Chapter 6 Peptide Alkaloids

Abstract

Cyclic peptide alkaloids as basic compounds embodying an ansa structure, in which a 10- or 12-membered peptide-type bridge spans the 1,3 or 1,4 positions of a benzene ring. Compounds that fit this definition have so far been isolated from Rhamnaceae, Sterculiaceae, Pandaceae, Rubiaceae, Urticaceae, Hymenocardiaceae, and Celastraceae. In an expansion of this definition, “linear peptide alkaloids” are defined as those compounds that can be formally derived from cyclic peptide alkaloids by scission of the bridge in an elimination reaction. Most of such compounds have been isolated from marine sponges. Almost all compounds feature a styrylamide group, which may arise by decarboxylation of a phenylalanine unit: this reaction can be easily carried out in vitro . This chapter presents structural and conformational studies of these alkaloids. It presents and elucidates new peptide alkaloids that have been isolated. Synthesis of peptide alkaloids have also been dealt with in the chapter, which explores early approaches to the synthesis of peptide alkaloids, model reactions directed toward total synthesis, synthesis of dihydropeptide alkaloids, and total synthesis of peptide alkaloids.