Image Based Question – 73797

III produce an enzyme that blocks the action of beta lactam antibiotics in periplasmic space. Which arrow in the structural diagram of Penicillin G denotes the site of action of this enzyme?

A. A

B. B

C. C

D. D

Correct Answer » B Explanation

Ans: B. B

(Ref: Goodman p1478; Katzung 13/e p770, KDT p /6, 6/c p694)

Beta-lactam:

• An amide bond.
• Found in Penicillin G structure is represented by ‘B’.

Beta lactam ring:

• Fused to five-membered thiazolidine ring.
• Fusion causes β-lactam ring to be more reactive (than monocyclic β-lactams).
• Two fused rings distort β -lactam amide bond à Removes resonance stabilization normally found in these chemical bonds.