A compound represented by formula (I): ##STR1## wherein R.sup.1 is an organic residue through a carbon atom, R.sup.2 is a carboxyl group which may be esterified or amidated, and X is an oxygen atom, or a sulfur atom which may be oxidized, or a salt thereof, which is useful as antibacterial agent or intermediate for synthesizing the same, and a process for preparing the same.
                            公式(I)所代表的化合物:##STR1## 其中R.sup.1是通过一个碳原子连接的有机残基,R.sup.2是可以酯化或酰胺化的羧基,X是一个氧原子或者可以被氧化的
硫原子,或其盐。该化合物可用作抗菌剂或合成该抗菌剂的中间体,并提供其制备方法。