Design, synthesis, and antiviral activity evaluation of the bis-ester prodrug of N4-hydroxycytidine phosphate.

Monophosphorylation is a key rate-limiting step for the efficacy of broad-spectrum nucleoside antiviral drugs, and designing phosphate prodrugs is an effective method to enhance antiviral efficacy. N4-hydroxycytidine (NHC) has a broad-spectrum antiviral effect. Based on the mechanism of action and metabolic inactivation characteristics of NHC, we designed a series of dual ester prodrugs targeting the N4-hydroxyl group and the 5'-phosphate of the ribose ring. Twenty-nine compounds were designed and synthesized. The cytotoxicity assay results showed low cytotoxicity (no significant toxicity at 160 μM). Using the Vesicular Stomatitis Virus expressing Green Fluorescent Protein (VSV-GFP) virus screen, it was found that all of them have antiviral activity. Compounds 2328 and 2322 showed better antiviral activity than molnupiravir. The EC50s of 2328 against VSV, HMPV-A2, and RSV-A2 viruses were 2.19 μM, 35.6 μM, and 53.5 μM, respectively, and the EC50s of 2322 against VSV, HMPV-A2, and RSV-A2 were 6.23 μM, 52.8 μM, and 28.2 μM, respectively. Structure-activity relationships indicate that the antiviral activity of compounds at the cellular level is closely linked to the structure of the prodrug's phosphate ester, whereas the ester group on the N4-hydroxyl is more tolerant of diverse functional groups.