CLASSIFICATION OF ALKALOIDS
The classification is mainly based on pharmacological activity, taxonomical distribution, their biogenetic origination and presence of chemical entities.
• Pharmacological Classification
Depending on the physiological response the alkaloids are classified under various pharmacological categories like CNS stimulants or depressant, sympathomimetics, analgesics, purgatives etc. Main drawback of this system is that it does not take into consideration about chemical nature of crude drug. Within the same drug the individual alkaloids may exhibit different action.
Example– 1) Morphine is narcotic and analgesic while codeine is mainly antitussive.
2) Cinchona quinine is antimalarial whereas quinidine is cardiac depressant.
• Taxonomic Classification
This method classifies the vast number of alkaloids based on their distribution in various plant families like solanaceous alkaloids in solanaceae family or papillionaceous alkaloids in papillionaceae family. The grouping of alkaloids are done as per the name of genus in which they occur e.g. Ephedra, cinchona etc. The chemotaxonomic classification has been further derived from this classification.
• Biosynthetic Classification
This method gives the significance to the precursor from which the alkaloids are biosynthesized in the plant. Hence the variety of alkaloid with different taxonomic Distribution and physiological activities can be brought under some group if they are derived from same precursor i.e. all indole alkaloid from tryptophan are grouped together.
Alkaloidal drugs are categorised on the fact whether they are derived from amino acids precursor as ornithine, lysine, phenylalanine, tryptophan etc.
• Chemical Classification
This is the most accepted way of classification of alkaloids which basically depends on ring structure present in the alkaloid. The alkaloidal drugs are broadly categorized into two divisions:
• True alkaloids (subdivided into 12 groups).
• Proto alkaloids or biological amines and pseudo alkaloids.
(a) True alkaloids
1). Pyrrole and pyrrolidine: Hygrine, coca species.
2). Pyridine and piperidine: Arecoline, Anabasine, coniine, trigonelline.
3). Pyrrolizidine: Echimidine, symphitine.
4). Tropane (piperidine/N-methyl pyrrolidine): Atropine, hyoscine.
5). Quinoline: Quinine, Quinidine, Chinchonine.
6). Isoquinoline: Morphine, codeine.
7). Aporphine (reduced isoquinoline – Naphthalene): boldine.
8). Indole (Benzpyrole): Vincristine, Ergometrine, Reserpine.
9). Imidazole: Pilocarpine, Isopilocarpine.
10). Norlupiname: Cytisine, Spartine.
11). Purine (pyrimidine/ imidazole): Caffine/ theofronine, theophylline.
12). Steroidal (cyclo pentano per hydro phenathrene ring): Solanidine, Conessine.
(b) Pseudo alkaloids
Diterpenes- Aconitine, Aconine
(c) Proto alkaloids
Alkylamines (amino alkaloids) – Ephedrine, colchinine
Synonyms: Catharanthus, Periwinkle
Biological source: It consists of dried whole plant of Catharanthus roseus L or Vinca rosea.
Geographical source: It is indigenous to Madagascar and cultivated in South Africa, India, USA, Europe and Australia.