Supramolecular photochirogenesis with novel cyclic tetrasaccharide: enantiodifferentiating photoisomerization of (Z)-cyclooctene with cyclic nigerosylnigerose-based sensitizers.

Isophthalic and terephthalic acid monoesters of cyclic nigerosyl-(1→6)-nigerose (CNN), a cyclic tetrasaccharide composed of four d-glucopyranosyl residues connected by alternating α-1,3- and α-1,6-linkages, were synthesized as novel chiral supramolecular sensitizers for enantiodifferentiating photoisomerization of (Z)-cyclooctene (1Z) to planar chiral (E)-isomer (1E). Despite the saucer-shaped shallow cavity of CNN that does not immediately guarantee strong ground-state interactions with 1Z, the sensitizer-appended CNNs afforded optically active 1E in such enantiomeric excesses that are much improved than those obtained with an α-cyclodextrin analog and comparable with those obtained with a β-cyclodextrin analog. Interestingly, the enantiomeric excess values obtained were a critical function of temperature and solvent to show an inversion of the product chirality by changing the environmental variants. Nevertheless, all of the differential activation parameters calculated from the temperature-dependent enantiomeric excesses gave an excellent compensatory enthalpy-entropy relationship, indicating an operation of a single enantiodifferentiating mechanism in the present chiral photosensitization with modified CNNs.