Thiamine Pyrophosphate (TPP)

Thiamine pyrophosphate is a coenzyme that is present in all living systems, in which it catalyzes several biochemical reactions. It was first discovered as an essential nutrient (vitamin) in humans through its link with the peripheral nervous system disease Beriberi, which results from a deficiency of thiamine in the diet.

The part of TPP molecule that is most commonly involved in reactions is the thiazole ring, which contains nitrogen and sulfur. Thus, the thiazole ring is the "reagent portion" of the molecule. The C2 of this ring is capable of acting as an acid by donating its proton and forming a carbanion. Normally, reactions that form carbanions are highly unfavorable, but the positive charge on the tetravalent nitrogen just adjacent to the carbanion stabilizes the negative charge, making the reaction more favorable.