A compound of the formula: wherein R1 is amino or protected amino; R2 is hydrogen, lower alkyl or hydroxy protective group; R3 is carboxy or protected carboxy; R4 is an unsubstituted 5, 6 or 7-membered heteromonocyclic group containing two nitrogen atoms as heteroatoms, and which optionally further contains one oxygen or sulfur atom; or R4 is said 5, 6 or 7-membered heteromonocyclic group substituted by 1 to 4 groups selected from the group consisting of lower alkyl, lower alkoxy, lower alkylthio, lower alkylamino, cyclo(lower)alkyl, cyclo(lower)alkenyl, halogen, amino, protected amino, protected hydroxy, cyano, nitro, carboxy, hydroxy(lower)alkyl, amino(lower)alkyl, and carbamoyloxy; and n is 1 or 2.