Ester compound and medicinal use thereof

A novel therapeutic agent for hyperlipidemia, which is an ester compound represented by the formula (1") (wherein R and R are each hydrogen atom or optionally substituted aryl, etc.; X is -COO- or -CON(R )-; R and R are each hydrogen atom, C1-C6 alkyl or C1-C6 alkoxy, etc.; R , R and R are each hydrogen atom, C1-C6 alkyl or C1-C6 alkoxy, etc.; R and R are each independently hydrogen atom, C1-C6 alkyl, -CON(R )(R ) or -COO(R ), etc.; ring A, ring B and ring C are each independently aryl or heterocycle residue, etc.; Alk and Alk are each independently alkanediyl, etc.; l and m are each an integer of 0 or 1 to 3) or a prodrug thereof, or a pharmaceutically acceptable salt of either. The therapeutic agent selectively inhibits MTP in the small intestine, thus causes no such side effect as a fatty liver.