134 VITAMIN D GROUP 



Sobotka,^^ Strain," Rosenberg,^* Fieser and Fieser,^^ Shoppee/^ and Deuel,^'' 

 and will not be repeated in detail. It is to be noted that the nomenclature 

 and symbolism of sterol chemistry are in a state of flux, the most recent 

 usage being that of Fieser and Fieser and of Shoppee. The book by Reed 

 et al}^ emphasizes the physiological and therapeutic aspects of vitamin D. 



The sterol skeleton is shown in Fig. 1. This is a perhydro-l,2-cyclopen- 

 tenophenanthrene ring system, with methyl groups at positions 10 and 12 

 and a side chain at position 17 . The conventional numbering of the carbon 

 atoms and the lettering of the rings are as indicated. The evidence leading 

 to this structural concept is briefly reviewed by Heilbron et al}^ Several 

 routes to the synthesis of the ring system have been described,^" and recently 

 Woodward et al}^ have achieved the total synthesis of cholesterol. 



The hydrocarbon skeleton common to the sterols is one of the largest 

 ring systems with which living cells have to deal. It occurs not only in the 

 common sterols, but also in the sex and cortical hormones, bile acids, car- 

 diac glucosides, toad poisons, and some carcinogens. But in vitamin D the 

 nucleus is broken in ring B, so that the structure is no longer a sterol in 

 the strictest sense. The several forms of vitamin D are sometimes classed 

 with the steroids in recognition of their origin, but properly they are not 

 sterols. 



As an introductory convenience, the student of vitamin D may narrow 

 the field to three types of naturally occurring sterols, differing in the degree 

 of saturation in their ring system. In any of these types the side chain may 

 or may not be saturated, and always there are possibilities of structural 

 and steric isomerism. 



1. The cholesterol type, characterized by just one double bond in the ring 



1* H. Sobotka, Chemistry of the Steroids. Williams and Wilkins Co., Baltimore, 



1938. 

 " W. H. Strain, in Organic Chemistry, 2nd ed., Vol. II, Chapter 19. John Wiley and 



Sons, New York, 1943. 

 ^* H. R. Rosenberg, Chemistry and Physiology of the Vitamins. Interscience Pub- 

 lishers, New York, 1945. 

 1^ L. F. Fieser and M. Fieser, Natural Products Related to Phenanthrene, 3rd ed. 



Reinhold Publishing Corp., New York, 1949. 

 ** C. W. Shoppee, Vitamins and Hormones 8, 255 (1950). 

 " H. J. Deuel, Jr., The Lipids. Interscience Publishers, New York, 1951. 

 18 C. I. Reed, H. C. Struck, and I. E. Steck, Vitamin D. University of Chicago Press, 



1939. 

 " I. M. Heilbron, J. C. E. Simpson, and F. S. Spring, /. Chem. Soc. 1933, 626. 

 20 J. W. Cook and C. L. Hewett, /. Soc. Chem. Ind. 52, 451 (1933); /. Chem. Soc. 



1933, 1098; L. Ruzicka, L. Ehmann, M. W. Goldberg, and H. Hosli, Helv. Chim. 



Acta 16, 833 (1933); G. A. R. Kon, /. Chem. Soc. 1933, 1081; A. Koebner and R. 



Robinson, ibid. 1938, 1994; C. K. Chuang, C. M. Ma, Y. L. Tien, and Y. T. Huang, 



Ber. 72, 949 (1939). 

 " R. B. Woodward, F. Sondheimer, and D. Taub, /. Am. Chem. Soc. 73, 3548 (1951). 



