CHEM 313 Lecture Notes - Imidazole, Pyruvic Acid, Pyridinium
Document Summary
Thiamin(e) pyrophosphate (tpp), also thiamin diphosphate (tdp) is vitamin b1. Like plp, tdp is a non-redox coenzyme, but it is sometimes associated with redox coenzymes such as nad/nadh. Tdp also catalyzes many reactions non-enzymatically; we will not discuss such reactions. Tdp catalyzes reactions such as decarboxylation and transketolation that involve c c bond making or breaking. It effectively allows formation of acyl anions (r co ), which would normally be highly unstable. There is a common organic reaction that provides a good analogy for tdp: the benzoin condensation. The benzoin condensation involves the addition of cyanide to the carbonyl of benzaldehyde (and other aldehydes). The high electron-withdrawing ability of the ensuing nitrile group is sufficient to allow a carbanion to form at what was the carbonyl carbon, even in the presence of the adjacent neutral oh group. Although this carbanion does form, it is fairly reactive. It adds as a nucleophile to the carbonyl of another benzaldehyde (or other aldehyde).
