonance spectrum of fendlerine ..... 52
Mass spectrum of fendlerine ................ 54
Nuclear magnetic resonance spectrum of aspidofendlerine . » 58
Nuclear magnetic resonance spectrum and spin decoupling experiments on taberpsychine ................ 63
Mass spectrum of taberpsychine ............... 65
Nuclear magnetic resonance spectrum and decoupling experiments on dihydrotaberpsychine-methine ........... 67
Nuclear magnetic resonance spectrum of taberpsychine-methine . 72
Mass spectrum of taberpsychidine .............. 78
Nuclear magnetic resonance spectrum of dihydrotaberpsychidine 81
Mass spectrometric fragmentation of dihydrotaberpsychidine . 82
Mass spectrometric fragmentation of taberpsychidine .... 85
Mass spectrum of 16-epi-vobasinic acid ........... 86
Mass spectrometric fragmentation of 16-epi-vobasinic acid . 88
INTRODUCTION
The study of indole alkaloids offers not only very interesting
chemical problems but also the possibility that the isolated materials
have a certain therapeutical value.
The extensive work done in recent years on Apocynaceae species has
proved them to be an excellent source of this type of alkaloid^.
These considerations and the relatively easy access to the abundant
Venezuelan flora, prompted us to start the examination of the different
species of this family found in Venezuela. To date five species have been
2 3 5examined, namely Aspidosperma vargasi , A. fendleri , A. cuspa , A. excel
sum ^ and Tabemaemontana psychotrifolia^ „
7Indole alkaloids have been isolated as early as 1841 when Goebel
obtained harmaline (1) from Peganum harmala L. (Rutaceae), but a really
explosive development occured in the last twenty years with the exploitation
of powerful physical methods such as nuclear magnetic resonance and mass
spectrometry.
1
2
The structures of indole alkaloids range from the bare indole itself
8 9(II), isolated from the flowers of many Jasminium and Citrus species, to
very complex polycyclic "dimers" such as Pleiomutine"*"** (III), obtained from
Pleiocarpa mutica"*""*".
IV
To give an idea of the power of nuclear magnetic resonance and mass
spectrometry in the study of the structures of alkaloids, we have chosen
as an example aspidospermine (IV) which embodies a particular pentacyclic
12skeleton characteristic of a well represented group of natural bases
Although nuclear magnetic resonance was only partly responsible for
the structure determination of aspidospermine and the mass spectrum of the
alkaloid was only measured after the structure was known, both physical
methods have had great application in the subsequent investigations of
3
related alkaloids.
The nuclear magnetic resonance spectrum helps to deduce the pattern
of the aromatic substitution from the absorption between 6.6 and 7.35,
especially when the data are compared with those obtained from the ultra
violet spectrum since the latter changes a great deal depending on the
13substitution on the indolic residue . Of the non-aromatic protons in
aspidospermine, the one found at lowest field is the hydrogen atom at C.2
which appears as a quartet centered at 4.0-4.56. The absence of this peak
is indicative of substitution at C.2 and this provides very useful infor
mation for the recognition of alkaloids such as aspidofractinine (V) where
C.2 is included in a sixth ring. In alkaloids where the C.2 proton is
absent but a carbomethoxy group is present at C.3, as for example refractine
(VI), a one proton quartet is observed at approximately 3.86 due to the
*hydrogen atom at C.3. The four protons adjacent to the basic nitrogen (at
positions 8 and 10) absorb in the region 2.9-3.36 and in all the alkaloids
As a convention, the nitrogen atom in the indolic residue (which as in aromatic amines has very little or no basicity at all) is referred to as Na and the second nitrogen atom present in the molecule is referred to as the basic nitrogen or N^.
4
of the aspidospermine type form what has been called the "finger print"
of the skeleton"*"^ ’ , a pattern which is not obscured by other absorption
and is profoundly altered in the spectrum of related hexacyclic bases.
The isolated proton at C.19 produces a singlet between 2.2 and 2.56
which in the case of alkaloids bearing an N&-acetyl group is sometimes
hidden under the absorption of the COCH^ but its presence can be deduced
from careful integration.
In addition to the absorptions mentioned, one finds frequently in the
aspidospermine group intense singlets at 3.75-3.906 due to the presence of
aromatic methoxyl groups and at 2.206 for the methyl groups of N-acetyl
residues. In the case of N-propionyl compounds a quartet can be observed
at 2.3-2.86 due to the protons of the methylene group which overlaps a little
with the absorption for the C.19 proton in 60-mc spectra. The methyl of the
propionyl group produces a triplet centered at approximately 1.256. There
is no possibility of confusion with the absorption for the terminal methyl
of the C-ethyl side chain, since the latter produces two principal peaks
centered at 0.656 separated by 5-6 cps. The absence of this absorption is
indicative of a substituent on the terminal carbon of the C-ethyl side chain
and this can be either an oxygenated function at C.21 as in the cases of
cylindrocarpine (VII) and limaspermine (VIII), or the. fact that C.20 and
C.21 are part of a sixth ring as in refractine (VI) or aspidoalbine (IX).
Other groups that can be recognized by means of the nuclear magnetic
resonance spectrum include phenolic hydroxyls whose presence can also be
observed by the change in the ultraviolet spectrum taken in neutral and then
in basic solution. Phenolic hydroxyls appear in this series generally at
5
position 17 where hydrogen bounding with the carbonyls of N-acyl groups is
possible, and in these cases the peaks for the OH protons appear at 10.7-
11.2Ô. When hydrogen bonding is absent, the absorption for the OH proton
is not at such low field, for example the hydroxyl at 0.16 in spegazzin-
idine (X) absorbs at 5.846.
The three proton singlet due to the methyl of a carbomethoxy function
appears in the region 3.55 to 3.706 at slightly higher field than those for
aromatic methoxyls. In some alkaloids of this group one finds a singlet at
about 9.56 due to the proton of an N-formyl residue.
6
The use of nuclear magnetic resonance spectrometry mainly for the
determination of the nature of peripheral groups has as its ideal comple
ment mass spectrometry, which gives direct information about the skeletal
structure. In some cases complete elucidation of a structure has been
possible by determining the mass spectrum using less than one milligram
of material; thus it was possible to investigate successfully some minor
bases of Aspidosperma which were present in quantities too small to permit
even elementary analysis'^.
In the mass spectrometer, the molecule is cleaved by electron impact
and those fragments which are sufficiently stable and which carry a positive
charge are collected following the order of their molecular weights . The
ions bearing a double charge appear at m/2 where m represents the molecular
weight. The information that can be derived from the pattern of the rela
tive intensities of peaks plotted against m/e (e representing the charge of
17the ion) can be divided in three parts .
First, the peak at highest molecular weight is generally"*^ that of the
molecular ion, this is the complete molecule with a single charge produced by
extrusion of one electron from the unshared pair of the basic nitrogen by
electron impact. This peak is referred to as M4" and is accompanied by smaller
peaks one and two units higher corresponding to molecular ions containing
heavier isotopes of nitrogen, hydrogen and carbon. Thus with the molecular
weight precisely determined the molecular formula is derived leaving no doubt
as to the correct number of hydrogen atoms present. Although this was also
possible by integration of the nuclear magnetic resonance spectrum, the quan
tity required for the mass spectral method is minute in comparison.
7
Second, it is possible to classify an unknown alkaloid within a struc
tural class provided that other alkaloids with the same skeleton are known.
The cleavage of the molecule is independent of many peripheral substituents.
In the aspidospermine group, it has been found that these include hydroxyls
or methoxyls on the aromatic ring, oxygenated functions in the C-ethyl side
chain, either at C.20 or at C.21, carbomethoxy or other one carbon groups
and hydroxyls at position 3, and carbonyl groups at C.4. Thus, the character
istic fragmentation pattern of aspidospermine can be recognized in all alka
loids containing the same skeleton, with the only differences being that the
peaks corresponding to the fragments containing extra substituents are dis
placed to higher molecular weight, in a number of units equal to the molecular
weight of the substituent, while alkaloids not containing the methoxyl group
present in aspidospermine exhibit a pattern for the aromatic fragments at
correspondingly lower molecular weight.
Third and most important, direct structural information can be obtained.
It is often possible, especially when the method is used in conjuction with
NMR and deuterium labelling, to determine the exact location of substituents
and establish the nature of new skeletons without in many cases any extensive
chemical degradation. The importance of this is observed mainly in the case
of alkaloids that do not lend themselves to facile degradation by classical
methods„
The investigation of new plants in search of alkaloids is by nature an
unpredictable venture and the results fall into three different categories.
First of all, the extraction could yield only bases which have been described
previously and which are more or less readily identified by their physical
8
constants and spectral data. This was the outcome of the investigation of
the alkaloids of Aspidosperma excelsum and Aspidosperma cuspa, presented
in Chapter I.
Some investigations present the case where the isolated alkaloids are
previously unknown but their structures can be recognized by non-destructive
spectral methods and the bases may be readily related to known compounds
through minor structural modifications. An illustration of this eventuality
is found in the study of the bases obtained from Aspidosperma fendleri as
described in Chapter II„
Finally, some plants yield new alkaloids which despite the powerful
physical methods available resist structure elucidation until a suitable
chemical degradation is performed. This was the case with the major alka
loid from Tabemaemontana psychotrifolia, where the presence of an oxide ring
of a type not encountered previously impeded the interpretation of both
spectral and chemical results for a long while. It was again nuclear magne
tic resonance spectrometry and in particular the use of spin-spin decoupling
techniques on a Hofmann degradation product which finally provided the neces
sary clue, allowing an un-ambiguous structure to be proposed for the alkaloid
(Chapter III),
-CHAPTER I. -
A. ALKALOIDS OF ASPIDOSPERMA EXCELSUM,-
10
Seeds and bark of the gigantic Venezuelan tree, Aspidosperma excelsum
IQ ^Benth. , were collected near Canaima , and both parts of the plant yielded
two known alkaloids in quantity.
The major constituent of the extracted crude base, a crystalline com
pound ^22^26^2^3' Presents an ultraviolet spectrum typical of unsubstituted
20indoles . Its infrared spectrum shows the presence of the indolic imino
group as well as that of a hydroxyl, an ester carbonyl and the Bohlmann
21bands typical of trans-quinolizidines.
From the nuclear magnetic resonance spectrum (Figure 1) it was possible
to determine that the carbonyl is that of a methyl ester (3 H singlet 3.786)
and the hydroxyl group is a secondary one (only 1 H adjacent to oxygen, broad
singlet 4.226). Assembling of this data permits an approach to the structure
as presented by (i).
- OH
Cj, H(, N
COOCHj
l
* In the Southern-Venezuelan jungle.
é values 5 2,
Figure 1.- Nuclear magnetic resonance spectrum of yohimbine
12
The mass spectrum of the base shows the molecular ion at 354 m/e (thus
confirming the elemental analysis), as well as an M-59 peak corresponding to
the expulsion of the ester residue and other peaks identical with those ob
served in the fragmentation of yohimbine-type alkaloids.
That the fragmentation observed in the mass spectrometer (Figure 2)
22was identical with that published for yohimbine must be interpreted with
caution since in this group of alkaloids the stereochemistry only influences
the fragmentation to a negligible extent. However, other characterizing phy-
20sical properties and the constancy of the melting point of the isolated base
when mixed with an authentic sample of yohimbine (XI) confirmed the identity
thus establishing the structure of the base.
OH
XI
The specific rotation and optical rotatory dispersion of the isolated
base showed that it is indeed yohimbine and not one of its several possible
naturally occuring stereoisomers.
relative intensity
N-H
M - CO, CH.
Figure 2.- Mass spectrum of yohimbine
14
The second base isolated from A. excelsum was obtained as the hydro
chloride by cooling and concentrating the chloroform obtained during the
separation of neutral materials from the crude alkaloid-containing extract.
This solubility of hydrochlorides in chloroform, while at first surprising,
is frequently encountered and provides a direct and efficient method of
separating particular bases from mixtures.
The alkaloid, , is also a member of the indole alkaloids,
as was demonstrated by its ultraviolet spectrum. Its infrared spectrum shows
the presence of the indolic NH, an ester group (1730 cm-1) and an 0-acetyl
(1725 and 1250 cm-1).
The nuclear magnetic resonance spectrum (Figure 3) confirms the presence
of the indolic imino group (1 H singlet 7.876) and of four aromatic protons
(multiplet 7.00-7.608). It also identifies the ester as being a methyl ester
(3 H singlet 3.696) and the 0-acetyl as being secondary (only one H adjacent
to oxygen, multiplet 5.476).
All the spectral data for this base suggested its close relation to
yohimbine, except for the presence of the 0-acetyl residue. Hydrolysis of
the acetate function under acidic conditions known not to affect the methyl
ester grouping, gave a crystalline solid identical in all respects with
yohimbine.
The naturally occuring alkaloid, which was formulated as O-acetyl-
yohimbine, (XII), was prepared by acetylation of yohimbine, thus confirming
the structure.
7
CHjOOC
OAc
I4 6 VALUES
Figure 3Nuclear magnetic resonance spectrum of 0-acetylyohimbine
2, \
16
O COCK
XII
This represents the first recorded isolation of O-acetylyohimbine from
natural sources, and since the base was obtained in the extraction before
any potential acetylating agents had been in contact with the material, the
probability of its being artifactual is minimal.
Later work performed on the mother liquors of the extracts led to the
4 23isolation of excelsinine (10-methoxycorynanthine) (XIII) and ct-yohimbine
(XIV).
CI-LOOC
XIII XIV
-CHAPTER I. -
B. ALKALOIDS OF ASPIDOSPERMA CUSPA.-
18
24Aspidospema cuspa is found in the coastal regions of Venezuela
close to Caracas, as a large shrub in contrast to the enormous trees which
characterize the species A. fendleri and particularly A. excelsum which are
2included in this study and A. vargasi which has also been examined in this
survey of Venezuelan plants. The crude alkaloids were obtained from the
aerial bark by a routine mild extraction procedure and separated by counter-
current distribution. Four relatively stable alkaloids were isolated and
characterized in this manner and all four were previously described but origi
nating from other species of Aspidosperma. A fifth base was isolated by
preparative paper chromatography on the crude mixture and a structure is pro
posed even though the lack of sufficient material did not allow a complete
structure proof.
The major base of A. cuspa, ^22^26^2^4’ Presents ultraviolet spectrum
typical of the unsubstituted dihydroindole type of alkaloid. Its infrared
spectrum shows the presence of the aromatic portion and of the indolic imino
group, as well as a hydroxyl, another NH group and a rather complicated car
bonyl absorption (3 bands at 1750, 1735 and 1720 cm-1) which was the origin
of some confusion but it was demonstrated later as being due to an ester car
bonyl (1750 cm-1). The two other accompanying bands are probably due to
25Fermi resonance or to hydrogen bonded species.
The nuclear magnetic resonance spectrum identifies the ester grouping
as a methyl ester (3 H singlet 3.766). An important feature in the spectrum
is a quartet for one olefinic proton (5.526, J=6.5 cps) coupled to a three pro
ton doublet of doublets (1.766, J=6.5 and 2 cps) which is indicative of an
19
ethylidene side chain. The nature of one of the oxygen functions remained
unknown and by analogy with many other Aspidosperma alkaloids it was assumed
to be ethereal.
With this data, the partial structure (ii) could be advanced for the
base.
-COOCH3
xd
H
— ON
H 1%, ~ N H
W
CH%
11
Pyrolysis of the base in vacuum in the presence of zinc powder pro
duced 3-ethylpyridine as the major volatile product as shown by direct vapor
phase chromatographical comparison and by the nuclear magnetic resonance
spectrum of the principal volatile fraction. This pyridine, or more speci
fically the corresponding pyridinium ion, is also observed as the base peak
in the mass spectrum of the A. cuspa alkaloid (108 m/e). A much smaller quan
tity of 3- or 4-methylpyridine was formed in the zinc pyrolysis but the yield
was too low to obtain a clear nuclear magnetic resonance spectrum and unfor
tunately the retention times of the two methyl-pyridines differ by too little
to be conclusive.
This major alkaloid has now been shown to be aspidodasycarpine
20
which appears in the literature in a preliminary communication^. Original
ly, this identification was considered and rejected due to an ostensibly
different melting point of the 0,N-diacetyl derivative (XVI) as described in
the literature (m.p. 110°) and that obtained from the plant (irup, 175°). How
ever, the constancy of the melting point of our aspidodasycarpine when mixed
with an authentic sample*, superposable infrared spectra and identical thin
layer chromatography results conclusively showed the A. cuspa base to be
aspidodasycarpine.
HOCH.
Our original uncertainty led us to prepare other derivatives, thinking
perhaps a structure elucidation would be necessary.
As suggested above, normal acetylation of aspidodasycarpine affords
the 0,N-diacetyl derivative (XVI) but the neutral N-acetyl derivative (XVII)
was prepared by carefully reacting the base with one mole of acetic anhydride
in pyridine at low temperature and the same product (XVII) was obtained by
We thank Dr. C. Djerassi for providing an authentic sample of aspidodasycarpine.
hydrolysis of the 0,N-diacetyl derivative (XVI) in dry methanol containing
a small amount of sulfuric acid.
21
Catalytic reduction of aspidodasycarpine in ethanol containing acetic
acid gave rise to a dihydro compound (XVIII) in which the exocyclic double
bond is reduced. The configuration of the newly formed asymétrie centre is
assumed to be as shown in XVIII with the C-ethyl residue cis to the ester
bearing bridge since examination of models reveals considerable hindrance
to the approach of a hydrogen bearing catalyst from the same side of the
molecule as the bridge. The nuclear magnetic resonance spectrum of the di
hydro derivative confirms the saturation of the double bond since the peaks
of the ethylidene residue in aspidodasycarpine (1 H quartet 5.526, J=6„5 cps
and 3 H doublet of doublets 1.76, J=6.5 and 2 cps) are no longer observed
and a resonance for a saturated methyl group is now found at 1.06 (doublet
J-6 cps).
Acetylation of the dihydro base (XVIII) afforded the expected 0,N-
diacetyldihydro derivative (XIX) which proved to be a remarkably insoluble
but clearly crystalline substance. The latter could also be prepared by
hydrogenation of 0,N-diacetylaspidodasycarpine (XVI).
HOCH COOCH
XVIII
R<*OCH. COOCH
Hydrolysis of the diacetyldihydro compound (XIX) using the conditions
described above which avoid the hydrolysis of the methyl ester group, led
to N-acetyldihydroaspidodasycarpine (XX) which again was more readily pre
pared by partial acetylation of the dihydro base (XVIII), Catalytic reduc
tion of N-acetylaspidodasycarpine (XVII) also afforded the N-acetyldihydro
compound XX.
HOCH COOCH HOCH COOCH
1 mole Aco0
XVIII XX
23
The spectral characteristics of these various acetyl derivatives are in
agreement with their- proposed functionality (see Experimental). These inter
conversions can be summarized as shown in Figure 4.
The carbinolamine ether structure of aspidodasycarpine suggests that
in acid solution the five-membered ethereal ring should open, affording the
indolenium structure XXI„
HOCH GOOCH
Indeed Djerassi used this protonated form of the alkaloid to explain
the degradation products isolated following reduction with zinc in hydro
chloric acid^„ We felt it would be of interest to characterize the in-
dolenine, the acetyl derivative of which we found to be readily obtained by
acetylation of dihydroaspidodasycarpine (XVIII), or its acetyl derivatives
XIX and XX, in acetic anhydride containing small quantities of concentrated
sulfuric acid. The product (XXII) absorbs in the ultraviolet spectrum at
222 and 261 my reflecting the expected change in chromophore and the infra
red and nuclear magnetic resonance spectra now show the absence of the in-
doline NH moiety. All attempts to hydrogenate the indolenine double bond
met with failure, however reduction with sodium borohydride afforded N-acetyl-
24
GOOCH.HOCH.
HOCK COOCH AcOO-L, GOOCH
COOCHHOCH
COOCHHOCH. GOOCH
XVIII
XXII
Figure 4.- a) 1 mole acetic anhydride in pyridine, 5°; b) Acetic
anhydride-pyridine ; c) Sulfuric acid-methanol ; d) PtC^, Hg, EtOH, HOAc
e) Acetic anhydride-sulfuric acid; f) NaBH^ - methanol.
25
dihydroaspidodasycarpine (XX) showing that the ethereal ring is very readily
re-established (Figure 4).
flcOCH COOCH
XXII
The mass spectra of aspidodasycarpine (XV), the dihydro base (XVIII)
and the indolenine (XXII) deserve some comment although no detailed analysis
of the fragmentations will be presented due to the lack of suitable deuter-
ated substrates «
Fragmentation of aspidodasycarpine is characterized by an intense peak
at 108 m/e presumably arising from the ethylpyridinium ion a. The only other
peak of comparable intensity is at 14 mass units lower„ The dihydro deriva
tive (XVIII) also shows a tendency to produce similar stable ions but as ex
pected the base peak is now at 110 m/e (b) with a much smaller peak at 108
m/e (a). Relatively pronounced peaks also appear at 130 and 144 m/e (from
the indole moiety).
The indolenine (XXII) also shows the dihydropyridinium ion (b) but as
a relatively weak peak while the major fragments arise from the loss of the
various oxygenated groupings and side chains = The cleavage of the acetyl
26
groups (as ketene) and the ester function is reflected by the M-42 and M-59
peaks respectively but the most intense peak by far arises from the expulsion
of -CHg-O-CO-CH^. The other alkyl chain -CH^-CH^-O-CO-CH^ is also extruded
as judged by the significant peak at M-87. One other intense peak at 385 m/e
(M-113) is postulated as arising from rupture of the piperidine ring and
release of the C-ethyl residue and carbon atoms C.20 and C.21 with the nitro
gen atom and the accompanying acetyl residue (heavy lines in XXII)„
HI
a (108 m/e) b (110 m/e)
The second alkaloid obtained from A. cuspa analysed for CgiHL.NJO.
and also belongs to the unsubstituted dihydroindole group of alkaloids
(Xmax 233 (10,000) and 283 (3,700) mp) and its ultraviolet spectrum changes
ostensibly when taken using 70% perchloric acid as solvent 274.5
and 302 mp). This is typical for carbinolamine-ethers due to rupture of the
27ether with formation of a quaternary indolenium ion „
The infrared spectrum confirms the presence of the indolic imino group
and the aromatic residue, and reveals the presence of an ester grouping (1747
cm-1) and a hydroxyl (3550 cm-1). In this case, as opposed to aspidodasy-
carpine, the basic nitrogen seems to be tertiary.
27
The nuclear magnetic resonance spectrum provides information which in
time proved to be decisive for the assignment of structure. A three proton
singlet at 3,606 serves to identify the ester residue as a methyl ester and
a four proton multiplet (centered at 7.066) accompanied by a one proton
singlet at 5.166 account for the dihydroindole residue. A quartet (5.386,
J=7.5 cps) ascribed to an olefinic proton coupled to a doublet for three
protons (1,566, J=7.5 cps) indicates the presence of an ethylidene side chain.
A very important feature is a doublet for one proton at 4.756 (J=2.5 cps),
which considering the extent of deshielding should be adjacent to both oxygen
and nitrogen.
This information is summarized in the partial structure (iii) :
IH
Cc, N
COOCH-
OH
KCH„
in
The mass spectrometric fragmentation corroborates the analytical fi
gures (M+=368). Other peaks are those at 350 (M-18), 337 (M-31) and 239
(M-129) m/e.
All the evidence obtained on this base pointed to a known alkaloid,
des-acetylpicraline (XXIII), first isolated by Britten et al. from Picralima
28
HOCH GOOCH,
N
H
XXIII
Of great help in the characterization of the base is the absorption
in the nuclear magnetic resonance spectrum at 4,755 mentioned earlier but
now attribuable to the lone proton at C.5 which is flanked on one side by
the more basic nitrogen atom and on the other side by the ethereal oxygen
atom. The infrared and ultraviolet spectra are in agreement with those
given in the literature and a mixed melting point with an authentic sample*
showed no depression, thus confirming the identity.
The third alkaloid obtained from A. cuspa belongs to a different group
of Aspidosperma bases and this was evident at an early stage. Absorption in
the ultraviolet spectrum showed the aromatic portion of the molecule to be a
hydroxylated N-acyl indoline. The N-acyl carbonyl group which produces an
intense peak at 1635 .cm-1 in the infrared spectrum is presumably strongly
We thank Dr. W.I. Taylor for kindly providing an authentic sample of des-acetylpicraline.
29
hydrogen bonded and the spectrum also shows an unbonded hydroxyl at 3360 cm-1.
Despite many attempts to dry the sample a peak of variable intensity at 1715
cm-1 persisted in the infrared spectrum. This peak was felt to be due to
acetone of crystallization and this was indeed shown to be the case by analy
sis and mass spectral determination of the molecular weight. Elemental analy
sis of the base although somewhat variable had indicated after several deter
minations a molecular formula of (mol.wt. 414) but the mass spectrum
showed the molecular ion to be at 356 m/e corresponding to
difference between the two formulae being essentially the elements of acetone*.
The possibility of a facile fragmentation in the mass spectrometer could not
be ruled out so the nuclear magnetic resonance spectrum was examined and the
expected peak arising from the methyl groups of a molecule of acetone was
observed at 2.145. The sample was evaporated to dryness and redissolved in
deuterioacetone and then taken to dryness again. This procedure was repeated
twice and the nuclear magnetic resonance spectrum which was then taken re
vealed the absence of the 2.145 peak. Other features of the nuclear magnetic
resonance spectrum included absorption arising from a saturated C-methyl
grouping which gave a doublet at 0.75 (J=6 cps), an N-acetyl three proton
singlet at 2.255, a complex pattern around 2.805 reminiscent of that con
sidered diagnostic of the aspidospermine skeleton^, a quartet centered at
4.005 also observed in aspidospermine type bases (C-H adjacent to the in-
do line nitrogen atom), a single peak at 6.365 integrating for two aromatic
protons and finally a low field singlet at 10.855 attributed to the chelated
phenolic hydroxyl group, The latter disappeared from the spectrum on shaking
* The formula was obtained by analysis after several weeks
of drying - see Experimental.
30
with deuterium oxide.
All the evidence accumulated was consistent with the formulation of this
base as a dihydroxy-N-acetyl derivative of aspidospermidine (XXIV) and the
mass spectral fragmentation (Figure 5) was typical for this type of skeleton.
H
XXIV
The loss of a fragment of mass 28 (ethylene) is now well established as the
first step in the fragmentation of aspidospermine derivatives and the peak
at M-43 is in keeping with the presence of an acetyl residue. The principal
indole ions appear at 190, 176 and 162 m/e as opposed to 144 and 130 m/e
in alkaloids bearing no substituents in the indoline moiety which confirms
the placing of the two hydroxyls groups in the aromatic ring. The remainder
of the molecule gives rise to significant peaks at 152 and 138 m/e with by
far the most intense peak at 124 m/e. These three peaks and especially the
29latter are found in the spectra of all bases embodying this skeleton . To
fully describe the structure of the alkaloid the substitution pattern on
the aromatic moiety needed clarification. The confusion arising from the
apparent singlet for the two aromatic protons in the nuclear magnetic reso
nance spectrum of the base was cleared up by acetylating the two phenolic
relative intensity
Kl-0-9M-28 M
3X
_____L___ 17->
_lL_350
!300 250 m/e
Figure 5„~ Mass spectrum of des-O-methylaspidocarpine
190
200
04
32
hydroxyls with acetic anhydride in pyridine and the spectrum of the acetate
showed not only the signal for two acetate residues but also a clear AB quar
tet for the aromatic protons (6.99 and 6.886, J=8.5 cps) (Figure 6).
This limits the possible structures for the base to XXV and XXVI,
XXV XXVI
The problem of assignment of structure was solved by methylating the
base by prolonged treatment with diazomethane. The dimethyl derivative
30obtained (XXVII) is known by the name of pyrifolidine and direct compari
son with an authentic sample* proved the identity. In this way the struc
ture for the base is established as being as shown in formula XXV which
is in fact O-des-methylaspidocarpine, The latter has been prepared from
31aspidocarpine and isolated later from A. album as one of the very minor
, 32bases
In the light of this structure the mass spectral fragmentation shown
We thank Dr. C. Djerassi for kindly providing an authentic sample of pyrifolidine.
? 4 3 é VALUES %
Figure 6Nuclear magnetic resonance spectrum of diacetyl-des-O-methylaspidocarpine
w
34
in Figure 7 explains all the principal peaks observed.
CI-LO
XXVII
A fourth alkaloid isolated from A. cuspa is a very minor constituent
obtained from a countercurrent distribution of the weaker bases. Its ultra
violet spectrum (Xmax 230 and 282 my) is that of an unsubstituted dihydro-
indole and suffers a bathochromic shift when measured in concentrated acid
solution 240, 247 and 315 my). This shift is characteristic ofÏÏlcLX.
27carbinolamine ethers ~ where rupture affords indo lenium ions.
The infrared spectrum confirms the presence of the indolic imino group
and shows the presence of a very strong carbonyl peak at 1745 cm-1 accompanied
by a strong band at 1240 cm-1 attributed to an 0-acetyl group. The oversized
carbonyl peak could be due to the presence of another ester-type carbonyl in
the molecule, whose absorption falls in the same region as that of the 0-ace-
tyl group.
The mass spectrum of the base is very similar to that of des-acetyl-
picraline (XXIII) except for the molecular ion peak which appears at 410 m/e
35
(42 units up from that of des-acetylpicraline). On the basis of its mass
spectrometric fragmentation the structure of this alkaloid has been proposed
as XXVIII which is that of picraline, first isolated by Thomas from Picra-
33lima klaineana .
GOOCH.
XXVIII
In effect the fragmentation of our base in the mass spectrometer is
identical to that given in the literature for picraline^. The extremely
small quantity of alkaloid obtained did not permit a more extensive confir
mation of this speculation.
A fifth product was obtained from the crude mixture of bases by pre
parative paper chromatography. This base gives a green colour with Vassler's
35reagent (which made its isolation very easy to follow) and is present in
the plant in very small quantities. Whatman paper N° 31 (double thick, 3 mm)
was used and the crude mixture applied in 30 spots per sheet of paper. After
the chromatogram had been developed (solvent: pyridine-ethyl acetate-water,
2.3 : 7.5 : 1.65)^ one strip was cut off the border and sprayed with
Vassler's reagent. The sheet was then divided horizontally following the
36
152, 138
Figure 7Mass spectrométrie fragmentation of des-O-methylaspidocarpine
37
distribution shown by the reagent. The band containing the green spot was
eluted with ethanol and then the solvent evaporated to dryness. The residue
was sublimed and the alkaloid obtained as low melting white crystals.
The ultraviolet spectrum C^mæc 255 and 262 my) is typical of a simple
pyridine and in keeping with this observation the infrared spectrum shows
only typical pyridine peaks (1600 and 1565 cm-1) and aromaticity (725 cm-1).
The mass spectrum of the compound (Figure 8) shows the molecular ion
peak at 149 m/e, which being an odd number indicates that the compound must
contain at least one nitrogen atom. The base peak (very intense) appeared
at 120 m/e.
Before following the discussion, we must point out that since the
amount of material obtained was very small, neither nuclear magnetic reso
nance spectrum nor elemental analysis were performed on this compound and
the speculation below is based on the limited information available, es
pecially on the mass spectrometric fragmentation very particular of pyri-
dines.
The data from the ultraviolet and infrared spectra point to a pyridine
and the mass spectrum definitely confirms this with the appearance of a peak
accounting for the loss of HCN (27 units; see Figure 8 : from 106 to 79 m/e)
which is only found in nitrogen containing hetero-aromatic compounds, Since
the molecular ion peak appears at 149 m/e and all the evidence excludes the
presence of oxygenated groups in the molecule (the presence of an ethereal
moiety would lead to structures that could not possibly account for the frag
mentation observed), this pyridine must have substituents accounting for five
100-
Figure 8,- Mass spectrum of pyridine XXIX
04CO
extra carbon atoms. These conditions could be met by several pyridines but,
on the basis of the mass spectrum, structures XXIX and XXX are favored.
39
XXIX
The placing of a side chain of at least three carbon atoms (in line)
37in the 3-position is in keeping with the view that in pyridine the electron
density is relatively high at the 3(5)-position but low at the 2(6)- and 4-
positions, thus making more stable the carbonium ions formed adjacent to the
ring at the 3(5)-position. In our case, by far the most favored fragment is
that at 120 m/e (M-29) which can be obtained from either one of the possible
structures by loss of and formation of carbonium ions such as (iv) and
(vi) which are stabilized as explained above and by ring expansion to give
the respective aza-tropilium ions (v) and (vii). \
Separate observations in the mass spectra of 4-propylpyridine and 2-
ethylpyridine show clearly that the ions formed in those cases by loss of
.C2H5 and .OHL respectively (affording viii and ix) are very much less stable
(as judged by the peak intensity) than that obtained in the case of 3-ethyl-
pyridine by loss of .CH_ (x).
40
For the location of the other substituent on the ring, several consi
derations have been taken in account. First of all, the already mentioned
loss of HCN from the molecule is a clear indication that at least one of the
positions adjacent to the nitrogen must be free. Furthermore, if one consi
ders the case with propyl and ethyl substituents (pyridine XXIX), the ethyl
41
chain could not be located in a position adjacent to the nitrogen since the
mass spectrum of a model compound (i.e. 2-ethylpyridine) shows that the M-15
peak is insignificant, while in our mass spectrum the M-15 (134 m/e) is a
fair-sized peak. Neither could it be in the 3(5)-position, in which case
the M-15 would be bigger than it appears in the spectrum of the unknown ma
terial .
Considering a sec-butyl and methyl substitution (as in pyridine XXX)
the case is not so clear cut since the M-15 peak could be produced by loss
of .CHj from the sec-butyl chain producing a well stabilized ion.
However, pyridine XXIX appears to be the more favoured if one considers
the biogenetic point of view. It is now well accepted that the Woodward
38fission unit (xi) is the biogenetic precursor (together with tryptamine)
of a great number of indole alkaloids. This fission unit has been explained
as derived from a polyacetate chain and the ringed carbon atoms in (xi) repre
sent those derived from the carbonyl groups.
©
I
I I
^© C
xi
©
i i
©"^© c
XI1
Later developments led to the discovery that the Woodward fission unit
is probably derived from a condensed chain of three acetate units and one
39malonate unit (xii) . This new aspect made it applicable to an even greater
number of indole alkaloids. For illustration we can use two apparently very
different alkaloids, vobasine (XXXI) and yohimbine (XXXII) where the strong
lines indicate the acetate-malonate chain.
42
COOCH
XXXI
CI-LOOC
XXXII
In the case of vobasine, one of the carboxyl groups of the malonate
residue has been lost leaving the fragment as the original tetraacetate unit.
In both structures the extra atom marked (B) is the so called berberine bridge,
present in all the alkaloids showing the "cryptic" unit and explained by
Robinson^ as originating from formaldehyde or its biochemical equivalent.
Comparing the tri-acetate-malonate unit (xii) with the fragment from
which pyridine XXIX (xiii) might originate one observes that in fragment
(xiii) the acetate and malonate units are arranged in a different fashion.
xiiiXll
43
However, this does not invalidate the hypothesis since, for example in
vincadifformine (XXXIII), a fragment (xiv) with a different arrangement is
observed ^1.
XXXIII xiv
Regarding pyridine XXIX as the possible structure, the mass spectro-
42metric fragmentation shown in Figure 9 accounts for all the important peaks
in the mass spectrum.
Here then, we have presented a series of facts consistent with struc
ture XXIX for the pyridine in discussion but, by no means intended to be pre
sented as categorical proof of the structure of this minor alkaloid of A.
cuspa.
XXIX
44
Figure 9-- Mass spectrométrie fragmentation of pyridine XXIX
45
The possible biogenetical importance of this compound has rendered it
more interesting than originally anticipated but further research is neces
sarily delayed until fresh plant material becomes available and a new quan
tity of the pyridine is obtained.
-.CHAPTER "II.-
ALKALOIDS OF ASPIDOSPERMA FENDLERI
47
Extraction of the seeds of A. fendleri Woodson^ yielded four alkaloids,
of which fendlerine, is the most abundant ; this alkaloid is also
found in large quantities in the trunk and root bark.
Fendleridine, is the simplest of the bases present and, on
the basis of its ultraviolet spectrum, belongs to the unsubstituted dihydro
indole group of alkaloids.
The infrared spectrum reveals peaks characterizing the dihydroindole
imino group and the aromatic ring but gives no information concerning the
nature of the oxygen atom, which is probably ethereal.
The nuclear magnetic resonance spectrum (Figure 10) confirms the pre
sence of four aromatic protons (multiplet 6.55 to 7.505), but absorption typi
cal of olefinic protons and of methyl groupings of any sort is absent. A two
proton quartet (centered at 3.985), which has also been observed in other di
hydro indo lie Aspidosperma alkaloids, has been shown to be characteristic of
the -O-CHg- grouping as found in aspidoalbine^ (XXXIVA) and aspidolimidine^
(XXXV).
CH,0
XXXIV A R=H, RicCOCHgCHg
XXXIV B R=CH3, Ri=H XXXV
IH
Figure 10.- Nuclear magnetic resonance spectrum' of fendleridine
00
49
This region of the nuclear magnetic resonance spectrum of fendleri-
dine is strikingly similar to that of O-methyl-N-despropionylaspidoaTbine
(XXXIVB), except for the methoxyl bands in the latter^. A plausible struc
ture for fendleridine is that shown by XXXVI ; this is supported by the mass
spectrometric fragmentation pattern (Figure 11).
XXXVI
In the mass spectrum, confirmation of the analytical figures was shown
by the molecular ion peak at 296 m/e; the typical aspidospermine type M-28
47 48peak ’ (a in Figure 11) arising from the loss of ethylene is also present.
Rupture of the C.10-C.11 bond (at x in a) gives rise to fragment b, which is
responsible for the most intense peak at 138 m/e. This fragment has also
been observed in the fragmentation of aspidoalbine^ (XXXIV) and aspidoli-
midine^ (XXXV). The indolic portion of the molecule gives rise to weaker
peaks at 144 m/e (rupture at y) and 130 m/e (rupture at x). The other sig
nificant peaks in the mass spectrum arise from expulsion of the oxide bridge
(intense peak at 252 m/e) and subsequent fragmentation as described above.
The analogy with aspidoalbine (XXXIV), aspidolimidine (XXXV) and haplo-
cine^g (XXXVII), and the other spectral evidence confirms the structure of
fendleridine (XXXVI) which is then the simplest representative of this hexa-
Figure 11.- Mass spectrum of fendleridine
180 140 IOO
51
cyclic type of Aspidosperma alkaloid.
CH3
XXXVII
The major base present in A. fendleri which we named fendlerine,
^23^30^2^4’ s^ows ultraviolet absorption attributable to a phenolic N-acyl-
dihydroindole and, as expected, the spectrum changes in basic solution.
The infrared spectrum confirms the presence of the N-acyl residue (in
tense band 1635 cm-1), which is presumably strongly hydrogen bonded to the
phenolic hydroxyl since the amide peak is at longer wavelength than expected
for the simple N-acyl dihydroindole system^5^ and virtually no absorption
is observed in the hydroxyl stretching region.
From the nuclear magnetic resonance spectrum (Figure 12) the N-acyl
grouping was shown to be a propionyl residue (triplet and quartet centered
at 1.246 and 2.536 respectively); this was confirmed by acidic hydrolysis
of fendlerine and vapor phase chromatography of the volatile acid. Only
propionic acid was detected. A one proton peak at 12.426 confirms the sus
picion that the phenolic hydroxyl is hydrogen bonded with the N-acyl residue.
The partial structure (xv) can then be written for the alkaloid.
4 3 <f VALUES
Figure 12,- Nuclear magnetic resonance spectrum of fendlerine
Ln
53
NOH
xv
Other peaks in the nuclear magnetic resonance spectrum include a quartet
for two aromatic protons (centered at 6.896) and one methoxyl residue (singlet
3.846). Since from spectral evidence the nature of one of the oxygen func
tions remained obscure, the probability that fendlerine contained an ethereal
moiety (other than the methoxyl) was a tempting assumption. This hypothesis
was to some extent strengthened by the appearance of a peak in the hydroxyl
region of the infrared spectrum of the product obtained by hydrogenating the
base over platinum on charcoal. The partial structure can then be extended
to (xvi).
Under the conditions employed, most of the peaks in the mass spectrum
of fendlerine (Figure 13) were of low intensity, but the most important peak
was at 138 m/e (fragment b, Figure 11) as in the case of fendleridine (XXXVI).
The analytical figures are confirmed by the molecular ion peak at 398
m/e; other peaks of importance are those associated with the loss of the N-
propionyl residue. The most prominent indolic fragment gives rise to a peak
at 161 m/e which can only be related to a dihydroxy derivative of fragment c
(Figure 11), and this serves to localize the methoxyl residue on the aromatic
relative intensity
COCHCH
%
3
325
50 -
3?0
338342
~T—350
ilL300400 m/e
Figure 15Mass spectrum of fendlerine
/38
â
no
too
Ul4*»
55
ring of the indole moiety.
OH 'O^CH^CHg
~ H (arom.)
N— OCH^
xvi
At this point, two structures (XXXVIII and XXXIX] are plausible for
fendlerine since the nuclear magnetic resonance spectrum indicates that the
two aromatic protons must be ortho to one another (quartet 6.896, J=8 cps).
Both structures are in all respects compatible with the spectral data of
fendlerine.
The location of the methoxyl residue was determined by conversion of
the base into aspidolimidine (XXXV). Acid hydrolysis of fendlerine gave the
des-N-propionyl derivative, which could not be crystallized but which was
acetylated with acetyl chloride in pyridine. The product, a mixture of the
N-acetyl and 0,N-diacetyl derivatives, was hydrolyzed in methanolic sodium
hydroxide under nitrogen to give the pure aspidolimidine (XXXV). That the
structure XXXVIII represents fendlerine is thus un-equivocally established.
Since the number of bases with this same hexacyclic skeleton is in
creasing, it would seem logical to name them as derivatives of the simplest
member. Preference is given to the name aspidoalbidine, which has already
52been used to describe this system . Thus fendlerine is N-propionyl-16-
methoxy-17-hydroxyaspidoalbidine (XXXVIII).
56
Ct-LO
CH, O
ch3 ch3
XXXVIII XXIX
The small amount of a high melting base, aspidofendlerine (m.p. 278°
(decomp.) was easily purified by fractional sublimation; analysis indicated
the molecular formula ^21^26^04* The ultraviolet spectrum is similar to
that of fendlerine (XXVIII), and changes in ethanol containing alkali and in
the presence of buffered boric acid, the latter suggesting the presence of
31a catechol residue
The infrared spectrum shows the presence of hydroxyl and N-acyl func
tions.
Peaks in the nuclear magnetic resonance spectrum (Figure 14) are inter
preted as showing that aspidofendlerine contains both bonded and unbonded
phenolic hydroxyl groups (singlets 11.06 and 5.795 respectively), two adja
cent aromatic protons (quartet centered at 6.845), and an N-acetyl residue
(singlet 2.305).
In this case, there was again one of the oxygen functions whose nature
remained unknown and as in the other examples it was assumed to be ethereal.
This supposition was justified since the mass spectrum of the base gave peaks
57
of extremely low intensity with the exception of the dominant peak at 138 m/e
(fragment b in Figure 11), showing that this base is also of the fendleridine
(XXXVI) skeletal type.
On a small scale, aspidofendlerine, assumed to be N-acetyl-16,17-di-
hydroxyaspidoalbidine (XL), was treated with diazomethane ; aspidol imidine
(XXXV) was isolated as the major product, thus confirming the structure.
XL
The fourth base obtained from the extraction appears to be unrelated
to the three already described. Absorption in the ultraviolet is similar to
that of a dihydroindole, and the infrared spectrum suggests the presence of
an ester residue. The mass spectrum is unlike that of a member of the hexa-
cyclic aspidoalbidine series.
Alkaloids of the trunk bark of Aspidosperma fendleri Woodson.-
Extraction and isolation of the alkaloids of the trunk bark yielded
almost exclusively fendlerine accompanied by smaller amounts of aspido-
limidine and fendleridine.
Alkaloids of the root bark of Aspidosperma fendleri Woodson.-
Extraction of the root bark has yielded, apart from large quantities
T“ / 3à values
Figure l4e- Nuclear magnetic resonance spectrum of aspi^ofendlerine
inCO
59
of fendlerine and aspidolimidine, three minor alkaloids, none of which seems
to be related to the aspidoalbidine type of alkaloids and, to date, their
structures remain unknown and will be discussed elsewhere.
-.CHAPTER III.-
ALKÀLOIDS OF TABERNAEMONTANA PSYCHOTRIFOLIA
61
The extraction of the alkaloids of Tabernaemontana (Ervatamia) Psycho-
trifolia H.B.K.* yielded four principal alkaloids but the abundance of the
major base taberpsychine, and the fact that it could not be readi
ly placed in a "skeletal" group by mass spectrometry made it the principal
area of interest.
The ultraviolet spectrum of taberpsychine shows absorption typical of
20the indole moiety , with no substituents other than the "normal" ones at
position two and three.
The infrared spectrum confirms the presence of the aromatic nucleus and
of the indolic NH, but the absence of absorption due to hydroxyl or carbonyl
groups fails to provide information concerning the nature of the oxygen atom
present. Since neither acetylation nor mild oxidation reactions produced
any change in the molecule the oxygen atom was, by exclusion assumed to be
ethereal. With this information, the partial structure (xvii) can be written
where the C^ residue could contain up to four rings.
H|q N O
xvii
* Collection of G. Agostini at the Botanical Garden of the Universidad Central de Venezuela, Caracas.
62
The nuclear magnetic resonance spectrum gives useful evidence about the
other half of the molecule, including the functionality of the second nitro
gen atom. A broad quartet at 5.385 (J=6.5 cps) integrating for one proton,
accompanied by a doublet of doublets for three protons at 1.685 (J=6.5 and
2.0 cps respectively) is clear evidence for an ethylidene side chain. De
coupling experiments (figure 15) left no doubt about this and at the same time
localised the origin of the small coupling observed in the methyl signal (and
also of the broadening of the quartet for the olefinic proton). In effect,
while irradiating the methyl signal, one finds that the broad lower field part
(H in Figure 15) of an AB quartet (3.605 and 2.935, J=14 cps) becomes a sharp
doublet ; while irradiating this broad doublet (3.605) the disappearance of
the small splitting of the methyl group signal is observed (this also sharpens
the quartet for the olefinic proton). This AB quartet is found in a region
typical for protons at carbon atoms adjacent to nitrogen, permitting the
placing of the ethylidene side chain in the sequence (xviii), with the methyl
ene group adjacent to the basic nitrogen atom responsible for the AB quartet
discussed above.
H
CH3
The sharp singlet at 2.535 integrating for three protons must be
assigned to a methyl group on the basic nitrogen (since the indolic nitrogen
j values
Figure 15 »- Nuclear magnetic resonance spectrum and spin decoupling experiments on t ab e rpsychine
64
does not bear a substituent). The spectrum also confirms the presence of
four aromatic protons (4H multiplet 7.07-7.666) and the indolic NH (singlet
8.426).
A very important feature in the nuclear magnetic resonance spectrum
is a pair of doublets at 5.136 (J=10 and 2 cps) integrating for one proton.
This signal is only ascribable to a proton adjacent both to an aromatic
moiety and an oxygen atom. The splitting pattern suggests that it is also
adjacent to a methylene. This information helps to reduce the possible lo
cation of the oxygen atom to one of the two carbons linked to the indole re
sidue. However, as yet, there is not enough evidence to decide which.
Zinc dust distillation of taberpsychine, following a small scale method
53described by Biemann coupled with gas-chromatographic analysis of the vola
tile distillate, furnished very important data. The major product was iden
tified, by direct comparison in the gas chromatograph with an authentic sample
and by nuclear magnetic resonance spectrometry of the material recovered, as
being 3-ethylpyridine. The product could only be formed from the part of the
molecule containing the basic nitrogen. This evidence, coupled to the fact
that the analogous pyridinium ion is observed in the fragmentation in the mass
spectrum (107 m/e) as one of the major peaks (Figure 16), permitted us to con
clude that the basic nitrogen atom is located in a six-membered ring.
Now the partial structure can be extended to (xix).
Hydrogenation of taberpsychine afforded a dihydro derivative,
in which the ethylidene side chain was no longer present as shown by the
nuclear magnetic resonance spectrum, while a signal due to a methyl group on
relative intensity
100-
122
50—
I0>
154
130
ISO 200 m/e
Figure 16„- Mass spectrum*ef talerpsychine
M* (x.308
5)
(H-15) 233
250
Ü
300
CT\U1
66
a saturated carbon appeared as a triplet at 0.986 (J=7 cps).
ÇH3
xix
The methiodide of the dihydro derivative undergoes Hofmann degradation
with potassium tert—>but oxide to give a major product, whose ultra
violet spectrum indicates the presence of a double bond conjugated to the in
dole chromophore^. The presence of this new double bond is corroborated
by the nuclear magnetic resonance spectrum of the dihydrotaberpsychine-methine,
in which one finds the signals for two olefinic protons at 6.696 (doublet
J=12 cps) and 5.556 (doublet of doublets J=12 and 8 cps) as the low field AB
part of an ABX system (see Figure 17). The fact that the double bond intro
duced during this reaction is conjugated with the aromatic moiety and the
assumption of a very likely tryptamine biogenesis allows the linkage of the
two units presented in partial structure (xix) and the placing of the oxygen
atom on the carbon attached to position 2 of the indolic portion as shown in
(xx) .
The methylene group adjacent to the carbon bearing the oxygen atom is
explained if one remembers the pattern for the proton adjacent to both the
aromatic residue and oxygen (doublet of doublets J=10 and 2 cps),
values
Figure IT.- Nuclear magnetic resonance spectrum and decoupling experiments on dihydrotaberpsychine-methine
o\
68
Spin decoupling experiments (Figure 17) on dihydrotaberpsychine-methine
provided precious information concerning the missing linkage of the oxygen
atom. In effect, it demonstrated that the X part (1 H) of the ABX system in
volving the olefinic protons formed by the degradation, is also coupled to an
A'B' system (doublet 4.216, J=ll cps and triplet 3.796, J=ll cps) appearing
in a region typical for protons adjacent to oxygen.
The Hofmann product must therefore contain the sequence:
ha hb h* ha, hI I I I I
INDOLE ---C---- C--C ----c — 0 -— c —- IND0LEi I I
C H», CHgxxi
This observation is only compatible with the partial structure shown
by (xxii) .
69
H H N
XXII
From the molecular formula of the base, which necessitates a pentacyclic
structure, we need now to close another ring and have only one possible point
of attachment (at the starred carbon) since the nature and number of protons
at all other positions has been demonstrated in the discussion above, thus
the complete structure for the major Hofmann product is given as XLI in which
the configuration of the C-ethyl residue must be as shown, arising from hydro
gen addition to the more exposed face of the molecule, and hence that for taber-
psychine as XLII which is compatible with all spectral data.
i i
H H
XLI XLII
70
A minor product from the Hofmann degradation of dihydrotaberpsychine
methiodide was also isolated although it could not be induced to crystallize.
However, the nuclear magnetic resonance spectrum shows apart from the expected
absorptions, a pair of doublets (4.98 and 5.636, J=1 cps) typical of a ter
minal methylene group, which together with the preceeding evidence permitted
the formulation of the material as structure XLIII.
H
XLIII
Once the structure of taberpsychine was elucidated, the result obtained
from the Hofmann degradation performed on the methiodide of taberpsychine
itself could be rationalized, whereas before a rather complex nuclear magne
tic resonance spectrum had rendered it difficult.
This degradation was effected using the same conditions as for the di
violet spectrum shows the presence of a conjugated diene in addition to the
original indole residue, was obtained. The nuclear magnetic resonance spec
trum of this taberpsychine-methine shows a very complex pattern in the region
where the absorption for olefinic protons is expected (see Figure 18). The
71
pattern is further complicated by the presence in the same area of the absorp
tion due to the C.3 proton adjacent to the aromatic ring and the oxygen atom.
It was analyzed to show that the olefinic protons are those of a conjugated
diene which could only be formed by elimination of one of the protons in the
methyl group and migration of the double bond to open the piperidinic ring,
leaving the nitrogen attached to the eight-membered ring. The structure of
this degradation product was assigned as shown in XLIV.
XL IV
A minor product of this Hofmann degradation was observed by thin layer
chromatography but could not be isolated. This is probably the isomer of the
diene as depicted in XLV.
H
XLV
<$ values
Igure l8.- Nuclear magnetic resonance spectrum of taterpsyehine-methine
OO
73
With structure XLII established as that of taberpsychine, the problem
of the stereochemistry of the molecule is almost reduced to a question of
absolute stereochemistry, since once the configuration of one of the asymétrie
centers is fixed the closing of the rings determines the configuration at the
other centers. Thus it is the choice of either the stereochemistry shown in
structure XLVI or its complete mirror image.
XL VI
The product distribution in the Hofmann degradation of taberpsychine
methiodide, about 80% of the diene, can be readily explained by the study
of models of the molecule. In effect, the tri-dimensional structure XLVII
shows taberpsychine methiodide and below are shown Newman projections of
the two systems where the elimination could take place. It is readily seen
XLVI I
74
that the more favored is that involving the double bond, which is quasi-anti
parallel to the bond to be broken, with the elimination taking place as shown
in partial structures (xxii) and (xxiii).
xxii XXlll
The small amount of the other isomer could not be produced by a normal
trans-elimination since the two activated "benzylic" protons are not suitably
placed to allow this, and probably the reaction proceeds through a carbanion
. intermediate.
75
Examination of molecular models of taberpsychine suggests that the hydro
genation of the exocyclic double bond would be specifically from that face of
the molecule which would lead to'an equatorial ethyl group (A->B). Hydrogena
tion from the other face, which should give the axial ethyl residue (as in C)
is seriously hindered by the eight-membered ring and the aromatic system.
The results of the Hofmann degradation of the methiodide of the dihydro com
pound show that the predominant reaction involves the elimination of one of
the protons adjacent to the indole ring. It would be difficult to rationalise
this observation on the basis of structure C where the equatorial hydrogen sub
stituent, introduced by hydrogenation, is stereochemically well situated for
a trans-elimination.
A
C
76
Another new alkaloid obtained from T. psychotrifolia was named taber-
psychidine, C ^qH24^2®2’
Its particular ultraviolet spectrum [^max 224 (10,000) and 318 (12,000)
20my] permitted its classification as a derivative of an a-acyl indole , as
shown by (xxiv).
iH
R
R'
O
XXIV
From the infrared spectrum one obtains information for the presence of
the carbonyl group (strong band 1650 cm-1) as well as that of the aromatic
moiety and the indolic NH. This spectrum also shows the presence of a hy
droxyl group.
The nuclear magnetic resonance spectrum was difficult to perform due
to the only slight solubility of the base in most organic solvents, but the
problem was partly solved by the use of a hot saturated chloroform solution.
The spectrum showed the presence of a methyl group attached to the basic nitro
gen (singlet 2.536) and of a methyl group on a tri-substituted double bond
(1 H quartet 5.406, J=6 cps and 3 H doublet 1.686, J=6 cps) in addition to
the information already known.
With this evidence in hand, the partial formula (xxv) is advanced.
77
Acetylation of the base with acetic anhydride in pyridine at room temper
ature gives a monoacetate (molecular weight by mass spectrometry 366) and while
this product is rather unstable it could be characterized spectrally.
- OH
XXV
The infrared spectrum proves that it is an O-acetyl derivative (peaks
at 1745 and 1235 cm-1) and the nuclear magnetic resonance spectrum reveals
that the acetyl methyl is unusually shielded (3 H singlet 1.776). The most
useful information, however, is given by the mass spectrum (see Figure 19).
In effect, the spectrum of the base itself shows two major peaks at 152 and
122 m/e while in the acetate one finds a new peak at 194 m/e (42 mass units
from 152 m/e). Analyzing this data, the peak at 122 m/e strongly suggests a
pyridinium ion of the type depicted by (xxvi), coming from the part of the
molecule which contains the basic nitrogen since the indolic residue could
not possibly give such a peak. This pyridinium ion has been proposed as oc
curring in the mass spectrometric degradation of alkaloids of this type^.
Following this reasoning, the peak at 152 m/e (30 mass units from 122
m/e) must be due to pyridinium (xxvi) plus a hydroxymethyl group, a fact which
seems to be confirmed by the appearance of the 194 m/e peak in the spectrum
of the acetate. The sequence of fragmentation would be then as given by
(xxvii).
relative intensity
H O CH
Figure 19»- Mass spectrum of tàberpsychidine
79
CH3i
xxvi (122 m/e)
194 m/e 152 m/e 122 m/e
xxvii
At this stage, the similarity to alkaloids related to vobasine (XLVII)
was evident and a derivative was prepared to help prove the structure chemi
cally.
Reduction of taberpsychidine with sodium borohydride yielded a compound,
^20^26^2^2’ wh°se ultraviolet spectrum no longer shows the presence of the
keto group conjugated to the aromatic residue but the absorption is typical
of an unsubstituted indole. The infrared spectrum confirms the absence of
80
the carbonyl at 1650 cm""1, while the original OH band is now considerably
broadened.
R = COOCH3
XLVII
The nuclear magnetic resonance spectrum (Figure 20) although exhibiting
very little change, presents some new absorption which is both indication
that the keto group has been reduced and support for an important statement
made earlier concerning the structure of taberpsychine. This absorption is
a broad doublet appearing at 5.276 (1 H, J=6 cps) ascribable to the proton
on the carbon atom, previously part of the carbonyl group, which is now ad
jacent to both oxygen and the aromatic moiety.
The mass spectrum of this derivative shows the appearance of a rather
strange peak at 154 m/e, which could be thought to arise from the half of the
molecule where the reduced center is found since in the base itself the peak
is insignificant. However, the relation with that center is only an indirect
one and it is produced by a different mode of fragmentation (Figure 21) in
volving the new hydroxyl groupé.
Dihydrotaberpsychidine was compared with the product obtained by Renner
x-z
HOCK
OH
<$ VALUES
Figure 20.- Nuclear magnetic resonance spectrum of dihydrata"berpsychidine
82
HOCH.
OH
32 fa
V
CHINs
I2X
ch3
Figure 21.- Mass spectrometric fragmentation of dihydrotaberpsychidine
83
et al. from vobasine (XLVII) by reduction first with sodium borohydride (to
give vobasinol) and then with lithium aluminum hydride (to produce vobasinediol)
or reduction of vobasine with lithium aluminum hydride, All the physical data
given in the literature for vobasinediol are identical with those measured for
our dihydrotaberpsychidine, thus allowing us to write structure XLVIII for the
reduction product and XLIX for the base itself.
57
CH,
<N,
HOCMjT
o
XLVII I XLIX
The structure proposed, which is justified by the mass spectrometric
fragmentation shown in Figure 22, is identical with that proposed for affi-
58nine and although the physical constants given in the literature for the
latter were misleading,taberpsychidine is in fact affinine.
That the stereochemistry at C.16 is as shown in structure V (the same
as in vobasine (XLVII)), can be readily seen from the extreme shielding of
the acetyl methyl (3 H singlet 1.776) observed in the nuclear magnetic reso
nance spectrum of O-acetyl taberpsychidine. In vobasine, the same shielding
is observed for the methyl of the ester group, this appearing at 2.636.
The third alkaloid whose structure was elucidated is a compound which
84
57 ■has been previously prepared by Renner et al. but never before reported as
a naturally occuring compound. It is known as 16-epi-vobasinic acid, and was
prepared from vobasine by hydrolysis with 20% methanolic potassium hydroxide.
The alkaloid, CgnHggNgO.,, is a high melting compound (m.p. 295° decomp.)
only sparingly soluble in most organic solvents which suggested it to be a
salt. However, no anion was detectable pointing to an internal salt or amino
acid.
The ultraviolet spectrum of the base C^max 283 (13,100) and 316 (20,000)
my] is that of an a-acyl indole and the infrared spectrum presents two very
typical bands in the region for carbonyl groups. One of them at 1650 cm-1
is assigned, in agreement with the ultraviolet spectrum, to a keto group on
carbon 3 conjugated to the indole moiety and the other at 1610 cm-1, a very
strong band which is only compatible with a carboxylate carbonyl.
The nuclear magnetic resonance spectrum (performed in 2% D^SO. in D2O
solution) shows the presence of an N-methyl group (3 H singlet at 3.005, dis
placed to lower field due to the quaternisation of the basic nitrogen) and of
an exocyclic ethylidene chain (1 H quartet 5.935 and 3 H doublet 1.685, J=7
cps) in addition to the absorption expected from the indolic residue.
The mass spectrum (Figure 23) of the base again presents its principal
peak at 122 m/e, very typical fragmentation in the mass spectrometric degra
dation of vobasine-like alkaloids, produced by the pyridinium ion of the type
shown by xxvi (page 79). Another important peak is that at 166 m/e (44 mass
units = -COO from 122) which coupled to the evidence for the presence of an
acidic residue in the molecule, leads to the conclusion that the latter is
Figure 22,- Mass spectrométrie fragmentation of taberpsychidine
CO -en
+ z
relative intensity
Figure 2$Mass spectrum of l6-epi-vobasinic acid
ooOx
attached to the six-membered ring producing the pyridinium ion (xxviii) in
the fragmentation.
87
ch3t
ch3
N + M-t-r ^ r ^
k--------- >HOOC
xxviii (166 m/e)
Based on this evidence, the structure for the alkaloid was proposed
as shown by L, which is that of 16 epi-vobasinic acid.
All spectral data are in agreement with this structure and a fragmen
tation pattern, as given in Figure 24, accounts for all the principal peaks
observed in the mass spectrum.
R = COOH
L
Further proof for the structure is provided by méthylation of the base
by prolonged treatment with diazomethane. The infrared spectrum of the
Z-I
Figure 24 0- Mass spectraaietric Tranent at sen of l6-epi-voilas inic acid
oo00
89
product obtained shows the absorption typical of esters (1740 cm-1), while
the nuclear magnetic resonance spectrum proves it is a methyl ester (3 H
singlet 3.536). The position of the absorption for the methyl group of the
ester in the spectrum determines the stereochemistry at carbon 16, as being
epimeric to that in vobasine (XLVII) where the same absorption shows the methyl
group of the ester to be very shielded (3 H singlet 2.636) presumably because
it lies immediately above the electronic cloud of the aromatic ring.
The methylated derivative presents the same physical properties, and
infrared, nuclear magnetic resonance and mass spectra identical with those of
5716-epi-vobasine given in the literature . Direct comparison however was not
possible due to the lack of an authentic sample.
A fourth alkaloid which was called base M for purpose of identification,
^21^26^2^3’ obtained from a countercurrent distribution, still remains with an
unknown structure.
Its ultraviolet spectrum is that of an unsubstituted indole [X 227 r max
(44,700), 278 (sh. 8,800), 286 (9,600) and 294 (8,600) mp]. The infrared
spectrum shows the absorption for the indolic NH and the aromatic protons, as
well as a hydroxyl group and an ester carbonyl (at 1730 cm-1) accompanied by
another slightly weaker band at 1710 cm-1 probably due to the presence of
hydrogen bonded species.
The nuclear magnetic resonance spectrum demonstrates the presence of
the indolic residue and identifies the ester grouping as being a methyl ester.
It also indicates the existence of an N-methyl residue (3 H singlet 2.26) and
of a saturated methyl group with only one adjacent proton (3 H doublet 1.266,
90
J=7 cps). The latter should be adjacent to oxygen or nitrogen since decoupling
experiments showed its appearance as a doublet of doublets at 3.906 (J=7 and
3 cps).
The mass spectrum confirms the analytical figures (M+= 354,1956; ^21^26
NgO? requires: 354.1943) but the fragmentation pattern does not fit a structure
related to that of the other alkaloids obtained from this plant.
The information obtained on this base can be resumed as in partial struc
ture (xxix) where the C-8 fragment can involve up to three rings.
— OH
Ce HS Ml0
:N- CH,
XCOOCH
H
CH,
xxix
With the
at a plausible
amount of material available it was not possible to arrive
structure for the alkaloid and further results will be re
ported elsewhere.
-.EXPERIMENTAL.-
-.GENERAL REMARKS.-
Melting points are uncorrected. Unless otherwise stated optical rota
tions and ultraviolet spectra (e values in parentheses) were measured in
ethanol. Ultraviolet spectra were registered on a Beckmann spectrophotometer
model DK-1A and optical rotations in a Carl Zeiss polarimeter with circular
scale (c = 1.0 unless otherwise stated). Infrared spectra were performed on
nujol mulls or potassium bromide pellets using a Beckmann spectrophotometer
model IR-4. Nuclear magnetic resonance (NMR) spectra were measured on 5-10%
solutions with Varian Associates spectrometers models HR-100 or A-60. Tetra-
methylsilane protons taken as 0 p.p.m. Mass spectra were registered using
either an AEI MS-2H or a Varian Associates M-66 spectrometer.
Countercurrent distribution fractions were numbered from the first sta
tionary phase (fraction N° 1) to the furthest advanced buffer phase (highest
numbered fraction). Aqueous phase was acetate buffer.
Elementary analyses were performed by Dr. Franz Pascher, Bonn, Germany.
The extractions of the alkaloids were performed in the following manner
(unless otherwise stated):
The plant material was dried in a current of warm air as soon as possible
after collection and then reduced to small pieces, about an inch long, with a
.chaff or tobacco cutting machine. A Wiley type grinding mill was then used
to further reduce the material to a coarse powder which was then extracted
by percolation with methanol or ethanol at room temperature. The volume of
solvent necessary varies with the plant but normally involves 10-20 litres
92
93
per kilo of ground material. The solvent is removed by distillation, or more
rapidly in a climbing film evaporator but care is taken not to heat the solu
tion excessively. At this stage the extract contains every conceivable type
of natural material and is a black viscous tar.
The crude extract is suspended or dissolved in dilute acid and the in
soluble portion removed by filtration where possible or by decantation. Ex
traction with chloroform and suitably changing the pH of the aqueous solution
enables one to obtain a crude base fraction which is predominantly alkaloidal.
To separate the individual alkaloids the most rewarding first step is
to distribute the crude base between an organic solvent and an aqueous buffer.
The pH of the buffer is chosen, in the first instance to give a distribution
coefficient of about 0.5 but depending on the complexity of the mixture it
may be changed. This first countercurrent, which could involve over 100 gms.
of base, is best performed in large separatory funnels. Depending on the
results of this first distribution, further separation is achieved by normal
manipulations. The experimental details of the individual separations have
been limited to those steps which provided the pure alkaloids discussed in
the thesis.
-.CHAPTER I.-
A. ALKALOIDS OF ASPIDOSPERMA EXCELSUM.
95
EXTRACTION AND ISOLATION OF THE ALKALOIDS.-
The A. excelsum bark (6.5 kg) was milled and extracted by methanol per
colation at room temperature„ Evaporation of the methanol was greatly com
plicated by foaming, and the tar like residue certainly contained a large
volume of water. The crude tar was mixed with 2% hydrochloric acid and the
acid solution continuously extracted with chloroform to remove non basic im
purities. Paper chromatography showed the presence of at least two alkaloids
in quantity in the resulting aqueous solution, and one of the bases had been
extracted, as the hydrochloride, into the chloroform.
Yohimbine (XI)
The hydrochloric acid solution above was basified with ammonia, and
the crude base (149 g) was obtained by chloroform extraction (entrainement of
some of the aqueous phase as an emulsion exaggerated the yield of basic ma
terial) . A portion of the crude base (49 g) was distributed in a counter-
current distribution apparatus between a stationary chloroform phase and ace
tate buffer (pH 3.72) for a total of 50 transfers. The tubes in the center
of the apparatus contained the major base, which crystallized from acetone
(6.39 g) and which was recrystallized for analysis from the same solvent,
m.p. 241-242°, [<x]D + 45°.
Anal. Found :: C, 71.2; H, 7.5; N,
OO ; o, 13.6. C21^26^2^3 squires
c, 71.2; H, 7.4; N, 7.9 ; o, 13.6%.
- UV spectrum : Amax 226 (36,500), 278 (7,400) and 286 (sh. 6,100) my.
IR spectrum : peaks at 3510 (OH), 3330 (NH), 2820 and 2780 (Bohlmann trans-
quinolizidine bands), 1735 (ester), 765 and 750 (aromatic)
cm-1.
96
NMR spectrum : 1 H broad singlet 7.806 (NH);4 H multiplet 7.00-7.626
(aromatic); 1 H broad singlet 4,226 (C.17 H); 3 H singlet
3.786 (methyl ester).
Mass spectrum : 354 (M+), 295 (M+ - COOCHj), 184, 170, 169, 156, m/e.
These spectral results agree with those given in the literature for
22yohimbine , and the identity was confirmed by direct comparison (infrared
and mixture melting point).
Q-acetylyohimbine (XII)
The chloroform containing the non-basic materials was concentrated to
about half volume and cooled. A crystalline substance, collected by filtra
tion (4.58 g), was shown to be an alkaloid hydrochloride and was recrystal
lized frapi methanol-acetone, m.p. 274-275° (decomp.).
Anal. Found
UV spectrum
C, 63.7; H, 6.9; Cl, 8.5. C^HggNgO^Cl requires :
C, 63.8; H, 6.8; Cl, 8.2%.
\nax 222 (39,500), 274 (7,500), 281 (7,500) and 290 (6,000)
my.
IR spectrum
NMR spectrum
Mass spectrum :
peaks at 3370 (NH), 1730 (ester), 1725 and 1250 (O-acetyl),
and 740 (aromatic) cm"1.
1 H broad singlet 7.876 (NH); 4 H multiplet 7.00-7.606
(aromatic); 1 H multiplet 5.476 (C.17 H); 3 H singlet 3.696
(methyl ester); 3 H singlet 2.046 (O-acetyl).
396 (M+), 395, 184, 170, 169, 156, m/e.
For direct comparison, a sample of yohimbine was acetylated in acetic
anhydride-pyridine at room temperature. The two samples were identical in all
97
respects and showed no depression of the melting point when mixed. A sample
of the natural 0-acetylyohimbine (300 mg) was hydrolyzed in anhydrous methanol
containing a small amount of concentrated sulfuric acid (conditions known not
to affect the methyl ester). The product was shown by direct comparison to
be yohimbine.
0-acetylyohimbine was also obtained from the countercurrent distribution.
A total of 6.31 g was isolated.
Further experiments with the mother liquors have yielded the minor bases
4 23excelsinine (10-methoxycorynanthine) and a-yohimbine .
-.CHAPTER I.-
B. ALKALOIDS OF ASPIDOSPERMA CUSPA.
99
EXTRACTION AND ISOLATION OF THE ALKALOIDS.-
The A. cuspa bark was air dried and finely divided (12.6 kg) and extrac
ted by percolation with ethanol until the percolate no longer gave positive
tests with the usual alkaloid reagents. The ethanolic solution was concentra
ted under reduced pressure to give a tar which was triturated several times
with 2% aqueous hydrochloric acid. The aqueous extracts were combined and
extracted continuously with chloroform to remove non-basic material and then
rendered alkaline with ammonia and the crude basic fraction (80 g) obtained by
chloroform extraction. The crude bases were redissolved in dilute hydrochloric
acid and after removing neutrals (as above), the crude base (54 g) was again
obtained by chloroform extraction.
The crude basic material (54 g) was distributed between a stationary
chloroform phase and acetate buffer (pH 3.72) in a fifty tube countercurrent
distribution apparatus. The most advanced aqueous phases (tubes 37-50) showed
by paper chromatography one principal alkaloid in quantity and aspidodasycar-
pine (12.5 g) was obtained from these tubes by normal manipulation. The crude
base from the remaining tubes was combined and distributed again between chloro
form (stationary) and acetate buffer (pH 3.42) for fifty transfers and tubes
40-48 afforded more aspidodasycarpine (1.5 g). Tubes 6-8 contained essential
ly one base, which was shown later to be des-O-methylaspidocarpine (978 mg)
and tubes 9-15 gave a crystalline alkaloid (1.089 g) shown to be bumamine
(des-acetylpicraline). The buffer phase in tubes 1-5 afforded picraline
(5 mg). Further countercurrent distribution of the mother liquors afforded
more burnamine (371 mg) and des-O-methylaspidocarpine (210 mg) .
From the crude mixture, pyridine XXIX (5 mg) was obtained by preparative
paper chromatography using Whatman paper N° 31 (double thick, 3 mm) and
pyridine-ethyl acetate-water (7.5:2.6:1.65) as solvent.
100
Burnamine (des-acetylpicraline) (XXIII)
The material obtained after recrystallizing from acetone gave m.p,
190-191° (decomp.), [a]D - 151° .
Anal. Found
UV spectrum
IR spectrum
NMR spectrum
C, 68.4; H, 6.7; N, 7.5; 0, 17.5. requires :
C, 68.5; H, 6.6; N, 7.6; 0, 17.4%.
X 233 (8,800) and 283 (3,660) my; ?0% 274.5 and
max ’ max
302 my,
peaks at 3550 (OH), 3050 (NH), 1747 (ester), 1615 (aromatic)
cm-1.
complex 4 H multiplet centered at 7.066 (aromatic); 1 H
singlet 5.166 (NH) ; 1 H quartet 5.386, J=7.5 cps (1 olefinic
proton); 3 H doublet 1.566, 0*7.5 cps (C-methyl); 1 H doublet
4.756, J=2.5 cps (C.5 H); 3 H singlet 3.606 (methyl ester).
Mass spectrum : 368 (M+), 350 (M - H^O), 337 (M - .CH^OH), 320, 309 (M -
.COOŒL), 239, 194, 180, 168, 157, 144, 130, m/e.
A mixed melting point with an authentic sample showed no depression and
the infrared spectrum was superposable with that of burnamine*.
Des-O-methylaspidocarpine (XXV)
The base crystallized from acetone to give a substance containing acetone
We thank Dr. W.I. Taylor for kindly providing an authentic sampleof burnamine.
101
of crystallization, m.p. 139-140°, [al^ + 97°. For analysis the sample was
dried in vacuo for several weeks during which time the analysis changed from
that of the hydrate to that of the base alone.
Anal. Found
UV spectrum
IR spectrum
NMR spectrum
C, 70.4; H, 8.0; Mol. Wt. (by mass spectrometry) 356.1978.
^21^28^2^3 reclui-res• C, 70.7; H, 8.0; Mol. Wt. 356.2022.
X 224.5 (18,800) and 259.5 (7,300) my; 236.5
(15,800) and 300 (3,000) my.
peaks at 3250 (OH), 1635 (N-acyl), 1580 (aromatic) cm-1.
1 H singlet 10.856 (chelated phenolic hydroxyl); 2 H singlet
6.366 (aromatic); 1 H quartet 4.006, J=5 cps (C.2 H); 3 H
singlet 2.256 (N-acetyl); 3 H doublet 0.706, J=4 cps (satu
rated C-methyl).
Mass spectrum : 356 (M^), 328 (M - CH.CH^), 327 (M - .C^Hg), 190, 162, 152,
124, m/e.
The di-O-acetyl derivative was prepared dissolving the base (100 mg) in
pyridine (5 ml) and adding an excess of acetic anhydride (0.5 ml). The mix
ture was left standing over night. Methanol was then added to hydrolyze the
excess acetic anhydride and the solution taken to dryness under reduced
pressure. The residue was redissolved in chloroform, backwashed twice with
ammonia-water, the chloroform dried over sodium sulfate and evaporated to
dryness. The acetate (120 mg) was crystallized from ethanol, m.p. 138-140°
(decomp.), [a]D - 19°.
IR spectrum : peaks at 1780 and 1210 (0-acetate), 1680 (N-acetyl), 1610
(aromatic) cm"1.
102
NMR spectrum : 2 H AB quartet 6.99 and 6.885, J=4.8 cps (aromatic); 6 H
singlet 2.215 (O-acetyl); 3 H singlet 2.155 (N-acetyl);
3 H triplet 0.615, J=3.6 cps (methyl on saturated ethyl
side chain).
Mass spectrum : nominal mass 440.
(-) Pyrifolidine (from des-O-methylaspidocarpine) (XXVII)
Des-O-methylaspidocarpine (130 mg) was dissolved in dry acetone (25 ml)
and anhydrous potassium carbonate (1 g) was added together with dimethyl sul
fate (0.5 ml). The mixture was refluxed for 17 hours and then another portion
of dimethyl sulfate (0.5 ml) added and the procedure was repeated after 30
hours. The reflux was continued for a total of 40 hours. The mixture was
then diluted with cold water, the acetone removed under reduced pressure and
the aqueous solution extracted four times with chloroform. The chloroform was
evaporated to dryness and the residue (100 mg) crystallized and recrystallized
from acetone-ether, m.p. 150-151°, [a]^ - 83.5°, [a]^ - 95° (CHCl^).
UV spectrum
IR spectrum
NMR spectrum
Mass spectrum
\nax 224 (28,900), 252 (11,700) and 288 (2,800) mp.
peaks at 1680 (N-acetyl), 1610 (aromatic) cm-1.
2 H AB quartet 6.49 and 6.685, J=8 cps (aromatic); 3 H
singlet 3.675 and 3 H singlet 3.596 (methoxyls); 3 H singlet
2.056 (N-acetyl); 3 H triplet 0,736, J=6 cps (methyl on sa
turated ethyl side chain).
384 (M+), 369 (M - 15), 356 (M - CH^CH^), 355 (M - .C^Hg),
353 (M - OCH3), 341 (M - 43), 190, 171, 152, 124, m/e.
Comparison of this product with an authentic sample* by spectral and
We thank Dr. Carl Djerassi for kindly providing an authentic sampleof pyrifolidine.
103
chromatographie methods confirmed their identity.
Aspidodasycarpine (XV)
The base was recrystallized several times from acetone, m.p. 207-209°
(decomp.), [ot]D - 130°, [a]D - 114° (CHClj).
Anal. Found
ÜV spectrum
IR spectrum
NMR spectrum
C, 68.2; H, 7.0; N, 7.8; 0, 17.5. requires :
C, 68.1; H, 7.1; N, 7.6; 0, 17.3%.
X 239 (10,000) and 292 (4,300) my.
peaks at 3360 (OH), 3580 (indoline NH), 3300 (N.-H), 1610
(aromatic) and 1720 (ester) cm-1.
4 H multiplet 7.005 (aromatic); 1 H quartet 5.525, J=6.5 cps
(1 olefinic proton); 3 H doublet of doublets 1.75, J=6.5 and
2 cps (unsaturated C-methyl); 3 H singlet 3.765 (methyl ester).
Mass spectrum : 370 (M+), 368, 339, 325; 267, 263, 232, 204, 172, 156, 144,
130, 108, m/e.
A mixed melting point with aspidodasycarpine*
the infrared spectra were identical.
showed no depression and
N,Q-diacetylaspidodasycarpine (XVI)
a) To aspidodasycarpine (3.02 g) in pyridine (20 ml) was added acetic
anhydride (10 ml). After 48 hours excess methanol was added with cooling and
the solution then evaporated to dryness under reduced pressure. The residue
was recrystallized from acetone (2.85 g), m.p. 175°, [a]^ - 174° (CHCl^),
* We thank Dr. Carl Djerassi for kindly providing an authentic sampleof aspidodasycarpine.
104
[alD - 161°.
Anal. Found : C, 66.2; H, 6.8; N, 6.0; 0, 21.0. CggH^NgOg requires:
C, 66.1; H, 6.7; N, 6.2; 0, 21.1%.
UV spectrum : A 241.5 (8,900) and 297.5 (3,100) mp.
IR spectrum : peaks at 3450 (indoline NH), 1750 and 1230 (0-acetyl),
1715 (methyl ester), 1630 (N-acetyl) cm-1.
NMR spectrum 4 H multiplet 7.086 (aromatic); 1 H quartet 5.676, J=7 cps
(olefinic); 1 H singlet 4.856 (indoline NH); 3 H singlet
3.786 (methyl ester); 3 H singlet 2.176 (N-acetyl); 3 H
singlet 1.926 (0-acetate); 3 H doublet 1.736, J=7 cps (un
saturated C-methyl).
b) The same N,O-diacetyl derivative (XVI) was obtained by similar
acetylation of N-acetylaspidodasycarpine (XVII).
N-acetylaspidodasycarpine (XVII)
a) To aspidodasycarpine (500 mg) dissolved in pyridine (10 ml) was
slowly added a cold solution of acetic anhydride (100 pi) in pyridine. After
6 hours at 5°C the solution was allowed to warm up to room temperature and
then evaporated to dryness under reduced pressure without heating. The resi
due, upon dissolving in acetone, afforded crystals of the N-acetyl deriva
tive (302 mg) and from the mother liquors a further quantity (103 mg) was
obtained by extraction of the neutral components in the usual manner. A
small amount of unchanged aspidodasycarpine (47 mg) was obtained from the
basic impurities separated by washing with hydrochloric acid.
105
The pure N-acetyl derivative showed m.p. 250-253°, [a]p - 147°.
Anal. Found
UV spectrum
IR spectrum
NMR spectrum
C, 66.8; H, 7.1; N, 7.0; 0, 19.2. ^23^28^2^5 re(lu^-res:
C, 67.0; H, 6.8; N, 6.8; 0, 19.4%.
X 241.5 (8,000) and 298.5 (2,800) my.
peaks at 3250 (indoline NH), 1760 (methyl ester), 1620
(N-acetyl) cm-1.
4 H multiplet 6.756 (aromatic); 1 H quartet 5.386, J=7 cps
(olefinic proton); 3 H singlet 2.056 (N-acetyl); 3 H doublet
1.656, J=7 cps (unsaturated C-methyl).
b) N,O-diacetylaspidodasycarpine (200 mg) was dissolved in dry methanol
(10 ml) and concentrated sulfuric acid (0.25 ml) was added. 18 hours of
reflux afforded a neutral product (80 mg) shown to be the N-acetyl derivative
(XVII) and a basic fraction (65 mg) identified as aspidodasycarpine.
c) N,O-diacetylaspidodasycarpine (200 mg) was reacted with excess
sodium borohydride in methanol (15 ml) at room temperature. Water was added
to the reaction after 18 hours and the foam obtained by chloroform extraction
(185 mg) crystallized upon solution in acetone. The product was identical
in all respects with the N-acetyl derivative (XVII) obtained previously.
Dihydroaspidodasycarpine (XVIII)
Aspidodasycarpine (500 mg) was dissolved in methanol (50 ml) containing
concentrated hydrochloric acid (3 ml) and platinum oxide (90 mg) was added.
The mixture was shaken with hydrogen at 50 p.s.i. for 22 hours, filtered and
part of the methanol was removed under reduced pressure. After diluting with
106
water and basi frying with ammonia, the product (500 mg) was obtained by chloro
form extraction. Only one component was present as shown by thin layer chroma
tography and this crystallized slowly from acetone, m.p. 209-211°, [a]^ - 212°.
Anal. Found
UV spectrum
IR spectrum
NMR spectrum
Mass spectrum
C, 67.6; H, 7.7; N, 7.7; 0, 17.4. CgiH^gN^O. requires:
C, 67.7; H, 7.6; N, 7.5; 0, 17.2%.
\nax 241 (9,500) and 297 (3,700) my.
peaks at 3550 (indoline NH), 3400 (OH), 3170 (N.-H), 1723
(methyl ester), 1610 (aromatic) cm-1.
4 H multiplet 7.435 (aromatic); 3 H singlet 3.966 (methyl
ester); 3 H doublet 1.005, J=6 cps (saturated C-methyl).
372.2054 (M+; calculated for C^H.gN^O.: 372.2049), 342
(M - .CHgO), 329, 282, 254, 253, 232, 226, 211, 194, 181,
144, 130, 110, m/e.
N,Q-diacetyldihydroaspidodasycarpine (XIX)
a) Dihydroaspidodasycarpine (350 mg) was acetylated using acetic
anhydride (1 ml) in pyridine (5 ml) for 20 hours. Crystals which appeared
in the solution during the reaction were filtered (129 mg) and washed with,
and then recrystallized from, ethanol, m.p. 321-324° (decomp.), [a]^ - 168°.
Anal. Found : C, 64.6; H, 6.8; N, 6.2; 0, 22.6. ^gH^NgOg,. 1/2 H^O requires :
C, 64.5; H, 7.1; N, 6.0; 0, 22.4%.
UV spectrum : X^^ 240 (6,000) and 295 (1,800) my.
IR spectrum : peaks at 3200 (indoline NH), 1755 (0-acetyl), 1735 (methyl
ester), 1645 (N-acetyl), 1230 (0-acetyl) cm-1,
due to the limited solubility of the compound, only the more
intense peaks were visible: 3 H singlet 2.255 (N-acetyl) and
NMR spectrum
107
3 H singlet 2,125 (O-acetyl).
Mass spectrum : 456 (M+), 425 (M - 31), 414 (M - 42), 397, 384, 237, 225, 172,
161, 152, 144, 130, 110, 108, m/e.
b) N,O-diacetylaspidodasycarpine (500 mg) was hydrogenated over Adams'
catalyst (100 mg) in ethanol (100 ml) containing acetic acid (50 ml). After
24 hours the catalyst was removed by filtration and the solution evaporated
to dryness under reduced pressure. The residue crystallized from methanol
(414 mg), m.p. 321-324° (decomp.) and was readily identified as the same N,0-
diacetyldihydro derivative obtained above.
N-acetyldihydroaspidodasycarpine (XX)
a) By partial acetylation of dihydroaspidodasycarpine.
To a cooled solution of dihydroaspidodasycarpine (134 mg) in pyri
dine (5 ml) was added acetic anhydride (25 pi). After 2 hours at 5°C and
standing at room temperature overnight, the solution was evaporated to dry
ness under reduced pressure and the white residue redissolved in chloroform.
Washing the chloroform with dilute hydrochloric acid afforded some unreacted
dihydroaspidodasycarpine (28 mg) and the residue obtained by evaporating the
washed (ammonia-water) chloroform solution crystallized from acetone, m.p.
262-264°, [a]D - 193°.
Anal. Found : C, 66.8; H, 7.1; N, 7.0; 0, 19.2. C^H^^Og requires:
C, 66.6; H, 7.3; N, 6.8; 0, 19.3%.
UV spectrum : 241 (8,000) and 298 (2,800) mp.
IR spectrum : peaks at 3550 (OH), 3200 (indoline NH), 1740 (methyl ester),
1640 (N-acetyl) cm-1.
108
NMR spectrum : 4 H multiplet 7.046 (aromatic) ; 3 H singlet 3.756 (methyl
ester); 3 H singlet 2.156 (N-acetyl); 3 H doublet 0.996,
J=5 cps (saturated C-methyl).
Mass spectrum : 414 (M+), 384 (M - CH^O), 352, 226, 172, 161, 152, 144,
143, 130, 110, m/e.
b) By hydrogenation of N-acetylaspidodasycarpine.
N-acetylaspidodasycarpine (200 mg) was dissolved in methanol (50 ml)
containing hydrochloric acid (3.5 ml). The solution was shaken under hydrogen
(50 p.s.i.) with Adams' catalyst (90 mg) for 48 hours and then filtered. Some
methanol was removed on a rotatory evaporator and the solution then diluted
with water (200 ml). Chloroform extraction gave a quantitative yield of a
pale yellow foam which crystallized on contact with acetone, m.p. 262-264°
(identical with the material obtained in (a) above).
c) By hydrolysis of N,O-diacetyldihydroaspidodasycarpine.
N,O-diacetyldihydroaspidodasycarpine (100 mg) dissolved in dry
methanol (10 ml) containing concentrated sulfuric acid (0.25 ml) was refluxed
for 20 hours. The foam (87 mg) obtained by chloroform extraction afforded a
crystalline product identical with that obtained above.
A1>2 dehydro-4,5,17-triacetyldihydroaspidodasycarpine (XXII)
To N,O-diacetyldihydroaspidodasycarpine (254 mg) suspended in acetic
anhydride (15 ml) was added concentrated sulfuric acid (9 drops) which suf
ficed to dissolve the suspended material. After 5 hours at room temperature
the mixture was poured onto crushed ice and dilute ammonia and then extracted
109
with chloroform. The latter was washed with water and dried over sodium sulfate,
and on filtration and evaporation to dryness yielded a foam (227 mg) extremely
soluble in acetone but which was crystallized from acetone-ether (148 mg), m.p.
166-168°, Co3d - 31°.
Anal. Found : C, 64.9; H, 6.8; N, 5.9; 0, 22.6. requires:
C, 65.0; H, 6.9; N, 5.5; 0, 22.5%.
UV spectrum : A 222 (24,200) and 261 (6,800) mp.
IR spectrum : peaks at 1755 (methyl ester), 1755 and 1230 (0-acetyl),
1655 (N-acetyl) cm-1.
NMR spectrum : 4 H multiplet 7.555 (aromatic); 3 H singlet 3.775 (methyl
ester); 3 H singlet 2.275 (N-acetyl); 6 H singlet 1.735
(2 0-acetyl); 3 H doublet 1.085, J=8 cps (saturated C-methyl)
Mass spectrum : 498.2368 (M+; calculated for ^ykL^F^Oy : 498.2366), 456
(M - CHg=C0), 439 (M - .C00CH_), 425, 411, 397, 385, 252,
152, 136, 128, 110, 97, m/e.
Sodium borohydride reduction of the indolenine XXII
The indolenine (102 mg) was reacted with sodium borohydride (25 mg) in
methanol (10 ml) for 24 hours. A crystalline product, which had separated
from the solution, was collected by filtration (15 mg) and shown by the normal
methods to be N,0-diacetyldihydroaspidodasycarpine, m.p. 325-327° (decomp.).
The mother liquors were diluted with water and the product isolated by chloro
form extraction. The resulting foam gave a further quantity of the diacetyl-
dihydroderivative (8 mg) and then the more soluble N-acetyldihydroaspidodasy-
carpine (54 mg) identified in the usual manner.
110
Picraline (XXVIII)
The base (5 mg) obtained by normal procedures from fractions 1-5 (buffer)
from a countercurrent distribution (chloroform-buffer acetate pH 3.42) showed
m.p. 170-175° (impure).
UV spectrum : 230 and 282 mu.
IR spectrum : peaks at 3340 (indoline NH), 1740 and 1240 (0-acetyl),
1740 (methyl ester), 1610 and 740 (aromatic) cm-1.
Mass spectrum : 410 (M+), 395, 382 (M - 28), 379 (M - .0CH3), 367 (M -
CH3C0) 351 (M - .COOCH3 or M - .OCOCHg), 337 (M - .CH^-
OCOCH3), 239, 194, 180, 157, 144, 130, 124, m/e.
The mass spectrometric fragmentation is identical with that of picraline
34reported in the literature
Pyridine XXIX
The base obtained by preparative paper chromatography was purified by
sublimation, m.p. 120° (probably a salt).
UV spectrum : X_ 256 and 262 my.r max
IR spectrum : peaks at 1600 and 1565 (pyridine), 725 (aromatic) cm-1.
Mass spectrum : 149 (M+), 134, 120, 106, 79, 77, 51, m/e (see figure 8,
page 38).
-.CHAPTER II.-
ALKALOIDS OF ASPIDOSPERMA FENDLERI.
112
ISOLATION OF THE ALKALOIDS FROM THE SEEDS.-
The dried seeds (480 g) of Aspidosperma fendleri Woodson‘S were conti
nuously extracted with methanol in a Soxhlet extractor until the extract showed
no further base with the common alkaloid reagents.
Concentration of the extract gave a brown tar which was dissolved in 2%
hydrochloric acid; after filtration the non-basic material was removed by con
tinuous extraction with chloroform. The aqueous solution was then basified
with ammonia and the crude mixture of bases (14.8 g) was obtained by chloro
form extraction. Shaking the chloroform containing the non-basic material with
hydrochloric acid, basification and extraction yielded a further quantity of
crude base (12.7 g; total: 27.5 g).
The crude base (27 g) was distributed between chloroform (stationary
phase) and acetate buffer (pH 4.45) in a countercurrent distribution apparatus
for a total of 20 transfers. The buffer entering the first tube of the appa
ratus was then replaced by acetate buffer of pH 4.00, and a further 20 trans
fers were completed. The mixture of stronger bases obtained in the leading
aqueous fractions (tubes 33 to 40; 917 mg) was chromatographed over type H
alumina in benzene. The first eluate which contained alkaloid (benzene-chloro
form, 3:1) gave white crystals of fendleridine (209 mg).
Fractions 15 to 32 (obtained from the countercurrent distribution)
yielded aspidofendlerine (135 mg) which was recrystallized from methanol.
Chromatography of countercurrent fractions 1 to 12 over alumina in
benzene gave the major base, fendlerine (12.6 g), as a thick, pale yellow oil
which crystallized on contact with acetone.
113
Fractions 13 and 14 from the countercurrent contained, in addition to
fendlerine, a small amount of another base which was purified by repeated
preparative chromatography on Whatman 3 mm paper. In this manner a total of
64 mg (m.p. 176-178°) was obtained but, apart from the UV spectrum [X 240
(8,000) and 290 (3,100) mpl and the IR spectrum (no OH or NH bands, an ester
carbonyl peak at 1735 cm-1), this base has resisted more positive charac
terization.
Fendleridine (Aspidoalbidine) (XXXVI)
The base was recrystallized from acetone.and then sublimed for analysis,
m.p. 185-186°.
Anal. Found
UV spectrum
IR spectrum
NMR spectrum
C, 77.0; H, 8.0; N, 9.4; 0, 5.8. C^gH^^N^O requires:
C, 77.0; H, 8.2; N, 9.4; 0, 5.4%.
\nax 242 (7,300) and 293 (3,050) mp.
peaks at 3300 (indoline NH) and 1600 (aromatic) cm-1,
nothing outstanding except for a 4 H complex multiplet from
6.55 to 7.506 (aromatic) and a 2 H AB quartet 3.93 and
4.036, J=3 cps (methylene adjacent to oxygen in the oxide
ring).
Mass spectrum : 296 (M+), 268 (M - OLrCHg), 252 (M - CH.CH0), 144, 138,
130, m/e.
Fendlerine (N-propionyl-16 methoxy-17 hydroxyaspidoalbidine) (XXXVIII)
After several recrystallizations from acetone the base melted at
179-181°.
114
Anal. Found
UV spectrum
G, 69.1; H, 7.5; N, 7.2; 0, 16.2; OCH^, 7.7 .
requires : C, 69.3; H, 7.6; N, 7.0; 0, 16.1; OCH^(one),
7.8%.
225 (19,200) and 258 (3,560) mp; 220
(17,200) and 300 (2,440) mp.
IR spectrum
NMR spectrum
Mass spectrum :
peaks at 1635 (N-acyl), and 1602 and 1570 (aromatic) cm-1.
1 H singlet 12.426 (chelated phenolic OH); 1 H singlet 10.756
(NH); 2 H AB quartet 6.71 and 7.056, J=8 cps (aromatic);
3 H singlet 3.856 (O-methyl); 2 H quartet 2.42 and 2.646,
J=7 cps, and 3 H triplet 1.256, J=7 cps (N-propionyl residue).
398 (M+), 370 (M - CH^CH^), 356, 355, 342 (M - propionyl),
325 (M - propionyl - CH^O), 176, 174, 161, 138, m/e.
To confirm the presence of the N-propionyl group, the base (50 mg) was
hydrolyzed in 20% sulfuric acid and a sample of the aqueous distillate was
injected into a vapor phase chromatograph, yielding only propionic acid (by
comparison with an authentic sample).
The perchlorate, m.p. 245-248°, was prepared by dissolving fendlerine in
dilute aqueous perchloric acid and extracting with chloroform. The chloroform
solution was dried over sodium sulfate and evaporated to give the crystalline
salt, which was recrystallized from ethanol.
Anal, Found : N, 5.0; 0, 26.6; Cl, 6.5 . C23^3. HCIO^. C2H ,-OH requires:
N, 5.1; 0, 26.4; Cl, 6.5%.
The characteristic peaks of ethanol (of crystallization) were clearly
visible in the NMR spectrum of this salt, determined as a solution in deuterium
oxide.
115
Aspidofendlerine (N-acetyl-16,17 dihydroxyaspidoalbidine) (XL)
The small amount of base was sublimed twice and then recrystallized from
ethanol, m.p. 278° (decomp.)»
Anal. Found
UV spectrum
IR spectrum
NMR spectrum
Mass spectrum :
C, 67.9; H, 7.2; N, 7.5; 0, 17.5 . C21H26N2°4 requires :
C, 68.1; H, 7.1; N, 7.6; 0, 17.3%.
\nax (H,500) and 259 (5,000) my; boric acid
250 (broad plateau) and 290 (shoulder) my.
peaks at 3240 (OH), 1635 (N-acyl), and 1615 and 1580 (aroma
tic) cm"1.
1 H singlet 11.066 (chelated phenolic OH); 2 H AB quartet
6.75 and 7.026, J=8.5 cps (aromatic); 3 H singlet 2.306
(N-acetyl).
384 (M^, 356 (M - CH^CH^), 341, 294, 242, 227, 138, m/e.
Aspidolimidine (from fendlerine) (XXXV)
Fendlerine (330 mg) was hydrolyzed by refluxing with 10% sulfuric acid
for four hours. The solution was then cooled and, in an atmosphere of nitro
gen, made basic with ammonia and extracted with chloroform. The dried solu
tion gave a glass (260 mg) which could not be induced to crystallize. The
UV spectrum showed peaks at 215, 240 (shoulder) and 296 my; N-acyl absorption
was absent in the infrared spectrum. The hydrolysis product (230 mg) was
dissolved in pyridine (10 ml), acetyl chloride was added and the mixture was
shaken well for 10 minutes, allowed to stand at room temperature for 2 hours
and then poured into ice water and basified with ammonia. Extraction with
chloroform gave a brown foam (240 mg), which showed both N-acetyl and 0-acetyl
absorption in the infrared spectrum. Under nitrogen, the crude product was
116
hydrolyzed with dilute methanelie sodium hydroxide (3 hours) and then poured
into water ; a yellow foam was obtained by extraction with chloroform and
evaporation of the chloroform solution to dryness . Alumina chromatography of
the foam gave a crystalline product (150 mg), which was recrystallized from
ethanol and sublimed for analysis, m.p. 194-197°.
The ultraviolet, infrared and NMR spectra were identical with those of
aspidolimidine, and a mixed melting point with a sample* of the latter gave no
depression.
Anal. Found : C, 68.6; H, 7.3; N, 7.3; 0, 16.6 . C22H28N2°4 recluires:
C, 68.7; H, 7.3; N, 7.3; 0, 16.6%.
NMR spectrum : 1 H singlet 10.746 (chelated phenolic OH); 2 H AB quartet
6.71 and 7.056, J=4.8 cps (aromatic); 3 H singlet 3.876
(0-methyl); 2 H multiplet centered at 4.086 (methylene ad
jacent to oxygen in the oxyde ring); 3 H singlet 2.306 (N-
acetyl).
Aspidolimidine (from aspidofendlerine) (XXXV)
Aspidofendlerine (35 mg) was dissolved in methanol and treated with
ethereal diazomethane for 4 hours. The volatile materials were removed at
the pump and the residue triturated with acetone. The insoluble part was
shown to be unchanged aspidofendlerine (15 mg) and the soluble portion was
repeatedly sublimed to give a crystalline product (17 mg), identical (mel
ting point, mixed melting point and infrared spectrum) with aspidolimidine.
We thank Dr. B. Gilbert for kindly providing an authentic sample of aspidolimidine.
117
Extraction and isolation of the alkaloids of the trunk bark.-
The dried trunk bark (10 kg) was ground and percolated with methanol
until the extract no longer gave a colour with Vassler's reagent.
Isolation of the alkaloids, following the procedure used for the seeds,
yielded almost exclusively fendlerine and small amounts of aspidolimidine and
fendleridine.
Alkaloids of the root bark.-
Extraction of the root bark yielded, apart from large quantities of
fendlerine and aspidolimidine, three minor alkaloids, none of which seems
to be related to the aspidoalbidine type of alkaloids and, to date, their
structures remain unknown.
-.CHAPTER III.-
ALKALOIDS OF TABERNAEMONTAM PSYCHOTRIFOLIA.
119
EXTRACTION AND ISOLATION OF THE ALKALOIDS.-
The ground trunk bark (6.5 kg) was extracted with methanol, until the
alcoholic extract gave a negative reaction with Vassler's reagent.
Evaporated to dryness this extract yielded a brown tar, which was
triturated five times with 200 ml fractions of 2% hydrochloric acid. The
acidic solution was then continuously extracted with chloroform to separate
non-basic materials. From this chloroform, after concentration and cooling,
was obtained the soluble hydrochloride of taberpsychine (6.627 g).
The aqueous solution was then basified with ammonia and again conti
nuously extracted with chloroform. The chloroform containing the basic ma
terial yielded, on cooling, a black powder (1.505 g) which was filtered,
redissolved in 2% hydrochloric acid and extracted once with chloroform. This
chloroform was discarded and the aqueous solution neutralized with ammonia
then extracted with chloroform four times. The chloroform was taken to dry
ness and the white amorphous 16-epi-vobasinic acid (454 mg) was obtained.
The chloroform solution containing the bases was evaporated to dryness
to give a semi-solid tar (61 g; total crude bases : 68.08 g)„
Part of the crude bases (10 g) was dissolved in acetone-ethanol and on
slow evaporation a fine precipitate was obtained. Filtered and washed with
cold acetone it resulted in a mixture of 16-epi-vobasinic acid and taberpsy-
chidine (300 mg). Both materials are virtually insoluble in all solvents,
but taberpsychidine is slightly soluble in hot methanol and so the mixture was
separated by boiling the solid in methanol and filtering while hot. Taberpsy
chidine (180 mg) precipitated from the methanol solution as an amorphous solid.
120
Another portion of the crude base (25 g) was submitted to a counter-
current distribution with acetate buffer, pH 3.4 (25 ml), using chloroform as
stationary phase (25 ml), for a total of fifty transfers.
The fractions 18 to 40 yielded taberpsychine (12.7 g).
Fractions 41 to 50 yielded taberpsychidine (1.22 g).
Fractions 8 to 17 yielded a minor base whose structure remains unknown
(60 mg) (Base M).
Fractions 1 to 7 (10 g) contained only neutral material and were not
investigated further.
In all, four bases were isolated and characterized. Two of them are
completely new, one whose structure remains unknown and although the fourth
57has been prepared previously by Renner et al , this is the first time it is
obtained as a naturally occurring compound.
Taberpsychine (XLII)
The base was recrystallized three times from acetone and sublimed for
analysis, m.p. 208° (decomp.), [a]^ - 243°.
Anal. Found : C, 77.9; H, 8.0; N, 9.0; 0, 5.2 . requires:
C, 77.9; H, 7.8; N, 9.1; 0, 5.2%.
UV spectrum : Xmax 222 (33,100), 272 (sh. 6,500), 280 (7,500) and 286
(6,650) my.
peaks at 3241 (NH), 2747 (N-methyl), 744 and 728 (aromatic)
cm-1.
IR spectrum
121
NMR spectrum : 1 H singlet 8.426 (NH); 4 H multiplet 7.07-7.666 (aromatic);
1 H broad quartet 5.386, J=6.5 cps, and 3 H doublet of
doublets 1.686, J=6„5 and 2.0 cps (ethylidene side chain);
3 H singlet 2.536 (N-methyl); 1 H doublet of doublets 5.136,
J=10 and 2 cps (C.3 H); 2 H AB quartet 2.93 and 3.606, J=14
cps (C.21 methylene).
Mass spectrum : 308.1849 (M*1-; ^20^24^2^ recluires: 308.1887), 293, 279, 154,
130, 122, 121, 108, 107, m/e.
Taberpsychine methiodide.-
Taberpsychine (409 mg) was dissolved in acetone (10 ml) and methyl
iodide (0.5 ml) added while heating. The solution was boiled for a few mir
nutes and then allowed to cool. The white needles of taberpsychine methiodide
obtained were filtered by suction, washed twice with cold acetone and dried
(574 mg). The product was recrystallized for analysis from hot acetone, m.p.
272-274° (decomp.).
Anal. Found : C, 55.7 ; H, 5.8 ; n, 6.4; 0, 3.9 ; i, 28.1 . Cg^HgyNgOI requires:
c, 56.0 ; H, 6.0 ; n, 6.2; 0, 3.6 ; i, 28.2%.
UV spectrum : X^^ 222 (34,400), 276 (sh. 7,200) and 284 (7,800) my.
IR spectrum : peaks at 3170 (NH), 2830 (N-methyl) and 780 (aromatic) cm-1.
NMR spectrum : 1 H singlet 8.356 (NH); 4 H multiplet 7.00-7.876 (aromatic);
1 H broad quartet 5.436, J-7 cps, and 3 H broad doublet 1.656,
J=7 cps (ethylidene side chain); 3 H singlet 3.286, and 3H
singlet 3.036 (2 N-methyls); 1 H doublet of doublets 5.236,
J=10 and 2 cps (C.3 H).
122
3-Ethyl pyridine from taberpsychine.-
Sublimed taberpsychine (194 mg) was mixed with dried zinc dust (1 g),
introduced in a glass tube (7 mm internal diameter) and an additional amount
of zinc dust (0.5 g) placed on top of the mixture. All this was covered with
glass wool and the tube sealed under vacuum. The tube was heated in the su
blimation block at 280°C for three hours. A yellow distillate was obtained in
the cooler part of the tube protuding from the block. The tube was allowed
to cool and then cut open. The distillate was dissolved in methanol and
analyzed in the gas chromatograph with a 4 ft. column of Apiezon L 10%. The
spectrum shows two peaks (3:1 ratio) with retention times of 6 and 12.5 mi
nutes respectively at a column temperature of 130°C and increasing at the
rate of l°/min., which were identified by direct comparison as corresponding
to 3-ethyl pyridine and 3-methyl-5-ethyl pyridine respectively. The major
fraction was recovered in a small U tube cooled by acetone-dry ice, dissolved
in deuterated chloroform and introduced into an NMR tube.
NMR spectrum : 2 H multiplet 8.27-8.476 (H.2 and H.6); 1 H broad doublet
7.406, J=8 cps (H.4); 1 H quartet 7.03 and 7.136, J=8 cps
(H.5); 2 H quartet 2.626, J=7 cps, and 3 H triplet 1.226,
J=7 cps (ethyl chain).
Dihydrotaberpsychine.-
Taberpsychine (1.210 g) was dissolved in ethanol (100 ml) and platinum
oxide (500 mg) added together with glacial acetic acid (10 ml). This mix
ture was left shaking for 50 hours in an atmosphere of hydrogen (50 p.s.i.).
The catalyst was then filtered off and the alcoholic solution evaporated to
dryness under reduced pressure. The resulting brown foam was redissolved in
123
2% hydrochloric acid, basified with ammonia and extracted four times with
chloroform. The chloroform was dried over sodium sulfate and evaporated to
dryness. The product (1.150 g) was dissolved in acetone and the dihydrotaber-
psychine obtained as white crystals, m.p. 191-193°.
Anal. Found
UV spectrum
IR spectrum
NMR spectrum
C, 77.2; H, 8.4; N, 8.9; 0, 5.4 . CggHg^NgO requires :
C, 77.4; H, 8.4; N, 9.0; 0, 5.2%.
X 223 (34,100), 277 (sh. 9,000), 284 (9,800) and 293
(8,300) my.
peaks at 3271 (indole NH), 2788 (N-methyl), 745 and 726
(aromatic) cm-1.
4 H multiplet 7.00-7.806 (aromatic); 1 H doublet of doublets
5.126, J=10 and 2 cps (C.3 H); 3 H singlet 2.536 (N-methyl);
3 H triplet 0.986, J=7 cps (methyl in saturated ethyl side
chain).
Mass spectrum : 310 #), 295 (M - 15), 279 (M - 31), 265, 251, 195, 180,
170, 168, 155 (M++), 144, 138, 130, 124, 122, 108, m/e.
Dihydrotaberpsychine methiodide.-
A sample of recrystallized dihydrotaberpsychine (650 mg) was dissolved
in acetone (15 ml) and methyl iodide (2.5 ml) was added to the warm solution.
The mixture was boiled for five minutes and then allowed to cool. The amor
phous dihydrotaberpsychine methiodide obtained was recrystallized for analy
sis from hot acetone, m.p. 255-258° (decomp.).
Anal. Found : C, 55.7; H, 6.5; N, 6.3; 0, 3.6; I, 28.3 . re“
quires: C, 55.8; H, 6.5; N, 6.2; 0, 3.5; I, 28.1%.
124
UV spectrum : Amax 221 (55,200), 275 (sh. 10,900), 284 (11,700) and 292
(10,400) my.
Dihydrotaberpsychine-methine (XLI)
Dihydrotaberpsychine methiodide (550 mg) was suspended in tert-butyl
alcohol (15 ml) and a solution (25 ml) of potassium (1 g) in tert-butyl al
cohol added slowly. The mixture was refluxed for 24 hours, then evaporated to
dryness under reduced pressure, the residue was redissolved in water and the
aqueous solution extracted four times with chloroform. After evaporation of
the chloroform to dryness, dihydrotaberpsychine-methine (418 mg) was obtained
as a pale yellow foam which was crystallized from acetone and sublimed for
analysis, m.p. 153-155°.
Molecular weight
UV spectrum
IR spectrum
NMR spectrum
by mass spectrometry : 324.2175 . £21^28^2^ reclu^Lres*
324.2202 .
A _ 229-5 (38,500), 271 (12,000), 284 (11,400) and 294
(sh. 9,000) my.
peaks at 3250 (indole NH), 2820 and 2760 (N-methyl), 745
and 730 (aromatic) cm”1.
1 H singlet 8.846 (indole NH); 4 H multiplet 7.00-7.646
(aromatic); 1 H doublet 6.696, J=12 cps (C.6 H) and 1H
doublet of doublets 5.556, J=12 and 8 cps (C.5 H), both
being the low field portion of an ABX system; 1 H doublet
of doublets 4.846, J=12 and 2 cps (C.3 H); AB part of a
second ABX system; 1 H doublet 4.216, J=ll cps and 1 H
triplet 3.796, J=ll cps (methylene adjacent to oxygen in
the oxyde ring); 6 H singlet 2.206 (N-dimethyl); 3 H triplet
125
0.875, J=7 cps (methyl on saturated ethyl side chain).
Mass spectrum : 324 (M+), 310, 295, 280, 266, 194, 185, 180, 169, 168, 162,
(M++), 156, 137, 130, 124, 58, m/e.
A minor product which could not be induced to crystallize was identified by
means of its NMR spectrum as the other isomer of dihydrotaberpsychine-methine
(structure XLIII).
NMR spectrum : principal feature was a pair of doublets at 4.97 and 5.635,
J=2 cps due to a terminal methylene.
Hydrogenation of dihydrotaberpsychine-methine.-
Dihydrotaberpsychine-methine (400 mg) was dissolved in ethanol (50 ml),
platinum oxide (150 mg) and glacial acetic acid (15 ml) were added and the
mixture left hydrogenating for 24 hours under hydrogen at a pressure of 52
p.s.i. The reaction mixture was then filtered and evaporated to dryness un
der reduced pressure. The residue was dissolved in water, basified with
ammonia and extracted four times with chloroform. The chloroform solution,
after drying over sodium sulfate and evaporating to dryness, yielded a yellow
foam (340 mg). This foam was dissolved in acetone and the crystalline deri
vative was obtained and recrystallized for analysis from the same solvent,
m.p. 184-186°.
Anal. Found : C, 77.5; H, 9.2; N, 8.4; 0, 5.1 . C^l^SO^^ recïuires:
C, 77.3; H, 9.3; N, 8.6; 0, 4.9%.
UV spectrum : Xjnax 224.5 (46,000), 279 (sh. 11,050), 285 (12,000) and
293 (10,300) mp.
peaks at 3250 (indole NH), 2750 (N-methyl) and 740 (aromatic)
cm-1.
IR spectrum
126
NMR spectrum : 1 H broad singlet 9.236 (indole NH); 4 H multiplet 6.92-
7.736 (aromatic); 1 H broad doublet 5.106, J=10 cps (C.3 H) ;
6 H singlet 2.206 (N-methyls); 3 H triplet 0.856, J=7 cps
(methyl in saturated ethyl side chain).
Mass spectrum : 326.2362 (M4"; Cg^HggNgO requires : 326.2358), 282, 281, 268,
226, 225, 180, 168, 156, 144, 130, m/e.
Taberpsychine-methine (XLIV)
Recrystallized taberpsychine (1.687 g) was suspended in tert-butyl
alcohol and a solution (25 ml) of potassium (1 g) in tert-butyl alcohol added.
The suspension was refluxed for 18 hours. The reaction mixture was then ta
ken to dryness under reduced pressure, redissolved in water and extracted
five times with ether. The ether was dried over sodium sulfate and evaporated
to dryness to give a brown foam (1.200 g). After redissolving the foam in
ether and reducing the solution to a small volume, taberpsychine-methine
crystallized selectively (589 mg). Recrystallization for analysis was from
ether, m.p, 194-196° (decomp.).
Anal. Found
UV spectrum
IR spectrum
MMR spectrum
C, 78.1; H, 8,0; N, 8.5; 0, 5.0 . ^21^26^0 requires:
C, 78.2; H, 8.1; N, 8.7; 0, 5.0%.
X 224 (46,300), 278 (sh. 8,800), 284 (9,200) and 292.5
(8,100) my.
peaks at 3270 (indole NH), 3075 (aromatic), 2766 (N-methyl),
1590, 740 and 725 (aromatic) cm-1.
I H broad singlet 8.186 (NH) ; 4 H multiplet 6.98-7.646
(aromatic); 1 H doublet of doublets 6.40 and 6.516, J=18 and
II cps (H ); 1 H doublet 5.286, J=18 cps (H^); 1 H doublet
127
5.216, Jrll cps (Hc); 2 H doublet 5.226, J=8 cps (2 Hd) ;
1 H doublet 5.096, J=ll cps (C.3 H); 6 H singlet 2.276 (2 N-
methyl).
Mass spectrum : 322 (M+), 278 (M - .N(CH3)2), 215, 194, 183, 180, 168, 156,
136, 130, m/e.
A minor product was observed by thin layer chromatography but could not be
isolated. This is probably the other isomer formed in small quantity.
Hydrogenation of taberpsychine-methine.-
Taberpsychine-methine (429 mg) was dissolved in ethanol (50 ml) and
introduced into a hydrogenation bottle together with acetic acid and plati
num oxide (200 mg). This mixture was shaken for 18 hours under hydrogen
(50 p.s.i.). The solution was then filtered, evaporated to dryness under
reduced pressure and the residue redissolved in water, basified with ammonia
and extracted five times with ether. The ether was evaporated to dryness
and a white foam (400 mg) was obtained. The tetrahydro compound was crys
tallized from acetone-ether and sublimed for analysis, m.p. 153-155°.
Anal. Found
UV spectrum
IR spectrum
NMR spectrum
C, 77.2; H, 9.3; N, 8.3; 0, 5.0 . C2jH3qN20 requires :
C, 77.3, H, 9.3; N, 8.6; 0, 4.9%.
^max 225 (29,300), 278 (7,500), 284.5 (8,100) and 293
(7,050) my.
peaks at 3250 (indole NH), 2766 (N-methyl), 740 and 730
(qromatic) cm"1,
1 H broad singlet 8.826 (indole NH); 4 H multiplet 6.97-
7.736 (aromatic); 1 H broad doublet 5.126, J=10 cps (C.3 H) ;
6 H singlet 2.356 (N-methyIs); 3 H triplet 1.256, J=9 cps,
and 3 H doublet 0.936, J=6 cps (saturated methyls).
128
Taberpsychidine (XLIX) ( = Affinine).-
The very insoluble base was recrystallized from a large volume of
ethanol and sublimed for analysis, m.p. 273-275° (decomp.).
Anal. Found
UV spectrum
IR spectrum
NMR spectrum
C, 73.8; H, 7.5; N, 8.5; 0, 10.0 . ^2{Fi2^'p2 acquires:
C, 74.0; H, 7.5; N, 8.6; 0, 9.9%.
X 236 (sh. 13,200) and 320 (13,400) mp.
peaks at 3150 (broad, NH and OH), 2800 (N-methyl), 1650
(3-keto), 740 (aromatic) cm-1.
1 H broad singlet 9.806 (indole NH); 4 H multiplet 7.00-
7.836 (aromatic); 1 H broad quartet 5.406, J=6 cps, and
3 H broad doublet 1.686, J=6 cps (ethylidene side chain);
3 H sharp singlet 2.536 (N-methyl).
Mass spectrum : 324 (M^, 293 (M - .CH^OH), 158, 152, 122, 108, m/e.
Taberpsychidine acetate.-
Taberpsychidine (150 mg) was dissolved in pyridine (5 ml) and an
excess of acetic anhydride (1 ml) added. The mixture was left standing
overnight at room temperature. Methanol was then added to hydrolyze the
excess anhydride and the solution evaporated to dryness under reduced pres
sure. The residue was redissolved in water, basified with ammonia and the
aqueous solution extracted with chloroform. The product is very unstable
and decomposes while in solution, so crystallization was not possible.
However IR, NMR and mass spectra indicate that it is indeed the mono-acetate
129
of the base.
UV spectrum (qualitative) : 223 (shoulder) 237 (shoulder) and 319 my.
IR spectrum : peaks at 3300 (indole NH), 1745 and 1235 (0-acetyl), 1650
(3-keto), 1575 and 740 (aromatic) cm-1.
NMR spectrum : 1 H singlet 9,806 (indole NH); 4 H multiplet 7.00-7.846
(aromatic); 1 H broad quartet 5.406, J=6 cps and 3 H
doublet 1.676, J=6 cps (ethylidene side chain); 3 H singlet
2.536 (N-methyl); 3 H singlet 1.776 (0-acetyl).
Mass spectrum : 366 (M+), 306 (M - acetic acid), 293 (M - CH^COOCH^.),
263, 194, 158, 122, m/e.
Vobasinediol (from taberpsychidine) (XLVIII)
Taberpsychidine (110 mg) was suspended in absolute methanol (25 ml)
and an excess of sodium borohydride (100 mg) added. A drying tube (CaCl^)
was placed on top of the flask and the mixture left standing overnight at
room temperature. Water (200 ml) was then added and the aqueous solution
extracted four times with ether. After evaporation to a small volume, colour
less needles of vobasinediol (100 mg) were obtained. The material was su
blimed for Analysis, m.p. 244-245° (decomp.), [al^ - 60° (Methanol).
Anal. Found : C, 73.6; H, 8.0; N, 8.4; 0, 9.7 . £‘2^2$'p2 requires :
C, 73.6; H, 8.0; N, 8.6; 0, 9.8%.
UV spectrum : X^x 224 (21,600), 283 (6,100) and 291 (5,400) my.
IR spectrum : peaks at 3300 (NH and OH), 2880 (N-methyl), 740 (aromatic)
cm-1.
130
NMR spectrum : 1 H singlet 9.756 (indole NH); 4 H multiplet 6.90-7.626
(aromatic); 1 H broad quartet 5.476, J=7 cps and 3 H
broad doublet 1.686, J=7 cps (ethylidene side chain);
1 H broad doublet 5.276, J=6 cps (C.3 H); 3 H singlet
2.436 (N-methyl).
Mass spectrum : 326 (M+), 308 (M - H^O), 293 (M - H^O - 15), 277 (M - H^O -
.CH^OH), 183, 180, 154, 152, 136, 130, 122, m/e.
16-epi-Vobasinic acid (L)
The base was recrystallized several times from large volumes of hot
ethanol, m.p. 295° (decomp.).
Anal. Found
UV spectrum
IR spectrum
NMR spectrum
Mass spectrum :
C, 70.8; H, 6.6 ; n,
oCO ; 0, 14.4 . requires
C, 71.0; H, 6.6 ; n,
to
00 ; 0, 14.2%.
A 238 (13,100) and 316 (20,000) mp.
peaks at 3105 (indole NH), 1650 (3-keto), 1610 (carboxyl-
ate) and 753 (aromatic) cm-1.
(in 2% DgSO^/DgO solution) 4 H multiplet 6.88-7.776 (aroma
tic) ; 1 H broad quartet 5.936, J=7 cps and 3 H broad
doublet 1.686, J=7 cps (exocyclic ethylidene); 3 H singlet
3.006 (N-methyl on quaternary nitrogen).
338 (M+), 293 (M - .COOH), 180, 166, 158, 122, m/e.
16-epi-Vobasine (from 16-epi-vobasinic acid).-
16-epi-Vobasinic acid (200 mg) was suspended in dry methanol (20 ml)
and ethereal diazomethane solution (20 ml) added. The mixture was refluxed
overnight on a water bath. The solution was then evaporated to dryness and
131
redissolved in ether. 16-epi-Vobasine (190 mg) crystallized on slow evapora
tion and was recrystallized from ether, m.p. 185-187°.
Anal. Found :: C, 71.5; H, 6.8; N, 8.0; 0, 13.8 . requires:
C, 71.6; H, 6.9; N, 8.0; 0, 13.6%.
UV spectrum :: X 237 (10,550) and 320 (12,000) my.
IR spectrum :: peaks at 3300 (indole NH), 2750 (N-methyl), 1740 (methyl
ester), 1645 (3-keto) and 740 (aromatic) cm-1.
NMR spectrum : 1 H broad singlet 9.575 (indole NH); 4 H multiplet 7.00-
7.835 (aromatic); 1 H broad quartet 5.515, J=7 cps and
3 H broad doublet 1.735, J=7 cps (exocyclic ethylidene);
3 H singlet 3.535 (methyl ester); 3 H singlet 2.525 (N-
methyl).
Mass spectrum :: 352 (M+), 293 (M - .COOCHJ, 180, 166, 158, 122, m/e.
Base M.-
The small amount of alkaloid (60 mg) obtained was recrystallized
twice from acetone, m.p. 162-164°, [alp - 129°.
Anal. Found :: C, 71.0; H, 7.3; N, 8.1; 0, 13.5 . requires:
C, 71.2; H, 7.4; N, 7.9; 0, 13.5%.
UV spectrum :: X^ax 22? (44,700), 278 (sh. 8,800), 286 (9,600) and 294
(8,600) my.
IR spectrum :: peaks at 3410 (OH), 3258 (NH), 1730 (methyl ester), 745
(aromatic) cm"1.
NMR spectrum :: 1 H broad singlet 7.905 (indole NH); 4 H multiplet 7.00-
7.525 (aromatic); 1 H singlet 4.095 (l^CHOH ); 3 H singlet
132
3.686 (methyl ester); 3 H singlet 2.126 (N-methyl); 3 H
doublet 1.266, J=7 cps (saturated methyl); 1 H doublet of
doublets 3.906, J=7 and 3 cps (H adjacent to methyl group).
Mass spectrum : 354.1956 (M+; requires: 354.1943), 339 (M - 15),
336 (M - 18), 308, 295 (M - 59), 213, 205, 194, 180, 168,
167, 154, 152, 140, 130, 122, 108, m/e.
133
-.SUMMARY.-
With the object of studying the alkaloids present in Venezuelan plants
we undertook the examination of several Apocynaceae species, of which a few
proved to contain little or no alkaloid at all. Only the plants yielding
significant amounts of natural bases are reported here, namely Aspidosperma
excelsum, A. cuspa, A. fendleri, and Tabernaemontana psychotrifolia. The
alkaloids were isolated and purified in most cases by countercurrent distribu
tion and their structures elucidated utilising non-destructive spectral methods
wherever possible. Correlation or comparison with known alkaloids afforded a
final proof for the majority of the assigned structures.
The alkaloids encountered can be roughly divided into five structural
types, apart from a simple pyridine which was isolated as a very minor product
from A. cuspa. While evidence is presented towards the elucidation of its
structure, lack of material precludes a definite proof at this time.
Pyridine XXIX R = H yohimbine R = COŒL 0-acetyl yohimbine
In the first group are found both principal alkaloids obtained from
A. excelsum which are of the yohimbine skeletal type. The two alkaloids are
yohimbine itself and O-acetylyohimbine. Both were previously reported in the
literature, but this is the first time O-acetylyohimbine is found as a natural
ly occurring base.
Representing a second structural group are fendlerine, fendleridine,
and aspidofendlerine, all obtained from A. fendleri and des-O-methylaspidocar-
pine, obtained from A. cuspa. All of these contain the aspidospermine type
skeleton or present small but important modifications.
R = R' = R'' = H fendleridine
R = OCHg; R' = OH; R'' = CXX^Hg fendlerine des-O-methylaspidocarpine
R = R' = OH; R'' = COCHL aspidofendlerine
A third group involves three alkaloids related to picraline, all ob
tained from A. cuspa. These are picraline itself, des-acetylpicraline and
aspidodasycarpine. The latter containing a skeleton biogenetically very close
ly related to that of picraline.
R = H desacetyl picraline
R = COCHg picralineaspidodasycarpine
135
The fourth group includes two alkaloids obtained from T. psychotrifolia
which are related to vobasine. These are affinine and 16-epi-vobasinic acid.
The latter had been prepared previously but never before reported as a natu
rally occurring compound. Another base, which we called base "M" for purpose
of identification, is believed to be of the same skeletal group, but its struc
ture remains unknown.
R = CH2OH; R' = H affinine
R = H; R' = CH^OH 16-epi-vobasinic acid
Finally, in the fifth group is the major base from T. psychotrifolia,
taberpsychine, which represents a new structural class derived from the
vobasine-like skeleton.
taberpsychine dihydrotaberpsychine-methine
136
It is noteworthy to mention the major product from the Hofmann degra
dation of dihydrotaberpsychine, which was principally responsible for the
structure elucidation of taberpsychine. In fact spin decoupling experiments
in the nuclear magnetic resonance spectrum of this methine revealed the size
of, and the substitution on, the oxide ring,
137
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