Class Notes (807,452)
Canada (492,628)
Chemistry (600)
CHEM 313 (7)
All (5)

Thiamin notes

2 Pages
Unlock Document

University of British Columbia
CHEM 313

Thiamin Thiamin(e) pyrophosphate (TPP), also thiamin diphosphate (TDP) is vitamin B1. The catalytic group is a thiazolium. Like PLP, TDP is a non-redox coenzyme, but it is sometimes associated with redox coenzymes such as NAD/NADH. We will not be discussing redox coenzymes. TDP also catalyzes many reactions non-enzymatically; we will not discuss such reactions. H3C O 1' O P O P N N N O O N S S S O O H3C N 4'NH 22 Thiazole 3' methylthiazolium TDP, Thiamin Diphosphate 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). Finally, after proton transfer, the alkoxide collapses and kicks out the cyanide. (The reaction is named after its product, benzoin.) Thus, cyanide is a catalyst: it accelerates the reaction and it is regenerated. It acts as a nucleophile, electron sink, and leaving group. Thiazolium performs the same functions in TDP. TDP protonation states: TDP can adopt a variety of protonation states. These are mediated by the enzymes the TDP is bound within via both control of the conformation of TDP and by the positioning of side chain groups, often a Glu carboxylic acid, near the 1' nitrogen (aK of that conjugate acid = 4.75) of the pyrimidine ring and/or the 4' amino group. This relay of protons is common in active sites. In the case of TDP, it allows formation of the thiazolium ylid (a positive and negative charge on adjacent atoms), which can also be drawn as a carbene (divalent neutral carbon with a lone pair of electrons). Carbenes exist, but are reactive, as they lack an octet. As in the benzoin reaction, the thiazolium ylid is stabilized with respect to a normal carbanion (enough to form), but it is still reactive. Many experiments have been performed on TDP and its derivatives to discern the mechanism of the reactions it catalyzes. One key experiment was an NMR run on a (now) ancient NMR machine in 1957: the signal for the C2–H was lost when a TDP derivative was dissolved in2D O. S
More Less

Related notes for CHEM 313

Log In


Don't have an account?

Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.