Pharmacognosy Lecture 4: Pipridine and Pyridine Alkaloids

Lysine-Derived Alkaloids

• Lysine serves as a precursor amino acid for pipridine alkaloids.
• Formation of pipridinium cation occurs through cadaverine intermediate.
• Chain elongation takes place via Mannich-like additions of acetates.

Pipridine Alkaloids

• Found in pomegranate and Lobelia inflata (Indian tobacco).
• Lobeline:
  • Stimulates nicotinic acetylcholine receptor sites, similar to nicotine but with a weaker effect.
  • Employed in smoking cessation preparations and to treat methamphetamine abuse.
• Other pipridine alkaloids are found in Piper nigrum and Conium maculatum.

Pyridine Alkaloids

• Found in tobacco alkaloids, specifically Nicotiana tabacum (Solanaceae).
• Nicotine:
  • A dibasic, volatile liquid with two different nitrogen atoms.
  • Forms salts with 2 moles of monobasic acids.
  • Toxic, with a fatal dose of 40 mg for humans and many animal species.
  • Stimulates respiratory processes in small doses, but causes inhibition in large doses.
  • Used as an insecticide in sulfate salt form.
  • Has negative effects on the cardiovascular system, increasing the risk of heart, lung, and respiratory diseases.
  • May have a positive effect on memory by stimulating nerve impulses.
• Other pyridine alkaloids include Nor-nicotine, Anabasine, and Nicoteine.

Trigonelline

• Occurs in the seeds of various plants, including Foenugreek, Coffea beans, Strophanthus, and Cannabis.
• Derived from nicotinic acid.
• Used as a hypoglycemic, hypolipidemic, and neuroprotective drug.
• May help prevent dental caries by preventing Streptococcus mutans from adhering to teeth.

Pyridone Alkaloids (Ricinine)

• Found in the seeds of Castor, Ricinus communis L.
• Occurs as colorless prisms or needles, soluble in water and organic solvents.
• Does not form salts with acids due to its non-basic character.
• Toxic, causing nausea, vomiting, hemorrhagic gastroenteritis, hepatic and renal damage, and death.

Areca Alkaloids

• Found in the seeds of Areca catechu (Palmae/Arecaceae).
• Arecoline:
  • An agonist for muscarinic acetylcholine receptors.
  • Has a central stimulant action, but large doses can cause depression and paralysis.
  • Used as an anthelmintic in veterinary medicine, employed as a vermicide and taenifuge.

This lecture covers lysine-derived alkaloids, pipridine alkaloids, and pomegranate alkaloids, including their formation and chain elongation mechanisms. It's part of a pharmacognosy course by Assistant Professor Ahmed Mohamed Essam El-Din at Ain Shams University.