New cyclopentenones, bromomyrothenone B (1) and botrytinone (2), and the known cyclonerodiol (3) were isolated
from the marine algicolous fungus of the genus Botrytis. The absolute stereostructures of compounds 1 and 2 were
elucidated on the basis of chemical and physicochemical evidence including quantum chemistry calculation, X-ray
analysis, and CD exciton chirality method.