cis-4-Phenylthio-N-benzyloxycarbonyl-L-Proline methyl ester; 1-Benzyl 2-methyl (2S,4S)-4-(phenylthio)pyrrolidine-1,2-dicarboxylate; (2S,4S)-1-benzyl 2-methyl 4-(phenylthio)pyrrolidine-1,2-dicarboxylate