Abstract: The present invention relates to a compound of the formula [I]: wherein A is lower alkylene or lower alkenylene; R1 is lower alkyl, hydroxy(lower)alkyl, protected hydroxy(lower)alkyl, amino(lower)alkyl or protected amino(lower)alkyl, and R2 is hydrogen or amino protecting group, or R1 and R2 are bonded together and form lower alkylene; R3 and R5 are independently amino or protected amino; and R4 is carboxy or protected carboxy, or a pharmaceutically acceptable salt thereof, a process for preparing a compound of the formula [I], and a pharmaceutical composition comprising a compound of the formula [I] in admixture with a pharmaceutically acceptable carrier.