Recognition of purine bases and nucleosides by the amino acid carboxylic group

Abstract

Interactions of adenosine, guanosine and some of their methyl derivatives, as well as hypoxanthine, xanthine and a number of their methyl and glycosyl derivatives with neutral and ionized forms of the carboxylic group in anhydrous DMSO, have been investigated by UV, IR and PMR spectroscopy. A consideration of our data and the results of other authors showed that the ionized carboxylic group specifically interacts with each of the unmethylated purine bases of the nucleosides. Monomethylation of adenosine and guanosine amino groups does not change the nature of their interactions with the carboxylate ion. Methylation of guanosine and inosine at the N1 positions makes them unable to interact with both forms of the carboxylic group, but imparts the ability to interact with the neutral carboxylic group through a proton transfer to adenosine. Inosine and guanosine methylated at the N7 positions become able to form complexes with the neutral carboxylic group through a proton transfer as well. Xanthosine and inosine methylated at the N7 atoms form weak complexes with the carboxylate ion involving C8H protons. Analysis of the data obtained and results of previous work provides spectroscopic evidence for the ability of the amino acid carboxylic group to differentiate between all the purine bases and most of their methyl derivatives.