Regioselective sugar epimerization to rare sugar on ruthenium surface

Rare sugars, monosaccharides that occur only rarely in nature, exhibit physicochemical and biological properties distinct from those of naturally abundant sugars such as D-glucose. Their widespread utilization has been hindered by limitations in existing production methods, which rely primarily on equilibrium-constrained biocatalytic cascades or on synthetic approaches requiring multiple steps or organic reagents. Here we show the one-pot heterogeneous catalytic epimerization of methyl glucosides into rare sugar derivatives over supported Ru catalysts under hydrogen atmosphere in water. Among the supported metals examined, Ru uniquely promotes regioselective stereoinversion of 1- O -methyl β-D-glucopyranoside at the C3 position to produce 1- O -methyl β-D-allopyranoside without requiring additional reagents or multistep reactions. Isotopelabeling experiments reveal that dehydrogenation and hydrogenation proceed substantially faster than net epimerization, identifying surface-confined molecular rotation of a keto intermediate as the rate-determining step. Computer simulations further show that the experimentally observed regioselectivity originates from the low rotational free energy barriers and relatively high stability of the keto intermediate on the Ru surface. These findings identify molecular rotational dynamics on catalyst surfaces as a governing principle for stereochemical inversion reactions.