Hystidine and deuterium labelled hystidine by catalytic reduction with Rh(I)-diphosphine complexes and non coordinating strong acids.

Non-proteinogenic aminoacids play an increasing role in oligopeptide chemistry. Their pharmacological and chemical properties, caused by unnatural D configuration are more and more used for drug design, in peptidomimetics and in the preparation of diet supplements. An example is D-carnosine which have an important role in detoxifying human muscles and tissue but is metabolized more slowly than the natural one.The optically active D or L histidine for carnosine synthesis can be preparated by asymmetric hydrogenation of the corresponding dehydro-aminoacid, this is a well know application of asymmetric reduction catalyzed by metal complexes, essentially Rh(I)-diphosphine compound. [1] We have demostrated [2] that the complete reduction is possible only when the poisonous nitrogen atom of imidazolyl moiety is protonated. We will present and discuss the effect of different non coordinating strong acids on chemical activity and stereoselectivity of Rh(I) complexes with commercially available Me-DUPHOS and PROLOPHOS.