Abstract: Provided herein are compounds, compositions and methods for the treatment of Flaviviridae infections, including HCV infections. In certain embodiments, compounds and compositions of nucleoside derivatives are disclosed, which can be administered either alone or in combination with other anti-viral agents. In certain embodiments, the compounds are 2?-cyano, azido or amino nucleosides according to Formula 1001 or 2001: or a pharmaceutically acceptable salt, solvate, stereoisomeric form, tautomeric form, or polymorphic form thereof, wherein Base, W, R1 and R2 are as described herein.