The instant invention relates to a novel compound representing a substituted phosphoramidic acid—a (2R,3R,5R)-3-hydroxy-(5-pyrimidin-1-yl)tetrahydrofuran-2-yl)methyl aryl phosphoramidate of formula 1 or a (S)-(2R,3R,5R)-3-hydroxy-(5-pyrimidin-1-yl)tetrahydrofuran-2-yl)methyl aryl phosphoramidate of formula 2, or a pharmaceutically acceptable salt, a hydrate, a crystalline form or a stereoisomer thereof, as defined in the specification.The novel compound is used for a pharmaceutical composition with at least one pharmaceutically acceptable excipient as well as with an inosine 5 monophosphate dehydrogenase inhibitor, HCV protease NS3 inhibitor, HCV protease NS3/4A inhibitor, and RNA polymerase NS5A inhibitor. The novel compound is useful as a viral polymerase HCV NS5B inhibitor and can be used for treating a disease caused by hepatitis C virus (HCV).