Biological Effects and Biosynthesis of Brominated Metabolites

On the basis of halogenated metabolites assembled by Gribble, an attempt is made to provide a hypothesis for the biosynthesis of representative groups. Examples of brominated and iodinated metabolites are drawn from the major classes of terpenoids and acetogenins, and related to the biosynthesis of their putative precursors. Brominated and iodinated carbocyclic and heterocyclic aromatic compounds are discussed as well as mechanisms for the oxidative coupling of phenolic substrates. A few chlorinated metabolites are introduced for additional illustration. Halogenation by cationoid (Hal+) reactions catalyzed by haloperoxidases is discussed, and attention drawn to the alternative role of anionoid (Hal-) halogenation. The presentation is extended to the biosynthesis of isonitriles and dichloroimines by anionoid reaction of precursors with cyanide. The range of biota that produce brominated substrates is briefly indicated, and comments made on the ecological significance of metabolites and associations among biota.