b - Lactam ring is present in: (A) Erythromycin, (B) Penicillin, (C) Tetracyclins, (D) Chloramphenicol
Answer is B. All penicillins have the basic structure. A thiazolidine ring (A) is attached to a b-lactam ring (B) that carries a secondary amino group (RNH-).Reference: Katzung&;s Pharmacology; 13th edition; Chapter 43; Beta-Lactam & Other Cell Wall- & Membrane-Active Antibiotics