342 IV. WAXES, HIGHER ALCOHOLS, ETC. 



the original alio arrangement. However, Grasshof-'^ was able to trans- 

 form the normal to the alio series by using the unsaturated ketone choles- 

 tenone as the starting material. This compound is readily reduced to the 

 saturated ketone coprostanone, which, on further reduction, gives rise to 

 the epimers coprosterol and epicoprosterol. The transformation of the 

 alio to the normal series is thus readily demonstrated. It is interesting 

 that the animal also follows this circuitous course in transforming dietary or 

 metabolic cholesterol into fecal coprosterol.-^* Cholestenone can be readily 

 synthesized from cholesterol by oxidation with copper oxide. '•*'*•-"' It is 

 also readily fonned when cholesterol dibromide is oxidized to the ketone 

 with potassium permanganate or chromic acid, followed by debromination 

 to reintroduce the unsaturated linkage. ^^^''^ Schoenheimer'^* was able to 

 improve the yield to 89% of the theoretical by using sodium or potassium 

 iodide, which results in debromination and a regeneration of the double 

 bond by the iodine which is liberated (see p. 343). 



b'. 7-Dehydrocholesterol : "While cholesterol itself is inactive as a pre- 

 cursor of vitamin D, 7-dehydrocholesterol is one of the most active provi- 

 tamins D. Although it has a limited distribution in nature, it is present to 

 the extent of 17 to 27% of the total sterols of a certain species of whelk 

 (Buccinum undatum) ,-^^-^^^ while as much as 6% of the sterols of pig skin 

 consist of this provitamin. ^^^ The methods of synthesis of 7-dehydro- 

 cholesterol from cholesterol are described earlier (see pages 334 and 335). 

 The properties of this alcohol closely simulate those of ergosterol. It melts 

 at 149-150 °C.,^i^ and it has a specific rotation of —122.5° in benzene, —82° 

 in ethyl acetate, and — 113.6° in chloroform. The formula is given here. 



-CH-CHz-CHz-CHzCHCHs 



7-Dehydrochole8terol 



"3 H. Grasshof, Z. phijsiol. Chem., 223, 249-251 (1934). 



"*R. Schoenheimer, D. Rittenberg, and M. Graff, J. Biol. Chem., Ill, 183-192 

 (1935). 



^^^ A. Windaus, Nachr. Ges. Wiss. Gottingen, *Malh. phi/sik. Klasse, Fachgntppen, III , 

 1936, 185-192. 



2'6 F. Bock and F. Wetter, Z. physiol. Chem., 256, 33-41 (1938). 



^1^ A. G. Boer, E. H. Reerink, A. van Wijk, and J. van Niekerk, Proc. Acad. Sci. 

 Amsterdam, 39, 622-632 (1936). 



