Efficient Solid-Phase Synthesis of a Complex, Branched N-Glycan Hexasaccharide: Use of a Novel Linker and Temporary-Protecting-Group Pattern

Abstract

Oligosaccharides are known to be important molecules in various biological processes; therefore, they have gained increasing interest in recent years. [1] However, in contrast to oligopeptides [2] and oligonucleotides [3] which are routinely constructed on automated synthesizers employing standardized building blocks and polymer supports, no generally applied synthetic methodology has yet appeared for the solidphase synthesis of complex oligosaccharides. [4] Success in this challenging task would provide several advantages over solution-phase techniques: 1) the required standardized building blocks could become commercially available, 2) an excess of building blocks and/or reagents could be used to drive reactions to completion, 3) the synthesis could become much faster, and 4) purification procedures could become simpler.Another fundamental key issue for solid-phase oligosaccharide synthesis is the availability of a high-yielding and stereoselective glycosylation strategy. Of the various glycosyl donors employed for this purpose, [5±11] O-glycosyl trichloroacetimidates [12] are suitable because of their high glycosyldonor properties in the presence of just catalytic amounts of a (Lewis) acid. In combination with solvent and temperature effects, type of catalyst, protecting-group pattern, and anchimeric assistance these donors also permit the desired control of the stereoselectivity at the anomeric center. [13] An additional requirement for solid-phase oligosaccharide synthesis is access to branching which is found in many oligosaccharides and glycoconjugates but not in peptides and oligonucleotides. Thus, for chain extension and branching, besides permanently protected functional groups, to be liberated only after completion of the solid-phase oligosaccharide synthesis, a suitable temporary-protectinggroup pattern is required. This temporary-protecting-group pattern provides the orthogonality required for branching and should also accommodate the demands of the linker which necessitates an additional temporary functional group.Based on our recent studies on new temporary protecting groups, [12, 14] new linker types, [14] and the synthesis of branched oligosaccharides, [12e, 15] we report herein a novel strategy which COMMUNICATIONS 4489 were measured at low temperatures (4.2 K or 78 K). The source was kept at room temperature. Spectra were recorded over a velocity range of AE 25 mm s À1 using an NaI(Tl) scintillation counter. Fitting of the spectra was carried out on the basis of the theoretically expected lineshape arising from the allowed transitions between the quadrupolar-split energy levels of the ground state (I ¼ 5/2) and the excited state (I ¼ 7/2).[10] a) The compound crystallizes in the monoclinic space group P2 1 /c, a ¼ 11.743 (2). Lorentz, polarization, and absorption corrections; 17 068 reflections; range 1.74 q 27.53; 9436 unique data; 8164 with I ! 2s(I). Structure solution was performed with SHELXS-97 using direct methods. [10b] Refinement was done against F 2 using SHELXL-97. [10c] All ...

Chiral-auxiliary-mediated 1,2-cis-glycosylations for the solid-supported synthesis of a biologically important branched α-glucan

“…It is important to note that different resin loadings could be achieved by employing different molar quantities of (4-trityloxymethyl-phenyl)-methanol. However, it was found that a loading of approximately 0.15 mmol g −1 resin gives optimal glycosylation results and further increases in loading led to decreases in coupling efficiencies 27,28…”

Oligosaccharide Synthesis on Solid, Soluble Polymer, and Tag Supports

“…27-31 Schmidt and coworkers have achieved solid-phase synthesis of a small library of N-glycan (Scheme 16.15). [32][33][34] They used the hydroxymethylbenzyl benzoate linker attached to the Merrifield resin. Glycosylation on the resin was successfully performed using the glycosyl trichloroacetimidates, 35 Later on, they have also investigated the orthogonality of the ester protecting groups at the vicinal hydroxyls on solid supports, that is, Fmoc, phenoxyacetyl (PA), allyloxycarbonyl (Alloc), and levulinoyl groups (Lev), at the C3 and C4 diols of the glucosamine as the model case.…”

Automated Chemical Oligosaccharide Synthesis: Novel Approach to Traditional Challenges

“…38 have stimulated many synthetic developments. 41,44–51 Another representative example is the globoside family of glycosphingolipids (Figure 1B; Neu, N -acetylneuraminic acid; Fuc, fucose), whose members present a broad range of significant biological roles as glycan biomarkers. For example, Gb3 is overexpressed in colorectal adenoma cells, 52 in Burkitt’s lymphoma cells, 53 and in breast and ovarian cancer.…”