The invention provides novel nucleoside compounds of formula I wherein R1, R2a, R2b, R3, R4, R5 R6, R8a, R9 and R10 are as defined herein which are useful for the treatment of Hepatitis C Virus (HCV) mediated diseases. The invention further provides methods for treatment or prophylaxis of HCV mediated diseases with compounds of formula I and pharmaceutical compositions comprising these compounds,