oxSTEF reagents are tunable and versatile electrophiles for selective disulfide-rebridging of native proteins

Site-selective disulfide rebridging has emerged as a powerful strategy to modulate structural and functional properties of proteins. Here, we introduce a novel class of electrophilic reagents, designated oxSTEF, that demonstrate excellent efficiency in disulfide rebridging via double thiol-exchange. The oxSTEF reagents are prepared using an efficient synthetic sequence which may be diverted to obtain a range of structural derivatives. We demonstrate highly selective rebridging of cyclic peptides and native proteins, such as human growth hormone, and absence of cross-reactivity with other nucleophilic amino acid residues. The oxSTEF-conjugates undergo glutathione-mediated disintegration under tumor relevant glutathione concentrations, which highlights the potential for use in targeted drug delivery. Finally, the α-dicarbonyl motif of the oxSTEF reagents enables “second phase” oxime ligation which furthermore increases the thiol-stability of the conjugates significantly.