B.Pharm 5th Semester Medicinal Chemistry II – Unit 1 Notes

5th Semester

B.Pharm 5th Semester Medicinal Chemistry II – Unit 1 Notes Antihistaminic drugs (H1, H2 blockers, Proton Pump Inhibitors) and Antineoplastic drugs (Cancer Chemotherapy agents).This unit is very important for university exams, GPAT, and other competitive pharmacy entrance tests.

Here you will get complete classification, SAR (Structure Activity Relationship), mechanism of action, important drugs, and exam tips in a simple way.

B.Pharm 5th Semester Medicinal Chemistry II – Unit 1 Notes

🔹 Antihistaminic Agents

👉 What is Histamine?

  • A naturally occurring amine stored in mast cells.
  • Involved in allergic reactions, gastric acid secretion, inflammation, and neurotransmission.
  • Acts on H1, H2, H3, and H4 receptors.

✅ H1-Receptor Antagonists (Anti-Allergic Drugs)

  • Examples: Diphenhydramine, Clemastine, Hydroxyzine, Loratadine, Cetirizine.
  • Uses: Allergy, hay fever, anaphylaxis, motion sickness.
  • Mechanism of Action (MoA): Block histamine binding at H1 receptors → prevent allergy symptoms.
  • SAR (Structure Activity Relationship):
    • Two aromatic/heteroaromatic rings required.
    • Spacer chain of 2–3 carbons.
    • Terminal tertiary or cyclic amine essential.

✅ H2-Receptor Antagonists (Anti-Ulcer Drugs)

  • Examples: Cimetidine, Ranitidine, Famotidine, Nizatidine.
  • Uses: Peptic ulcer, GERD, Zollinger–Ellison syndrome.
  • MoA: Block H2 receptors in gastric parietal cells → inhibit acid secretion.
  • SAR:
    • Heteroaromatic nucleus (imidazole, thiazole, etc.) required.
    • Polar substituents improve potency.
    • Side chain length modifies activity.

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✅ Proton Pump Inhibitors (PPIs)

  • Examples: Omeprazole, Pantoprazole, Lansoprazole, Esomeprazole.
  • Uses: Severe gastric ulcers, GERD, H. pylori infection (with antibiotics).
  • MoA: Irreversibly inhibit H⁺/K⁺ ATPase (proton pump) → strong and long-lasting acid suppression.
  • SAR:
    • Benzimidazole nucleus required.
    • Sulfoxide group essential.
    • Substituents on pyridine/benzimidazole rings affect potency.

🔹 Antineoplastic (Anticancer) Drugs

👉 Introduction

  • Neoplasia = uncontrolled and abnormal cell growth.
  • Cancer chemotherapy drugs target DNA, RNA, enzymes, or mitosis to kill/inhibit cancer cells.

✅ Classification of Antineoplastic Drugs

1. Alkylating Agents

  • Examples: Cyclophosphamide, Melphalan, Chlorambucil, Carmustine, Busulfan.
  • MoA: Crosslink DNA → block replication and transcription.
  • SAR:
    • Mustard group (–N(CH2CH2Cl)2) essential.
    • Lipophilicity ↑ → better CNS penetration.

2. Antimetabolites

  • Examples: Methotrexate, 5-Fluorouracil (5-FU), Cytarabine, 6-Mercaptopurine.
  • MoA: Mimic natural metabolites → inhibit nucleotide/DNA synthesis.
  • SAR:
    • Structural similarity to purines/pyrimidines/folates required.

3. Antitumor Antibiotics

  • Examples: Doxorubicin, Daunorubicin, Bleomycin, Mitomycin.
  • MoA: Intercalate DNA, produce free radicals, inhibit topoisomerase → DNA damage.

4. Plant Alkaloids (Mitotic Inhibitors)

  • Examples: Vincristine, Vinblastine, Paclitaxel, Docetaxel.
  • MoA: Bind tubulin → inhibit microtubule formation → arrest cell division (mitosis).

5. Hormones & Antagonists

  • Examples:
    • Corticosteroids – Prednisolone.
    • Anti-estrogen – Tamoxifen.
    • Aromatase inhibitor – Letrozole.
    • Anti-androgen – Flutamide.
  • MoA: Inhibit hormone-dependent tumor growth.

6. Miscellaneous / Targeted Drugs

  • Examples: Cisplatin, Carboplatin (platinum complexes), Imatinib (TK inhibitor).
  • MoA: Bind DNA or block oncogenic signaling pathways.