O-Methylation of phenylphenalenone phytoalexins in Musaacuminata and Wachendorfia thyrsiflora

Abstract

Biosynthetic O-methylation at various sites along the backbone of inducible phenylphenalenones in Musaacuminata var. "Williams" (Musaceae) and Wachendorfiathyrsiflora (Haemodoraceae) was investigated using 13C-labelled precursors. The inducibility of O-methylated metabolites was demonstrated in both species and the origin of methoxyl group from [methyl-13C]L-methionine was confirmed. In addition to known phenylphenalenones, a methoxylated metabolite, 4-(4-hydroxy-3-methoxy-phenyl)-benzo[de]isochromene-1,3-dione, was detected and its structure elucidated mainly by NMR spectroscopic techniques. The experiments were used to discriminate methionine-derived and artificial methoxy groups formed during methanolic extraction. Finally, demethylation of 4'-methoxycinnamic acid and subsequent conversion to 3',4'-methylenedioxycinnamic acid was demonstrated in M.acuminata.