Design and synthesis of novel symmetric diaminofluorene prolinamide analogues as potent hepatitis C virus inhibitors

Hepatitis C virus (HCV) is a major health challenge worldwide, since the discovery of NS5A direct acting antivirals; pharmaceutical researchers turned their attention to the design, synthesis, and optimization of novel NS5A inhibitors, outside the chemical space of commercially available drugs. This study describes the discovery of highly potent hepatitis C virus (HCV) NS5A inhibitors based on symmetrical prolinamide derivatives of diaminofluorene. Modification on the diaminoflourene backbone included the use of (S)-prolinamide or its isostere(S,R)-piperidine-3-caboxamide both bearing S, R-phenylglycine with different terminal carbamate groups. Compound 26 (Diethyl ((1R,1'R)-((2S,2'S)-(((9H-fluorene-2,7-diyl)bis(azanediyl))bis(carbonyl)) bis(pyrrolidine-2,1-diyl))bis(2-oxo-1-phenylethane-2,1-diyl))dicarbamate) exhibited potent inhibitory activity against HCV genotype (GT) 1b (EC₅₀= 40 pM and an approximate selectivity index of > 2.8 x10⁶) and a high selectivity on (GT) 1b versus GT 4a. Interestingly, it exhibited a significant effect on GT 3a (EC₅₀ = 1.2 nM) as well. The SAR analysis revealed that a picomolar inhibitory activity is attained with the use of S-prolinamide capped with R-phenylglycine residue bearing a terminal alkyl carbamate group.