Biosynthesis of bryonolic acid in cultured cells of watermelon

Bryonolic acid, a pentacyclic triterpene having an anti-allergic activity, was biosynthesized from R-[2- 14C]mevalonate or [2- 14C]acetate administered to cell cultures of watermelon ( Citrullus lanatus). The radioactivity of the labelled mevalonate added to cell-free extracts in the presence of ATP, Mg 2+ and NADPH was also incorporated into bryonolic acid as well as into the possible intermediates, isomultiflorenol, bryonolol and bryonolal. Furthermore, [ 14C]2,3-oxidosqualene added to the microsomal solution of the same cell-free extracts was converted enzymatically into isomultiflorenol, which is considered to be the first cyclization product in the biosynthesis of bryonolic acid. These results indicate that bryonolic acid is biosynthesized from 2,3-oxidosqualene via isomultiflorenol and subsequent oxidations of the methyl group at C-29.