Eq.) in dichloromethane, promoted by BF3.Et2O have been performed and when compared with a comparable glycosylation making use of the peracetylated Kdo-fluoride donor 2, lacking a stereodirecting group.[20d, 21] The latter glycosylation afforded a moderate yield (48 ) of an /-glycoside mixture (4.8:1) and generated massive amounts of glycal ester three (31 ). By contrast, application with the new donor five revealed an -specific outcome, providing the two,3trans-ketoside six in a high yield (83 ) accompanied by only extremely minor formation of 3 (five ); for further particulars see Supporting Info. For the subsequent dehalogenation of six, free radical chain reduction using AIBN / tributyltin hydride gave moderate yields after comprehensive purification to remove the tin reagent. Hydrogenation more than diverse Pd catalysts gave irreproducible yields as a consequence of concomitant epimerization with the 3-iodo substituent among other side reactions. Sooner or later, on the other hand, the 3-iodo-substituent was cleanly removed by way of hydrogen transfer from cyclohexane[23] induced by lauroyl peroxide to furnish the Kdo -glycoside 7 (Scheme 1) in near-quantitative yield. The -anomeric configuration was then confirmed around the basis in the chemical shift difference between the axial and equatorial protons at C-3, the low-field shift ( five ppm) observed for H-4 in 4-O-acetylated Kdo derivatives too as 13C NMR chemical shifts for C-4 and C-6 that are shifted to higher field when when compared with the -anomers.Fumonisin B2 supplier [18] We additional evaluated the practicability with the dehalogenation approach for Kdo-glycosides containing functionalized linkers, which are needed for conversion into neoglycoconjugates and for preparation of glycoarrays.Kainic acid Autophagy Following the described procedure we obtained azido-3-iodo-glycoside eight because the -anomer exclusively and in outstanding yields (83 primarily based onEurope PMC Funders Author Manuscripts Europe PMC Funders Author ManuscriptsChemistry. Author manuscript; obtainable in PMC 2016 February 26.Pokorny and KosmaPagethe quantity of donor). Notably, for the duration of subsequent dehalogenation by hydrogen transfer the azide moiety remained unaffected giving the Kdo-spacer glycoside 9 in comparable yields.PMID:23927631 In an effort to assess the glycosylation prospective with the 3-iodo fluoride donor five, the structurally conserved -(24)-linkage on the enterobacterial Kdo area was then assembled inside a highly efficient strategy. Coupling of 10 with a single equivalent only (!) of donor 5 proceeded smoothly and regioselectively and furnished the disaccharide 11 in 78 yield without having formation on the -anomeric item and only minor elimination (four of three) and donor hydrolysis (5 ) (Scheme 2). Due to poor solubility of the 5-OH disaccharide derivative 11 in cyclohexane, the subsequent dehalogenation never reached completion and separation from unreacted beginning material could only be achieved applying HP-chromatography. To be able to safe a smooth dehalogenation, disaccharide 11 was as a result acetylated (98 ) – to provide fully protected 12 – prior to dehalogenation towards 13 (97 ). International deprotection via sodium-methoxide catalyzed transesterification and alkaline hydrolysis of the methyl ester group afforded the identified disaccharide methyl glycoside 14.[24] To further extend the scope of Kdo-glycoside synthesis beyond the frequent enterobacterial -(24)-linked Kdo disaccharide, the Chlamydia-specific[6] -(28)-disaccharide 18 was then ready along equivalent lines capitalizing on a glyco-desilylation method.[25] Coupling with the 8-O-triethylsilyl (TES)-protected derivative 15 with 1.two eq.