538 



BIOTIN 



R H NH2 



\l/ 

 C 



I 



c 



/l\ 



R H NH2 



+ 



r\/\ 



.^ 



R H N 



R N I 



R H N 



Dihydroquinoxaline 



R N 



Quinoxaline 



by condensing 3 , 4-diaminotetrahydrothiophene" with phenanthrene- 

 quinone. 



N' 



< 



H 



H 



N 



3 , 4-Diaminothiophene 

 (dihydroquinoxaline) 



3 , 4-Diaminothiophene 

 (quinoxaline) 



As shown in Fig. 3, the absorption curve of the derivative obtained from 

 biotin was very similar to that of the quinoxahne derivative from 3,4- 

 diaminothiophene and was distinctly different from that pertaining to the 

 dihydroquinoxaline. This finding strongly indicated that the condensation 

 product of the diaminocarboxylic acid with phenanthrenequinone is a 

 dibenzoquinoxaline derivative. Thus, the 1,2-diamine structure of the 

 diaminocarboxylic acid was firmly established, providing proof for the 



3' G. W. Kilmer, M. D. Armstrong, G. B. Brown, and V. du Vigneaud, J . Biol. Chem. 

 145, 495 (1942). 



