✍ Scribed by Yao-Hua Zhu; Pierre Vogel
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Nucleophilic additionsto D-isolevoglucosenone are face selectiveand generatethe corresponding enoiateswhichreact with l,2:3,4-di-04sopropylidene-a-r)[email protected],5-!3Woseto givealdolr3dduc@. ne* w ~reduced stereoselectively intoC(I+3) glycosides of 1,6anhydro-u-gahwta-pyranose. @1997 ElsevierScience
The interactionbetweencell surfacecarbohydratesand their proteinreceptorsis implicatedin several importantbiological events.l Carbohydratemimics are potentially useful tools to study cellular interactions andmay representleads for dmg discovery.zIn particular,C-linkeddisaccharides offerthe advantageof being resistantto acidic and enzymatichydrolysis.They are thereforepotentirdinhibitorsof glycosidasesand may representnon-hydrolysableepitopes. Since the first synthesisof a ~-(1+6)-C-disaccharideby Rouzaud and SinaY4 in 1983,severalapproachesto C-disaccharideshavebeenproposed.3's Theyare invariablymultiple-step syntheseswhich do not always offer the necessaryversatilityfor wide moleculardiversity.bHence, there is still a need for shorter and more convergentsyntheticschemes.We report our latest efforts toward this goal which feature the conjugate additions of nucleophilesto isolevoglucosenone(1) followed by electrophilic quenchingof the intermediateenolate2 andreductionof the ketone3 (Scheme1).
Recently, Witczak and coworkers'used levoglucosenone(1,6-anhydro-3,4-dideoxy-~-D-glycero-hex-3-enopyran-2-ulose)to generate C-disaccharides through Michael addition of (@D-gluco-pyranosyl) nitromethane. This provided j3-C(l+4)glucopyranosidesof 3-deoxy-tkghcose. Isolevoglucosenone(1) is readilyderivedhorn D-glucosein four syntheticsteps.*Enone 1 is knownto add nucleophilesa'y and radicals]o exclusivelyon its less hinderedface (synwithrespectto the oxabridge).Oshirnaand Co-workersi* have shown that conjugateaddition of Me2AlSPhto simple enones,followedby reaction of the aluminum enolates with aldehydesallow the preparationof the correspondingaldols in one-potprocedures.When a
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