540 BIOTIN 



nickel in alcoholic solution is followed by cleavage of the molecule according 

 to the following formula. 



R— S— S— Ri Raney nickel _^ R— SH + HS— R^ 



Similar treatment of organic sulfides results with good yield in cleaved 

 products from which the sulfur is removed. In the case of biotin methyl 

 ester the end product is desthiobiotin methyl ester, CUH20O3N2, which 

 by hydrolysis with either Ba(0H)2 at 140° or concentrated HCl at 200° 

 gives the desthiodiaminocarboxylic acid, C9H2o02N2.'^ 



If formula VII (p. 536) represents the correct structure of biotin, desul- 

 furization and hydrolysis of the urea ring should end in f , 17-diaminopel- 

 argonic acid, and in 5-methyl-e,f-diaminocaprylic acid if biotin possesses 

 the structure shown by formula X. 



H2N NH2 H2N NHo 



II II ^.. 



HC— CH HC— CH 



II I \ 



H3C CHzCHz-CHa-CHaCHsCOOH H3C CH-CHaCHsCHaCOOH 



/ 

 CH3 



f,ij-Diaminopelargonic acid 5-Methyl-e, {"-diaminocaprylic acid 



Carbon methyl determination and oxidative cleavage of the desthio- 

 diaminocarboxylic acid favored the structure corresponding to f,r?-di- 

 aminopelargonic acid with one carbon meth}^ group and pimelic acid 

 as oxidative cleavage product. 



Condensation of the desthiodiaminocarboxylic acid with phenanthrene- 

 quinone resulted in the formation of the quinoxaline, C23H2202N2.^* In 

 contradistinction to dihydroquinoxaline the compound gave a red color 

 with sulfuric acid and in its ultraviolet absorption spectrum it was very 

 similar to that of the quinoxaline derivative of 3 , 4-diaminotetrahydro- 

 thiophene. 



If the quinoxaline is formed from the diaminopelargonic acid, the result- 

 ing product should be represented by the following formula. 



CH3 CH3— CH2— CH2— CH2— COOH 



39 V. du Vigneaud, D. B. Melville, K. Folkers, D. E. Wolf, R. Mozingo, J. C. Keresz- 

 tesy, and S. A. Harris, ./. Biol. Chem. 146, 475 (1942). 



