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.

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.