CONVERSION OF PROVITAMINS TO VITAMINS D 750 



view of the demons! fation by lless, Weiiislock, and Ilelniair'*^ llial j)hyto- 

 sterol, cholesterol, and — to a lesser extent — lanolin could be activated. As 

 has been discussed elsewhere, several provitamins were shortly re(;ognized. 

 These included ergoslei'oi'" '' and later 7-dehydi-ocholestcrol/'" as well as 

 22-dihydroergosterol.''''^ A number of additional pro\ntamin D compounds 

 have since been discovered, but none possesses the potential activity of the 

 groups which were first recognized. 



2. Processes of Activation 



Ultraviolet irradiation has been most widely employed for the activation 

 of the provitamins D. It was first assumed that the reaction could be car- 

 ried out with equal efficiency by light of wave lengths within the principal 

 absorption range of ergosterol, which lies between 305 and 230 mM.^"*'"^^^ 

 However, Rosenberg'^^ states that the greatest efficiency obtains with 

 ergosterol when light of a wave length of 281 m/x is employed. This value 

 coincides with the principal absorption peak of this sterol. In the case of 

 7-dehydrocholesterol, Bunker, Harris, and Mosher^^^ obtained the best re- 

 sults when monochromatic light of 296.7 m/u was employed for activation. 

 These workers state that light of the same wave length is most effective in 

 curing rickets in rats when a direct irradiation of the animals is employed; 

 however, Knudson and Benford"^ found that light with a wave length of 

 280.4 mju is best for this purpose. Since it is known that several inter- 

 mediate products are produced before vitamin D is ultimately formed, it is 

 surprising that light Avith such a narrow range should act most effectively 

 in the total conversion. However, two of these intermediate compounds — 

 lumisterol and tachysterol — do exhibit absorption maxima at 280 myu. 



Several types of lamps have been successfully employed for providing 

 the ultraviolet light for the irradiation process. These include the mag- 

 nesium and carbon arcs, the mercury vapor lamp, and cored carbon elec- 

 trodes impregnated with different metals.''^ The bismuth vapor lamp has 

 also been shown to give satisfactory results. ^^^ The best products are ob- 

 tained for commei'cial use when the range of light is limited to the area be- 

 tween 275 and 300 mju.^^^*^^^ This is done by the use of certain filters. To 



1" S. K. Kon, F. Daniels, ami H. Steenbock, /. Am. Chem. Soc, 50, 2573-2581 (1928). 



»« T. A. Webster and R. B. Bourdillon, Biochem. J., £2, 1223-1230 (1928). 



'" A. L. Marshal] and A. Ivnudson, J. Am. Chem. Soc, 52, 2304-2314 (1930). 



'^* J. W. M. Bunker, R. S. Harris, and L. AI. Mosher, /. Am. Chem. Soc., 62, 508-511 

 (1940). 



•« A. Knudson and F. Benford, ./. Biol Chem., 124, 287-299 (1938). 



■^* E. H. Reerink and A. van Wijk (to N. V. Philips' Gloeilampenfal>rieken, Holland), 

 IJ. S. Patent No. 1,904,751 (.\pr. 18, 1933). 



1^' E. H. Reerink and A. van Wijk, Strahlentherapie, 40, 728-732 (1931). 



>« T. H. Rider, G. Sperti, G. P. Goode, and H. G. Ga.ssidv, ./. Am. Med. As.^oc, 106 

 452-45() (1936). 



