THE CHEMICAL CONSTITUTION OF ITS UNITS 65 



COOC 2 H 5 COOH H 



CBr. CH 2 . CH.CH 2 C1 - CBr . CH 2 . CH . CH 2 C1 -> CBr . CH 2 . CH . CH 2 C1 -> 



CO O CO O CO O 



CH(NH 2 ) . CHo . CH . CH 2 NH 2 NH 



I I -> X\ 



CO O CH 2 CH . COOH 



CHOH CH 



As this compound contains two asymmetric carbon atoms, four 

 stereoisomeric forms are possible ; by synthesis these must occur in two 

 inactive forms. These forms Leuchs separated by crystallisation of 

 the copper salts, the more insoluble acid being termed (a)-7-oxy-proline, 

 the other (b)-7-oxyproline. 



The constitution of these acids was confirmed in 1908 by Leuchs 

 and Felser, who converted them, by reduction with hydriodic acid, into 

 proline. Their attempt to determine whether natural oxyproline was 

 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, 



I. CH 2 CH 2 II. CH 2 CH 2 III. (HO)CH CH 2 



I I /OH || i| 



CH 2 C< (HO)CH CH.COOH CH 2 CH . COOH 



\/ \COOH \/ \/ 



NH NH NH 



IV. CH 2 -CH(OH) 



CH 2 CH.COOH 



\/ 

 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 ft- oxyproline. 



Tryptophane. 



The isolation of tryptophane by Hopkins and Cole in 1902 from 

 the mixture of products formed by the tryptic digestion of caseinogen 

 by precipitation in sulphuric acid solution with mercuric sulphate, 

 besides adding to our list of foundation-stones or units of the protein 

 molecule, gave us the explanation of three phenomena long known in 



connection with the chemistry of the proteins, namely (i) of the reddish- 

 PT. i. 5 



