II. CHEMISTRY 315 



starting materials. Riboflavin (III) could be obtained by condensation of 

 1 ,2-(rMU('thyl-4-aniino-5-(D-l'-ribityl:iiuiiic)l)CiiZ(Mie (I) with alloxan, wliicii 

 reacts in its lactimi form (II). 



The reaction is carried out in acid solution. Boric acid as a catalyst in- 

 creases the yield considerably.^*^- ■'^ Other catalysts are H2S, SnCl^ , or allox- 

 antin in the presence of 1 mole of HCl.'^" 



Four representative examples of riboflavin synthesis are given in the 

 following, which differ in the preparation of the intermediate I. 



(1) This intermediate can be prepared by condensation of o-nitroxylidine 

 (IV) with D-ribose^' and catalytic reduction of the formed riboside (V) 

 to the diamine (I).^" The yield was 16% riboflavin, calculated on the 

 amount of ribose used. 



, O 1 



IV 



H3C NH2 H3C NHCHCH(OH)3CH2 



w 



+ D-ribos e I -rr + H , 



H3C X02 H3C N02 



Recently, 6,7-diethyI-9-(D-r-ribityl)isoalloxazine has been prepared by 

 this method. ^^ 



(2) o-Nitrochlorobenzenes have been reacted with amino sugars or amino 

 alcohols, and the condensation product was hydrogenated to the diamine. *'' 

 Poor yields are obtained with sugars containing four and five hydroxyl 

 groups, but sugars with shorter chains (n < 4) give satisfactory yields. 



The required glycamines can be prepared by hydrogenation of the cor- 



« R. Kuhn, Angew. Chem. 49, 6 (1936). 



" R. Kuhn and F. Weygand, Ber. 68, 1282 (1935). 



5» Hoffmann-La Roche and Co., British Pat. 628,410 (Aug. 29, 1949) [C.A. 44, 4935 

 (1950)]. 



^^ By condensation of aromatic amines with D-ribose, two isomers are obtained which 

 have been considered to be the corresponding N-arylribofuranosylamines (A) and 

 N-arylriboi)yranosylamines (B); A is converted to B in the presence of water, 

 [L. Berger and J. Lee, J. Org. Chem. 11, 75, 84, 91 (1946); G. P. Ellis and J. Honey- 

 man, A'ature 167, 239 (1951); /. Chem. Soc. 1952, 1490 2053]. The Na,S04 complexes 

 of arylamine-N-u-ribopyranosides can l>e hydrogenated to the corresponding 

 ribitylamines in excellent yield [Hoffmann-La Roche, Inc., U. S. Pats. 2,384,102, 

 2,384,105 (Sept. 4, 1945) [C.A. 40, 600, 2854 (1946)]. 



" R. Kuhn and R. Strobele, Ber. 70, 773 (1937). 



" J. P. Lambooy, J. Am. Chem. Soc. 72, 5225 (1950). 



" P. Karrer, H. Salomon, K. Schopp, and E. Schlittler, Helv. Chim. Acta 17, 1165 

 (1934); P. Karrer, E. Schlittler, K. Pfaehler, and F. Benz, ibid. 17, 1516 (1934). 



