Antimicrobial Polyketide Metabolites from Penicillium bissettii and P. glabrum .

Screening of several fungi from the New Zealand International Collection of Microorganisms from Plants identified two strains of Penicillium, P. bissettii and P. glabrum , which exhibited antimicrobial activity against Escherichia coli, Klebsiella pneumoniae , and Staphylococcus aureus. Further investigation into the natural products of the fungi, through extraction and fractionation, led to the isolation of five known polyketide metabolites, penicillic acid ( 1 ), citromycetin ( 2 ), penialdin A ( 3 ), penialdin F ( 4 ), and myxotrichin B ( 5 ). Semi-synthetic derivatization of 1 led to the discovery of a novel dihydro ( 1a ) derivative that provided evidence for the existence of the much-speculated open-chained form of 1 . Upon investigation of the antimicrobial activities of the natural products and derivatives, both penicillic acid ( 1 ) and penialdin F ( 4 ) were found to inhibit the growth of Methicillin-resistant S. aureus . Penialdin F ( 4 ) was also found to have some inhibitory activity against Mycobacterium abscessus and M. marinum along with citromycetin ( 2 ).