Cytotoxic, antimicrobial and antiviral secondary metabolites produced by the plant pathogenic fungus Cytospora sp. CCTU A309.

Chemical analysis of extracts from cultures of the plant pathogenic fungus Cytospora sp. strain CCTU A309 collected in Iran led to the isolation of two previously unreported heptanedioic acid derivatives namely (2R,3S) 2-hydroxy-3-phenyl-4-oxoheptanedioic acid (1) and (2S,3S) 2-hydroxy-3-phenyl-4-oxoheptanedioic acid (2) as diastereomers, four previously undescribed prenylated p-terphenyl quinones 3-6 in addition to five known metabolites. Their structures were elucidated on the basis of extensive spectroscopic analysis and high-resolution mass spectrometry. For metabolites 1 and 2, the absolute configurations at C-2 were deduced from comparison of the 1H NMR difference of their (S)- and (R)-phenylglycine methyl ester derivatives while the relative configurations were tentatively assigned by a J-based analysis and confirmed by comparison of 13C chemical shifts to literature data. The isolated compounds were tested for their cytotoxic, antimicrobial (including biofilm inhibition), antiviral, and nematicidal activities. While only moderate antimicrobial effects were observed, the terphenyl quinone derivatives 3-6 and leucomelone (10) exhibited significant cytotoxicity against the mouse fibroblast L929 and cervix carcinoma KB-3-1 cell lines with IC50 values ranging from 2.4 to 26 µg/mL. Furthermore, metabolites 4-6 showed interesting antiviral activity against hepatitis C virus (HCV).