Carbazole to indolazepinone scaffold morphing leads to potent cell-active dengue antivirals.

According to WHO, dengue virus is classed among major threats for future pandemics and remains at large an unmet medical need as there are currently no relevant antiviral drugs whereas vaccine developments have met with safety concerns, mostly due to secondary infections caused by antibody-dependant-enhancement in cross infections among the four dengue serotypes. This adds extra complexity in dengue antiviral research and has impeded the progress in this field. Following through our previous effort which born the allosteric, dual-mode inhibitor SP-471P (a carbazole derivative, EC50 1.1 µM, CC50 100 µM) we performed further optimisation while preserving the two arylamidoxime arms and the bromoaryl domain present in SP-471P. Examination of the relative positions of these functionalities within this three-point pharmacophore ultimately led us to an indolazepinone scaffold and our lead compound SP-1769B. SP-1769B is among the most cell-efficacious against all serotypes (DENV2/3 EC50 100 nM, DENV1/4 EC50 0.95-1.25 µM) and safest (CC50 > 100 µM) anti-dengue compounds in the literature that also completely inhibits a secondary ADE-driven infection.

Sustainable, three-component, one-pot procedure to obtain active anti-flavivirus agents.

The mosquito-borne viruses belonging to the genus Flavivirus such as Dengue virus (DENV) and Zika virus (ZIKV) cause human infections ranging from mild flu-like symptoms to hemorrhagic fevers, hepatitis, and neuropathies. To date, there are vaccines only for few flaviviruses while no effective treatments are available. Pyridobenzothiazole (PBTZ) derivatives are a class of compounds endowed with a promising broad-spectrum anti-flavivirus activity and most of them have been reported as potent inhibitors of the flaviviral NS5 polymerase. However, synthesis of PBTZ analogues entails a high number of purification steps, the use of hazardous reagents and environmentally unsustainable generation of waste. Considering the promising antiviral activity of PBTZ analogues which require further exploration, in this work, we report the development of a new and sustainable three-component reaction (3CR) that can be combined with a basic hydrolysis in a one-pot procedure to obtain the PBTZ scaffold, thus reducing the number of synthetic steps, improving yields and saving time. 3CR was significantly explored in order to demonstrate its wide scope by using different starting materials. In addition, taking advantage of these procedures, we next designed and synthesized a new set of PBTZ analogues that were tested as anti-DENV-2 and anti-ZIKV agents. Compound 22 inhibited DENV-2 NS5 polymerase with an IC50 of 10.4 µM and represented the best anti-flavivirus compound of the new series by inhibiting DENV-2- and ZIKV-infected cells with EC50 values of 1.2 and 5.0 µM, respectively, that translates into attractive selectivity indexes (SI - 83 and 20, respectively). These results strongly reaffirm PBTZ derivatives as promising anti-flavivirus agents that now can be synthesized through a convenient and sustainable 3CR in order to obtain more potent compounds for further pre-clinical development studies.

Pyridobenzothiazolones Exert Potent Anti-Dengue Activity by Hampering Multiple Functions of NS5 Polymerase.

Treatment of dengue virus (DENV) and other flavivirus infections is an unmet medical need. The highly conserved flaviviral NS5 RNA-dependent RNA polymerase (RdRp) is an attractive antiviral target that interacts with NS3 and viral RNA within the replication complex assembly. Biochemical and cell-based evidence indicate that targeting cavity B may lead to dual RdRp and NS5-NS3 interaction inhibitors. By ligand-based design around 1H-pyrido[2,1-b][1,3]benzothiazol-1-one (PBTZ) 1, we identified new potent and selective DENV inhibitors that exert dual inhibition of NS5 RdRp and NS3-NS5 interaction, likely through binding cavity B. Resistance studies with compound 4 generated sequence variants in the 3'-untranslated region of RNA while further biochemical experiments demonstrated its ability to block also RNA-NS5 interaction, required for correct RNA synthesis in cells. These findings shed light on the potential mechanism of action for this class of compounds, underlying how PBTZs are very promising lead candidates for further evaluation.

Cell-active carbazole derivatives as inhibitors of the zika virus protease.

Zika virus (ZIKV) infection recently resulted in an international health emergency the Americas in and despite its high profile there is currently no approved treatment for ZIKV infection with millions of people being at risk. ZIKV is a member of Flaviviridae family which includes prominent members such as dengue virus (DENV) and West Nile virus (WNV). One of the best validated targets for developing anti-flaviviral treatment for DENV and WNV infection is the NS2B/NS3 protease. However the inhibitors reported to date have shown limited promise for further clinical development largely due to poor cellular activity. Prompted by the conserved nature of the viral NS2B/NS3 protease across flaviviruses, we envisaged that small molecule inhibitors of the ZIKVpro may be developed by applying rational design on previously reported scaffolds with demonstrated activity against other flaviviral proteases. Starting with an earlier WNVpro hit we performed a scaffold hopping exercise and discovered that certain carbazole derivatives bearing amidine groups possessed submicromolar potency and significant cellular activity against ZIKV. We successfully addressed various issues with the synthesis of novel N-substituted carbazole-based amidines thus permitting a targeted SAR campaign. The in vitro biochemical and cell-based inhibitory profiles exhibited by the lead molecule described in this work (ZIKVpro IC50 0.52 µM, EC50 1.25 µM), is among the best reported to date. Furthermore, these molecules possess capacity for further optimization of pharmacokinetics and may evolve to broad spectrum flaviviral protease inhibitors.