Ergosteroid derivatives from an algicolous strain of <i>Aspergillus ustus</i>

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