First Chemoenzymatic Synthesis of (+)-2-Carboxypyrrolidineacetic Acid, the Nucleus of Kainoid Amino Acids.

The distinctive nucleus of kainoid amino acids, (2S,3R)-(1)-2-carboxypyrrolidine-3-acetic acid 6, was synthesized by a chemoenzymatic process, exploiting the diastereomeric cis/trans methyl pyroglutamate derivatives as key intermediates. These mixtures, when subjected to a kinetic resolution mediated by a-chymotrypsin, reacted diastereo-, regio-,and enantioselectively to give the trans derivatives (1)-c possessing the correct (2S,3R) configuration. Subsequently, the desired product could be obtained after well-established transformations.