A-level Chemistry/OCR (Salters)/Penicillins

The penicillin nucleus The pharmacophore (part of a molecule that confers pharmacological activity) of penicillins is called the penicillin nucleus. It contains a β-lactam ring. The β-lactam ring The penicillin nucleus found in all penicillins contains a so-called β-lactam ring. This is a four-membered cyclic amide that is unstable in acidic or alkaline conditions. The small ring is under a great deal of strain, making the normally unreactive amide group more susceptible to hydrolysis, resulting in ring-opening to form open-chain compounds. β-lactamase inhibitors β-Lactamase is an enzyme produced by certain penicillin-resistant bacteria. It inactivates penicillin antibiotics by disrupting their β-lactam ring. Once way to protect penicillins against β-lactamase is to modify their side chains − methicillin and flucloxacillin are examples of penicillins whose side chains make them β-lactamase resistant. Another tactic is to protect vulnerable penicillins with a β-lactamase inhibitor. These compounds, such as clavulanic acid, are not antibiotics, but they allow penicillin antibiotics to do their job by inhibiting β-lactamase. Table of penicillins NameR group in side-chainNatural/semi-syntheticUses/propertiesSkeletal formula3D modelbenzylpenicillinpenicillin Gnaturalgeneral infections, gonorrhoea and syphilis200px200pxflucloxacillinsemi-syntheticcontrolling resistant Staphylococcus200px200pxpenicillin Fnaturalnot used commercially200pxpenicillin Xnaturalnot used commercially200pxpenicillin Knaturalnot used commercially200pxpenicillin Vnatural and semi-syntheticgeneral infections, ear, nose and throat200pxmethicillinsemi-syntheticcontrolling resistant Staphylococcus200pxampicillinsemi-syntheticlung and wound infections200pxamoxycillinsemi-syntheticlung and urinary tract infections200px200pxcarbenicillinsemi-syntheticpneumonia, burns200px