Preparation and Reactivity of Model Compounds Related to Oligomers from Thiamin. A Mechanism for Oligomerization

Article abstract of DOI:10.1021/ja00406a038

Compounds were synthesized having a pyrimidilmethyl groups as found in oligomers formed from thiamin.These compounds contain two such groups and a thiazole, phenylthio, or sulfonato substituent at terminal methylene position and undergo nucleophilic substitution with aqueous sulfite ion.Comparison of the rate constants for reaction with sulfite ion involving a bis(pyrimidine) and 1'-methylthiaminium ion, both having the same thiasole leaving group, reveals that an N-pyrimidinylmethyl substituent increases reactivity over that by an N-methyl griup by factor of 19.Other comparisons show that a thiazole is replaced about 1.9 times faster than a pyrimidine ring by the action of sulfite ion.Addoitives can increase or decrease by induction period for the oligomerization of thiamin chloride in methanol.A mechanism similar to that for sulfite ion substitution is suggested for oligomerization; a key feature is the conversion of thiamin to a more reactive oligomer by quaternization with introduces a pyrimidinmethyl unit.