An optically active N-protected azetidine-2-carboxylic acid (5) can be produced by preparing an optically active 4-amino-2-halobutyric acid (3) by halogenating an optically active 3-hydroxy-2-pyrrolidinone (1) with inversion of configuration to prepare an optically active 3-halo-2-pyrrolidinone (2) followed by hydrolysis or by halogenating an optically active 4-amino-2-hydroxybutyric acid ester (6) with inversion of configuration to prepare an optically active 4-amino-2-halobutyric acid ester (7) followed by hydrolysis or by halogenating the compound. (6) with inversion of configuration to prepare the compound (7), cyclizing the same to prepare the compound (2) followed by hydrolysis,
further cyclizing the compound (3) followed by treating the reaction product with an amino group-protecting agent. The thus-obtained compound (5) can be improved its optical purity further by recrystallization.
通过对光学活性的3-羟基-2-
吡咯酮(1)进行卤代反应,反演构型制备光学活性的3-卤代-2-
吡咯酮(2),并
水解或通过对光学活性的4-
氨基-2-羟基
丁酸酯(6)进行卤代反应,反演构型制备光学活性的4-
氨基-2-卤代
丁酸酯(7),再
水解,或通过卤代反应制备化合物(6),反演构型制备化合物(7),环化得到化合物(2),
水解,进一步环化化合物(3),再用
氨基保护试剂处理反应产物,可以制备出光学活性的N-保护的氮杂环丙
氨酸(5)。通过重结晶可以进一步提高化合物(5)的光学纯度。