Methylation study of ribonucleosides, deoxyribonucleosides, and 2′-O-methylribonucleosides with trimethylsulphonium hydroxide and trimethylsulphonium iodide. Influence of the 2′-hydroxy-groups on the reactivity of the base moieties of ribonucleosides

Abstract

Methylations of the naturally occuring ribonucleoside (1), deoxyribonucleoside (2), and 2′-O-methylribonucleoside (3) were carried out using trimethylsulphonium hydroxide (Me₃SOH) and trimethylsulphonium iodide (Me₃Sl). The base moiety of (2) and (3) are more reactive than the corresponding base moiety of (1). The sites and extent of methylation of (2) are considerably different from those of (1), but are almost identical with those of (3). The reactivities of (1)–(3) are discussed in connection to an intramolecular interaction of the 2′-OH groups with the base moiety of (1). The methylating characteristics of Me₃SOH and Me₃Sl are also described. The kinetics indicate an S_N2 mechanism for methylation of nucleosides by Me₃S⁺ ions.