Structure of a nucleoside analogue, 3'-deoxy-3'-fluorothymidine.

1-(2,3-Dideoxy-3-fluoro-beta-D-erythro-pentofuranosyl)thymine, C10H13FN2O4, Mr = 244.22, monoclinic, P21, a = 6.408 (14), b = 18.716 (26), c = 9.329 (7) A, beta = 98.4 (1) degrees, V = 1107 (3) A3, Z = 4, Dm = 1.46, Dx = 1.465 Mg m-3, graphite-monochromated Mo K alpha radiation, lambda = 0.71073 A, mu = 0.1169 mm-1, F(000) = 512, T = 298 K, final R = 0.035 for 1425 unique observed reflections. The asymmetric unit contains two molecules (A and B). For molecule A: the N-glycosidic torsion angle chi has a value of -138.4 (5) degrees in the anti range; the sugar pucker is 2E with P = 164 (1) degrees and psi m = 36 (1) degrees and the C4'--C5' conformation is +sc with gamma = 50.2 (7) degrees. For molecule B: the N-glycosidic torsion angle chi has a value of -159.6 (5) degrees in the anti range; the sugar pucker is 2T3 with P = 169 (1) degrees and psi m = 32 (1) degrees and the C4'--C5' conformation is + sc with gamma = 52.8 (7) degrees. The conformational parameters are in accordance with the IUPAC-IUB Joint Commission on Biochemical Nomenclature [Pure Appl. Chem. (1983), 55, 1273-1280] guidelines. Base-pair formation occurs between the two molecules A and B.