Bimodal concentration-dependent reactivity pattern of a glycosyl donor: Is the solution structure involved?

Changes in concentration (0.001–0.1 M) of an arabinofuranosyl donor (1) have been shown to modulate the temperature T at which activation of 1 occurs (from −23 °C to +7 °C), the reaction time (from 1.5 h to 3 days) and the yield of the disaccharide formed (from 14% to 82%). At concentrations exceeding 0.01 M, these parameters, as well as the specific optical rotation of the solution of 1, virtually do not depend on concentration suggesting formation of reacting species (supramers) of glycosyl donor with similar structures, hence reactivities, but considerably different from those formed in more dilute solutions. The found critical concentration (0.01 M) separates two concentration ranges of reaction solutions corresponding to two types of solution structure that are featured by the presence of fundamentally different supramers of glycosyl donor, which have distinct chemical properties. These results allow a fresh look at the problems of reactivity of chemical compounds and selectivity of the reactions in which they participate. [Display omitted] •Influence of concentration on outcome of arabinofuranosylation was studied.•Two concentration ranges of solutions with different structures were revealed.•Bimodal reactivity pattern of glycosyl donor was discovered.•Bimodality was linked to the presence of two types of supramers of glycosyl donor.