Anomeric Effect of the Nitrogen Atom in the Isocyano and Urea Groups

Abstract

The anomeric effect associated with the nitrogen atom in the isocyano group was investigated by using 1H NMR spectroscopic analysis of an anomeric pair of xylopyranosyl isocyanides 8 and 7. We found that β‐anomer 7 prefers to exist in the 1C4 conformation in which the nitrogen atom in the isocyano group adopts an axial orientation. This observation, coupled with the results of X‐ray crystallographic analysis establishes that the nitrogen atom in the isocyano group displays the anomeric effect. Furthermore, xylopyranosyl isocyanides 8 and 7 were transformed into the corresponding xylopyranosyl ureas 10 and 11. In the case of the urea group, a normal sterically determined preference is observed in which the bulky urea substituents at the pyranose anomeric position occupy the equatorial position.

Structure and Reactivity of Glycosyl Isocyanides

“…The conformational analysis in the crystalline state revealed also the anomeric effect of the nitrogen atom of the isocyanide group which verifies the NMR studies and results of Ichikawa et al They described that in certain xylopyranosyl isocyanides, the isocyano group adopts an axial orientation displaying the anomeric effect. The inspection of bond lengths and angles confirms the anomeric effect.…”

“…First to obtain structural information of the synthesized sugar formamides and isocyanides by the X‐ray structure analysis. This is of outmost importance since crystal structures of sugar formamides and isocyanides are scarce in literature , …”

“…This is of outmost importance since crystal structures of sugar formamides and isocyanides are scarce in literature. [26,27] Apart of the crystal structural insights, our second objective is to effectively design novel glycoconjugates with bioactive molecules of general interest such as lactones or macrocycles ( Figure 1). Figure 1.…”

Neighboring‐Group Participation by C‐2 Ether Functions in Glycosylations Directed by Nitrile Solvents

“…It is worth noting that the b-anomeric configuration of 3 a is attributable to a known sterically driven (a!b) isomerization of the free amino function. [32] At this stage, we outlined a mechanism for the formation of 3 a and 3 b (Scheme 2b) with reference to Pavias proposal. Activation of 3 in the nitrile solvent could produce an oxazolinium intermediate through C-2 ether participation.…”

Protecting group free synthesis of urea-linked glycoconjugates: efficient synthesis of β-urea glycosides in aqueous solution

“…In order to increase the yield and to reduce the amount of loading urea, we further investigated the conditions which led The reaction was carried out on the 300 mg scale of D-glucose (12). b Yields obtained employing 10 equiv.…”