5-chloro-3-(2-(2,4-dinitrophenyl) hydrazono)indolin-2-one: synthesis, characterization, and biochemical and computational screening against SARS-CoV-2

Abstract 2,4-dinitrophenylhydrazone of 5-chloroisatin (H 2 L) was synthesized and characterized by elemental and spectral (IR, electronic, Mass) analyses. The NMR spectrum of H 2 L indicated keto-enol tautomerism, with the keto form being more abundantin solution. H 2 L was found to selectively interfere with binding of the SARS-CoV-2 spike receptor binding domain (RBD) to the host angiotensin-converting enzyme 2 receptor with a 50% inhibitory concentration (IC 50 ) of 0.26 μM, compared to an unrelated PD-1-PD-L1 ligand-receptor binding pair with an IC 50 of 2.06 μM in vitro (Selectivity index = 7.9). Molecular docking studies revealed that the synthesized ligand preferentially binds within the ACE2 receptor binding site in a region distinct from where spike mutations in SARS-CoV-2 variants occur. Consistent with these models, H 2 L was able to disrupt ACE2 interactions with the RBDs from beta, delta, lambda, and omicron with similar activities. These studies indicate that H 2 L-derived compounds are potential inhibitor(s) of multiple SARS-CoV-2 variants of concern including those capable of circumventing vaccine and immune responses.