Conformationally restricted 3,5-O-(di-tert-butylsilylene)-d-galactofuranosyl thioglycoside donor for 1,2-cis α-d-galactofuranosylation

Total Synthesis of Marine Glycosphingolipid Vesparioside B

“…The total synthesis of 1 commenced with the development of a new method for stereoselective synthesis of 1,2- cis -α-galactofuranoside which is found in a number of bacterial and fungal glycoconjugates . In fact, a few strategies have been employed for this in the past. , Among them, the 2′-carboxybenzyl (CB) glycoside method, developed by Kim and co-workers, has proved to be useful for direct α-galactofuranosylation. , Besides, the 2,3-anhydro- d -gulofuranosyl thioglycoside and sulfoxide activators, reported by Lowary et al, have also shown validity in stereocontrolled preparation of α- d -Gal f -containing oligosaccharides, but the regioselective opening of the 2,3-epoxide ring structure increases the synthetic steps. , …”

Stereocontrolled Synthesis of α-Xylofuranosides Using a Conformationally Restricted Donor

“…In contrast, 3 J is ∼2.5 Hz for the 1,2-trans (β) isomer. 14 Further support for these assignments came from the 1 H and 13 C NMR spectra of deprotected compounds, including a hexasaccharide target synthesized (see below), using this methodology. Data obtained from these deprotected compounds was consistent 23 with the assignments made using the trends outlined above.…”

“… 5 , 6 Such methods have previously been applied to the synthesis of β-arabinofuranosides ( 3 , Figure 1 B), 7 − 9 β-fructofuranosides ( 4 ), 10 and α-galactofuranosides ( 5 ). 11 − 13 …”

“…Optimization of Glycosylation Conditions. With donors 7 and 8 in hand, we first explored their reaction with a model acceptor, 1,2:3,4-di-O-isopropylidene-α-D-galactopyranose (13), as detailed in Table 1. The stereochemistry of the newly introduced glycosidic linkage could be identified by the coupling constant between H-1 and H-2 ( 3 J) in the 1 H NMR spectrum of the product.…”

Stereodirecting Effect of Cyclic Silyl Protecting Groups in Chemical Glycosylation

“…It has been suggested that a stereoelectronic effect owing to the presence of an electronwithdrawing group is involved, even though the detailed mechanism is still unknown and requires further study. S u b s e q u e n t l y, Ti l v e a n d G a l l o -R o d r i g u e z ( 2014 ) had examined the application of 3,5-O-DTBS-protected D-galactofuranosyl thioglycoside donors for stereoselective 1,2-cis -D-galactofuranosylation, in which the influence of the reaction solvent, temperature, and activating system was evaluated (Tilve and Gallo-Rodriguez, 2014). Interestingly, in contrast to the use of the trichloroacetimidate donor, -selectivity is obtained when the corresponding thioglycoside donor is activated using the p-NO 2 PhSCl/AgOTf system in CH 2 Cl 2 rather than in diethyl ether, regardless of the reaction temperature (Table 3).…”