GS-441524 is the parent nucleoside and active metabolite of the SARS-CoV2 drug remdesivir. Displayed broad spectrum antiviral activity against HCV, YFV, DENV-2, influenza A, parainfluenza 3, and SARS-CoV.1 It has been suggested that GS-441524 is superior as an anti-SARS-CoV2 drug due to simplicity of preparation compared to remdesivir, lack of on-target liver toxicity, and the fact that remdesivir is prematurely hydrolysed to GS-441524 in human serum.2 Additionally, the enzymes that hydrolyze remdesivir to active metabolite GS-441524 are hardly expressed in lungs.
1) Cho, et al. (2012), Synthesis and antiviral activity of a series of 1'-substituted 4-aza-7,9-dideazaadenosine C-nucleosides; Bioorg. Med. Chem. Lett. 22 2705
2) Yan and Muller (2020), Advantages of the Parent Nucleoside GS-441524 over Remdesivir for Covid-19 Treatment; ACS Med. Chem. Lett. 11 1361