THE CHEMICAL CONSTITUTION OF ITS UNITS 43 



phenyl-a-aminopropionic acid and to exchange the sulpho-group for the 

 hydroxyl group was not successful, as in the fusion with potash the side 

 chain also became oxidised and no tyrosine resulted. They then pre- 

 pared p-nitrophenylalanine, and converted it into p-amidophenylalanine ; 

 on treating this latter compound with the calculated quantity of sodium 

 nitrite and warming, they obtained p-oxyphenylalanine, thus, 



C 6 H 5 C,H 4 .NO 2 C 6 H 4 .NH 2 C 6 H 4 .OH 



i Hi i Ha ^ ^ 



CH.NH 2 CH.NH 2 CH.NH 2 CH.NH 2 



COOH COOH COOH COOH 



This compound had the same properties as the natural tyrosine, which 

 was thus proved to be p-oxyphenyl-a-aminopropionic acid. 



Erlenmeyer jun., and Halsey, in 1899, synthesised tyrosine by the 

 condensation of hippuric acid with p-oxybenzaldehyde in the presence 

 of acetic anhydride. The reactions are the same as those described by 

 Erlenmeyer for the synthesis of phenylalanine, except that the hydroxyl 

 group of the p-oxybenzaldehyde becomes acetylated in the process : 



/OH /NHCOC 6 H 5 



C 6 H 4 / + CH/ ' +(CH 3 CO) 2 = 



\CHO \COOH 



/O.COCH 3 

 C 6 H/ /NH.COC 6 H 5 



\ 



\ +2H 2 O + CH 3 COOH 



\COOH 



The lactimide is again formed, but, on hydrolysis by alkali, the 

 acetyl group is removed and p-oxy-a-benzoylaminocinnamic acid is 

 obtained. On reduction it yields benzoyltyrosine, from which tyrosine 

 is formed by hydrolysis : 



OH /OH 



NH.COC 6 H 5 -> C 6 H 4 / 



COOH \COOH 



\CH 2 .CH(NH 2 )COOH 



Just as in the case of phenylalanine, p-oxy-a-benzoylaminocinnamic 

 acid when treated with ammonia yields an a-oxo acid, which reacts with 

 ammonia, giving a complex compound ; this, on hydrolysis, by heating 

 in a sealed tube with hydrochloric acid, is converted into tyrosine. 



