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Cette membrane a des pores tres droits et une distribution etroite des dimensions des pores. Etude experimentale de la validite de la theorie des pores

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.

The novel metabolites, named macommelin, macommelin-9-ol, macommelin-8-ol and macommelin-8, 9-diol, were isolated from the culture broth of Macrophoma commelinae IFO 9570. The structures were determined to be 5-ethyl-, 5-(2'-hydroxyethyl)-, 5-(1'S-hydroxyethyl)- and 5-(1'S, 2'-dihydroxyethyl)-4-methoxy-6-methyl-2H-pyran-2-one, respectively. This fungus also produced rosellisin, an antibiotic α-pyrone.

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.