d-ARABINOFURANOSIDES FROM MYCOBACTERIA: SYNTHESIS AND CONFORMATION

Stereocontrolled 1,2-cis glycosylation as the driving force of progress in synthetic carbohydrate chemistry

“…Nevertheless, their presence in a variety of polysaccharides from plants, bacteria, parasites, and fungi makes this type of glycosidic linkage an important synthetic target. 20 The synthesis of 1,2- trans furanosides is relatively straightforward and, similarly to that of pyranosides, can be reliably achieved with the use of glycosyl donors bearing a participating group at C-2. In contrast, the synthesis of 1,2- cis furanosides is difficult, even more so than with pyranosides due to the lack of anomeric effect and the conformational flexibility of the five-membered ring.…”

Novel carbohydrate modified berberine derivatives: synthesis andin vitroanti-diabetic investigation

“…In parallel, treatment of pentaacetyl β-D-glucose 9 with HBr (33% in AcOH) afforded glycosyl bromide 11, which was immediately converted into compound 13 in the presence of NaN 3 and DMF with 69% overall yield. Due to the neighboring group participation effect [29][30][31][32][33] of the 2-Oacetyl group in 11, this reaction was highly stereoselective and gave β-linked azido sugar 13 as the only product. Thereafter, the acetyl groups in 13 were removed with CH 3 ONa, and the resultant 15 was subjected to the Cu-catalyzed "click" reaction with alkylated berberine derivative 8 to afford the desired compound 1 in 56% total yield.…”

Formation of the Glycosidic Linkage

“…We have already discussed the synthesis of a sialoside (utilizing a glycosyl ester as a donor), and some of the common donors discussed earlier in this chapter are also employed, e.g. A judicious choice of solvent (acetonitrile) maximizes the amount of a-anomer, 375 but a concerted effort is still needed to develop better methods for the synthesis of a-sialosides: 376,377 Furanosides [378][379][380] The discussion in this chapter has been restricted mainly to the synthesis of pyranosides. 67 The challenges in any synthesis of an a-sialoside are fairly obvious: the presence of an electron-withdrawing group at C1 slows the whole process, there is no substituent at C3 to control the stereoselectivity of the glycosidation (reminiscent of the discussion above on 2-deoxy sugars), the hydrogen atoms on C3 are always available to participate in unwanted 2,3-ene formation and the gain from any anomeric effect has to be shared between the two substituents (at C2).…”