Received 2 August 2012
Three derivatives of 4-fluoro-5-sulfonylisoquinoline
aResearch and Education Center for Natural Sciences, Keio University, Hiyoshi 4-1-1, Kohoku-ku, Yokohama 223-8521, Japan, and bTokyo New Drug Research Laboratories, Pharmaceutical Division, Kowa Company Ltd, 2-17-43 Noguchicho, Higashimurayama, Tokyo 189-0022, Japan
In 4-fluoroisoquinoline-5-sulfonyl chloride, C9H5ClFNO2S, (I), one of the two sulfonyl O atoms lies approximately on the isoquinoline plane as a result of minimizing the steric repulsion between the chlorosulfonyl group and the neighbouring F atom. In (S)-(-)-4-fluoro-N-(1-hydroxypropan-2-yl)isoquinoline-5-sulfonamide, C12H13FN2O3S, (II), there are two crystallographically independent molecules (Z' = 2). The molecular conformations of these two molecules differ in that the amine group of one forms an intramolecular bifurcated hydrogen bond with the F and OH groups, whilst the other forms only a single intramolecular N-HF hydrogen bond. The N-HF hydrogen bonds correspond to weak coupling between the N(H) and 19F nuclei, observed in the 1H NMR solution-state spectra. In (S)-(-)-4-[(4-fluoroisoquinolin-5-yl)sulfonyl]-3-methyl-1,4-diazepan-1-ium chloride, C15H19FN3O2S+·Cl-, (III), the isoquinoline plane is slightly deformed, suggestive of a steric effect induced by the bulky substituent on the sulfonyl group.
Fasudil hydrochloride, (IV) (see Scheme), is a synthetic protein kinase inhibitor which is known to have a potent vasodilatory effect on the vertebral arteries (Morikawa et al., 1992). Crystal structure analyses of complexes of protein kinase A with fasudil or related compounds have been undertaken to investigate the nature of these ligands in the binding pocket (Engh et al., 1996; Breitenlechner et al., 2003). Various derivatives of fasudil have been explored and it was found that (S)-(-)-4-[(4-fluoroisoquinolin-5-yl)sulfonyl]-3-methyl-1,4-diazepan-1-ium chloride, (III), has a much more potent and selective Rho-kinase inhibitory activity than (IV), i.e. the incorporation of an F atom at the 4-position of the isoquinoline system and the chiral attachment of a methyl group at the 2-position of the 1,4-diazepane ring dramatically improve the pharmacological action. As an illustration, the half-maximum inhibitory concentration (IC50) of (III) and fasudil are 0.03 and 0.50 µM, respectively (Gomi et al., 2011). A practical synthesis of (III) may be achieved by starting from 4-fluoroisoquinoline and passing through the intermediates 4-fluoroisoquinoline-5-sulfonyl chloride, (I), and (S)-(-)-4-fluoro-N-(1-hydroxypropan-2-yl)isoquinoline-5-sulfonamide, (II) (Gomi et al., 2011), despite (I) being less reactive than its nonfluorinated analogue.
The 1H NMR spectra of (II) suggested a coupling between N(H) and 19F through an intramolecular N-HF hydrogen bond (Manjunatha Reddy et al., 2010). In the present study, the structures of (I), (II) and (III) have been determined in order to investigate the intramolecular interactions between the sulfonyl and F atoms at the vicinal positions. Although there is no entry for such an SO2F combination in a naphthalene-like compound in the Cambridge Structural Database (CSD, Version 5.33 of November 2011; Allen, 2002), the structures of four naphthalene-1-sulfonates (e.g. Vennila et al., 2008) and seven naphthalene-1-sulfonamides (e.g. Navarrete-Vázquez et al., 2010) are available. These all show similar conformations of the S(=O)2O or S(=O)2N groups with the naphthalene ring, namely that the C6-C5-S=O torsion angles range from -7 to 7°. This suggests that there is an intramolecular repulsion between the H atom at the vicinal 4-position and the sulfonyl O atoms. An exception is N-(2-aminoethyl)-N-methylisoquinoline-5-sulfonamide hydrochloride (Vasdev et al., 2008). There, the C6-C5-S=O torsion angle is ca -86°, with a short C4-HO(=S) nonbonded distance of 2.28 Å. Replacing the H atom at the 4-position with an F atom should mean that such short contacts are not allowed.
The orientations of the S(=O)2Cl group in (I) and the S(=O)2N groups in (II) and (III) relative to the isoquinoline ring are similar to each other, as expected (Figs. 1-3). The C6-C5-S12-O13 torsion angle in (I) is 1.6 (3)°, the corresponding angles for the two crystallographically independent molecules in (II) are -2.5 (5) and -0.2 (5)°, and that in (III) is 9.3 (6)°. In (I), the F11S12, F11O14 and F11Cl15 distances are 3.037 (3), 2.667 (4) and 3.104 (3) Å, respectively, which are shorter by 0.1 to 0.3 Å than the sum of their van der Waals radii (Bondi, 1964). The molecular packing pattern of (I) is a typical herringbone (Fig. 4), and there is an intermolecular short contact, the N2Cl15(-x + , y - , -z - ) distance being 3.129 (3) Å.
In the 1H NMR spectrum of (II), the multiplicity of the amide proton is triplet ( 5.34), but doublet ( 5.40) for the nonfluorinated analogue, suggesting spin-spin coupling between the amide N-H group and the active 19F nuclei (JN-HF = 7.1 Hz). Similar through-space nuclear spin-spin couplings due to intramolecular N-HF hydrogen bonds have been observed for 2-fluoro-N-(pyridinyl)benzamides, the NF distances being 2.722 (5)-2.753 (6) Å (Mocilac et al., 2012). The 2-fluorophenylsulfonamides do not show such intramolecular spin-spin coupling (Samarakoon et al., 2010), and this agrees with the fact that the conformations of these molecules are not suitable for the formation of intramolecular N-HX hydrogen bonds (X = Cl: Fernandes et al., 2011; Shakuntala et al., 2011; X = I: Arshad et al., 2011). Somewhat weaker intramolecular N-HF hydrogen bonds are observed in (II), with NF distances of 2.884 (5) and 2.893 (6) Å and N-HF angles of 115 (5) and 137 (6)° (Fig. 2 and Table 1).
In the following discussion, the two independent molecules of (II) are labelled A and B (for the molecules containing atoms S12 and S31, respectively). The amide N15-H15 group has another hydrogen-bond acceptor, O14(-x + 1, y + , -z), and this hydrogen bond links molecule A and its equivalents to form a chain around the twofold screw axis parallel to b passing through (, 0, 0) (Fig. 5 and Table 1). Molecules A and B are connected by an O38-H38N2(x, y - 1, z) hydrogen bond, and these pairs are further connected by another hydrogen bond, O19-H19O38(x, y + 1, z - 1), to form a zigzag molecular chain along the c axis. The N34-H34 group in molecule B forms an intramolecular bifurcated hydrogen bond, which is achieved by a pyramidal configuration around atom N34.
In (III), the isoquinoline ring is a little skewed, the C8-C9-C10-C5 torsion angle being 6.1 (8)°. Atoms F11 and S12 are displaced below and above the average plane of the isoquinoline ring by -0.233 (8) and 0.556 (7) Å, respectively, and the resulting FS distance is 3.053 (5) Å. This may be due to the strain introduced by the bulky group attached to the sulfonyl group. A similar twist in the naphthalene ring was observed in 1,8-bis(methylsulfanyl)naphthalene, which has nonbonded SS distances of 2.918 (2)-2.934 (2) Å. There, the S atoms are displaced from the naphthalene ring by 0.306 (2) and -0.291 (2) Å (Glass et al., 1989). On the other hand, the twist of the naphthalene ring in 1-bromo-8-(ethylsulfanyl)naphthalene is very slight, with the shifts of the S and Br atoms from the naphthalene plane both less than 0.12 Å and with SBr distances of 3.050 (2)-3.056 (2) Å. This relative planarity is achieved mainly by the imbalance of the Br-C-C angles, viz. 124.1 (4)-124.5 (4)° inside and 112.3 (5)-112.8 (5)° outside (Fuller et al., 2007). In the packing structure of (III), the 1,4-diazepan-1-ium group acts as a hydrogen-bond donor to the chloride anions (Fig. 6 and Table 2). A (ClH-N-H)n chain is formed around the twofold screw axis parallel to c, passing through (, 0, 0).
| || Figure 1 |
The molecular structure of (I), showing the atom-numbering scheme. Displacement ellipsoids are drawn at the 30% probability level.
| || Figure 2 |
The molecular structure of (II), showing the atom-numbering scheme. Displacement ellipsoids are drawn at the 30% probability level. Dashed lines indicate N-HF and N-HO interactions.
| || Figure 3 |
The molecular structure of (III), showing the atom-numbering scheme. Displacement ellipsoids are drawn at the 30% probability level. The dashed line indicates the N-HCl interaction.
| || Figure 4 |
The crystal structure of (I), projected along c.
| || Figure 5 |
The crystal structure of (II), projected along b. Dashed lines indicate hydrogen bonds. [Symmetry codes: (i) -x + 1, y + , -z; (ii) x, y + 1, z - 1.]
| || Figure 6 |
The crystal structure of (III), projected along c. Dashed lines indicate hydrogen bonds. [Symmetry code: (iv) -x + , -y, z - .]
A pilot-scale production of (III) was achieved, where (I) and (II) were the reaction intermediates (Gomi et al., 2011). Compound (I) was synthesized from 4-fluoroisoquinoline. Plate-like crystals of (I) were grown by slow diffusion of hexane vapour into a chloroform solution.
Compound (II) was prepared by the reaction of (I) with (S)-(+)-2-aminopropan-1-ol. The specific rotation, D, of (II) at 292 K is -18.36° (c = 0.54, CHCl3, where c is the concentration in units of grams per 100 ml). 1H NMR (400 MHz, CDCl3): 1.06 (3H, d, J = 6.3 Hz), 1.78 (1H, t, J = 5.1 Hz), 3.43-3.59 (3H, m), 5.34 (1H, t, J = 7.1 Hz), 7.77 (1H, t, J = 7.8 Hz), 8.23-8.28 (1H, m), 8.60 (1H, d, J = 5.4 Hz), 8.68 (1H, dd, J = 7.8, 1.2 Hz), 9.19 (1H, s) (Gomi et al., 2011). Plate-like crystals of (II) were grown by slow diffusion of hexane vapour into an acetone solution.
Compound (III) was prepared from (I) and (S)-(+)-tert-butyl 3-methyl-1,4-diazepane-1-carboxylate (Gomi et al., 2012). The specific rotation, D, of (III) at 293 K is -8.82° (c = 1.00, H2O). Plate-like crystals of (III) were grown by slow diffusion of ethyl acetate vapour into a methanol solution.
The coordinates of the amide H atoms in (II) were refined with the N-H distances restrained to 0.86 (1) Å. This revealed a pyramidal configuration around the N34 atom of molecule B with reasonable hydrogen-bond geometry in contrast to the almost flat configuration around the N15 atom of molecule A. All the other H atoms were positioned geometrically and refined as riding, with C-H = 0.93 (aromatic), 0.96 (methyl), 0.97 (CH2) or 0.98 Å (sp3 CH), O-H = 0.82 Å and N-H = 0.90 Å, and with Uiso(H) = 1.2Ueq(parent). Methyl-group orientations were obtained by allowing rotation about the C-C bond.
For (II), Friedel pairs were averaged before the final refinement, since the Flack (1983) parameter was estimated to be 0.4 (3). The absolute structure was assigned based on the known absolute configuration of the (S)-2-aminopropan-1-ol group.
For (III), the absolute structure was assigned based on the known absolute configuration of the (S)-3-methyl-1,4-diazepane group. This assignment is tentatively supported by the value obtained for the Flack (1983) parameter.
For all compounds, data collection: WinAFC Diffractometer Control Software (Rigaku, 1999); cell refinement: WinAFC Diffractometer Control Software; data reduction: CrystalStructure (Rigaku, 2010); program(s) used to solve structure: SIR92 (Altomare et al., 1994); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEPII (Johnson, 1976); software used to prepare material for publication: CrystalStructure.
Supplementary data for this paper are available from the IUCr electronic archives (Reference: KY3019 ). Services for accessing these data are described at the back of the journal.
Allen, F. H. (2002). Acta Cryst. B58, 380-388.
Altomare, A., Cascarano, G., Giacovazzo, C., Guagliardi, A., Burla, M. C., Polidori, G. & Camalli, M. (1994). J. Appl. Cryst. 27, 435.
Arshad, M. N., Khan, I. U., Rafique, H. M., Asiri, A. M. & Shafiq, M. (2011). Acta Cryst. E67, o1327.
Bondi, A. (1964). J. Phys. Chem. 68, 443-451.
Breitenlechner, C., Gaßel, M., Hidaka, H., Kinzel, V., Huber, R., Engh, R. A. & Bossemeyer, D. (2003). Structure, 11, 1595-1607.
Engh, R. A., Girod, A., Kinzel, V., Huber, R. & Bossemeyer, D. (1996). J. Biol. Chem. 271, 26157-26164.
Fernandes, W. B., Aragão, A. Q., Martins, F. T., Noda-Perez, C., Lariucci, C. & Napolitano, H. B. (2011). Acta Cryst. C67, o226-o229.
Flack, H. D. (1983). Acta Cryst. A39, 876-881.
Fuller, A. L., Knight, F. R., Slawin, A. M. Z. & Woollins, J. D. (2007). Acta Cryst. E63, o3957.
Glass, R. S., Andruski, S. W., Broeker, J. L., Firouzabadi, H., Steffen, L. K. & Wilson, G. S. (1989). J. Am. Chem. Soc. 111, 4036-4045.
Gomi, N., Ohgiya, T. & Shibuya, K. (2012). PCT Int. Appl. WO 2012026529.
Gomi, N., Ohgiya, T., Shibuya, K., Katsuyama, J., Masumoto, M. & Sakai, H. (2011). Heterocycles, 83, 1771-1781.
Johnson, C. K. (1976). ORTEPII. Report ORNL-5138. Oak Ridge National Laboratory, Tennessee, USA.
Manjunatha Reddy, G. N., Vasantha Kumar, M. V., Guru Row, T. N. & Suryaprakash, N. (2010). Phys. Chem. Chem. Phys. 12, 13232-13237.
Mocilac, P., Donnelly, K. & Gallagher, J. F. (2012). Acta Cryst. B68, 189-203.
Morikawa, A., Sone, T. & Asano, T. (1992). Chem. Pharm. Bull. 40, 770-773.
Navarrete-Vázquez, G., Morales-Vilchis, G., Estrada-Soto, S., Rodríguez-López, V. & Tlahuext, H. (2010). Acta Cryst. E66, o2744.
North, A. C. T., Phillips, D. C. & Mathews, F. S. (1968). Acta Cryst. A24, 351-359.
Rigaku (1999). WinAFC Diffractometer Control Software and NUMABS. Rigaku Corporation, Tokyo, Japan.
Rigaku (2010). CrystalStructure. Rigaku Corporation, Tokyo, Japan.
Samarakoon, T. B., Hur, M. Y., Kurtz, R. D. & Hanson, P. R. (2010). Org. Lett. 12, 2182-2185.
Shakuntala, K., Foro, S. & Gowda, B. T. (2011). Acta Cryst. E67, o1400.
Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.
Vasdev, N., LaRonde, F. J., Woodgett, J. R., Garcia, A., Rubie, E. A., Meyer, J. H., Houle, S. & Wilson, A. A. (2008). Bioorg. Med. Chem. 16, 5277-5284.
Vennila, J. P., Thilagavathi, R., Kavipriya, R., Kavitha, H. P. & Manivannan, V. (2008). Acta Cryst. E64, o1124.