SYNTHESES OF (2S,3R)-METHYLGLUTAMIC AND (2S,3S)-3-METHYLGLUTAMIC ACID

Arndt-Eistert homologation of suitably-protected (2S,3S)-3-methylaspar tic acid occurs with retention of configuration at C-3 to give, ultima tely, (2S,3R)-3-methylglutamic acid. (2S,3R)-3- Methylglutamic acid wa s also prepared in good yield via the conjugate addition of the lithia ted anion of the bis-lactim ether. of cyclo-(R-Val-Gly) to methyl (E)- butenoate. The analogous reaction performed using isopentyl (Z)-buteno ate ultimately gave (2S,3S)-3-methylglutamic acid. Both conjugate addi tions occurred with high diastereoselectivity.