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

Abstract

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.