It is currently well established [1-4] that most aqueous and non-aqueous macroscopically homogeneous solutions of various low-molecular mass substances can be structured at nano- and mesoscale level (the size of inhomogeneities, aka supramers , ranges from ca. 1 nm to 10²–10³ nm). This novel type of very subtle (if judged by the energies involved, which are comparable with kT or even lower ) but spontaneous and powerful structuring of liquids was overlooked for a long time by researchers, and only very recently its importance for chemical reactions has been found and emphasized [4, 5].
We have been developing an approach, which explicitly accounts for the structure of a reaction solution and is based on the hypothesis that in many cases the real reactive species in solution are non-covalently-bonded supramolecular aggregates, supramers , rather than isolated molecules of reagents. According to the supramer approach, molecular structure and reaction conditions determine the structure of the resulting supramers, hence their chemical properties. An overview of the published and novel data will be presented, which suggests that the reaction solution structure cannot be ignored when analyzing the results of glycosylation and other reactions with carbohydrate derivatives. For example, a change in the quality of reaction solvent can (1) lead to substantial changes in density of supramers hence to dramatic reduction of reactivity of a glycosyl donor upon dilution  or (2) promote an efficient pyranose-to-furanose ring contraction . An abrupt change in the structure of supramers of glycosyl donor, which occurs at the “critical” concentration, can lead to a switch of glycosylation pathway  resulting in dramatic changes in reaction time and stereoselectivity [9, 10]. Protective groups pattern is also capable of influencing the structure hence properties of suparmers. N-Acetyl- and N,N-diacetylsialyl chlorides form supramers differing in size and density, which results in dramatic differences in their reactivity . Apparent nucleophilicity of glycosyl acceptors can be influenced by groups remote from the reacting hydroxy group but capable of influencing the structure of reaction solution .
This work was supported by the Russian Science Foundation (Project No. 16-13-10244-P).
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