Synthesis and application of RG-II oligosaccharides

Carbohydrates are the predominant component of biomass on earth as they are an integral part of all living species, including plants, animals, and bacteria. Carbohydrates have important structural and functional roles in biology but remain, in contrast to the other two main classes of biopolymers, oligonucleotides and proteins, poorly understood. Plants produce an enormous diversity of carbohydrates that fulfill essential roles during the life cycle of the plant. Plants contain many unique carbohydrates that are not found in animals but are still mostly conserved across the plant kingdom. The vast majority of plant carbohydrates are part of the cell wall. Plant carbohydrates are major nutritional resources in food and feed and receive an enormous interest as sources of renewable materials and for the production of fuels and chemicals. A prerequisite to enhance the economic viability of plant biomass as a renewable resource is a detailed knowledge of the carbohydrate structures in the cell wall and how they are constructed by the plant. However, access to pure carbohydrates for structural and biological studies is difficult due to their high molecular complexity. The structurally most complex carbohydrate in nature is rhamnogalacturonan-II (RG-II), a highly conserved pectic polysaccharide, containing twelve different types of monosaccharides that are connected through 20 different linkages. The complex structure of RG-II poses enormous challenges for organic chemists, including the synthesis of rare and acidic monosaccharides, a highly congested structure, and a high number of 1,2 -cis-glycosidic bonds. We will develop new synthetic strategies to access oligosaccharide fragments of the RG-II structure, which will be printed on glass slides in a robot assisted manner to investigate carbohydrate-protein interactions. The availability of such glycan arrays with highly complex RG-II fragments will for the first time enable the systematic elucidation of enzymes (glycosyltransferases) involved in RG-II biosynthesis and the characterization of molecular tools (antibodies), aiming at detecting and monitoring specific RG-II epitopes within plant cell walls. The generated knowledge will facilitate future developments towards improved biomass digestibility, material strength of plant-derived products, and the shelf life of fruits and vegetables.