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Buenos Aires, Argentina

A conformationally restricted 2-O-benzyl-3,5-O-di-tert-butylsilylene- β-d-thiogalactofuranoside donor was prepared from benzyl α-d-galactofuranoside and its donor capability was studied for stereoselective 1,2-cis α-d-galactofuranosylation. An unusual chemical behavior in benzylation and hydrogenolysis reactions was observed after the introduction of the 3,5-O-di-tert-butylsilylene protecting group into the galactofuranosyl moiety. The influence of the solvent, temperature, and activating system was evaluated. The NIS/AgOTf system, widely used in 1,2-cis β-arabinofuranosylation, was not satisfactory enough for 1,2-cis galactofuranosylation. However, moderate to high α-selectivity was obtained with all the acceptors employed when using p-NO2PhSCl/AgOTf as a promoting system, in CH2Cl2 at -78 °C. The order of the addition of the reactants (premixing or preactivation) did not affect substantially the stereochemical course of the glycosylation reaction. The α-d-Galf-(1→6)-d-Man linkage was achieved with complete diastereoselectivity by preactivation of the conformationally constrained thioglycoside donor. © 2014 Elsevier Ltd. All rights reserved. Source

Eugenia Giorgi M.,CIHIDECAR | De Lederkremer R.M.,CIHIDECAR
Carbohydrate Research | Year: 2011

A dense glycocalix covers the surface of Trypanosoma cruzi, the agent of Chagas disease. Sialic acid in the surface of the parasite plays an important role in the infectious process, however, T. cruzi is unable to synthesize sialic acid or the usual donor CMP-sialic acid. Instead, T. cruzi expresses a unique enzyme, the trans-sialidase (TcTS) involved in the transfer of sialic acid from host glycoconjugates to mucins of the parasite. The mucins are the major glycoproteins in the insect stage epimastigotes and in the infective trypomastigotes. Both, the mucins and the TcTS are anchored to the plasma membrane by a glycosylphosphatidylinositol anchor. Thus, TcTS may be shed into the bloodstream of the mammal host by the action of a parasite phosphatidylinositol-phospholipase C, affecting the immune system. The composition and structure of the sugars in the parasite mucins is characteristic of each differentiation stage, also, interstrain variations were described for epimastigote mucins. This review focus on the characteristics of the interplay between the trans-sialidase and the mucins of T. cruzi and summarizes the known carbohydrate structures of the mucins. © 2011 Elsevier Ltd. All rights reserved. Source

Glycosylation studies for the construction of 1,2-cis α-linkages with O-(2,3,5,6-tetra-O-benzyl-β-d-galactofuranosyl) trichloroacetimidate (1) and several acceptors, including d-mannosyl and l-rhamnosyl derivatives were performed. The reactions were conducted at low temperatures using CH 2Cl2, Et2O, and acetonitrile as solvents. A non-participating solvent such as CH2Cl2 at -78 °C, favored the α-d-configuration. In contrast, acetonitrile strongly favored the β-d-configuration, whereas no selectivities were observed with Et 2O. The use of thiophene as an additive did not enhance the α-d-selectivity as in the pyranose counterpart. Although selectivities strongly depended on the acceptor, trichloroacetimidate 1 constitutes a valuable donor for the synthesis of α-d-Galf-(1→2)-l-Rha and α-d-Galf-(1→6)-d-Man. As these motifs are present in pathogenic microorganisms, these procedures described here are useful for the straightforward synthesis of natural oligosaccharides. © 2011 Elsevier Ltd. All rights reserved. Source

Gandolfi-Donadio L.,CIHIDECAR | Santos M.,CIHIDECAR | De Lederkremer R.M.,CIHIDECAR | Gallo-Rodriguez C.,CIHIDECAR
Organic and Biomolecular Chemistry | Year: 2011

Mycolyl-arabinogalactan (mAG) complex is a major component of the cell wall of Mycobacterium tuberculosis, the causative agent of tuberculosis disease. Due to the essentiality of the cell wall for mycobacterium viability, knowledge of the biosynthesis of the arabinogalactan is crucial for the development of new therapeutic agents. In this context, we have synthesized two new branched arabinogalactafuranose tetrasaccharides, decenyl β-d-Galf-(1→5)- β-d-Galf-(1→6)[α-d-Araf(1→5)]-β-d-Galf (1) and decenyl β-d-Galf-(1→6)-[α-d-Araf-(1→5)]-β-d-Galf-(1→5)- β-d-Galf (2), as interesting tools for arabinofuranosyl transferase studies. The aldonolactone strategy for the introduction of the internal d-Galf was employed, allowing the construction of oligosaccharides from the non-reducing to the reducing end. Moreover, a one-pot procedure was developed for the synthesis of trisaccharide lactone 21, precursor of 2, which involved a glycosylation-deprotection-glycosylation sequence, through the use of TMSOTf as catalyst of the trichloroacetimidate method as well as promoter of TBDMS deprotection. © 2011 The Royal Society of Chemistry. Source

Mendoza V.M.,CIHIDECAR | Kashiwagi G.A.,CIHIDECAR | de Lederkremer R.M.,CIHIDECAR | Gallo-Rodriguez C.,CIHIDECAR
Carbohydrate Research | Year: 2010

The trisaccharides β-d-Galf-(1→2)-β-d-Galf-(1→4)-d-GlcNAc (5) and β-d-Galp-(1→2)-β-d-Galf-(1→4)-d-GlcNAc (6) constitute novel structures isolated as alditols when released by reductive β-elimination from mucins of Trypanosoma cruzi (Tulahuen strain). Trisaccharides 5 and 6 were synthesized employing the aldonolactone approach. Thus, a convenient d-galactono-1,4-lactone derivative was used for the introduction of the internal galactofuranose and the trichloroacetimidate method was employed for glycosylation reactions. Due to the lack of anchimeric assistance on O-2 of the galactofuranosyl precursor, glycosylation studies were performed under different conditions. The nature of the solvent strongly determined the stereochemical course of the glycosylation reactions when the galactofuranosyl donor was substituted either by 2-O-Galp or 2-O-Galf. © 2009 Elsevier Ltd. All rights reserved. Source

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