SYNTHESIS OF 1,2-CIS GLYCOSIDES VIA CHELATION INDUCED ANOMERISATION

Glycosides with 1,2-cis linkages are commonly found in naturally occurring molecules (e.g. KRN7000, heparan sulphate, trehalose) and there has been much interest in development of highly stereoselective methods for synthesis of such linkages.¹ Thus far the utilization of non-participating protecting groups, solvent assisted glycosidations, and various glycosyl donors have lead to respectable anomeric ratios in particular cases.

The utilisation of anomerisation as a means towards 1,2-cislinkages has been reported in the literature^2-6, the majority of these methods involve glycosides which have protecting groups that could be considerd more electron releasing. These reactions are not applicable to a wide range of substrates. Certain protecting groups (e.g. benzyl groups) are also susceptible to cleavage under Lewis acidic conditions and consequently may not be suitable to be used under some anomerisations conditions. The Murphy group at NUI Galway have previously shown that chelation induced anomerisation of 1,2-transglycosidic linkages can be successful in the presence of acyl protecting groups. Although acyl groups are more electron withdrawing, highly stereoselective synthesis of 1,2-cis glycosides can be achieved.^7-8In this presentation anomerisation studies on disaccharide substrates not reported to date will be discussed.

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