Natural Products
Natural Products in NIPER JEE tests pharmacognosy, phytochemical classes, extraction, chromatographic fingerprinting, and standardization of herbal drugs.
Core rules and concepts
- Secondary metabolites include alkaloids, terpenoids, glycosides, flavonoids, tannins, and polyketides; primary metabolites are carbohydrates, proteins, and lipids.
- Alkaloids are basic nitrogenous compounds; Dragendorff and Mayer reagents give precipitates. Examples: berberine (isoquinoline), quinine (quinoline), morphine (morphinan), caffeine (purine).
- Terpenoids follow the isoprene rule: monoterpenes (C10), sesquiterpenes (C15), diterpenes (C20), triterpenes (C30). Essential oils are volatile terpenes; fixed oils are triglycerides.
- Cardiac glycosides (digoxin, digitoxin) contain a steroid nucleus and lactone; saponins lyse red cells and form froth.
- Extraction: maceration, percolation, Soxhlet for thermostable solvents, supercritical CO2 for heat-labile nonpolar compounds. HPTLC is used for herbal fingerprinting; a marker compound is not necessarily the active constituent.
Worked example
100 g of dried powdered bark yields 2.5 g of crude alkaloid residue. Percentage yield = (2.5/100) × 100 = 2.5% w/w. If 1.2 g of pure berberine is isolated from that residue, purity relative to the crude residue is (1.2/2.5) × 100 = 48%, while the overall yield from bark is 1.2%. Report both denominators clearly.
Traps that cost marks
- Calling essential oils fixed oils; fixed oils leave a grease spot and are not volatile.
- Assuming Dragendorff is specific for every alkaloid; it is a general alkaloid reagent.
- Equating marker content with therapeutic activity.
- Ignoring seasonal, geographical, and harvest variation in phytochemical content.