Hochkonvergente „Zwei-Wege-Strategie” zur Synthese des tumorassoziierten Antigens Globo-H

Recognition and site-selective transformation of monosaccharides by using copper(II) catalysis

We demonstrate copper(II)-catalyzed acylation and tosylation of monosaccharides. Various carbohydrate derivatives, including glucopyranosides and ribofuranosides, are obtained in high yields and regioselectivities. Using this versatile strategy, the site of acylation can be switched by choice of ligand. Preliminary mechanistic studies support nucleophilic addition of a copper-sugar complex to the acyl chloride to be turnover limiting.

Toward automated oligosaccharide synthesis

Carbohydrates have been shown to play important roles in biological processes. The pace of development in carbohydrate research is, however, relatively slow due to the problems associated with the complexity of carbohydrate structures and the lack of general synthetic methods and tools available for the study of this class of biomolecules. Recent advances in synthesis have demonstrated that many of these problems can be circumvented. In this Review, we describe the methods developed to tackle the problems of carbohydrate-mediated biological processes, with particular focus on the issue related to the development of the automated synthesis of oligosaccharides. Further applications of carbohydrate microarrays and vaccines to human diseases are also highlighted.

Chemoenzymatic Syntheses of Tumor-Associated Carbohydrate Antigen Globo-H and Stage-Specific Embryonic Antigen 4

Gangliosides have attracted much attention due to their important biological properties. Herein, we report the first chemoenzymatic syntheses of two globo series of ganglioside oligosaccharides, Globo-H 1 and stage-specific embryonic antigen-4 (SSEA-4) 2. The common precursor SSEA-3 pentasaccharide for these two compounds was assembled rapidly using the pre-activation based one-pot glycosylation method. The stereoselectivity in forming the 1,2-cis linkage in SSEA-3 was attributed to a steric buttressing effect of the donor rather than electronic properties of the glycosyl donors. SSEA-3 was then successfully fucosylated by the fucosyltransferase WbsJ and sialylated by sialyltransferases CST-I and PmST1 producing Globo-H and SSEA-4 respectively.

A highly efficient synthetic strategy for polymeric support synthesis of Le(x), Le(y), and H-type 2 oligosaccharides

The O-protecting groups Levulinoyl (Lev) and 9-fluroenylmethoxycarbonyl (Fmoc) offer an attractive set of orthogonal protecting groups which are compatible with base sensitive N-trichloroethoxylcarbonyl (Troc) group. B exploiting these orthogonal protecting groups and a novel phenolic ester linker, a series of oligosaccharide of biological importance, Le(x), H-type 2, and Le(y), were synthesized on the polytheylene glycol resin MPEG (Mw 5000). The products bearing a p-hydroxybenzyl group could be easily converted into glycosyl donors for further synthesis. Using this strategy, a spacer containing tumor antigen Le(y)-Lac hexasaccharide was described. The artificial spacer at the reducing end provides an opportunity for selective conjugation to an appropriate carrier protein for immunlogical studies.

The 2-naphthylmethyl (NAP) group in carbohydrate synthesis: first total synthesis of the GlyCAM-1 oligosaccharide structures

Total syntheses of the GlyCAM-1 (glycosylation-dependent cell adhesion molecule-1) oligosaccharide structures: [alpha-NeuAc-(2 --> 3)-beta-Gal-(1 --> 4)-[alpha-Fuc-(1 --> 3)]-beta-(6-O-SO3Na)-GlcNAc-(1 --> 6)]-[alpha-NeuAc-(2 --> 3)-beta-Gal-(1 --> 3)]-alpha-GalNAc-OMe (1) and [alpha-NeuAc-(2 --> 3)-beta-Gal-(1 --> 4)-[alpha-Fuc-(1 --> 3)]-beta-GlcNAc-(1 --> 6)]-[alpha-NeuAc-(2 3)-beta-Gal-(1 --> 3)]-alpha-GalNAc-OMe (2) through a novel sialyl LewisX tetrasaccharide donor are described. Employing sequential glycosylation strategy, the starting trisaccharide was regio- and stereoselectively constructed through coupling of a disaccharide imidate with the monosaccharide acceptor phenyl-6-O-naphthylmethyl-2-deoxy-2-phthalimido-1-thio-beta-D-glucopyranoside with TMSOTf as a catalyst without affecting the SPh group. The novel sialyl Lewisx tetrasaccharide donor 3 was then obtained by alpha-L-fucosylation of trisaccharide acceptor with the 2,3,4-tri-O-benzyl-1-thio-beta-L-fucoside donor. The structure of the novel sialyl Lewisx tetrasaccharide was established by a combination of 2D DQF-COSY and 2D ROESY experiments. Target oligosaccharides 1 and 2 were eventually constructed through heptasaccharide which was obtained by regioselective assembly of advanced sialyl Lewisx tetrasaccharide donor 3 and a sialylated trisaccharide acceptor in a predictable and controlled manner. Finally, target heptasaccharides 1 and 2 were fully characterized by 2D DQF-COSY, 2D ROESY, HSQC, HMBC experiments and FAB mass spectroscopy.