| Mandelylthiamin (MTh) is an accurate model of the pre-decarboxylation intermediate formed on benzoylformate decarboxylase (BFDC). In solution, it decarboxylates to the Breslow intermediate 108 times slower than on the enzyme. Earlier studies proposed that the C--C bond-breaking step in the decarboxylation of MTh is highly reversible, and thus possibly impeding the overall reaction rate. More recently, it was observed that the decarboxylation of MTh could be more effective through formation of HCO 3-, suggesting the enzyme could be applying a similar strategy to maximize its catalytic efficiency. This thesis investigates in detail the decarboxylation of MTh and related analogs in solution phase, and proposes possible enzymic strategies for catalysis.;Research on MTh had suffered from a low yield synthesis and ineffective purification. The work in this thesis was made possible because lithium ions were discovered to greatly promote formation of the MTh ester and its analogs. Using the new synthetic methodology I could synthesize previously unattainable MTh variants.;This thesis can be divided into three main sections: 1) the study of MTh analogs and other compounds to understand molecular features responsible for decarboxylation by formation of HCO3-. This was probed through observation of base catalysis and a solvent kinetic isotope effect (SKIE), which are indications of a decarboxylation by formation of HCO3-. Based on the collected results, it was concluded that a base catalyzed decarboxylation is a unique phenomenon. A coincidental outcome of this study was the discovery of intramolecular cyclization reactions of the Breslow intermediate. 2) the study of substituent effects on the decarboxylation of MTh to probe the nature of the BF-derived Breslow intermediate in solution and comparison of results to the enzymic decarboxylation. This revealed that certain enzymes likely enforce an unnatural geometry of the Breslow intermediate to achieve catalytic perfection. 3) the study of the fragmentation of the BF-derived Breslow intermediate from a radicals' formation perspective. This was done after recent reports that radicals are involved in related transformations. My results lead to a conclusion that radicals are unlikely to be involved, and instead a simple polar alternative that is consistent with experimental observations was proposed. |
