A Novel, Degraded Polyketidic Lactone, Leptosphaerolide, and Its Likely Diketone Precursor, Leptosphaerodione. Isolation from Cultures of the Marine Ascomycete Leptosphaeria oraemaris (L INDER )

Acetone extraction of cultures of the marine ascomycete Leptosphaeria oraemaris (LINDER) on cornmeal disk gave the novel polyketide derivative leptosphaerolide ( = (+)‐7‐[(1 E )‐l,3‐dimethylpent‐1‐enyl]‐10‐hydroxy‐3‐methoxybenzo[1,2‐b:5,4‐ c ′]dipyran‐2(9 H )‐one; (4+)‐8) besides the o ‐dihydroquinone 3‐[(1 E )‐1,3‐dimethylpent‐1‐euyl]‐8,10‐dihydroxy‐7‐methoxy‐8‐(2‐oxopropyl)‐1 H ‐naphtho[2,3‐c]pyran‐9(8 H )‐one ( 1 ) as a 10:9 mixture of epimers. retro ‐Aldol reaction of 1 gave leptosphaerodione ( = (−)‐3‐[(1 E )‐1,3‐dimethylpent‐1‐enyl]‐10‐hydroxy‐7‐methoxy‐1 H ‐naphtho[2,3‐c]pyran‐8,9(8 H )‐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 CO 2 .