| abstract |
A compound of the following formula: wherein, R1 is hydrogen, fluorine, cyano, trifluoromethyl or methoxy; R2 is hydrogen, fluorine or trifluoromethyl; R3 is hydrogen or chlorine, as long as at least one of R2 and R3 is hydrogen; R4 is chlorine, fluorine, cyano, trifluoromethyl, difluoromethoxy, methoxy or trifluoromethoxy; represents a substituted piperazin-1,4-diyl selected from the group consisting of or a pharmaceutically acceptable salt thereof. |