RIBOFLAVINE 



A somewhat better method (p. 143) was that of T. Reichstein 

 and M. Steiger ; ^^ this gave about 36 g. of ribose from i kg. of 

 calcium gluconate. 



The mixture of ribonic acid and unchanged arabonic acid was 

 freed from the latter by conversion to the calcium salt, and the ribonic 

 acid was then isolated as the cadmium salt and converted to ribose 

 by reduction with sodium amalgam. 



Ribose can also be made in one stage from calcium altronate by 

 oxidation with hydrogen peroxide in presence of ferric acetate ^^ but, 

 unfortunately, altronic acid is not readily available, although it can 

 be made from cellobiose acetate : 



Cellobiose octaacetate > Acetochloro-celtrobiose 



(H-acetochloro-cellobiose) > celtrobiose ^ altronic acid 



or from sedoheptulose, a seven-carbon sugar occurring in Sedum 

 spectaUle}'^ 



CH2OH 



CO 



COOH 



HO 

 H— 

 H— 

 H— 



— H 

 —OH 

 —OH 

 —OH 



CH2OH 

 Sedoheptulose 



HO— 

 H— 

 H— 

 H— 



— H 



H20, 

 —OH > H- 



— OH 

 —OH 



CH2OH 



Altronic 

 acid 



H— 

 H— 



CHO 

 —OH 

 —OH 

 —OH 



CH2OH 

 Ribose 



Methods of Synthesis not involving Ribose 



A method that avoided the use of D-ribose was discovered by F. 

 Weygand,^^ who showed that the Amadori rearrangement was not 

 limited to glucose, as had been previously supposed. He prepared, 

 inter alia, 3 : 4-dimethylaniline-D-arabinoside by condensing D-arab- 

 inose with 0-4-xylidine, and converted it into the D-isoarabinosamine 

 by heating at 75° C. This yielded 3 : 4-dimethyl phenyl-D-ribamine 

 on hydrogenation in alkaline solution. The product obtained by 

 coupling with a diazo compound was reduced to the corresponding 

 amine by the method of Karrer and Meerwein.^ (See opposite page) 

 Incidentally Weygand suggested that the vitamin Bg activity of 

 araboflavine (see page 206) might be due to contamination with ribo- 

 fiavine formed by an Amadori rearrangement. 



A variant of Weygand's method was patented by the Miles Labs. 

 Inc.^* 0-4-Xylidine was condensed with D-arabinose under conditions 



144 



