Fluorous-tag assisted solution phase synthesis of mannose and heptomannose oligosaccharides and study of their binding interactions using carbohydrate microarray technology

Abstract

<p>Oligosaccharide synthesis is one of the challenging problems in carbohydrate chemistry. Carbohydrates are found in nature but they are present in heterogeneous form and in very small quantity. Over the past few decades chemical synthesis of carbohydrates has took off because of their biological properties. Since solution phase synthesis is very long and tedious, solid-phase synthesis took carbohydrate chemist to a new level. With the advent of automated solid phase synthesis developed by Seeberger and coworkers, many complex oligosaccharides were readily available for biological studies. The major drawback of solid-phase synthesis is it uses huge amount of sugar donors in each coupling cycle. In this dissertation, we use fluorous support for carbohydrate synthesis. This method requires only 1.5 equivalent of sugar donor as the reaction takes place in solution phase. The fluorous tail can be used for direct formation of carbohydrate microarrays to study protein-carbohydrate interactions;The first syntheses are reported of galactose, and fucose tagged with a single C8F17-tail for ease of purification as well as for facile array formation. Benzyl carbonate was used for neighbouring group participation in the synthesis of fluorous-tagged fucose. Screening of these carbohydrate microarrays against two lectins demonstrates that the noncovalent fluorous-fluorous interaction is sufficient to retain monosaccharides;A surface patterning method based on noncovalent immobilization of fluorous-tagged sugars on fluorous-derivatized glass slides allows the facile fabrication of carbohydrate microarrays. To expand the scope of these arrays, the first syntheses are reported of mannose and heptomannose oligosaccharides tagged with a single C8F17-tail for ease of purification as well as array formation. The fluorous-tag allows synthesis of mannose tetrasaccharide in a manner as to mimic automated synthesizer. High purity of oligosaccharides was obtained by just filtering the reaction mixture on a fluorous solid-phase extraction (FSPE) column. D-glycero-D-manno and L-glycero-D-manno heptoses were synthesized using similar method. The binding of these heptoses with mannose binding lectin Con A is not known. By using microarrays of fluorous-tagged heptoses, we discovered that these C-6 modified mannose binds to Con A.</p>