ChemInform Abstract: SYNTHESIS AND REACTIONS OF CARBOHYDRATE TRIFLUOROMETHANESULFONATES (CARBOHYDRATE TRIFLATES)

Binkley, Roger W.; Ambrose, Michael G.

doi:10.1002/chin.198441348

Cited by 2 publications

(2 citation statements)

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“…It is noteworthy in this sequence that a secondary triflate is displaced in preference to a primary arenesulfonate ester, testifying to the power of the trifloxy group as a nucleofuge in substitution reactions. 98 Subsequently, the triisopropylbenzenesulfonyl group was displaced with sodium iodide in hot acetone to give an 81% yield of 40 , which on hydrogenolysis over palladium on carbon in ethyl acetate and triethylamine afforded 91% of the 9-deoxy compound 41 . Standard acetylation then gave the triester 42 in excellent yield, from which the naphthylmethyl ether and the levulinate ester were removed sequentially with DDQ and hydrazine hydrate giving 43 and 44 , respectively, in good yields.…”

Section: Resultsmentioning

confidence: 99%

Synthesis and Stereocontrolled Equatorially Selective Glycosylation Reactions of a Pseudaminic Acid Donor: Importance of the Side-Chain Conformation and Regioselective Reduction of Azide Protecting Groups

Dhakal

Crich

2018

J. Am. Chem. Soc.

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Pseudaminic acid is an amino deoxy sialic acid whose glycosides are essential components of many pathogenic Gram-negative bacterial cell walls including those from Pseudomonas aeruginosa, Vibrio cholerae, Campylobacter jejuni, Campylobacter coli, Vibrio vulnificus, and Pseudoalteromonas distincta. The study of pseudaminic acid glycosides is however hampered by poor availability from nature, the paucity of good synthetic methods, and limited to no understanding of the factors controlling stereoselectivity. Conformational analysis of the side chains of various stereoisomeric sialic acids suggested that the side chain of pseudaminic acid would take up the most electron-withdrawing trans,gauche-conformation, as opposed to the gauche,gauche conformation of N-acetyl neuraminic acid and the gauche,trans-conformtion of 7-epi N-acetyl neuraminic acid, leading to the prediction of high equatorial selectivity. This prediction is borne out by the synthesis of a suitably protected pseudaminic acid donor from N-acetyl neuraminic acid in 20 steps and 5% overall yield, and by the exquisite equatorial selectivity it displays in coupling reactions with typical glycosyl acceptors. The selectivity of the glycosylation reactions is further buttressed by the development and implementation of conditions for the regioselective release of the two amines from the corresponding azides, such as required for the preparation of the lipopolysaccharides. These findings open the way to the synthesis and study of pseudaminic acid-based bacterial lipopolysaccharides and, importantly in the broader context of glycosylation reactions in general, underline the significant role played by side chain conformation in the control of reactivity and selectivity.

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Section: Resultsmentioning

confidence: 99%

Synthesis and Stereocontrolled Equatorially Selective Glycosylation Reactions of a Pseudaminic Acid Donor: Importance of the Side-Chain Conformation and Regioselective Reduction of Azide Protecting Groups

Dhakal

Crich

2018

J. Am. Chem. Soc.

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“…The inversion of hydroxyl groups has also been investigated as a means for synthesizing rare 6-deoxy- l -hexoses. This can be accomplished by nucleophilic displacement of sulfonates with inversion of stereochemistry. − In an early report by Jones and Nicholson 2- O -tosyl- l -fucoside 547 was heated in aqueous hydrochloric acid resulting in the formation of 6-deoxy- l -taloside 548 (Scheme a) . Methyl 2,5-di- O -methyl-α- l -rhamnofuranoside has also been converted by treatment with sodium benzoate to afford the l -altrofuranoside .…”

Section: Synthesis Of 6-deoxy-l-hexoses From Carbohydratesmentioning

confidence: 99%