Aspects of the Biosynthesis of Carolic and Carlosic Acids in Penicillium charlesii. A 13C NMR Study.

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Abstract
The origin of 2 metabolic products of P. charlesii NRRL 1887, carolic and carlosic acids was reinvestigated in a 13C labeling study. The main biosynthetic pathway was the combination of a C6 polyketide unit with a C4 compound closely related to succinic acid in agreement with earlier findings. A bilateral mixing of intact acetate units occurred between the acetate pool and the incorporated C4 unit. Dehydrocarolic acid could be converted to carolic acid in a cell free extract of P. charlesii; an earlier proposal of carlosic acid as a precursor of carolic acid could not be confirmed. A new biosynthetic scheme is proposed considering oxalacetate as the actual C4-precursor. On reaction with a .beta.-ketocaproyl moiety the formed .alpha.-(.alpha.-ketosuccinyl)-.beta.-ketocaproate is considered the key intermediate in the biosynthesis of the 3-acyltetronic acids of the 5-methyl series and of the 5-carboxymethyl series. The occurrence of viridicatic acid as a metabolite of P. charlesii was established.