Structure of Vitamin

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... 

The structure of vitamin E in its most active form, o-tocopherol, is shown in Figure 18.38. a-Tocopherol is a potent antioxidant, and its function in animals and humans is often ascribed to this property. On the other hand, the molecular details of its function are almost entirely unknown. One possible role for... 

Macrocyclic polyamines may be viewed as an extended form of linear polyamines 13-161 with one less degree of saturation. Polyamines with lower degrees of saturation, have important biological functions. Compounds such as macrocyclic polyimines 171 and porphyrines 18), function as 02 carriers and activators, promote photosynthesis, form the basic structure of vitamine B12, etc., and for these reasons have been subjects of intense investigation. 

Molecular structures of vitamin 02 and vitamin B(. Polar groups are shown in color. Vitamin D2 is water-insoluble and vitemin Be is water-soluble. 

Hodgkin DC, Kamper J, Mackay M, Pickworth J, Trueblood KN, White JG. Structure of Vitamin B12. Nature 1956 178 64-6. 

FIGURE 10.3 Structural formula of vitamin B[2 and partial structures of vitamin B[2 compounds. The partial structures of vitamin B,2 compounds show only those portions of the molecule that differ from vitamin B[2. 1 — 5 -deoxyadenosylcobalamin, 2 — methylcobal-amin, 3 — hydroxocobalamin, 4 — cyanocobalamin, 5 — benzimidazolyl cyanocobamide, 6 — pseudovitamin B[2, 7 — 5-hydroxybenzimidazolyl cyanocobamide, 8 — p-cresolyl cyanocobamide. 

In comparison to the porphyrins, the corrin nucleus contains one less atom in its innermost ring (that is, it contains a 15-membered ring) and, on coordination, only one NH proton is lost to give the macrocycle a single negative charge. A cobalt corrin complex occurs as part of the structure of vitamin B12. 

D. M. E. Szebenyi, S. K. Obendorf, and K. Moffat, Structure of vitamin D-dependent calcium-binding protein from bovine intestine, Nature 294, 327-332 (1981). 

The isolation of the pure material was not the end of the story. Deducing the structure of vitamin B12 was a saga itself. Dorothy Crowfoot Hodgkin, an English scientist, won a Nobel Prize in Chemistry in 1964 in part for getting this structure. This was one of the early triumphs of the technique of X-ray diffraction. She was a amazingly productive structural chemist, getting the structures for cholesterol and insulin as weU. 

In 1952, Bloch and Woodward suggested a mechanism for the cycliza-tion of squalene to cholesterol. In 1962, Francis Crick and James Watson described the double helix structure of proteins. Hodgkin determined the structure of vitamin B12 and of penicillin through collaboration between Woodward and Eschenmoser, involving postdoctoral fellows. In 1877, Alexander Fleming discovered penicillin which was active against tuberculosis. 

The structure of vitamin B12 complex consists of four principal components... 

Vitamin Bi2 is a D-ribofuranose derivative, and the structure of vitamin B12 5 -phosphate, a precursoi 11 of vitamin B12, has been determined. The a-D-glycosidic bond lies 16° (0.51 A) out of the plane of the 5,6-dimethylbenzimidazole ring, because of steric or nonbonded interactions. The D-ribofuranose moiety has that envelope conformation having C-2 exo (0.77 A exoplanar) C-3 and C-5 bear phosphate groups. 

The structure of vitamin K is characterized by methylnaphthoquinone rings with a side chain at position 3. It exists naturally in two forms phylloquinone (vitamin Kt 6.13) occurs only in plants, while menaquinones (vitamin K2 6.14) are a family of compounds with a side chain consisting of between 1 and 14 isoprene units. Menaquinones are synthesized only by bacteria (which inhabit the human gastrointestinal tract and thus provide some of the vitamin K required by the body). Menadione (vitamin K3 6.15) is a synthetic compound with vitamin K activity. Unlike Kj and K2, menadione is water soluble and is not active until it is alkylated in vivo. 

Structure of vitamin B12 (cyanocobalamin) and its coenzyme forms (methylcobalamin and 5 -deoxyadenosyl-cobalamin). 

Structures of vitamin B6 and and the anti-tuberculosis drug isoniazid. 

HODGKIN. DOROTHY C. (1910-1994). An Egyptian-born chemist who was recipient of the Nobel prize for chemistry in I9b-I. for her determinations by X-ray techniques of the structures of Important biochemical substances. Her work involved determining the structure of vitamin Bo, cholesterol iodide, and the antibiotic penicillin hy using X-ray crystallographic analysis. She was educated at Oxford and Cambridge. 

The structure of vitamin Kj has been established by degradation and by synthesis. Surprisingly, the long alkyl side chain of vitamin K, is not necessary for its action in aiding blood clotting because 2-methyl-l,4-naphthoquinone is almost equally active on a molar basis. 

The structure of vitamin Bi2 shown in Section 30-6B with a cyanide ion coordinated with cobalt is not the active form of the vitamin but is a particularly stable form, convenient to isolate and handle. The active form is a coenzyme that is remarkable in having a carbon-cobalt bond to an essentially alkyl-type carbon. The carbon-cobalt bond is to a 5 -deoxyadenosyl group, and if we abbreviate vitamin B12 coordinated to cyanide as 23, the coenzyme can be written, in the same style, as 24. (You will notice that 23 is an abbreviation of the formula of Section 30-6B turned 180°)... 

Structures of vitamin B6 derivatives and the bonds cleaved or formed by the action of pyridoxal phosphate (a). The reactive part of the coenzyme is shown in red in (a). The bonds shown in red in (d) are the types of bonds in substrates that are subject to cleavage. 

Structures ot vitamins K and K2. K is found in plants, K2 in Structure of vitamin E (a-tocopherol). 

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