Constituents of Withania somnifera Dun. Part VI. The stereochemistry of withaferin A
Withaferin A, the steroidal lactone isolated from the leaves of Withania somnifera Dun. (Solanaceae), has been degraded to bisnor-(5α)-cholanic acid. The β-orientation of the 5,6-epoxide has been demonstrated by optical rotatory dispersion and n.m.r. data. Consequently, withaferin A is a 5β-steroid with the usual stereochemistry at all asymmetric centres, possessing a six-membered-ring lactone in the side-chain.