Patent ID: 8173770

Claim:
A process for preparing an LHRH antagonist or a pharmaceutically acceptable salt thereof, comprising the following consecutive steps: (a) reacting Boc-D-4ClPhe-OH with HONSu to form Boc-D-4ClPhe-OSu (VII); (b) reacting Boc-D-4ClPhe-OSu (VII) with H-D-3Pal-OH to form Boc-D-4ClPhe-D-3Pal-OH (VIII); (c) reacting Boc-D-4ClPhe-D-3Pal-OH (VIII) with Boc-D-2Nal-OSu to form Boc-D-2Nal-D-4ClPhe-D-3Pal-OH (IX); (d) reacting Boc-D-2Nal-D-4ClPhe-D-3Pal-OH (IX) with acetic acid to form Ac-D-2Nal-4ClPhe-D-3Pal-OH (I); and coupling tripeptide Ac-D-2Nal-D-4ClPhe-D-3Pal-OH (I) with a heptapeptide (IV) of the general formula P 1 -Ser(P 2 )-AA1-AA2-Leu-Lys(iPr,P 4 )-Pro-D-AlaNH 2 (IV), wherein P 1 is selected from H or amino protecting group, P 2 is H or OH-protecting group, P 4 is H or an amino protecting group, AA1 is natural or synthetic amino acid and AA2 is natural or synthetic amino acid or zero.