Synthesis and Evaluation of ATP-Binding Site Directed Potential Inhibitors of Nucleoside Triphosphatases/ Helicases and Polymerases of Hepatitis C and other Selected Flaviviridae Viruses

Abstract

5′-O-(4-fluorosulphonylbenzoyl)-esters of ribavirin (FSBR), adenosine (FSBA), guanosine (FSBG) and inosine (FSBI) were obtained by acylation of the 5′-OH of adenosine, guanosine, inosine, and ribavirin with 4-fluorosulphonylbenzoyl chloride (FSBCl) in HMPA. The above derivatives were tested as inhibitors of nucleoside triphosphatase (NTPase)/helicase activities of Flaviviridae: hepatitis C virus (HCV), West Nile virus (WNV), Japanese encephalitis virus (JEV) and dengue virus (DENV) and polymerase activity of HCV and WNV. When the unwinding activity of viral NTPase/helicases was tested under standard conditions, only weak inhibition was obtained with FSBI (IC50≥120 μM) and in the case of FSBG even an activation was seen. The preincubation of the NTPase/helicases with the 5′-O-FSB derivatives increased the inhibitory effect. Screening of the 5′-O-FSB derivatives on inhibition of the WNV and HCV RNA polymerases employing GTP or UTP substrates revealed rather modest inhibitory effect. FSBI exhibited the highest inhibitory activity against WNV (IC50=70 μM with UTP substrate) and HCV polymerase (IC50=80 μM with GTP substrate). Other 5′-O-FSB derivatives were very weak inhibitors or completely failed to show any activity against HCV and WNV enzymes. In contrast to the NTPase/helicases the preincubation of the polymerases did not influence the inhibition.