Structure Activity\nof β‑Amidomethyl Vinyl\nSulfones as Covalent Inhibitors of <i>Chikungunya</i> nsP2\nCysteine Protease with Antialphavirus Activity

Despite their widespread impact on human health, there\nare no approved\ndrugs for combating alphavirus infections. The heterocyclic β-aminomethyl\nvinyl sulfone RA-0002034 (<b>1a</b>) is a potent irreversible\ncovalent inhibitor of the alphavirus nsP2 cysteine protease with broad-spectrum\nantiviral activity. Analogs of <b>1a</b> that varied each of\nthe three regions of the molecule were synthesized to establish structure–activity\nrelationships for the inhibition of <i>Chikungunya</i> (CHIKV)\nnsP2 protease and viral replication. The vinyl sulfone covalent warhead\nwas highly sensitive to modifications. However, alterations to the\ncore five-membered heterocycle and aryl substituent were well tolerated.\nThe 5-(2,5-dimethoxyphenyl)pyrazole (<b>1o</b>) and 4-cyanopyrazole\n(<b>8d</b>) analogs exhibited <i>k</i><sub>inact</sub>/<i>K</i><sub>i</sub> ratios >9000 M<sup>–1</sup> s<sup>–1</sup>. 3-Arylisoxazole (<b>10</b>) was identified\nas an isosteric replacement for the five-membered heterocycle, which\ncircumvented the intramolecular cyclization of pyrazole-based inhibitors\nlike <b>1a</b>. A ligand-based model of the enzyme active site\nwas developed to aid the design of nsP2 protease inhibitors as potential\ntherapeutics against alphaviruses.