STRUCTURAL STUDIES ON MODIFIED NUCLEOSIDES .12. STRUCTURE OF 1-(2-DEOXY-2-FLUORO-ALPHA-D-ARABINOPYRANOSYL)-5-IODOURACIL

1-(2-Deoxy-2-fluoro-alpha-D-arabinopyranosyl)-5-iodouracil, C9H10FIN2O5, M(r) = 372.09, triclinic, Pl, a = 5.098 (2), b = 6.470 (2), c = 9.293 (6) angstrom, alpha = 81.10 (2), beta = 84.91 (3), gamma = 79.38 (2)-degrees, V = 297.1 (2) angstrom3, Z = 1, D(m) = 2.08, D(x) = 2.080 Mg m-3, lambda(Mo K-alpha) = 0.71069 angstrom, mu = 2.692 mm-1, F(000) = 180, T = 293 K, final R = 0.024 for 1702 unique observed [F greater-than-or-equal-to 4-sigma(F)] reflections. The pyranose ring adopts a chair conformation with phi-2 = - 19 (4)-degrees, theta-2 = 8.9 (5)-degrees and Q(t) = 0.596 (5) angstrom. The N-glycosidic torsion angle chi [O(5')-C(1')-N(1)-C(2)] between this ring and the pyrimidine base is oriented + ac [95.1 (4)-degrees]. The conformational parameters are in accordance with the IUPAC-IUB Joint Commission on Biochemical Nomenclature [Pure Appl. Chem. (1983), 55, 1273-1280] guidelines.