- Synthesis of a dimer of β-(1,4)-l-arabinosyl-(2 S,4 R)-4-hydroxyproline inspired by art v 1, the major allergen of mugwort
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Nα-tert-Butoxycarbonyl-l-trans-4-hydroxyproline allyl ester (Boc-Hyp-OAll) was glycosylated with 2,3,5-tri-O-benzyl-l-arabinose p-cresylthioglycoside in 60% yield with 4:1 β:α stereoselectivity. Deprotection of N- and C-terminii independently gave a prolyl amine and prolyl carboxylate respectively that were coupled under standard conditions with 1-[bis-(dimethylamino)methylene]-1H-1,2,3-triazolo-[4,5,b]-pyridininium hexafluorophosphate 3-oxide (N-HATU) to give the dimer 1 in 46% yield. These results represent the first steps toward the production of homogeneous oligomers to determine the minimal epitope of the Art v 1 allergen.
- Xie, Ning,Taylor, Carol M.
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supporting information; experimental part
p. 4968 - 4971
(2010/12/25)
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- On the use of 3,5-O-benzylidene and 3,5-O-(Di-tert-butylsilylene)-2-O- benzylarabinothiofuranosides and their sulfoxides as glycosyl donors for the synthesis of β-arabinofuranosides: Importance of the activation method
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A 2-O-benzyl-3,5-O-benzylidene-α-D-thioarabinofuranoside was obtained by reaction of the corresponding diol with α,α-dibromotoluene under basic conditions. On activation with 1-benzenesulfinyl piperidine, or diphenyl sulfoxide, and trifluoromethanesulfonic anhydride in dichloromethane at -55 °C, reaction with glycosyl acceptors affords anomeric mixtures with little or no selectivity. The analogous 2-O-benzyl-3,5-O-(di-tert-butylsilylene)- α-D-thioarabinofuranoside also showed no significant selectivity under the 1-benzenesulfinyl piperidine or diphenyl sulfoxide conditions. With N-iodosuccinimide and silver trifluoromethanesulfonate the silylene acetal showed moderate to high β-selectivity, independent of the configuration of the starting thioglycoside. High β-selectivity was also obtained with a 2-O-benzyl-3,5-O-(di-tert-butylsilylene)-α-arabinofuranosyl sulfoxide donor on activation with trifluoromethanesulfonic anhydride. The high β-selectivities obtained by the N-iodosuccinimide/silver trifluoromethanesulfonate and sulfoxide methods are consistent with a common intermediate, most likely to be the oxacarbenium ion. The poor selectivity observed on activation of the thioglycosides with the 1-benzenesulfinyl piperidine, or diphenyl sulfoxide, and trifluoromethanesulfonic anhydride methods appears to be the result of the formation of a complex mixture of glycosyl donors, as determined by low-temperature NMR work.
- Crich, David,Pedersen, Christian Marcus,Bowers, Albert A.,Wink, Donald J.
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p. 1553 - 1565
(2007/10/03)
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