THE CHEMICAL CONSTITUTION OF THE UNITS 133 



the active form of one of the synthetical compounds by converting the 

 natural substance into its racemic form by heating with baryta to 

 200 C. was unsuccessful, since complete racemisation did not occur. 

 As, however, all compounds containing one asymmetric carbon atom 

 to which a carboxyl group is attached are easily racemised, the result 

 led to the conclusion that oxyproline contains two asymmetric carbon 

 atoms. Of the four possible formulae, 



III. (HO)CH CH 2 



CH 2 CH.COOH 



\/ 



NH 



NH 



formula I. is therefore excluded ; and formula II. is not possible on 

 account of the great stability of the acid to baryta ; consequently the 

 natural product can only be a 7- or a /3-oxyproline. 



