Alkaloids: Their Origins and Properties

Alkaloids

• Alkaloids are naturally occurring amines produced by plants, animals, and fungi.
• Many alkaloids have pharmacological effects on humans and other animals.
• The name "alkaloid" comes from the word "alkaline," originally used to describe any nitrogen-containing base.
• Alkaloids are typically derivatives of amino acids and often have a bitter taste.
• They are found as secondary metabolites in plants (e.g., potatoes, tomatoes), animals (e.g., salamanders, frogs), and fungi.
• Alkaloids can be purified from crude extracts using acid-base extraction.
• While many alkaloids are poisonous, some have medicinal uses, including analgesics (pain relievers) and anesthetics (e.g., morphine, codeine).

Examples of Alkaloids

• Morphine (analgesic) – derived from Papaver somniferum (opium poppy)
• Vinblastine (anti-cancer) – derived from Catharanthus roseus (Madagascar periwinkle)
• Lysergic acid (hallucinogenic) – derived from Claviceps purpurea (ergot fungus)
• Saxitoxin (neurotoxic) – produced by Gonyaulax tamarensis (dinoflagellate)
• Tetrodotoxin (neurotoxic) – produced by pufferfish

Indolizidine Alkaloids

• Indolizidine alkaloids are isolated from various plants, animals (including insects, ants), and fungi.
• They have diverse biological activities.
• Examples include swainsonine, isolated from the fungus Rhizoctonia leguminicola (used for clinical testing as a potential anti-cancer drug) and pumiliotoxin B, from Dendrobatid Amazonian frogs (used as a potent cardiovascular agent).

Alkaloid Characteristics

• Alkaloids often contain one or more nitrogen atoms, especially in cyclic forms.
• Various amino acids (e.g., phenylalanine, tyrosine, lysine, ornithine, tryptophan) are involved in their biosynthesis.
• Alkaloids usually have good solubility in organic solvents (e.g., chloroform) but poor solubility in water. Their salts, however, are water-soluble.
• Alkaloids can exhibit color reactions with specific reagents (e.g., blue with Ehrlich reagent, orange with Dragendorff reagent).
• Alkaloids are generally unstable at temperatures above 70°C and can degrade at high temperatures.

Alkaloid Classification

• Alkaloids with exocyclic nitrogen and aliphatic amines (e.g., ephedrine)
• Putrescine, spermidine, spermine alkaloids (e.g., pausine, cadonocarpine)
• Peptide alkaloids (e.g., integerine)
• Steroid and terpenoid alkaloids (e.g., aconitine, solonidine)
• Heterocyclic alkaloids (various subtypes)
• Examples of heterocyclic alkaloids: pyridine, pyrrolidine, tropane, quinoline, isoquinoline, phenethylamine, indole, purine.
• Specific examples of alkaloids grouped by structure:
  • Pyridine: Nicotine, lobeline
  • Tropane: Atropine, scopolamine, cocaine
  • Quinoline: Quinine, quinidine
  • Isoquinoline: Papaverine, morphine
• Alkaloid examples grouped by activity
  • Anti-cancer: vinblastine, vincristine
  • Anti-malarial: quinine
  • Narcotic Analgesic: Morphine
  • Stimulant: Caffeine, nicotine

Alkaloids in Plants and Animals

• Approximately 15% of plants contain alkaloids.
• Various plants, including trees, fungi, insects, ants, frogs, and toads, produce alkaloids.
• Examples of plant sources for alkaloids: Opium poppy (Papaver somniferum), Madagascar periwinkle (Catharanthus roseus), Ergot fungus (Claviceps purpurea) -Examples of animal sources for alkaloids: Salamanders, poison dart frogs.

Specific Alkaloid Examples (with their sources and uses)

• Alkaloid Sources and Examples:

  • Papaver somniferum: Morphine, codeine, thebaine (opioids with pain-relieving and sleep-inducing properties, but are highly addictive)
  • Catharanthus roseus: Vinblastine, vincristine (treating cancer)
  • Claviceps purpurea: Lysergic acid amide (LSD) (hallucinogen and psychoactive effects)
  • Gonyaulax tamarensis: Saxitoxin (neurotoxic)
  • Spheroides rubripes: Tetrodotoxin (neurotoxic)
  • Dendrobates tinctorius (Poison Dart Frogs): pumiliotoxins (toxic to other animals)

• Phyllobates species:* Batrachotoxin (potent neurotoxin)

  • Nicotiana species: Nicotine (insecticide and psychoactive)
  • Other sources: A multitude of species yielding alkaloids for medicinal, industrial, and other purposes.

• Alkaloid Families and Their Roles:

  • Isoquinolines: Morphine, papaverine
  • Quinolines: Quinine, quinidine

Other Alkaloids (Further Examples)

• Quinoline alkaloids: Quinine

• Isoquinoline alkaloids: Morphine, codeine, thebaine

• Indole alkaloids: LSD, psilocybin

• Various other alkaloids (grouped by structural characteristics/chemical properties) exist in nature

Biosynthesis of Tropane

• Tropane biosynthesis starts with the amino acid ornithine and proceeds through methylornithine, another intermediate
• Other chemical reactions occur during the biosynthesis of tropane
• These reactions, including methylation, decarboxylation, oxidation, and aldol condensation, eventually produce tropinone

Tropane Alkaloids

• Tropane alkaloids are a group of compounds derived from tropane.
• Important examples include atropine, scopolamine, and cocaine
• These compounds are found in various plants like Solanaceae (mandrake, henbane, deadly nightshade)

Cinchona Species

• Cinchona species are the source of quinine and related alkaloids
• These alkaloids have historical and ongoing importance for treating malaria.
• The various alkaloids, like quinine, quinidine, cinchonine, cinchonidine are extracted from Cinchona species
• The amount of different alkaloids extracted depends on species, tree age, and tree environment.

Specific Alkaloids (with their Sources and Uses)

• Additional Notes:

    - Many plants and animals produce alkaloids that have interesting and useful properties
    - The structures of many alkaloids are essential for understanding their function and role
    - Multiple alkaloids are used for various medical and pharmaceutical purposes.
  

Summary of Alkaloids' Roles

• Often serve as defense mechanisms for plants and animals against predators or competitors.
• Possess various pharmacological or physiological effects; some can be medicinal, others are toxic
• Used in various products (e.g. medicines).
• Some alkaloids show significant pharmacological properties; often used in minute quantities
• Understand the broad classification systems and the families to which various alkaloids belong