38 W. G. OVEREND AND M. STAGEY 



3'-positions, but not necessarily respectively.^"^- ^oe [Compare Chapters 4 

 and 12.] The structures of the subsequently isolated isomeric pairs of 

 guanylic,^^ cytidylic^*'^ and uridylic acids-"^ have been assumed to be the 

 same as the adenylic acid pair. The demonstrated acid-catalyzed migra- 

 tion of the phosphate group^''^-^"^ made difficult a decision as to which 

 nucleotide was 2'- and which 3'- in synthetic^"* and degradative^o^ ap- 

 proaches to the problem. The problem has been solved in elegant fashion 

 by Cohn et a/./^° who succeeded in identifying the isomeric adenylic acids 

 "a" and "b" as the adenosine-2'- and -3 '-phosphates, respectively. They 

 were able to hydrolyze catalytically the iV-glycoside linkage of the individ- 

 ual adenylic acid isomers with the hydrogen form of a polystyrene sulfonic 

 acid resin (Dowex 50) at a rate comparable to the rate of isomerization. The 

 advantage of this method of hydrolysis lies in the fact that the ribose phos- 

 phates are released from the resin at the time of formation (in contrast to 

 adenine and most of the adenylic acid) and, therefore, little or no iso- 

 merization takes place subsequent to their formation. The two ribose 

 phosphates obtained were separated by an ion-exchange procedure.'*^ The 

 ribose phosphate "a" (derived from adenyhc acid "a") could be converted 

 to a methyl phosphoribopyranoside which consumed one mole of periodate, 

 and to a ribitol phosphate with a marked optical activity which is en- 

 hanced by borate. The reverse properties (i.e., no periodate oxidation of the 

 methyl phosphoriboside, no optical activity of the ribitol phosphate with 

 or without borate) were noted for the "b" ribose phosphate. The possi- 

 bility of the 1- or 5-phosphate isomers arising was excluded by the ion- 

 exchange behavior of the substances, and the 4-phosphate ester is a 'priori 

 excluded by the furanoside structure of the parent nucleotide.^^" Hence it 

 follows that ribose phosphate "a" and *'b" are ribose-2- and -3-phosphate, 

 respectively. This is the first isolation of ribose-2-phosphate. Moreover 

 the work proved that Levene and his colleagues in their earlier structural 

 studies of the purine nucleotides were dealing with the "b" isomers which 

 would be expected to give rise to ribose-3-phosphate if no migration oc- 

 curred during isolation. 



Initial attempts by Levene and Jorpes^^^ to prepare ribose-3-phosphate 

 by acidic hydrolysis of adenosine-3 '-phosphate, were unsuccessful as 

 cleavage of the basic and phosphate residues proceeded at about the same 



206 D. M. Brown and A. R. Todd, J. Chem. Soc. 1952, 44, 52. 



206 D. M. Brown, D. I. Magrath, and A. R. Todd, J. Chem. Soc. 1952, 2708. 



207 W. E. Cohn, /. Am. Chem. Soc. 72, 2811 (1950). 



208 D. M. Brown, L. J. Haynes, and A. R. Todd, J. Chem. Soc. 1950, 408. 



209 D. G. Doherty, Abstracts Papers 118th Meeting Am. Chem. Soc. 56 (1950). 



2>o p. A. Levene and R. S. Tipson, J. Biol. Chem. 94, 809 (1932); 97, 491 (1932); 101, 



529 (1933). 

 2" P. A. Levene and E. Jorpes, J. Biol. Chem. 81, 575 (1929). 



