Studies on the synthesis of cardiotonic steroids. I. Efficient synthesis of cardenolides.

Abstract

Practical synthetic methods of natural cardenolides are illustrated in the syntheses of xysmalogenin and digitoxigenin. The new routes employ pregn-14-en-20-one as key intermediate which was prepared by partial reduction of 14, 16-dien-20-one with triphenylstannane or triethylsilane. A general and efficient method was devised for obtaining cardenolides consisting of (1) 21-methylsulfenylation of pregnen-20-one, (2) the reaction of the resulting 21-methylthio derivative with bromoacetate and zinc, (3) alumina chromatography of epoxy ester obtained from the S-methylated Reformatsky product.