Class (49) = Alkaloid (Part 05) | Types of Alkaloids | Classification of Alkaloids (Parts 03)

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Classification of Alkaloids (Part-02)=    • Class (48) = Alkaloid (Part 04) | Types of...  
CLASSIFICATION OF ALKALOID
The alkaloids, as an important naturally occurring nitrogen containing plant substances having very specific as well as most diversified pharmacological properties may be classified in a number of modes and means. Hegnauer (1963) conveniently classified alkaloids into six important groups, corresponding to the six amino-acids legitimately considered as the starting points for their biosynthesis, such as: anthranilic acid, histidine, lysine, ornithine phenylalanine and tryptophan. Price (1963) further took a leading clue from the earlier observation and considered in details the alkaloids present in one of the families, (Rutaceae) and logically placed them in the following nine chemical-structural categories, namely: acridines, amides, amines, benzylisoquinolines, canthinones, imidazoles,indolquinazolines, furoquinolines, and quinazolines.

(a) Biosynthetic Classification In this particular instance the significance solely lies to the precursor from which the alkaloids in question are produced in the plant biosynthetically. Therefore, it is quite convenient and also logical to group together all alkaloids having been derived from the same precursor but possessing different taxonomic distribution and pharmacological activities.
Examples
(i) Indole alkaloids derived from tryptophan.
(ii) Piperidine alkaloids derived from lysine.
(iii) Pyrrolidine alkaloids derived from ornithine.
(iv) Phenylethylamine alkaloids derived from tyrosine.
(v) Imidazole alkaloids derived from histidine.
(b) Chemical Classification It is probably the most widely accepted and common mode of classification of alkaloids for which the main criterion is the presence of the basic heterocyclic nucleus (i.e., the chemical entity).
Examples
1. Pyrrolidine alkaloids e.g., Hygrine;
2. Piperidine alkaloids e.g., Lobeline;
3. Pyrrolizidine alkaloids e.g., Senecionine;
4. Tropane alkaloids e.g., Atropine;
5. Quinoline alkaloids e.g., Quinine;
6. Isoquinoline alkaloids e.g., Morphine;
7. Aporphine alkaloids e.g., Boldine;
8. Indole alkaloids e.g., Ergometrine;
9. Imidazole alkaloids e.g., Pilocarpine;
10. Purine alkaloids e.g., Caffeine;
11. Steroidal alkaloids e.g., Solanidine;
12. Amino alkaloids e.g., Ephedrine;
13. Diterpene alkaloids e.g., Aconitine.
14. Quinazoline e.g. Vasicine
(c) Pharmacological Classification Interestingly, the alkaloids exhibit a broad range of very specific pharmacological characteristics.
Examples
(i) Morphine as Narcotic analgesic;
(ii) Quinine as Antimalarial;
(iii) Strychnine as Reflex excitability;
(iv) Lobeline as Respiratory stimulant;
(v) Boldine as Choleretics and laxatives;
(vi) Aconitine as Neuralgia;
(d) Taxonomic Classification This particular classification essentially deals with the ‘Taxon’ i.e., the taxonomic category. The most common taxa are the genus, subgenus, species, subspecies, and variety. The taxonomic classification based on their respective distribution in a variety of Plant Families,
a. Cannabinaceous Alkaloids: e.g., Cannabis sativa Linn., (Hemp, Marijuana).
b. Rubiaceous Alkaloids: e.g., Cinchona Sp. (Quinine); Mitragyna speciosa Korth (Katum, Kratum, Kutum); Pausinystalia johimbe (K. Schum) (Yohimbe).
c. Solanaceous Alkaloids: e.g., Atropa belladona L., (Deadly Nightshade, Belladona); Capsicum annuum L., (Sweet Peppers, Paprika); Datura candida (Pers.)

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