2‐Phenylquinolines Exhibit Anti‐Severe Acute Respiratory Syndrome Coronavirus‐2 Activity Through the Nonstructural Protein 13 Helicase Inhibition

The Severe Acute Respiratory Syndrome Coronavirus‐2 (SARS‐CoV‐2) pandemic has highlighted the fragility of our therapeutic arsenal against human coronaviruses and the urgent need to develop new antivirals. They should exhibit broad‐spectrum activity to address future pandemics and target alternative viral proteins to mitigate resistance. We have previously identified a hit compound based on a 2‐phenylquinoline scaffold that is able to hinder SARS‐CoV‐2 replication through nonstructural protein 13 (nsp13) helicase inhibition. Here we reported a SAR study that led to identify new analogs such as 2‐(4‐butoxyphenyl)‐4‐[2‐(6,7‐dimethoxy‐3,4‐dihydroisoquinolin‐2(1H)‐yl)ethoxy]−5,7‐dimethoxyquinoline ( 14 ) and 4‐[2‐(6,7‐dimethoxy‐3,4‐dihydroisoquinolin‐2(1H)‐yl)ethoxy]‐2‐(4‐isopropoxyphenyl)−5,7‐dimethoxyquinoline ( 15 ), which exhibited a good antiviral profile (EC 50 = 8.06 and 9.11 µM) coupled with a low micromolar inhibition of nsp13 helicase. Time‐of‐addition assays and binding analyses confirmed helicase as their primary target, while kinetic studies revealed ATP‐competitive inhibition. The butoxy derivative 14 also inhibited HCoV‐229E and HCoV‐OC43 replication, indicating broad‐spectrum potential. The safety of the compounds was validated in bronchial epithelium cells BEAS‐2B cells and H9c2 cardiac cells, where they did not affect cell viability or reactive oxygen species (ROS) production. Finally, preliminary ADME studies on 15 showed a positive profile in terms of membrane permeability and metabolic stability in plasma and human liver microsomes. This SAR study, along with mechanistic exploration, paves the way for further optimization of 2‐phenylquinoline‐based compounds.