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Three new metabolites, named macommelinal, macrophin and macrophic acid, were isolated from the culture broth of Macrophoma commelinae IFO 9570. Their structures were determined to be 2-(4-methoxy-6-methyl-2-oxo-2H-pyran-5-yl)ethanal, 3-methyl-2-butenoic acid (E)-[5-hydroxymethyl-4-methoxy-6-(2-methoxycarbonylethenyl)-2-oxo-2H-pyran-3-ly]methyl ester and 3-(4-methoxy-3,5-dimethyl-2-oxo-2H-pyran-6-yl)-2-propenoic acid, respectively. 4 Acetyl-3-methoxy-5-methylbenzoic acid, now named macrophomic acid, was also isolated from a large-scale culture.The biosynthesis of the macommelin group, novel 5-substituted 2-pyrone metabolites, has been investigated by feeding experiments with [1-^C]-, [1,2-^C_2]- and [1-^C, 2-^2H_3]acetate and [2-^C]malonate. It was concluded that all these metabolites originated from a single straight tetraketide chain. Furthermore, the biogenetic mutual relationships of these metabolites including potential intermediates were estabished through incorporation experiments with ^C-labeled compounds.

Substrate specificity in the novel biotransformation from 2-pyrone derivatives to substituted benzoic acids by Macrophoma commelinae (IFO 9570) was investigated by means of feeding experiments with various compounds. Among them, 2-pyrone derivatives substituted by an electron-donating group at C-4,by an electron-withdrawing group at C-5 and by an alkyl group at C-6 were converted to the corresponding benzoic acid derivatives in fairly good yields. The C_3-unit precursors and intermediates were examined in stationary or shaking culture. Based on the experimental results obtained, a mechanism for this unique reaction is proposed.

It was found that Macrophoma commelinae (IFO 9570) had an ability to transform 5-acetyl-4-methoxy-6-methyl-2-pyrone (1) to 4-acetyl-3-methoxy-5-methylbenzoic acid (2). This biotransformation was investigated using 13C- and 14C-labeled compounds. It is likely that 2 is formed by condensation of the added 2-pyrone and a catabolic pyruvate.