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-isopro pylidene-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-galac to-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) A, beta = 97.32(1) degrees; and for 3, a = 6.103(1), b = 15.954(1), c = 28.855(3) A. 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 (RW = 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.