Six-membered and Higher Heterocyclic Rings

Jul 17, 2024

Six-membered and Higher Heterocyclic Rings

Introduction

  • Previous video covered three to five-membered heterocyclic rings and their nomenclature.
  • Current focus: six-membered and higher heterocyclic rings, their nomenclature, and numbering.

Six-Membered Ring Systems

  • Pyridine: Six-membered ring with one nitrogen atom (hetero atom).
  • 2H-pyran: Six-membered ring with one oxygen atom at the second position, which is saturated (indicated as 2H).

Six-Membered Rings with Two Hetero Atoms

  1. Pyrazine: Nitrogens at 1st and 2nd positions.
    • Naming: Pyridine with an extra nitrogen. Pyrid + az + ine = Pyrazine.
  2. Pyrimidine: Nitrogens at 1st and 3rd positions.
    • Naming: Pyr + imid + ine = Pyrimidine.
  3. Pyridazine: Nitrogens at 1st and 4th positions.
    • Naming: Pyr + az + ine = Pyridazine.

6+5 Membered Ring Systems

  • Benzo derivatives: Fusion of benzene with five-membered heterocycles.
    • Indole: Benzene fused with pyrrole.
    • Benzofuran: Benzene fused with furan.
    • Benzothiophene: Benzene fused with thiophene.
  • Benzimidazole: Benzene fused with imidazole.
  • Benzoxazole: Benzene fused with oxazole.
  • Benzothiazole: Benzene fused with thiazole.

6+6 Membered Ring Systems

  • Quinoline: Nitrogen at the 1st position.
  • Isoquinoline: Nitrogen at the 2nd position.
    • Examples: Found in drugs like chloroquine, mefloquine, and muscle relaxant papaverine.
  • Quinoxaline: Two nitrogens at 1st and 2nd positions.
  • Cinnoline: Two nitrogens at 1st and 3rd positions.
  • Phthalazine: Two nitrogens at 2nd and 3rd positions.
    • Example: Found in vasodilator drug hydralazine.

Higher Ring Systems (6+7 Membered Rings)

  • Benzodiazepine: Seven-membered ring with nitrogen at positions 1 and 4.
    • Example: Common in drugs like diazepam (Valium).
  • Benzothiazepine: Seven-membered ring with sulfur and nitrogen.
    • Naming: Benzo + thia + zepine.
  • Phenothiazine: Tri-cyclic system with sulfur and nitrogen.
    • Example: Found in antipsychotic drugs like chlorpromazine.

Complex Ring Systems

  • 9H-Purine: Fusion of imidazole and pyrimidine rings.
    • Nitrogen at 9th position.
    • Example: Found in DNA and RNA.

Summary

  • Various heterocyclic ring systems exist and have specific nomenclature rules.
  • Prefixes and suffixes help in naming complex ring systems.
  • Fusion of rings leads to specific well-known names for derivatives.
  • Remembering these can be simplified by breaking down the names and deriving from base structures.
  • Practical importance in pharmacology and drug design.

Remember: Practice naming and numbering these compounds, and refer to common examples to solidify understanding. Share knowledge and keep engaging with the material for better retention.