P-28 海洋渦鞭毛藻Heterocapsa circularisquamaから単離された二枚貝致死活性物質Heterocapsatoxin類の単離,構造解析(ポスター発表の部) P-28 Isolation and Structure Elucidation of Toxic Substance towards Oyster from Red Tide Phyroplankton Heterocapsa circularisquama

Harmful phytoplankton blooms have caused serious social and environmental problems and heavy damage to fishery 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 bays of Japan. In our search for toxic substances in this plankton, two novel compounds which exhibit toxicity towards oysters 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 biologically active fractions. Further separation by silica gel column chromatography, gel permeation chromatography, and HPLC (reverse phase) yielded two toxic substances, which were named heterocapsatoxin A (HTX-A, molecular weight 5024) and heterocapsatoxin B (HTX-B, molecular weight 1980). Analysis of the ^1H and ^<13>C NMR spectra of HTX-A and HTX-B revealed that they commonly bear several C=C double bonds and many oxygen functionalities. In order to elucidate the structure of HTX-A, it was subjected to ozonolysis to give two major products, which were named HTX-A_1 and HTX-A_2. HTX-A_1 was determined to have the molecular formula C_<46>H_<84>O_<22> by high-resolution FABMS. The structural elucidation of HTX-A_1 was performed mainly by NMR experiments consisting of ^1H and ^<13>C NMR, ^1H-^1H COSY, HMQC, and HMBC. As for HTX-B, NMR experiments have allowed us to assign two-thirds of the structure. Efforts towards full characterization of HTX-A and HTX-B are on-going.