Phosphine-promoted Thiol-Specific Bioconjugation with Allylic Acetates

Thiol-specific modification of proteins through conjugation with small molecules represents a critical advancement in biological research and therapeutic development, particularly in the context of antibody-drug conjugates (ADCs) for targeted cancer therapy. Despite the widespread use of maleimide-based linkers, their stability under physiological conditions remains a major limitation, often compromising therapeutic efficacy. In this investigation, we developed a novel and efficient thiol-specific bioconjugation strategy that employs allylic acetate, activated by a recyclable solid phosphine catalyst. This approach achieves high yields and demonstrates robust stability under bio-compatible, room-temperature conditions. Notably, it sets a new record for the fastest cysteine-conjugation reaction rate reported to date, with a rate constant of k ₂  = 1.49 × 10 ⁶ M ^− 1 s ^− 1 . The method expands the substrate scope and introduces a sustainable, environmentally friendly approach to ADC linker design, offering a significant advancement in the creation of stable, biocompatible, and therapeutically effective compounds.