12 渦鞭毛藻Gambierdiscus toxicus培養株の生産する有毒成分の構造決定(口頭発表の部)

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Identification of a probable ciguatoxin precursor, GT4B, in the dinoflagellate Gambierdiscus toxicus collected from the wild suggested the organism as the primary source of toxins implicated in ciguatera. Nevertheless, unsuccessful results in many laboratories to prove the toxins in cultured organisms have casted a doubt about the true origin of the toxins. In view of the frequent intraspecies variation in the type of secondary metabolites of microorganisms, we tested four different strains of G. toxicus production of ciguatoxin congeners. One strain collected at Rangiroa Atoll of French Polynesia was proven for the first time to produce three ciguatoxinlike toxins coded RGT1, CTX3C, and CTX4A, respectively. HR-FABMS data of RGT1 gave a molecular formula C_<43>H_<64>O_<11>. Extensive 2D NMR experiments revealed that RGT1 has a novel skeleton consisting of eight contiguous ether rings (6/6/6/6/7/6/6/7) fused in trans (Fig. 1). The structure of CTX3C (C_<57>H_<82>O_<16>, Fig. 3c) closely resembled that of GT4B (Fig. 3b) but lacked the butadiene side chain of the latter. The oxepene ring (E) of GT4B was replaced by an oxocene ring in CTX3C. The molecular formula of CTX4A was the same as that of GT4B (C_<60>H_<84>O_<16>). Comparison of NMR data revealed that the two are the epimers at the spiroketal carbon.
1992-09-10