Transimination, catalysis

Dirksen, A., Dirksen, S., Hackeng, T.M., Dawson, P. E. Nucleophilic catalysis of hydrazone formation and transimination implications for dynamic covalent chemistry. J. Am. Chem. Soc. 2006, 128, 15602-15603. 

Giuseppone N, Schmitt JL, Schwartz E, Lehn JM (2005) Scandium(III) catalysis of transimination reactions. Independent and constitutionally coupled reversible processes. J Am Chem Soc 127 5528-5539... 

As already described in Sect. 2.2, the use of scandium(III) ions is also an efficient way to catalyze transimination reactions. The most effective catalysis was observed with the exchange reaction between an oxime of cyclohexanone and benzylhydroxylamine. Interestingly, crossover experiments mixing hydrazones and oximes also proved successful [24]. 

In the first step of transamination, a proton is removed from the a-carbon of the amino acid bound to PLP. Rearrangement of the electrons and protonation of the carbon attached to the pyridine ring, followed by hydrolysis of the imine, forms the a-keto acid and pyridoxamine. At this point, the amino group has been removed from the amino acid, but pyridoxamine has to be converted back to enzyme-bound PLP before another round of catalysis can occur. Pyridoxamine forms an imine with a-ketoglutarate, the second substrate of the reaction. Removal of a proton from the carbon attached to the pyridine ring, followed by rearrangement of the electrons and donation of a proton to the a-carbon of the substrate forms an imine that, when transiminated with a lysine side chain, releases glutamate and reforms enzyme-bound PLP. 

Ciaccia M, Pdati S, Cacciapagha R, Mandolini L, Di Stefano S. Effective catalysis of imine metathesis by means of fast transiminations between aromatic-aromatic or aro-matic-abphatic amines. Org Biomol Chem. 2014 12 3282-3287. 

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