Pharmacognosy II Study Notes - Pyridine and Tropane Alkaloids

Pyridine Derivative Alkaloids Overview

  • Instructor: Sule Nur Karavus
  • Course: Pharmacognosy II
  • Semester: Spring 2025
  • Lecture Number: 3

Nicotinic Acid and Its Role in Alkaloids Synthesis

  • Nicotinic Acid
    • Serves as a crucial precursor in the synthesis of various alkaloids.
    • Key contributor to the formation of pyridine and pyridine-derived alkaloids.
    • Alkaloids synthesized from nicotinic acid demonstrate diverse pharmacological activities.

Precursor Molecules

  • Quinolinic Acid
    • Synthesized in plants through the condensation of aspartic acid and glyceraldehyde.
    • Leads to the formation of nicotinic acid through specific biosynthetic pathways.

Biosynthetic Pathway Diagram

  • The biosynthetic route involving the precursor molecules, including [3-14C] D-glyceraldehyde-3-phosphoric acid and L-aspartic acid, ultimately results in the synthesis of quinolinic acid and nicotinic acid, reflected in a detailed pathway diagram (not visually included here).

Specific Plant Alkaloids

1. Nicotiana tabacum (Tobacco Leaf)

  • Drog Name: Nicotianae folium
  • Family: Solanaceae
  • Originated from the dried leaves of Nicotiana tabacum.
  • Contains primarily nicotine, with smaller amounts of other alkaloids, including nornicotine and anabasine.
  • Total Alkaloid Content: Ranges from 2% to 10%.
  • Nicotine is characterized as a volatile, oxygen-free liquid alkaloid that can be easily entrained by water vapor.
  • Comparison with Nicotiana rustica: Higher alkaloid concentration than N. tabacum.

Pharmacological Activity of Nicotine

  • Absorption: Rapidly absorbed through mucous membranes and lungs.
  • Dose-dependent effects:
    • Low doses: Stimulate respiration.
    • High doses: Act as a respiratory depressant.
  • Physiological Effects:
    • Increases motor activity by stimulating intestinal smooth muscles.
    • Causes vasoconstriction, increasing arterial blood pressure affecting the cardiovascular system.
    • Exhibits both psychological and physical addiction potential.

Chronic Toxicity and Health Risks

  • Prolonged nicotine exposure leads to conditions collectively referred to as tabacism, characterized by:
    • Laryngitis, gingivitis, gastralgia, emphysema, arrhythmia, palpitations, arteriosclerosis, insomnia, and cognitive impairments (e.g., forgetfulness).
  • Carcinogenic Risks:
    • Tobacco combustion generates carcinogenic compounds (e.g., nitrosamines and 3,4-benzopyrene derivatives), leading to accumulation in the lungs.

Applications and Uses of Nicotine

  • Utilized in smoking cessation therapies, including:
    • Nicotine gum, nasal sprays, and transdermal patches.

2. Areca catechu (Areca Nut)

  • Drog Name: Arecae Semen
  • Family: Arecaceae
  • Alkaloid Content: 0.2-0.5% of pyridine-derived alkaloids; principal active compound is arecoline.
  • Physiological Effects of Arecoline:
    • Acts as a parasympathomimetic agent affecting the autonomic nervous system.
    • Stimulates bowel movements and increases sweat and saliva secretion.
    • Functions as a hypotensive agent, lowering blood pressure.
    • Induces miosis (pupil constriction) when applied to the eye.

Traditional and Cultural Uses of Areca catechu

  • Crushed seeds used as a digestive and psychoactive substance.
  • Commonly combined with lime, tobacco leaves, and spices in regions where grown.
  • Traditionally wrapped in Piper betle leaves and chewed for extended periods.

Tropane Alkaloids

  • Tropane Skeleton: General structure of tropane alkaloids (with representations of compounds like cocaine, hyoscyamine, and scopolamine).

Effects of Parasympathetic Stimulation and Blockade

  • Overview of how tropane alkaloids function as parasympatholytic agents, inhibiting the parasympathetic nervous system and inducing various physiological responses.
  • Use cases include gastrointestinal effects (e.g., relief from gastrointestinal spasms) and their roles in anesthesia and ophthalmology.
  • Cardiovascular Applications:
    • Atropine, for instance, used in managing acute myocardial infarction and treating severe bradycardia (slow heart rate).
  • Neurological and Analgesic Effects:
    • Atropine and scopolamine reduce pain, discomfort, and are helpful in managing Parkinson's disease symptoms (e.g., hypersalivation, tremors).

Side Effects of Tropane Alkaloids

  1. Cardiovascular Effects:
    • Palpitations resulting from increased heart rate (tachycardia).
    • Elevated blood pressure, potentially causing hypertension.
  2. Oral and Ocular Effects:
    • Dry mouth due to inhibition of salivary gland secretion.
    • Increased intraocular pressure; contraindicated in glaucoma.
  3. CNS Effects:
    • Initial stimulation followed by depression, leading to drowsiness or fatigue.
    • Neuropsychiatric symptoms with overdose: hallucinations and confusion.

Plants and Their Alkaloids

1. Atropa belladonna (Deadly Nightshade)
  • Drog Name: Belladonnae folium/Radix
  • Contains 0.3-0.6% total alkaloids, primarily hyoscyamine.
  • Historical uses for cosmetic pupil dilation and enhancing rosy cheeks.
2. Hyoscyamus niger (Black Henbane)
  • Drog Name: Hyoscyami folium
  • Contains 0.04-0.15% total alkaloids; primarily hyoscyamine with scopolamine.
  • Traditionally utilized for treating pain and insomnia.
3. Datura stramonium (Devil Apple)
  • Drog Name: Stramonii folium
  • Ethnomedicinal uses include managing asthma and chronic cough due to its bronchodilator properties.
4. Mandragora officinarum (Mandrake)
  • Drog Name: Mandragorae radix
  • Total alkaloid content of approximately 0.4%, predominantly hyoscyamine and scopolamine.

Microscopic Examination of Alkaloid Sources

  • Common and distinguishable microscopic features of Belladonnae folium, Stramonii folium, and Hyoscyami folium observed under a microscope, highlighting key characteristics for plant identification.
  • Common Features: Stomatal subsidiary cells and Solanaceae-type glandular hairs.
  • Distinguishable Features:
    • Belladonnae folium: Crystal sand and specific glandular hair types.
    • Stramonii folium: Presence of druze crystals.
    • Hyoscyami folium: Unique glandular hair types and crystal formations.

Conclusion

  • The knowledge of pyridine and tropane alkaloids combines their biosynthetic pathways, pharmacological effects, traditional uses, and health implications, forming a foundation for understanding their roles in medicine and toxicity.