Dissecting the Influence of Oxazolidinones and Cyclic Carbonates in Sialic Acid Chemistry

Abstract

Polarisierende Wirkung: Die thermische Gleichgewichtseinstellung für 1 und eine massenspektrometrische Analyse von Sialylphosphaten sprechen dafür, dass das 4O,5N‐Oxazolidinon‐ und das 4,5‐O‐Carbonat‐System den anomeren Effekt und den Sialidierungsmechanismus durch ihr Dipolmoment in der Ebene des Pyranoserings beeinflussen. Die elektronenziehende Wirkung destabilisiert 2 und begünstigt assoziative Glycosylierungsmechanismen. TEMPO=2,2,6,6‐Tetramethylpiperidin‐N‐oxid.

The Experimental Evidence in Support of Glycosylation Mechanisms at the SN1–SN2 Interface

“…The data were correlated with the electron-withdrawing ability of the protecting group pattern at the 4- and 5-positions as suggested by the expected dipole moments (Scheme 13). 91 In effect, the more electron withdrawing oxazolidinone and cyclic carbonates, with a single large dipole in the plane of the pyranose ring required the greatest energy for fragmentation. A caveat arises from the possible formation of the observed ion by McLafferty rearrangement rather than stepwise fragmentation and deprotonation.…”

“…The use of thioglycosides as anomeric leaving groups in this study was thwarted by the preferential loss of an acetoxy group from the side chain. 91 Indeed, in subsequent work on the CID-ESIMS of sialyl S - and O -glycosides, Chizhov and coworkers also found the loss of carboxylate groups to compete with that of the anomeric functionality. 92,93…”

Unique Stereoselective Homolytic C−O Bond Activation in Diketopiperazine‐Derived Alkoxyamines by Adjacent Amide Pyramidalization

“…The most promising examples for directed isomerizationsh ave so far provent o be cyclic sialic acid derived anomeric alkoxyamines 11,r ecently reported by Crich, providinga7:1r atio of a/b anomers at 90 8Cd epending on the protecting groups. [70,71] Alkoxyamines 11 are also interesting in that the nitroxide unit is attached to an atural product core structure, providing the bias, buti t shows that as imple cyclic constraint as in 11 is not sufficient to induce complete isomerization. However,c ombining the cyclic constraint with the strain induced by amide distortion in DKP alkoxyamines (Figure 10 B) provides the necessary driving force for au nidirectionalt hree-point redox-fueleds witching system based on central chirality (see Figure 9).…”

Mini Review: Oxazolidinone and Other Sialic Acid C5 Modifications Over the Past Decade

“…Significant improvements in sialylation observed when oxazolidinone is trans-fused to pyranose rings result from the strong influence of its dipole moment which creates an electron-withdrawing effect that causes the destabilization of the oxocarbenium ion. This destabilization then favors SN2-like mechanistic pathways (Kancharla et al, 2012). Capitalizing on this and the thiocarbonyl (Liang et al, 2009): NIS/TfOH.…”