ビタミンB₁類の安定性に関する研究(第11報) : 酸性水溶液中のO, S-Bis (alkoxycarbonyl) thiaminesの安定性

抄録

Analysis with an analog computer was made on the degradation of O, S-bis (ethoxycarbonyl) thiamine (I) in aqueous solution at 100° in a pH range from of 1 to 5. The analyses were based on both the results of the separate determination of the degradation products including thiamine (B₁), O-ethoxycarbonylthiamine (II), S-ethoxycarbonyl thiamine (V), 2-methyl-4-amino-5-hydroxymethylpyrimidine (III), and 2-methyl-4-amino-5-aminomethylpyrimidine (IV), and on the results previously reported for the degradation of II and V. Four different degradation routes of I were found : the two first ones are hydrolyses of -O-COOC₂H₅ and -S-COOC₂H₅ to -OH and -SH, respectively, and the other two are direct formations from I to III and to IV. At lower pH values, below or around 1.5, the reaction I→IV proceeded more easily than the other reactions and the reaction I→V was faster than the reaction I→II, where the product V was further converted to II. At the higher pH values, however, the rate of the reaction I→V was small compared with the overall degradation rate of I, and -S-COOC₂H₅ of I was hydrolysed faster than -O-COOC₂H₅ of I. These results are supported because we found relative amounts of two different O-alkoxycarbonylthiamines (B₁-O-COOR₁ and B₁-O-COOR₂) produced from O, S-bis (alkoxycarbonyl) thiamines (R₁-OOC-O-B₁-S-COOR₂). Furthermore, the stability of I was compared with the stabilities of fifteen different B₁ derivatives of acyl, a1koxycarbonyl, and disulfide types in aqueous solutions under the conditions mentioned above.