π-Interactions of Modified Nucleobases. On Mesomeric Purine Betaines with Inversed Charge Properties.

Abstract

Abstract Intermolecular interactions of modified nucleobases with altered charge properties in relation to natural systems are studied. We prepared conjugated mesomeric betaines of purines and examined their properties by semiempirical calculations, 1H NMR titrations and ESI mass spectrometry. Thus, nucleophilic substitutions of 4-(dimethylamino)pyridine and pyridine, respectively, on 2-amino-6-chloropurine 1 and 2,6-dichloropurine 2 resulted in the formation of purin-6-yl hetarenium salts 3–6. These were converted into the conjugated mesomeric betaines 7–10, respectively, on treatment with the anion exchange resin Amberlite® IRA-400 in its hydroxy form. The betaines 7–10 possess umpoled purine rings in relation to 7-methylguanine that forms the betainic 5′-cap structure of m-RNA. We studied the π-stacking interactions of the conjugated mesomeric betaine 8 and of its cationic precursor 4 with l-tryptophan, adenine, adenosine, and guanosine in deuterated water.