A compound represented by the following formula (1): (wherein the carbon atom denoted by * is in the R-configuration R 1 and R 2 are each independently a hydrogen atom, a halogen atom, an amino group, a hydroxyl group, a hydroxyamino group, a nitro group, a cyano group, a sulfamoyl group, a C 1 -C 6 alkyl group, a C 1 -C 6 alkoxy group, a C 1 -C 6 alkylsulfanyl group, a C 1 -C 6 alkylsulfinyl group or a C 1 -C 6 alkylsulfonyl group andA is a substituted or unsubstituted heteroaryl group), or a pharmaceutically acceptable salt thereof.
