ISOLATION OF A NEW OKADAIC ACID ANALOG FROM PHYTOPLANKTON IMPLICATED IN DIARRHETIC SHELLFISH POISONING

A new analogue of okadaic acid (OA), the toxin mainly responsible for diarrhetic shellfish-poisoning (DSP) phenomena in Europe, has been iso lated from toxic phytoplankton (Dinophysis acuta) collected in Irish w aters. Fluorimetric LC analyses of the extracts of bulk phytoplankton samples using derivatisation with 9-anthryldiazomethane (ADAM) showed a complex toxin profile, with peaks corresponding to OA and dinophysis toxin-2 (DTX-2) as well as a third unidentified compound. This minor u nidentified component was isolated by chromatographic techniques such as normal-phase chromatography, gel permeation on Sephadex, solid-phas e extraction and reversed-phase separations. Ionspray mass spectrometr y (MS) was used for structural investigation on this compound due to t he very small amount of isolated material. Flow injection analysis (FL A)-MS of the isolated compound gave positive-ion mass spectrum dominat ed by the protonated molecule, [M+H](+), at signal mit 805, whereas th e deprotonated molecule [M-H](-) was observed in the negative-ion spec trum at signal m/z 803, thus indicating the molecular weight of 804 fo r the new toxin, the same as OA and its known isomers, DTX-2 and DTX-2 B. Collision-induced dissociation (CID) as obtained by positive and ne gative tandem mass spectrometry (MS-MS) showed a fragmentation pattern far the new compound which was very similar to that of OA, DTX-2 and DTX-2B. Ionspray microLC-MS of a mixture containing the compound under investigation together with OA analogues showed the compound eluted a fter OA, DTX-2, DTX-2B and before DTX-1. All the chromatographic and m ass spectrometric data indicated the compound to be another OA isomer and it was therefore coded DTX-2C. To the best of our knowledge this i s the first report on the isolation of a new compound related to DSP t oxins from natural communities of toxic phytoplankton. (C) 1998 Elsevi er Science B.V.