Synthesis of a representative fragment of the side chain A belonging to Rhamnogalacturonan II

FABIAN PFRENGLE; SEBASTIÁN O. SIMONETTI

Riva di Garda

Simposio; 19th Tetrahedron Symposium; 2018

Elsevier

Pectin is astructural heteropolysaccharide found in the primary cell wall of terrestrialplants. It is composed of different polysaccharide domains, among which Rhamnogalacturonan-II(RG-II) is particularly remarkable due to its unprecedentedly complex structureconsisting of twelve different monosaccharides connected by more than 20different glycosidic linkages. Despite this complexity, the molecular structureof RG-II is highly conserved throughout the plant kingdom. RG-II consists of ahomogalacturonan backbone that is substituted with four different side chains(A-D). In side chain A, two apiose residue of neighboring polysaccharides form boratediesters that are essential for a normal growth of the plant.1 Despitethe importance of RG-II for plant survival, the biological function as well asthe biosynthesis of RG-II is mostly unknown.2 Synthetic oligosaccharidefragments of RG-II are promising molecular tools to characterize biosyntheticenzymes implicated in RG-II synthesis, as they can serve as acceptor substratesfor glycosyltransferases. Here, we present our studies towards the synthesis ofrepresentative oligosaccharide fragments of the side chain A such as tetrasaccharide1. The synthesis is based onbuilding blocks 2-5, which were designed to function inboth solution-phase and automated solid-phase synthesis (Scheme 1). Thesebuilding blocks can be easily further modified to allow for the incorporation ofadditional monosaccharide residues from the side chain A, or the attachment ofthe oligosaccharide to the galacturonic acid residues of the linear backbone.Monosaccharide building blocks 2-5 were obtained in few steps and boththe reactivity and the selectivity in the formation of the desired glycosidiclinkages were evaluated in solution-phase and automated solid-phase synthesis.