II. CHEMISTItY 



493 



OH 



H3C 



HO 



H3C HO 



< 



CH3 



CieHs 



CHj/^ 

 a-Toc opherylhydroquinone 



a reducing agent, the original tocopherol can be regenerated by reduction 

 and cyclization.^*'- 



The biological inactivity of tocopherykiuinone is an indication that this 

 reaction does not occur in vivo, at least not as regards its effect on repro- 

 duction. 



Tocopherylhydroquinone is also inactive in the rat,^"^ but when it was 

 given intravenously every 5 days in a water emulsion^"^ to dystrophic rab- 

 bits it was equivalent to a-tocopherol itself, the quinone being less effec- 

 tive.^"^ The conclusion was drawn that the hydroquinone was the anti- 

 dystrophic agent, and, being unstable, it was oxidized before it could be 

 converted to tocopherol for storage purposes. 



With more vigorous oxidation of tocopherol, as with nitric acid, a red 

 color develops. Since its depth is proportional to the amount of tocopherol, 

 it was proposed as the basis of a quantitative method."'^ This "red" qui- 

 none, which is biologically inactive^"^ and has resisted all attempts at 

 crystallization, was first assigned a p-quinone structure.^"*' ^°^ It remained 

 for Smith and his colleagues^i" to show that by the action of nitric acid 

 any substituent on carbon 5 is replaced by oxygen and that the substance 

 was a chi-oman-5,6-quinone. 



H3C 



CH3 



CieHa 



o II 

 o 



Chrornaii-5,6-quinone 



i"2 W. John, E. Dietzel, and W. Emte, Z. physiol. Chem. 257, 173 (1939). 



'"3 A. Issidorides and H. A. Mattill, J. Biol. Chem. 188, 313 (1951). 



'"^ H. Rosenkrantz and A. T. Milhorat, Proc. Soc. Exptl. Biol. Med. 74, 468 (1950). 



1"= J. B. Mackenzie, H. Rosenkrantz, S. Ulick, and A. T. Milhorat, /. Biol. Chem. 183, 



655 (1950j. 

 los M. Furter and R. E. Meyer, Helv. Chim. Acta 22, 240 (1939). 

 "' C. Golumbic, J. Am. Chem. Soc. 64, 2337 (1942). 

 »»8 W. John and W. Emte, Z. physiol. Chem. 261, 24 (1939). 

 "» P. Karrer, H. Fritzsche, and R. Escher, Helv. Chim. Ada 22, 661 (1939). 

 "0 L. I. Smith, W. B. Irwin, and H. E. Ungnade, J. Am. Chem. Soc. 61, 2424 (1939). 



