Identification of Penicillic Acid as the Active Principle of Penicillium polonicum Inhibiting the Plant Pathogen Pythium aphanidermatum, and Elucidation of Its Crystal Structure

Abstract Pythium aphanidermatum , an oomycete, is a serious, broad host‐range plant pathogen infecting seeds, seedlings and mature plants. It also causes serious losses under post‐harvest conditions. While isolating P. aphanidermatum from an infected bean, we have co‐isolated a fungus that was identified as Penicillium polonicum by using molecular tools. Crude extract obtained from the culture broth exhibited strong inhibitory activity against P. aphanidermatum by agar well assay. Bioassay guided fractionation of crude extract was carried‐out by gradient solvent elution. The major chemical constituent was purified by PTLC followed by crystallization. The structural assignment was done by spectrometric methods and confirmed by single crystal X‐ray diffraction study. Based on these studies, the compound was identified as penicillic acid, in cyclic form. Pure penicillic acid exhibited anti‐proliferative activity against various human cancer cell lines. This is the first report on the crystal structure of penicillic acid, a mycotoxin and an antimicrobial bioactive metabolite.