Tansu – Ketan + SusuHISTORY
The alkaloids comprise an array of structure types, biosynthetic and pharmacologic activities unmatched by any other group of natural products. The history of alkaloid is almost as old as civilizations. Human kind has used drugs containing alkaloids in potions, medicines, teas, poultices for more than 4000 years. Coniine, an alkaloid of considerable historical significance, is responsible for the death of Socrates from a draught of poison hemlock.
The molecular complexity of the majority of alkaloids precluded their structure elucidation during the nineteenth century or even the early twentieth century. The case of Strychnine is a good example. First obtained in 1819 by Pelletier and Caventou , It took nearly 140 years of extremely arduous, very frustrating chemical investigation before the structure was finally determined in 1946 by Robinson and co-workers.
OCCURRENCE
The major source of alkaloids in the past has been the flowering plants, the angiosperms. In recent years how ever there have been increasingly numerous example of the occurrence of alkaloids in animals, insects, marine organism, microorganism and the lower plants. Some examples of this very diverse occurrence of alkaloids are the isolations of Muscopyridine from the musk deer ; Castoramine from the Canadian beaver; the Pyrrole derivative, a sex pheromone of several insects; Saxitoxin , the neurotoxic constituent of the red tide Gonyaulax cantenella; Pyocyanine from bacterium Pseudomonas aeruginosa; Chanoclavine from the ergot fungus.
Because the alkaloids as a class of compounds have been found predominantly in the flowering plants, certain groups (chemical classes) of alkaloids are associated whith particular families or genera plants. However, only quite recently it has proved possible to attach any taxonomic significance to their distribution. Even when the alkaloids do occur in particular plant part, the range of concentration not only of the total alkaloid, but also of the alkaloid of pharmacological significance, many vary enormously. The most widely accepted classification system, due to the Hegnauer, groups the alkaloids as (a) true alkaloids, (b) proto alkaloids and (c) pseudo alkaloid.
CLASSIFICATION
TRUE ALKALOIDS
The true alkaloids ,which are toxic and show a wide range of physiological activity, normally contain nitrogen in a heterocyclic ring. They, that are derived from amino acids, are almost invariably basic. They are of limited taxonomic distribution, and they normally occur in the plant as the salt of inorganic acid. Some exeptons to these “rules” are colchicines and aristolochic acid, which are not basic and have a heterocyclic ring, and the quaternary alkaloids, which are acidic rather than basic.
PROTOALKALOID
The protoalcaloids are relatively simple amines in which the amino acid nitrogen is not heterocyclic ring. They are biosynthesized from amino acids and are basic. The term “biological amines” is often used for this group of compounds. Examples are mescaline, ephedrine, and N.N-dimethyltryptamine.
PSEUDOALkALOID
The pseudoalkaloids are not derived from an amino acid precursor. they are usually basic. they are two important series of alkaloids in this class, the steroidal alkaloids (e.g., conessine and purines (e.g., caffeine).
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