INTRODUCTION 625 



credited with having made the first pure preparation. Schenck®" prepared 

 pure vitamin D3 from irradiated 7-dehydrocholesterol in 1937. 



The terminology still used in relation to the ^dtamins D is that introduced 

 by the Askew and Angus groiips^^^®^ and by Windaus et al}^-'^'^-^ The 

 product originally given the designation of vitamin Di was later shown to be 

 impure, and therefore this term is not employed. Vitamin D2 is the name 

 given to the active principle obtained on irradiation of ergosterol; it is 

 likewise referred to as activated ergosterol and also as calciferol. Windaus 

 and co-workers^® assigned the name, \'itamin D3, to the product prepared 

 by activation of 7-dehydrocholesterol, while the designation xatamin D4 is 

 used for the active vitamin obtained by Windaus and Langer^^ on irradia- 

 tion of 22-dihydroergosterol. 



In addition to ergosterol, 7-dehydrocholesterol and 22-dihydroergosterol 

 themselves, many of their derivatives have been found to be highly potent 

 pro\dtamins D. Thus, the following esters of cholesterol (7-dehydrocholes- 

 terol) can be activated into potent antirachitic substances: acetate;®''"®^ 

 benzoate;®^ isobutyrate;®^ palmitate;®^ and phosphate.''" Ergosterol also 

 is as readily activated in the form of the ester as in that of the free alcohol. - 

 On the other hand, it is reported that the esters of calciferol are not mii- 

 formly converted to active vitamin D on irradiation. Although irradiated 

 ergosteryl acetate,^^'''- irradiated ergosteryl ethyl carbonate,''^ and ir- 

 radiated diergosteryl phosphate" have been found to be equally active, 

 the pro\'itamin activity of the benzoate ester was reported to be consider- 

 ably reduced,^- except when doses of 10 m/z or over were given.'^^ It had 



60 F. Schenck, Naturwissenschaften, 25, 159 (1937). 



61 F. A. Askew, R. B. Bourdillon, H. M. Bruce, R. G. C. Jenkins, and T. A. Webster, 

 Proc. Roil. Soc. (London), B 107, 76-90, 91-100 (1930). 



" T. C. Angus, F. A. Askew, R. B. BourdUlon, H. M. Bruce, R. K. Callow, C. Fischer- 

 mann, J. S. L. Philpot, and T. A. Webster, Proc. Roy. Soc. (London), B 108, 340-359 

 (1931). 



" F. A. Askew, R. B. Bourdillon, H. M. Bruce, R. K. Callow, J. S. L. Philpot, and 

 T. A. Webster, Proc. Roij. Soc. (London), B 109, 488-506 (1932). 



" A. Windaus, A. Liittringhaus, and M. Deppe, Ann., 489, 252-269 (1931). 



«5 A. Windaus, F. v. Werder, and A. Liittringhaus, Ann., 499, 188-200 (1932). 



«6 A. Windaus, F. Schenck, and F. v. Werder, Z. phijsiol. Chem., 241, 101-103 (1936). 



67 O. Rosenheim and T. A. Webster, Biochem. J., 20, 537-544 (1926). 



6« A. F. Hess, M. Weinstock, and E. Sherman, /. Biol. Chem., 67, 413-423 (1926). 



69 C. E. Bills and F. G. McDonald, /. Biol. Chem., 72, 13-19 (1927). 



"> H. von Euler and A. Bernton, Ber., 60, 1720-1725 (1927). 



71 O. Rosenheim and T. A. Webster, Lancet, 1927, II, 622-625; Biochem. J., 22, 762- 

 766 (1928). 



'2 R. K. CaUow, Biochem. J., 25, 79-86 (1931). 



" H. von Euler, A. Wolf, and H. Hellstrom, Ber., 62, 2451-2456 (1929). 



7^ A. Windaus and O. Rygh, Nachr. Ges. Wiss. Gottingen, Math.-physik. Klasse, III. 

 202-216(1928). 



