The development of sulfonium-based ABPs for lysine-directed labeling under basic conditions. Through this work the authors are seeking to address an important unmet need, namely the development of new chemotypes that show high selectivity for lysine labeling and improved cell stability, when compared to activated ester probes. The sulfonium probes reported here are an extension of the group’s earlier work (Org. Lett. 2022, 24, 2, 581–586) developing and applying propargyl sulfonium probes to the formation of ester and amide reagents for bioconjugation. In this previous work the authors used the propargyl sulfonium reagents for three component reactions.