Serine protease inhibitors, particularly NS3 protease Hepatitis C virus.

A compound of formula ** ** in which: R1 is selected from alkyl (C1-C6) alkyl, or alkenyl or alkynyl (C2-C6) alkyl, wherein up to 4 carbon atoms in R1 they are optionally independently substituted with a halogen; and wherein any hydrogen atom bound to any terminal carbon atom in R1 is optionally independently substituted in with SH u OH; R3 is selected from wherein each R2 is independently selected Write R11, -Ar, -O-R11, -O-Ar, -O-R11 -Ar, -R11-C (O) -R11, -N (R11 ) 2, -N (R11) -C (O) O-R11, -N (R11) -C (O) O-R11 -Ar, - C (O) O-R11, -OC (O) -N ( R11) 2, halo, -CN, -NO2, -R11-C (O) -R 11, -R 11 C (O) O-R11, -C (O) -N (R11) 2, -C (O) -N (R11) -Ar, -S (O) 2-R11, o S (O) 2-N (R11) 2; wherein up to 2 hydrogen atoms in R2 are optionally and independently substituted with a different group selected Write R11, -Ar, -O-R11, -O-Ar, -O-Ar R11, -R11-C (O ) -R11, -NH- (R11) 2, -N (R11) -C (O) O-R11, - N (R11) -C (O) O-R11 -Ar, -C (O) O-R11 , -OC (O) - N (R11) 2, halo, -CN, -NO2, -R11-C (O) -R 11, -R 11 C (O) O-R11, -OC (O) -R 11, -C (O) -N (R11) 2, -C (O) -N (R11) -Ar, -N (R11) -C (O) - R11, -R11-C (O) -N (R11) 2, -S (O) 2-R11 or is S (O) 2-N (R11) 2; wherein each R11 is selected from hydrogen, (C1-C6) -straight or branched alkenyl or alkynyl (C2-C6) linear or branched, and in which up to 3 hydrogen atoms in said alkyl, alkenyl or alkynyl are optionally and independently substituted with halo.