92 SCIENCE PROGRESS 



brominating the monoalkylmalonic acid, which, on heating, 

 loses carbonic acid and is converted into the bromo fatty acid. 

 Leucine can be readily prepared by this method from isobutyl- 

 bromide and malonic ester ; this method is especially useful for 

 the synthesis of phenylalanine which is carried out by the 

 following stages : 



COOQ.H5 COOC,H 5 COOC 2 H 5 COOH 



I Na I QH5.CH..CI I KOH I Br 

 CH, -> CHNa -> CH.CH 2 .C 6 H 5 -> CH . CH 2 . C 6 H 5 -> 



II I I 

 COOC,H 5 COOC,H 5 COOC,H s COOH 



COOH H H 



I I NH 3 I 



C(Br).CH,.C 6 H 6 -> C(Br) . CH,C 6 H 5 -> C(NH,) . CH, C 6 H 5 



I I I 



COOH COOH COOH 



Isoleucine, which was discovered by F. Ehrlich in 1904 in 

 beetroot residues, and later as a product of hydrolysis of 

 proteins, is isomeric with leucine, but is not identical with the 

 a-amino-w-caproic acid. Ehrlich considers it has the constitution of 



a-aminomethylethylpropionic acid ™ 3 \CH . CH . NH 2 . COOH 



on account of its synthesis from ^-amylalcohol, which was 

 oxidised to ^/-valeraldehyde and then combined with hydrogen 

 cyanide and ammonia, according to the second method of 

 preparation ; further, it gives tf'-amylalcohol on fermentation, 

 whereas leucine gives isoamylalcohol. Bouveault and Locquin 

 have also synthesised an a-aminomethylethylpropionic acid which 

 appears to be identical with Ehrlich's isoleucine. 



Tyrosine was not prepared by either of the above methods ; 

 benzoyltyrosine, as first synthesised by Erlenmeyer and Halsey 

 by the reduction of/-oxy-a-benzoylaminocinnamic acid obtained 

 from hippuric acid and /-oxybenzaldehyde, was employed by 

 Fischer for the separation of the optically active isomers. 



The second method was employed for the synthesis of the 

 oxyamino acids. Serine, discovered by Cramer in 1864, is the 

 simplest representative of this series, and was obtained by 

 Fischer and Leuchs from glycollic aldehyde, hydrogen cyanide, 

 and ammonia. Not only did this synthesis serve to definitely 

 establish the constitution of serine, but it was the first instance 

 of the employment of Strecker's method to build up oxyamino 

 acids from oxyaldehydes. The constitution of serine was deter- 

 mined a little later by Erlenmeyer by a different method. It 



