2006 Volume 18 Issue 104 Pages 353-370
The mechanochemical studies of carbohydrate ring flipping by both top-down and bottom-up approaches are surveyed. In the top-down approaches, the traction studies of polysaccharides by atomic force microscopy (AFM) disclosed their interesting behavior: they become abruptly flexible at certain pulling forces due to the synchronous ring flips of the monosaccharide units. This abrupt flexibility confers a shockabsorbing mechanism on glycoproteins and glyco-coated cells. Regarding the bottom-up approach, we succeeded in controlling the ring flip of carbohydrates to find that a 2, 4-diaminoxylose derivative (hinge sugar) easily undergoes the ring flip by chelation to a metal ion at the amino groups. The metal-ion-induced bending of the hinge sugar was even more efficient when it was incorporated in a trisaccharide, probably due to the interaction between the reducing and non-reducing terminus sugars. For application, we invented a hinge-sugar-based metal ion sensor, in which a chelationdriven and pliers-like motion of the dipyrenylmethyl hinge sugar causes stacking of two pyrene groups, giving rise to excimer fluorescence. Hinge sugar was also applicable to the tether in a [2+2] cycloaddition reaction. These studies emphasize a new aspect of carbohydrates as motional components in biology and material science.
