1,3-Dipolar cycloaddition enabled isoxazole-fused spiropyrrolidine oxindoles syntheses from 3-methyl-4-nitro-5-alkenyl-isoxazoles and azomethine ylides

A facile and efficient methodology was developed for the synthesis of isoxazole-fused spiropyrrolidine oxindoles 3–5 via a 1,3-dipolar cycloaddition reaction of 3-methyl-4-nitro-5-alkenyl-isoxazoles with azomethine ylides (thermally generated in situ from isatin derivatives and proline or thioproline or sarcosine). Products bearing adjacent quaternary-tertiary centers were smoothly obtained in high yields (up to 90% yield) with good diastereoselectivity (up to 20:1). Furthermore, their biological activity has been preliminarily demonstrated by in vitro evaluation against human prostate cancer cells PC-3, human lung cancer cells A549 and human leukemia cells K562 by the MTT-based assays using the commercially available standard drug Cisplatin as a positive control. These results suggested that most of isoxazole-fused spiropyrrolidine oxindoles 3–5 showed considerable cytotoxicities to these three cell lines K562, A549 and PC-3, and that isoxazole-fused spiropyrrolidine oxindoles may be potential leads for further biological screening.