the present invention discloses compounds of formula i or ii , or pharmaceutically acceptable salts , esters , or prodrugs thereof : which inhibit serine protease activity , particularly the activity of hepatitis c virus ns3 - ns4a protease . consequently , the compounds of the present invention interfere with the life cycle of the hepatitis c virus and are also useful as antiviral agents . the present invention further relates to pharmaceutical compositions comprising the aforementioned compounds for administration to a subject suffering from hcv infection . the invention also relates to methods of treating an hcv infection in a subject by administering to the subject a pharmaceutical composition comprising a compound of the present invention .