An enantiomer, diastereoisomer or tautomer of a compound, represented by formula I: wherein A, B, R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , R 8 , R 9 , and R 10 are as defined herein, or a salt or ester thereof, as an inhibitor of HCV NS5B polymerase.