206 



Biological Chemistry. 



or oxidized to acids 



COOH 



(CH(OH)), 



COOH 



In both cases the terminal groups are identical. The 

 acids yielded by the above four isomeric sugars will be 



COOH COOH COOH COOH 



OH 

 OH 



H 

 H 



H- 

 H 



OH 

 -OH 



H 



OH 



OH 



H 



OH 

 H 



H 



-OH 



COOH COOH COOH COOH 



(A) (B) (C) (D) 



These acids are all tartaric acids. Now acids (A) and (B] 

 are mesotartaric acid, the internally compensated form 

 (see p. 173), and must therefore be optically inactive. If 

 therefore, a sugar yields on oxidation an inactive tartario 

 acid, it must have the formula of either (1) or (2). If (<T 

 be taken (conventionally) as the formula of (i-tartari( 

 acid, the sugar yielding it must have formula (3), whilst 

 sugar (4) will have formula (4). To decide between for-i 

 mulae (1) and (2), both of which yield the inactive meso 

 acid on oxidation, other reactions might be employed 

 For example, it is possible to convert a sugar with termina, 

 group 



H 1 OH 



OH H 



CHO 



into a sugar with terminal group 



JHO 



(reaction I. given above). Sugar (1) would by this re 

 action be obtainable from (3), which yields the dextro-aci< 

 on oxidation, and sugar (2) from (4). In this way th< 

 constitution of the erythroses could be settled. 





