A compound of Formula (1): ** Formula ** or a pharmaceutically acceptable salt thereof where R1 and R2 are independently selected from the group consisting of a hydrogen atom, a C1-6 alkyl group and a C3- cycloalkyl group 8, R3 and R4 are independently selected from the group consisting of a hydrogen atom and a C1-6 alkyl group, R5 is an optionally substituted C4-7 alkyl group or - (CR8R9) rE, R6, R7, R8 and R9 are independently selected from the group consisting of a hydrogen atom, a fluorine atom and an optionally substituted C1-6 alkyl group, A is an optionally substituted C6-10 aryl group or an optionally substituted 5-10 membered heteroaryl group, r is 1, 2, 3 or 4, E is an optionally substituted C3-8 cycloalkyl group, an optionally substituted C4-8 cycloalkenyl group, an optionally substituted 5-10 membered heterocyclic group comprising 1 to 3 independently selected heteroatoms e between the group consisting of an oxygen atom and a sulfur atom such as a ring constituent atom, an optionally substituted C6-10 aryl group or an optionally substituted 5-10 membered heteroaryl group, L is an oxygen atom, a sulfur atom or -NR10-, n is 1, 2 or 3, R10 is a hydrogen atom, a C1-6 alkyl group or a C3-8 cycloalkyl group, and X is a hydrogen atom, a C1 alkyl group -6 optionally substituted with a fluorine atom or a halogen atom, where the one or more substituents of the "optionally substituted C6-10 aryl group" and "optionally substituted 5-10 membered heteroaryl group" mentioned above are independently selected from the group consisting of a halogen atom, a C1-6 alkyl group optionally substituted with a fluorine atom, a C1-6 alkyloxy group optionally substituted with a fluorine atom, a hydroxy group, a C1-6 alkylthio group, a group C6-10 aryloxy, one gr upo arylthio C6-10, a cyano group, -CO2R11, -SO2R11, -NR10SO2R11, -OSO2R11, -COR12, -SO2NR12R13, -CONR12R13, -NR12R13, -NR10CONR12R13, -NR10COR12, -CR12>；, N (ORCR12) - = (( an oxime group, a C3-8 cycloalkyl group, a C6-1
