A NOVEL, DEGRADED POLYKETIDIC LACTONE, LEPTOSPHAEROLIDE, AND ITS LIKELY DIKETONE PRECURSOR, LEPTOSPHAERODIONE - ISOLATION FROM CULTURES OF THE MARINE ASCOMYCETE LEPTOSPHAERIA-ORAEMARIS (LINDER)

Acetone extraction of cultures of the marine ascomycete Leptosphaeria oraemaris (LINDER) on cornmeal disk gave the novel polyketide derivative leptosphaerolide (= (+)-7-[(1E)-1,3-dimethylpent-1-enyl]-10-hydroxy-3-methoxybenzo[1,2-b:5,4-c']dipyran-2(9H)-one; (+)-8) besides the o-dihydroquinone 3-[(1E)-1,3-dimethylpent-1-enyl]-8,10-dihydroxy-7-methoxy-8-(2-oxopropyl)-1H-naphtho[2,3-c]pyran-9(8H)-one (1) as a 10:9 mixture of epimers. retro-Aldol reaction of 1 gave leptosphaerodione (=(-)-3-[(1E)-1,3-dimethylpent-1-enyl]-10-hydroxy-7-methoxy-1H-naphtho[2,3-c]pyran-8,9(8H)-dione; (-)-6) which was also present in small amounts in the extracts and which gave 1 on reaction with acetone. It is thus likely that 1 is an artefact of the extraction by acetone. Biogenetically (+)-8 might derive from (-)-6 via an unusual oxidation with loss of CO2.