Figure 2.

Assembly of electrophilic warhead library for structure/reactivity studies. General structures of R/R′-functionalized 2-SP (A) and azine (B) and representative synthetic routes for their preparation: (a) R′-SNa, THF, 0 °C to rt, 15–24 h; (b) R′-SH, K₂CO₃, THF, 0 °C to rt, 15–24 h; (c) m-CPBA, DCM, rt, 16 h to 4 d; (d) 30% w/w aq. H₂O₂, AcOH, rt, 16–24 h; (e) (NH₄)Mo₇O₂₄·4H₂O, 30% w/w aq. H₂O₂, EtOH, 0 °C to rt, 24–48 h; (f; i) aq. HCl, NaOCl, DCM, −20 to −5 °C, 30 min; (ii) BnNH₂ or C₆F₅OH/Et₃N, DCM, −20 °C to rt, 2.5 h. (C–E) Common literature electrophiles used in protein bioconjugation, for benchmarking against 2-SPs.