A compound of formula or a pharmaceutically acceptable ester, amide, solvate or salt thereof, including a salt of such an ester or amide, and a solvate of such an ester, amide or salt, wherein G represents one of the groups: R 1 is selected from the group consisting of halogen, cyano, nitro, OR A, N(R B) 2, -C C 1-4 alkyl, -SO 2 C 1-4 alkyl, C 1-6 alkyl, C 2-6 alkenyl, C 2-6 alkynyl, haloC 1-6 alkyl, dihaloC 1-6 alkyl, trihaloC 1-6 alkyl, haloC 2-6 alkenyl, dihaloC 2-6 alkenyl, trihaloC 2-6 alkenyl, cyanoC 1-6 alkyl, C 1-4 alkoxyC 1-6 alkyl, C 3-8 cycloalkyl, C 3-8 cycloalkylC 1-6 alkyl, phenyl, benzyl, and 5-10 membered heterocyclyl, wherein said benzyl or heterocyclyl group is either unsubstituted or said phenyl, benzyl or heterocyclyl group is substituted with from 1 to 3 substituents, each substituent being independently selected from the group consisting of OR A, N(R B) 2, halogen, cyano, nitro, -C C 1-4 alkyl, C 1-6 alkyl, C 2-6 alkenyl, C 2-6 alkynyl, haloC 1-6 alkyl, dihaloC 1-6 alkyl and trihaloC 1-6 alkyl; R 2 is selected from the group consisting of -CH=N-OH and -C(NH 2)=N-OH; R 3 is selected from the group consisting of hydrogen, halogen, C 1-6 alkyl, C 2-6 alkenyl, C 2-6 alkynyl, C 3-8 cycloalkyl, C 3-8 cycloalkylC 1-6 alkyl; haloC 1-6 alkyl, dihaloC 1-6 alkyl, trihaloC 1-6 alkyl, phenyl, benzyl and 5-10 membered heterocyclyl wherein said benzyl or heterocyclyl group is either unsubstituted or said said phenyl, benzyl or heterocyclyl group is substituted with from 1 to 3 substituents each substituent being independently selected from the group consisting of OR A, halogen, cyano, nitro, C 1-6 alkyl, C 2-6 alkenyl, C 2-6 alkynyl, haloC 1-6 alkyl, dihaloC 1-6 alkyl and trihaloC 1-6 alkyl; and wherein only one of R 1 and R 3 may simultaneously be a substituted or unsubstituted phenyl; each of R 4, R 5, R 6 and R 7 is independently selected from the group consisting of hydrogen, OR A, halogen, cyano, nitro, C 1-6 alkyl, C 2-6 alkenyl, C 2-6 alkynyl, haloC 1-6 alkyl, dihaloC 1-6 alkyl and trihaloC 1-6 alkyl; each R A is independently selected from the group consisting of hydrogen, C 1-6 alkyl, C 2-6 alkenyl, C 2-6 alkynyl, C 3-8 cycloalkyl, C 3-8 cycloalkylC 1-6 alkyl, phenyl, benzyl and 5-10 membered heterocyclyl, each optionally substituted by from 1 to 3 halogen atoms; and each R B is independently selected from the group consisting of hydrogen, C 1-6 alkyl, C 2-6 alkenyl, C 2-6 alkynyl, C 3-8 cycloalkyl, C 3-8 cycloalkylC 1-6 alkyl, phenyl, benzyl and 5-10 membered heterocyclyl, each optionally substituted by from 1 to 3 halogen atoms. R 1 is selected from the group consisting of halogen, cyano, nitro, OR A, N(R B) 2, -C C 1-4 alkyl, -SO 2 C 1-4 alkyl, C 1-6 alkyl, C 2-6 alkenyl, C 2-6 alkynyl, haloC 1-6 alkyl, dihaloC 1-6 alkyl, trihaloC 1-6 alkyl, haloC 2-6 alkenyl, dihaloC 2-6 alkenyl, trihaloC 2-6 alkenyl, cyanoC 1-6 alkyl, C 1-4 alkoxyC 1-6 alkyl, C 3-8 cycloalkyl, C 3-8 cycloalkylC 1-6 alkyl, phenyl, benzyl, and 5-10 membered heterocyclyl, wherein said benzyl or heterocyclyl group is either unsubstituted or said phenyl, benzyl or heterocyclyl group is substituted with from 1 to 3 substituents, each substituent being independently selected from the group consisting of OR A, N(R B) 2, halogen, cyano, nitro, -C C 1-4 alkyl, C 1-6 alkyl, C 2-6 alkenyl, C 2-6 alkynyl, haloC 1-6 alkyl, dihaloC 1-6 alkyl and trihaloC 1-6 alkyl; R 2 is selected from the group consisting of -CH=N-OH and -C(NH 2)=N-OH; R 3 is selected from the group consisting of hydrogen, halogen, C 1-6 alkyl, C 2-6 alkenyl, C 2-6 alkynyl, C 3-8 cycloalkyl, C 3-8 cycloalkylC 1-6 alkyl; haloC 1-6 alkyl, dihaloC 1-6 alkyl, trihaloC 1-6 alkyl, phenyl, benzyl and 5-10 membered heterocyclyl wherein said benzyl or heterocyclyl group is either unsubstituted or said said phenyl, benzyl or heterocyclyl group is substituted with from 1 to 3 substituents each substituent being independently selected from the group consisting of OR A, halogen, cyano, nitro, C 1-6 alkyl, C 2-6 alkenyl, C 2-6 alkynyl, haloC 1-6 alkyl, dihaloC 1-6 alkyl and trihaloC 1-6 alkyl; and wherein only one of R 1 and R 3 may simultaneously be a substituted or unsubstituted phenyl; each of R 4, R 5, R 6 and R 7 is independently selected from the group consisting of hydrogen, OR A, halogen, cyano, nitro, C 1-6 alkyl, C 2-6 alkenyl, C 2-6 alkynyl, haloC 1-6 alkyl, dihaloC 1-6 alkyl and trihaloC 1-6 alkyl; each R A is independently selected from the group consisting of hydrogen, C 1-6 alkyl, C 2-6 alkenyl, C 2-6 alkynyl, C 3-8 cycloalkyl, C 3-8 cycloalkylC 1-6 alkyl, phenyl, benzyl and 5-10 membered heterocyclyl, each optionally substituted by from 1 to 3 halogen atoms; and each R B is independently selected from the group consisting of hydrogen, C 1-6 alkyl, C 2-6 alkenyl, C 2-6 alkynyl, C 3-8 cycloalkyl, C 3-8 cycloalkylC 1-6 alkyl, phenyl, benzyl and 5-10 membered heterocyclyl, each optionally substituted by from 1 to 3 halogen atoms.