Rasagiline ethanedisulfonate: an inhibitor for monoamine oxygenase B (MAO_B)

Rasagiline is a selective and potent drug used for the treatment of Parkinson's disease. The first crystal structure of a salt of rasagiline, the title compound, bis­[(1R)-N-prop-2-ynyl-2,3-dihydro-1H-inden-1-aminium] ethanedisulfonate, 2C₁₂H₁₄N⁺·C₂H₄O₆S₂⁻, was determined from crystals grown by gas diffusion. The compound has monoclinic (C2) symmetry. The ethane group of the ethanedisulfonate anion is disordered over three positions. The C₂-symmetric ethanedisulfonate anions are connected by four N—H...O hydrogen bonds to four rasagiline cations. This leads to large 18-membered rings which are arranged in ladders in the [010] direction. The extended hydrogen-bonding architecture may explain the stability of the structure. Rasagiline ethanedisulfonate is nonhygroscopic. During a polymorph screen, no hydrates, solvates or polymorphs were found.

S1. Comment

Rasagiline [(1R)-N-prop-2-ynyl-2,3-dihydro-1H-inden-1-amine] is one of the most potent selective and irreversible monoaminoxygenase B (MAO_B) and apoptosis inhibitors known to date (Nayak & Henchcliffe, 2008; Kupsch, 2002). However, despite its pharmaceutical importance, no crystal structure of any rasagiline salt has been published to our knowledge. The compound is traded by Teva Pharmaceutical Industries Ltd under the brand name Azilect as drug against Parkinson's disease (Frenkel et al., 2007). The compound shows few side effects and is generally well tolerated. One major problem in the production of rasagiline is that most salts of the compound are hygroscopic. This property leads to agglutinates during the synthesis which cause problems in the tabletting of rasagiline. Therefore, most rasagiline salts cannot be directly compressed into tablets (Stahl, 2008). In contrast, the new title compound, rasagiline ethanedisulfonate, (I), is not hygroscopic; in the synthesis it is obtained as a fine crystalline powder which is easy to handle and can be compressed into tablets. Furthermore, the storage stability is increased.

To understand why rasagiline ethanedisulfonate shows these good stabilities, the crystal structure was determined. Additionally, in order to search for hitherto unknown crystallographic phases, hydrates or solvates, a polymorph screen was carried out on this ethanedisulfonate salt. Different crystallization methods were applied including: (i) recrystallization from various solvents and solvent mixtures by heating and subsequent slow cooling; (ii) diffusion by overlaying a solution of the compound with an anti-solvent (Fock, 1888); (iii) diffusion of an anti-solvent into a solution of the compound via the gas phase. Numerous crystallization experiments were performed using the most common organic solvents, e.g. dimethylsulfoxide, N-methylpyrrolidone, dimethylformamide, ethers, esters, alcohols and water. Even acids like acetic acid and bases like sodium hydroxide were used. The powder patterns of all samples were recorded and examined for polymorphs. The samples were measured on a Stoe Stadi-P powder diffractometer [curved Ge(111) primary monochromator, λ = 1.5406 Å] in transmission geometry from 2 to 74° in 2θ. Samples were prepared between two polyacetate films. For detection, an image-plate position-sensitive detector was used with a resolution ~0.1° in 2θ. For data acquisition, the program WINXPOW (Stoe & Cie, 2008) was used.

All powder patterns obtained from recrystallizations, gas diffusions and overlays showed the same phase (a representative powder pattern can be found in the Supplementary material). From dimethylsulfoxide, single crystals suitable for X-ray structure analysis could be grown. To check if the measured single crystal corresponded to the same phase as all other experiments, a powder diagram of the single-crystal data was simulated and compared with the experimental powder diagram. It proved to be the same phase.

The molecular structure of (I) is shown in Fig. 1. In the crystal structure, the five-membered ring has a conformation close to an envelope. Atom C2 deviates by 0.40 Å from the plane through C1/C3/C4/C9. The ring-puckering parameters defined by Cremer & Pople (1975) are q = 0.256 (3) Å and ϕ = 210.4 (8)°. The C1—N1 bond is in a pseudo-axial position with respect to the five-membered ring. The benzene ring shows a very small deviation from planarity, which may result from crystal packing forces. The mean deviation from the best plane is 0.012 (2) Å.

The ethanedisulfonate fragment displays threefold disorder on the CH₂—CH₂ moiety. Both H atoms of the –NH₂⁺– group are involved in N—H···O hydrogen bonding (Table 1). Each rasagiline cation is hydrogen bonded to two ethanedisulfonate anions and each anion accepts hydrogen bonds from four cations (Fig. 2). The rasagiline and ethanedisulfonate ions form 18-membered rings. These rings are annellated and form a ladder structure in the [010] direction. Using the graph-set analysis of Etter et al. (1990) and Bernstein et al. (1995), the hydrogen-bonding pattern is reported as C₂²(6)[R₄⁴(18)]. The ethanedisulfonate anion is the central element in the formation of the ladder; a monoanion such as methane sulfate would probably lead to the formation of two individual chains. The extended ladder-type hydrogen-bond system stabilizes the crystal structure and may explain why the ethandisulfonate salt is not hygroscopic and does not form hydrates. The ladders are connected in the a-axis direction by a weak intermolecular C—H···O interaction to form layers parallel to the [001] direction. Along the c-axis direction, the rasagiline cations are connected by a weak intermolecular C(benzene)—H···π(benzene) interaction (Table 1).

Related literature

For related literature, see: Bernstein et al. (1995); Cremer & Pople (1975); Etter et al. (1990); Fock (1888); Frenkel et al. (2007); Kupsch (2002); Nayak & Henchcliffe (2008); Stahl (2008); Stoe & Cie (2008).

S2. Experimental

All solvents and reagents were of reagent grade and were used without further purification. Single cystals of rasagiline ethanedisulfonate, (I), were obtained by gas diffusion as follows. Rasagiline ethanedisulfonate (50 mg) was dissolved in dimethylsulfoxide (1 ml) in a small flask at room temperature. The small flask was placed inside a larger flask and acetone (5 ml) was placed next to the smaller flask. The larger flask was sealed and left for crystallization. After 1 d, colourless crystals were formed.

S3. Refinement

The anion was found to be disordered. Three positions were found for the central ethane fragment. Thus, the C atom of the ethane group was refined as a split atom using three positions. The occupancy factors refined to 0.276 (6) for atoms C13A and C13B and 0.448 (12) for atom C13C. The rather large displacement parameters of the sulfonate atoms also showed this group to be disordered, but it was not possible to resolve this disorder. H atoms were positioned geometrically with C_planar—H = 0.95, C_alkyne—H = 0.95, C_primary—H = 1.00, C_secondary—H = 0.99 and N—H = 0.92 Å, and they were treated as riding, with U_iso(H) = 1.2U_eq(C,N). Friedel opposites were not averaged. The absolute configuration was determined from 1487 Friedel pairs.

Computing details

Data collection: SMART (Siemens, 1995); cell refinement: SMART (Siemens, 1995); data reduction: SAINT (Siemens, 1995); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: Mercury (Macrae et al., 2008); software used to prepare material for publication: publCIF (Westrip, 2008).

Figures

	Fig. 1. A view of the molecular structure of (I), showing the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level and H atoms are shown as small spheres of arbitrary radii. Only the atoms in the major component of the disorder of the ethanedisulfonate anion are shown. Hydrogen bonds are drawn as dashed lines.
	Fig. 2. The hydrogen-bonded architecture of (I). Hydrogen bonds are drawn as dashed lines. H atoms that are not involved in the hydrogen bonding have been omitted for clarity.

bis[(1R)-N-prop-2-ynyl-2,3-dihydro-1H-inden-1-aminium] ethanedisulfonate

Crystal data

2C12H14N^+·C2H4O6S2^2^−	F(000) = 564
Mr = 532.66	Dx = 1.341 Mg m^−3
Monoclinic, C2	Melting point: 475 K
Hall symbol: C 2y	Mo Kα radiation, λ = 0.71073 Å
a = 17.483 (3) Å	Cell parameters from 226 reflections
b = 5.8363 (9) Å	θ = 3–23°
c = 13.086 (2) Å	µ = 0.25 mm^−1
β = 99.033 (6)°	T = 166 K
V = 1318.7 (4) Å^3	Rod, colourless
Z = 2	0.7 × 0.14 × 0.04 mm

Data collection

Siemens SMART 1K CCD area-detector diffractometer	3400 independent reflections
Radiation source: normal-focus sealed tube	2109 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.051
ω scans	θmax = 29.9°, θmin = 2.4°
Absorption correction: multi-scan (SADABS; Sheldrick, 2000)	h = −22→23
Tmin = 0.862, Tmax = 0.990	k = −7→8
10594 measured reflections	l = −18→17

Refinement

Refinement on F^2	Hydrogen site location: inferred from neighbouring sites
Least-squares matrix: full	H-atom parameters constrained
R[F^2 > 2σ(F^2)] = 0.056	w = 1/[σ^2(Fo^2) + (0.04P)^2 + 1P] where P = (Fo^2 + 2Fc^2)/3
wR(F^2) = 0.117	(Δ/σ)max < 0.001
S = 1.01	Δρmax = 0.36 e Å^−3
3400 reflections	Δρmin = −0.33 e Å^−3
169 parameters	Extinction correction: SHELXL97 (Sheldrick, 2008), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
1 restraint	Extinction coefficient: 0.0045 (8)
Primary atom site location: structure-invariant direct methods	Absolute structure: Flack (1983), with 1487 Friedel pairs
Secondary atom site location: difference Fourier map	Absolute structure parameter: 0.05 (11)

Special details

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Refinement. Refinement of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq	Occ. (<1)
S1	0.02762 (5)	0.26510 (13)	0.84446 (6)	0.0494 (3)
O1	0.10968 (14)	0.3068 (4)	0.85282 (17)	0.0609 (7)
O2	−0.01857 (15)	0.4368 (4)	0.7888 (2)	0.0730 (9)
O3	0.00967 (15)	0.0340 (4)	0.8144 (3)	0.0755 (9)
N1	0.13611 (12)	0.7582 (5)	0.80748 (14)	0.0344 (5)
H1B	0.0920	0.8377	0.8157	0.041*
H1C	0.1259	0.6047	0.8138	0.041*
C1	0.15370 (16)	0.8022 (6)	0.6995 (2)	0.0390 (8)
H1A	0.1681	0.9663	0.6915	0.047*
C2	0.08329 (18)	0.7381 (7)	0.6198 (2)	0.0513 (9)
H2A	0.0790	0.8402	0.5588	0.062*
H2B	0.0351	0.7498	0.6502	0.062*
C3	0.09768 (19)	0.4873 (7)	0.5890 (2)	0.0536 (10)
H3A	0.0715	0.3780	0.6299	0.064*
H3B	0.0793	0.4613	0.5144	0.064*
C4	0.18399 (18)	0.4645 (6)	0.6139 (2)	0.0408 (8)
C5	0.2312 (2)	0.2934 (6)	0.5842 (2)	0.0506 (9)
H5A	0.2094	0.1678	0.5436	0.061*
C6	0.3100 (2)	0.3085 (7)	0.6147 (2)	0.0552 (10)
H6A	0.3424	0.1893	0.5966	0.066*
C7	0.3430 (2)	0.4927 (7)	0.6709 (2)	0.0554 (10)
H7A	0.3977	0.5026	0.6890	0.067*
C8	0.29576 (19)	0.6652 (6)	0.7013 (2)	0.0448 (8)
H8A	0.3179	0.7931	0.7400	0.054*
C9	0.21651 (18)	0.6468 (5)	0.6743 (2)	0.0369 (7)
C10	0.19928 (18)	0.8249 (5)	0.8918 (2)	0.0444 (8)
H10A	0.2452	0.7269	0.8892	0.053*
H10B	0.2143	0.9860	0.8822	0.053*
C11	0.17375 (18)	0.7995 (7)	0.9924 (2)	0.0475 (8)
C12	0.1511 (2)	0.7805 (9)	1.0710 (2)	0.0664 (10)
H12A	0.1327	0.7650	1.1352	0.100*
C13A	−0.0122 (6)	0.1906 (18)	0.9581 (7)	0.022 (3)*	0.276 (6)
H13A	−0.0695	0.1962	0.9426	0.027*	0.276 (6)
H13B	0.0032	0.0323	0.9793	0.027*	0.276 (6)
C13B	−0.0161 (7)	0.354 (2)	0.9541 (8)	0.028 (3)*	0.276 (6)
H13C	−0.0005	0.5133	0.9740	0.033*	0.276 (6)
H13D	−0.0732	0.3483	0.9369	0.033*	0.276 (6)
C13C	0.0403 (4)	0.2895 (15)	0.9893 (5)	0.043 (3)*	0.448 (12)
H13E	0.0698	0.1577	1.0230	0.051*	0.448 (12)
H13F	0.0673	0.4333	1.0135	0.051*	0.448 (12)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
S1	0.0827 (7)	0.0294 (4)	0.0445 (4)	−0.0051 (5)	0.0361 (4)	−0.0025 (5)
O1	0.0781 (18)	0.0371 (16)	0.0629 (14)	−0.0112 (13)	−0.0036 (12)	0.0060 (12)
O2	0.0686 (19)	0.0459 (15)	0.114 (2)	0.0107 (14)	0.0429 (16)	0.0309 (16)
O3	0.0580 (17)	0.0378 (14)	0.130 (3)	0.0007 (12)	0.0118 (16)	−0.0279 (15)
N1	0.0422 (13)	0.0289 (11)	0.0332 (11)	−0.0023 (13)	0.0091 (10)	−0.0019 (14)
C1	0.0442 (17)	0.042 (2)	0.0336 (14)	−0.0007 (16)	0.0136 (12)	0.0072 (14)
C2	0.0472 (19)	0.073 (2)	0.0351 (15)	0.006 (2)	0.0093 (14)	0.0073 (19)
C3	0.053 (2)	0.076 (3)	0.0333 (17)	−0.022 (2)	0.0131 (15)	−0.0045 (17)
C4	0.057 (2)	0.0465 (19)	0.0222 (14)	−0.0140 (17)	0.0152 (14)	0.0009 (14)
C5	0.083 (3)	0.041 (2)	0.0335 (15)	−0.010 (2)	0.0283 (15)	−0.0006 (16)
C6	0.074 (3)	0.059 (3)	0.0392 (16)	0.014 (2)	0.0292 (16)	0.0066 (18)
C7	0.048 (2)	0.086 (3)	0.0357 (18)	0.013 (2)	0.0150 (15)	0.009 (2)
C8	0.048 (2)	0.056 (2)	0.0315 (16)	−0.0071 (17)	0.0115 (15)	−0.0004 (14)
C9	0.042 (2)	0.0425 (17)	0.0278 (15)	−0.0044 (15)	0.0098 (14)	0.0068 (13)
C10	0.0475 (19)	0.046 (2)	0.0401 (16)	−0.0057 (15)	0.0081 (14)	−0.0099 (14)
C11	0.0546 (19)	0.051 (2)	0.0363 (16)	0.0075 (18)	0.0050 (14)	−0.0096 (17)
C12	0.079 (2)	0.082 (3)	0.0385 (17)	0.017 (3)	0.0105 (17)	−0.013 (3)

Geometric parameters (Å, º)

S1—O2	1.415 (3)	C5—H5A	0.9500
S1—O3	1.426 (3)	C6—C7	1.377 (5)
S1—O1	1.442 (2)	C6—H6A	0.9500
S1—C13A	1.792 (10)	C7—C8	1.399 (5)
S1—C13B	1.805 (11)	C7—H7A	0.9500
S1—C13C	1.879 (6)	C8—C9	1.379 (4)
N1—C10	1.485 (3)	C8—H8A	0.9500
N1—C1	1.514 (3)	C10—C11	1.463 (4)
N1—H1B	0.9200	C10—H10A	0.9900
N1—H1C	0.9200	C10—H10B	0.9900
C1—C9	1.501 (4)	C11—C12	1.164 (4)
C1—C2	1.530 (4)	C12—H12A	0.9500
C1—H1A	1.0000	C13A—C13B^i	1.516 (12)
C2—C3	1.549 (5)	C13A—H13A	0.9900
C2—H2A	0.9900	C13A—H13B	0.9900
C2—H2B	0.9900	C13B—C13A^i	1.516 (12)
C3—C4	1.499 (4)	C13B—H13C	0.9900
C3—H3A	0.9900	C13B—H13D	0.9900
C3—H3B	0.9900	C13C—C13C^i	1.479 (15)
C4—C5	1.389 (5)	C13C—H13E	0.9900
C4—C9	1.392 (4)	C13C—H13F	0.9900
C5—C6	1.376 (5)
O2—S1—O3	116.40 (18)	C6—C5—H5A	120.5
O2—S1—O1	113.60 (15)	C4—C5—H5A	120.5
O3—S1—O1	110.71 (15)	C5—C6—C7	121.4 (3)
O2—S1—C13A	109.5 (3)	C5—C6—H6A	119.3
O3—S1—C13A	84.4 (4)	C7—C6—H6A	119.3
O1—S1—C13A	119.3 (3)	C6—C7—C8	119.8 (3)
O2—S1—C13B	85.8 (4)	C6—C7—H7A	120.1
O3—S1—C13B	113.0 (4)	C8—C7—H7A	120.1
O1—S1—C13B	115.5 (4)	C9—C8—C7	119.0 (3)
O2—S1—C13C	115.6 (3)	C9—C8—H8A	120.5
O3—S1—C13C	109.7 (3)	C7—C8—H8A	120.5
O1—S1—C13C	87.3 (2)	C8—C9—C4	120.6 (3)
C10—N1—C1	114.4 (2)	C8—C9—C1	129.5 (3)
C10—N1—H1B	108.7	C4—C9—C1	109.8 (3)
C1—N1—H1B	108.7	C11—C10—N1	110.2 (2)
C10—N1—H1C	108.7	C11—C10—H10A	109.6
C1—N1—H1C	108.7	N1—C10—H10A	109.6
H1B—N1—H1C	107.6	C11—C10—H10B	109.6
C9—C1—N1	111.5 (2)	N1—C10—H10B	109.6
C9—C1—C2	103.9 (3)	H10A—C10—H10B	108.1
N1—C1—C2	109.6 (2)	C12—C11—C10	177.9 (4)
C9—C1—H1A	110.6	C11—C12—H12A	180.0
N1—C1—H1A	110.6	C13B^i—C13A—S1	110.7 (6)
C2—C1—H1A	110.6	C13B^i—C13A—H13A	109.5
C1—C2—C3	105.2 (3)	S1—C13A—H13A	109.5
C1—C2—H2A	110.7	C13B^i—C13A—H13B	109.5
C3—C2—H2A	110.7	S1—C13A—H13B	109.5
C1—C2—H2B	110.7	H13A—C13A—H13B	108.1
C3—C2—H2B	110.7	C13A^i—C13B—S1	107.0 (6)
H2A—C2—H2B	108.8	C13A^i—C13B—H13C	110.3
C4—C3—C2	103.1 (3)	S1—C13B—H13C	110.3
C4—C3—H3A	111.1	C13A^i—C13B—H13D	110.3
C2—C3—H3A	111.1	S1—C13B—H13D	110.3
C4—C3—H3B	111.1	H13C—C13B—H13D	108.6
C2—C3—H3B	111.1	C13C^i—C13C—S1	103.0 (6)
H3A—C3—H3B	109.1	C13C^i—C13C—H13E	111.2
C5—C4—C9	120.0 (3)	S1—C13C—H13E	111.2
C5—C4—C3	128.7 (3)	C13C^i—C13C—H13F	111.2
C9—C4—C3	111.3 (3)	S1—C13C—H13F	111.2
C6—C5—C4	119.0 (3)	H13E—C13C—H13F	109.1
C10—N1—C1—C9	68.3 (3)	C5—C4—C9—C1	−177.6 (3)
C10—N1—C1—C2	−177.3 (3)	C3—C4—C9—C1	2.8 (3)
C9—C1—C2—C3	25.5 (3)	N1—C1—C9—C8	−80.7 (4)
N1—C1—C2—C3	−93.8 (3)	C2—C1—C9—C8	161.4 (3)
C1—C2—C3—C4	−23.7 (3)	N1—C1—C9—C4	100.0 (3)
C2—C3—C4—C5	−166.2 (3)	C2—C1—C9—C4	−18.0 (3)
C2—C3—C4—C9	13.3 (3)	C1—N1—C10—C11	173.8 (3)
C9—C4—C5—C6	−0.6 (4)	O2—S1—C13A—C13B^i	−84.7 (6)
C3—C4—C5—C6	178.9 (3)	O3—S1—C13A—C13B^i	159.3 (5)
C4—C5—C6—C7	−2.1 (4)	O1—S1—C13A—C13B^i	48.7 (6)
C5—C6—C7—C8	2.3 (5)	O2—S1—C13B—C13A^i	174.7 (5)
C6—C7—C8—C9	0.1 (5)	O3—S1—C13B—C13A^i	57.8 (6)
C7—C8—C9—C4	−2.7 (4)	O1—S1—C13B—C13A^i	−71.1 (6)
C7—C8—C9—C1	178.0 (3)	O2—S1—C13C—C13C^i	56.5 (2)
C5—C4—C9—C8	3.0 (4)	O3—S1—C13C—C13C^i	−77.49 (18)
C3—C4—C9—C8	−176.6 (3)	O1—S1—C13C—C13C^i	171.48 (14)

Symmetry code: (i) −x, y, −z+2.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1B···O3^ii	0.92	1.84	2.747 (4)	169
N1—H1C···O1	0.92	1.85	2.755 (4)	169
C7—H7A···O3^iii	0.95	2.36	3.218 (5)	151
C5—H5A···Cg^iv	0.95	2.79	3.512	133

Symmetry codes: (ii) x, y+1, z; (iii) x+1/2, y+1/2, z; (iv) −x+1/2, y−1/2, −z+1.