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: 
COOC;Hs COOC,H; COOC,H,; COOH 
| Na C;Hs.CH,Cl | KOH | Br 
Gk -> CHNa —> CH .CH,.C,Hs —> a . CH,. C,H; > 
| | 
COOC,H,; COOC,H; COOC,H; COOH 
COOH H H 
| NE 
C(Br).CH,.C,H;-> C(Br).CH,C,Hs —> C(NH,). CH, C,H; 
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-#-caproic acid. Ehrlich considers it has the constitution of 
a-aminomethylethylpropionic acid oe »CH ~CH. NA. COGH 
2445 
on account of its synthesis from d-amylalcohol, which was 
oxidised to d-valeraldehyde and then combined with hydrogen 
cyanide and ammonia, according to the second method of 
preparation; further, it gives d-amylalcohol on fermentation, 
whereas leucine gives isoamylalcohol. Bouveault and Loequin 
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 
