Pharmacognosy: Natural Products and Crude Drugs
Core concepts
Pharmacognosy questions test recognition of plant/animal sources, active constituents, and standard uses. Build a mental table by chemical class: alkaloids (morphine from Papaver somniferum; quinine from Cinchona; atropine from Atropa belladonna; caffeine from Coffea/Thea; vinca alkaloids from Catharanthus roseus), glycosides (cardiac glycosides from Digitalis purpurea/lanata; sennosides from Senna; glycyrrhizin from Glycyrrhiza), terpenoids (artemisinin from Artemisia annua; ginkgolides from Ginkgo biloba), and phenylpropanoids (eugenol from clove; cinnamaldehyde from cinnamon).
Quality and identification
Know pharmacopoeial identity tests and markers: TLC/HPLC fingerprints, organoleptic characters, and specific chemical tests (e.g., Keller–Killiani for cardiac glycosides, Dragendorff for alkaloids, Molisch for carbohydrates). Understand that alkaloid content varies with plant part and harvest time, and that adulteration is detected by marker compounds. Standardization is expressed as a percentage of a marker constituent.
Biosynthesis and classification
Alkaloids derive largely from amino acids (tyrosine, tryptophan, ornithine); terpenes from the mevalonate/deoxyxylulose pathways; phenolics from shikimate. This helps answer "which precursor" questions. Know that some drugs are semisynthetic (e.g., etoposide from podophyllotoxin; galantamine from daffodil sources).
Traps and rule of thumb
A frequent trap is confusing the source plant with a similar-sounding one, or asking which constituent is the active marker versus a toxic one. Rule of thumb: match the chemical class to the reagent - alkaloids with Dragendorff, cardiac glycosides with Keller–Killiani, tannins with ferric chloride.