A compound of formula (I): ** Formula ** in which R1 represents hydrogen, (C1-C4) alkyl, (C1-C4) alkoxy, (C1-C4) fluoroalkyl, (C1-C4) alkylsulfonyl, halogen or cyano； R2 represents hydrogen or halogen； one of R3, R4 and R5 represents carboxy-(C1-C3) alkyl, carboxy-cyclopropyl or carboxy-alkoxy (C1-C3) and the other two independently represent hydrogen, (C1-C4) alkoxy or halogen； R6 represents hydrogen, (C1-C4) alkoxy or halogen； R7 represents hydrogen, (C1-C4) alkyl, (C1-C4) alkoxy, (C3-C6) cycloalkylmethoxy, (C3-C6) cycloalkyloxy, methoxyethoxy, di- (C1-C2) alkyl - amino, fluoroalkyl (C1-C4), fluoroalkoxy (C1-C4), halogen or alkylsulfonyl (C1-C4)； or R6 and R7 together represent methylenedioxy or ethylenedioxy； R8 represents: - (C2-C5) alkyl； - (C1-C5) alkyl which is mono- or di-substituted where the substituents are independently selected from the group consisting of hydroxy, (C1-C4) alkoxy, oxo, -NR9R10, cycloalkyl (C3-C6) in which the (C3-C6) cycloalkyl groups are unsubstituted or mono-substituted with (C1-C4) alkyl, (C1-C4) alkoxy, hydroxyl or phenyl which is unsubstituted or mono-substituted with halogen, and in which a cycloalkyl group which contains four, five or six carbon atoms may be optionally bound to a benzene ring or a pyridine ring, in which the benzene ring is optionally mono-substituted with methoxy； aryl in which the term "aryl" means a phenyl group or a naphthyl group groups that are independently unsubstituted, mono-, di- or tri-substituted, in which the substituents are independently selected from the group consisting of halogen, alkyl (C1-C4), (C1-C4) alkoxy fluoroalkyl (C1-C4) and fluoroalkoxy (C1-C4)； heteroaryl in which the term "heteroaryl" means a 5- to 10-membered monocyclic or bicyclic aromatic ring containing 1, 2, 3 or 4 heteroatoms independently selected from oxygen, nitrogen and sulfur and in which the heteroaryl groups are independently unsubstituted , mono-, di- or tri-substituted, in which the substituents are independently selec
