Phenylalanine and Tyrosine Synthesis 



219 



to CO2. Suitable nitro-derivatives must therefore be prepared 

 (Fig. 2). 



Phenylalanine and tyrosine isolated from the experiment 

 with labelled glucose show no significant radioactivity at 

 ring carbon atoms 1, 3, 4 and 5. On the other hand, C2 and 



( 3i|) 



HO^/ \_CH2CJcppJH ^ CO 



NH- 



[ 2^-= ' 



H0/\ 



cop: H 



N02' 

 NO2 



I 



3 CBr3 NO2 



C,.3.5 

 (2tl) 



NO2 (2314) 



(a) Tyrosine. 



(77+8) 



CO2 

 



3 2 



/ 



( 1*1) 



» H 

 CHg cIcOO^'h— COs 



NH- 



^^ 



_-y 



/ 



22t 2 



I I 



ICOOlH 



(97*10) 

 ■* CO2 

 B 



^«H. 



Br/^''"'">">f\„„. 



1 NO2 



HO 2^^ 



/| NO. 



CBfjNOg 

 (37±4) 



2 CBt J NOg 

 (Cg .OR Cg.C^) 

 (22±2) 



(b) Phenylalanine. 



Fig. 2. Degradation of Benzenoid amino-acids. 



Cq in the phenylalanine ring account for a minimum of three 

 <juarters of the ^*C content of the benzene nucleus. Chemical 

 methods which allow to distinguish between these two carbon 

 atoms in compounds possessing the symmetry of phenylala- 

 nine and tyrosine do not exist, and therefore we are unable to 

 say whether C2 and Cg or only one of the two positions is 

 labelled. 



For reasons to i3e given below, we favour the alternative 

 that only one of the two locations contains ^*C. The absence 



