LC-MS/MS analysis of novel ovatoxin isomers in several Ostreopsis strains collected in Japan

► Detailed toxin profiles of palytoxin analogues in several Japanese Ostreopsis strains were clarified for the first time by liquid chromatography-mass spectrometry (LC-MS). ► The most dominant palytoxin analogue in Japanese Ostreopsis was a novel ovatoxin, which was identified as an isomer of ovatoxin-a. ► Novel isomers of ovatoxin-b, -d, and -e were also found in Japanese Ostreopsis.