You are given four drug candidates for development: (A) a fungal metabolite that disrupts bacterial peptidoglycan synthesis, (B) a synthetic compound that inhibits a viral protease, (C) a soil actinomycete product that binds ergosterol, and (D) a synthetic compound that inhibits mammalian mitochondrial ribosomes more than bacterial ones. Rank them from best to worst candidates for safe antimicrobial therapy, and justify your synthesis based on selective toxicity.

• A. All are equally good because origin and molecular target do not affect safety or efficacy once a compound is purified to pharmaceutical standards
• B. Best to worst: A (high bacterial selectivity), B (viral protease inhibitor with good selectivity), C (binds ergosterol — effective antifungal but risk depends on host sterol similarity), D (poor candidate because it preferentially harms mammalian mitochondria and would have high host toxicity); this ranking weighs target uniqueness and host similarity
• C. Best to worst: D, C, B, A because any compound affecting mitochondria is preferable for therapy, and natural products are always less desirable than synthetics
• D. B, D, C, A because viral protease inhibitors always cure bacterial infections as well, followed by mitochondrial inhibitors which are broad-spectrum agents

Answer: (B)