Structure of a dideoxynucleoside active against the HIV (AIDS) virus.

N4-Benzoyl-2',3'-dideoxycytidine, C16H17-N3O4.2H2O, M(r) = 351.4, monoclinic, P2(1), a = 4.691 (1), b = 14.448 (2), c = 12.924 (3) A, beta = 97.63 (1) degree, V = 868.2 (1) A3, Dm(flotation) = 1.34 (1), Dx = 1.344 Mg m-3, Z = 2, F(000) = 372, lambda = 1.5418 A, mu(Cu K alpha) = 0.65 mm-1, T = 292 (1) K, final R = 0.038 for 1437 observed data. The glycosidic torsion angle C(6)--N(1)--C(1')--O(4') is 20.6 (5) degrees and the pucker of the furanose ring is C(3') endo. Free rotation about the exocyclic C(4')--C(5') bond allows the hydroxymethyl substituent to adopt two orientations, trans and gauche, the latter resulting in a short contact, H(6)...O(5") of 2.21 (4) A, indicative of a relatively strong C--H...O intramolecular hydrogen-bonding interaction.