[PSCI-08] Medicinal Chemistry II: Structure–Activity Relationships (SAR) of Major Therapeutic Classes

PSCI-08 • 3. Pharmaceutical Chemistry

Learning Objectives

Analyze the SAR of β-lactam antibiotics (Penicillins, Cephalosporins, Carbapenems), Fluoroquinolones, Tetracyclines, and Sulfonamides.; Map the SAR of 1,4-Dihydropyridines ([3.1] Amlodipine, [3.2] Nifedipine), ACE inhibitors, Statins ([3.34] Atorvastatin, [3.35] Rosuvastatin), and Benzodiazepines ([11.1] Diazepam, [11.2] Lorazepam).; Relate heterocyclic ring nuclei (Quinoline, Indole, Imidazole, Triazole, Phenothiazine, Benzimidazole) to canonical drugs.

Chapter Overview & Core Explanation

Structure–Activity Relationships (SAR) reveal which exact atoms on a drug's skeleton are essential for binding its target ('pharmacophore') and which side chains can be modified to prevent stomach acid destruction, resist bacterial enzymes, or extend half-life.

Key Exam & Clinical Takeaways

• In Fluoroquinolones ([8.33] Ciprofloxacin, [8.34] Levofloxacin), the 3-carboxyl (-COOH) and 4-carbonyl (=O) groups chelate divalent cations (Ca2+, Mg2+, Al3+, Fe2+, Zn2+), explaining why antacids ([5.9]), iron ([10.6]), and calcium ([10.9]) reduce oral fluoroquinolone absorption by >70%.
• [11.2] Lorazepam possesses a free C3-OH group and undergoes direct glucuronidation (LOT drugs: Lorazepam, Oxazepam, Temazepam), avoiding active metabolites in hepatic impairment.

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