TOXIC SUBSTANCES, HETEROCAPSATOXIN A AND B TOWARDS OYSTER FROM RED TIDES, HETEROCAPSA CIRCULARISQUAMA, APPREARED IN SETO INLAND SEA

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Harmful phytoplankton blooms have caused serious social and environmental problems and heavy damage to fisheries throughout the world. In recent years, a novel dinoflagellate Heterocapsa circularisquama has caused mass mortality of bivalves, e.g. oysters and pearl oysters, in several inner bay of Japan. In our research the toxic substance in this plankton, two novel compounds exhibit the toxicity towards oyster were isolated.The algae of cultured H.circularisquama was extracted with 1-BuOH, and the 1-BuOH extract was partitioned between hexane and 80% MeOH. The residue from the 80% MeOH-soluble fraction was subjected to column chromatography on reversed phase silica gel to afford the biologically active fractions. Further separation by silica gel column chromatography, gel permeation chromatography, and HPLC (reverse phase) yielded two toxic substances named heterocapsatoxin A (HTX-A, molecular weight 5024) and heterocapsatoxin B (HTX-B, molecular weight 1980). Analysis of ^1H and ^<13>C NMR spectra of HTX-A and HTX-B, they have a very similar structures which contained the several C=C double bonds and many oxygen functionalities.In order to elucidate the structure of HTX-A,HTX-A was subjected to ozonolysis to give two major products, which were named HTX-A1 and HTX-A2. HTX-A1 was determined to have the molecular formula C_<46>H_<84>O_<22> by high-resolution FABMS. The structural elucidation of HTX-A1 was performed mainly by NMR experiments consisting ^1H and ^<13>C NMR,COSY,HMQC, and HMBC.