Chapter 10 Synthetic Studies in Alkaloid Chemistry

Abstract

This chapter is dedicated to the synthetic studies in alkaloid chemistry. It describes the synthesis of ipecacuanha alkaloids, yohimbine alkaloids, corynantheidine alkaloids, Rauwolfia alkaloids, berbanes, vincamine, aspidosperma alkaloids and alkaloids from Catharanthus roseus . The ipecacuanha alkaloid emetine has been used for the treatment of amoebic dysentery, amoebic hepatic ulcers, and other ailments since the beginning of this century. The easily accessible ketone (R = C 2 H 5 ) is used to prepare the alkaloid (−)-corynantheidine. The ketone is allowed to react with cyanoacetic acid methyl ester followed by reduction with sodium borohydride and methanolysis giving in excellent yield. The Rauwolfia alkaloids, such as reserpine, deserpidine, and a few semisynthetic derivatives, are still widely used drugs. Berbanes are isoquinoline derivatives, but at the same time they can be regarded as depyrrolo-yohimbine derivatives. The biological effects depend very much on the stereochemistry of the berbanes. Derivatives with normal- or pseudo arrangements have been ineffective, while in the allo-series many potent compounds have been found. Even changing the configuration of the hydroxyl group causes a significant loss of biological activity. (+)-Vincamine, an alkaloid isolated from Vinca minor, proved to be a useful pharmaceutical and is on the market as a specific brain vasodilator agent.