Catalytic reduction of the 4-alkylidenepyroglutamate derivatives (3) a
ffords an effective route to (2S,4S)-4-alkylglutamic acids and (2S,4S)
-4-alkylprolines. The route has also been used to prepare a 4-alkylpyr
oglutamic acid derivative which is stereospecifically labelled in the
side chain. Synthesis of the (2S,4R)-epimers using cuprate addition ha
s also been investigated.