2'-Fluoro-5-methylarabinosyluracil, with CAS number 69256-17-3, is a nucleoside analogue. Its chemical structure features a uracil base modified with a 5-methyl group and a 2'-fluoro substitution on the arabinose sugar moiety. This specific modification is designed to mimic natural nucleosides. This compound is a key intermediate in the synthesis of sofosbuvir (PSI-7977), a direct-acting antiviral agent and a nucleotide polymerase inhibitor. Sofosbuvir is a cornerstone medication used for the treatment of chronic hepatitis C virus (HCV) infection. The 2'-fluoro-2'-C-methyl modification confers metabolic stability and enhances its potency as a chain terminator during viral RNA replication. As a critical synthetic precursor to a major antiviral drug, its primary significance lies in pharmaceutical manufacturing. It belongs to the class of modified nucleosides, which are fundamental building blocks in both medicinal chemistry and biochemical research for developing antiviral and anticancer therapies.