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ASYMETRYCZNA SYNTEZA a-AMINOKWASÓW 3

Contrary to the “electrophilic”, a “nucleophilic amination” reąuires a “ca-tion equivalent” obtained from a chiral N-acyl-derivatives [54-55]. The reac-tion usually yields a desired product of good enantiomeric ąuality. In most cases azide anion is a source of “nucleophilic aminę equivalent” (Schemes 22 and 23). The chiral 2,3-epoxy-l-ols can be also applied in this methodology [57, 58], (Scheme 24).

Asymmetric catalytic hydrogenation of a dehydro derivatives of amino acids and peptides is another valuable group of synthetic routes to the single enantiomer of the amino acid. There is a possibility of heterogenous and homo-geneous catalysis involving insoluble catalysts [60, 61], (Schemes 25, 26) or soluble [62, 63], (Schemes 27, 28) in medium of the reaction. The best results (yield ~ 100% and ee ^ 99%) were reported for the complexes of Rh with chiral phosphines ligands like BINAP or DIPAMP (Scheme 28), [67].

The last method reported in our review is based on the usage of enzymes. The most widely used in this field are the following enzymes: acylases — catalyzing stereoselective removal or synthesis of N-acyl derivatives [70], (Scheme 30) and proteases — catalyzing hydrolysis or synthesis of esters [71], (Scheme 31). Additionally, enzymatic methods give in many cases both enantiomers at the same time.