Jean-Marie Beau

The use of 2-deoxy-2-trichloroacetamido-d-glucopyranose derivatives in syntheses of oligosaccharides

3,4,6-Tri-O-acetyl-2-deoxy-2-trichloroacetamido-alpha-D-glucopyran osyl trichloroacetimidate and its O-benzylated analogue were tested as glycosyl donors in the reaction with a set of sugar acceptors unsubstituted on O-3 and O-4, typically encountered in the synthesis of oligosaccharides. Glycosides were obtained in good to excellent yields with only a slight excess (1.1-1.2 equiv) of the donor, and with a high degree of 1,2-trans stereoselectivity. The corresponding 2-(trichloromethyl)oxazolinium ion was postulated to be the major reactive intermediate. The N-trichloroacetyl groups in the disaccharide products were easily transformed into N-acetyl under neutral conditions by reduction with tributylstannane.

Preparation and use of lithiated glycals: vinylic deprotonation versus tin-lithium exchange from 1-tributylstannyl glycals1☆

Abstract Methods for preparing glycals lithiated at the C-1 atom by either direct vinylic deprotonation or by tin-lithium exchange from the corresponding 1-tri-n-butylstannyl glycals are described. Alkylation of these lithiated anions with various electrophiles leads to products of potential interest for further synthetic manipulations.

Selenium-mediated glycosidations: A selective synthesis of β-2-deoxyglycosides

Abstract 1,2-Trans diequatorial acetoxy-selenides are selectively prepared from glycals. Their activation by trimethylsilyl trifluoromethanesulfonate in the presence of sugar alcohols followed by reductive deselenation leads to an efficient access to β-2-deoxyglycosides.

Synthesis of glycopeptides from the carbohydrate-protein linkage region of proteoglycans.

2,3,4,6-Tetra-O-benzoyl-alpha-D-galactoyranosyl trichloroacetimidate was condensed with benzyl 2,3-O-isopropylidene-beta-D-xylopyranoside to give the corresponding beta-(1----4)-linked disaccharide derivative, which was transformed into 2,3-di-O-benzoyl-4-O-(2,3,4,6-tetra-O-benzoyl-beta-D-galactopyranosyl)- alpha-D-xylopyranosyl trichloroacetimidate. This glycosyl donor was condensed with a set of selectively C,N-protected L-seryl-glycine dipeptide units. Selective deblocking at the C- or N-termini of the glycosylated or non-glycosylated dipeptide segments, and coupling using the mixed-anhydride procedure allowed the construction in high yield of partially or fully glycosylated oligopeptides from the carbohydrate-protein linkage region of proteoglycan.

Arylation of 1-tributylstannyl glycals catalyzed by palladium: A synthetic route to the basic skeleton of the papulacandins and chaetiacandin

Abstract The palladium-catalyzed coupling reaction of 4,6- O -benzylidene-3- O-tert -butyldimethylsilyl-1-tri- n -butylstannyl-D-glucal 7 with 3,5-dibenzyloxy-2-bromo-benzyl alcohol 8 gave a 78% yield of the C -arylated glycal 11 , stereoselectively transformed into the structural units of the papulacandins and chaetiecandin.

Radical cyclization on carbohydrate pyranosides: a controlled formation of functionalized ring-fused bicyclic acetals

Abstract Cis-fused chiral bicyclic acetals are readily prepared from glycals in a two-step procedure via the tri-n-butylstanne-mediated cyclization of simple ω-unsaturated glycosides of 2-bromo- 2-deoxy-glycopyranosides.

Complete stereostructure of nystatin A1: A proton NMR study

Abstract Using the sugar -mycosamine as an internal chiral probe for nmr spectroscopy, the absolute configuration at the asymmetric centers of the C10–C19 fragment of nystatin A 1 , as well as the β-configuration of the -mycosamine unit, were assigned by a combination of 2D-proton phase-sensitive DQF-COSY, NOESY and ROESY experiments.

An expeditious and stereocontrolled preparation of 2-azido-2-deoxy-β-D-glucopyranose derivatives from D-glucal

1,6-Anhydro-2-azido-2-deoxy-β-D-glucopyranose has been prepared by a two-step procedure from D-glucal and transformed into precursors useful in the synthesis of oligosaccharides.

Synthesis of C-glycopyranosyl compounds by a palladium-catalyzed coupling reaction of 1-tributylstannyl-D-glucals with organic halides

1-Tributylstannyl-D-glucals, prepared from the corresponding 1-phenylsulfonyl-D-glucals, were coupled efficiently to various organic halides in the presence of a palladium(0) catalyst. This mild reaction is specially useful for the preparation of 1-C-aryl-D-glucals and compatible with unprotected hydroxy groups or hindered aromatic bromides. It has been shown that the resulting 1-C-aryl(alkyl)-D-glucals are suited for further synthetic manipulation of the enol ether group, including stereoselective hydrogenation, hydroboration-oxidation, or epoxidation. All compounds formed resulted from the attack of the alpha-face of the glucal derivatives by the reagent. The reaction, extended to 1,3-, 1,4-di-, and 1,3,5-tri-bromobenzenes, leads to the corresponding symmetrical di-(tri)-C-glucosylbenzenes. Finally, a sequential di-C-glucosylation of 1,3-dibromobenzene with two different 1-stannylated glucals was obtained.

Syntheses of β-2-deoxy-D-glycosides assisted by glycosidases

Abstract Enzyme-catalyzed preparation of β-2-deoxy-D-glucosides and galactosides including disaccharides has been achieved using the corresponding glycals as substrates.