Phenylalanine-independent biosynthesis of 1,3,5,8-tetrahydroxyxanthone. A retrobiosynthetic NMR study with root cultures of Swertia chirata.

Root cultures of Swertia chirata (Gentianaceae) were grown with supplements of [1-13C]glucose, [U-13C6]glucose or [carboxy-13C]shikimic acid. 1,3,5,8-Tetrahydroxyxanthone was isolated and analysed by quantitative NMR analysis. The observed isotopomer distribution shows that 1,3,5,8-tetrahydroxyxanthone is biosynthesized via a polyketide-type pathway. The starter unit, 3-hydroxybenzoyl-CoA, is obtained from an early shikimate pathway intermediate. Phenylalanine, cinnamic acid and benzoic acid were ruled out as intermediates.