Anodic Reactivity of Alkyl <i>S</i>-Glucosides

Abstract

A voltammetric study of a series of alkyl and aryl <i>S</i>-glucosides unveiled the reactivity patterns of alkyl <i>S</i>-glucosides toward anodic oxidation and found noteworthy differences with the trends followed by aryl derivatives. The oxidation potential of alkyl <i>S</i>-glucosides, estimated herein from square-wave voltammetry peak potentials (<i>E</i>_p), depends on the steric properties of the aglycone. Glucosides substituted with bulky groups exhibit <i>E</i>_p values at voltages more positive than the values of those carrying small aglycones. This relationship, observed in all analyzed alkyl series, is evidenced by good linear correlations between <i>E</i>_p and Taft's steric parameters (<i>E</i>_S) of the respective alkyl substituents. Moreover, the role of the aglycone's steric properties as a primary reactivity modulator is backed by poor correlations between <i>E</i>_p and the radical stabilization energies (RSEs) of the aglycone-derived thiyl radicals (RS•). In contrast, aryl glucosides' <i>E</i>_p values exhibit excellent correlations with the aryl substituents' Hammett parameters (σ+) and the ArS• RSEs, evidencing the inherent stability of the reactive radical intermediate as the primary factor controlling aryl glucoside's electrochemical reactivity. The reactivity differences between alkyl and aryl <i>S</i>-glucosides also extend to the protective group's effect on <i>E</i>_p. Alkyl <i>S</i>-glucosides' reactivity proved to be more sensitive to protective group exchange.