Carneic acids A and B, chemotaxonomically significant antimicrobial agents from the xylariaceous ascomycete Hypoxylon carneum.

Carneic acids A and B (1, 2) are polyketide antibiotics structurally related to phomopsidin. They were isolated as major constituents of the stromata of Hypoxylon carneum, a species that had shown a highly specific secondary metabolite profile in a survey of xylariaceous ascomycetes based on HPLC profiling. Their chemical structures were elucidated by a combination of spectroscopic methods and by preparation of derivatives. An X-ray crystal structure of the dinitrobenzoate of carneic acid B methyl ester (8) was obtained, even allowing for determination of its absolute structure. The carneic acids showed weak antibacterial and moderate antifungal activities in the serial dilution assay against selected microbial organisms. They appear to be species-specific marker molecules in H. carneum from different geographic regions, but do not constitute major metabolites of more than 100 species of Xylariaceae. Their biological and chemotaxonomic significance is discussed.