Synthesis and use of a pseudo-cysteine for native chemical ligation.

The process of native chemical ligation (NCL) is well described in the literature. An N-terminal cysteine-containing peptide reacts with a C-terminal thioester-containing peptide to yield a native amide bond after transesterification and acyl transfer. An N-terminal cysteine is required as both the N-terminal amino function and the sidechain thiol participate in the ligation reaction.