Isolation of a 1,3-enone isomer of heptanor-41-oxoyessotoxin from Protoceratium reticulatum cultures

The 1,3-enone isomer ( 1) of heptanor-41-oxoyessotoxin ( 2) was isolated from extracts of Protoceratium reticulatum during large-scale production of yessotoxin ( 4). We found that 2 readily isomerizes to 1 in the presence of dilute ammonia and present evidence for the existence of 40- epi- 2 ( 3) that also isomerizes to 1. 1– 3 were detected by LC–MS methods both in extracts of P. reticulatum cultures and in mussels contaminated with yessotoxins. The isomerization of 2 and 3 into 1 occurs so readily that purification on basic alumina needs to be conducted carefully. No toxic effects were recorded in mice injected intraperitoneally with 1 at a dose of 5000 μg/kg.