Modular Vinyl Phosphonamidates for Cysteine-Directed Protein Targeting

Covalent inhibitors and chemical probes targeting ligandable cysteine residues have emerged as powerful tools for drug discovery and proteomics. In this study, we introduce vinyl phosphonamidates (VPAs) as a novel class of latent cysteine electrophiles and assess their reactivity, selectivity, and potential for developing covalent inhibitors. Compared to well-established chloroacetamide and acrylamide electrophiles, VPAs exhibit a significantly lower intrinsic reactivity toward the model thiol glutathione. Moreover, VPA-derived covalent fragments displayed only very limited nonspecific reactivity in human cell lysate. Encouraged by these results, we developed VPA-functionalized derivatives of the FDA-approved covalent inhibitors Afatinib and Ibrutinib and evaluated their ability to engage the target protein by gel-based and mass spectrometry-based activity-based protein profiling (ABPP). Compared to commonly employed Michael acceptor-based electrophilic groups, VPA-functionalized drug ligands displayed significantly less off-targets while maintaining inhibitor efficiency. Furthermore, we leveraged the modular nature and accessibility of VPAs to develop a bifunctional proteolysis targeting chimera (PROTAC) for targeted protein degradation. The demonstrated selectivity and modularity, as exemplified by the incorporation of various ligands on the phosphorus O-substituent, of the vinyl phosphonamidate group as a cysteine-directed electrophile highlight its ability to expand the chemical space in the development of covalent inhibitors with a favorable proteome-wide reactivity profile.