Unit 5- Drug Discovery
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What are antibiotics?
Compounds produced by bacteria & fungi that ca kill or inhibit competing microbial species.
What type of bacteria are cephalosporin effective against?
Some penicillin-resistant bacteria.
What is the target of penicillins & cephalosporins in bacteria?
The bacterial cell wall, specifically the peptidoglycan structure.
How do penicillins & cephalosporins kill bacteria?
They act as suicide inhibitors of the enzyme transpeptidase, preventing peptidoglycan maturation.
Why are penicillins & cephalosporins selectively toxic to bacteria?
Mammalian cells lack the peptidoglycan structure & transpeptidase enzyme found in bacteria cell walls.
What is peptidoglycan, & why is it important for bacteria?
A strong, skeleton-like structure of amino acids & sugars that support the bacterial cell wall.
Why is B-lactase ring in penicillin essential?
Provides structural strain needed for antibacterial activity.
What is the importance of the free carboxylate group in penicillins?
Crucial for the drug’s antibacterial efficiency.
What is the role of the bicyclic system in penicillins?
Confers strain on the B-lactam ring, which is important for activity.
How are semisynthetic penicillins manufactured?
Using 6-amainopenicillanic acid (6-APA) produced by bacterial fermentation, with side chains added via amide synthesis.
Why are natural penicillins unstable in acid?
The side chain amide assists in acid-catalysed cleavage of the B-lactam ring.
How was the issue of acid instability in penicillins solved?
By adding an electron-withdrawing group to the “R” side chain to reduce amide electron donation.
What are B-lactamase, & how do they cause resistance?
These are mutated transpeptidase that cleave the B-lactam ring, inactivating penicillin.
How do penicillins counteract transpeptidase enzymes?
Penicillins act as suicide inhibitors, forming a covalent bond to permanently inactivate the enzyme.
What strategy is used to counter B-lactamase resistance?
Adding bulking groups to penicillins to block access to B-lactamase active sites while retaining activity against transpeptidase.
Why are G-ve bacteria harder to treat than G+ve bacteria.
G-ve bacteria have an additional outer membrane that acts as a permeability barrier.
What are porins, & how are they relevant to drug action?
Porins are protein structures in G-ve bacteria’s outer membrane that allow drug entry but impose structural constraints.
How can G-ve activity of penicillins be enhanced?
By attaching hydrophilic groups (e.g. NH2, OH, CO2H) to the a-carbon of the side chain carbonyl group.
What are broad-spectrum penicillins?
Penicillins which are active against both G+ve & G-ve bacteria.