Hongoquercins A and B, new sesquiterpenoid antibiotics: isolation, structure elucidation, and antibacterial activity.

Two new sesquiterpenoid antibiotics, hongoquercins A and B, were isolated from the extracts of an unidentified fungus. The structures of both metabolites were determined by spectroscopic analysis. They are related to a class of compounds commonly found in brown algae and dictyoceratid sponges. Hongoquercin A exhibited moderate activity against gram-positive bacteria.