Crystal Structure of 6α,7α:24α,25α-Diepoxy-5α,12α-dihydroxy-1-oxo-20S,22R-witha-2-enolide Isolated from Datura quercifolia Leaves

Abstract

Phytochemical investigations of the Datura quercifolia (Solanaceae) plant yielded a minor withanolide. The structure of the withanolide was established by spectral analysis and X-ray diffraction studies as 6α,7α:24α,25α-diepoxy-5α,12α-dihydroxy-1-oxo-20S,22R-witha-2-enolide (C₂₈H₃₈O₇. CH₃OH). The withanolide crystallizes in the orthorhombic space group P2₁2₁2₁ with unit cell parameters a = 6.916(4), b = 19.199(2), c = 20.138(5)Å, Z = 4, D_cal = 1.288 Mg m^-3. The crystal structure was solved by direct methods and refined to R = 0.0462 for 1628 observed reflections. The ring conformations are: A and B, half-chair; C, chair; D, intermediate between half-chair and envelope; E, diplanar. The geometry of the rings is trans at the A/B, B/C and C/D ring junctions. The twist along the length of the steroid nucleus is negligible [C19-C10…C13-C18 = 3.3°]. The crystal structure is stabilized by intra- and intermolecular O-H…O and C-H…O hydrogen bonds.