Abstract
6 alpha,7 alpha-epoxy-5 alpha,17 alpha,dihydroxy-1-oxo-22R-witha-2,24-dienolide (C28H38O6) was isolated from Withania somnifera leaves. The structure of the withanolide was established by spectral analysis and X-ray diffraction studies as withanone. The compound crystallizes in the orthorhombic space group P2(1)2(1)2(1) with unit cell parameters: a = 9.191(10) angstrom, b = 12.858(6) angstrom, c = 21.400(16) angstrom, Z = 4. The crystal structure was solved by direct methods and refined to R = 0.0603 for 1742 observed reflections. There is positional disorder of the H atom in a hydroxy group (O5), resulting in two possible hydrogen-bond linkages. All the rings of the steroid skeleton are trans connected. Ring A exists in a half-chair conformation, ring B is intermediate between a half-chair and a sofa, ring C a distorted chair, and five-membered ring D is intermediate between a half-chair and an envelope. The delta-lactone ring E adopts a sofa conformation. The twist along the length of the steroid nucleus is negligible [C19-C10 center dot center dot center dot C13-C18=1.8 degrees]. Both the hydroxy groups are involved in hydrogen bonding.