Isolation of an antimicrobial racemic phenalenone derivative from a marine-derived Penicillium sp. fungus

A new phenalenone derivative, 2,4,6,9-tetrahydroxy-7-methyl-2-prenyl-1H-phenalene-1,3(2H)-dione (1), was isolated from the ethyl acetate extract of a marine derived Penicillium sp. fungus that exhibited a unique antimicrobial activity profile. The planar structure of 1 was determined through a combination of 1D and 2D NMR experiments, and circular dichroism and polarimetry indicated that it was isolated as a racemic mixture of enantiomers. The antimicrobial activity of 1 was assessed against a panel of Gram-positive and Gram-negative bacteria and fungal strains and it was found to selectively inhibit the growth of Staphylococcus aureus and Mycobacterium tuberculosis.