β-Lactams with 6α (penicillins) or 7α (cephalosporins) substituents are often β-lactamase inhibitors. This paper assesses the effect of such substituents on acyclic β-lactamase substrates. Thus, a series of m-carboxyphenyl phenaceturates, substituted at the glycyl α- carbon by–OMe,–CH2OH,–CO2−, and–CH2NH3+, have been prepared, and tested for their reactivity against serine β-lactamases. The latter two are novel substituents in β-lactamase ...