Pharmacognosy with the Basics of Plant Biochemistry - Kovalyov V. M. 2004

Special Part
Vitamins

Vitamins are low-molecular-weight Organic compounds of diverse chemical Structure that are essential for the normal functioning of living organisms.

The Study of vitamins began with the research of the Russian physician N. I. Lunin in 1880. The term "vitamins" was coined in 1912 by the Polish scientist K. Funk, who was the first to isolate a crystalline substance from Yeast containing an amino group (from the Latin vita — life and aminus — nitrogen). Diseases resulting from a deficiency or complete lack of these substances were termed hypo- and avitaminoses. It was later proven that not all vitamins contain an amino group, but this Class of natural compounds has traditionally been called vitamins worldwide.

Vitamins are synthesized primarily by plants and partially by microorganisms. In some cases, they are formed from so-called provitamins (for instance, vitamin A from carotenoids, while certain sterols are converted into group D vitamins under METABOLISM/18.html">The Influence of UV radiation).

Human and Animal organisms either do not synthesize vitamins or do so in insufficient quantities. Today, about 30 vitamins are known, of which approximately 20 enter The Human Body through PLANT AND ANIMAL foods. Vitamins possess high biological activity and are required by the body in very small doses — ranging from a few micrograms to tens of milligrams per day.

Classification. There are three classifications of vitamins. One of the earliest proposed was the letter-based system. As individual vitamins were discovered, they were designated by capital letters of the Latin alphabet (A, B, C, D, etc.) and named according to their biological role in the body: vitamin D (cholecalciferol/calciferol) regulates the calcium-to-phosphorus ratio in bones; vitamin E (tocopherol) Supports reproductive capacity (from the Greek tokos — childbirth, and pherein — to bear); vitamin A (axerophtol) — when deficient, causes xerophthalmia (an eye disease), and so on. As new individual vitamins were isolated, scientists noticed similarities in their structure combined with differences in biological activity, leading to The addition of numerical subscripts to the letters — A₁, A₂, B₁, B_2, K₁, K₂, D₂, D₃, etc.

Once the Chemical Structure of many vitamins was determined, their names began to reflect their chemical composition, such as thiamine (B₁), riboflavin (B₂), pyridoxine (B₆), and so forth. Later, it turned out that some long-known organic substances also exhibited vitamin properties (nicotinic acid, Flavonoids, etc.).

Vitamins are also classified based on their Physical and Chemical properties. According to their solubility, they are divided into fat-soluble and Water-soluble. Fat-soluble vitamins include group A vitamins (retinols) and provitamins — a-, ß-, y-carotenes; group D vitamins — ergosterol and other phytosterols; group E vitamins — a-, ß-, y-, o-tocopherols; group K vitamins — phylloquinone and menaquinone (K₃ and K₃ respectively); and factor F — highly Unsaturated Fatty acids and Prostaglandins.

Water-Soluble Vitamins: B₁ — thiamine, B₂ — riboflavin, B₃ — pantothenic acid, B₆ — pyridoxine, B₉ (B_c) — folic acid, B₁₂ — cyanocobalamin, PP — nicotinic acid, C — ascorbic acid, H — biotin, U — S-methylmethionine sulfonium chloride.

Alongside vitamins, the necessity of which for humans and animals is firmly established, food contains certain biologically active compounds whose deficiency does not lead to overt Metabolic Disorders because their Functions are closer to those of standard nutrients (Essential Amino Acids, polyunsaturated fatty acids). Such substances are called Vitamin-like compounds. They include bioflavonoids (Vitamin P), Choline, inositols, carotenes (vitamin B_T), lipoic, orotic, and pangamic acids (vitamin B₁₅), and p-aminobenzoic acid (PABA).

The aforementioned classifications have their drawbacks. Specifically, they fail to reflect the chemical and pharmacological properties of vitamins. Furthermore, following the synthesis of various vitamin derivatives, the solubility-based classification has become somewhat conventional, since attaching lipophilic groups to the molecules of water-soluble vitamins can turn them into fat-soluble ones, and vice versa.

The most rational classification is based on the chemical structure of vitamins. It was adopted by the Commission on Nomenclature of the Biological Chemistry Division of the International Union of Pure and Applied Chemistry (IUPAC). According to this nomenclature, vitamins are divided into the following groups: aliphatic, alicyclic, aromatic, and heterocyclic.

Apart from vitamins, compounds exist in nature that are converted into vitamins within the bodies of animals and humans — these are provitamins. They include carotenoids, which take part in the synthesis of vitamin A.

Antivitamins are compounds that closely resemble vitamins in their chemical structure but lack their biological properties. Once inside the body, antivitamins substitute for vitamins in metabolic reactions, inhibiting or disrupting their course. This leads to vitamin deficiency even when the corresponding vitamin is ingested in sufficient quantities through food or synthesized by the body. Antivitamins are known for almost all vitamins. For instance, the antivitamin of vitamin B₁ (thiamine) is pyrithiamine, which induces polyneuritis. Certain medications are also antivitamins. For example, sulfonamides are antagonists of p-aminobenzoic acid, while aminopterin and methotrexate (antitumor agents) are antagonists of folic acid.

The specific function of water-soluble vitamins (aside from ascorbic acid) in the Organism is The formation of Coenzymes and prosthetic groups of Enzymes. Bound to various vitamins, enzymes participate in critical metabolic processes: Energy Metabolism (thiamine, riboflavin, Vitamin PP), Biosynthesis and transformation of amino acids (vitamins B₆, B₁₂), fatty acids (pantothenic acid), purine and pyrimidine bases (folacin), and the synthesis of many vital compounds such as acetylcholine, Steroids, etc.