420 



D. M. BROWN AND A. R. TODD 



is a prerequisite for alkali-lability. It is for this reason that they are not 

 degraded to small molecules by alkali,*^ '^^ and their stability in this respect 

 is in accord with the generally accepted resistance of dialkyl phosphates to 

 alkaline hydrolysis. ^^•*'- Acid hydrolysis of deoxyribonucleic acids clearly 

 depends on other factors and will be discussed later. 



Arguments based on complete hydrolysis to mononucleotides do not, of 

 themselves, permit rigid conclusions to be drawn regarding the precise 

 position of the internucleotidic linkages in ribonucleic acids, but they cer- 

 tainly limit the number of possible structures. In addition to structure 

 XVI, in which the linkage is shoASTi joining C3- in one nucleoside residue 

 to C5' in the next, a comparable structure in which C2' is linked to Cs- can 

 be drawn, which would be indistinguishable from XVI by alkaline hydroly- 

 sis. Such structures as XVIII, which involve C^r — Cs- linkages can, how- 

 ever, be dismissed, since they should yield dinucleotides stable to further 

 hydrolysis. This conclusion that Cb- — C5. linkages are incompatible with 

 hydrolysis to mononucleotides is implicit in the stability of adenosine-5' 

 benzyl phosphate towards alkali and acid, and is confirmed by the stability 

 of synthetic dinucleoside-5', 5 '-phosphates. Diuridine-5', 5 '-diphosphate*^ 

 (originally synthesized by Gulland and Smith, and believed erroneously to 

 be the 2 ',2 '-isomer), and adenosine-5' uridine-5' phosphate^^ (XIX) are 

 both stable to alkali under conditions which bring about complete hydroly- 

 sis of ribonucleic acid to mononucleotides; this stability is due to the ab- 

 sence of the vicinal hydroxyl group necessary for cyclization and hence 

 easy fission of the phosphoryl group in these substances. 



-c. 



C 



Co. 



Cs- P Co- 



C3-P- 



C,.-P — c, 



C,,-P-C,. 

 XVIIl 



NH, 



0- 



i OH OH 

 CH I I 

 I H H H 



N' 



O 



II 

 ■CH.-O-P-O-CH-r 

 I 

 OH 



XIX 



— — 

 OH OH 



■CH 



H H H 



0=f 



N 



OH 



" J. M. Gulland and H. Smith, J. Chem. Soc. 1948, 1532. 

 8« D. T. Elmore and A. R. Todd, J. Chem. Soc. 1952, 3681. 



