sup.1 of the compound of the formula (I) is a group of the formula: --X--R.sup.1e--C(.dbd.O)OR.sup.1a, more concretely, such a group is a group of the following formula:##STR00012## (in which R.sup.b is a hydrogen atom, an optionally substituted lower alkyl group, an optionally substituted lower alkoxycarbonyl group or a carboxyl group, R.sup.bb is an optionally substituted lower alkoxycarbonyl gr