Biosynthesis of palitantin, a polyketide metabolite of Penicillium brefeldianum: 13C n.m.r. assignment and incorporation of 13C-, 2H-, and 18O2-labelled acetates
The biosynthesis of palitantin (1), a metabolite of Penicillium brefeldianum, has been studied using sodium [1,2-13C2]-, [2-2H3]-, [2-13C,2-2H3]-, and [1-13C,1-18O2]-acetate as simple precursors. Analysis of the labelled products by both n.m.r. and mass spectrometry established that no aromatic intermediates are involved in the generation of the six-membered carbocyclic ring. The assignment of the 1H and 13C n.m.r. spectra was made with the aid of two-dimensional homonuclear correlation experiments as well as more standard techniques. Incidentally, O-methyl fulvic acid (2) and O-methyl anhydrofulvic acid (3) were discovered as metabolites of P. brefeldianum.