Active Constituents in Plants

Active Constituents

• Chemical substances synthesized by plants and found in crude drugs.
• Cannot be identified microscopically, but chemically identifiable using chemical tests.
• Classified based on their effect on plant life (primary and secondary metabolites) and chemical nature.

Classification

• Primary Metabolites: Essential for plant growth (carbohydrates, proteins, lipids, vitamins, hormones, enzymes).
• Secondary Metabolites: Cause plant protection (alkaloids, glycosides).

Volatile Oils

• Also known as essential oils or ethereal oils.
• Plant products producing characteristic odors and tastes.
• Secreted by plant structures like cells, glands, and ducts.
• Properties include oily liquids, volatile without decomposition (volatile in steam), ether-like volatility, soluble in organic solvents, sparingly soluble in water, presence as a mixture, not a single compound.
• Composition may be hydrocarbons or oxygenated hydrocarbons, free or combined with resins, gums, or sugars (forming glycosides).

Methods for Extraction of Volatile Oils

• Steam Distillation
• Organic Solvent Extraction
• Enzymatic Hydrolysis (in case of glycoside combination).

Plants Containing Volatile Oils

• Coriander (Fruit, Linalool)
• Clove (Flower, Eugenol)
• Eucalyptus (Leaves, Cineol)
• Peppermint (Herb, Menthol)
• Cinnamon (Bark, Cinnamic aldehyde)
• Cumin (Fruits, Cuminaldehyde)

Glycoside

• Natural products chemically bonded to sugar (glycone) and non-sugar part (aglycone).
• Non-reducing compounds.
• Can be linked by O-, S-, N-, or C-links.
• Non-sugar part can be terpenes, coumarins, anthraquinones, flavonoids, etc.
• Sugar part can be monosaccharides or deoxy sugars.
• Properties include colorless crystalline, soluble in water and diluted alcohol, insoluble in organic solvents.
• Functions include detoxifying agents, stabilizers for labile compounds, protection against microorganisms and insects, energy producers, and decorative substances.

Cardiac Glycosides

• Present in Digitalis purpurea and Digitalis lanata, Strophnthus.
• Used in treating heart diseases.
• The genin (non-sugar part) consists of a steroidal nucleus with four rings (three six-member rings and one five-member ring) attached to a lactone ring.
• The sugar part may consist of one to four molecules.
• Include tests like Killer Killiani's test, Liebermann's test, and Kedde's test.

Phenolic Glycosides

• Usually occur as glycosides and are soluble in water.
• Amphoteric, meaning properties can change depending on pH (affected by acids and alkalis producing color change).
• Examples include Salicin (a salicylate).

Flavonoid Glycosides

• Yellow colored polyphenolic compounds
• Soluble in water and alcohol
• Used as antiseptics, antioxidants, and anti-aging agents.
• Include tests involving alkali, ferric chloride, and aluminum chloride.

Anthraquinone Glycosides

• Contain an anthraquinone nucleus.
• Examples include Senna, rhubarb, aloe, and cascara.
• Used as laxatives, but not recommended in pregnancy due to irritation.
• Include Borntrager's test to detect free anthraquinone.

Thioglycosides (Sulfur Glycosides)

• Common in Cruciferae family.
• Hydrolyses produce glucose, potassium bisulfate and allylisothiocyanate (mustard volatile oil).
• Examples include black mustard (Sinigrin).

Cyanogenic Glycosides

• Hydrolyze to produce hydrogen cyanide (HCN).
• Examples include bitter almond (Amygdalin).

Saponin Glycosides

• Produce foam on shaking in aqueous solution.
• Hemolyse red blood cells.
• Lower surface tension.
• Examples include steroidal saponins (Digitalis) and triterpenoidal saponins (Licorice and quillaia).
• Applications include detergent, sex hormone preparation, and preparing cortisone.

Plant Pigments

• Classified as plastid pigments and other soluble pigments.
• Chlorophyll are complex Mg tetrapyrrole compounds, soluble in lipids/organic solvents, but insoluble in water.
• Carotenoids are tetraterpenes hydrocarbon compounds, soluble in lipids/organic solvents and appear as orange or red.
• Tests for fat-soluble pigments include tests of SbCl3/CHCl3, conc. HCl with phenol, and conc. H2SO4.
• Other soluble pigments include betacyanins, colored alkaloids, and some vitamins.

Alkaloids

• Basic nitrogenous compounds from plants.
• Do not form strong alkalis, but form salts when reacting with acids, usually have a complex, heterocyclic nitrogen structure.
• Properties includes solid, colorless, crystalline, and odorless to nonvolatile.
• Some are liquid (volatile or non-volatile), some are colored.
• Can be identified using reagents (e.g., Mayer's reagent, Wagner's reagent, Dragendorff's reagent).

Resins

• Solid or semisolid amorphous products of complex chemical processes.
• Soften when heated, melt and burn with smoky flames.
• Often contain resinotannols, positive for FeCl3 and are insoluble in water, readily soluble in alcohol.
• Includes colophony, ammoniacum, jalap, and guaiacum.

Tannins

• Water-soluble polyphenolic compounds.
• Have high molecular weight and widely distributed.
• Used to tan animal hides (precipitating proteins).
• Possess astringent taste.
• Classified as condensed (non-hydrolysable and catechol) or hydrolysable (gallic or ellagic and pyrogallol).
• Include testing for presence of tannins using acid, bromine, iron chloride and lead acetate.

Bitter Principles

• Aromatic heterocyclic compounds with bitter taste, absence of nitrogen.
• Diverse chemical structures.
• Examples include khellin from Ammi visnaga (furanochromone class) and xanthotoxin from Ammoidin (furanocaumarin class).
• Identification testing includes using potassium hydroxide (KOH).