Chemical and enzymatic approaches to the synthesis of cyclic oligosaccharides

Display of Rich Reactivities of Endo‐ and Exocyclic Unsaturated Sugars that Parallel the Native Sugars

“…Solvents occupy the interstitial spaces and molecules arrange in a brick‐wall type arrangement in the solid state. The cyclic tetramer and pentamer, as adjudged through MD simulations, would show more elongated structures, by which the distances between the alternate glycosidic oxygens were altering [54] . As a result of the methylene insertion at the glycosidic bond, inner cavity dimensions of cyclic structures of the small‐rings matched that of larger ring CDs of similar dimensions.…”

“…Cyclo‐oligomerization of sugar monomers to the corresponding macrocycles is an outstanding approach advanced by Kochetkov and co‐workers, [13] Takahashi and Ogawa earlier, [14] and further by Stoddart and co‐workers [15,16] . In this approach, the sugar monomers possessing the glycosyl donor and acceptor sites initially undergo reaction and form the linear oligomer, which, in turn, cyclizes intramolecularly to complete the glycosylation and affords the sugar macrocycle [17,18] . Key to the cyclization is role of the conformation of the growing oligomer.…”

“…ESI‐mass spectrometric analysis suggested cyclic hexamer and nonamer formation also, however, efforts of chromatographic isolation was not successful for these higher macrocycles. The cyclization of the linear pentamer and subsequent deprotection of benzyl moieties afforded the cyclic pentasaccharide 64 (Scheme 9), apart from hydrolyzed pentasaccharide lactol monomer [48,51‐54] …”

“…As the macrocyclic ring size became larger, from tri‐ to pentasaccharide, the guest/host ratio increased too. For amantadine, the guest/host ratio was 2 : 1, as adjudged by isothermal titration calorimetry for the pentasaccharide, whereas that for the trisaccharide was 1 : 1 guest/host stoichiometry [18,54] …”

“…[15,16] In this approach, the sugar monomers possessing the glycosyl donor and acceptor sites initially undergo reaction and form the linear oligomer, which, in turn, cyclizes intramolecularly to complete the glycosylation and affords the sugar macrocycle. [17,18] Key to the cyclization is role of the conformation of the growing oligomer. A helical conformation might enforce the intramolecular cyclization.…”