Process for the preparation of Cilastatin and sodium salt

An improved process for the preparation of Cilastatin Acid of formula (I),

• the process comprises the steps of:
• i) condensing 7-chloro-2-[[(1S)-2,2-dimethylcyclopropane]carboxamide]-2-heptenoic acid of formula (II)
• with L-Cysteine in the presence of a base and an alcoholic solvent or an aqueous alcoholic solvent;
• ii) optionally removing inorganic salts by filtration and concentrating filtrate;
• iii) optionally adding water;
• iv) adjusting pH to 2.0 to 4.0;
• v) extracting the Cilastatin acid into C4-C8 alcohol selected from the group consisting of n-butanol and cyclohexanol;
• and
• vi) isolating Cilastatin acid.