Enantioselective synthesis of epimeric cis-3-carboxycyclopentylglycines

Two epimeric chiral cyclopentylglycines (-)-16 and (+)-17, functionalised with a carboxy group cis to the amino acid group, were prepd. starting from chiral 2-amino-3-oxo-norbornanecarboxylic acid deriv. I by combining two classical reactions such as the Diels-Alder and retro-Claisen reactions. Compds. II (R1= CO2H, R2= NH2; and R1= CO2H, R2= NH2) are non-proteinogenic amino acids of biol. interest contg. conformational constraints in which the skeletons of both 2-aminoadipic acid and 2-aminopimelic acid are include