INTERCONVERSION OF SUGARS 



CHO 



HCOH 

 I 

 HOCH 



I 

 HOCH 

 I- 

 HCOH 

 I 

 CHoOH 



(xx"i) 



D-Galactose 



COOH 



I 

 HOCH 



I 

 HCOH 



I 

 HCOH 



I 

 HOCH 



I 



CH2OH 



(XXHI) 

 L-Galactonic acid 



+ 



-2 H 



CHO 



_ I 

 HCOH 



I 

 HOCH 



HOCH 



I 

 HCOH 



COOH 



COOH 



HOCH 



I 

 HCOH 



I 

 HCOH 

 I 

 HOCH 

 I 

 CHO 



+2 n 



(xxn)_ 



D-Galacturonic acid 

 (Right: formula turned through 180°) 



(13) 



O 



-2 H 



- H,0 



CO 



HOC 



II 

 HOC 



I 

 HC — I 



I 

 HOCH 



I 



CH2OH 



(XXIV) 

 L-Ascorbic acid 



1 at the top, it is necessary to rotate the formula for XXII through 

 180°. 



Some of the experimental facts supporting such a mecha- 

 nism are the following. Tracer experiments show that D-glucose 

 is transformed into ascorbic acid without breakage of the carbon 

 chain. Glucose labeled at carbon atom 1 is converted into ascor- 

 bic acid labeled at carbon atom 6, and similarly, glucose labeled 

 at 6 gives ascorbic acid labeled at 1 . Moreover, administration 

 of some intermediates such as D-galacturonic and L-galactonic 

 acids give rise to an increased formation of ascorbic acid in the 

 rat and in cress seedlings. 



Another problem which on paper can be solved by the 

 simple expedient of turning the molecule around through 180° 

 is that of the formation of L-galactose, which is found in agar and 

 flaxseed mucilage. If the primary alcohol group of galactose is 

 oxidized to an aldehyde, a substance would be obtained which 

 on reduction can yield either d- or L-galactose. 



599 



