A highly stereoselective 1,2-cis-α-glucosylation reaction was developed, in which the use of a strongly electron-donating tert-butyldimethylsilyl protecting group on the C-2 hydroxy group of a glycosyl donor enhanced the α-favoured transition state, and thus resulted in high yield and α-selectivity. Synthetic utility of this α-glucosylation was demonstrated by the generation of a triglucoside moiety in high-mannose-type oligosaccharides.

A systematic series of chitobiose-modified pentapeptides with sequence variations of hydrophobic leucine and hydrophilic serine were synthesized. The resulting glycopeptides were used as molecular probes to elucidate aglycon peptide specificity of the glycoprotein-folding sensor enzyme UGGT. Inhibitory experiments with a synthetic fluorescent glyco-substrate and the glycopeptides revealed that UGGT prefers a serine residue directly linked to C-terminal of the N-glycosylation site in its substrate recognition.Chitobiose-pentapeptide probes revealed the glycoprotein-folding sensor enzyme UGGT prefers a Ser residue C-terminal to the Asn in its substrate recognition.

Investigating unidentified weak-acting lectins is important for understanding glycan-related phenomena. We have developed an improved screening method for weak-acting lectins using glycan-conjugated magnetic beads (or glycobeads) involving a partial washing method and named it the mild enrichment procedure. Weak-acting lectins exist in equilibrium between bound lectin and free lectin produced by dissociation, whereas most tight-binding lectin exists in a bound state. The conventional washing step, in which the solution phase is replaced, may remove dissociated lectin from around the glycobeads; therefore, we attempted to leave a buffer space around the glycobeads to maintain the association–dissociation equilibrium of weak-acting lectins. Our results revealed that our mild enrichment procedure for screening for weak interactions, such as maltose–concanavalin A (Ka ∼ 104 M−1) and lactose–peanut agglutinin (Ka ∼ 103 M−1) interactions, was more effective than conventional batch methods.

•We prepared glycan-probes having a hydrophobic portion separated by various linkers.•The ER glucose transfer had higher activity for glycan probes with shorter linkers.•The ER mannose trimmings had higher activity for glycan probes with shorter linkers.•The ER glucose trimming had higher activity for glycan probes with longer linkers.•Calreticulin-binding was enhanced for glycan probes with shorter linkers.Glycoprotein N-linked oligosaccharides in the endoplasmic reticulum function as tags to regulate glycoprotein folding, sorting, secretion and degradation. Since the N-glycan structure of a glycoprotein should reflect the folding state, N-glycan processing may be affected by the aglycone state. In this study, we examined the influence of aglycone structures on N-glycan processing using synthetic substrates. We prepared (Glc1)Man9GlcNAc2 linked to hydrophobic BODIPY-dye with a systematic series of different linker lengths. With these compounds, glucose transfer, glucose trimming and mannose trimming reactions of an endoplasmic reticulum fraction were examined. The results showed that substrates with shorter linkers between the N-glycan and hydrophobic patch had higher activities for both the glucose transfer and the mannose trimming reactions. In contrast, the glucose trimming reaction showed lower activity when substrates had shorter linkers. Thus, the reactivity for N-linked oligosaccharide processing of glycoproteins in the endoplasmic reticulum might be tunable by the aglycone structure, e.g., protein portion of glycoproteins.