Karounidiol [D:C-friedo-oleana-7,9(11)-diene-3α,29-diol] and its 3-o-benzoate: novel pentacyclic triterpenes from Trichosanthes kirilowii. X-Ray molecular structure of karounidiol diacetate

Abstract

Spectroscopic data were used to propose a probable structure for karounidiol [D:C-friedo-oleana-7,9(11)-diene-3α,29-diol] and its 3-benzoate, triterpenes isolated from the seeds of Trichosanthes kirilowii(Cucurbitaceae). The structure of the skeleton was proved by conversion of the natural product into multiflora-7,9(11)-dien-3βol [D:C-friedo-oleana-7,9(11)-dien-3β-ol], a known synthetic compound. The configuration at C-20 was determined by X-ray analysis of karounidiol diacetate after an attempt to obtain this information by chemical correlation with naturally occurring 3α-hydroxy-D:C-friedo-oleana-7,9(11)-dien-29-oic acid had failed. N.m.r. evidence and the results of the X-ray analysis indicate that the configuration at C-20 of the latter compound and of two structurally related natural products {bryocoumaric acid [3α-(p-hydroxycinnamoyl)-D:C-friedo-oleana-7,9(11)-dien-29-oic acid] and bryonolic acid (3β-hydroxy-D:C-friedo-olean-8-en-29-oic acid)} was wrongly assigned: all three have a 20β-carboxy configuration (i.e. they are the -30-oic acids according to the usual convention).