Here, we report the synthesis, structure–activity relationship studies, enzyme inhibition, antiviral activity, and X-ray crystallographic studies of 5-chloropyridinyl indole carboxylate derivatives as a potent class of SARS-CoV-2 chymotrypsin-like protease inhibitors. Compound 1 exhibited a SARS-CoV-2 3CLpro inhibitory IC 50 value of 250 nM and an antiviral EC 50 value of 2.8 μM in VeroE6 cells. Remdesivir, an RNA-dependent RNA polymerase inhibitor, showed an antiviral EC 50 value of 1.2 μM in the same assay. Compound 1 showed comparable antiviral activity with remdesivir in immunocytochemistry assays. Compound 7d with an N -allyl derivative showed the most potent enzyme inhibitory IC 50 value of 73 nM. To obtain molecular insight into the binding properties of these molecules, X-ray crystal structures of compounds 2 , 7b , and 9d -bound to SARS-CoV 3CLpro were determined, and their binding properties were compared.

We report the design and synthesis of a series of new 5-chloropyridinyl esters of salicylic acid, ibuprofen, indomethacin, and related aromatic carboxylic acids for evaluation against SARS-CoV-2 3CL protease enzyme. These ester derivatives were synthesized using EDC in the presence of DMAP to provide various esters in good to excellent yields. Compounds are stable and purified by silica gel chromatography and characterized using 1H-NMR, 13C-NMR, and mass spectral analysis. These synthetic derivatives were evaluated in our in vitro SARS-CoV-2 3CLpro inhibition assay using authentic SARS-CoV-2 3CLpro enzyme. Compounds were also evaluated in our in vitro antiviral assay using quantitative VeroE6 cell-based assay with RNAqPCR. A number of compounds exhibited potent SARS-CoV-2 3CLpro inhibitory activity and antiviral activity. Compound 9a was the most potent inhibitor, with an enzyme IC50 value of 160 nM. Compound 13b exhibited an enzyme IC50 value of 4.9 µM. However, it exhibited a potent antiviral EC50 value of 24 µM in VeroE6 cells. Remdesivir, an RdRp inhibitor, exhibited an antiviral EC50 value of 2.4 µM in the same assay. We assessed the mode of inhibition using mass spectral analysis which suggested the formation of a covalent bond with the enzyme. To obtain molecular insight, we have created a model of compound 9a bound to SARS-CoV-2 3CLpro in the active site.

The rapid synthesis of the isoindolinone skeleton has been accomplished by a palladium‐catalyzed one‐pot tandem process, which consists of an isocyanide insertion/hydration (carboxamidation) and 5‐exo‐dig cycloisomerization (hydroamidation) reaction sequence that afforded the products in good to excellent yields. Preliminary mechanistic studies of this sequential C–C/C–O/C–N bond formation process suggests that the carboxamidation step is palladium‐dependent, whereas the hydroamidation step is solely mediated by the base and is driven by the electrophilicity of the alkyne.

No abstract

We have the investigated base mediated asymmetric intramolecular oxidopyrylium-alkene [5 + 2]-cycloaddition reaction which resulted in the synthesis of functionalized tricyclic ring systems containing an 8-oxabicyclo­[3.2.1]­octane core. Intramolecular cycloaddition constructed two new rings, three new stereogenic centers, and provided a tricyclic cycloadduct with high diastereoselectivity and isolated yield. We incorporated an α-chiral center and an alkoxy alkene tether on the substrates and examined the effect of the size of alkyl groups and alkene tether length on diastereoselectivity. The requisite substrates for the oxidopyrylium-alkene cycloaddition reaction were synthesized in a few steps involving alkylation of optically active α-hydroxy amide, furyllithium addition, reduction of resulting ketone, and Achmatowicz reaction followed by acylation of a lactol intermediate. We have proposed stereochemical models for the [5 + 2] cycloaddition reaction via the oxidopyrylium ylide. Interestingly, the alkoxy substituent on the stereocenter and the chain length are responsible for the degree of stereoselectivity of the cycloadduct.