322 RIBOFLAVIN 



a method for small-scale preparation of ribofiavin-5'-phosphate. The origi- 

 nal method of Kuhn and Rudy" yields mainly a cyclic phosphate, ribo- 

 flavin-4' , 5'-phosphate, as shown by Forrest and ToddJ^ Acid hydrolysis 

 of the cyclic ester gives ribofiavin-5'-phosphate, which is identical with the 

 natural riboflavin phosphate. 



OH 

 OH OH OH / 



CH2— C— C— C— CH20P=0 

 H H H \ 



OH 

 H3C N N 



\ 

 CO 



I D-Riboflavin-5'-phosphate 



NH 

 / 

 H3C N CO 



A more complicated way of synthesis was carried out previously by con- 

 version of riboflavin into the 5-trityl ether, acetylation, removal of the 

 ether group, and phosphorylation of the exposed 5'-hydroxyl group with 

 phosphorous oxychloride; hydrolysis then gave D-riboflavin-5'-phosphate7^ 



Dichlorophosphoric acid seems to be a more useful reagent for the 

 phosphorylation of riboflavin than phosphorous oxychloride; FMN has 

 been prepared by this method in quantities greater than milligrams.^" 



The most recent method for the synthesis of riboflavin-5'-phosphoric 

 acid uses anhydrous metaphosphoric acid as a phosphorylating agent.^"^ 



FMN gives a crystallized monodiethanolamine salt with a water solubil- 

 ity of more than 200 times that of riboflavin. 



2. Biochemical Formation 



1 , 2-Dimethyl-4 , 5-diaminobenzene (I) seems to be the first biogenetic 

 precursor of vitamin B2 and vitamin B12 , both substances containing I 

 as a structural element.^^ 



" R. Kuhn and H. Rudy, Ber. 68, 383 (1935). 



78 H. S. Forrest and A. R. Todd, J. Chem. Soc. 1950, 3295. The cyclic riboflavin-4',5'- 



phosphate seems to be contained in a new flavin nucleotide (FAD-X), isomeric 



with flavin adenine dinucleotide (FAD). It cannot be stated at present whether 



FAD-X occurs naturally or is produced artificially during the isolation of FAD; 



F. M. Huennekens, D. R. Sanadi, E. Dimant, and A. I. Schepartz, /. Am. Chem. 



Soc. 75, 3611 (1953). 

 '9 R. Kuhn, H. Rudy, and F. Weygand, Ber. 69, 1543, 1974, 2557 (1936). 

 *" L. A. Flexser and W. G. Farkas, Xllth Intern. Congr. Pure Appl. Chem. New 



York, Abstr. Papers p. 71, 1951; Chem. and Eng. Chem. 1951, 3947. 

 80" M. Viscontini, C. Ebnother, and P. Karrer, Helv. Chim. Acta 35, 457 (1952). 

 81 D. W. Woolley, /. Exptl. Med. 93, 13 (1951); Proc. Soc. Exptl. Biol. Med. 75, 745 



(1950). 



