Patent ID: 7642362

Claim:
A compound represented by the general formula (1): wherein R 1 , R 2 , R 3 and R 4 represent one of the following [I] to [IX]: [I] R 1 represents a hydrogen atom or a carboxyl group, R 2 represents a hydrogen atom or a hydroxyl group, and R 3 and R 4 are joined to form a divalent group of the formula (2): wherein R 5 represents a hydrogen atom or a carboxyl group and R 6 represents a hydrogen atom or a hydroxyl group; [II] R 1 represents a hydrogen atom or a carboxyl group, R 2 represents a hydrogen atom or a hydroxyl group, and R 3 and R 4 are joined to form a divalent group of the formula (3): wherein R 5 and R 6 have the same meanings as above; [III] R 1 represents a hydrogen atom or a carboxyl group, represents a hydrogen atom or a hydroxyl group, and R 3 and R 4 are joined to form a divalent group of the formula (4): wherein R 5 and R 6 have the same meanings as above; [IV] R 1 represents a hydrogen atom or a carboxyl group, R 2 represents a hydrogen atom or a hydroxyl group, and R 3 and R 4 are joined to form a divalent group of the formula (5): wherein R 5 and R 6 have the same meanings as above; [V] R 1 represents a hydrogen atom or a carboxyl group, R 2 represents a hydrogen atom or a hydroxyl group, and R 3 represents a hydrogen atom and R 4 represents a group of the formula (6): [VI] R 1 represents a hydrogen atom or a carboxyl group, R 2 represents a hydrogen atom or a hydroxyl group, and R 3 and R 4 are joined to form a divalent group of the formula (7): wherein R 5 and R 6 have the same meanings as above; [VII] R 1 represents a hydrogen atom or a carboxyl group, R 2 represents a hydrogen atom or a hydroxyl group, and R 3 represents a group of the formula (8): wherein R 7 represents a hydrogen atom or a carboxyl group and R 8 represents a hydrogen atom or a hydroxyl group, and R 4 represents a group of the formula (9): wherein R 5 represents a carboxyl group and R 6 has the same meaning as above; [VIII] R 1 represents a carboxyl group, R 2 represents a hydroxyl group, and R 3 and R 4 are joined to form a divalent group of the formula (10): wherein R 5 represents a carboxyl group and R 6 represents a hydroxyl group; [IX] R 1 represents a carboxyl group, R 2 represents a hydroxyl group, and R 3 and R 4 are joined to form a divalent group of the formula (11): or a pharmaceutically acceptable salt thereof.