Pharmacognosy and Phytochemistry-II
Unit-II: Secondary Metabolites – Chemistry, Biosources, Therapeutic Uses & Commercial Applications
1. Learning Objectives
Understand
Understand the major classes of plant secondary metabolites and their chemical characteristics.
Identify
Identify important crude drugs containing alkaloids, glycosides, volatile oils, tannins, resins, terpenoids and related constituents.
Correlate
Correlate major phytoconstituents with their therapeutic and commercial applications.
Compare
Compare the biosources, principal constituents and uses of important pharmacognostic drugs.
2. Overview of Secondary Metabolites
| Class | Important Examples in Unit-II | Major Significance |
|---|---|---|
| Alkaloids | Vinca, Rauwolfia, Belladonna, Opium | Nitrogen-containing bioactive compounds |
| Phenylpropanoids & Flavonoids | Lignans, Tea, Ruta | Phenolic and antioxidant constituents |
| Steroids / Cardiac Glycosides / Triterpenoids | Liquorice, Dioscorea, Digitalis | Hormonal, cardiotonic and saponin-related compounds |
| Volatile Oils | Mentha, Clove, Cinnamon, Fennel, Coriander | Aromatic and volatile constituents |
| Tannins | Catechu, Pterocarpus | Astringent polyphenolic compounds |
| Resins | Benzoin, Guggul, Ginger, Asafoetida, Myrrh, Colophony | Oleoresin/resinous natural products |
| Glycosides | Senna, Aloes, Bitter Almond | Pharmacologically active glycosidic constituents |
| Other Terpenoids & Naphthoquinones | Gentian, Artemisia, Taxus, Carotenoids | Terpenoid and quinone natural products |
3. Alkaloids
Alkaloids are naturally occurring nitrogen-containing organic compounds, generally possessing pronounced physiological activity. Many alkaloids are basic because of the presence of nitrogen in their structure.
General Classification of Alkaloids
A. Vinca
Biological source: The dried leaves or aerial parts of Catharanthus roseus are associated with important indole alkaloids.
Family: Apocynaceae
Major constituents: Vincristine, vinblastine, vindoline and related indole alkaloids.
Therapeutic importance: Vincristine and vinblastine are important antineoplastic alkaloids.
Commercial importance: The Vinca alkaloids are important pharmaceutical products used in anticancer therapy.
B. Rauwolfia
Biological source: Dried roots of Rauvolfia serpentina.
Family: Apocynaceae
Major constituents: Reserpine, rescinnamine, ajmaline and related indole alkaloids.
Therapeutic importance: Historically important in the management of hypertension and certain neuropsychiatric conditions.
Commercial importance: A classical source of pharmacologically active indole alkaloids.
C. Belladonna
Biological source: Leaves and roots of Atropa belladonna.
Family: Solanaceae
Major constituents: Atropine, hyoscyamine and scopolamine.
Therapeutic importance: Tropane alkaloids possess antimuscarinic activity and have several clinical applications.
D. Opium
Biological source: Dried latex obtained from the unripe capsules of Papaver somniferum.
Family: Papaveraceae
Major constituents: Morphine, codeine, papaverine and noscapine.
Therapeutic importance: Opium alkaloids have important analgesic, antitussive and other pharmacological applications.
Vinca → Vincristine / Vinblastine
Rauwolfia → Reserpine
Belladonna → Atropine / Scopolamine
Opium → Morphine / Codeine
4. Phenylpropanoids and Flavonoids
Phenylpropanoids and flavonoids are major groups of plant phenolic compounds. They occur widely in medicinal plants and contribute to colour, antioxidant properties, defense and other biological functions.
A. Lignans
Lignans are phenylpropanoid-derived compounds generally formed by oxidative coupling of two phenylpropanoid units.
Lignans occur in several medicinal plants and may exhibit antioxidant, anti-inflammatory and other biological activities.
B. Tea
Biological source: Young leaves and leaf buds of Camellia sinensis.
Family: Theaceae
Major constituents: Catechins, caffeine, tannins and related polyphenols.
Important catechins: Epigallocatechin gallate (EGCG), epigallocatechin, epicatechin and epicatechin gallate.
Uses: Tea is consumed as a beverage and is widely investigated for antioxidant and other biological effects.
C. Ruta
Biological source: Leaves and aerial parts of Ruta graveolens.
Family: Rutaceae
Important constituents: Rutin, flavonoids, furanocoumarins and volatile constituents.
Therapeutic importance: Traditionally associated with antioxidant, vascular and other pharmacological properties.
5. Steroids, Cardiac Glycosides and Triterpenoids
A. Liquorice
Biological source: Dried roots and stolons of Glycyrrhiza glabra.
Family: Fabaceae
Major constituents: Glycyrrhizin (glycyrrhizic acid), glycyrrhetinic acid and flavonoids.
Chemical class: Triterpenoid saponin.
Uses: Expectorant, demulcent and flavouring agent.
B. Dioscorea
Biological source: Tubers/rhizomes of species of Dioscorea.
Family: Dioscoreaceae
Major constituent: Diosgenin, a steroidal sapogenin.
Commercial importance: Diosgenin is an important starting material/intermediate for the semisynthesis of several steroidal drugs.
C. Digitalis
Biological source: Dried leaves of Digitalis purpurea and related Digitalis species.
Family: Plantaginaceae
Major constituents: Cardiac glycosides including digitoxin and related cardenolides.
Therapeutic importance: Cardiac glycosides exert positive inotropic effects and have a historical role in heart failure and certain supraventricular arrhythmias.
6. Volatile Oils
Volatile oils, also called essential oils, are odorous mixtures of volatile constituents obtained mainly from aromatic plants by distillation or other appropriate methods.
| Drug | Biological Source | Major Constituents | Important Uses |
|---|---|---|---|
| Mentha | Mentha species | Menthol, menthone | Flavouring, cooling preparations, carminative |
| Clove | Syzygium aromaticum | Eugenol | Dental preparations, flavouring, aromatic use |
| Cinnamon | Cinnamomum verum / related species | Cinnamaldehyde | Carminative, flavouring and aromatic preparations |
| Fennel | Foeniculum vulgare | Anethole, fenchone | Carminative and flavouring agent |
| Coriander | Coriandrum sativum | Linalool | Carminative and flavouring agent |
Volatile Oil – Key Constituents
7. Tannins
Tannins are high-molecular-weight polyphenolic compounds capable of precipitating proteins and producing an astringent taste.
Classification
A. Catechu
Biological source: Dried aqueous extract obtained from the heartwood of Acacia catechu.
Family: Fabaceae
Major constituents: Catechin and condensed tannins.
Uses: Astringent and traditional applications in oral and gastrointestinal conditions.
B. Pterocarpus
Biological source: Heartwood of Pterocarpus marsupium.
Family: Fabaceae
Major constituents: Pterostilbene, epicatechin and related phenolics.
Importance: Traditionally important medicinal plant and source of bioactive phenolic compounds.
8. Resins
Resins are amorphous, non-volatile plant exudates or products of plant secretions that are generally insoluble in water and soluble in many organic solvents.
| Resin Drug | Biological Source | Important Constituents / Type | Major Uses |
|---|---|---|---|
| Benzoin | Styrax species | Benzoic acid, cinnamic acid and esters | Expectorant, topical preparations, perfumery |
| Guggul | Commiphora wightii | Guggulsterones and resin | Traditional medicinal applications |
| Ginger | Zingiber officinale | Oleoresin, gingerols, shogaols | Carminative, digestive and flavouring agent |
| Asafoetida | Ferula species | Resin, gum and volatile oil | Carminative and flavouring agent |
| Myrrh | Commiphora species | Resin, gum and volatile oil | Traditional topical and oral applications |
| Colophony | Pinus species | Resin acids, especially abietic acid | Adhesives, varnishes and industrial applications |
Benzoin → Benzoic / Cinnamic acid derivatives
Guggul → Guggulsterones
Ginger → Gingerols / Shogaols
Asafoetida → Resin + Gum + Volatile oil
Colophony → Abietic acid
9. Glycosides
Glycosides are compounds that yield a sugar component (glycone) and a non-sugar component (aglycone/genin) on hydrolysis.
A. Senna
Biological source: Dried leaflets and pods of Senna alexandrina (syn. Cassia angustifolia and related taxa).
Family: Fabaceae
Major constituents: Sennosides, particularly sennosides A and B.
Chemical class: Anthraquinone/dianthrone glycosides.
Therapeutic use: Stimulant laxative.
B. Aloes
Biological source: Dried latex obtained from the leaves of Aloe species.
Major constituent: Aloin (barbaloin) and related anthraquinone glycosides.
Use: Historically used as a stimulant laxative.
C. Bitter Almond
Biological source: Seeds of bitter varieties of Prunus dulcis.
Family: Rosaceae
Major constituent: Amygdalin, a cyanogenic glycoside.
10. Iridoids, Other Terpenoids & Naphthoquinones
A. Gentian
Biological source: Roots and rhizomes of Gentiana lutea.
Family: Gentianaceae
Major constituents: Secoiridoid glycosides such as gentiopicroside and amarogentin.
Uses: Bitter tonic and digestive stimulant.
B. Artemisia
Species of Artemisia are important sources of terpenoid natural products.
Artemisinin, obtained from Artemisia annua, is an important antimalarial natural product.
C. Taxus
Taxus species are important sources of taxane diterpenoids.
The most important pharmaceutical example is paclitaxel (Taxol), a taxane anticancer agent.
D. Carotenoids
Carotenoids are naturally occurring pigments belonging mainly to the terpenoid family.
Important examples include β-carotene, lycopene, lutein and zeaxanthin.
They occur in fruits, vegetables, leaves and other plant tissues and have important nutritional and commercial applications.
11. Master Comparison of Important Crude Drugs
| Drug | Major Constituent | Class | Key Therapeutic / Commercial Importance |
|---|---|---|---|
| Vinca | Vincristine, Vinblastine | Indole alkaloids | Anticancer |
| Rauwolfia | Reserpine | Indole alkaloids | Antihypertensive historical use |
| Belladonna | Atropine | Tropane alkaloid | Antimuscarinic |
| Opium | Morphine, Codeine | Isoquinoline alkaloids | Analgesic / antitussive |
| Tea | EGCG, Caffeine | Polyphenols / alkaloid | Beverage / antioxidant research |
| Liquorice | Glycyrrhizin | Triterpenoid saponin | Demulcent / expectorant |
| Dioscorea | Diosgenin | Steroidal sapogenin | Steroid-drug precursor |
| Digitalis | Cardiac glycosides | Cardenolides | Cardiotonic |
| Clove | Eugenol | Volatile oil | Dental / flavouring |
| Cinnamon | Cinnamaldehyde | Volatile oil | Flavouring / aromatic |
| Senna | Sennosides | Anthraquinone glycosides | Laxative |
| Artemisia | Artemisinin | Sesquiterpene lactone | Antimalarial |
| Taxus | Paclitaxel | Taxane diterpenoid | Anticancer |
12. High-Yield Points for Examination
Rauwolfia → Reserpine
Belladonna → Atropine + Scopolamine
Opium → Morphine + Codeine
Liquorice → Glycyrrhizin
Dioscorea → Diosgenin
Digitalis → Cardiac glycosides
Clove → Eugenol
Cinnamon → Cinnamaldehyde
Fennel → Anethole
Coriander → Linalool
Senna → Sennosides
Bitter Almond → Amygdalin
Artemisia → Artemisinin
Taxus → Paclitaxel
13. Important Examination Questions
Long Answer Questions
- Discuss the biological source, chemical constituents, chemistry, therapeutic uses and commercial applications of Vinca.
- Write a detailed account of Rauwolfia and its important alkaloids.
- Discuss the pharmacognosy and phytochemistry of Opium.
- Describe steroids, cardiac glycosides and triterpenoids with suitable examples.
- Write an account of volatile oils with reference to Mentha, Clove, Cinnamon, Fennel and Coriander.
- Discuss the chemistry, sources and uses of tannins.
- Write a detailed note on resins with suitable examples.
- Discuss glycosides with reference to Senna, Aloes and Bitter Almond.
- Write a note on Artemisia, Taxus and carotenoids.
Short Answer Questions
- What are alkaloids?
- Write two constituents of Vinca.
- What is the major alkaloid of Rauwolfia?
- Name the principal alkaloids of Belladonna.
- Name four important alkaloids of Opium.
- What are lignans?
- Name important catechins present in Tea.
- What is glycyrrhizin?
- What is diosgenin?
- What are cardiac glycosides?
- Name the major constituent of Clove oil.
- Name the major constituent of Cinnamon oil.
- What is a tannin?
- What are resins?
- What are sennosides?
- What is amygdalin?
- What is artemisinin?
- What is paclitaxel?
14. One-Minute Revision
B.Pharm 5th Semester • BP504T Pharmacognosy & Phytochemistry-II
Concepts • Crude Drugs • Phytoconstituents • Examination Preparation
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