XLIII.-Researches on the Comtitution o j Physo- stigmine. Part II. The Synthesis of %Dimethyl- aminoacetyl-2-methylindole and 2-a-Dimethyl- amino- y-hydroxyprop ylindole.

By ARTHUR HENKY SALWAY.

PREVIOUS investigations on the constitution of physostigmine (merim), C15H2,02X3, have shown that the prinaipal degradationi product of the alkaloid is eseroline, C13H180N2, this substance being derived from' the parent compound by alkaline hydrolysis with

A A 2

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352 SALWAY: RESEAHCHES ON THE

elimination of carbon dioxide and methylamine, according to the equation :

Cl,H,70N,-CO*NHMe+ H20 = C13H180N,+ CO, + N q M e . The solution of the problem of the constitution of phy8atigmine

thus depends on the determination of the constitution of eseroline. The investigation of the latter was recently undertaken by the present author (T., 1912, 101, 978), who showed that this substance is in all probability an indole derivative, since it yields 2-methyl- indole when distilled with zinc dust in a current of hydrogen. Moreover, it was also shown that eseroline is a, tertiary monacid base containing a methyl group attached t o nitrogen, that it pos- sesses weakly acid properties, and that it rapidly absorbs oxygen in the presence of alkalis with the formation of rubreserine, eserine- blue, and other oxidation products. Whilst this knowledge concern- ing the properties of eseroline and its degradation products is insufficient to enable the author to propose a constitution for the alkaloid with a reasonable degree of certainty, it iievertheless seeiiied desirable for the purpose of the present i nvestigatiori to construct a hypothetical fornula which would serve as a basis for some sya thetical experiments.

In the construction of such a formula it is evident that the rnethylindole complex, which eseroline presumably contains, will account for the group of atoms C,H,N, the nitrogen atom of which will correspond with the non-basic nitrogen atom of eseroline. The remainicg part of the molecule, CkH,ON, will contain a tertiary basic nitrogen atom attached to a methyl group, and also, in all probability, a hydroxyl group,’” and may therefore be further resolved into tlhe group C,H,(OH)(NMe). The nature of the union between the indole complex and the group C,H,(OH)(NMe) now remains t o be considered. I n the first place, the latter might be in combination with the indole nucleus as an aliphatic side- chain, in which case eseroline would be represented by a formula of the type 1:

HO*CH CH,Ct€

(1.1 (11.)

On the other hand, there exists the possibility that the group, C,H,(OH)(NMe), forms a closed chain with the indolic part of the molecule. I n this case the simplest formula which can be con-

* The presence of a liydroxyl group in eseroline is probable, but lins not beeii established beyond qnestion.

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CONSTITUTION OF PHYSOSTIGMINE. PART 11. 353

structed in agreement with the known properties of eseroline is of the type 11.

The author has now undertaken the synthesis of compounds belonging to the types I and I1 in the hope of obtaining more definite Irnuwledge regarding the constitution of eseroline. I n the present investigation two derivatives of indole containing a basic and oxygenated side-chain? namely, 3-ddmet7~ylnminoncet~/E-2-methyl- indole (111) and 2-a-dimethylamino- y-h ydroxypropylindole (IV),

(111.)

c , H , < ~ ~ > c ~ c H (N M~J.CH,~CH,~OH

(IV.) have been prepared, and their properties compared with those of eseroliiie. It has been found that these synthetic compounds possess properti- which differ greatly from thaw of eseroline, and i t may therefore be concluded that the latter is not a simple sub- stituted indole of the type represented by formula I.

It is proposed in subsequent investigations to attempt the synthesis of compounds of the kind reprmented by formula 11.

A number of general methods are known for the synthesis of substituted indoles, but whilst a few of these can be applied with good results in the preparat>ion of the simpler indole derivatives, none of them appears to be of much service in the preparation of indoles with am extended sidechain. Recently, however, Odd0 (Gazzetta, 1311, 41, i, 234) has indicated the possibility of prepar- ing indoles, substituted in the 3-position, by the aid of the Grignard reaction, whilst Bladelung (Ber., 1912, 45, 1128, 3541) has found that o-tohidides may be converted into substituted indoles by heating with sodium ethoxide a t a high temperature. These methods have now been used by the author for the prepara- tion of the indole compounds described in the present investigation.

EXPERIMENTAL. I.-Syn thcsis o j 3-Dimet?~.~lamirroacet?/l-2-methyli.ndole (111).

Odd0 has shown (loc. c i t . ) that indole reacts with magnesium methyl iodide with the formation of magnesium indolyl iodide, which by subsequent treatment with acetyl chloride yields 3-acetyl- indole. I n the present. experiments a similar process has been employed for thc conversion of a-methylindole into 3-chloroacetyl- 2-methylindole, which then yielded 3-dimethylaminoacetyl-2-methyl- indole on treatment with dimethylamine. These changes are repre- sented in the following scheme:

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554 SAL.WAY: RESEARCHES ON THE

3-C'hloroace tyl-2-me thy l ido le (V). For the preparation of this compound two parts of magnesium

powder were mixed with nine parts of ethyl bromide in the presence oE dry ether. After the magnesium had completely dissolved, eleven parts of 2-methylindole, dissolved in dry ether, were added drop by drop, and the mixture kept a t the ordinary temperature for about an hour. Chloroacetyl chloride (nine parts), dissolved in &her, was then slowly added in the cold. A t first the addition of t h e latter caused the precipitation of a viscid, yellow solid, which finally became cherry-red. After all the chloroacetyl chloride had been added, the upper layer of ethereal liquid was decanted, and the viscid solid which remained was agitated vigorously with ai l aqueous solution of sodium hydrogen carbonate, when an almost colourless solid, insoluble in the alkaline liquid, was obtained. This wahs collected, dried, and crystallised several times from ethyl acetate, from which i t was deposited in sleiider, coloiirless needlw, melting a t 2 2 0 O : O.0830 gave 0.1 946 GO2 a id 0.0380 H,O. C = 63.9 ; H = 5.1. 0.1286 ,, 0.0876 AgCl. C1=16.9.

C,,H,,ONCl requires C = 63.6 ; H = 4.8 ; C1= 17.1 per cent. 3-Cirlo~oacety2-2-meth.ylindole is sparingly soluble in ether,

benzene, or chloroform, but more readily so ilz alcohol or ethyl acetate. Its chlorine atom is very reactive, being quickly removed when heated witlh alkalis, and also to some extent when heated with alcohol.

I n one experiment for the preparation of the above compound magnesium methyl iodide was employed in the place of magnesium ethyl bromide with a somewhat unexpected result. The product of the reaction in this case was a mixture of two compounds in approximately equal proportions. One of these compounds was the desired 3-chloroacetyl-2-methylindole melting at 220°, whilst the other melted at 197O, and did not contain chlorine. The latter substance on analysis gave the following figures :

0,1075 gave 0.3011 (20, and 0.0642 H20.

It appeared probable from this result that the compound melting

C=76*4; H=6.6. C,,H,,ON requires G'= 76.3 ; H = 6.4 per cent.

a t 1 9 7 O possessed tllie constitut.ion C,H,<;$>CAIe, and had been

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CONSTITUTION OF PHYSOSTIGMINE. PART Ir. 355

formed in the above reaction by the reducing action of the liberated hydriodic acid on the 3-chloroacetyl-2-methylindole. I f this supposi- tion regarding the constitution of the compound melting a t 197O were correct, then the same substance should be obtained by the action of acetyl chloride on magnwium 2-methylindolyl iodide. This experiment, conducted in a manner similar to that employed in the preparation of 3-c3hloroacetyl-2-methylindole, yielded a product identical with ths above-mentioned substance melting a t 197O.

3-A cetyl-2-methylindole is moderately soluble in chloroform or alcohol, but only sparingly so in benzene or ether. It crystallises from hot alcohol in slender, colourless needles, and from chloroform in thin, colourless plates, melting a t 197O. It does not give the pine-shaving colour reaction of indole. It yields an oxa'me, which crystallises from dilute alcohol in glistening leaflets, melting and decomposing a t 199O :

The latter is therefore 3-acetyl-2-methylindole.

0.0972 gave 0.2502 C'O, and 0.0568 H,O. C= 70.2 ; H = 6.5. C,,H,,0N2 requires C = 70.2 ; H = 6.4 per cent.

3-Dime thylaminoncetyL2-rn ethylindole (111).

A quantity of 3-chloroacetyl-2-methylindole was heated for four hours at looo in a sealed tube with an excess of dimethylamiiie dissolved in alcohol. The solvent and the excess of dimethylamiiie were first removed in a current of steam, and the mixture then acidified with dilute hydrochloric acid, when a quantity of non- basic material remained undissolved, the l&ter being collected and set aside for subsequent examination. The acid liquid was now made alkaline with sodium carbonate, and the precipitated base collect,ecl, washed with water, and purified by crystallisation from alcohol. It was obtained in colourless, rhombahedral prisms, which melted at, 201O. The yield of pure substqnce amounted to 62 per cent. of the theoretical:

0.0958 gave 0.2540 CO, and 0.0640 H,O. C=72.3; H=7.4.

The non-basic by-product in the above reaction waa very sparingly soluble in the usual organic solvents. It was crystallised, however, from much hot acetic acid, and then obtained in small, colourless, square prisms, which melted and decomposed at 270O:

CI3H,,ON2 requires @= 72.2 ; H = 7.4 per cent.

0.1304 gave0.3243 CO, and 0.0760 H,O. 0.1980 ,, 0*0640 AgCl. Cl=8.0. 0.1718 ,, 14.4 C.C. N, a t 1 2 O and 775 mm. N=10.2.

C,,H,,O2N,C1 requirec; C= 68.0 ; H = 6.1 ; N = 9.9 ; C1= 8.4 per cent. I t appears from these results pnd tlie properties of the componnd

C=67.8; H=6*5.

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356 SALWAP: RESEARCHES ON THE

that, the latter is a quaternary ammonium salt formed by the union of one molecule of 3-dimethylaminoacetyl-2-methylindole and one of 3-chloroacetyl-2-methylindole, and therefore has the constitution :

3-DimethylaminoacetyE-2-meth~ylindole is sparingly soluble in ether, chloroform, or benzene, and moderately so in alcohol. It is a stable base, showing no tendency to absorb oxygen in the presence of alkalis. It does not respond to the pineshaving test for indoles. Its hydrochloride, prepared by dissolving the base in dilute hydro- chloric acid, evaporating the solution to dryness and crystallising the residue from alcohol, was obtained in colourless, rhombohedra1 crystals, melting at 258O.

Many attempts were made to reduce the above base in order to obtain from it by the addition of two atoms of hydrogen a substance of the same empirical formula as eseroline, but reduction could not be effected; thus, when the base was heated with tin and hydro- chloric acid, or with sodium in amyl alcohol, no change occurred, whilst treatment with hydriodic acid and red phosphorus a t 120° caused disruption of the molecule with formation of 2-methylindole.

I1 .-Syn th ssis of 2-a-Dim e t h y lumino- y -h ydr o zy pro py l indol e (IV) . -4s already indicated, Madelung (Zoc. cit.) has shown that

o-toluidides may be converted into substituted indole derivatives by heating with sodium ethoxide. Although this reaction has hitherto only been applied to the o-toluidides of acetic, benzoic, and oxalic acids, it appeared probable that the method might be extended to the preparation of any indole derivative, C6H4<NH> CH- CR, provided

that the acid R*CO,H could be obtained. For the purpose of the present synthesis the radicle R was required to consist of an oxygen- ated my1 group containing a tertiary basic nitrogen atom, and the correspondicg acid, R*CO,H, chosen as best fitted to meet these requirements, was a-dimeth yl amino- y-hydroxybutyric acid,

HO CH,*CH2*CH (NMe,) C0,H. The steps which were necessary for the preparation of this compound and for its conversion into the desired indole derivative are as follows : CH,Br*CH,Br - j PhO°CH2*CH2Br -+ PhO*CH,*CH,*CH(CO,H),

--+ PhO*CH2*CH,*CBr(C0,H), + PhO*C€I,*CH,*CHBr*CO,H -+ (VIII.) (IX. 1

FhO*CH2*CH2*C: H( NMe,)*CO,H and IX.1

(VI .I (VII.)

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COXSTITUTION OF PHYSOSTIGMIKE. PART 11. 357

PhO*CH,*CH,*CHBr*CO*NH*C6H4Me -+ (XI.)

PhO CH,* CH, * CH( NMe,). CO *NH* C,H,Me -+ (XII.)

PhO*CH,*CH ,*CH(NMe,)*C<NH>C,H, CH -+

(XIII . ) HO*CH,*CH,*CH( NMe2)*CeNH>C6H, CH

(XIV.) The compounds represented by the formulae (VI) and (VII) in

the above scheme have already been described by Perkin, Bentley, and Haworth (T., 1896, 69, 169), whilst the compounds (VIII) and (IX) have been synthesised by Fischer (Ber., 1907, 40, 106).

a-nim'e t hylamino- y-phenoxy b u ty ric A cid (X).

For the preparation of this compound one part of a-bromo-y- phenoxybutyric acid, obtained from ethylene dibromide as described by the above-mentioned investigators (Zoc. cit.), was heated in a sealed tube for six hours a t looo with two parts of an aqueous solution (33 per cent.) of dimethylamine. The product was then distilled in a current of steam with a known amount of sodium hydroxide until the excess of dimethylamine had been removed. A quantity of hydrobromic acid equivalent in amount to the sodium hydroxide employed was then added, and the liquid concentrated to dryness under diminished pressure. The residue was then digested with absolute alcohol, the alcoholic liquid filtered to remove the sodium bromide, and the filtrate evaporated. The amineacid was thus obtained as a viscid oil, which did not crystallise on keeping. When a.gitated with a little aqueous hydrobromic acid, however, it immediately solidified, with the formation of a crystal- line hydrobromide. This was purified by recrystallisation from water, and was then obtained in colourless, thin plates, melting at 86O:

0.1183 (air-dried), heated a t llOo, lost 0.0124 H20. H20=10*5. 0.1445 ,, gave 0.0784 AgBr. Br=23'1.

C12H,,0,NBr,2H20 requires H20 = 10.6 ; Br = 23.5 per cent. 0*1059* gave 0.1824 CO, and 0.0562 H,O. @=47.0; H=5*9.

ClaHl,O,NBr requires C= 47.4 ; H = 5.9 per cent. In order to obtain the free base, the above-described hydro-

bromide was dissolved in water, and an amount of sodium carbonate added just sufficient t o combine with the hydrobromic acid. The mixture was then evaporated to dryness under diminished pressure,

* Anhydrous substance.

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358 SALWAF: BESEAWHES ON THE

and the amineacid extracted from the residue by means of absolute alcohol. After evaporating the alcoholic extract, the amino-acid was obtained as a very hygroscopic, amorphous solid, which could not be obtained crystalline.

a-Dimethyla??zirlo-y-~he7.lo~~~tutyric acid (X) is readily soluble in alcohol or water, insoluble in ether, benzene, or chloroform. It yields a hydrochloride, which crygtallises from water in prismatic needles melting a t 83O.

PhO*CH,*CH,*CH( C0,Me) *NM%,HCl, crystallises from hot ethyl acetate in colourless aggregates of flat, plates, which melt a t 130O:

The mefhyl ester of the latter,

0*1000 gave 0.2086 CO, and 0.0666 H,O. C=56*9; H = 7.4.

For the next stage in the synthesis it was necessary to prepare the o-hluidide of the above-described amino-acid (XII). Attempts were first made to obtain this compound from the acid chloride, PhO*CH2*C€12*CH(NMe2)*COCl, but the latter could not be prepared. Ultimately the difficulty wm overcome by first prepar- ing the o-toluidide of a-bromo-y-phenoxybutyric acid (XI), and sitbsequsntly displacing the bromine in this compound hy thr tlimeth ylarnino-group.

C,,H,,O,N,H@l requires C= 57.0 ; H = 7.3 per cent.

a-Bromo-y-pltenoxybubyro-o-tolzridide (XI).

Seven parts of a-bromo-y-phenoxybutyric acid were dissolved in ether, and six parts of phoephorus pentachloride added. After the reaction had subsided, the ether, together with the phosphoryl chloride which had been formed, was removed on the water-bath under diminished pressure, and the residual crude acid chloride then added to an excess of o-toluidine dissolved in ether. A volu- minous precipitate of the o-toluidide was thus formed, which was collected, washed with water, and recrystallised from hot alcohol, when it separated in colourless, prismatic needles, melting at 147O:

0.1000 gave 0.2145 CO, and 0.0478 H20. C,,H,,O,NBr requires C'= 58.6; H= 5.2 per cent.

a-nro?n,o-y-pT~e72oxyb.zctyro-o-tolua~i~e is only moderately soluble in ether, but momre readily so in chloroform, ethyl acetate, or alcohol.

C = 58.5 ; H= 5.3.

a-Dimethylamino- y-phenoxyb ut yro-o-t oluidide (XII). This substance was prepared by heating the foregoing compound

in a sealed tube at looo for two hours with an excess of dimethyl- amine dissolved in alcohol. The alcohol and excess of dimethyl- ainiue were theii reinoved iu a currefit; of steaiii, wheu the required

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CONSTITUTION OF PHYSOSTIGMINE. PART 11. 359

base was precipitated as a colourless oil. This was dissolved in ether, the ethereal solution dried, and the solvent removed. The residual oil slowly mlidified, and wm then purified by crystallisa- tion from light petroleum, when it separated in radiating clusters of colourless, prismatic needles, melting a t 5 4 O :

0.1265 gave 0.3376 (70, and 0.0898 H,O. C,9HB0,N2 requires C=73.1; H=7*7 per cent.

a-dime thylamino-y-phenoxy butyro-o-toluidide is very readily soluble in the usual organic solvents, and can only be crystallised with difficulty. It is a, we& base, forming salts which are acid towards litmus, and also possess an extremely bitter taste. The hydrochloride, prepared by passing a current of dry hydrogen chloride into an ethereal solution of the base, crystallises from a mixture of alcohol and ethyl acetate in slender, colourless needles, melting at 169O :

C= 72.8 ; H = 7.9.

0*1010 gave 0.2410 CO, and 0.0646 H,O. C=65-1; H=7.1 . C,,H,,O,N,,HCl require8 C = 65.4 ; H = 7.2 per cent.

The pZatinichZoricle of the above base crystallises from elcohd, containing a, little hydrochloric acid, in small, brown prisms, meltiug at, 2 1 5 O .

2-a-Dim e thy lamino- y-7~ydroxy~rop~lindole.

In order to prepare this compound 0.3 gram of sodium was dissolved in absolute alcohol in a capacious flask, and the alcohol removed under diminished pressure; to the sodium ethoxide thus obtained, 2 grams of a-dimethylaminol-y-phenoxybutyro-o-toluidide were added, and the mixture heated in a metal bath to a tempera- ture of 250-300° in a current of hydrogen. A t this temperature reaction took place with effervescence and a considerable darkening in colour, and the process was soon complete. The entire operation wm repeated four times with the same quantities of material, and the products from the several reactions were then united and acidified with dilute hydrochloric acid. The acid liquid was next shaken with ether, which removed a considerable quantity of phenol, identified by means of its tribromtlderivative, then made alkaline with sodium carbonate, and the mixture repeatedly extracted with chloroform. The chloroform extracts were washed, dried, and the solvent removed, when an oily, basic residue was obtained, which did not crystallise on keeping. For its purification it was dissolved in dilute hydrochloric acid, the solution evaporated to dryness under diminished pressure, and the solid residue thus obtained crystallised from a mixture of alcohol and ethyl acetate. The hydrochloride of the base then separated in colourlw, prieruatic

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360 RESEARCHES ON THE CONSTITUTION OF PHYSOSTIGMINE.

needles, melting a t 218O. The amount of pure hydrochloride obtained from 10 grams of the o-toluidide was 3.3 grams:

0.0962 gave 0.2166 CO, and 0-0646 H,O. C',,H180N,,HC1 requires c'= 61.3 ; Rl= 7.5 per cent.

It is evident from this result that the sodium ethoside in the above reaction has not only effected the expected indolic condensa, tion, but has also simultaneously removed the phenyl group with the formation of 2 -a-dimethylamino-y-hydroxypropylindole, as repre-

C=61*4; €I=7.5.

sented by the following equation:

PhO*CH2*CH2*CH(NMe,)*CO*NH<I) + NaOEt =

CH,

/NH\/\

\ O R / \ / HO*CH,*CH,*CH( NMe,)*C I I + EtOH + KaOPh.

2-a -Di ,ne t l~? /dan~ i ,~o -y -h~dToxy~op~ l~ndo le . -~he pure base was prepared from the abovedescribed hydrochloride by treating the latter with aqueous sodium carbonate, and extracting the alkaline liquid with chloroform ; after the removal of the chloroform, the base was obtained as a colourless, volatile oil, which did not solidify in a freezing mixture. It was miscible with ether, chloroform, ethyl acetate, alcohol, or water:

0*0910 gave 0.2375 CO, and 0.0698 H,O. C,,H,,ON, requires C = 71.6 ; H = 8.3 per cent.

The uurichloride of the above base crystallises from dilute alcohol in yellow prisms, which melt a t 133O and are anhydrous:

0.1140 gave 0.1174 CO,, 0.0353 H,O, and 0.0400 Au. C= 28.1 ;

C,,H180N2,HAuC14 requires C= 28.0 ; H = 3.4 ; Au = 35.3 per cent. The picrate crystallises from dilute alcohol in spherical aggregates

of bright yellow rhombs, which melt a t 140O. The base, 2-a-dimethylamino-y-hydroxyprop-ylindole, which has

now been synthesised, is isomeric with the alkaloid eseroline. The properties of these two compounds are, however, very dissimilax, as a comparison shows : thus, eseroline in the presence of alkalis readily absorbs oxygen with the production of intensely coloured solutions, whilst the synthetic base is quite stable under similar conditions. Moreover, eseroline readily reduces gold and silver salts, and is also a strong base, which yields neutral salts. The synthetic base, on the other hand, possesses no reducing properties, and is a weak base yielding salts with a strongly acid reaction. The synthetic base, furthermore, differs considerably from eseroline in physiologi- cal action, as shown by eome experiments kindly conducted by Dr,

C= 7 1 2 ; €I = 8.5.

H=3*4; Au=35*1.

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HOPE AND ROBINSON : ISOQUINOLINE ALKAL01DS. 361

H. I€. Dale, director of the Wellcome Physiological Research Laboratories, to whom the author here wishes to express his best thanks: thus, on the one hand, eiseroline was found to produce the characteridic myotic action of physostigmine (but in a diminished degree) when injected into the eye, and also to effect a slowing of the hearbbeat after intravenous injection. The synthetic base, 2-a-dimethylamino-y-hydroxypropylindole, on the other hand, pos- sessed none of these physiological properties.

T H E WELLCOME CHEMICAL RESEARCH LBBORATOILIES, LONDON, E.C.

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