CHEMISTRY OF NUCLEOSIDES AND NUCLEOTIDES 141 



point, rotation, etc. On oxidation it gave, first, D-ribonic acid and then an 

 optically inactive trihydroxyglutaric acid. 



Full identification was obtained by the synthesis of D-ribose.^" 



More diflficulty was experienced in the identification of the carbohydrate 

 component of the pyrimidine nucleosides. These substances are stable to 

 dilute acids and concentrated acids convert the liberated pentose to furfural. 

 However, simultaneous hydrolysis and oxidation of cytidine with hydro- 

 bromic acid and bromine gave 5-bromouracil and D-ribonic acid,^^ indicating 

 that this nucleoside contains a D-ribosyl residue. Furthermore, pyrimidine 

 glycosides may be reduced catalytically to 4 , 5-dihydropyrimidine glyco- 

 sides which are quite labile towards acids, giving the pyrimidines and free 

 sugar. Thus uridine is converted into dihydrouridine (XI) and this, after 

 acid hydrolysis, gives D-ribose." 



-0- 



OH OH 

 I I 

 ^CH-CH-CH-CH-CH^-OH 



O^N 



OH 



XI 



4,5-dihydrouridine 



The presence of D-ribose in the four nucleosides obtained from ribonucleic 

 acid has been confirmed by the conversion of their sugar components into 

 D-ribobenziminazole. The suggestion that this type of nucleic acid may con- 

 tain small amounts of L-lyxose derivatives is now believed to be incorrect.'^ 



The sugar component of the deoxyribonucleosides proved very difficult 

 to identify. Acid hydrolysis under conditions similar to those employed with 

 the purine ribonucleosides effects complete conversion of the deoxysugar 

 to levulinic acid. Howe\xr, short hydrolysis of the guanine deoxynucleoside 

 with very dilute acid gave the base and a crystalline deoxypentose.^' ^^ 



" W. A. van Ekenstein and J. J. Blanksma, Chem. Weekblad 10, 664 (1913). 



" P. A. Levene and F. B. La Forge, Ber. 45, 608 (1912). 



12 J. M. Gulland and G. R. Barker, /. Cheyn. Soc. 1943, 625; J. M. Gulland, ibid. 1944, 



208; G. R. Barker, K. R. Cooke, and J. M. Gulland, ibid. 1944, 339; G. R. Barker, 



K. R. Farrar, and J. M. Gulland, ibid. 1947, 21. 

 " P. A. Levene and T. Mori, J. Biol. Chem. 83, 803 (1929). 



