2 ニュージーランドで発生した赤潮渦鞭毛藻が産生する巨大ポリ環状エーテル化合物の構造決定(口頭発表の部)

抄録

The dinoflagellate Karenia brevisulcata (Fig. 2) caused a devastating algal bloom in Wellington Harbor, New Zealand, in early 1998 that killed marine life over a wide area. More than 150 people along the coastline were also reported to have adverse affects. In this presentation, the isolation, biological activity, and structural studies of the causative toxins will be reported. Bulk cultures of K brevisulcata were extracted using 5%#aq. acetone and absorbed on HP-20 resin followed by elution with acetone. The crude extract showed cytotoxicity and mouse lethality. The extract was partitioned between chloroform and aqueous methanol under neutral and acidic conditions. Each fraction contained different toxins. The neutral lipophilic fraction was separated on a diol column guided by cytotoxicity against mouse leukemia P388 cells. Final purification by HPLC on a C30 column led to isolation of four major toxins, tentatively named KBT-F, KBT-G, KBT-H, and KBT-I. (Fig. 3) Their MALDI MS spectra showed their very high molecular weights over 2000. The UV maxima at 227 nm suggested that these molecules have conjugated structures. The IC50 against P388 cells were estimated to be 0.3-5.5 ng/ml. The mouse lethality (i.p.) of KBT-F and KBT-G were 40 and 30 pg/kg, respectively. In the complex proton NMR spectrum of KBT-F, two doublet and eleven singlet methyls, an aldehyde conjugated to a double bond could be observed. In addition, widespread oxygen-bearing methine signals in the spectra suggested polycyclic ether structures (Fig. 5, 6). The planar structures of KBT-F (Cio7Hiso038) and KBT-H (Cio7Hi6o039), each of which have 24 ether rings, 13 hydroxyl groups, 2 doublet methyl, 11 singlet methyl, and an enal side chain (Fig. 8) were successfully assigned by using several 2D NMR measurements and high resolution MALDI MS.