Oxepine-containing pyrazinopyrimidine alkaloids and quinolinone derivatives produced by Aspergillus versicolor AS-212, a deep-sea-derived endozoic fungus

Four new oxepine-containing pyrazinopyrimidine alkaloids, versicoxepines A - D (1-4), two quinolinone alkaloid analogs including 3-hydroxy-6-methoxy-4-phenylquinolin-2(1H)-one (5) and 3-methoxy-6-hydroxy-4-phenylquinolin-2(1H)-one (6) which were new naturally occurring compounds, together with two known compounds (7 and 8) were isolated from Aspergillus versicolor AS-212, an endozoic fungus isolated from the deep-sea coral Hemicorallium cf. imperiale, which was collected from the Magellan Seamounts in the Western Pacific Ocean. Their structures were determined by extensive analysis of the spectroscopic and X-ray crystallographic data as well as by chiral HPLC analysis, ECD calculation, and DP4+ probability prediction. Structurally, versicoxepines B and C (2 and 3) represent the first example of a new oxepine-containing pyrazinopyrimidine alkaloid whose cyclic dipeptide moiety is composed of the same type of amino acid (Val or Ile). Compound 5 displayed antibacterial activity against aquatic pathogens, Vibrio harveyi and V. alginolyticus, with MICs of 8 μg/mL.