Biosynthetic studies on the botcinolide skeleton:: New hydroxylated lactones from Botrytis cinerea

The biosynthetic origin of the botcinolide skeleton was investigated by means of feeding C-13- and H-2-labeled precursors to Botrytis cinerea. Three new compounds, two homobotcinolide derivatives, 3-O-acetylhomobotcinolide (5) and 8-methylhomobotcinolide (6), and a new 11-membered lactone (7), were isolated. Their structures were elucidated on the basis of spectroscopic data, including one-bond and long-range H-1-C-13 correlations. The relative stereochemistries were determined by combined analyses of NOE data and H-1-H-1 coupling constants. According to the results of feeding experiments with C-13- and H-2-labeled acetate and L-S-methylmethionine, 5 is an acetate-derived polyketide whose methyl groups originate from L-S-methylmethionine. This is a rare example of the incorporation of a methyl from methionine into a supposed C-3 starter unit of the polyketide synthesis.