Vitamin calciferol

An especially important case is the thermal equilibrium between precalciferol (pre-vitamin Dj, 22) and calciferol (vitamin D2, 23). ... 

An X-ray crystal structure determination of calciferol (vitamin D-2,71) showed that steric crowding in the s-cis diene system resulted in a twisted conformation with a dihedral angle of 53° [59], On irradiation with a mercury lamp, it was partially converted into ergosterol (72) and tachysterol (73) [60, 61]. When a solution of calciferol in light petroleum containing a trace of iodine was exposed to diffuse daylight, the vitamin was photoisomerized to (74) [62],... 

Vitamin D is the collective term for a group of compounds formed by the action of ultraviolet irradiation on sterols. Cholecalciferol (vitamin D3) and calciferol (vitamin D2) are formed by irradiation of the provitamins 7-dehydrocholesterol and ergosterol, respectively. The conversion to vitamin D3 occurs in the skin. The liver is the principal storage site for vitamin D, and it is here that the vitamin is hydroxylated to form 25-hydroxyvitamin D. Additional hydroxylation to form 1,25-dihydroxyvita-min D occurs in the kidney in response to the need for calcium and phosphate. A discussion of the role of vitamin D in calcium homeostasis is provided in Chapter 66. 

The term vitamin D is used for a range of compounds which possess the property of preventing or curing rickets. They include ergocalciferol (calciferol, vitamin D ), chole-calciferol (vitamin Dg), dihydrotachysterol, alfacalcidol (la-hydroxycholecalciferol) and calcitriol (1,25-dihydroxycholecalciferol). 

Triglycerides, lecithin, and ergosterol are the main constituents of yeast lipid (feu. Oleic and palmitic acids predominate in yeast fet. These resemble the composition of common vegetable fats. Ergosterol. the precursor of calciferol (vitamin D2) varies from 1 to 3% of yeast dry matter. 

The action of heat on calciferol (Vitamin D2 10), or on pre-calciferol (2), with which it is in chemical equilibrium (see below), gives two further isomers, pyrocalciferol (ii) and isopyrocalciferol (12), both of which have sy i-9,io-configura-tions [ii]. Although these reactions were incomprehensible before the orbital-symmetry principles were developed, we can now see that the formation of sy i-isomers is the consequence of a preference for overlap of C<9) and C io) orbital envelopes on the same side of the molecule. The necessary conformations of the open-chain triene systems for these reactions are considerably strained, but no doubt the elevated temperature (180-200 ) at which cyclisation occurs makes the transition states accessible. 

The biologically important transformation of pre-calciferol (2) into calciferol (vitamin D2 10) is a thermsd and not a photochemical process [6]. By employing C(i9)-tritiated material it has been shown to proceed by a completely intramolecular (and reversible) hydrogen transfer (18) between C(i9) and C(9) [13]. A i i stribution of tritium between C(9) and C[Pg.215]

Only a very small r.moimt of vitamin D is necessary for health-approximately 0.01 mg per day. The vitamin is a fat soluble itamin, occurring in cod liver oil, egg yolks, milk, and in very small amounts in other foods. Cereals, yeast, and milk acquire an added vitamin D potency when irradiated with ultraviolet light. The radiation converts a fatty substance (a lipid) that is present in the food, a substance called ergosterolj into another substance, calciferol (vitamin D.), tv hich has vitamin D activity. The structure of calciferol is closely related to that of vitamin Dg. 

Fig. 3A illustrates the CCC separation of fat-soluble vitamins using the cross-axis CPC equipped with eccentric coil assemblies. Calciferol, vitamin A acetate, and ( )-oc-tocopherol acetate were well resolved from each other and eluted within 2.5 h. Vitamin K3 and Vitamin Ki were also completely resolved with the same solvent system, as shown in Fig. 3B. 

VITAMIN D Vitamin T>2=erjyocalciferol (calciferol) Vitamin D2=cholecalciferol... 

Geometrical isomerization and sigmatropic and electrocyclic rearrangements are all observed in the family of vitamin D, as shown for the case of calciferol (vitamin D2, 7) in Scheme 4.5 (Jacobs and Havinga, 1979 Mermet-Bouvier, 1973). 

An elderly woman with atrial fibrillation, successfully treated for over a year with verapamil, developed atrial fibrillation within a week of starting to take an oral calcium compound 1.2 g with calciferol (vitamin D) 3000 units daily for difluse osteoporosis. Her serum calcium levels had risen from 2.45 to 2.7 mmol/L. Normal sinus rhythm was restored by giving 500 mL of saline and repeated doses of furosemide 20 mg and verapamil 5 mg by intravenous injection. ... 

Physiological forms of vitamin D include vitamin D2 (calciferol, ergocalciferol), vitamin D3 (cholecalciferol), phosphate esters of D2, D3, 25-hydroxycholecalciferol, 1,25-dihydroxycholecalciferol, and 5,25-dihydroxychole-calciferol. Vitamins D2 and D3 are 9,10-secosteroids that differ stmcturally in the degree of saturation of an... 

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