One‐Pot Four‐Segment Ligation Using Seleno‐ and Thioesters: Synthesis of Superoxide Dismutase

The synthesis of a peptide selenoester was efficiently carried out by the 9‐fluorenylmethoxycarbonyl (Fmoc) method using N‐alkylcysteine, at the C‐terminus of the peptide, as the N‐to‐S acyl shift device. The selenoester selectively reacted with the terminal amino group of the peptide aryl thioester in the presence of N,N‐diisopropylethylamine and dipyridyldisulfide, thus leaving the aryl thioester intact. Combined with silver‐ion‐promoted and silver‐ion‐free thioester activation methods, a one‐pot four‐segment ligation was realized. The method was successfully used to assemble the entire sequence of superoxide dismutase (SOD), which is composed of 153 amino‐acid residues, in one pot. After the folding reaction, the fully active SOD was obtained. The old SOD: A peptide selenoester was efficiently prepared by the 9‐fluorenylmethoxycarbonyl method using N‐alkylcysteine as an N‐to‐S acyl shift component. The selenoester exhibited higher reactivity than the aryl thioester. Combined with silver‐ion‐promoted and silver‐ion‐free ligation, a one‐pot four‐segment ligation was developed and successfully applied to the synthesis of superoxide dismutase (SOD), which comprises 153 amino‐acid residues.