Читать книгу Encyclopedia of Renewable Energy - James Speight G., James G. Speight - Страница 79

Alkaloids are a class of nitrogenous organic compounds of plant origin which have pronounced physiological actions on humans and include many drugs (morphine, quinine) and poisons (atropine, strychnine). Alkaloids are naturally occurring chemical compounds containing basic nitrogen atoms and are produced by a large variety of organisms, including bacteria, fungi, plants, and animals.

The alkaloids are perhaps the last class of organic compounds which originate in plants that are of any importance in the formation of the organic substance of coal. These compounds all contain basic nitrogen in the molecule with the nitrogen frequently occurring in a cyclic system; in addition, most of the alkaloids also contain oxygen functions.

Alkaloids are biologically active, organic compounds that contain a nitrogen atom which compounds have many structural frameworks, and are therefore highly variable. Alkaloids occur in the roots, bark, leaves, and within the cells of many plants. The structural chemistry of the alkaloids is variable because of the many locations in which nitrogen can occur in organic systems. However, it is generally recognized that the alkaloids may be based on any one of several individual (or even on a combination of two or more) systems.

Alkaloids are divided into the several large groups, such as pyrrolidine, pyridine, quinoline, isoquinoline, indole, and quinazoline. They are often divided into main groups including peptides and cyclopeptide alkaloids, and true-alkaloids, proto-alkaloids, polyamine-alkaloids, and pseudo-alkaloids. Although most alkaloids are pharmacologically active or poisonous in high doses, there are some alkaloids in foods that are often consumed daily, of which the common examples are caffeine, theobromine, and theophylline (members of the purine alkaloid family) which are mainly found in coffee, cocoa beans, and tea leaves.

Alkaloids have been isolated as crude extracts from plants for many millennia as part of folk medications. However, since the 20^th Century, individual alkaloids with defined and scientifically verified pharmacological properties have been purified and produced commercially as fine chemicals.

The complexity of the chemical structures of the alkaloids makes them, in most cases, impossible to produce by chemical synthesis, so extraction from a crude plant mixture remains the most economically viable strategy. However, plants normally produce complex mixtures of alkaloids (rather than a single alkaloid) with the desirable types often at low levels, with the result that commercially produced specific alkaloids are expensive. As the genetic manipulation of plants becomes more sophisticated, research has focused on the engineering of alkaloid biosynthesis to generate transgenic or cell lines that overproduce specific alkaloids. This can be achieved by increasing the synthesis of a particular alkaloid and/or inhibiting the synthesis of related compounds to increase the ease of purification.