Chapter 3 - Biogenesis of Carbazole Alkaloids

Abstract

Publisher Summary The chapter presents a study on biogenesis of carbazole alkaloids. A closer examination of all the carbazole alkaloids isolated and studied so far presents several interesting biogenetic features of these molecules. The most important one is the origin of the indole nucleus and of the ring A. With some rare exceptions, the alkaloids having an extra methyl group (or its equivalent) at the 3-position are isolated from higher plants, whereas the others are obtained from several different sources. Based on their natural occurrence, the carbazole alkaloids isolated to date were classified under these two main categories, and their biosyntheses is discussed consequently. The chapter discusses some of the biosynthetic pathways based on rational, delineated proposals. The chapter discusses carbazole alkaloids from higher plants and other sources. The occurrence of 3-methylcarbazole and its oxidative congeners 3-formylcarbazole and methyl carbazole-3-carboxylate, from the taxonomically related genera Murraya, Clausena, and Glycosmis of the family Rutaceae, sub-family Aurantoidae, of higher plants, provides clear evidence for the in vivo oxidation of the methyl group in 3-methylcarbazole. This was supported by the photochemical oxidation of the 3-methyl group of carbazole alkaloids. All of the biogenetic proposals of the carbazole alkaloids isolated from other sources have indicated L-tryptophan has a progenitor. The occurrence of pityriazole, along with malasseziazoles A, B, and C, in the same source—namely, cultures of the human pathogenic yeast Malassezia furfur, indicates a common biogenesis among these structurally diverse carbazole derivatives.