Crystal and molecular structures of methyl 2,3-anhydro-4-deoxy-α- dl- ribo- and -α- dl- lyxo-hexopyranosides

Abstract

Single crystals of methyl 2,3-anhydro-4-deoxy-α- dl- ribo- (1) and -α- dl- lyxo-hexopyranoside (2) have been investigated by X-ray diffraction methods. Compound 1 crystallises in the monoclinic system, space group P2 1/c, with cell dimensions a = 7.694(1), b = 12.954(1), c = 8.415(1) Å, and β = 110.34(1)°. Compound 2 crystallises in the tetragonal system, space group I4 1/a (No. 88, origin at 1 ), with cell dimensions a = 22.995(2) and c = 6.086(1) Å. The intensity data were collected in a four-circle CAD-4D automatic diffractometer, with 1623 reflections for 1, and 2421 for 2. The structures were solved by direct methods. The atomic parameters were refined in an anisotropic mode by the full-matrix, least-squares procedure against 1456 and 1109 observed reflections for 1 and 2, respectively, resulting in R = 0.049 for 1, and R = 0.042 for 2. A hybrid conformation 5 E + 5 H 0 was found for the anhydrohexopyranose ring in 1, whereas a slightly deformed 5 H 0 conformation was assigned to that in 2. Relatively strong intermolecular hydrogen-bonds were observed in each compound. In 1 (acceptor atom O-5), they result in dimers of pairs of enantiomeric molecules; in 2 (acceptor atom O-6), the molecules form helices around the four-fold screw axes in the crystal.