Pharmacognosy and Natural Products
Core concepts
Focus on the source, active constituent class, and pharmacologic use of major natural products. Alkaloids (morphine from opium poppy, quinine from cinchona, atropine from belladonna, vinca alkaloids) are nitrogen-containing, usually basic, and often extracted by acid–base methods. Glycosides (cardiac glycosides like digoxin from foxglove; sennosides as laxatives) combine a sugar with an aglycone. Also know terpenes/essential oils, resins, gums, and tannins. Understand standardization (assay of marker compounds), the difference between crude drug, extract, and isolated constituent, and quality indicators such as moisture, ash value, and foreign matter.
Question traps
Examiners like to swap the plant and the constituent (e.g., attributing quinine to a plant other than cinchona). Another common trap is confusing the pharmacologic action of a crude drug with that of its purified alkaloid. Be careful with "which part of the plant is used" items - leaf, root, bark, and seed sources are frequently tested. Also distinguish true alkaloids from protoalkaloids and from non-nitrogenous principles.
Worked rule of thumb
When asked how to isolate a basic alkaloid from plant material, the classic sequence is: extract with acidified water (alkaloid salt dissolves), basify, then extract into an organic solvent. Reverse the logic if the compound is acidic. This acid–base partition reasoning answers many isolation and identification questions.
Study approach
Build a three-column table: plant source → active constituent class → clinical use. Add a fourth column for standardization marker. That table covers most recall items.