Polycyclic acid compounds useful as CRTH2 antagonists and antiallergic agents

A compound represented by the formula (I):

• is a ring represented by the formula (i)
• X1 is —N═;
• ---- is single bond or double bond;
• Y1 and Y2 are each C1-C6 alkylene or C2-C6 alknylene,
• wherein each methylene unit may be replaced with —O—, —NH—,
• —N(CH3)—, —NHC(═O)—, —N{C(═O)CH3}—, —S—, —S(═O)—, —S(═O)2—, phenylene, pyridinediyl, oxazolediyl, imidazolidiyl or C3-C10 cycloalkylene;
• E1 is phenyl which may be substituted with one or more
• substituents R1;
• E2 is phenyl or xanthenyl,
• each of which may be substituted with one or more substituents R2;
• E3 is a ring selected from the group consisting of
• (a),(b),(c),(d) and (e),
• each of which may be substituted with one or more substituents represented by R3;
• wherein
• R1 is halogen, —CH3 or —OCH3;
• R2 is R1, phenyl, naphthyl, —O-phenyl, thienyl or quinolyl,
• each of which may be substituted with one or more substituents R1;
• R3 is halogen or —CH3;
• R4 is —H, C1-C6 alkyl or alkali metal;
• R5 is —H or halogen;
• and
• n is 1;
• or a pharmaceutically acceptable salt thereof.