RECOGNITION OF PURINE-BASES AND NUCLEOSIDES BY THE AMINO-ACID CARBOXYLIC GROUP

Interactions of adenosine, guanosine and some of their methyl derivati ves, as well as hypoxanthine, xanthine and a number of their methyl an d glycosyl derivatives with neutral and ionized forms of the carboxyli c group in anhydrous DMSO, have been investigated by UV, IR and PMR sp ectroscopy. A consideration of our data and the results of other autho rs showed that the ionized carboxylic group specifically interacts wit h each of the unmethylated purine bases of the nucleosides. Monomethyl ation of adenosine and guanosine amino groups does not change the natu re of their interactions with the carboxylate ion. Methylation of guan osine and inosine at the N1 positions makes them unable to interact wi th both forms of the carboxylic group, but imparts the ability to inte ract with the neutral carboxylic group through a proton transfer to ad enosine. Inosine and guanosine methylated at the N7 positions become a ble to form complexes with the neutral carboxylic group through a prot on transfer as well. Xanthosine and inosine methylated at the N7 atoms form weak complexes with the carboxylate ion involving C8H protons. A nalysis of the data obtained and results of previous work provides spe ctroscopic evidence for the ability of the amino acid carboxylic group to differentiate between all the purine bases and most of their methy l derivatives.