Question

Which antibiotic undergoes light catalysed autoxidation:

• A. Polyene antibiotics
• B. Beta lactum antibiotics
• C. Sugar derived antibiotics
• D. Macrolide antibiotics

Hint:

Polyene antibiotics, like amphotericin B, are sensitive to light and oxygen, which can cause autoxidation. Always store them in dark conditions to preserve their efficacy.

Answer 1

The Correct Option is A

Polyene antibiotics undergo light-catalysed autoxidation, a process where exposure to light accelerates the oxidation of the antibiotic. This leads to the breakdown of the polyene structure, rendering the antibiotic less effective. This is a significant consideration in the storage and handling of such antibiotics.

Answer 2

The question asks which class of antibiotics degrades through light catalysed autoxidation. Let's look at the chemical structure of each class to see which one is prone to this kind of breakdown.

1. Polyene antibiotics: These drugs, such as amphotericin B and nystatin, carry a long chain of conjugated carbon-carbon double bonds in their structure. A conjugated system like this absorbs light easily, and the absorbed energy can trigger a reaction with atmospheric oxygen. This oxygen attack breaks the conjugated chain apart, so the drug loses potency when left in light. This is exactly what light catalysed autoxidation means, so this class fits the question.
2. Beta lactum antibiotics: Penicillins and cephalosporins carry a strained four-membered beta lactam ring. This ring opens up through hydrolysis when it comes into contact with moisture or the wrong pH, not through exposure to light. Their main stability problem is water, so this option does not match.
3. Sugar derived antibiotics: Aminoglycosides such as streptomycin are built from amino sugar units joined by glycosidic bonds. These bonds break down mainly through acid or base catalysed hydrolysis. There is no extended conjugated system here to absorb light, so autoxidation is not their typical degradation route.
4. Macrolide antibiotics: Drugs like erythromycin have a large lactone ring with sugar substituents. Their biggest stability concern is acid catalysed hydrolysis of the lactone ring and the glycosidic bonds, which is why they are often given as enteric coated tablets. Light is not the main factor that breaks them down.

Only the polyene class carries the conjugated double bond system that reacts with light and oxygen together, so this is the antibiotic class that undergoes light catalysed autoxidation.

Therefore, the correct answer is Polyene antibiotics.