Kinetics and mechanism of the acid-catalysed hydrolysis of regioisomeric benzotriazole and 8-azaadenine nucleosides
First-order rate constants for the acid-catalysed hydrolysis of ribo- and 2′-deoxyribonucleosides derived from 1H-, 2H- and 3H-benzotriazoles and 7H-, 8H- and 9H-8-azaadenines have been determined over a wide pH range. Partial rate constants for reactions via mono- and di-protonated substrates have been calculated with the aid of spectrophotometrically determined pKa values. The mechanisms of hydrolysis reactions have been elucidated by the effects that polar substituents on the base moiety exert on the protonation and heterolysis steps. Reactivities of various regioisomers have been compared, and reasons for the exceptional hydrolytic instability of N3-alkylated purine nucleosides briefly discussed.