Vitamins structure

Defection of Light-Catalyzed Changes m Vitamin Structure... 

The medicinal chemistry of vitamins is fundamental not only to the therapeutics of nutritional problems but also to the understanding of the biochemical actions of other medicinal agents that directly or indirectly affect the metabolic functions of vitamins and coenzymes. Accordingly, this chapter includes a brief sununary of the basic biochemislry of vitamins, structure-activity relationships, physicochemical properties and some stability considerations, nutritional and therapeutic applications, and brief characterizations of repre.sentative pharmaceutical products. 

As a matter of record. Table 3.2 lists vitamins, chemical names, and stoichiometric chemical formulas. In many or most cases, however, the vitamin structure is too complicated for any kind of simplified representation. 

Table 7.1.1 Vitamins—Structure, Function, and Daily Requirements ...

Answers to many basic problems of biology—nature of growth, mechanism of duplication of viruses and genes, action of enzymes, mechanism of physiological activity of drags, hormones, and vitamins, structure and action of nerve and brain tissue— may lie in knowledge of molecular structure and intermolecvlar reactions. 

Two most important classes of biological amphiphiles are lipids and salts of bile acids (bile salts). Lipids serve as the building blocks of biological membranes, while the bile salts are soluble compounds that play an important role in digestion and other biological processes. They are produced by the liver and stored in the gall bladder, and solubilize apolar compounds, in particular, cholesterol and fat-soluble vitamins. Structures of several most frequently used bile salts are shown in Figure 8. 

The determination of crystal structures is one of the outstanding triumphs of 20th century science and dates back to the discovery of X-ray diffraction in crystals by von Laue in 1912. Several Nobel prizes have been awarded for the X-ray determination of protein and vitamin structures, testifying to the power of the method in determining complex atomic arrangements. Less well publicized are the numerous crystallographic studies of smaller molecules and solid-state materials. Thousands of crystal structures have been worked out, and the results are of inestimable value in understanding the properties of materials. 

Determination of structural features. The ultraviolet spectrum has been of value in the determination of the structure of several vitamins. Thus the presence of an a-naphthoquinone system in vitamin K was first detected by this means. Also the 4-methylthiazole and the 2 5-dimethyl-6-aminopyridine system was first identified in vitamin Bj (thiamine), a- and /3-Ionones can be distinguished since the former contains two conjugated chromophores and the latter three conjugated chromophores. 

Porphyrins and chlorophylls are the most widespread natural pigments. They are associated with the energy-converting processes of respiration and photosynthesis in living organisms, and the synthesis of specific porphyrin derivatives is often motivated by the desire to perform similar processes in the test tube. The structurally and biosynthetically related corrins (e.g. vitamin B,j) catalyze alkylations and rearrangements of carbon skeletons via organocobalt intermediates. The biosyntheses of these chromophores are also of topical interest. 

Firefly lucifenn is an example of an azole that contains a benzene ring fused to the five membered ring Such structures are fairly common Another example is benzimidazole present as a structural unit m vitamin B12 Some compounds related to benzimidazole include purine and its ammo substituted derivative adenine one of the so called het erocychc bases found m DNA and RNA (Chapter 28)... 

Naturally occurring compounds with carbon-metal bonds are very rare The best example of such an organometallic compound is coenzyme Bi2 which has a carbon-cobalt ct bond (Figure 14 4) Pernicious anemia results from a coenzyme B12 deficiency and can be treated by adding sources of cobalt to the diet One source of cobalt IS vitamin B12 a compound structurally related to but not identical with coen zyme B12... 

Sorbitol is a sweetener often substituted for cane sugar because it is better tolerated by dia betics It IS also an intermediate in the commercial synthesis of vitamin C Sorbitol is prepared by high pressure hydrogenation of glucose over a nickel catalyst What is the structure (including stereochemistry) of sorbitoP... 

Structural drawings of carbohydrates of this type are called Haworth formulas, after the British chemist Sir Walter Norman Haworth (St Andrew s University and the University of Birmingham) Early m his career Haworth contributed to the discovery that carbohydrates exist as cyclic hemiacetals rather than m open chain forms Later he col laborated on an efficient synthesis of vitamin C from carbohydrate precursors This was the first chemical synthesis of a vitamin and provided an inexpensive route to its prepa ration on a commercial scale Haworth was a corecipient of the Nobel Prize for chem istry m 1937... 

A steroid very closely related structurally to cholesterol is its 7 dehydro derivative 7 Dehydrocholesterol is formed by enzymatic oxidation of cholesterol and has a conju gated diene unit m its B ring 7 Dehydrocholesterol is present m the tissues of the skin where it is transformed to vitamin D3 by a sunlight induced photochemical reaction... 

The structure of vitamin D2 is the same as that of vitamin D3 except that vitamin D2 has a double bond between C 22 and C 23 and a methyl substituent at C 24... 

Methanol, which elutes at 4.69 min, is included as a neutral species to indicate the electroosmotic flow. When using standard solutions of each vitamin, CZE peaks are found at 3.41 min, 4.69 min, 6.31 min, and 8.31 min. Examine the structures and p/Ca information in Figure 12.47, and determine the order in which the four B vitamins elute. 

The structure of the first isolated vitamin cyanocobalamin [68-19-9] (la) is known to occur only sporadically, at best, in biological systems. Its isolation... 

Isolation and Structure Determination. The isolation and stmcture elucidation of vitamin D are closely related to the efforts to understand and cure tickets and related bone diseases. The advent of the use of soft coal, the migra tion of people to cities, and the tendency of people and animals to spend less time in sunshine caused a decline in the abiUty of populations to synthesize sufficient quantities of vitamin D. This led to the increased incidence of tickets, beginning around the mid-1600s (3). 

A. W. Norman, R. Bouillon, M. Thomasset, eds.. Vitamin D. A Pluripotent Steroid Hormone Structural Studies, Molecular Endocrinology and Clinical Applications. Proceedings of the Ninth Workshop on Vitamin D, Orlando, Florida, May 1994, Walter de Gmyter, Berlin, 1994, p. 89. 

Low-molecular-weight products, generally secondary metabolites such as alcohols, carboxyhc and an iino acids, antibiotics, and vitamins, can be recovered using many of the standard operations such as liquid-hquid extraction, adsorption and ion-exchange, described elsewhere in this handbook. Proteins require special attention, however, as they are sufficiently more complex, their function depending on the integrity of a delicate three-dimensional tertiaiy structure that can be disrupted if the protein is not handled correctly. For this reason, this section focuses primarily on protein separations. Cell separations, as a necessary part of the downstrean i processing sequence, are also covered. 

Plant and animal cells have numerous chromosomes. Growth rates are relatively slow. A typical nutrient medium will contain a large number of vitamins and growth factors in addition to complex nitrogen sources, because other specialized cells in the original structures supply these needs. A plant or animal cell is not hke a microbial cell in its ability to function independently. 

Figure S.3 Schematic diagram of the structure of human plasma retinol-binding protein (RBP), which is an up-and-down P barrel. The eight antiparallel P strands twist and curl such that the structure can also be regarded as two p sheets (green and blue) packed against each other. Some of the twisted p strands (red) participate in both P sheets. A retinol molecule, vitamin A (yellow), is bound inside the barrel, between the two P sheets, such that its only hydrophilic part (an OH tail) is at the surface of the molecule. The topological diagram of this stmcture is the same as that in Figure 5.2. (Courtesy of Alwyn Jones, Uppsala, Sweden.)...

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