Occurrence in Nature

OCCURRENCE IN NATURE

Alkaloids are substances very well known for their biological activity at the beginning of world civilization. They were used in shamanism, in traditional herbal medicine for the cure of diseases and in weapons as toxins during tribal wars and during hunting. They also had, and still have, socio-cultural and personal significance in ethnobotany. Moreover, they have been and continue to be the object of human interest concerning new possibilities for their safe utilization and ensuing health benefits. Of all sec-ondary compounds, historically and contemporaneously, only alkaloids are molecules of natural origin with highly important benefits and diagnostic uses. They can be char-acterized as the most useful and also the most dangerous products of nature.

Alkaloids are most abundant in higher plants. At least 25% of higher plants contain these molecules. In effect, this means that on average; at least one in fourth plants contains some alkaloids. In reality, it is not impossible that alkaloids occur more commonly. Using the latest equip-ment and technology, such slight traces of alkaloids may be detected (e.g. less than l0 gigagrams per kg of plant mass) that these have no real influence on biological receptors and activity. Generally these species are not considered as alkaloid species. Hegnauer has defined alkaloid plants as those species which contain more than 0.0l% of alkaloids. This is right from the point of view of the classification. From the genetic point of view, and the genetic mechanism of alkaloid synthesis, it is a real limitation. Paying attention to slight traces of alkaloids in plants, we see the members of the plant family which are relatives. They have a genetically determined alkaloid mechanism with a species expression. Moreover, this expression is also on the hybrid level.

The distribution of alkaloids in nature is restricted to some specific plants, animals or lower plants. The pattern of distribution of compound and its pharmacological activity have a great role in chemotaxonomical classification. Alkaloids are chiefly found to be distributed in angiosperms and to some extent in lower plants (mosses, liverworts) and animals. Nearly about 47–50% of various bacterial species also contain alkaloids, for example, pyocyanine from Pseudomonas aeruginosa. Alkaloids are commonly found in the families like, Chenopodiaceae, Lauraceae, Berberidaceae, Menispermaceae, Ranunculaceae, Papaveraceae, Fumari-aceae, Leguminosae, Papilionaceae, Rutaceae, Apocynaceae, Loganiaceae, Rubiaceae, Boraginaceae, Convolvulaceae, Solanaceae, Campanulaceae, Compositae, etc. They may be present in any part of the plant like, roots (reserpine from Rauwolfia), aerial parts like (Ephedra), barks (quinine from cinchona), leaves (Cocaine from Coca), seeds (caffeine from Coca seeds) or even in entire plant (vinblastin from Vinca). 300 alkaloids belonging to more than 24 classes are reported to occur in the skins of amphibians.