Active Constituents in Plants

Active Constituents

• Chemical substances synthesized by plants, found in crude drugs.
• Cannot be identified microscopically; chemically identified using tests.
• Classified based on their effect on the plant and chemical nature.

Classification

• Primary Metabolites: Essential for plant growth.
  • Major components: Carbohydrates, proteins, lipids.
  • Minor components: Vitamins, hormones, enzymes.
• Secondary Metabolites: Provide protection for the plant.
  • Examples: Alkaloids, glycosides.

Volatile Oils

• Also called essential oils or ethereal oils.
• Plant products giving characteristic odors and flavors.
• Secreted by various structures (e.g., cells, glands, ducts, hairs).
• Properties: oily liquids, volatile without decomposition, ether-like in volatility, soluble in organic solvents, sparingly soluble in water, don't leave permanent marks (disappear over time), always a mixture of compounds.
• Composition: Organic compounds (hydrocarbons or oxygenated hydrocarbons). May be free, combined as resins (oleoresins/oleogums/oleo-gum-resins), or combined with sugars as glycosides.
• Methods of isolation: Steam distillation, organic solvent extraction, enzymatic hydrolysis.

Plants Containing Volatile Oils

• Examples of plants and their parts used, and important constituents: Coriander (fruit - linalol), Clove (flower - eugenol), Eucalyptus (leaves - cineol), Peppermint (herb - menthol), Cinnamon (bark - cinnamic aldehyde), Cumin (fruit - cuminaldehyde).

Color Tests

• Specific tests (Sudan III, FeCl3, etc.) are used to identify the type of volatile oil.

Uses of Volatile Oils

• Carminative (expelling gas), antiseptic, stimulant, perfumery and flavoring agents.

Glycosides

• Natural products, chemically bonded to sugars.
• Glycone (sugar part) + Aglycone (non-sugar part).
• Glycosides are typically non-reducing compounds.
• Non-sugar part examples: Terpenes, coumarins, anthraquinones, flavonoids.
• Sugar part examples: Glucose, other monosaccharides; deoxysugars are also possible.
• Properties: often colorless, bitter and crystalline, usually insoluble in water and organic solvents, soluble in alcohol.
• Hydrolyzed to sugar and aglycone; aglycone often soluble in organic solvents.

Physical Properties of Glycosides

• Colorless, bitter, crystalline.
• Insoluble in organic solvents; slightly soluble in water or alcohol.
• Hydrolyzed and broken down into aglycones and sugars.

Functions of Glycosides

• Detoxifying harmful compounds.
• Stabilizing labile compounds; protecting against microorganisms and insects.
• Energy producers (from hydrolysis); providing decorative substances like pigments.

Cardiac Glycosides

• Found in Digitalis purpurea and Digitalis lanata, Strophnthus.
• Used for heart disease treatment.
• Genin (non-sugar part): Steroidal nucleus (4 ring structures).
• Sugar part: Usually 1-4 sugar molecules.

Tests for Cardiac Glycosides

• Killiani's test, Liebermann's test, Kedde's test.

Phenol Glycosides

• Usually occur as glycosides (sugar bonded).
• Properties: Soluble in water, amphoteric (affected by pH); with acids/alkalies, they display different colors (Rose, Violet/Cornflower).

Anthraquinone Glycosides

• Contains anthraquinone nucleus.
• Examples of drugs: Senna, Rhubarb, Aloe, and Cascara.
• Used as laxatives (treat constipation).
• Modified Borntrager's test used to differentiate free anthraquinone from combined types.

Thioglycosides

• S-glycosides commonly found in Cruciferae family, as in black mustard (sinigrin).
• Hydrolyzed into glucose, potassium sulfate, and allylisothiocyanate (Mustard volatile oil).

Cyanogenic Glycosides

• Hydrolyzed to produce hydrogen cyanide (HCN).
• Example: Amygdalin (in bitter almond plants).

Saponin Glycosides

• Aqueous solutions produce frothy effects; they hemolyze red blood cells; reduce surface tension; soluble in water and alcohol.
• Steroid saponin: e.g., in Digitalis.
• Triterpenoid saponin: e.g., in Licorice and Quillaia.
• Uses: Detergent agent, sex hormone/cortisone preparation.

Plastid Pigments

• Chlorophylls: Complex Mg tetrapyrrole methane compounds.
• Carotenoids: Highly conjugated hydrocarbons; present in carrots, tomatoes, etc. as lycopene, responsible for orange/red colors.

Other Soluble Pigments

• Betalains: Yellow to red pigments.
• Alkaloids: Basic nitrogenous compounds from plants.
  • Physical properties: crystalline, odorless, nonvolatile (often). Exceptions: volatile liquids (nicotine, coniine), colored compounds (emetine).
  • Chemical properties: usually contain nitrogen, may be amphoteric (react with acids/bases).
  • Alkaloidal reagents used for identification.

Resins and Resin Combinations

• Solid/semisolid amorphous products from complex chemical reactions.
• Soften when heated, melt, and burn with smoky flames.
• Give positive FeCl3 test if resinotannols are present.
• May contain resin acids, resinotannols, and glycosides.
• Insoluble in water, soluble in alcohol/organic solvents.

Tannins

• Water-soluble polyphenolic compounds.
• High molecular weight; widely distributed in plants.
• Used to tan animal hides, making leather.
• Astringent taste.
• Two types: Condensed (catechol) and Hydrolysable (pyrogallol).

Bitter Principles

• Aromatic, heterogeneous compounds with bitter tastes.
• Diverse chemical structures, not part of other classes (e.g., alkaloids).
• Examples: Khellin (furanochromone class), xanthotoxin (furanocaumarin class).

Tests for the Identifiaction of the Different groups of compounds

• Various tests are given for the different groups of compounds of interest to distinguish between them.

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