Ergocalciferol, structure

Vitamin D is represented by cholecalciferol (vitamin D3) and ergocalciferol (vitamin D2), which are structurally similar secosteroids derived from the UV irradiation of provitamin D sterols. In vertebrates, vitamin D3 is produced in vivo by the action of sunlight on 7-dehydrocholesterol in the skin. Vitamin D2 is produced in plants, fungi, and yeasts by the irradiation of ergosterol. On irradiation, the provitamins are converted to previtamin D, which undergoes thermal transformation to vitamin D. 

X-ray diffraction showed that DOTAP/DOPC-DNA complexes containing added cholesterol or structurally related molecules form a single lamellar phase. The only exception is ergocalciferol, where two lamellar phases coexist for 4>e,gocaiciicroi > 0.2. 

Ergocalciferol (vitamin D2) is produced in plants from ergosterol on UV irradiation. Vitamin D2 is the form most often used in commercial products and to fortify foods. Although different in structure, its biological activity is comparable to that of vitamin and mu.st be bioactivated in a similar fa.shion. 

Figure 49-17 Structure of vitamin D3 (choiecalciferol) and vitamin D2 (ergocalciferol) and their precursors. 7-Cholecalciferol is produced in the skin from 7-dehydrocho esterol on exposure to sunlight. Ergocalciferol is produced commercially by irradiation of ergosterol. (Modified from Holick MF,AdamsJS.Vitamin D metabolism and biological function. ln Avioli LV, Krone SM, eds. Metabolic bone disease, 2nd ed. Philadelphia WB Saunders, 1990 155-95.)...

Vitamin D and its metabolites play an important role in the maintenance of extracellular calcium concentrations and in normal skeletal structure and mineralization. Vitamin D is necessary for the optimal absorption of calcium and phosphorus. On a worldwide basis, the most common cause of hypocalcemia is nutritional vitamin D deficiency. In malnourished populations, manifestations include rickets and osteomalacia. Nutritional vitamin D deficiency is uncommon in Western societies because of the fortification of miUc with ergocalciferol. " The most common cause of vitamin D deficiency in Western societies is gastrointestinal disease. Gastric surgery, chronic pancreatitis, small-bowel disease, intestinal resection, and bypass surgery are associated with decreased concentrations of vitamin D and its metabolites. Vitamin D replacement therapy may need to be administered by the intravenous route if poor oral bioavailability is noted. Decreased production of 1,25-dihydroxyvitamin D3 may occur as a result of a hereditary defect resulting in vitamin D-dependent rickets. It also can occur secondary to chronic renal insufficiency if there is insufficient production of the 1 -a -hydroxylase enzyme for the... 

This material was also detectable in crude cholesterol from animals. Later it was found, that irradiation of ergosterol, a steroid from baker s yeast, led to a mixture of products with extraordinarily high anti-rachitic activity. At the end of the 1920s, Otto Rosenheim, Thomas Arthur Webster and Adolf Windaus succeeded, independently of each other, in isolating first the unpurified Vitamin D (Vitamin Dj, a mixture of ergocalciferol and lumisterolj) and later the pure crystalline Vitamin D (Vitamin D2, ergocalciferol). The structure determination followed by classical chemical degradation. 

The biological activity of a pure V. can be expressed in International Units (lU). Thus, 0.3 mg V.A (retinol), 8 mg thiamin hydrochloride, 0.18 mg biotin, 50 mg L-ascorbic acid, 0.025 mg ergocalciferol or 1 mg DL-a-tocopherol acetate each corresponds to 1 lU. The system of lU is retained, even though the structures of all V. are known, because in most cases a V. is a family of closely related compounds all with the same action, but with different activities. 

Figure 3 Structure of vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol).

The term vitamin D designates two 9,10-secosteroids which differ structurally in the degree of saturation of an isopienoid side chain (Fig. 3). Vitamin I>2 (ergocalciferol) is of vegetable origin. 

Fig. 5 Structures of OH-functionalized terpenes used as initiators for the ROP of lactide (a) a-tocopherol, (b) ergocalciferol, (c) menthol, (d) geraniol, (e) testosterone, and (f) pregnenolone...

Ergocalciferol and cholecalciferol (I) have a common ring structure as represented in Fig. 1 characterized by an open ring B with three conjugated double bonds. In later sections certain pertinent structural aspects of vitamin D are discussed to present the reader with basic concepts upon which methods have been based. 

Figure 2 Structures for 7-dehydrocholesterol (provitamin D3), ergosterol (provitamin D2), vitamin D3 (cholecalciterol), and vitamin Da (ergocalciferol). The carbons are numbered and the ring systems are labeled.

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