Native chemical ligation in unprotected or protected N-terminal cysteines in aqueous solution in solid phase of peptides.

A method of preparing an assembled peptide comprising: a) binding a first peptide segment to a solid phase through a linker to form a peptide bound to the solid phase; b) ligating a second peptide segment to said peptide bound to the solid phase in aqueous solution to form a peptide bound to the solid phase; wherein: (i) said first peptide segment has a C-terminal thioester and said second peptide segment has an N-terminal cysteine ​​group and a C-terminal thioacid; or (ii) said first peptide segment has an N-terminal cysteine, and said second peptide segment has an N-terminal cysteine ​​protected and C-terminal thioester.