It is intended to provide a novel compound that has an excellent ³-secretase inhibitory effect and specifically inhibits A² production. The present invention provides a compound of the following formula (1) or a pharmaceutically acceptable salt thereof: wherein R 1 represents a linear or branched alkyl group having 1 to 4 carbon atoms or a phenyl group； R 2 represents a linear or branched alkyl group having 1 to 4 carbon atoms which may be substituted by one or more phenyl or halogenophenyl groups； R 3 represents a linear or branched alkyl group having 1 to 4 carbon atoms which may be substituted by one or more hydroxyl groups； R 4 represents a linear or branched alkyl group having 1 to 4 carbon atoms； and the symbol "*" represents a chiral center.
