| 摘要 |
A compound of the formula: <CHEM> wherein R<1> is amino or protected amino, R<2> is carboxy (lower) alkyl or protected carboxy (lower) alkyl, R<3> is halogen or lower alkoxy, and R<4> is carboxy or protected carboxy, and a pharmaceutically acceptable salt thereof, and processes for their preparation and also a pharmaceutically composition comprising, as an effective ingredient, the above compound in association with pharmaceutically acceptable carriers. |
