Isotope effect, mechanism, and origin of catalysis in the decarboxylation of mandelylthiamin.

ABSTRACT: The mechanism of decarboxylations in water and the catalysis of mandelylthiamin (MTh) decarboxylation by pyridinium ions is explored. It has been recently proposed that a decarboxylation step forming an intermediate molecule/CO(2) pair is reversible and that pyridinium ions catalyze the MTh decarboxylation by trapping the intermediate, preventing reversion to MTh. A calculation of the barrier for the back reaction goes against this proposal, as the diffusional separation of CO(2) would be on the order of 10,000 times faster. A comparison of predicted and experimental isotope effects for a series of decarboxylations including the MTh reaction shows in each case the absence of significant reversibility of the decarboxylation step. An alternative origin of the pyridinium catalysis of decarbox

SUBMITTER: Gonzalez-James OM 

PROVIDER: S-EPMC2880891 | biostudies-literature | 2010 May

REPOSITORIES: biostudies-literature