A Facile Synthesis of (-)-Cucurbitine

In recent years, there has been much interest in structurally unique pyrrolidines, which were isolated from natural sources and could be utilized as common synthetic subunits of products with biological activity.1 In the course of our work related to the synthesis of a series of novel quinolone antibiotics2 having a pyrrolidine moiety at the 7-position, we searched for the pyrrolidine derivatives, bearing a chiral amino acid function at C-3 position, which could be substi-tuted at C-7 position of the quinolone nucleus. (−)-Cucurbitine, bearing the α-amino acid function at the C-3 position in the pyrrolidine ring, has been isolated from the seeds of several species of cucurbitaceaes, and has been known to inhibit the growth of the immature Schistosomas japonicum.3 However, only two asymmetric syntheses4c,4e of cucurbitine are found in the literature4 despite of its interest-