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Introduction to Organic Chemistry

The Isolation of Pure Natural Products from Plants

Why do some plants show pharmaceutical activity and other plants do not? Why is the activity different according to the type of plant? Is it important when a plant has been picked, e.g. at full moon shortly before dawn? What is the mode of action of plants and their extracts? Not until the isolation of pure active natural products from plant extracts, e.g. morphine (German learning unit) by Friedrich Wilhelm Sertürner, has their importance been detected and their mode of action investigated.

Mouse
Fig.1
Poppy
Fig.2
Morphine

Now it is evident that plants contain pharmaceutically active compounds and that the type and concentration of these compounds determine the activity of a plant extract. The full moon is not important, but the concentration of active compounds in a plant nevertheless depends on the time of day. So it can be useful to pick the plants at a certain time or weather, as in the early morning or when the sun is shining, because the metabolic activity and therefore the concentration of the different natural products depends on parameters like temperature and action of light. Not only the methods of treatment but also the techniques of isolation of pure active compounds have been changed very much. Today, for example, even the smallest amounts of a mixture of natural products can be separated by liquid (LC) or gas chromatography (GC).

The term "Organic Chemistry" is historic and was first used by T. Bergman to name the chemistry of the living world. In the 17th century, the investigation of materials from the vegetable and animal kingdom started in addition to the existing studies of minerals. In many cases, a very different behavior of compounds from the living world in contrast to minerals was discovered. As a result of the combustion of materials from the vegetable or animal kingdom, carbon dioxide and water were always formed. The chemical elements carbon and hydrogen have therefore been found to be components of life. All compounds which were investigated by that time had been derived from living organisms and could not be synthesized in the laboratory. It was therefore considered to be impossible to synthesize organic compounds. In contrast to the inorganic compounds of inanimate objects, the synthesis of organic compounds seemed to require a mysterious force of life (vis vitalis).

Fig.3
Urea synthesis

Starting material: Ammonium cyanateProduct: Urea

This vitalism theory was accepted until the beginning of the 19th century. In 1828 it was thrown into doubt by Friedrich Wöhler, who managed the synthesis of urea CO(NH2)2 from the inorganic salt ammonium cyanate. At that time, urea had only been known from extraction from human urine. With that an organic compound had been synthesized from an inorganic salt for the first time. A few years later in 1844 the vitalism theory was delivered its final deathblow by Hermann Kolbe, who prepared acetic acid from carbon and an inorganic starting material.

Exercise 1

Exercise 2

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