EXTENDING THE APPLICABILITY OF NATIVE CHEMICAL LIGATION

A more general approach to native (amide-forming) chemical ligation of unprotected peptide segments is described that extends the technique beyond the previously reported X-Cys ligation site to now include X-Gl y and Gly-X ligation sites. A peptide, [peptide(1)](alpha)COSR, is rea cted with a second peptide, HSCH2CH2(O)-N-alpha[peptide(2)], under con ditions promoting thioester exchange. The intermediate thioester-linke d product rearranges to form a ligation product linked by an N-substit uted amide bond. If desired, the -oxyalkyl substitution on the amide b ond can be removed by facile treatment with Zn in acidic medium to giv e a native peptide bond at the ligation site. The techniques described have been employed to ligate small model peptide segments to yield pe ptides with native or modified backbones, proving the feasibility of t his approach.