Project Summary Every living cell on the planet is covered by a dense layer of glycans. These complicated structures play critical roles in many biological and disease processes. Functional studies and medical applications require well-defined glycan structures. While automated peptide and nucleic acid syntheses have matured and allow non-specialists to access defined standards, the synthesis of glycans and glycoconjugates is still often laborious, time- consuming, and requires specialties. So far, only a few platforms have been introduced to automate chemical syntheses of glycans but suffer from slow reaction rates, low selectivity, efficiency, and yields, especially in preparing complex glycans. A mature and practical automated system to synthesize complex glycans is not available. In the past decade, glycosyltransferases (GTs)-catalyzed reactions have been widely explored to prepare diverse complex glycans. With perfect regio- and stereo-selectivity as well as high conversion rates, they are attractive for automation. The challenge is tedious repeated process of separating intermediates and the final product. This has been well overcome by solid-phase-based automation in peptide and nucleic acid synthesis. But GTs are often much less active when the acceptor substrate is immobilized, causing slow conversions and low yields. Catch-and-release strategies have the potential to solve the problem. In such strategy, acceptors are tagged with a functional group, and “captured” on solid phase through specific interactions between the group and the solid phase. After cleanup, they can be “released” using appropriate solvents to disrupt the interaction. Several “catch-and-release” strategies have been introduced to expedite enzymatic assembly of glycans, but all suffer from one major drawback: chemicals, organic solvents, high concentrations of salts, etc, must be introduced to release glycans from solid phase. Thus, extra steps which often cannot be easily realized on automated platforms have to be involved to clean up each intermediate for the next round reaction and catch-and-release separation. This will greatly complicate and prolong automated synthesis and decrease efficiency. We propose a simple catch-and-release strategy enabled by DNA hybridization (Catch) and dehybridization (Release). In this strategy, the glycan an conveniently “captured” with any GT reaction mixtures, and “released” using pure water. We believe this catch-and-release strategy is the missing puzzle to tackle practical automated glycan synthesis. Iterative enzymatic assembly is already widely employed to prepare complex glycans, and many liquid handling systems are commercially available. Upon the success of current technology, these can be readily integrated to generate a practical and costless automated platform for glycan synthesis (future work).

Project Narrative A practical automated system for complex carbohydrate synthesis is currently unavailable. Iterative enzymatic assembly of carbohydrates is attractive for automation, the final roadblock is the lack of simple and efficient methods for rapid intermediate and product separation. Here we propose a DNA hybridization/dehybridization- based catch-and-release method to tackle the remaining challenge toward the automatic enzymatic synthesis of complex carbohydrates.