As a coenzyme, Thiamine exists as Thiamine Pyrophosphate (TPP).
- It contains a pyrimidine ring and a thiazole ring (only natural compound containing thiazole ring) held by a methylene bridge.
- Thiazole ring is also a functional part of TPP. Its hydrogen of C-atom 2 is relatively acidic because of the adjacent positively charged Quaternary N-atom, which electrostatically stabilize the carbanion formed on dissociation of the proton.
- This dipolar carbanion is active form of the coenzyme.
- To thiazole ring, pyrophosphate is also attached (which is donated by ATP).