抄録
It was previously demonstrated by the authors that dihyhydrothiamine (DHB_1) was stable in alkaline solution, whereas it was very unstable in acidic solution. Now stability of n- and pseudo-isomers of DHB_1 in aqueous diluted solution was again checked and the both were unstable in acid media, as they were ionized into the same quarternary thiazolim form (III). n-DHB_1 was decomposed easily in alkaline solution, when it was carefully dissolved with alcohol, while pseudo-DHB_1 was stable in alkaline solution even on heating. The difference would be based on their constitutions I and II ; pseudo-DHB_1 took II in alkaline media while n-DHB_1 (I) would be transformed into I'and then into the opened ring form (IV) which was further decomposed to the pyrimidine moiety and a mercaptol. Sulfite cleavage of n- and pseudo-DHB_1 at 3.75 mM concentration occured just similarly to that of thiamine between pH 4〜7 but at pH more than 8. pseudo-DHB_1 was not decomposed by sulfite, while n-DHB_1 was still unstable at these ranges of pH. n-DHB_1 at such a diluted concentration as 0.05 μM was very unstable and neither further cleavage nor preservation of DHB_1 was observed by addition of sulfite to it. Thus n- and pseudo-DHB_1 indicated different attitudes at alkaline media and alkaline sulfite treatment.
