The present invention provides compounds used as a remedy or a preventive for diseases that are induced by the production, secretion and/or deposition of amyloid β protein. The compounds are compounds represented by formula (I), pharmaceutically acceptable salt thereof, or solvate of the compounds.(In formula(I), R1, R2a, R2b, R3, R4a, R4b, ring A and dash lines are as described in the description.)本發明係提供一種化合物,例如如下所示式(I)之化合物、及其製藥上可容許之鹽或此等之溶劑化物等,作為由類澱粉蛋白β蛋白質之產生、分泌及/或沈積所誘發疾病之治療劑或預防劑:(式中,R1、R2a、R2b、R3、R4a、R4b、環A、及虛線係如說明書所記載)。
