| abstract |
1. A compound of the formula: n<CHEM>nwherein R<1> is lower alkyl, lower alkanoyl, aryl, ar(lower)alkyl or a heterocyclic group, each of which may have suitable substituent(s),nR<2> is carboxy or protected carboxy,nR<3> is hydrogen, halogen, hydroxy, lower alkoxy, acyloxy, lower alkylthio, lower alkenyl, lower alkenylthio, lower alkynyl, heterocyclicthio or a heterocyclic group, in which lower alkylthio, lower alkenyl, lower alkenylthio, heterocylicthio and a heterocyclic group may have suitable substituent(s),nR<4> and R<5> are each hydrogen, halogen or arylthio,nA is lower alkylene, andnn is an integer of 0 or 1,nand a pharmaceutically acceptable salt thereof,nprocesses for preparation thereof and pharmaceutical composition comprising the same. |