A compound, represented by formula (I): ##STR00001## wherein A, B, R.sup.1, R.sup.2, R.sup.3, R.sup.5, R.sup.6, R.sup.7, R.sup.9, and R.sup.10 are as defined herein, or an enantiomer, diastereoisomer or tautomer thereof, including a salt, ester or derivative thereof, as an inhibitor of HCV NS5B polymerase.