Practical large-scale synthesis of the 2-aminomethylpyrrolidin-4-ylthio-containing side chain of the novel carbapenem antibiotic doripenem

The first synthesis using an original procedure and a practical large-scale process using an improved procedure for the synthesis of the N-PNZ-protected 2-aminomethylpyrrolidin-4-ylthio-containing side chain of doripenem hydrate (S-4661), a novel parenteral 1beta-methylcarbapenem antibiotic, are described. trans-4-Hydroxy-L-proline (4) was converted in an efficient process to (2S,4S)-4-acetylthio-2-(N-sulfamoyl-tert-butoxycarbonylaminomethyl)-1-(4-nitrobenzyloxycarbonyl)pyrrolidine (3) in 55-56% overall yield via a six-step sequence, which includes the two alternative routes to intermediate 13. This process requires no chromatographic purifications, no cryogenic temperatures, no haloalkane solvents, and short operating times and is amenable to a multikilogram-scale preparation. Several kilograms of the side chain 3 were successfully prepared by this process.