64(P-21) 沖縄産二枚貝の超微量毒性物質pinnatoxin類とpteriatoxin類のナノモル構造決定(ポスター発表の部)

High resoluble NMR instruments make strucuture determination of small amount of compounds possible. Nevertheless, it is actual condition that more than 0.5 μmol of sample is necessary for structure determination by analyses of NMR spectra. Recently, pinnatoxins and pteriatoxins, extremely small amount of toxins, were obtained from the Okinawan bivalves Pinna muricata and Pteria penguin. But, obtained pinnatoxins and pteriatoxins were too small to determine these structures by usual NMR analyses. We reported here that nano-mole-order structure determination of extremely small amount of toxins (4μg, 5 nmol) was achieved by the detailed analyses of positive ESI CAD MS/MS spectra. (1) Structure determination of Pinnatoxins B and C Pinnatoxins B and C, the most potent toxins in the pinnatoxin series, were isolated from the Okinawan bivalve P. muricata. The chemical shifts and the coupling constants of protons in pinnatoxins B and C strongly resembled those in pinnatoxin A. This result suggested that pinnatoxins B and C consisted of the same polyether macrocycles as pinnatoxin A. Furthermore, positive ion ESI CAD MS/MS spectrum of pinnatoxin A showed a series of prominent fragment ions generated by a G ring-opening reaction, the retro Diels-Alder reaction of pinnatoxin A, followed by bond cleavage of carbocycles. As expected, the fragment ions of pinnatoxins B and C were identical to those of pinnatoxin A. Therefore, it was decided that pinnatoxins B and C had the same macrocycles as in pinnatoxin A. Furthermore, relative stereochemistry of macrocycles in pinnatoxins B and C were determined to be same as those in pinnatoxin A by performing degradation reactions. Kishi's group achieved the total synthesis of pinnatoxin A and ent-pinnatoxin A. They reported that only natural pinnatoxin A was toxic. Therefore, based on this observation, the absolute stereostructures in pinnatoxins B and C were determined. (2) Structure determination of pteriatoxins A, B, and C Pteriatoxins A, B and C, extremely small amount of toxins, were obtained from the Okinawan bivalve P. penguin. These weights were estimated by comparison of the S/N ratio of 67 μM okadaic acid with those of pteriatoxins in CD_3OD (0.18 mL). As mentioned above, positive ion ESI CAD MS/MS spectra of pteriatoxins exhibited the same series of prominent fragment ions as the carbocyclic moiety in pinnatoxins. Therefore, pteriatoxins had the same polyether macrocycles as in pinntoxins.