In the first scheme you can see four representative examples of the main types of the §-lactam antibiotics. With the exeption of carbapenems, all of them bear on acylamido side chain, responsible for the antibacterial spectrum. In additon, cephalosprins have different substituents at C-3. The free carboxyl at C-3(4) is also necessary for the antibacterial activity:
The §-lactamase enzyme inhibitors have no amide side chain, and the ring sulphur may be in the oxidized sulphoxide or sulphone form, or can be replaced by oxygen, as in the natural clavulanic acid. The C-2 position in penicillins or cephalosporins may be substituted:
Among cephalosporin sulphones several HLE inhibitors can be found, synthetized mostly by the Merck and Pharmacia-Farmitalia researchers. Different 2-substituents and bulky ester or amide groups instead of the 4-carboxyl function may enhance HLE inhibitory activity:
