A compound of the formula :
wherein R1 is amino or a protected amino,
R2 is lower alkyl, carboxy (lower) alkyl, protected carboxy (lower) alkyl or cycloalkyl, and
R3 is carboxy or a protected carboxy,
and pharmaceutically acceptable salts thereof, processes for preparation thereof and pharmaceutical compositions containing them in association with a pharmaceutically acceptable, substantially non-toxic carrier or excipient.
式中的化合物:
其中 R1 是
氨基或受保护的
氨基、
R2 是低级烷基、羧基(低级)烷基、受保护的羧基(低级)烷基或环烷基,以及
R3 是羧基或受保护的羧基、
及其药学上可接受的盐、其制备工艺以及含有它们与药学上可接受的、基本上无毒的载体或赋形剂的药物组合物。