Chemoselective glycosylation of carboxylic acid with glycosyl ortho-hexynylbenzoates as donors

The gold(I)-catalyzed glycosylation of acid alcohols with glycosyl ortho-hexynylbenzoates in the presence of BF₃·Et₂O and DBU provided the corresponding ester glycosides chemoselectively in high yield; while with DTBP as an additive instead, orthoester formation with the alcohol was effected selectively.     

An efficient glycosylation protocol with glycosyl ortho-alkynylbenzoates as donors under the catalysis of Ph3PAuOTf

A new and powerful glycosylation protocol with glycosyl ortho-alkynylbenzoates as donors and Ph₃PAuOTf as a promoter is disclosed. The donors are readily available and stable; the glycosidic coupling yields are generally excellent; the promotion system is catalytic, neutral, and orthogonal to the known glycosylation conditions.     

Amberlyst 15 as a mild and effective activator for the glycosylation with disarmed glycosyl trichloroacetimidate donors

Amberlyst 15 acidic resin has been shown to be a mild and effective activator for the glycosylation with commonly used disarmed glycosyl trichloroacetimidate donors. Glucosylation, galactosylation, rhamnosylation, and lactosylation of a panel of representative alcohol and thiol acceptors promoted by Amberlyst 15 allowed for the formation of structurally diverse O- or S-linked oligosaccharides and glycosylated amino acids in moderate to excellent yields.     

Catalytic and stereoselective glycosylation with glycosyl N-trichloroacetylcarbamate

Catalytic and stereoselective glycosylation efficiently proceeded by activating a glycosyl N-trichloroacetylcarbamate with a catalytic amount of Lewis acids in the presence of a glycosyl acceptor and molecular sieves 5 Å. Catalytic and one-pot dehydrative glycosylation of a 1-hydroxy carbohydrate was also performed stereoselectively by the reaction with trichloroacetyl isocyanate followed by activation with a catalytic amount of activators.     

Synthesis of ginsenoside Rh2 and chikusetsusaponin-LT8 via gold(I)-catalyzed glycosylation with a glycosyl ortho-alkynylbenzoate as donor

Glycosylation of the acid labile protopanaxadiol derivatives was succeeded with a glycosyl ortho-hexynylbenzoate as donor under the catalysis of PPh₃AuNTf₂, leading to the subsequent elaboration of ginsenoside Rh2 and chikusetsusaponin-LT8 in a concise manner.     

ortho-Alkynylphenyl thioglycosides as a new type of glycosylation donors under the catalysis of Au(I) complexes

ortho-Alkynylphenyl thioglycosides, prepared readily via Sonagashira coupling of ortho-bromophenyl thioglycosides with alkynes, could undergo glycosidation effectively under the catalysis of a gold(I) complex.     

Glycosylation reactions with ‘disarmed’ thioglycoside donors promoted by N-iodosuccinimide and HClO4-silica

Glycosylation of ‘disarmed’ thioglycosides promoted by NIS in the presence of HClO₄ immobilized on silica compares very favourably with the accepted NIS-TfOH procedure.     

Efficient synthesis of lupane-type saponins via gold(I)-catalyzed glycosylation with glycosyl ortho-alkynylbenzoates as donors

Glycosylation of the acid labile betulin and betulinic acid derivatives was achieved with glycosyl ortho-hexynylbenzoates as donors under the catalysis of PPh(3)AuNTf(2); this enabled the efficient synthesis of lupane-type saponins, as exemplified by the total synthesis of the proposed betulinic acid trisaccharide from Bersama engleriana.     

Sequential one-pot glycosylation with glycosyl N-trichloroacetylcarbamate and trichloroacetate including dehydrative approach using 1-hydroxy sugars

An efficient sequential one-pot glycosylation has been developed with glycosyl trichlorocarbamate and trichloroacetate activated by the same Lewis acid and enabled by a change in reaction temperature. The αα-selective glycosylation was achieved using glucose, galactose, and mannose substrates after investigation into the reactivities of the two types of glycosyl donors. Sequential one-pot dehydrative glycosylation, including in situ preparation of glycosyl donors followed by generation of two glycosyl bonds, provided three types of trisaccharide.     

A novel glycosylation of inactive glycosyl donors using an ionic liquid containing a protic acid under reduced pressure conditions

The glycosylation of inactive glycosyl donors, such as methyl glycosides and 1-hydroxy sugars with nearly stoichiometric amounts of various alcohols (1.1 equiv) in an ionic liquid containing a protic acid (acid-IL) under reduced pressure conditions proceeded effectively to give the corresponding glycosides in good to high yields. Furthermore, the acid-IL could be reused for additional glycosylations without the loss of efficiency.     

A new efficient glycosylation method employing glycosyl pentenoates and PhSeOTf

The PhSeOTf promoted glycosylations of various glycosyl acceptors with mannosyl pentenoates and glucosyl pentenoates as glycosyl donors afforded corresponding disaccharides in high yields. And the present glycosyl pentenoates/PhSeOTf method showed that the complete -selective mannosylation of secondary alcohol acceptors was achieved with 2,3,4,6-tetra-O-benzyl-d-mannopyranosyl pentenoate to give -disaccharides in good yields.     

HClO4-SiO2 catalyzed glycosylation using sugar trichloroacetimidates as glycosyl donors

Silica-supported perchloric acid (HClO₄-SiO₂) has been used as an efficient promoter, as a replacement of TMSOTf, in various glycosylation reactions using sugar trichloroacetimidates as glycosyl donors. Operational simplicity, economic considerations, high yield, short reaction time and low toxicity were the key features associated with this protocol.     

A novel glycosylation concept; microwave-assisted acetal-exchange type glycosylations from methyl glycosides as donors

Efficient microwave-assisted glycosylations from methyl glucopyranosides are described. We have discussed the effects of microwave irradiation on this unique glycoside exchanging reaction from view points such as amount of Lewis acid promoters and acceptors, hydroxyl protecting groups of methyl glucopyranosides donors for reactivity, and neighboring effect.     

Propargyl/methyl furanosides as potential glycosyl donors

Transfuranosylations are not well studied though many similar studies exist for transpyranosylation; herein, we report that propargyl/methyl D-ribf- and D-lyxf- give only 1,2-trans glycosides whereas D-araf- and D-xylf- result in a mixture of 1,2-trans and 1,2-cis glycosides; observed facts are rationalised by computational studies.     

Electrochemical O-glycosylation using thioglycosides as glycosyl donors in the presence of a catalytic amount of sodium trifluoromethanesulfonate as a supporting electrolyte

Electrochemical O-glycosylation of primary alcohols with O-protected thioglycosides was performed in the presence of a small amount of sodium trifluoromethansulfonate (12.5 mol % to glycosyl acceptor) as a supporting electrolyte. The reaction was successfully carried out in an undivided cell to give O-glycosides in good yields with a high electro-efficiency (ca. 1 F/mol) at 15 °C in acetonitrile.     

The Michaelis-Arbuzov rearrangement of anomeric thiocyanates: synthesis and application of S-glycosyl thiophosphates, thiophosphonates and thiophosphinates as glycosyl donors

Reaction of anomeric thiocyanates with triethyl phosphite, dimethyl phenylphosphonite and methyl diphenylphosphinite afforded the corresponding S-glycosyl thiophosphates, thiophosphonates and thiophosphinates in good yields. These derivatives were applied as glycosyl donors in the synthesis of benzyl glycosides and disaccharides with excellent stereoselectivity.     

Synthesis and use of glycosyl phosphates as glycosyl donors

Differentially protected glycosyl phosphates prepared by a straightforward synthesis from glycal precursors are used as powerful glycosyl donors. Activation of beta-glycosyl phosphates by TMSOTf at -78 degrees C achieves the selective formation of beta-glycosidic linkages in excellent yields with complete stereoselectivity. Reaction with thiols results in the conversion of glycosyl phosphates into thioglycosides in nearly quantitative yield. An orthogonal coupling strategy using glycosyl phosphate donors and thioethyl glycoside acceptors allows for the rapid synthesis of a trisaccharide.     

S-Benzoxazolyl (SBox) glycosides as novel,versatile glycosyl donors for stereoselective 1,2-cis glycosylation

[reaction: see text] Novel glycosyl donors, S-benzoxazolyl (SBox) glycosides, have been synthesized, tested toward various protecting group manipulations, and applied to the highly stereoselective 1,2-cis glycosylation. These compounds fulfill the requirements for a modern glycosyl donor such as accessibility, high stability toward protecting group manipulations, and mild activation conditions. It was also demonstrated that SBox glycosides withstand other glycosyl donor activation conditions and therefore allow selective glycosylations of O-pentenyl and thioglycosides.     

N-Dimethylphosphoryl-protected glucosamine trichloroacetimidate as an effective glycosylation donor

Glycosylation of a variety of alcohols with 3,4,6-tri-O-acetyl-2-N-dimethylphosphoryl-2-deoxy-α-d-glucopyranosyl trichloroacetimidate as a glycosyl donor provided the corresponding coupled products in high yields and good β-selectivity. N-Dimethylphosphoryl-protection stayed stable under acidic and basic conditions for further elaboration of the glucosamine-containing oligosaccharides.     

Effective synthesis of nucleosides with glycosyl trifluoroacetimidates as donors

Glycosyl trifluoroacetimidates have been disclosed to be effective glycosyl donors for the synthesis of nucleosides; the present N-glycosylation protocol requires only a catalytic amount of TMSOTf as promoter and proceeds smoothly at room temperature.