Chapter 19 - The Biogenesis of Terpenes and Steroids

Abstract

Publisher Summary Terpenes are formed by the combination of isoprenoid units to form compounds, such as geraniol (C10), farnesol (C15), geranylgeraniol (C20), squalene (C80), and others of a similar kind, and can be derived from these precursors by accepted cyclization and, in certain cases, rearrangement mechanisms. This chapter describes the biosynthesis of isopentenyl pyrophosphate (IPP) and dimethylallyl pyrophosphate (DMAPP). Hemiterpenes are classified as free hemiterpenes, phenolic hemiterpenes, alkaloids with hemiterpene residues, isopentenyl adenosine, and related compounds. Similarly, monoterpenes are grouped into acyclic monoterpenes, monocyclic monoterpenes, bicyclic monoterpenes, phenolic monoterpenoids, alkaloids with monoterpene residues, and atypical monoterpenes. The main groups of sesquiterpenes are: acyclic compounds such as farnesol; monocyclic systems such as bisabolol; and bicyclic systems, which are subdivided into four main groups, the cadalene type [e.g., (+)-γ-cadinene], the eudesmol type (e.g. α-eudesmol), the iresin type, and the spiro-4,5-decane type (e.g.β-vetivone). Diterpenes are studied as monocyclic diterpenes, bicyclic diterpenes, tricyclic diterpenes, tetracyclic diterpenes, and diterpene derivatives. All triterpenes are formed by cyclization of all-transsqualene in various chair-boat conformational sequences. Biosynthesis of tetraterpenoids, pentaterpenoids, and polyterpenoids are also discussed. Rubber is a polyterpenoid with a molecular weight that varies from 20,000 to several millions according to source and location in the plant.