Natural products found in crude drugs contain a wide range of chemical compounds known as phytochemicals. Among them, alkaloids, terpenoids, glycosides, volatile oils, tannins, and resins are some of the most important groups. These compounds are responsible for the therapeutic properties of many medicinal plants. Below is a brief outline of their occurrence, distribution, isolation, identification tests, therapeutic activities, and pharmaceutical applications.
1. Alkaloids
Occurrence and Distribution
Alkaloids are nitrogen-containing compounds widely found in plant families such as Solanaceae, Papaveraceae, Rubiaceae, and Apocynaceae.
Isolation
Alkaloids are generally isolated by:
- Extraction with organic solvents
- Acid-base extraction method
- Solvent partition techniques
Identification Tests
- Dragendorff’s test – Orange precipitate
- Mayer’s test – Cream precipitate
- Wagner’s test – Reddish-brown precipitate
Therapeutic Activity
Alkaloids exhibit analgesic, antimalarial, anticancer, antispasmodic, and cardiotonic properties.
Pharmaceutical Applications
Common alkaloid drugs include morphine (analgesic), quinine (antimalarial), atropine (antispasmodic), and reserpine (antihypertensive).
2. Terpenoids
Occurrence and Distribution
Terpenoids occur in essential oils, resins, and oleo-gum resins of plants. They are widely distributed in species like eucalyptus, mentha, and citrus plants.
Isolation
- Steam distillation
- Solvent extraction
- Supercritical CO₂ extraction
Identification Tests
- Salkowski test – Red coloration
- Liebermann–Burchard test – Green or blue color
Therapeutic Activity
Terpenoids possess antimicrobial, anti-inflammatory, anticancer, bronchodilator, and hepatoprotective activities.
Pharmaceutical Applications
Used in perfumes, disinfectants, flavoring agents, balms, expectorants, and aromatherapy products.
3. Glycosides
Occurrence and Distribution
Glycosides occur in plants such as Digitalis, Senna, Aloe, and Rauwolfia.
Isolation
- Solvent extraction
- Enzyme hydrolysis
- Column chromatography
Identification Tests
- Keller-Killiani test – For cardiac glycosides
- Bornträger’s test – For anthraquinone glycosides
- Legal test – For sterol glycosides
Therapeutic Activity
Shows cardiotonic, laxative, anti-inflammatory, and anticancer activities.
Pharmaceutical Applications
Digitalis glycosides for heart failure, senna glycosides as laxatives, aloe glycosides for skin care.
4. Volatile Oils
Occurrence and Distribution
Volatile oils are aromatic compounds found in flowers, leaves, bark, and seeds of plants like cinnamon, peppermint, clove, and eucalyptus.
Isolation
- Steam distillation
- Cold pressing (for citrus oils)
- Solvent extraction
Identification Tests
- Solubility test – Soluble in alcohol
- Odor test – Characteristic aroma
- Thin Layer Chromatography
Therapeutic Activity
Volatile oils show antiseptic, carminative, expectorant, antispasmodic, and antioxidant actions.
Pharmaceutical Applications
Used in inhalers, liniments, balms, mouthwashes, perfumes, and flavoring agents.
5. Tannins
Occurrence and Distribution
Tannins are polyphenolic compounds found in bark (cinchona), leaves (tea), fruits (amla), and galls (nutgall).
Isolation
- Water or hydroalcoholic extraction
- Precipitation using gelatin or lead acetate
Identification Tests
- Ferric chloride test – Blue-black or green color
- Gelatin test – White precipitate
- Bromine water test – Decolorization
Therapeutic Activity
Tannins exhibit astringent, antioxidant, antimicrobial, and wound-healing properties.
Pharmaceutical Applications
Used in antidiarrheal preparations, mouthwashes, burn treatments, and tanning industry.
6. Resins
Occurrence and Distribution
Resins are nonvolatile, solid or semi-solid plant exudates produced by conifers and various angiosperms.
Isolation
- Collection from natural exudates
- Solvent extraction
- Distillation of oleo-resins
Identification Tests
- Solubility test – Insoluble in water but soluble in alcohol
- Heat test – Softens on heating
- Chemical tests for resin acids
Therapeutic Activity
Resins possess antiseptic, cathartic, irritant, and antimicrobial activities.
Pharmaceutical Applications
Used in varnishes, adhesives, incense, plasters, ointments, and controlled-release formulations.
