Synthesis of O-Glycosides of Heteroatom Aroyl-Substituted Heterocyclic Ketene Aminals

Heteroatom aroyl-substituted heterocyclic ketene aminals 1 reacted with 2,3,4,6-tetra-O-acetyl-α-glucopyranosyl bromide 2 under the catalysis of Hg(CN)2 or CaH2 to give E- or Z-O-glycosides of heterocyclic ketene aminals 3 or 4 in moderate yields.

Ortho-(1-phenylvinyl)benzyl glycosides: Ether-type glycosyl donors for the efficient synthesis of both O-glycosides and nucleosides

Both O-glycosides and nucleosides are essential biomolecules with important roles in a variety of biological processes.Chemical synthesis of both O-glycosides and nucleosides is a scalable and reliable method to develop new therapeutic agents and decipher their functions.However,the efficient synthesis of both O-glycosides and nucleosides remains one of long-standing challenges in chemical synthesis.In particular,ether-type glycosyl donors are rarely developed to achieve the efficient synthesis of both O-glycosides and nucleosides due to the stronger conditions required for breaking of the glycosidic C–O bond.Here we report that ortho-(1-phenylvinyl)benzyl glycosides are new ether-type donors for efficient synthesis of both O-glycosides and nucleosides under mild reaction conditions.This glycosylation method enables glycosylation with both alcoholic acceptors and nucleobases with a variety of reactive functionalities.Furthermore,the latent-active synthesis of glycans and the efficient synthesis of nucleosides antibiotics have also been successfully demonstrated in the current glycosylation protocol,thereby representing an important step toward streamlining the chemical synthesis of both O-glycosides and nucleosides.

H_2SO_4-SiO_2:Highly efficient and novel catalyst for the Ferrier-type glycosylation

Sulfuric acid immobilized on silica gel is designed as a very useful catalyst for synthesis of 2,3-unsaturated glycopyranosides. This handy,metal-free,environment friendly transformation provides high yields andα-stereoselectivities in a very few amount （0.02 eq.） of catalyst and in short reaction times（10 min）.

Structural mechanism of a dual-functional enzyme Dgp A/B/C as both a C-glycoside cleaving enzyme and an O-to C-glycoside isomerase

The C-glycosidic bond that connects the sugar moiety with aglycone is difficult to be broken or made due to its inert nature.The knowledge of C-glycoside breakdown and synthesis is very limited.Recently,the enzyme Dgp A/B/C cascade from a human intestinal bacterium PUE was identified to specifically cleave the C-glycosidic bond of puerarin(daidzein-8-C-glucoside).Here we investigated how puerarin is recognized and oxidized by Dgp A based on crystal structures of Dgp A with or without substrate and biochemical characterization.More strikingly,we found that apart from being a C-glycoside cleaving enzyme,Dgp A/B/C is capable of efficiently converting O-to C-glycoside showing the activity as a structure isomerase.A possible mechanistic model was proposed dependently of the simulated complex structure of Dgp B/C with 3’’-oxo-daidzin and structure-based mutagenesis.Our findings not only shed light on understanding the enzyme-mediated C-glycosidic bond breakage and formation,but also may help to facilitate stereospecific C-glycoside synthesis in pharmaceutical industry.

UGT88B2: A promiscuous O-glycosyltransferase from Carthamus tinctorius

Objective:In order to obtain new glycosyltransferases with highly efficient catalysis,the glycosyltransferases from Carthamus tinctorius which contains diverse types of glycosides were mined.Methods:A new glycosyltransferase gene(UGT88B2)with full length was obtained by PCR and further transformed into Escherichia coli for heterologous expression.The catalytic activity of recombinant UGT88B2 was determined by HPLC-MSn.The structures of representative catalytic products were elucidated by MS and NMR.Results:UGT88B2 exhibited catalytic promiscuity and various patterns in glycosylation of flavonoids with high efficiency.Conclusion:A new glycosyltransferase named UGT88B2 was successfully mined and can be employed as enzymatic tools in glycosylation of flavonoids.

Catalysis and deactivation of montmorillonite K10 in the aryl O-glycosylation of glycosyl trichloroacetoimidates

The catalysis of montmorillonite K10(MK10)for aryl O-glycosylation of glycosyl trichloroacetimidates was investigated.It was found that the catalyst MK10 is deactivated gradually in the recycle glycosylation.The fresh and the deactivated catalysts were characterized by X-ray diffraction(XRD),X-ray photoelectron spectroscopy(XPS),Thermogravimetric analysis(TGA),and N_(2)adsorption-desorption.The results show that the eliminated trichloroacetamide molecule deposits on the MK10,which blocks and poisons the active sites,resulting in the deactivation of the catalyst.The regeneration of the deactivated MK10 by calcination was studied preliminarily.