The present invention provides HCV polymerase inhibiting compounds having the formula (I): ##STR00001## where R.sup.1 is cyclobutyl-N(R.sub.a)--, n is 1, 2, 3 or 4, and at least one R.sup.5 is R.sub.aSO.sub.2N(R.sub.j)alkyl-. In a non-limiting example, a compound of the present invention is N-[(3-{1-[(cyclobutyl)amino])-4-hydroxy -2-oxo-1,2-dihydro-quinolin-3-yl}-1,1-dioxo-1,4-dihydro-1.lamda..sup.6-th- ieno[2,3-e][1,2,4]thiadiazin-7-yl)methyl]methane-sulfonamide. The present invention also features compositions comprising the compounds of the present invention or pharmaceutically acceptable salts, stereoisomers or tautomers thereof, and methods of using the same to treat or prevent HCV infection.