II. CHEMISTRY 



VIII IX X 



R = — CHzCHjCHz-COOH 



/3-keto acid arising during the oxidation, \\-ith the consequence of three 

 additional structural possibilities, VIII, IX, and X.'* 



X-ray diffraction study gave no unequivocal answer in favor of any of 

 the above five possibilities.^^ 



4. The Size of the Urea Ring 



In three of the discussed structural formulas the urea rings were five- 

 membered, whereas the remaining two were trimethylene derivatives.'^*' 



The size of the urea ring was established by condensation of the di- 

 aminocarboxylic acid with phenanthrenequinone.^^ A crystalline quinox- 

 aline derivative was thus obtained, C23H20O2N2S, m.p. 202 to 204°. Al- 

 though the formation of quinoxaline derivatives by the condensation of 

 1,2-diamines with orthoquinones is well established, no examples of the 

 condensation of 1 , 3-diamines with phenanthrenequinone could be found 

 in the literature. 



Two different compounds, dihydroquinoxalines or quinoxalines, may 

 be obtained through the condensation of non-aromatic 1,2-diamines with 

 phenanthrenequinone, according to the reaction on following page 



The analytical composition as well as certain color reactions of the con- 

 densation product derived from biotin appeared to favor the quinoxaline 

 structure rather than that of a dihydroquinoxaline. The ultraviolet ab- 

 sorption spectrum of the condensation product was compared with the 

 spectra of the quinoxaline and dihydroquinoxaline derivatives obtained 



"V. du Vigneaud, K. Hofmann, and D. B. Melville, ./. Am. Chem. Soc. 64, 188 



(1942). 

 " I. Fankuchen, /. Am. Chem. Soc. 64, 1742 (1942). 

 3« K. Hofmann, G. W. Kilmer, D. B. Melville. V. du Vigneaud, and H. H. Darby, 



J. Biol. Chem. 145, 503 (1942). 



