An enantiomer, diastereoisomer or tautomer of a compound, represented by formula (I): wherein either A or B is nitrogen and the other B or A is C, and the radicals R1, R2, R3, R4, R5, R6, R7, R8, R9, and R10 are as defined herein, or a salt or ester thereof as viral polymerase inhibitors. The compound is used as an inhibitor of RNA dependent RNA polymerases, particularly those viral polymerases within the Flaviviridae family, more particularly to HCV polymerase.