Tyrosine phosphatase inhibitors

A protein tyrosine phosphatase inhibitor comprising a compound of the formula:

• 17
• wherein X1 and X2 are the same or different and each is a bond or a spacer having 1 to 20 atom(s) in the main chain;
• one of R1a and R2a is a cycle group having substituent(s) selected from 1) an optionally substituted carboxy-C1-6 alkoxy group and 2) an optionally substituted carboxy-C1-6 aliphatic hydrocarbon group, wherein the cycle group optionally has additional substituent(s), and the other is an optionally substituted cycle group or a hydrogen atom;
• and
• R3, R4 and R5 are the same or different and each is a hydrogen atom or a substituent, or R4 may link together with R3 or R5 to form an optionally substituted ring, or a salt thereof.

A prophylactic or therapeutic agent of diabetes comprising a compound of the formula:

• 18
• wherein X1 and X2 are the same or different and each is a bond or a spacer having 1 to 20 atom(s) in the main chain;
• one of R1a and R2a is a cycle group having substituent(s) selected from 1) an optionally substituted carboxy-C1-6 alkoxy group and 2) an optionally substituted carboxy-C1-6 aliphatic hydrocarbon group, wherein the cycle group optionally has additional substituent(s), and the other is an optionally substituted cycle group or a hydrogen atom;
• and
• R3, R4 and R5 are the same or different and each is a hydrogen atom or a substituent, or R4 may link together with R3 or R5 to form an optionally substituted ring, or a salt thereof.

A method for preventing or treating diabetes in a mammal in need thereof, which comprises administering to said mammal an effective amount of a compound of the formula

• 19
• wherein X1 and X2 are the same or different and each is a bond or a spacer having 1 to 20 atom(s) in the main chain;
• one of R1a and R2a is a cycle group having substituent(s) selected from 1) an optionally substituted carboxy-C1-6 alkoxy group and 2) an optionally substituted carboxy-C1-6 aliphatic hydrocarbon group, wherein the cycle group optionally has additional substituent(s), and the other is an optionally substituted cycle group or a hydrogen atom;
• and
• R3, R4 and R5 are the same or different and each is a hydrogen atom or a substituent, or R4 may link together with R3 or R5 to form an optionally substituted ring, or a salt thereof.

Use of a compound of the formula

• 20
• wherein X1 and X2 are the same or different and each is a bond or a spacer having 1 to 20 atom(s) in the main chain;
• one of R1a and R2a is a cycle group having substituent(s) selected from 1) an optionally substituted carboxy-C1-6 alkoxy group and 2) an optionally substituted carboxy-C1-6 aliphatic hydrocarbon group, wherein the cycle group optionally has additional substituent(s), and the other is an optionally substituted cycle group or a hydrogen atom;
• and
• R3, R4 and R5 are the same or different and each is a hydrogen atom or a substituent, or R4 may link together with R3 or R5 to form an optionally substituted ring,
• or a salt thereof, for manufacturing a prophylactic or therapeutic agent for diabetes.