Evidence for numerous analogs of yessotoxin in Protoceratium reticulatum

A solid-phase extract from Protoceratium reticulatum was partitioned between water and butanol and the two fractions purified on an alumina column. Fractionation was monitored by ELISA and LC–MS. Results indicate that while almost all yessotoxin (1) was extracted into butanol, large amounts of yessotoxin analogs remained in the aqueous extract along with lesser amounts in the butanolic extract. NMR analysis of selected fractions from reverse-phase chromatography of the extracts confirmed the presence of yessotoxin analogs, although structure determinations were not possible due to the complexity of the mixtures. Analysis of fractions with LC–MS3 and neutral-loss LC–MS/MS indicated the presence of more than 90 yessotoxin analogs, although structures for most of these have not yet been determined. These analogs provide a mechanism to rationalise the discrepancy between ELISA and LC–MS analyses of algae and shellfish.