Synthesis of branched–backbone oligosaccharides of the pectic RG-I plant cell wall polysaccharide

摘要

Plants are an essential part of life on earth. They are the primary food producers, climate regulators and provide habitats for other organisms. The dependence of industrialized nations on plant cell walls due to their industrial applications has rapidly increased. Cellulose, hemicelluloses, and pectin polysaccharides are the main structural components of the plant cell wall. Among plant carbohydrates, pectins are highly heterogeneous polysaccharides. They are mainly found in the primary plant cell wall and contribute to various cell functions, including support, defense, signaling, and cell adhesion. Rhamnogalacturonan I (RG-I) is one of the structural classes of pectic polysaccharides, along with homogalacturonan, rhamnogalacturonan II, and xylogalacturonan. The chemical structure of RG-I is complex having a backbone consisting of alternating α-linked L-rhamnose and D-galacturonic acid units with numerous branches of galactan, arabinan, or arabinogalactan positioned at C-4 of the rhamnose residues. The use of defined oligosaccharides rather than isolated polysaccharides can aid in obtaining detailedinformation about biosynthetic pathways, plant evolution, and agronomical properties. Furthermore,biological testing can provide new insight into plant biology; important for plant preservation, engineering,and utilization of plants as a source of bioenergy. Present work towards defined RG-I substructures involvesa [4+3]-coupling to furnish a heptasaccharide backbone unit (see Figure 1). Moreover, installation of sidechains of different lengths and nature can be installed at the C-4 position of rhamnose unit. Finally, theseoligosaccharides will be deprotected to furnish target molecules to pursue biological studies.