| 摘要 |
The present invention relates to a compound of the formula [I]: wherein R<1 >is lower alkyl, hydroxy(lower)alkyl or halo(lower)alkyl, and R<2 >is hydrogen or amino protecting group, or R<1 >and R<2 >are bonded together and form lower alkylene or lower alkenylene; R<3 >is hydrogen or lower alkyl; R<4 >is R<5 >is carboxy or protected carboxy; and R<6 >is amino or protected amino, 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.
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