One new ergosteroid derivative, isocyathisterol (1), and eight known compounds (2-9) were isolated from the culture of an algicolous strain (cf-42) of Aspergillus ustus obtained from the fresh tissue of marine green alga Codium fragile. The structure and absolute configuration of 1 were unequivocally identified by using NMR and mass spectroscopic methods as well as quantum chemical calculations. Compound 1 exhibited weak antibacterial activity.
Keywords: algicolous fungus; Aspergillus ustus; ergosteroid; isocyathisterol.