Structural Study of Benzidamine Salicylate in the Solid State and in Solution

ENRIQUE GALVEZ'~, CONCEPCION FERNANDEZ-SANCHEZ', JULIA SANZ-APARIClO*, FELfCfANA FLORENClO*, ENRIQUETA FERNANDEZ-NAVARRO~, AND JUANA BELIANATO' Received April 27, 1990, from the 'Departamento de Qulmica Orgclnica, Universidad de Alcalcl de Henares, 28871 AlcalA de Henares, Madrid, Spain, the *lnstifufo "Rocasolano': Departamento de Rayos X, C.S.I.C. Serrano 119, 28006 Madrid, Spain, the *Laboratorios Liade, S.A. Joaquln Costa 26, 28002 Madnd, Spam, and the @lnstituto de Optrca, C.S.I.C. Serrano 121, 28006 Madrid, Spain. Accepted for publication March 2, 1991.

Ab8tract 0 The vibrational (IR and Raman) and 'H and 13C NMR spectra of the analgesic and anti-inflammatory benzldamine salicylate (Benzasal) have been examined, and the results are described. The crystal structure of this compound has been determined by X-ray diffraction. To assist in interpretation of the spectroscopic data, some measurements of benzidamine, benzidamine hydrochloride, and sali- cylic acid have also been made. The most important intermolecular interactions of benzidamine salicylate in the solid state are N(')H-O(-YC hydrogen bonds involving both salicylate oxygen atoms (d = 2.658 A and 3.228 A). At least the stronger hydrogen bond remains in CDCI, solution. Moreover, the strong Intramolecular hydrogen bond O-H--O-)~C within the salicylate anion has also been observed in the solid state and in solution.

Like benzidamine hydrochloride and related compounds,1-4 benzidamine salicylate [(l-benzyl-3-(y-dimethylamino- propoxy)-lH-indazole) salicylate] is a potent analgesic and anti-inflammatory drug which contains a trimethylene group on the side chain.67 In this paper we report the spectroscopic study of benzidamine salicylate (1) and of the corresponding base (21, and also of the hydrochloride (3) (see structure), using a combination of IR, Raman and NMR spectroscopy, and DSC and X-ray crystallography. Some measurements of salicylic acid (4) have also been made.

I I CH2

I .I

4'

0.. ..O,.-O.. 'c' "M

4

Experimental Section Compounds 1 and 2 were synthesized and purified in the Research

Center of Chemistry Department of "Laboratorios Liade, S.A.", Madrid. Benzidamine hydrochloride, salicylic acid, and sodium sa- licylate were commercial products, and the former was purified for this study.

The IR spectra were recorded on a Perkin-Elmer 599 B spectro- photometer in the solid state (KBr) in the cases of 1 and 3, as a liquid in the case of 2, and in CDCl, and (CD,),SO solutions in the cases of 1 and 2 at 0.06-0.5 M concentration depending on the solvent; 0.2-0.03-mm cells were used for all cases. Indene and polystyrene were used for instrument calibration.

The Raman spectra were measured using either a powdered sample (1 and 3), a liquid (2), or CHC1, solution (1) on a Jobin-Yvon Ramanor U-1000 double monochromator (5145 A). A photon counting detector was employed.

The 'H NMR spectra were recorded at 200 MHz on a Bruker AC 200P instrument using 13% (w/v) CDCI, or D20 solutions. Conven- tional irradiation was used for the double resonance (DR) experi- ments. The 13C NMR spectra (proton noise decoupled spectra and DEPT spectra) were obtained at 50 MHz on the same instrument using -25% solutions. The measurements were carried out a t 303 K with Me,Si or DSS as internal standards.

Experimental X-ray data, structure solution, and refinement pro- cedures for 1 are collected in Table I+lZ

The differential scanning calorimetric (DSC) analysis was carried out in a Perkin-Elmer instrument (DSC-2C). The substances were encapsulated in aluminum. The scanning was done over the range 30-350 "C at a heating rate of 5 or 200 "Clmin.

Results and Discussion Description of the Structure of Compound 1-Figure 1

shows the numbering for the crystallographic study and a view of adduct 1.19 The indazole (benzopyrazole) ring is planar. The bond lengths and valence angles agree with those described in the literature for benzazole14 and related com- pounds.16.16 Table I1 summarizes the characteristics of the hydrogen bonds of adduct 1. As expected, in the salicylate group there is a strong intramolecular hydrogen bond, O(30)- H(30)-0(33), between one carboxylate oxygen atom and the hydroxyl group. Moreover, there is some intermolecular hydrogen bonding interaction between the O(33) atom and the N(14) atom (dimethylamino group). A strong intermolec- ular hydrogen bond between the N(14) atom and the other carboxylate oxygen atom O(32) stabilizes the adduct. Similar hydrogen bonds have been found in other trisubstituted ammonium carboxylates and salicylates.17-19

Therefore, the above data reveal that the two carboxylate oxygen atoms take part in different hydrogen bonds involving the protonated N(14) amino atom (intermolecular bonding) and the OH group (intramolecular bonding). On the contrary, in one trisubstituted ammonium salicylate described in the literature,lg no intramolecular hydrogen bond exists in the

84 I Journal of Pharmaceutical Sciences Vol. 81, No. 1, January 1992

w)22-3549/92/0 1 OO-OU94$02.50/0 0 1992, American Pharmaceutical Association

Table CExperlmental Data and Structural Rdlnment Procedure8

Parameter Data Crystal data

Formula Crystal habit Crystal size, mm Symmetry Unit cell determination

Unit cell dimensions

Packing: v(A3), Z Dc(g * M, F (OOO) d C u , K,, cm-')

Experimental data Technique

Number of reflexions Measured Independent Observed

Range of hkl Value of Rint

Solution Refinement Parameters

Solution and refinement

Number of variables Degrees of freedom Ratio of freedom

H atoms

Final shWerror wscheme

Final AF peaks Final Rand R, Computer and programs

Scattering factors

Cl,H,N,O * C,H,O, Prismatic 0.15 x 0.20 x 0.30 Monoclinic P2,ln Least-squares fit from 57 reflexions (0 < 48") 13.089(1), 17.016(1), 10.896(1) A 90.0, 95.61 (l), 90.0" 24.15.1 (1),4 1.231, 447.533, 952 6.421

Four circle diffractometer: Philips PW1 loo Bisecting geometry Graphite oriented monochromator: CuK, 0/2e SCMS Detector apertures 1 x 1, up Om, 65 "C 1.5 minlreflex

4568 4091 2907 (2 u ( I ) criterion) &16, 0-20, -13-13, (sin MA), 0.60 0.014

Direct methods L.S. on Fobs with 1 blocks

41 4 2491 6.0 Difference Fourier synthesis and refined with isotropic temperature factors 0.02 Empirical so as to give no trends in cwA2F> versus <If,I> or < sin M y

0.069, 0.076 Vax 11/750, Multan 80 (ref 8), Dirdif (ref 9), X-ray 76 (ref lo), Pesos (ref 11) Int. Tables for X-ray Crystallography (ref 12)

0.21 e A - 3

molecule. Differential Scanning Calorimetry-The results of DSC

indicated that there is only one crystalline form for 1, with a purity of 99.6% (T, = 94.3 "C; Tg = 92.2 "C).

Infrared and Raman Spectra-The IR spectrum of I in the solid state is given in Figure 2 and the Raman spectrum is shown in Figure 3. Table III shows the frequencies and assignments of the most characteristic bands in the spectra of 1. The corresponding data for 2 and 3 are also included in this table. It can be seen that the vibrational characteristics of 1 clearly correspond to a salicylate,20 this conclusion being in agreement with the X-ray data.

According to this structure, the spectrum shows a very broad band of medium intensity with submaxima between 3000 and 1700 cm-I assigned to the u(0H) vibration, the OH group being strongly hydrogen bonded to the anionic CO, group. The broad band at 914 cm-' is assigned to the y (0-H) (out of plane deformation of the OH group) appearing at higher frequency than in salicylic acid (890 cm-'), but at lower frequency than in sodium salicylate (980 cm-').

P

Figure 1-Perspective view of molecule 1 and atomic numbering for the crystallographic study.

Table ICDletancw (A) end Angles (") of Posoibk Hydrogen Bond8 of 1

Donor-H, A A H-Acceptor, A Donor Angle, H.-Acceptor O

N(14)-H(14) N(14)*-0(32)' H(14)**.0(32)s N(14)-H(14)-*0(32)

N( 14)-H( 14) N( 14)...0(33)' H( 14).-0(33)' N( 14)-H( 14)-0(33)

0(30)-H(30) O(30)-.0(33)b H(30)***O(33)b 0(30)-H(30)...0(33)

1.01 (4) 2.658(4) 1.66(4) 175(4)

1.01 (4) 3.228(4) 2.55(4) 125(3)

1.1(1) 2.513 1.5(1) 150(1)

' EqUivalent positions: -~+2, -y, -z+l. Equivalent positions X, y, I.

The bands at 1575 (strong) and 1380 cm-' (very strong) are mainly related with the antisymmetric and symmetric CO, stretching vibration, respectively. Both bands are of medium intensity in the Raman spectrum. It is observed, however, that the asymmetric mode is not always resolved from the ring Y (CC) mode veb.

The expected characteristic h H stretching band is not clearly distinguished in the spectrum of 1 since it appears overlapped by the Y (OH) absorption. However, its presence may be suggested by the intensity and breadth of the abeorp tion at 3000-1700 cm-' compared, for example, with the absorption observed in the spectrum of sodium salicylate.

The indazole (benzopyrazole) ring in 1 is mainly charac- terized by the very strong band at 1530 cm-' (medium in Raman), which is also present in the spectra of benzidamine and benzidamine hydrochloride and is related to a ring stretching mode [v (C=N) of the pyrazole ring*'].

It is expected that the frequencies of the bands of the fused benzene ring do not differ much from the corresponding frequencies of the salicylate aromatic ring. In fact, double bands are observed in the characteristic regions for ortho disubstituted compounds. Moreover, characteristic bands of monosubstituted benzene derivatives are also observed in the spectra.

The broad band at 1625 cm-' in the solid state and at -1630 cm-' (sh) in CDCl,, which disappears on N-deuteri- ation, is assigned to dH). The high frequency is explained by the strong hydrogen bond in which this charged group takes part (dN-0 = 2.658 A). This band only appeared 88 a shoulder in the Raman spectrum.

The spectra in CDCl,:CHCl, solution show several changes with respect to the solid state, indicating changes of the strength of the hydrogen bonds inside the complex. The main changes affect the NH, OH, and COO- vibrations, although interpretation is not quite clear. The band which appears at 2952 cm-I in CDC1, and at 2945 cm-' in CCl,, which is not

Journal of Pharmaceutical Sciences I 95 Vol. 81, No. 1, January 1992

4 0 0 0 3000 2 0'0 0

Figure 2-Infrared spectrum of 1 in the solid state (KBr).

N

1500 1250 1000 750 500 250

Flgure 3-Raman spectrum of 1 in the solid state.

apparently sensitive to deuteration, is tentatively assigned to v (OH) of molecules with weaker intramolecular hydrogen bonding than in solid state. Changes are also observed in the 1650-1550-cm-' region in the bands &NH) and v(COO-) (see Table III), this fact being due to the influence of the solvent in the strength of the hydrogen bonds of this molecular complex.

It must be remarked that an intense continuum is found in the IR spectrum of 1 which has been described in the literature in cases where heteroconjugated AH- A--'B bonds are formed [for instance, in systems such as the acetic acid:imidazole system, in which the two proton limiting structures (I) OH-.N= O--* hN(I1) have comparable weight- 1.22

Nuclear Magnetic Resonance Spectra-Proton Nuclear Magnetic Resonance-The 'H NMR data of 1-3 are summa- rized in Tables IV and V. Assignment of proton resonances were made taking into account literature data for several indazole systems.23-26 For comparative purposes, the 'H spectrum of salicylic acid (4) in (CD&SO was also recorded (Table V). The assignment and analysis of the aromatic signals of 1-3 have been carried out by means of double resonance experiments.

In the 'H NMR spectra of 1 and 2, the signals corresponding to the phenyl protons are complex multiplets, this fact accounting for a predominant conformation of the phenyl group with respect to the indazole ring. In this conformation, the benzyl methylene protons would be situated in a position

16'00 1200 800 1100

cm-l

almost coplanar with respect to the phenyl and the indazole rings, and, by this way, the low field value (-5.4 ppm) of the signal due to these protons could be attributed to the deshield- ing anisotropic effect exerted by the phenyl and the indazole rings.

The slight nonequivalence of the signals corresponding to the p and ymethylene protons of the aliphatic chain in the 'H NMR spectra of 1-3 could be explained in terms of two preferred orientations of the chain with respect to the indazole ring.

By comparing the chemical shifts of N-methyl (2.701, y (3.12), and p (2.30) protons of the trimethylene chain in 1 with the same protons in 2 (2.24, 2.47, and 2.03, respectively), a protonation of the acyclic nitrogen atom in 1 can be deduced, as expected. Furthermore, results for 1 (in CDC1,) are in close agreement with those obtained for 3 (in D,O).

Finally, in the spectrum of 1, the wide singlet a t 13.5 ppm is assigned to the ammonium proton. The low field signal accounts for a fi-H.-.U = C strong hydrogen bond. As expected, the signal corresponding to the intramolecularly bonded OH group of the salicylate anion coalesces with the AH signal.

Carbon-13 Nuclear Magnetic Resonance-Table VI shows the 13C NMR chemical shifts of 1-3 with signal assignments. Signal multiplicity obtained from DEFT spectrum and pre- vious literature data of related compounds were taken into consideration.26-28 For comparison, the 13C spectra of salicylic acid and of the salicylate anion of 1 were also registered (Table VII).

References and Notes 1.

2. 3.

4.

5.

6.

7.

8.

9.

Bertolini, A.; Mucci, P.; Sternieri, E. Boll. SOC. Ital. Biol. Sper. 1965,41,243-246. Fala, F.; Silvestrini, E. B. Boll. Chim. Farm. 1965,104,705-709. Silvestrini, B.; Garau, A.; Pozzati, C.; Cicli, V. Arzneim.-Forsch. 1966,16, 5 W 3 . Palazzo, G.; Corsi, G.; Baiocchi, L.; Silvestrini, B. J . Med. Chem. 1966.9. 38-41. Spain pat. 468785,20 Oct. 1978; Ger. pat. 2915158,08 July 1981; Jp. pat. 1284190, 27 Sept. 1985. Caeals Coll, J.; Villela Torellas, J . Miinch. Med. Wschr. (Spanish Edition) 1980, No. 4. Concejero Mpez, V.; Marttnez IbAiiez, J. Med. Klin. (Spanish Edition) 1980,20, 59-61. Main, P.; Fiske, S. J.; Hull, S. E.; Leesinger, L.; Germain, G.; Declerq, J. P.; Woolfson, M. M. Fultan 80 program,; University of York, England, and University of Louvain, Belpum, 1980. Beurskem, P. T.; Bosman, W. P.; Doesburg, H. M.; Van den Hark, Th.; Prick, P. A. J.; Noovdik, J. H.; Beurskens, G.; Fuld , R. 0.; Parthasarathi, V. DIRDIF programs, Conformatwn in Biology; Srinivasan, R.; Sarma, R., Eds.; Academic: New York, 1982; pp 389-406.

96 I Journal of Phannaceufical Sciences Vol. 81, No. 1, January 1992

Table Ill-lnfrared and Raman' Frequencies of Compounds 1-3

Frequency, cm-' Corn- Medium pound ~ o - H ) ~o-H)/L(~JH) s($i~) BKce 4COO-),, 4C-N) L(COO-), 4C-0) cS(O-H)~ AO-H)

1 CDCI, 2952 w' 32W17,p brd 1630 sh 1618 s 1595s 1530vs 1362vs 1259s l l6Osh 1048m 1618vS -1590sh 1 5 3 0 ~ 1 3 6 2 ~ ~ 1252s 9 1017m - 2952 w - -

- 2952 w --B - 7675 vw 7593vw 7528w -0 7249m -P -B

['H,JMe,SO: - 2410 br 1630rn 1616s 1592s 1530vs 1382s 1257rn 1150sh -h Me,SO

2 KBr - 3200-1700br' 1625s 1613m 1575s 153Ovs 1380vs 1264s 1185sh 914m Solid - A 7625sh 1672w 7575rn 7525rn 7373m 7267m -B 974ww CDCI, - - - 1615 rn - 1530 vs - - - - CHCI, - - - 7675vw,pp - 7529w,P - - - - [2H,JMe,S0 - - - 1614 rn - 1529 vs - - - -

1616 rn - 1530 vs Liquid - - - 7674vW,pp - 7528~,p - - - -

3 KBr - 3100-2000 br - 1611 rn - 1529 vs - - - - Solid - 3700-2000br - 7 6 0 4 ~ - 7525 m - - - -

a Rarnan frequencies are shown in italics. Tentative assignation. Abbreviations: s, strong; rn, medium; w, weak; v, very; br, broad; sh, shoulder; p, polarized; pp, padally polarized. Continous absorption (see text). Measured after addition of D,O. 'Weaker intensity than in the nondeuteriated derivative. Not detected. Obscured by the solvent.

e

CHCI, 2952 w 9 7630sh 7677vw,pp 7590sh 7529w,p 7360sh 7253m,pp -B A e

1365 s

- - - -

Table IV-Proton Chemlcal Shlfta and Some Coupllng Constants (J) of Compounds 1-3

Table V-Chemlcal Shlfts and Coupllng Constants (J) of Sallcyllc Acld (4) and of the Sallcylete Anlon of 1

Proton Chemical Shm (ppm) and Coupling Atom - (W

1a.c 2a.c 36,'

7.65 (d) 3 J 8

7.04 (td) 4J1 .7

7.13-7.37 (m) 7.13-7.37 (m)

4.45 (t) 3J5.8

2.28 (4) 3J5.4

2.30 (4) 3J5.4

3.13 (1) 3.12 (1) 2.70 (s)

7.3-7.4 (rn) 5.34 (s)

13.47 (ws)

7.67 (dt) 3J8;4J = 'J0.9

7.0 (td) 'J1.5

7.1-7.3 (m) 7.1-7.3 (m)

4.42 (t) 3J6.5

2.02 (4) 3J6.5

2.03 (4) 3J6.5

2.46 (1) 2.47 (1) 2.24 (s) 5.35 (s)

7.1-7.3 (m) -

7.87 (d) 3J6.7

7.10 (rn)

7.10 (rn) 6.89 (d) 3J8.3 4.5 (1) 3J5.5

2.36 (4) 3J5.5

2.38 (4) 3J5.5

-3.4 (t)d

5.20 (s) 3.10 (s)

7.22 (s)

'Spectra were recorded in CDCI,; TMS was used as the internal standard. Spectra were recorded in D,O; DSS was used as the internal standard. ' Abbreviations: d, doublet; dd, doublet of doublets; dt, doublet of triplets; rn, multiplet; q, quintuplet; s, singlet; 1, triplet; td, triplet of doublets; ws, wide singlet. Not resolved.

10.

11.

12.

13.

14. 15. 16.

17.

Stewart J. M.; Machin, P. A.; Dickinson, C. W.; Ammon, H. L.; Heck, d.; Flack, C. H. The X-RAY-76 System. Com uter pro-

ram' Com uter Science Center, University of Maqfand: Col- t g e Park, b, 1976. Martinez-Ripoll, M.; Cano, F. H. PESOS. A com uterprogmm for the automutrc trecrtment of weighting schemes; fnstituto Rocam- lano. C.S.I.C.: Madrid, Spain, 1975. Zntematwnnl Tables for X-Ray Crystallogmphy, Vol. N, Kynoch: Birmingham, U.K., 1974; pp 72-98. Crystallo aphic supplementary material may be solicited from pmf. E. &1vez Escaude, A,, Lapasset, J. ActaCrystallogr. 1974, B30,2009-2012. Wei, C. H. Acta Crystallogr. 1983, C39,1371-1382. Cuevas, J.C.; Mendoza, J.; Prados, P.; HernBndez-Cano, F.; Foces-Foces, C. J. Chem. Soc. Chem. Commun. 1986,1641-1642. Marsau, P. Actu Ctystallogr. 1978, B34,2370-2372.

1' 46

6.91 (dd) 6.91 (d)

H(4) 7.1-7.4 (m) 7.46 (td) 3J8.2; 4J0.9 327.9

H(3)

6.79 (td)

7.91 (dd) 3~6.8; 461 .I

3~7.8 ; 4 ~ 1 .I 13.47 (ws)

3J7.8; 4J1.7

3~7.8; 4~1 .5

6.87 (t) 3J7.5 7.78 (dd)

a.b As in Table IV; abbreviations as in Table IV.

Table VCCarbon-13 Chemlcal Shlfts for 1-3

Atom

~ ~~~ ~

Carbon-13 Chemical Shift. DDrn

1' 2' 30

155.08 155.41 157.64 112.40 112.53 114.54 1 19.66' 1 19.49" 122.61 ' 119.18" 1 18.49' 122.04' 130.45 126.81 130.15 108.74 108.20 111.15 141.33 140.93 143.46 65.58 66.68 68.62 24.19 54.72

ETCH, 42.29 c,. 52.02

137.15 1 28.40d C(2',6')

C(3',5) 1 26.8ad C(4') 127.36

c,

C(1')

26.99 55.75 44.88 51.53

136.99 1 27.93d 126.3ed 126.70

26.45 57.14 45.08 53.76

139.49 1 30.95d 129.49d 129.99

a*b As in Table IV. ' e d These values may be interchanged.

18. Warner. A. Acta Crvstallom. 1980.836. 813-818. 19. Shimizu., N.; Nishi aki, S . ;hka i , Y.; O&ki, K. Actu Crystallogr.

20. Green, J. H. S.; Kynaston, W.; Lindsey, A. S. Spectrochim. Acta 1983, C39,891-89$.

1961,17,468-502.

Journal of Pharmaceutical Sciences I 97 Vol. 87, No. 7, January 7992

Tabk VIcclrbon-13 Chemlcal ShHk of 4 and pf the Salicylete Anion of 1

Ca@on-13 Chemical Shift, ppm

1. 46

117.w 119.28 161 5 1 161.41 116.30 113.04 137.15 135.76 1 17.72 1 17.25 13g.43 130.45

174.23

Atom

C(l) (32) C(3) C(4) C(5) C(6l COOH 175.13

I" CDCI,. b In (cD~)~so.

21. Katritzky, A. R.; Ambler, A. P. in Physical Methods in Hetern-

22. Zundel, G.; Eckert, M. J . Mol. Struct. (Theochem.) 1989,200, cyclic Chembtiy, Vol

73-92 and referencee therein.

Academic: New York, 1963; p 232.

23. Elguem, J.; Fruchiey, A.; Jacquier, R. Bull. SOC. Chzm. 1966, 2076-2084.

24. Elguero, J.; Fruchier, A.; Jacquier, R. BuEl. SOC. Chim. 1967, 261s-2629.

25. Elguero, J.; Fruchier, A.; Jacquier, R.; Scheidegger, U. J . Chem. Phvs. 1971.68, 1113-1121.

26. Elbero, J.f Fruchier, A.; Pardo, M. C. Can. J . Chem. 1976,54, 1329-1331. -. - _ -

27. Bouchet, P.; mchier , A.; Joncheray, C.; Elguero, J. Org. Magn.

28. Faure, R.; em, J.; Vincent, E. J.; Lazaro, R. Org. Magn. Reson. 19'77,9, 716-718.

1 Reson. 197f 617427.

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