Biotin vitamin structure

Given its systematic name 5-[(3aS,4S,6a )-2-oxohexahydrothieno[3,4-d]-imidazol-4-yl]pentanoic acid, draw a structural formula with complete specification of the configuration for biotin (vitamin H). 

R=NH2, niacinamide biotin, vitamin H Figure 3.4. Structures of some vitamins. 

B vitamins. Among the 13 vitamins, B vitamins are eight water-soluble vitamins (vitamin Bp thiamine vitamin B2 riboflavin vitamin B3 niacin vitamin B5 pantothenic acid vitamin Bg pyridoxine, pyridoxal or pyridoxamine vitamin B7 biotin vitamin B9 folic acid or folate and vitamin B cyanoco-balamin). Folate and vitamins Bg and B12 have joint effects on homocysteine. Cardiovascular disease. Cardiovascular disease (CVD) is a group of disorders of the heart and blood vessels and includes coronary heart disease, cerebrovascular disease, peripheral arterial disease, rheumatic heart disease, congenital heart disease (malformations of heart structure existing at birth) and deep vein thrombosis and pulmonary embolism. 

The structure determination by Du Vigneaud and co-workers AO was completed in 1942 and it was established that biotin (vitamin H) was i -2 -keto-... 

Biotin is an optically active organic acid. The vitamin has the structure shown in (II). Only the dextrorotary form shows activity. Its chemistry and physiology have been extensively reviewed (Tl). 

As aromatic compounds have been exhausted as building blocks for life science products, A-heterocyclic structures prevail nowadays. They are found in many natural products, such as chlorophyll hemoglobin and the vitamins biotin (H), folic acid, niacin (PP), pyridoxine HCl (Be), riboflavine (B2), and thiamine (Bi). In life sciences 9 of the top 10 proprietary drugs and 5 of the top 10 agrochemicals contain A-heterocycIic moieties (see Tables 11.4 and 11.7). Even modern pigments, such as diphenylpyrazolopyrazoles, quinacri-dones, and engineering plastics, such as polybenzimidazoles, polyimides, and triazine resins, exhibit an A-heterocydic structure. 

The vitamin biotin is formed in nature (left) by condensation of L-alanine with pimeloyl-CoAto form 8-amino-7-oxononanoate (AON). This compound is seen at the upper left of the center structure joined as a Schiff base with the coenzyme pyridoxal phosphate (PLP). This is a product complex of the enzyme AON synthase (see Webster et ah, Biochemistry 39,516-528,2000) Courtesy of D. Alexeev,... 

A biochemical curiosity is the presence in egg white of the glycoprotein avidin.ab Each 68-kDa subunit of this tetrameric protein binds one molecule of biotin tenaciously with Kf 1015 M 1. Nature s purpose in placing this unusual protein in egg white is uncertain. Perhaps it is a storage form of biotin, but it is more likely an antibiotic that depletes the environment of biotin. A closely similar protein streptavidin is secreted into the culture medium by Streptomyces avidinii.c Its sequence is homologous to that of avidin. It has a similar binding constant for biotin and the two proteins have similar three-dimensional structures.3/d i Biotin binds at one end of a P barrel formed from antiparallel strands and is held by multiple hydrogen bonds and a conformational alteration that allows a peptide loop to close over the bound vitamin. 

While Tetrahymena must have lipoic acid in its diet, we humans can make our own, and it is not considered a vitamin. Lipoic acid is present in tissues in extraordinarily small amounts. Its major function is to participate in the oxidative decarboxylation of a-oxoacids but it also plays an essential role in glycine catabolism in the human body as well as in plants.295 296 The structure is simple, and the functional group is clearly the cyclic disulfide which swings on the end of a long arm. Like biotin, which is also present in tissues in very small amounts, lipoic acid is bound in covalent amide linkage to lysine side chains in active sites of enzymes 2963... 

DU VIGNEAUD, VINCENT (1901-1978). An American biochemist who won the Nobel prize lor chemistry in 1955. His work involved Ihe study of the metabolism of biologically significant sulfur compounds, which led to the finding of transmethylation in mammalian metabolism. He isolated and proved the structure of Ihe vitamin biotin, and synthesized penicillin, oxytocin, and the vasopressin hormone of the posterior pituitary. His education was at Rochester. Yale. St. Louis, and George Washington Universities. 

The uptake and accumulation of various amino acids in Lactobacillus arabinosus have been described. Deficiencies of vitamin B6, biotin, and pantothenic acid markedly alter the operation of these transport systems. Accumulation capacity is decreased most severely by a vitamin B6 deficiency. This effect appears to arise indirectly from the synthesis of abnormal cell wall which renders the transport systems unusually sensitive to osmotic factors. Kinetic and osmotic experiments also exclude biotin and pantothenate from direct catalytic involvement in the transport process. Like vitamin B6, they affect uptake indirectly, probably through the metabolism of a structural cell component. The evidence presented supports a concept of pool formation in which free amino acids accumulate in the cell through the intervention of membrane-localized transport catalysts. 

Therefore, the three vitamin deficiencies so far studied in detail appear to affect amino acid transport and accumulation in similar but indirect ways. The accumulation defect is most pronounced in vitamin B6-deficient cells, for which there is also strong evidence implicating an abnormality in cell wall composition as a likely source of the change in transport activity. Direct evidence for a cell wall change in biotin- and pantothenate-deficient cells has not yet been obtained. The possibility remains, therefore, that the change in accumulation activity may be caused by an abnormality in some other structural component such as the peripheral cell membrane. 

Vitamins of group B were analysed in different forms [530]. Isopropylidene derivatives showed selectivity of the chromatographic separation which was caused by even minor structural differences. Several compounds from the pyridoxine group can be analysed after their conversion into acetates acetylation followed by GC also appeared suitable for three vitamins and 4-pyridoxic lactone. TMS derivatives were recommended for GC separation of the phosphate form of vitamins. When treated with BSTFA—pyridine (1 1) at 60°C for 15 min, biotin provides a completely silylated derivative, which was analysed on a column packed with 3% of OV-17 [531 ]. 

The structural formula (Figure 9-23) contains three asymmetric carbon atoms, and eight different stereoisomers are possible. Only the dextrorotatory D-biotin occurs in nature and has biological activity. Biotin occurs in some products in free form (vegetables, milk, and fruits) and in other products is bound to protein (organ meats, seeds, and yeast). Good sources of the vitamin are meat, liver, kidney, milk, egg yolk, yeast, vegetables, and mushrooms (Table 9-27). 

Biotin is a water-soluble vitamin. It is a cofactor for four ATP-dependent carboxylases acetyl-CoA carboxylase, pyruvate carboxylase, propionyl-CoA carboxylase, and p-methylcrotonyl-CoA carboxylase. Biotin occurs covalently bound to the enzymes via the terminal amino group of a lysine residue. With the normal and continual turnover of these enzymes in the body, the biotin is released, but then utilized again as a cofactor when the enzymes are re-synthesized. The structure of biotin is shown in Figure 9.32,... 

FIGURE 3.10 Structure of queuosine. Queuosine is incorporated into certain types of transfer RNA. The importance of queunosine to human health is not certain. A great quantity of compoimds are s)mthesized by the gut microflora, including vitamin B12, vitamin K, and biotin (a vitamin). In some cases, these sources of vitamin contribute to the nutritional requirements of the host animal. Essentially all of otir vitamin 612 is acquired from bacteria, but indirectly via meat. Beef cattle acquire their vitamin Bj2 from their gut bacteria, and people, in turn, acquire this vitamin from meat. 

Most vitamins function either as a hormone/ chemical messenger (cholecalciferol), structural component in some metabolic process (pantothenic acid), or a coenzyme (phytonadi-one, thiamine, riboflavin, niacin, pyridoxine, biotin, folic acid, cyanocobalamin). At least one vitamin has more than one biochemical role. Vitamin A as an aldehyde (retinal) is a structural component of the visual pigment rhodopsin and, in its acid form (retinoic acid), is a regulator of cell differentiation. The precise biochemical functions of ascorbic acid and a-tocopherol still are not well defined. 

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