92844-28-5Relevant academic research and scientific papers
Reaction of Thiamin Analogues with Sulfite Ion: An Example of Zero-Order Kinetics
Uray, Georg,Kriessmann, Ingo
, p. 802 - 805 (2007/10/02)
Although the cleavage of thiamin (vitamin B1, 1) and N-methyl vitamin B1 (1a) with sulfite ion is known to be first order in sulfite ion, two molecules of this nucleophile are involved in the complex process.By contrast, the N-methyl analogue 1e having 3-cyanopyridine as a leaving group does not show any kinetic dependence on the sulfite ion concentration.A proton NMR investigation of the reaction mixture clearly shows the formation of a sulfite adduct, reducing the concentration of the quaternized leaving group dramatically.Coupling constants are observed for the first time in a sulfite adduct of a nitrogen heterocycle.The equilibrium constant was estimated from kinetic data to be 5 * 106 M-1, the highest ever reported.The analogue having nicotinamide as a leaving group has an equilibrium constant of only 62 M-1.A model pyrimidine having a cyano group in position 5 and a 4-nitrobenzyl group in position 1 clearly adds sulfite mainly at position 6 to form adduct 4a, revealing the likely site of attack of this nucleophile during substitution.
Preparation and Reactivity of Model Compounds Related to Oligomers from Thiamin. A Mechanism for Oligomerization
Zoltewicz, John A.,Uray, Georg,Kauffmann, Glenn M.
, p. 4900 - 4904 (2007/10/02)
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.
