2-phenylthiophene derivative

A compound represented by the following general formula (I) or a salt thereof:

• wherein the symbols have the following meanings:
• R1:
• —CO2H, —CO2-lower alkyl, or a tetrazolyl group,
• R2:
• H, halogen, lower alkyl, or —O-lower alkyl,
• R3:
• H, lower alkyl, or halogen,
• R4:
• —CN, —NO2, —Br, halogeno-lower alkyl, or —(CO)-lower alkyl,
• R5:
• H, lower alkyl, —O-lower alkyl, halogen, —NO2, or —CN,
• X:
• —O—, —N(R7)—, or —S—,
• wherein the group represented by R4 is bonded to the phenyl group at the meta- or para- position relative to the thienyl group and the group represented by —X—R6 is bonded to the phenyl group at the meta- or para- position relative to the thienyl group,
• R7:
• H or lower alkyl,
• R6:
• linear or branched alkyl having 1 to 8 carbon atoms, linear or branched alkenyl having 3 to 8 carbon atoms, —Y-(cycloalkyl which may contain an oxygen atom), —Y-phenyl, or —Y-heteroaryl,
• where the linear or branched alkyl having 1 to 8 carbon atoms, linear or branched alkenyl having 3 to 8 carbon atoms, cycloalkyl which may contain an oxygen atom, phenyl, and heteroaryl may be substituted with a group selected from the group consisting of hydroxy, —CN, —O-lower alkyl, —S-lower alkyl, —NR9(R9), and —(CO)NR9(R9),
• Y:
• a bond, lower alkylene, or lower alkenylene,
• R8 and R9:
• the same or different from each other, H or lower alkyl,
• where, when X is a group represented by —N(R7)—, R7 and R6 may be combined together with the nitrogen atom to form a nitrogen-containing saturated heterocycle and the nitrogen-containing saturated heterocycle may be substituted with an lower alkyl.