Studies on the neutral constituents of Pachysandra terminalis Sieb. et Zucc. Part IV. X-Ray structure of 3-O-acetyl-16-O-p-bromobenzoylpachysandiol B: new conformation of a friedelin-type triterpene

Abstract

Crystals of the title compound (IVc) are orthorhombic, a= 15·58, b= 30·88, c= 7·40 Å, space group P2₁2₁2₁, and Z= 4. The structure was solved from visually estimated three-dimensional X-ray data by the heavy-atom method, and refined by block-diagonal least-squares to R 14·3%(1722 independent reflections). A chair–chair–chair–boat–boat conformation of the five six-membered-ring skeleton was found, and it was confirmed that this and the quasi-all-chair are the stable conformations in friedelin-type triterpenes.