| Popis: |
The conjugate acid of pyridine had been found to catalyze decarboxylation of alpha-mandelylthiamin (MTh). It was proposed this occurs by association between the substrate and pyridinium ion in a pi-stacked complex prior to cleavage of the C-C bond. Despite the evidence for selective acid catalyzed decarboxylation of MTh with pyridine and its derivatives, the nature of proton transfer occuring after the C-C bond breaks and before the final products form had not been investigated. General base catalyzed deprotonation of hydroxybenzylthiamin (HBnTh) has been applied as a model for the reverse reaction of acid-catalyzed decarboxylation. Kinetic analysis of this process suggests the acceleration by a preassociated pyridinium ion and the product-determining step in the decarboxylation of MTh are facilitated by independent sequential proton transfers. |
