chemistry of nucleosides and nucleotides 157 



4. General Properties of Nucleosides 



The nucleosides in general are colorless, crystalline substances with 

 rather high melting points. They vary somewhat in their solubility in water, 

 but most representatives are readily soluble in hot, considerably less soluble 

 in cold water. The pyrimidine nucleosides uridine and cytidine are more 

 soluble in water than are the purine nucleosides. Both pyrimidine and purine 

 nucleosides are insoluble in the more common organic solvents. Nucleosides 

 containing amino groups (adenosine, cytidine) are rather weak bases, while 

 those containing hydroxy 1 groups on the heterocyclic nucleus (xanthosine, 

 inosine, uridine) are weak acids. 



Physical properties and useful derivatives of some of the better known 

 natural nucleosides are listed in Table I. 



5. Miscellaneous Nucleosides 



The nucleosides inosine, xanthosine, hypoxanthine deoxyriboside, and 

 uracil deoxyriboside which have been described in the previous sections 

 are thought to be absent from the native nucleic acids, but frequently arise 

 during isolation, or during hydrolysis of the isolated macromolecule to its 

 component nucleosides. In addition to these, some nucleosides which have 

 been isolated from natural sources are neither components nor degradation 

 products of nucleic acids. These are discussed below. 



a. Adenine Thiomethyl Pentoside {5^ -deoxy-5' -methylthioadenosine) 



This nucleoside was first isolated from yeast, ^^ but is probably present in 

 the tissues of many animals. On hydrolysis it gives adenine and a sulfur- 

 containing sugar, 5-deoxy-5-methylthioribose. The structure of the aldo- 

 pentose follows from its reduction to the pentitol, periodate titration, and 

 direct comparison with synthetic 5-deoxy-5-methylthiopentose deriva- 

 tives. ^^'^"^ The ultraviolet absorption spectrum of the nucleoside supports a 

 9-glycoside structure."'- With nitrous acid it gives "hypoxanthine thio- 

 methyl pentoside, "^°^ the structure of which has been proved by synthe- 

 gjgio4,io5 Thig synthesis starts from 2',3'-isopropylidene-5'-p-toluene 

 sulfonylinosine,^^ from which is prepared 2',3'-isopropylidene-5'-methyl- 

 thio-5'-deoxyinosine. The isopropylidene residue may be removed by 



" J. A. Mandel and E. K. Dunham, J. Biol. Chem. 11, 85 (1912). 



98 P. A. Levene and H. Sobotka, J. Biol. Chem. 65, 551 (1925). 



" G. Wendt, Z. physiol. Chem. 272, 152 (1942). 

 lo" K. Satoh and K. Makino, Nature, 165, 769 (1950). 

 >»' F. Weygand, O. Trauth, and R. Lowenfeld, Ber. 83, 563 (1950). 

 '»2 R. Falconer and J. M. Gulland, J. Chem. Soc. 1937, 1912. 

 i°3 R. Kuhn and K. Henkel, Z. physiol. Chem. 269, 41 (1941). 

 lo^ J. Baddiley, /. Chem. Soc. 1951, 1348. 

 •"^ K. Satoh and K. Makino, Nature 167, 238 (1951). 



