Non-Conventional Activation Methods in Carbohydrate Chemistry

Abstract:

Carbohydrate chemistry remains a cornerstone of contemporary organic and medicinal chemistry owing to the structural complexity and biological significance of saccharides. However, traditional synthetic techniques are frequently limited by poor regio- and stereoselectivity, long reaction times, harsh reaction conditions, and a heavy dependence on protecting-group strategies and organic solvents. In recent years, non-conventional activation techniques have emerged as effective and sustainable alternatives for carbohydrate transformations. This review summarizes recent developments in mechanochemical, photochemical, microwave-assisted electrochemical, and continuous-flow methods. Mechanochemical techniques, especially ball milling, have been applied to glycosylation, protection-deprotection, and biomass valorization, enabling solvent-free or minimal-solvent reactions with increased efficiency, selectivity, and reduced environmental impact. Photochemical activation, including visible-light-mediated and photocatalyst-free methods, has enabled radical-driven, site-selective functionalization under mild conditions, facilitating access to structurally complex glycoconjugate. Microwave-assisted synthesis, through rapid and uniform heating, substantially shortens reaction times and increases yields. Electrochemical activation, which promotes transformations in glycosylated compounds by direct electron transfer at an electrode without stoichiometric chemical oxidants, and continuous-flow (microreactor) technology that increases heat and mass transfer, safety, and scalability compared with batch processing are also further emerging as complementary green tools and are increasingly being combined as ‘flow-electrochemical platforms’. Despite these advances, challenges remain, including limited substrate scope, scalability, inadequate mechanistic understanding, and the need for specialized equipment. Taken together, these non-conventional techniques offer effective, sustainable, and adaptable alternatives to standard methods in carbohydrate synthesis, and are reshaping the field.