X-RAY AND CONFORMATIONAL INVESTIGATION OF 6-DEOXY-6-C-(1,5-DI-O-ACETYL-2,3-O-ISOPROPYLIDENE-BETA-D-ALLO- PENTOFURANOS-5-YL)-1,2/3,4-DI-O-ISOPROPYLIDENE-ALPHA-D-GALACTOPYRANOSE AND 6-C-(BENZYL 5-DEOXY-2,3-O-ISOPROPYLIDENE-BETA-D-RIBOFURANOSID-5-YL)-1,2/3,4-DI-O-ISOPROPYLIDENE-D-GLYCERO-ALPHA-D-GALACTO-HEXOPYRANOSE

The structures of the title compounds (2b and 3) have been investigated in the solid state by X-ray methods. The crystals of 2b are monoclinic, space group P2(1), and of 3 orthorhombic, space group P2(1)2(1)2(1). The cell dimensions are: for 2b, a = 9.910(2), b = 11.745(1), c = 11.810(3) Angstrom, beta = 97.32(1)degrees; and for 3, a = 6.103(1), b = 15.954(1), c = 28.855(3) Angstrom. Both structures were solved by direct methods, and refined by a full-matrix, least-squares procedure giving for 2b, R = 0.0541 (unit weight), and for 3, R = 0.0451 (R(w) = 0.0445). The galactopyranose rings of 2b and 3 adopted a twist and a mixed twist-screw conformation, respectively. The absolute configuration at C-7 in 2b, as well as at C-6 in 3, was determined to be (R). Relatively strong intermolecular hydrogen bonds were observed in the crystal structure of 3.