II. CHKMISTRY 



539 



3000 

 WAVELENGTH A 



Fk;. 3. Ultraviolet absorption spectra of the condensation product of phenan- 

 threnequinone with (1) the diaminocarboxylic acid from biotin; (2) 3,4-diaminotetra- 

 hydrothiophene, oxidized form; (3) 3,4-diaminotetrahydrothiophene, reduced form. 

 From D. B. Melville, Vitamins and Hormones 2, 55 (1944). 



presence of a five-membered urea ring in biotin, in Avhich the carbon atoms 

 bearing the amino groups must carry hydrogen atoms. 



CO 



NH 



NH 



lie 



CH 



Of the possible biotin structures (pp. 536, 537) only formulas VII and 

 X may comply with these conclusions; the other three are eliminated from 

 further consideration. 



5. Desthiobiotin 



Further fairly conclusive evidence for the correct structure of biotin 

 was furnished by the study of "desthiobiotin," the compound corresponding 

 to biotin with the sulfur atom removed and replaced by two hydrogen 

 atoms. Bougault et al.^^ have shown that treatment of disulfide with Raney 



38 J. Bougault, E. Cattelain, and P. Chabrier. Bull. Soc. chim. France 7, 781 (1940). 



