roxvERsrox of trovitamixs to vitamixs d 



763 



as illustratod in Figure 5. If the irradiation is prolonged over too long 

 an interval, a decomposition of vitamin D obtains. 



Ergostcrol, iii.p. 166 T'., [«]?? = -132° (CHCI3), 260, 270, 294 ni/x 



Luniisterolo, m.p. 118°C., [a]\? = +192 (acetone), 265, 280 m,x 



TMcliysterol,, \a]\f = -70° (benzene), 268, 280, anrl 294 m^ 



Vitamin D., m.p. 116°C., [a]?? = +106° (ethanol), 265 m^ 



Toxisterol) 

 248 mM 



Suprasterol-> I 

 m.p., 104° C, {a]h' = 

 -76° (CHCI3), absorption 

 in far ultraviolet only 



Supra-sterob II 



m.p., 110°C., [a]]^ = +63° 



(CHCI3), absoiption in far 



ultraviolet onh' 



Fig. 5. Products formed by the irradiation of ergosterol.'^"'^'* 



The various intermediary compounds produced on irradiation are Avell- 

 defJned compounds, the structures of which have been accurately deter- 

 mined. It is not certain whether or not the same intermediate compounds 

 are formed when activation is brought about by methods other than ir- 

 radiation. However, the vitamin D produced from any one provitamin D 

 has been shown to be uniform, irrespective of the method of activation. ^*^ 

 When the different provitamins are activated, the same parallel sets of inter- 

 mediates are formed.'*"''*'' Thus, in the case of ergosterol, these are de- 

 signated as lumisterol2, tachysterol2, etc., while the irradiation products of 

 7-dehydrocholesterol (provitamin D3) are referred to as lumisterola, 

 tachysterola, etc. Any of the photochemical intermediates are capable of 

 further alteration on irradiation, and are to be considered as provitamins 

 D. However, none except vitamin D itself is able to exert antirachitic ac- 

 tion. None of the steps in the irradiation mechanism is reversible. '^^ 

 The names of the irradiation products were assigned by Windaus, Deppe, 

 and Wunderlich.^**^ 



>" O. Rosenheim and T. A. Webster, Lancet, 1921, II, 622-625. 

 IS" P. Setz, Z. phijsiol. Chem., 215, 183-192 (1933). 



'** I. McQuurrie, W. F. Thompson, A. V. Stoesser, and Iv. (J. Rigler, ./. Pedint., 10, 

 295-316 (1937). 



"• A. ^yindaus and B. CUintzel, Ann., 538, 120-127 (1939). 



'" A. Windaus, M. Deppe, and W. Wunderlich, Ann., 533, 118-127 (1937). 



