Crystal and molecular structure of abieslactone, (23R)-3α-methoxy-5α,9β-lanosta-7,24-diene-26,23-lactone

Abstract

Crystals of the triterpene abieslactone (III), are orthorhombic, a= 6·633(3), b= 11·761(6), c= 35·009(19)Å, Z= 4, space group P2₁2₁2₁. The structure was determined by direct methods from diffractometer data, and refined by least-squares methods to a final R of 0·098 for 1860 reflexions. The analysis establishes the existence of a double bond in the 7,8- and not in the 9,11-position as previously suggested. The three six-membered rings (A, B, C) adopt the chair, sofa, and twist-boat conformations respectively; the cyclopentane ring D is a half-chair while the lactone ring is planar.