Use of singly and doubly labelled 13C-acetate in the elucidation of the structures and biosynthesis of multicolic and multicolosic acids, new tetronic acids from Penicillium multicolor

Multicolic and multicolosic acid, isolated from cultures of Penicillium multicolor, are shown to have structures (I) and (II) respectively by 1H- and 13C-n.m.r., and u.v. spectroscopic studies, 13C-couplings observed in the spectrum of methyl O-methylmulticolate (III), prepared from multicolic acid enriched with [1,2-13C]acetate establishing the substitution pattern in the tetronic acid chromophore; the biosynthesis of these metabolites from acetate, via oxidative fission of a preformed aromatic precursor, e.g., 6-pentylresorcylic acid, is suggested by the 13C-n.m.r. spectra of derivatives, enriched with [1-13C]-, [2-13C]-, and [1,2-13C]-acetate.