Chemical Classification

Chemical Classification

The crude drugs are divided into different groups according to the chemical nature of their most important constituent. Since the pharmacological activity and therapeutic significance of crude drugs are based on the nature of their chemical constituents.
The chemical classification of drugs is dependent upon the grouping of drugs with identical constituents.

An out of this classification is as follows:
1. Carbohydrates– Carbohydrates are polyhydroxy aldehydes or ketones containing an unbroken chain of carbon atoms.
Gums - Acacia, Tragacanth, Guargum
Mucilages - Plantago seed
Others - Starch, Honey, Agar, Pectin, Cotton

2. Glycosides – Glycosides are compounds which upon hydrolysis give rise to one or more sugars (glycone) and non-sugar (aglycone).

Anthraquinone Glycosides- Aloe, Cascara, Rhubarb, Senna

Saponins Glycosides- Quillaia, Arjuna, Glycyrrhiza

Cyanophore Glycosides- Wild cherry bark
Isothiocyanate Glycosides- Mustard
Cardiac Glycosides- Digitalis, Strophantus
Bitter Glycosides- Gentian, Calumba, Quassia, Chirata, Kalmegh

3. Tannins– Tannins are complex organic, non-nitrogenous derivatives of polyhydroxy benzoic acids. Examples- Pale catechu, Black catechu, Ashoka bark, Galls, Myrobalan, Bahera, Amla

4. Volatile oils– Monoterpenes and sesquiterpenes obtained from plants. Examples- Cinnamon, Fennel, Dill, Caraway, Coriander, Cardamom, Orange peel, Mint, Clove, valerian

5. Lipids Fixed oils – Castor, Olive, Almond, Shark liver oil Fats – Theobroma, Lanolin Waxes – Beeswax, Spermaceti

6. Resins– Complex mixture of compounds like resinols, resin acids, resinotannols, resenes. Examples Colophony, Podophyllum, Cannabis, Jalap, Capsicum, Turmeric, Balsam of Tolu and Peru, Asafoetida, Myrrh, Ginger

7. Alkaloids – Nitrogenous substance of plant origin Pyridine and Piperidine – Lobelia, Nicotiana Tropane - Coca, Belladonna, Datura, Stramonium, Hyoscyamus, Henbane Quinoline – Cinchona Isoquinoline – Opium, Ipecac, Calumba Indole – Ergot, Rauwolfia Amines – Ephedra Purina – Tea, coffee
8. Protein – Gelatin, Ficin, Papain

9. Vitamins - Yeast

10. Triterpenes – Rasna, Colocynth

Merits : It is a popular approach for phytochemical studies

Demerits: Ambiguities arise when particular drugs possess a number of compounds belonging to different groups of compounds.

Chemotaxonomic Classification

This system of classification relies on the chemical similarity of a taxon i.e. it is based on the existence of relationship between constituents in various plants. There are certain types of chemical constituents that characterize certain classes of plants. This gives birth to entirely new concept of chemotaxonomy that utilizes chemical facts/characters for understanding the taxonomical status, relationships and the evolution of the plants. For example, tropane alkaloids generally occur among the members of Solanaceae thereby, serving as a chemotaxonomic marker. Similarly other secondary plant metabolites can serve as the basis of classification of crude drugs. The berberine alkaloid in Berberis and Argemone; Rutin in Rutaceae members, ranunculaceous alkaloids among its members etc are other examples.

It is the latest system of classification and gives more scope for understanding the relationship between chemical constituents, their biosynthesis and their possible action.