in the presence of both 0.1% TFA and 30 mM MgCl2 (Condition B). Under these conditions the corresponding Trp-modified peptides 7a, 7b and 7d were obtained in quantitative conversion yields after 6 h (Figure (inside the red frame) and Figures and)). Having confirmed the versatility of the reactions against a variety of substrates, we next evaluated applying the Cys(Acm)(O) modifier agents to substrates possessing an alkyne or biotin unit (Biotin-Gly-miniPEG-Phe-miniPEG-Cys(Acm)(O)-NH2 (8) or Ac-propargyl-Gly-miniPEG-Phe-miniPEG-Cys(Acm)(O)-NH2 ( )). The reactions of modifiers 8 and 9 (1.5 mM) with model substrate 2a using 30 mM MgCl2-0.1% TFA in 2% BMPy•OTf/AcOH (Condition B for 8) or in AcOH (Condition A for 9) at 37 °C or 25 °C, respectively, for 6 h also gave the desired modified materials 10 and 11 in high conversion yields (Figure (inside the blue frame) and Figures )).