Pyrazolopyrimidines: Potent Inhibitors Targeting the Capsid of Rhino- and Enteroviruses

There are currently no drugs available for the treatment of enterovirus (EV)-induced acute and chronic diseases such as the common cold, meningitis, encephalitis, pneumonia, and myocarditis with or without consecutive dilated cardiomyopathy. Here, we report the discovery and characterization of pyrazolopyrimidines, a well-tolerated and potent class of novel EV inhibitors. The compounds inhibit the replication of a broad spectrum of EV in vitro with IC₅₀ values between 0.04 and 0.64 μM for viruses resistant to pleconaril, a known capsid-binding inhibitor, without affecting cytochrome P450 enzyme activity. Using virological and genetics methods, the viral capsid was identified as the target of the most promising, orally bioavailable compound 3-(4-trifluoromethylphenyl)amino-6-phenylpyrazolo[3,4-d]pyrimidine-4-amine (OBR-5-340). Its prophylactic as well as therapeutic application was proved for coxsackievirus B3-induced chronic myocarditis in mice. The favorable pharmacokinetic, toxicological, and pharmacodynamics profile in mice renders OBR-5-340 a highly promising drug candidate, and the regulatory nonclinical program is ongoing. Curing the common cold! A cluster of pyrazolopyrimidines with potent broad-spectrum activity against enteroviruses was discovered. Extensive structure-property relationship analyses led to the identification of 3-(4-trifluoromethyl-phenyl)amino-6-phenylpyrazolo[3,4-d]pyrimidine-4-amine, shown to be a blocker of the viral capsid protein, as a lead compound for drug development with favorable physicochemical, pharmacokinetic, and toxicological properties.