Process for the low-racemization preparation of peptide intermediates of the synthesis of gonadorelin and gonadorelin analogs, and new intermediates for this process

Abstract From the Canadian patent

The invention relates to a process for the preparation of peptides of the formula I, U - A1 - A2 - A3 - A4 - A5 - X (I) in which, U denotes a urethane protective group A1 denotes Trp or D-Trp, A2 denotes Ser Ala or Thr, A denotes Tyr or Phe, A4 denotes Gly the residue of a D-amino acid, or the residue of a D-amino acid derivative A5 denotes Leu, N-methyl-Leu, N-ethyl-Leu Ser(But), Cys(But), Asp(OBut), Glu(OBut) Orn(Boc) or, Lys(Boc) and, X denotes OBut or A6-Pro-Y where, A6 represents Arg, Orn, Lys or homoarginine and, Y repre-sents Gly-NH2, NH-NH-CO-NH2 (C1-C3)-, alkylamino, cyclopropylamino (C1-C3)-alkylamino, which is substituted with hydroxyl or fluorine or cycloalkylamino which is …