The invention relates to compounds of formula (I) wherein R', R.sup.2, R.sup.3, R.sup.4, R.sup.5, R.sup.6, Y, n and m are as defined herein. The compounds are useful for the treatment and prevention of hepatitis C viral infections in mammals by inhibiting HCV NS3 protease. The invention further relates to azalactone compounds of the formula (III) which can be reacted with an amide anion to produce the compounds of formula (I). ##STR00001##