6 - The Shikimate Pathway in Higher Plants: Extension of the Phenylpropanoid Unit: Miscellaneous Metabolites

Abstract

The two carbon unit of acetic acid, as acetyl co-enzyme A or its activated form malonyl co-enzyme A, is of central importance in plant biochemistry for it not only provides the starting point for the biosynthesis of fatty acids, polyacetylenes, and the whole range of isoprenoid compounds but is also one of the fundamental building blocks for many characteristic groups of plant phenols. The major groups found in plants are the anthocyanins, flavones, and flavonols, but less widely distributed are minor groups such as the chalcones, aurones, flavan-3-ols, flavanones, and the oligomeric biflavonoids and proanthocyanidins. Closely related both structurally and biogenetically to the flavonoids are two groups of natural products—the isoflavonoids and neoflavonoids. The structures of many of the naturally occurring flavonoids, isoflavonoids, and neoflavonoids contain C5 units, which are apparently derived from mevalonate the precursor of the isoprenoid units of terpenes and steroids.