This invention relates to novel compounds having antimicrobial activity of the formula ##STR1## in which R.sup.1 is amino or a protected amino group, R.sup.2 is cyclo(lower)alkyl, cyclo(lower)alkenyl, lower alkyl, lower alkynyl, carboxy(lower)alkyl, protected carboxy(lower)alkyl or lower alkylthio(lower)alkyl, and Y is hydrogen, amino or a protected amino group, and pharmaceutically acceptable salts thereof.