Medicinal chemistry of polyene antibiotics Polyene antifungal antibiotics (for example, amphotericin B, nystatin) are best described structurally as which type of molecules?

Introduction / Context:
Drug class recognition by structure helps predict mechanism and toxicity. Polyene antifungals are a key class whose structural features explain their affinity for ergosterol and characteristic adverse effects.

Given Data / Assumptions:

• Representative drugs: nystatin and amphotericin B.
• Target: ergosterol in fungal membranes.
• Focus: core structural description.

Concept / Approach:
Polyenes are macrocyclic (large ring) lactones with extended chains of conjugated double bonds (polyene). This conjugation aligns hydrophobic segments that insert into membranes and bind ergosterol, facilitating pore formation. The macrolide ring distinguishes them from beta-lactams and simple monocyclic compounds.

Step-by-Step Solution:
Match class name “polyene” with conjugated double bonds.Recall macrocyclic lactone core typical of macrolide-like antifungals.Exclude beta-lactam–thiazolidine fused rings (penicillins) and small rings.Select the macrocyclic polyene description.

Verification / Alternative check:
Chemical structures of amphotericin B and nystatin show a large macrolactone with a polyene chromophore, consistent with the selected option.

Why Other Options Are Wrong:
Beta-lactams describe penicillins/cephalosporins; small rings do not capture polyene character; peptides and steroids do not fit polyene antifungal chemistry.

Common Pitfalls:
Confusing “macrolide antibiotics” (for example, erythromycin) with “polyene macrolides.” Both are macrocycles but target different organisms.

Final Answer:
Large macrocyclic molecules with multiple conjugated double bonds (polyene macrolides).