The synthesis of ganirelix was performed using usual solid-state peptide synthesis with a Beckman 990 or a 5.0 L Vega 296 automated solid-phase peptide synthesizer. The synthesis was initiated by condensation of chloromethylated polystyrene/divinylbenzene resin (Merrifieled resin) (II) with Boc-D-alanine (I) by means of cesium carbonate, giving Boc-D-ala-RESIN (III), which was submitted to successive cycles of deprotection with TFA or HCl and addition of a new protected amino acid by means of DCC or HOBt. The following amino acids were added successively: Boc-L-proline (IV), Nalpha-Boc-Nomega,N'omega-diethyl-L-homoarginine (VI), Boc-L-leucine (VIII), Nalpha-Boc-Nomega,N'omega-diethyl-D-homoarginine (X) and Boc-L-tyrosine (XII), yielding successively the peptide resins (V), (VII), (IX), (XI) and (XIII).
The synthesis of ganirelix was performed using usual solid-state peptide synthesis with a The following amino acids were added successively to intermediate (XIII): N-Boc-O-benzyl-L-serine (XIV), Boc-(3-pyridyl)-D-alanine (XVI) and Boc-4-chloro-D-phenylalanine (XVIII), yielding successively the peptide resins (XV), (XVII) and (XIX).
The amino acid Boc-(2-naphthyl)-D-alanine (XX) were added to intermediate (XIX), yielding the peptide resin (XXI). When the integration of amino acids was completed, the peptide resin (XXI) was deprotected with TFA, acetylated with acetic anhydride and finally treated with ammonia in methanol in order to eliminate the resin matrix and form the final amide group.