show a good reactivity profile and are abundant in biological systems . The versatility of sulfur-based chemistry and the ease of modification makes it an attractive choice in organic chemistry and life science . A multitude of chemoselective reactions utilizes sulfur chemistry with application in many fields, including self-healing materials or drug delivery systems . One particular thiol-based reagent, 4-(methylthio)phenol (4MTP), has been described long ago for peptide coupling, but to date, has not been investigated for PPM bioconjugation. Johnson et al. reported on the use of 4MTP esters as a carboxyprotecting group during polypeptide synthesis in 1968. When 4MTP is oxidized to yield 4-(methylsulfonyl)phenyl (4MTO2P), it transforms a protected ester into an activated activate ester, allowing further aminolysis and amide formation . Chen introduced 4MTP esters for quinoxaline antibiotic synthesis . Later, Siemens applied activated 4MTP esters during peptide solid-phase synthesis . Cho also reported on the application of 4MTP moieties as a safety-catch protecting group during peptide coupling or as an active ester that can act with other N-free peptide fragments to form new bonds . More recently, Popovic' et al. reported on peptide 4MTP ester synthesis suitable for peptide segment coupling or direct amidation with peptide N-termini . However, to the best of our knowledge, 4MTP has not been utilized or suggested for any PPMs.