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Updated: Jul 26, 2025

Synthesis of Protein Bioconjugates via Cysteine-maleimide Chemistry
Published on: July 20, 2016
Site-Selective Aryl Diazonium Installation onto Protein Surfaces at Neutral pH using a Maleimide-Functionalized
Nicholas D J Yates1, Natasha E Hatton1, Martin A Fascione1
1Department of Chemistry, University of York Heslington, York, YO10 5DD, UK.
Abstract:
Aryl diazonium cations are versatile bioconjugation reagents due to their reactivity towards electron-rich aryl residues and secondary amines, but historically their usage has been hampered by both their short lifespan in aqueous solution and the harsh conditions required to generate them in situ. Triazabutadienes address many of these issues as they are stable enough to endure multiple-step chemical syntheses and can persist for several hours in aqueous solution, yet upon UV-exposure rapidly release aryl diazonium cations under biologically-relevant conditions. This paper describes the synthesis of a novel maleimide-functionalized triazabutadiene suitable for site-selectively installing aryl diazonium cations into proteins at neutral pH; we show reaction with this molecule and a surface-cysteine of a thiol disulfide oxidoreductase. Through photoactivation of the site-selectively installed triazabutadiene motifs, we generate aryl diazonium functionality, which we further derivatize via azo-bond formation to electron-rich aryl species, showcasing the potential utility of this strategy for the generation of photoswitches or protein-drug conjugates.
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