Provided are a compound represented by Formula (I): wherein R 1 , R 2 , R 3 , and R 4 are each independently selected from a hydrogen atom, a C 1-6 alkyl group which may be substituted, a C 7-14 aralkyl group which may be substituted and -C(=O)Rx； n denotes an integer selected from 1 and 2； and ring Ar is selected from the groups represented by the following Formula (a) to (f). , or a prodrug thereof or a pharmaceutically acceptable salt thereof as well as a pharmaceutical agent and a pharmaceutical composition containing such a compound or a prodrug thereof, or a pharmaceutically acceptable salt thereof.
