Systematic synthesis of rare sugars and stereospecific conversion via photocatalysis.

Rare sugars have gained attention as potential raw materials for pharmaceuticals and functional foods. Photocatalysis presents a promising approach for rare sugar synthesis due to its mild reaction conditions and environmental compatibility. While previous photocatalytic methods reported individual routes for specific rare sugars, systematic synthesis through a unified methodology has not been achieved, and control of optical isomers remains insufficiently explored. This study investigated a comprehensive photocatalytic approach for the systematic conversion of monosaccharides with stereochemical configuration preservation. When D-glucose in aqueous solution underwent photocatalytic treatment under UV irradiation, D-arabinose formation was confirmed through HPLC, LCMS, and ¹H NMR analyses. Similarly, D-lyxose, D-ribose, and D-xylose were produced from D-galactose, D-allose, and D-gulose, respectively. Further photocatalytic treatment of these aldopentoses yielded corresponding aldotetroses-D-erythrose from D-ribose and D-arabinose, and D-threose from D-lyxose and D-xylose. This demonstrated successful systematic conversion from aldohexoses to aldopentoses and subsequently to aldotetroses in a single reaction system. Moreover, when L-glucose and L-arabinose were used as starting materials, L-arabinose and L-erythrose were obtained, respectively, confirming stereochemical configuration preservation throughout the conversion process. This method provides a systematic approach for rare sugar synthesis while controlling stereochemical configurations.