Disclosed are 6-amido-3-substituted-amino-1-azabicyclo[3.2.0]hept-2-en-7-one-2-carboxylic acids (I): ##STR1## wherein R.sup.1 is hydrogen or acyl; and R' and R" are independently selected from the group consisting of: hydrogen, substituted and unsubstituted: alkyl and aralkyl, or together form a substituted or unsubstituted cyclic group. Such compounds and their pharmaceutically acceptable salt, ester and amide derivatives are useful as antibiotics. Also disclosed are processes for the preparation of such compounds, pharmaceutical compositions comprising such compounds and methods of treatment comprising administering such compounds and compositions when an antibiotic effect is indicated.