A compound represented by the following general formula or a salt thereof: wherein X is SO 2 or CO; R 1 is n is 1, 2 or 3; R 2 is a hydrogen atom or an alkyl group having 1 to 3 carbon atoms; R 3 is (i) an aralkenyl group or an aralkyl group, the alkenyl moiety being substituted or unsubstituted and having 2 to 6 carbon atoms, the alkyl moiety being substituted or unsubstituted and having 1 to 6 carbon atoms and the aryl moiety may have one or more substituents selected from the group consisting of a halogen atom, -NH 2, -NO 2, -CN, -OH, a C 1 -C 4 alkyl group, a C 1 -C 4 alkoxy group and -COOR 5 wherein R 5 is a hydrogen atom or a C 1 -C 4 alkyl group, and wherein two adjacent substituents of the aryl moiety may be connected to form a methylenedioxy group or an ethylenedioxy group; (ii) an aryl group or a heteroaryl group, both of which may have one or more substitutents selected from the group consisting of a halogen atom, -NH 2, -NO 2, -CN, -OH, a C 1 -C 4 alkyl group, a C 1 -C 4 alkoxy group and -COOR 5 wherein R 5 is a hydrogen atom or a C 1 -C 4 alkyl group, and wherein two adjacent substituents of the aryl group may be connected to form a methylenedioxy group or an ethylenedioxy group, and wherein if R 1 is formula, R 2 is a hydrogen atom and X is CO, R 3 is not an o-nitrophenyl group; or (iii) a heteroaralkenyl group or a heteroaralkyl group, the alkenyl moiety being substituted or unsubstituted and having 2 to 6 carbon atoms, the alkyl moiety being substituted or unsubstituted and having 1 to 6 carbon atoms and the heteroaryl moiety may have one or more substituents selected from the group consisting of a halogen atom, -NH 2, -NO 2, -CN, -OH, a C 1 -C 4 alkyl group, a C 1 -C 4 alkoxy group and -COOR 5 wherein R 5 is a hydrogen atom or a C 1 -C 4 alkyl group; R 4 is a C 1 -C 4 alkyl group or an aryl group; and when n is 2, the moiety of the formula or may be substituted with a hydroxyl group. wherein X is SO 2 or CO; R 1 is n is 1, 2 or 3; R 2 is a hydrogen atom or an alkyl group having 1 to 3 carbon atoms; R 3 is (i) an aralkenyl group or an aralkyl group, the alkenyl moiety being substituted or unsubstituted and having 2 to 6 carbon atoms, the alkyl moiety being substituted or unsubstituted and having 1 to 6 carbon atoms and the aryl moiety may have one or more substituents selected from the group consisting of a halogen atom, -NH 2, -NO 2, -CN, -OH, a C 1 -C 4 alkyl group, a C 1 -C 4 alkoxy group and -COOR 5 wherein R 5 is a hydrogen atom or a C 1 -C 4 alkyl group, and wherein two adjacent substituents of the aryl moiety may be connected to form a methylenedioxy group or an ethylenedioxy group; (ii) an aryl group or a heteroaryl group, both of which may have one or more substitutents selected from the group consisting of a halogen atom, -NH 2, -NO 2, -CN, -OH, a C 1 -C 4 alkyl group, a C 1 -C 4 alkoxy group and -COOR 5 wherein R 5 is a hydrogen atom or a C 1 -C 4 alkyl group, and wherein two adjacent substituents of the aryl group may be connected to form a methylenedioxy group or an ethylenedioxy group, and wherein if R 1 is formula, R 2 is a hydrogen atom and X is CO, R 3 is not an o-nitrophenyl group; or (iii) a heteroaralkenyl group or a heteroaralkyl group, the alkenyl moiety being substituted or unsubstituted and having 2 to 6 carbon atoms, the alkyl moiety being substituted or unsubstituted and having 1 to 6 carbon atoms and the heteroaryl moiety may have one or more substituents selected from the group consisting of a halogen atom, -NH 2, -NO 2, -CN, -OH, a C 1 -C 4 alkyl group, a C 1 -C 4 alkoxy group and -COOR 5 wherein R 5 is a hydrogen atom or a C 1 -C 4 alkyl group; (i) an aralkenyl group or an aralkyl group, the alkenyl moiety being substituted or unsubstituted and having 2 to 6 carbon atoms, the alkyl moiety being substituted or unsubstituted and having 1 to 6 carbon atoms and the aryl moiety may have one or more substituents selected from the group consisting of a halogen atom, -NH 2, -NO 2, -CN, -OH, a C 1 -C 4 alkyl group, a C 1 -C 4 alkoxy group and -COOR 5 wherein R 5 is a hydrogen atom or a C 1 -C 4 alkyl group, and wherein two adjacent substituents of the aryl moiety may be connected to form a methylenedioxy group or an ethylenedioxy group; (ii) an aryl group or a heteroaryl group, both of which may have one or more substitutents selected from the group consisting of a halogen atom, -NH 2, -NO 2, -CN, -OH, a C 1 -C 4 alkyl group, a C 1 -C 4 alkoxy group and -COOR 5 wherein R 5 is a hydrogen atom or a C 1 -C 4 alkyl group, and wherein two adjacent substituents of the aryl group may be connected to form a methylenedioxy group or an ethylenedioxy group, and wherein if R 1 is formula, R 2 is a hydrogen atom and X is CO, R 3 is not an o-nitrophenyl group; or (iii) a heteroaralkenyl group or a heteroaralkyl group, the alkenyl moiety being substituted or unsubstituted and having 2 to 6 carbon atoms, the alkyl moiety being substituted or unsubstituted and having 1 to 6 carbon atoms and the heteroaryl moiety may have one or more substituents selected from the group consisting of a halogen atom, -NH 2, -NO 2, -CN, -OH, a C 1 -C 4 alkyl group, a C 1 -C 4 alkoxy group and -COOR 5 wherein R 5 is a hydrogen atom or a C 1 -C 4 alkyl group; R 4 is a C 1 -C 4 alkyl group or an aryl group; and when n is 2, the moiety