Accelerated Solid Phase Glycan Synthesis: ASGS.

Solid phase synthesis is the most dominant approach for the preparation of biological oligomers as it enables the introduction of monomers iteratively. Accelerated solid phase synthesis of biological oligomers is crucial for chemical biology, but its application to the synthesis of oligosaccharides is not trivial. Solid-phase oligosaccharide assembly is a slow process performed in a variety of conditions and temperatures, requires an inert gas atmosphere, and demands high excess of glycosyl donors. The process is done in special synthesizers and poor mixing of the solid support increases the risk of diffusion-independent hydrolysis of the activated donors. High shear stirring is a new way to accelerate solid phase synthesis. The efficient mixing ensures that reactive intermediates can diffuse faster to the solid support thereby increasing the kinetics of the reactions. We report here a stirring-based accelerated solid-phase oligosaccharide synthesis. We harnessed high shear mixing to perform diffusion-dependent glycosylation in a short reaction time. We minimized the use of glycosyl donors and the need to use an inert atmosphere. We showed that by tailoring the deprotection and glycosylation conditions to the same temperature, assembly steps are performed continuously, and full glycosylation cycles are completed in minutes.

Translating solution to solid phase glycosylation conditions.

Optimization of glycosylation conditions for automated glycan assembly is highly challenging, demands wasteful use of precious building blocks, and relies on nontrivial analyses. We developed a semi-quantitative method for automated optimization of glycosylation temperature that utilized minute quantities of donors and translated those conditions to solid-phase glycan assembly.

The breaking beads approach for photocleavage from solid support.

Photocleavage from polystyrene beads is a pivotal reaction for solid phase synthesis that relies on photolabile linkers. Photocleavage from intact porous polystyrene beads is not optimal because light cannot penetrate into the beads and the surface area exposed to irradiation is limited. Thus, hazardous, technically challenging and expensive setups are used for photocleavage from intact beads. We developed a new concept in which grinding the beads during or prior to irradiation is employed as an essential part of the photocleavage process. By grinding the beads we are exposing more surface area to the light source, hence, photocleavage can be performed even using a simple benchtop LED setup. This approach proved very efficient for photocleavage of various model compounds including fully protected oligosaccharides.