History of penicillins: The first penicillin isolated by Alexander Fleming, known as penicillin F, is also called what?

Introduction / Context:
Early penicillins were differentiated by the acyl side chain attached to the 6-aminopenicillanic acid nucleus. Historical nomenclature (Penicillin F, G, V, etc.) reflects distinct side chains and discovery chronology.

Given Data / Assumptions:

• We must match “penicillin F” to its side chain name.
• Common penicillins: G (benzyl), V (phenoxymethyl); others (K, F) have different alkyl/alkenyl side chains.

Concept / Approach:
Penicillin F corresponds to an n-heptyl side chain. In contrast, penicillin G is benzyl penicillin and penicillin V is phenoxymethyl penicillin; 2-pentenyl penicillin aligns with other labeled variants (e.g., K), not F.

Step-by-Step Solution:
Recall mapping: F → n-heptyl; G → benzyl; V → phenoxymethyl. Eliminate distractors that match G or V. Choose n-heptyl penicillin.

Verification / Alternative check:
Reference tables of early penicillins list Penicillin F as n-heptyl based on side-chain analysis.

Why Other Options Are Wrong:

• 2-Pentenyl: not Penicillin F.
• Phenoxymethyl: Penicillin V.
• Benzyl: Penicillin G.

Common Pitfalls:
Assuming alphabetical letters map to common clinical penicillins only (G or V) and overlooking historic variants.

Final Answer:
n-heptyl penicillin