Syntheses of Isatins and Oxindoles Derivatives as SARS-CoV-2 Inhibitors Evaluated through Phenotypic Screening with Vero Cells

To expand the variety of density functionalized compounds evaluated against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), we decided to prepare new acetylated and disubstituted 3-hydroxy bis-oxindoles and isoindigos coupling compounds using known protocols. The corresponding isatin derivatives were synthesized by ZrCl4/EtOH/reflux or HCl/AcOH/ reflux coupling conditions using oxindole and functionalized isatins, furnishing new 3-hydroxy bis‑oxindoles, which were dehydrated into new isoindigos. A total of 27 compounds bearing halogen, nitro and/or hydroxy groups on the isatin moiety, at the 3-, 5- and 7-positions, were prepared, including 5 new 3-hydroxy bis-oxindoles and 3 new halogenated isoindigos prepared according adapted procedures described in the literature. This library of nitrogen-isatin derivatives was evaluated against SARS-CoV-2 using a phenotypic screening assay. In this investigation, isatin derivatives 3d, 3e, 3h and 3i showed antiviral activity when tested at a single concentration. Compound 3e showed antiviral activity against SARS-CoV-2 in the concentration-response assay, however, it showed cellular toxicity in Vero cells. The present study identified substituted isatins as a promising new starting point for the development of anti-SARS-CoV-2 agents.