Alkaloids Overview and Functions

Alkaloids

• Derived from Arabic "al kaly" (soda or basic)
• Natural organic nitrogenous bases, found mainly in plants (also microorganisms and animals)
• Contain at least one nitrogen atom in a heterocyclic ring and physiologically active.
• Nitrogen atoms are present as secondary, tertiary, or quaternary amines (rarely primary amines).
• Classified by the basic nitrogen-containing structures. (e.g., piperidine, quinoline, indole)
• Dicots are richer in alkaloids than monocots.
• Families rich in alkaloids include Apocynaceae, Rubiaceae, Solanaceae, and Papaveraceae.
• Families free from alkaloids include Rosaceae and Labiatae.

Functions

• Defense mechanism (nitrogen source or waste)
• Most have pharmacological activities.
• CNS: depressant (morphine), stimulant (caffeine)
• Autonomic NS: sympathomimetic (ephedrine), sympatholytic (yohimbine), parasympathomimetic (pilocarpine), anticholinergic (atropine), ganglioplegic (nicotine)
• Anaesthesia (cocaine), treat fibrilation (quinidine), antitumor (vinblastine), antimalaria (quinine), antibacteria (berberine), amebicide (emetine)
• Starting materials for drug synthesis.

Classification of Alkaloids

• Biogenetic: Based on the biogenetic pathway, either acetate or shikimate pathway.
• Botanical Source: Classified according to the plant source.
• Type of Amines: Primary, secondary, and tertiary alkaloids.

Basic Alkaloid Skeletons

• Various chemical structures, including quinoline, quinazoline, isoquinoline, pyrrolidine, pyrrolizidine, purine, indole, imidazole, indolizidine, isoquinoline, tropane, pyridine, piperidine, quinoline, quinoline, and others.

Tropane Alkaloids

• Local anaesthetic
• Primarily used for abuse to create stimulation & euphoria but can lead to dependence and depression.
• Examples: Cocaine, (S)-(-)-hyoscyamine, (S)-(-)-scopolamine.

Piperidine Alkaloids

• Relieve asthma & bronchitis
• Example: Lobelin

Pyrrolizidine Alkaloids

• Inflammatory, rheumatic, and GI disorders
• Example: Acetyl-lycopsamine

Quinoline Alkaloids

• Potentially toxic to humans
• Examples: Sparteine, Cytisine, Lupinidine

Indodilizidine Alkaloids

• Active against AIDS (HIV) virus
• Examples: Swainsonine, Castanospermine

Pyridine Alkaloids

• Respiratory stimulant/depressant
• Nicotine patch for smoking cessation
• Example: Nicotine

Tetrahydroisoquinoline Alkaloids

• Example: Anhalamine, Lophocerine

Benzyltetrahydroisoquinoline Alkaloids

• Used as expectorant and for male impotence
• Example: Papaverine

Modified Benzyltetrahydroisoquinoline Alkaloids

• Powerful analgesic & narcotic
• Example: Morphine, Codeine, Thebaine or Paramorphine.

Indole Alkaloids

• Examples: Vinblastine, Vincristine, Reserpine, Deserpidine, Rescinnamine.

Ergot Alkaloids

• Example: Lysergic acid, ergometrine, ergotamine.

Imidazole Alkaloids

• Used as miotic eyedrops and glaucoma treatments
• Example: Pilocarpine

Purine Alkaloids

• Caffeine (CNS stimulant & weak diuretic), Theobromine (diuretic & smooth muscle relaxant), Theophylline (smooth muscle relaxant for bronchospasm & diuretic).