Artificial Amino Acids Racemase: Stereoselective Deuteration of Amino Acids

An efficient catalytic system is developed for racemization of amino acids. The system consists of a biphasic mixture of water and chloroform. The zwitterionic amino acid in the water layer is catalytically transported to the chloroform layer with a chiral guanidine base. The amino acid salt is then reversibly converted to an imino acid salt with an aldehyde. The guanidine base then racemizes the imino acid salt. The racemized amino acid is released to the water layer upon hydrolysis. The catalytic system is highly efficient at neutral pH and ambient temperature. In addition, similar to racemases in nature, an equilibrium `overshoot' is observed in D2O when the amino acid and the base have the same configurations. Thus L-alanine gives enantiomeric excess of deuterated D-alanine (20% ee) when S form of the chiral guanidine. The catalytic system can be used to perform crystallization induced diastereomer transformation (CIDT) of amino acids.M.Sc