Isolation of analogues of Okadaic acid from cultures of Prorocentrum lima

A chloroform extract of cultured Prorocentrum lima was analyzed for carboxylic polyethers related to okadaic acid (OA). The extract was derivatized with 1-(bromoacetyl)pyrene to give the fluorescent pyrenacyl esters of OA and other carboxylic acids. The resulting mixture was subjected to preparative high performance liquid chromatography with fluorescence detection. Positive chemical ionization mass spectrometry indicated that four OA-related compounds were present, including two methylated analogues. The fragmentation pattern of at least one of these suggests it is not the previously reported 35-methylokadaic acid.