# Antiviral Activity of Pyrazolopyrimidine and Triazolopyrimidine Derivatives Against SARS-CoV-2 In Vitro: Identifying PZP25 as a Promising Scaffold

## TL;DR

This study identifies pyrazolopyrimidine and triazolopyrimidine compounds, especially PZP25, as promising antiviral agents against SARS-CoV-2 in laboratory tests.

## Contribution

The study introduces PZP25 as a novel and potent scaffold for antiviral development against SARS-CoV-2.

## Key findings

- PZP25 showed strong antiviral activity with an IC50 of 8.2 µM and a selectivity index >100.
- PZP and TZP derivatives exhibited potent in vitro inhibition of SARS-CoV-2 without cytotoxicity.
- PZP25's effects were strongest when administered post-infection and showed modest virucidal activity at higher temperatures.

## Abstract

Prior molecular docking and dynamics studies indicated a pyrazolopyridine–sulfonamide derivative (L87/PPS2, or simply PPS2) as a potential interactant with SARS-CoV-2 protein targets. The in vitro anti-SARS-CoV-2 activity and cytotoxicity profile of PPS2 were screened alongside a series of pyrazolopyrimidine (PZP) and triazolopyrimidine (TZP) derivatives. PPS2 demonstrated only partial inhibition of SARS-CoV-2 growth in Vero E6 cells at 100 µM. Crucially, however, four out of five PZPs and eight out of fourteen TZPs exhibited potent in vitro inhibitory activity against SARS-CoV-2 at 100 µM, with none of the tested compounds displaying cytotoxicity against Vero E6 cells at this concentration. Further characterization of one compound, PZP25, revealed an inhibitory concentration (IC50) of 8.2 µM, combined with low cytotoxicity (CC50 > 800 µM), yielding a selectivity index greater than 100. Time of addition assays indicated that PZP25’s antiviral effects were most pronounced when administered post-infection. While cellular pre-treatment provided a partial reduction in virus growth, modest virucidal activity was also observed at warmer temperatures (20 °C and 37 °C). Collectively, our findings demonstrate that PZP and TZP derivatives possess potent inhibitory activity of SARS-CoV-2 replication in vitro and highlight such compounds as promising chemical scaffolds for the development of novel antiviral agents targeting coronaviruses.