Patent ID: 6911468

Claim:
A compound of the formula: wherein X 1 and X 2 are; one of R 1 and R 2 is a C 6-14 aryl group having substituent(s) selected from 1) an optionally substituted carboxy-C 1-6 alkoxy group and 2) an optionally substituted carboxy-C 1-6 aliphatic hydrocarbon group, wherein the C 6-14 aryl group optionally has additional substituent(s), and the other is an optionally substituted C 6-14 group or a hydrogen atom; and R 3 , R 4 and R 5 are the same or different and each is a hydrogen atom or a substituent, or R 4 may link together with R 3 or R 5 to form an optionally substituted ring; provided that when R 3 is a hydrogen atom, R 4 is a hydrogen atom and R 5 is methyl, X 2 —R 2 is not 4-cyclohexylphenyl; when R 3 is 4-metboxyphenyl, R 4 is a hydrogen atom and R 5 is methyl, X 2 —R 2 is not 4-methoxyphenyl; or a salt thereof.