Synthesis of (2S,3S)-3-aroyl pyroglutamic acid amides

A new methodology for the asymmetric synthesis of enantiomerically enriched 3-aroyl pyroglutamic acid derivatives has been developed through an effective 5-exo-tet cyclization of N-chloroacetyl aroylalanines. The three-step sequence starts with the N-substituted (S,S)-2-amino-4-aryl-4-oxobutanoic acids synthesis via the highly diastereoselective tandem of aza-Michael addition and crystallization-induced diastereomer transformation (CIDT). Their N-chloroacetylation followed by base-catalyzed cyclization and ultimate acid-catalyzed removal of chiral auxiliary without a loss of stereochemical integrity furnishes the target substituted pyroglutamic acids. Finally, several series of their benzyl amides were prepared as 3-aroyl analogues of known P2X7 antagonists.