Studies in relation to biosynthesis. XLI. Canescin

Abstract

The biosynthesis of canescin (I) has been investigated. The isocoumarin portion is derived from a polyketide chain. One carbon atom of the γ- lactone ring and the carbon atom of the methoxyl group originate from methionine whilst the other three carbon atoms of the γ-lactone have a symmetrical C₄-acid of the citric acid cycle as their precursor. This metabolite is most unusual in that an oxygenated methionine-derived carbon atom provides the growing point of a new carbon chain. A possible mechanism for the attachment of the lactone is suggested.