Crystal structure of a nucleoside analogue, 2′,3′-dideoxy-3′-fluoro-5-chlorocytidine

The title compound, 1-(2,3-dideoxy-3-fluoro-β-d-erythro pentofuranos-1-yl)-5-chlorocytosine, crystallises in the orthorhombic space group P212121 with a=5.142(1), b=14.177(2), c=15.721(2) Å, Z=4. The crystal structure was solved by the heavy atom method and refined by full-matrix least-squares method to a final R value of 0.031 for 1629 unique observed reflections. The N-glycosidic torsion angle is -156.1(2)° and the sugar moiety is anti to the cytosine base. The sugar pucker is23T with P=178.2(1)° and ψ=31(1)°. The atom 05′ is in a +sc conformation with respect to the furanose ring. The molecular packing in the crystal is stabilized by N-H⋯N, N-H⋯O, O-H⋯O hydrogen bonds and C-H⋯O close contacts. © 1993 Plenum Publishing Corporation.