144985-19-3Relevant articles and documents
Neighboring group participation in glycosylation reactions by 2,6-disubstituted 2-O-benzoyl groups: A mechanistic investigation
Williams, Rohan J.,McGill, Nathan W.,White, Jonathan M.,Williams, Spencer J.
experimental part, p. 236 - 263 (2011/04/22)
Variable yields and glycosylation stereoselectivity were obtained for NIS/TfOH-medi- ated reaction of 4-methoxyphenyl 2,4,6-tetra-O-acetyl-β-D- galactopyranoside and thiogalactosides bearing acetyl, benzoyl, 2,6-dimethoxylbenzoyl, 2,4,6-trimethylbenzoyl, or 2,6-dichlorobenzoyl groups at the 2-positions and acetyl at the remainder. X-ray structures of 4-methylphenyl 2,3,4,6-tetra-O-(2,4,6-trimethylbenzoyl)-1-thio-β-D-galactopyr anoside and 4-methylphenyl 3,4-O-isopropylidene-2,6-di-O-(2,4,6-trimethylbenzoyl)-1-thio- β-D-galactopyranoside revealed slightly distorted 4C1 chair conformations. Variable temperature NMR revealed that activation of 4-methylphenyl 2,3,4,6-tetra-O-(2,4,6-trimethylbenzoyl)-1-thio-β-D- galactopyranoside afforded only dioxolenium ion, whereas 4-methylphenyl 3,4,6-tri-O-acetyl-2-O-(2,4,6-trimethylbenzoyl)-1-thio-β-D- galactopyranoside gave a 1:1 mixture of dioxolenium ion and glycosyl triflate. However, the reaction intermediates formed from these deactivated donors do not influence the glycosylation stereoselectivity; instead, it is influenced by steric and electronic interactions at the transition states. Copyright Taylor & Francis Group, LLC.
A practical synthesis of β-D-GlcA-(1→3)-β-D-Gal-(1→3)-β-D-Gal-(1→4)-D- Xyl, a part of the common linkage region of a glycosaminoglycan
Chen, Langqiu,Kong, Fanzuo
, p. 1373 - 1380 (2007/10/03)
A practical synthesis of β-D-GlcA-(1→3)-β-D-Gal-(1→3)-β-D-Gal-(1→4)- β-D-Xyl-(1→OMe) was achieved by coupling of methyl 2,3,4-tri-O-acetyl-α-D-glucopyranosyluronate trichloroacetimidate with a trisaccharide acceptor. The trisaccharide acceptor was obtained by condensation of 3-O-allyl-2,4,6-tri-O-benzoyl-β-D-galactopyranosyl-(1→3)-2,4,6- tri-O-benzoyl-α-D-galactopyranosyl trichloroacetimidate with methyl 2,3-di-O-benzoyl-β-D-xylopyranoside, followed by deallylation. The β-(1→3)-linked disaccharide was prepared readily with p-methoxyphenyl 3-O-allyl-2,4,6-tri-O-benzoyl-β-D-galactopyranoside as the key synthon. The α-(1→3)-linkage was formed in considerable amount with galactose mono- and disaccharide trichloroacetimidate donors with C-2 neighboring group participation.
Directed and efficient syntheses of β(1→4)-linked galacto-oligosaccharides
Lichtenthaler, Frieder W.,Oberthuer, Markus,Peters, Siegfried
, p. 3849 - 3869 (2007/10/03)
Straightforward, preparatively efficient procedures are described for the construction of β(1→4)-intergalactosidic linkages up to the hexasaccharide level. Key elements were the use of phenylthio and/or phenyl sulfoxide functionalities for glycosylations and a judiciously designed blocking group pattern for donor and acceptor alike: pivaloyl protection at O-2 for securing β-selectivity, sterically undemanding allyl or benzyl groups at O-3 and O-6 to minimise the steric bulk around the unreactive galactosyl-4-OH, the p-methoxyphenyl moiety, readily replaceable by SPh, as an intermediate anomeric substituent, and an acetyl group for temporary protection of the terminal Gal-4-OH. This strategy lends itself to iterative block synthesis and interchange of donors and acceptors, thereby demonstrating the broad scope and generality of the overall approach. Although predicted by molecular modelling, inclinations towards starch-like coiling could not so far be verified in any of the galacto-tetra-, -penta-, or -hexaoses or their p-methoxyphenyl glycosides.