Macrocyclization of peptides with increasing lengths. Reaction
conditions: 0.1 mM peptide 2a–4a,
0.2 mg/mL GST, 20 mM TCEP·HCl, 0.1 M phosphate, pH 8.0, room
temperature (25 °C), 2 h. (A) Reaction yields of cyclization
reactions with and without the addition of GST (C(S-tBu): tert-butylthio-protected cysteine; C*: perfluoroaryl-modified
cysteine). The two cysteines that were cross-linked together are highlighted
in red. (B) LC–MS analysis of reactions of peptide 2a to 4a with the addition of GST. LC–MS data shown
are total ion currents (TIC); mass spectra at the highest points of
the TIC peaks are shown as insets.