Crystal and molecular structure of showdomycin

Abstract

The crystal structure of showdomycin, C₉H₁₁NO₆, has been determined by a three-dimensional X-ray analysis. The crystals are monoclinic, a= 15·454, b= 6·547, c= 11·425, β= 121°16′, Z= 4, space group C2. The intensities were measured with a Hilger and Watts automatic four-circle diffractometer using Mo-K_α radiation. The structure was solved by the symbolic addition procedure for phase determination as applied to noncentrosymmetric crystals, and refined by full-matrix least-squares calculations to a final R of 0·050 for 1092 independent observed reflexions. Atom C(2′) of the sugar residue is displaced by ca. 0·58 Å from the least-squares plane through the other four ring atoms and lies on the same side of the plane at C(5′). This plane also makes an angle of ca. 46° with the least-squares plane through the five atoms of the pyrroline ring. The torsion angle with respect to the glycosidic bond, according to the Sundaralingam and Jensen definition, is 129·5°, and the conformation therefore is syn.