More than an Amide Bioisostere: Discovery of 1,2,4-Triazole-containing Pyrazolo[1,5-a]pyrimidine Host CSNK2 Inhibitors for Combatting β-Coronavirus Replication

24 April 2024, Version 1


The pyrazolo[1,5-a]pyrimidine scaffold is a promising scaffold to develop potent and selective CSNK2 inhibitors with antiviral activity against β-coronaviruses. Herein, we describe the discovery of a 1,2,4-triazole group to substitute a key amide group for CSNK2 binding present in many potent pyrazolo[1,5-a]pyrimidine inhibitors. Crystallographic evidence demonstrates that the 1,2,4-triazole replaces the amide in forming key hydrogen bonds with Lys68 and a water molecule buried in the ATP-binding pocket. This isosteric replacement improves potency and metabolic stability at a cost of solubility. Optimization for potency, solubility and metabolic stability led to the discovery of the potent and selective CSNK2 inhibitor 53. Despite excellent in vitro metabolic stability, rapid decline in plasma concentration of 53 in vivo was observed and may be attributed to lung accumulation, although in vivo pharmacological effect was not observed. Further optimization of this novel chemotype may validate CSNK2 as an antiviral target in vivo.


Host-Directed Therapy

Supplementary materials

Supplementary Information
Eurofins KinaseProfiler radiometric enzymatic assay results; NanoBRET in digitonin-permeabilized cells; phosphorylation of EIF2S2 in A549ACE2 cells in vitro; comparison between CSNK2A2 and CSNK2A1 NanoBRET pIC50s; crystallographic refinement statistics; NanoBRET K192 Selectivity Panel results; 1H and 13C NMR spectra for analogues synthesized; HPLC trace for compound 53.


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