Synthesis of 1,2-O-cyanoethylidene derivatives of alkyl glycopyranuronates by oxidation of the 6-trityl ethers of their hexose analogues

Reaction of Glyconitriles with Organometallic Reagents: Access to Acyl β-C-Glycosides

A new strategy for the synthesis of acyl β-C-glycosides is described. The reactivity of glyconitriles toward organometallic reagents such as organomagnesium or organolithium derivatives was studied, affording acyl β-C-glycosides in moderate to good yields. In this study, glycal formation was efficiently prevented by deprotonating the hydroxyl group in position 2 of the glyconitriles during the process.

Difluorotetrahydropyridothiazinone: a selective β-galactosidase inhibitor

Selective difluorination, introducing a lactame moiety (instead of an amine) and a double bond in a trihydroxy-2-thiaquinolizidine derivative reverses the selectivity of the glycosidase inhibitor - a selective inhibitor for an α-glucosidase is altered into an excellent, competitive inhibitor for a β-galactosidase.

Regioselective synthesis of long-chain ethers and their sulfates derived from methyl beta-D-galactopyranoside and derivatives via dibutylstannylene acetal intermediates

A number of different conditions were investigated for the alkylation of the dibutylstannylene acetals of methyl beta-d-galactopyranoside with long-chain primary alkyl bromides, decyl, dodecyl, and tetradecyl bromide. The best yields of the major products, the 3-O-alkyl ethers, were obtained by reaction of the alkyl bromide with the monodibutylstannylene acetal in DMF in the presence of cesium fluoride for extended periods of time at moderate temperatures (65 degrees C). These products were always accompanied by minor amounts of the 3,6-di-O-alkyl derivative. Performing the reaction with excess alkyl halide on the bis(dibutylstannylene) acetal resulted in more of the 3,6-di-O-alkyl derivative, particularly for the shorter alkyl bromides, but this product was never predominant. Sulfation of the dibutylstannylene acetal of methyl 3-O-tetradecyl-beta-D-galactopyranoside resulted in the 6-sulfate in 96% yield.

Synthesis of degraded cyanogenic glycosides from Sambucus nigra

Two natural cyanohydrins, isolated from Sambucus nigra, have been synthesised from mandelonitrile and penta-O-acetyl-beta-galactopyranose. The synthesis confirmed the stereochemistry of the compounds, which had been assigned on biogenetic grounds.

Glycosylation by sugar 1,2-O-(1-cyanobenzylidene) derivatives: influence of glycosyl-donor structure and promoter

3,4,6-Tri-O-acetyl-1,2-O-(1-cyanobenzylidene)-alpha-D-galactopy ranoses with differently substituted aromatic nuclei have been synthesised and used as glycosyl donors in reactions with the acceptors methyl 2,3,4-tri-O-acetyl-6-O-trityl-beta-D-galactopyranoside (11) and methyl 2,4,6-tri-O-acetyl-3-O-trityl-beta-D-galactopyranoside (12). The glycosylation of 11 gave only beta products. The effeciency and stereoselectivity of the glycosylations of 12 depend on the nature of the substituent in the aromatic ring. The stereoselectivity for the formation of 1,2-trans-glycosidic bonds was the highest with the p-methoxy-benzylidene derivative with triphenylmethylium triflate as the promoter.

D-galacturonic acid derivatives as acceptors and donors in glycosylation reactions

Jones oxidation of suitably protected allyl beta-D-galactopyranosides and subsequent esterification were reinvestigated. Partial deprotection of the resulting D-galacturonic acid derivatives afforded compounds suitable for transformation into glycosyl acceptors. The synthesis of 2-, 3-, and 4-trityl ethers, relying on efficient differential protecting-group strategies, is described. Trityl-cyanoethylidene condensation of these trityl ethers, leading to the protected disaccharide units beta-D-GalpA-(1-->2)-D-GalpA and beta-D-GalpA-(1-->3)-GalpA with high stereoselectivity, is demonstrated. A beta-D-GalpA-(1-->4)-D-GalpA disaccharide was also prepared.

Synthesis of a heteroglycuronan derivative containing the beta-D-galactopyranosyluronic acid (1-->3)-L-rhamnose repeating unit

Helferich glycosylation of the cyanoethylidene L-rhamnose derivative 3 with the galactosyluronic bromide 2 gave the disaccharide 4 as a key intermediate in the synthesis of the monomer 13 for trityl-cyanoethylidene condensation (TCC). The following formation of the monomer 13, including introduction of a trityl group at O-3', proceeded in six steps. Because of the difficulty of some steps, an alternative route for 13 was tested. Model compounds 20, 21, and 22 were synthesized in order to confirm the stereoregularity of the products of the polycondensation. The polycondensation of the monomer gave D-GalpA-(1-->3)-L-Rha-oligomer derivatives consisting mainly of three repeating units. This result is in contrast with the degree of polymerisation (dp > or = 22) of other synthetic rhamnans, but is very similar to dp 2-7 of homo- and hetero-glucuronan derivatives.

Synthesis of glycuronamides of amino acids, constituents of microbial polysaccharides and their conversion into neoglycoconjugates of copolymer type

Glycopyranosiduronic acids, amidically linked to amino acids (alanine, serine, threonine, and lysine) were prepared. O-tert-Butyl and N epsilon-tert-butyloxycarbonyl protected amino acid tert-butyl esters were used in ethyl 2-ethoxy-1,2-dihydroquinoline-1-carboxylate promoted condensation with 2-azidoethyl glycosides of glucuronic and galacturonic acid. Reduction of the azido-function followed by N-acryloylation and removal of blocking groups with trifluoroacetic acid gave the target monomers. These were converted into neoglycoconjugates of copolymer type, potentially useful for immunochemical studies.