Ergosterol derivative provitamin

Irradiated ergosterol was found not to be as antirachitic in the chick as in the rat, whereas the chick could be protected by direct kradiation. The provitamin in cholesterol was shown not to be ergosterol. Rygh (14) in 1935 found that 1 rat unit of cod Hver oil was 100 times more potent in chicks than 1 rat unit of vitamin D2. Brockmann (15) in 1936, prepared the pure crystalline 3,5-dinitrobenzoate derivative of vitamin D obtained from tuna Hver oil... 

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. 

P-Hydroxy steroids which contain the 5,7-diene system and can be activated with uv light to produce vitamin D compounds are called provitamins. The two most important provitamins are ergosterol (1) and 7-dehydrocholesterol (3). They are produced in plants and animals, respectively, and 7-dehydrocholesterol is produced synthetically on a commercial scale. Small amounts of hydroxylated derivatives of the provitamins have been synthesized in efforts to prepare the metabolites of vitamin D, but these products do not occur naturally. The provitamins do not possess physiological activities, with the exception that provitamin D is found in the skin of animals and acts as a precursor to vitamin D, and synthetic dihydroxalated... 

It would seem that ergosterol, provitamin D2 (la), would serve as an ideal precursor for side chain oxygenated vitamin D derivatives because of its ready availability from yeast and its preexisting 5,7-diene system. However, the reactivity of the diene moiety in its free or protected form (vide infra) has complicated the selective manipulation of the side chain. Eyley and Williams have studied the reactions of the aldehyde (43) obtained in modest yield by selective ozonization of... 

Animal and plant tissues contain several provitamin D s (see Fig. 5-3). They all are composed of a steroid ring substituted by a hydroxyl on carbon 3, a methyl on carbons 18 and 19, and a side chain on carbon 17. All provitamin D s have the same steroid derivative 3(j8)-hydroxy-zl-5,7-steroid. Ergosterol was the first provitamin the structure of which was elucidated. It carries an extended side chain on carbon 17 as indicated by the formula, and the configuration of the side chain of ergosterol has been established by studies with the aid of X-ray crystallography. All other provitamins have a different side chain. There is no vitamin Di because the compound originally referred to as vitamin was found to be vitamin D2. 

The first vitamin D was isolated from the irradiation of the yeast sterol ergosterol (Figure 2). This vitamin D was thought to be identical to that produced in the skin of animals and humans. However, studies revealed that when vitamin D produced from yeast was fed to chickens, they were unable to utilize it and developed rickets. When chickens were fed natural vitamin D from fish liver oil, rickets was prevented. This led to the conclusion that vitamin D originating from yeast was different from that in fish liver oil and animal and human skin. In 1937, this mystery was solved when the structure of provitamin D from pig skin was determined. A structural analysis revealed that provitamin D derived from ergosterol differed from that derived from pig skin. The provitamin D (ergosterol provitamin D2) that came from yeast had a double bond between carbons 22 and 23 and a methyl group on carbon 24. 

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