Synthesis and anti-SARS-CoV-2 evaluation of lipid prodrugs of ?-D-N4-hydroxycytidine (NHC) and a 3?-fluoro-substituted analogue of NHC

beta-D-N4-hydroxycytidine (NHC, EIDD-1931) is a nucleoside analogue that exhibits broad spectrum antiviral ac-tivity against a variety of RNA viruses. Herein, we report the synthesis of a series of lipid prodrugs of NHC and a novel 3 '-fluoro modified NHC analogue, and evaluation of their antiviral activity against five variants of SARS-CoV-2. All lipid prodrugs showed potent antiviral activity against the tested SARS-CoV-2 variants with EC50 values in the range of 0.31-3.51 mu M, which were comparable to those of NHC or higher than those of remdesivir and molnupiravir. An increase in the cytostatic activity of the lipid prodrugs was found, but prodrug 2d proved equally selective as molnupinavir. The 3 '-F analogue of NHC (6) only displayed minor antiviral activity against the SARS-CoV-2 Omicron variant (EC50 = 29.91 mu M), while no activity was found for other variants at the highest concentration tested. The promising antiviral data of the lipid prodrugs of NHC suggest that they deserve further investigation as new anti-SARS-CoV-2 drugs.