CRYSTAL-STRUCTURE OF A NUCLEOSIDE ANALOG, 2',3'-DIDEOXY-3'-AZIDO-5-CHLOROCYTIDINE

The title compound, 1-(2,3-dideoxy-3-azido-beta-D-erythro pentofuranos -1-yl)-5-chlorocytosine, crystallizes in the orthorhombic space group P2(1)2(1)2(1) with a = 5.840(1), b = 13.780(1), c = 15.396(2) angstrom , Z = 4. The structure was solved by direct methods and refined by ful l-matrix least-squares calculations to a final R value of 0.033 for 16 88 unique observed reflections. The N-glycosidic torsion angle chi has a value of -160.8(1)degrees, in the anti range. The sugar pucker is 2 (3)T with P = 180(1)degrees and psi = 34(1)degrees. The C4'-C5' confor mation is +sc with gamma = 50.8(2)degrees. The azido group is nonlinea r and oriented trans to the C3'-C4' bond. The molecular packing in the crystalline space is stabilized by N-H...N, N-H...O, O-H...O hydrogen bonds and C-H...O close contacts.