MOLECULAR AND CRYSTAL-STRUCTURE OF METHYL HEPTA-O-ACETYL-ALPHA-LAMINARABIOSIDE

The molecular and crystal structure of methyl 2,3,4,6,2',4',6'-hepta-O-acetyl-alpha-laminarabioside (methyl alpha-laminarabioside heptaacetate) was determined by the X-ray diffraction method. The crystal belongs to the monoclinic system, space group P2(1), a = 13.179(3), b = 22.832(3), c = 5.555(2) Angstrom, beta = 95.91(3)degrees D-obsd = 1.32 g/cm(3), D-calcd = 1.300 g/cm(3), Z = 2. The structure was obtained by the direct method and refined by the full-matrix least-squares procedure to R = 0.061 for 2097 observed reflections with \F-o\ greater than or equal to 2 sigma (F-o). The difference Fourier synthesis showed all the hydrogen atoms except those of the methyl moieties. The linkage conformation angles, phi = Theta(0-5-C-1-0-1-C-3') and psi = Theta(C-1-O-1-C-3'-C-2'), are - 85.5 and - 111.9 degrees, respectively. These are similar to those of other beta-(1 --> 3)-linked acetylated disaccharide compounds. The acetate substituent at C-6 of the reducing residue was in the gg conformation, while the gt conformation was observed in the nonreducing residue. The conformational analysis using the bond lengths and angles obtained revealed that the energy map for phi and psi angles was independent of the orientation of the C-6 acetate. In the crystal structure D-glucopyranose rings are amassed along the c axis and parallel to the ab-plane. These molecules interact with their surrounding molecules only by van der Waals forces.