Provided are a compound represented by general formula (I), or the pharmaceutically acceptable salt thereof, (wherein R a represents a hydrogen atom or the like, R 1 and R 2 may be the same or different, and each represents a hydrogen atom, optionally substituted lower alkyl or cycloalkyl, or R 1 and R 2 are combined together with the adjacent nitrogen atom thereto to form nitrogen-containing heterocyclic group, and Z represents a bicyclic heterocyclic group in which optionally substituted two six-membered rings are fused to each other, or the like) and the like.
