Abstract
Abstract The title compound, C15H16O9·2H2O, crystallizes in orthorhombic space group P212121 with a=7.082(2), b=34.789(5), c=6.867(2) Å, and Z=4. The structure was solved by direct method and refined by least-squares to a final R of 0.038 based on 1841 observed reflections measured on a four-circle diffractometer. The coumarin ring is approximately planar and the torsion angle around the glucosidic C–O bond is 13.5°; this is much smaller than the corresponding value in 8-glucosyloxy-7-hydroxycoumarin, and causes considerable intramolecular repulsion around the glucosidic linkage. The valence angle of the oxygen atom linking the coumarin and glucose moieties is quite large, 118.5°. The glucopyranose portion is in a C1 chair conformation. Glucosidation at the 7-hydroxyl group brings about considerable decrease of the resonance system of the 7-hydroxylated coumarin moiety. Such an effect seems to play an important role in the transglucosidation of dihydroxycoumarin glucosides.
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