Rigid Dipeptide Mimetics. Stereocontrolled Synthesis of All Eight Stereoisomers of 2-Oxo-3-(N-Cbz-amino)-1-azabicyclo[4.3.0]nonane-9-carboxylic Acid Ester

Stereopure 2-oxo-3-(N-Cbz-amino)-1-azabicyclo[4.3.0]nonane-9-carboxylic acid (AZABIC) methyl and ethyl esters (14a/b and 23a/b, respectively) have been synthesized from readily available (R)- and (S)-pyroglutamic esters 1 and 15. Altogether all eight possible stereoisomers of this type of compound have been prepared in gram quantities.