THE CHEMISTRY OF THE PROTEINS 95 



Y-cyanopropylmalonic ester, on treatment with nitrous acid, 

 loses one of its carboxyethyl groups and forms the ethyl ester 

 of a-oximido-S-cyanovalerianic acid. On reduction with sodium 

 amalgam this compound yields a-e-diaminocaproic acid, thus : 



NC . CH,, . CH*. CH 2 . CH <coOCH 5 ~* NC - CH - -CH,C(: N .OH) . COOC 2 H 5 -> 

 H*N . CH... CH, . CH, . CH(NH,) . COOH 



This acid has also been synthesised by Sorensen by a very 

 similar method, but its separation into its stereoisomers has not 

 yet been carried out and identity of one of its isomers with 

 natural lysine confirmed. 



Fischer and Schlotterbeck have prepared another diamino- 

 caproic acid by heating sorbic acid with ammonia, but its 

 structure has not yet been determined ; another diaminovalerianic 

 acid has been obtained from /3-vinylacrylic acid. 



The other hexone base, histidine, has not been synthesised 

 by Fischer. Its constitution, as suggested by Pauly and proved 

 by Windaus and Knoop, though not yet quite definitely 

 determined, is that of imidazoleaminopropionic acid : 



NH - CH^ 

 I >N 



CH = C/ — CH,.CH. NH,.COOH 



Most probably the amino group is in the a-position, but this 

 still awaits the final proof. 



Of the heterocyclic products, proline, as above mentioned, 

 was prepared synthetically by Willstatter. 



Two oxypyrrolidine carboxylic acids have recently been 

 obtained by Leuchs in Fischer's laboratory, and deserve mention 

 here in order to complete our knowledge of the amino acids. 

 They were obtained as follows : 



Y-chlor-/3-oxypropylmalonic ester, prepared from epichlor- 

 hydrin and sodium malonic ester, loses alcohol and passes into 

 the ester of S-chlor-7-valerolactone-a-carboxylic acid : 



O CO 



I I 



CH,. C1.CH.CH 2 .CH . COOC,H 5 



This compound on bromination, hydrolysis with concen- 

 trated hydrobromic acid and subsequent splitting off of carbonic 

 acid, gives a-brom-S-chlor-7-valerolactone, which on treatment 



