Efficient synthesis of α(1,2)-linked oligomannoside derivatives through one-pot glycosylation.

An α(1,2)-linked oligomannoside derivative having a free C-2 hydroxyl group and a C-3 pivaloyl group was synthesized from a thiophenyl mannose derivative 1 using a one-pot self-condensation and applying a α-stereoselective procedure. The mannosylation exclusively generated α-mannoside linkages. The observed α-directing effect was rationalized by the remote participation of the pivaloyl group in C-3 position. The polymerization degree was controlled by the promoter amount providing the mannobiose derivative as a major product. Applying this method eliminated many synthetic steps. The α(1,2)-linked oligomannoside derivatives, which are key intermediates for the synthesis of oligomannose type N-glycans for glycoproteins, were easily prepared.

Fluorescence Quenching-based Assay for Measuring Golgi endo-α-Mannosidase.

Golgi endo-α-mannosidase (G-EM) catalyzes an alternative deglucosylation process for N-glycans and plays important roles in the post-endoplasmic reticulum (ER) quality control pathway. To understand the post-ER quality control mechanism, we synthesized a tetrasaccharide probe for the detection of the hydrolytic activity of G-EM based on a fluorescence quenching assay. The probe was labeled with an N-methylanthraniloyl group as a reporter dye at the non-reducing end and a 2,4-dinitrophenyl group as a quencher at the reducing end. This probe is hydrolyzed to disaccharide derivatives by G-EM, resulting in increased fluorescence intensity. Thus, the fluorescence signal is directly proportional to the amount of disaccharide derivative present, allowing the G-EM activity to be evaluated easily and quantitatively.