Chemo-enzymatic synthesis of semaglutide, liraglutide and GLP-1

The invention relates to a method for preparing a coupling product comprising the sequence Pq-Wv-His-X-Glu-Gly-Thr-Phe-Thr-Ser-Asp-Val-Ser-Ser-Tyr-Leu-Glu-Gly-Gln-Ala-Ala-Y-Glu-Phe-lle-Ala-Trp-Leu-Val-Z-Gly-Arg-Gly, comprising enzymatically coupling (a) a peptide C-terminal ester or thioester comprising a first peptide fragment represented by the formula Pq-Wv- His-X-Glu-(thio)ester; and (b) a peptide nucleophile having an N-terminally unprotected amine comprising a second peptide fragment comprising the sequence H-Gly-Thr-Phe-Thr-Ser-Asp-Val-Ser-Ser-Tyr-Leu-Glu-Gly-Gln-Ala-Ala-Y-Glu-Phe-lle-Ala-Trp-Leu-Val-Z-Gly-Arg-Gly wherein - P represents a protective group at the N-terminal a-amino function of said peptide C-terminal ester or thioester and q is an integer having a value of 1 or 0; - W represents one or more amino acid residues, which may be the same or different and v is an integer having a value of 1 or more representing the number of amino acid residues W; - X is Ala or an α-amino-isobutyric acid unit (Aib); - Y is Lys, which Lys has a free side-chain ε-amino group or a side-chain ε-amino group that is protected with a protective group or a side-chain ε-amino group that is functionalised with an amino acid or another functional group; - Z is Arg or Lys.