The worldwide COVID-19 pandemic caused by the coronavirus SARS-CoV-2 urgently demands novel direct antiviral treatments. The main protease (Mpro) and papain-like protease (PLpro) are attractive drug targets among coronaviruses due to their essential role in processing the polyproteins translated from the viral RNA. In the present work, we virtually screened 688 naphthoquinoidal compounds and derivatives against Mpro of SARS-CoV-2. Twenty-four derivatives were selected and evaluated in biochemical assays against Mpro using a novel fluorogenic substrate. In parallel, these compounds were also assayed with SARS-CoV-2 PLpro. Four compounds inhibited Mpro with half-maximal inhibitory concentration (IC50) values between 0.41 μM and 66 μM. In addition, eight compounds inhibited PLpro with IC50 ranging from 1.7 μM to 46 μM. Molecular dynamics simulations suggest stable binding modes for Mpro inhibitors with frequent interactions with residues in the S1 and S2 pockets of the active site. For two PLpro inhibitors, interactions occur in the S3 and S4 pockets. In summary, our structure-based computational and biochemical approach identified novel naphthoquinonal scaffolds that can be further explored as SARS-CoV-2 antivirals.

The worldwide COVID-19 pandemic caused by the coronavirus SARS-CoV-2 urgently demands novel direct antiviral treatments. The main protease (M pro ) and papain-like protease (PL pro ) are attractive drug targets among coronaviruses due to their essential role in processing the polyproteins translated from the viral RNA. In this study, we virtually screened 688 naphthoquinoidal compounds and derivatives against M pro of SARS-CoV-2. Twenty-four derivatives were selected and evaluated in biochemical assays against M pro using a novel fluorogenic substrate. In parallel, these compounds were also assayed with SARS-CoV-2 PL pro . Four compounds inhibited M pro with half-maximal inhibitory concentration (IC 50 ) values between 0.41 μM and 9.0 μM. In addition, three compounds inhibited PL pro with IC 50 ranging from 1.9 μM to 3.3 μM. To verify the specificity of M pro and PL pro inhibitors, our experiments included an assessment of common causes of false positives such as aggregation, high compound fluorescence, and inhibition by enzyme oxidation. Altogether, we confirmed novel classes of specific M pro and PL pro inhibitors. Molecular dynamics simulations suggest stable binding modes for M pro inhibitors with frequent interactions with residues in the S1 and S2 pockets of the active site. For two PL pro inhibitors, interactions occur in the S3 and S4 pockets. In summary, our structure-based computational and biochemical approach identified novel naphthoquinonal scaffolds that can be further explored as SARS-CoV-2 antivirals.

In 2021, our research group published the prominent anticancer activity achieved through the successful combination of two redox centres (ortho-quinone/para-quinone or quinone/selenium-containing triazole) through a copper-catalyzed azide-alkyne cycloaddition (CuAAC) reaction. The combination of two naphthoquinoidal substrates towards a synergetic product was indicated, but not fully explored. Herein, we report the synthesis of 15 new quinone-based derivatives prepared from click chemistry reactions and their subsequent evaluation against nine cancer cell lines and the murine fibroblast line L929. Our strategy was based on the modification of the A-ring of para-naphthoquinones and subsequent conjugation with different ortho-quinoidal moieties. As anticipated, our study identified several compounds with IC50 values below 0.5 µM in tumour cell lines. Some of the compounds described here also exhibited an excellent selectivity index and low cytotoxicity on L929, the control cell line. The antitumour evaluation of the compounds separately and in their conjugated form proved that the activity is strongly enhanced in the derivatives containing two redox centres. Thus, our study confirms the efficiency of using A-ring functionalized para-quinones coupled with ortho-quinones to obtain a diverse range of two redox centre compounds with potential applications against cancer cell lines. Here as well, it literally takes two for an efficient tango!

CH activation has proven to be one of the most versatile synthetic strategies developed so far for the functionalization of sp 2 centers, due to the large variety of reaction conditions available to the practitioner including choice of catalyst, oxidant, additives and also directing group. Regarding the latter, one possibility is to use an intrinsic directing group. These are functional groups resident in the substrate containing a pair of nonbonding electrons, which can interact with the metal center of a catalyst and therefore control the site of CH activation. The use of a directing group that is intrinsic to the molecule is advantageous, as additional synthetic steps are not required for its installation and removal. The implementation of this directing group strategy is therefore guided by the structure of the desired compound and the coordinating ability of heteroatoms within it.