Figure 1:

Extent of deprotection of Cys(Acm) by TIS at 37 ºC as measured by HPLC. (A) No reduction of the S-Acm bond in the Cys(Acm) test peptide was observed by HPLC after incubation in neat TFA for 12 h at 37 ºC. (B) In contrast, incubation of the test peptide with TFA/TIS (98/2) for 12 h at 37 ºC resulted in conversion of S-Acm to S-H (35%) and peptide disulfide (35%) as evidenced by the HPLC trace. (C) Addition of 5-fold excess TCEP to the reaction in (B) for 12 h resulted in nearly complete reduction of the disulfide to the reduced form. Traces D, E, and F are zoomed in views of traces A, B, and C, respectively.