48 



UNITY AND DIVERSITY IN BIOCHEMISTRY 



C 



/ \ 

 HC CH 



II II 



HC CH 



\ / 

 O 



Pyran 



H H2 



Cv .c 



^ \ / \ 



HC C CH 



I II II 



HC C CH 



% / \ / 

 C O 



H 



Chroman 



H H2 



^ \ / \ 

 HC C CH 



H 



H 



HC C C-C^ 



CO \. 



H " 



Flavan 



=c 



H 





CH 



Chroman derivatives, called tocopherols, are widely distributed in the 

 biosphere. Although their metabolic role is not yet precisely defined, it is 

 known that they antagonize certain oxidations. The vitamins E are toco- 

 pherols. 



CH, 



CH, 

 I 

 - CH, - CH, - CHj -CH - CHj - CH, - CH, - CH' 



C - CHj - CHj - CHj - CH - <_i-ij - v-n, - ^n, -».. . - v. .j 

 o . Tocopherol 



CH, 



CH,, 



CH, 



HO 



H 



H, 



C 

 \ 



CH, 



CH, 



CH, 



o/| 



,C - CH, - CH, - CH, - CH - CHj - CH, - CH, - CH - CHj - CH, - CH^ - CH 



CH, 



CH- 



CH, 



CH, 



B • Tocopherol 



In plants there is a family of yellow pigments, the anthoxanthins, which are 

 derived from the flavan ring, from flavone, flavonol and flavanone. 



