Abstract
Dihydrothiamine (pseudo-DHB_1) was oxidized quantitatively into thiamine by 2,6-dichlorophenolindophenol, while n-DHB_1 was oxidized partly yielding varied amounts of thiamine according to solvents used for dissolving DHB_1. The yield of thiamine from n-DHB_1 was 58-64% to the theoretical value when n-DHB_1 was dissolved in dilute alcohol or water but it was much higher (e.g. 87%) when n-DHB_1 in absolute alcohol. If n-DHB_1 was first dissolved in HCl and then made alkaline by addition of NaHCO_3 or NaOH, the yield of thiamine was as high as that from pseudo-DHB_1 which was nearly quantitative. It was suggested, therefore, that n-DHB_1 had been converted into the pseudo-isomer in this prosedure. n-DHB_1 was unstable in its aqueous or dilute alcoholic solution resulting in hydrolysis into 5-hydroxy-3-mercapto-2-pentanone which was demonstrated by SH-detection by bis-(p-nitrophenyl)-disulfide, but n-DHB_1 in absolute alcohol showed a higher yield of thiamine indicating scarce hydrolysis. Comparing to the n-isomer, pseudo-DHB_1 was stable in aqueous dilute alcoholic or alkaline soluton and practically no presence of SH-radical by bis-(p-nitrophenyl)-disulfide in these solutions was indicated.
