Pharmacognosy and Natural Products
Core Concepts
Pharmacognosy covers drugs from natural sources: plants, animals, minerals, and microorganisms. Candidates must know plant classification, active constituents (alkaloids, glycosides, tannins, volatile oils), and standardization methods. Important crude drugs include digitalis (cardiac glycosides), opium (alkaloids), and cinchona (quinine). Herbal medicine quality, adulteration, and extraction techniques are also tested.
Question Traps
- Primary vs. secondary metabolites: Primary metabolites (carbohydrates, proteins) are essential for growth; secondary metabolites (alkaloids, terpenes) are often bioactive.
- Glycoside vs. alkaloid: Glycosides contain sugar moieties (e.g., digitoxin); alkaloids are nitrogen-containing basic compounds (e.g., morphine).
- Standardization: Herbal products are standardized to a marker compound, not necessarily the active constituent.
Worked Example / Rule of Thumb
Question: Which natural product is a source of quinine? Cinchona bark. Rule of thumb: “Name the plant, know the constituent” – e.g., Papaver somniferum → morphine; Digitalis purpurea → digitoxin.