A new approach has been demonstrated for the asymmetric synthesis of a-amino acids from a-keto acids using chiral reagents which are regenerated by the synthesis. The chiral reagents used were the N-amino-2-hydroxymethylindolines (9-9 and (9-16. The synthesis, resolution, and assignment of absolute configuration for these reagents is described. The application of ( 9 -9 and (9-16 to the asymmetric synthesis of a-amino acids depends on their combination with a-keto acids to form chiral hydrazono lactones (see Chart IX). Reduction of the C=N unit in these lactones (23,24, and 25) affords the corresponding hydrazino lactones (29,30, and 31) which are transformed to a-amino acids by hydrogenolysis of the N-N linkage and ester hydrolysis. By this process o-alanine and D-butyrine have been synthesized from pyruvic acid and a-ketobutyric acid using the reagent ( 3 -9 in optical purities of 80 and 90%, respectively. As a result of these studies, a solid basis exists for the design of chiral indoline reagents of still greater eficiency in the asymmetric synthesis of a-amino acids.(13) For another asymmetric synthesis of aspartic acid (optical purity ca. 88 %), involving the addition OF a-methylbenzylamine to maleic acid followed by catalytic hydrogenolysis, see A. P. Terent'ev, R. A.
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