Structures of the 4-cyano and 4-methylamidate analogs of tiazofurin

4-Cyanotiazofurin [2-(beta-D-ribofuranosyl)thiazole-4-carbonitrile, (1)], C9H10N2O4S, M(r) = 242.3, monoclinic, P2(1), a = 7.329(1), b = 8.295 (1), c = 8.697(1) A, beta = 90.90 (1) degree, V = 528.7(1) A3, Z = 2, Dx = 1.52 g cm-3, Cu K alpha, lambda = 1.54178 A, mu = 27.2 cm-1, F(000) = 252, T = 293 K, R = 0.0487 for all 1171 unique reflections. 4-Methylamidatetiazofurin [methyl 2-(beta-D-ribofuranosyl)thiazole-4-carboximidate, (2)], C10H14N2O5S, M(r) = 274.3, orthorhombic, P2(1)2(1)2(1), a = 8.596(1), b = 11.060(1), c = 26.064(1) A, V = 2478.1(2) A3, Z = 8, Dx = 1.47 g cm-3, Cu K alpha, lambda = 1.54178 A, mu = 24.5 cm-1, F(000) = 1152, T = 293 K, R = 0.0374 for all 2902 unique reflections. Compound (2) crystallizes with two crystallographic unique structures in the asymmetric unit [(2a) and (2b)]. All three structures show a close contact between the thiazole sulfur and the pentose oxygen O(1'). S...O(1') distances are 2.936 (3) A in (1), 2.773 (2) A in (2a) and 2.878 (2) A in (2b), resulting from C-glycosidic torsion angles of 34.5 (4), 15.6 (3) and 27.2 (3) degrees respectively. This interesting feature is conserved in the crystal structures of other thiazole nucleosides [Burling & Goldstein (1992).