Colomitides A and B: novel ketals with an unusual 2,7-dioxabicyclo[3.2.1]octane ring system from the aquatic fungus YMF 1.01029.

Two novel diastereoisomeric bicyclic ketals, colomitides A and B (1 and 2, resp.), together with the known (4RS)-3,4-dihydro-4,8-dihydroxynaphthalen-1(2H)-one (3) and preussomerin E (4), were isolated from liquid cultures of an unidentified freshwater fungus YMF 1.01029. Colomitides possess an unusual 2,7-dioxabicyclo[3.2.1]octane skeleton. The chemical structures and relative configurations of compounds 1 and 2 were elucidated by spectroscopic means, including 2D-NMR (HMBC, HMQC, TOCSY, ROESY, and 1H,1H-COSY). Compounds 1, 2, and 4 showed noticeable antifungal and antibacterial activities.