Recent advances in chemoselective protein desulfurization: from VA-044 to emerging boron, photochemical, iron-catalyzed, and ultrasound methods.

Native chemical ligation (NCL) represents a powerful strategy for the chemical synthesis of tailor-made proteins that are difficult to obtain via biological expression approaches. Early desulfurization methods, particularly VA-044-based desulfurization, have profoundly advanced the field by enabling the post-ligation conversion of cysteine to alanine, thereby expanding the sequence space accessible for protein synthesis. In recent years, a variety of innovative desulfurization technologies have emerged that achieve superior reaction kinetics, broader functional group compatibility or elimination of harmful additives, significantly broadening the scope and practicality of desulfurization strategies. This review summarizes key enabling desulfurization methodologies developed in recent years, including boron reagent-based desulfurization, photochemically induced reactions, iron-catalyzed systems, and ultrasound-driven processes. We highlight their core mechanisms, technical advantages, and substrate tolerability, and showcase representative applications that have expanded the synthetic protein landscape. Finally, we provide an outlook on future directions, encompassing precise mechanistic elucidation, desulfurization-functionalization tandem strategies, and industrial scale-up, which are expected to further drive innovations in protein therapeutics, chemical biology, and novel biomaterials.