Foundations of organic and natural product chemistry

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Foundations of organic and natural product chemistry

The concept of natural products dates back to the early 19th century, when the foundations of organic chemistry were laid. Organic chemistry was then considered as the chemistry of substances derived from plants and animals. It was a relatively complex form of chemistry and stood in stark contrast to inorganic chemistry, the principles of which had been established in 1789 by the Frenchman Antoine Lavoisier in his book Traité Élémentaire de Chimie.

Preliminary investigations

During the first half of the 19th century, some of the first systematic studies on organic compounds were reported. Around 1816, Michel Chevreul undertook a study on soaps based on different fats and alkalis. This process is called saponification. You will notice that the ester bonds of triacylglycerides (fats and oils) are broken down during the saponification process into salts of fatty acids and glycerol. He separated the different salts from the fatty acids that, in combination with alkali, produce soap. Since these were individual compounds, he demonstrated that it was possible to effect chemical change in various fats (which traditionally come from organic sources) by producing new compounds. This was an important discovery, because until then, chemists believed that it was not possible to alter or synthesize organic compounds.

Structural theories

In addition to being able to synthesize organic molecules, another critical aspect of the development of organic chemistry has been the isolation and structural elucidation of organic substances: although the elementary composition of pure organic substances (whether of natural or synthetic origin) can be determined quite precisely, the molecular structure is always a problem. The desire to do structural elucidation results from a dispute between Friedrich Wöhler and Justus von Liebig, who both studied a silver salt of the same composition, but with different properties. Wöhler studied silver cyanate, a harmless substance, while von Liebig studied silver fulminate, a salt with explosive properties. Elemental analysis shows that the two salts contain equal amounts of silver, carbon, oxygen and nitrogen. According to popular opinion, the two substances should have the same properties, but this was not the case. This apparent contradiction was later resolved by Berzelius isomer theory, according to which not only the number and type of elements are important for chemical properties and reactivity, but also the position of atoms in space in a compound.

It is a direct cause of the development of structural theories, such as the radical theory of Jean-Baptiste Dumas and the theory of substitution of Auguste Laurent. However, it was not until 1858, however, that Kekulé formulated a theory of defined structure in August. He postulated that carbon is tetravalent and can bind to other carbon atoms to form organic molecules. Archibald Scott Couper independently came up with the idea of the self-locking of carbon atoms (his article appeared in June 1858), and provided the first molecular formulas where the lines symbolize the bonds connecting the atoms. For organic chemists, structural theory has provided dramatic clarity of understanding and a reliable guide for both analytical and especially synthetic work. As a result, the field of organic chemistry developed rapidly from this point.

Expand the concept

The concept of natural product chemistry, initially based on organic compounds that can be isolated from plants, was extended in the mid-19th century by the German Justus von Liebig to animal matter. In 1884, Hermann Emil Fischer became interested in the study of carbohydrates and purines, for which he received the Nobel Prize in 1902. He has also successfully manufactured a variety of synthetic carbohydrates in the laboratory, including glucose and mannose. After Alexander Fleming discovered penicillin in 1928, fungi and other microorganisms were added to the arsenal of natural product sources.

Important steps to take

In the 1930s, several major categories of natural products were known. Important milestones in natural products research include several noteworthy Nobel Prize winners:

Terpenes, first systematically studied by Otto Wallach (Nobel Prize 1910) and later by Leopold Ružička (Nobel Prize 1939)

Dyes based on porphins (including chlorophyll and heme), studied by Richard Willstätter (Nobel Prize 1915) and Hans Fischer (Nobel Prize 1930)

Steroids, studied by Heinrich Otto Wieland (Nobel Prize 1927) and Adolf Windaus (Nobel Prize 1928)

Carotenoids, studied by Paul Karrer (Nobel Prize 1937)

Vitamins, studied by Paul Karrer, Adolf Windaus, Robert R. Williams, Norman Haworth (Nobel Prize 1937), Richard Kuhn (Nobel Prize 1938) and Albert Szent-Györgyi

Hormones studied by Adolf Butenandt (Nobel Prize 1939) and Edward Calvin Kendall (Nobel Prize 1950)

Alkaloids and anthocyanins, studied by Robert Robinson (Nobel Prize 1947) among others

The discovery of anti-parasitic compounds, Avermectin and Artemisinin. Avermectin was discovered by William C. Campbell and Satoshi Omura, and Artemisinin by Youyou Tu (Nobel Prize 2015).

Chapter summary

The interest in the biological activities of natural products from different organisms, including the discovery of useful drugs, has been a major driver in the development of organic chemistry concepts and laboratory techniques.

Natural products can be divided into two main categories: primary metabolites, which are necessary for the survival of an organism, and secondary metabolites, which are not necessary for the survival of an organism, but which usually give it some form of growth or survival in its environment.

Natural products are often classified according to their main structural characteristics. Four of the main classes of natural products are alkaloids, which are organic molecules containing nitogens, phenylpropanoids derived from phenylalanine or tyrosine amino acids, polyketides derived from acetate and malonate, and terpenoids, derived from isoprene, a five carbon component.

The process of research and discovery of new natural products in the world is called bioprospecting and the discipline that elucidates the structure of natural products and studies their biological activity is called pharmacognosy.

Biologically active natural products are found in all life forms on the planet. The natural world is divided into two main types of organisms: single-celled prokaryotic organisms without membrane organelles, and single-celled or multicellular eukaryotic organisms with a nucleus and other membrane-related organelles. Biologists classify prokaryotic organisms into two main areas of life, bacteria and archaea. The third domain, Eukaryota, is home to all eukaryotic organisms. The Eukaryota estate is subdivided into four large kingdoms, Animalia, Plantae, Fungi and Protista. Some scientists divide the Protista Kingdom into smaller sub-categories. The discovery of natural products from organisms in all major fields of life has made a lasting contribution to Western medicine.

Early research on organic chemistry and structural elucidation included Michel Chevreul's work on the study of soaps. The process of making soaps from fats and alkalis (basic substances) is called saponification. In the saponification reaction, an alkaline base, such as sodium hydroxide, is used to break down an ester bond into an alcohol and the salt of a carboxylic acid (in this case, the fatty acid). These first studies, as well as those of Wohler and others, paved the way for the field of synthetic organic chemistry, the study of the manufacture of organic molecules.