Beta-lactam biosynthesis: Which precursor feeds are used to produce the side chain of Penicillin G in industrial fermentation?

Introduction / Context:
In industrial beta-lactam production, the side chain of penicillins can be directed by adding precursor molecules to the fermentation. Matching the correct precursor to the desired penicillin is essential for product specificity.

Given Data / Assumptions:

• Penicillin G is benzylpenicillin.
• The benzyl side chain is derived from an aromatic acid precursor.
• Different precursors yield different penicillins (e.g., V vs. G).

Concept / Approach:
For Penicillin G, the side chain is benzyl (phenylmethyl). Feeding phenylacetic acid to Penicillium fermentation directs acyltransfer to form benzylpenicillin. In contrast, feeding phenoxyacetic acid leads to Penicillin V (phenoxymethylpenicillin).

Step-by-Step Solution:

Verification / Alternative check:
Process manuals for penicillin fermentation describe precursor feeding strategies to direct side-chain composition, including phenylacetic acid for G.

Why Other Options Are Wrong:

• Phenoxy acetic acid: used for Penicillin V, not G.
• Hydroxy phenyl acetic acid: not the standard industrial precursor for Penicillin G.
• None of these: incorrect because phenylacetic acid is correct.

Common Pitfalls:
Confusing “phenyl” and “phenoxy” leads to mixing up G and V variants.

Final Answer:
Phenyl acetic acid