Carboxylic acid derivative and salt thereof

The present invention provides a novel carboxylic acid compound, a salt thereof or a hydrate of them useful as an insulin sensitizer, and a medicament comprising the compound as an active ingredient. That is, the present invention provides a carboxylic acid compound represented by the following formula, a salt thereof, an ester thereof or a hydrate of them. Wherein R represents a hydrogen atom, hydroxyl group, halogen, carboxyl group, or a C1-6 alkyl group etc., each of which may have one or more substituents; L represents a single bond, or a C1-6 alkylene group, a C2-6 alkenylene group or a C2-6 alkynylene group, each of which may have one or more substituents; M represents a single bond, or a C1-6 alkylene group, a C2-6 alkenylene group or a C2-6 alkynylene group, each of which may have one or more substituents; T represents a single bond, or a C1-3 alkylene group, a C2-3 alkenylene group or a C2-3 alkynylene group, each of which may have one or more substituents; W represents a carboxyl group; represents a single bond etc.; X represents a single bond, oxygen atom, a group represented by -NRCQ O- (wherein Q represents an oxygen atom or sulfur atom; and R represents a hydrogen atom, formyl group, or a C1-6 alkyl group etc., each of which may have one or more substituents), -OCQ NR- (wherein Q and R are as defined above), -CQ NRO- (wherein Q and R are as defined above), ONRCQ - (wherein Q and R are as defined above), -Q SO2- (wherein Q is an oxygen atom or -NR- (wherein R represents a hydrogen atom, formyl group, or a C1-6 alkyl group etc., each of which may have one or more substituents)) or -SO2Q - (wherein Q is as defined above), (wherein, provided that R and R, and/or R and R may together form a ring, Q and Q are the same as or different from each other and each represents an oxygen atom, (O)S(O) or NR