A compound of formula (I) or a pharmaceutically acceptable salt thereof: R 1 is aryl; R 2 is selected from C 1 -C 24 -alkyl, C 3 -C 24 -alkenyl, C3-C24-alkynyl, C 0 -C 4 -alkylene-C 3 -C 7 -cycloalkyl or C 0 -C 4 -alkylene-aryl; R 3 and R 4 are each independently selected from H, C 1 -C 6 -alkyl and C 1 -C 3 -alkylene-R 9 ; or wherein R 3 and R 4 together with the atom to which they are attached form a 3- to 6-membered cycloalkyl or heterocycloalkyl group; R 5 and R 7 are each independently selected from H and C 1 -C 4 -alkyl; R 6 is independently selected from H and C(O)R 10 ; R 8 is independently selected from H, C(O)OR 10 and C(O)R 10 ; R 9 is independently selected from aryl (e.g. phenyl), imidazole, indole, SR a , OR a , CO 2 R a , CO 2 NR a R a , NR a R b and NH(=NH)NH 2 ; R 10 is independently at each occurrence selected from C 1 -C 24 -alkyl, C 3 -C 24 -alkenyl, C3-C24-alkynyl, C 0 -C 4 -alkylene-C 3 -C 7 -cycloalkyl or C 0 -C 4 -alkylene-aryl; wherein any aryl group is phenyl, naphthyl or tetrahydronaphthyl and wherein any phenyl, alkyl, alkyne, alkene, alkylene, cycloalkyl, naphthyl or tetrahydronaphthyl group is optionally substituted with from 1 to 4 substituents selected from: halo, nitro, cyano, NR a R a , NR a S(O) 2 R a , NR a C(O)R a , NR a CONR a R a , NR a CO 2 R a , OR a ; SR a , SOR a , SO 3 R a , SO 2 R a , SO 2 NR a R a , CO 2 R a C(O)R a , CONR a R a , CR a R a NR a R a , C 1 -C 4 -alkyl, C 2 -C 4 -alkenyl, C 2 -C 4 -alkynyl and C 1 -C 4 -haloalkyl; wherein R a is independently at each occurrence selected from: H and C 1 -C 4 -alkyl; and R b is independently at each occurrence selected from: H, and C 1 -C 4 -alkyl, C(O)-C 1 -C 4 -alkyl, S(O) 2 -C 1 -C 4 -alkyl. R 1 is aryl; R 2 is selected from C 1 -C 24 -alkyl, C 3 -C 24 -alkenyl, C3-C24-alkynyl, C 0 -C 4 -alkylene-C 3 -C 7 -cycloalkyl or C 0 -C 4 -alkylene-aryl; R 3 and R 4 are each independently selected from H, C 1 -C 6 -alkyl and C 1 -C 3 -alkylene-R 9 ; or wherein R 3 and R 4 together with the atom to which they are attached form a 3- to 6-membered cycloalkyl or heterocycloalkyl group; R 5 and R 7 are each independently selected from H and C 1 -C 4 -alkyl; R 6 is independently selected from H and C(O)R 10 ; R 8 is independently selected from H, C(O)OR 10 and C(O)R 10 ; R 9 is independently selected from aryl (e.g. phenyl), imidazole, indole, SR a , OR a , CO 2 R a , CO 2 NR a R a , NR a R b and NH(=NH)NH 2 ; R 10 is independently at each occurrence selected from C 1 -C 24 -alkyl, C 3 -C 24 -alkenyl, C3-C24-alkynyl, C 0 -C 4 -alkylene-C 3 -C 7 -cycloalkyl or C 0 -C 4 -alkylene-aryl; wherein any aryl group is phenyl, naphthyl or tetrahydronaphthyl and wherein any phenyl, alkyl, alkyne, alkene, alkylene, cycloalkyl, naphthyl or tetrahydronaphthyl group is optionally substituted with from 1 to 4 substituents selected from: halo, nitro, cyano, NR a R a , NR a S(O) 2 R a , NR a C(O)R a , NR a CONR a R a , NR a CO 2 R a , OR a ; SR a , SOR a , SO 3 R a , SO 2 R a , SO 2 NR a R a , CO 2 R a C(O)R a , CONR a R a , CR a R a NR a R a , C 1 -C 4 -alkyl, C 2 -C 4 -alkenyl, C 2 -C 4 -alkynyl and C 1 -C 4 -haloalkyl; wherein R a is independently at each occurrence selected from: H and C 1 -C 4 -alkyl; and R b is independently at each occurrence selected from: H, and C 1 -C 4 -alkyl, C(O)-C 1 -C 4 -alkyl, S(O) 2 -C 1 -C 4 -alkyl. <EOS>