FIELD: medicine, pharmaceutics.
SUBSTANCE: present invention refers to compounds of formula 
(I) where R1 is chosen from ethyl, n-propyl, isopropyl or isobutyl, and to its pharmaceutically acceptable salts. Besides, the invention refers to a pharmaceutical composition on the basis of said compounds used for treating a hepatitis C virus (HCV) mediated disease, and also to a method of treating the hepatitis C virus (HCV) mediated disease, and to the method of selective O-acylation nucleoside 
II for producing O-acyl nucleoside I in an alkaline reaction medium including the stages: (i) dissolution of II and DMAP in a heterogeneous mixture of water and a solvent and addition of a water base for pH control between approximately 7.5 to approximately 12; (ii) optional addition of a sufficient amount of saturated aqueous NaCl for preparing a diphase reaction mixture; (iii) addition of an acidating agent and an accessory base sufficient for pH preservation between approximately 7.5 to approximately 12; (iv) reaction monitoring and interruption of adding said acidating agent and said base after sufficient conversion provided; (v) optional contact of O-acylnucleoside with the pharmaceutically acceptable acid to produce a pharmaceutically acceptable salt.
EFFECT: production of the pharmaceutical composition for treating the hepatitis C virus (HCV) mediated disease.
9 cl, 2 tbl, 8 ex
