Process for the preparation of Cetrorelix acetate

A process for the preparation of Cetrorelix acetate

• comprising:
• a) loading first protected amino acid Fmoc-D-Alanine
• on a suitable acid sensitive resin to obtain intermediate
• using solid phase synthesizer;
• b) deprotecting the Fmoc group of intermediate and coupling intermediate with the required amino acids using a suitable coupling agent in the said order, wherein the order of amino acids are Fmoc-D-alanine, Fmoc-L-proline, Fmoc-D-Arginine(Pbf), Fmoc-L-leucine, Fmoc-D-citruline, Fmoc-O-tert-butyl-L-tyrosine, Fmoc-O-tert-butyl-L-serine, D-3-(3′-pyridyl)-D-alanine, Fmoc-D-4-chlorophenyl alanine, N-acetyl-D-3-(2-naphthyl)alanine to form protected peptide intermediate;
• c) cleaving protected peptide intermediate from the resin and deprotecting the side chain protecting groups to yield Cetrorelix trifluoro acetate;
• d) purifying Cetrorelix trifluoro acetate by Flash chromatography;
• e) converting Cetrorelix trifluoro acetate to Cetrorelix acetate by salt exchange method to obtain pure Cetrorelix acetate.