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Chemical O-glycosylation is a key step for the synthesis of sugar-containing molecules such as glycolipids. However, traditional carbohydrate chemistry is characterized by extensive use of protective groups, resulting in laborious manipulations and poor atom economy. Here, we present a protecting-group-free glycosylation strategy employing dibenzyloxy-1,3,5-triazin-2-yl glycosides (DBT-glycosides) as glycosyl donors. The DBT-glycosyl donors could be prepared directly through an alkaline nucleophilic substitution from unprotected sugars in aqueous media. The O-glycosylation of alcohols by using DBT-glycosyl donors has been carried out under mild hydrogenolytic conditions, affording the corresponding alkyl glycosides stereo-selectively in good yields., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

A monoselective synthesis of aryl-C-Δ(1,2)-glycosides from 1-iodoglycals via palladium-catalyzed ortho-C-H activation of N-quinolyl benzamides has been developed. An amino acid derivative was used as a crucial ligand to improve the yield and monoselectivity of the coupling reaction. The utility of this protocol was demonstrated by a concise synthesis of key moieties of some natural products.

A glycosyl coupling reaction via photoinduced direct activation of thioglycosides and subsequent O-glycosylation in the absence of photosensitizer was developed for the first time. This reaction underwent a selectively homolytic cleavage of a C-S bond to generate a glycosyl radical, which was oxidized to an oxacarbenium ion by Cu(OTf)2, and a sequential O-glycosylation. A wide range of glycosides were synthesized in moderate to excellent yield using sugars, amino acids, or cholesterol as the acceptors.

A mild, efficient, and practical transformation for the direct C-H trifluoromethylation of glycals under visible light has been reported for the first time. This reaction employed fac-Ir(3+)(ppy)3 as the photocatalyst, Umemoto's reagent as the CF3 source, and a household blue LED or sunlight as the light source. Glycals bearing both electron-withdrawing and -donating protective groups performed this reaction smoothly. This visible light-mediated trifluoromethylation reaction was highlighted by the trifluoromethylation of the biologically important Neu2en moiety.

Several phenylethanoid glycoside derivatives were designed and synthesized. Most of the synthetic compounds showed significant neuroprotective effects, including antioxidative and anti-apoptotic properties. Specifically, target compounds displayed potent effects against various toxicities such as H2O2 and 6-hydroxydopamine (6-OHDA) in PC12 cells. Among the synthetic derivatives, three compounds (5, 6, 8) exhibited much superior activities to the marketed drug Edaravone. The compounds were able to prevent the 6-OHDA-induced damage in PC12 cells in a dose-dependent manner. The anti-apoptotic effects could be observed via cell morphological changes. Moreover, the compounds significantly reduced the intracellular ROS increase resulting from 6-OHDA treatment. The preliminary structure-activity relationships were also explored. Compounds 5, 6, 8 may hold the potential as promising neuroprotective agents and new lead compounds for the treatment of neurodegenerative diseases or cerebral ischemia., (Copyright © 2015 Elsevier Masson SAS. All rights reserved.)

A new "ring-opening-ring closure" strategy for the synthesis of aryl-C-glycosides was described. This strategy exploited the nickel-catalyzed regioselective β-O elimination of glycals by reactions with various aryl boronic acids or potassium aryltrifluoroborates to yield the ring-opened products, which underwent the Lewis acid, protonic acid, PhSeCl, or NBS mediated ring closure reactions to afford diverse aryl-C-glycosides. After Lewis acids and protonic acids were screened, it was found that, starting from the ring-opened substrates, the Ph3PHBr or Sc(OTf)3 mediated ring closure reaction provided α- or β-preferred aryl-C-Δ(2,3)-glycosides, respectively. Furthermore, β-D-phenyl-C-glycosides were successfully prepared via the PhSeCl-mediated cyclization reaction, whereas the α-D-phenyl-C-glycoside was obtained via the NBS-mediated cyclization reaction. After removal of the 2-substituted functionalities by Bu3SnH/AIBN, the synthesis of 2-deoxy-aryl-C-glycosides was ultimately realized in a stereoselective manner.

A facile, versatile and stereoselective synthesis of bicyclic polyhydroxylated alkaloids as castanospermine analogues is described. The synthetic route started from methyl pyranosides. The key steps involved a high-yielding expeditious one-pot tandem reaction from alkenes to N-substituted delta-lactams. The delta-lactams were stereoselectively vinylated to give the dienes, which were followed by the ring-closing metathesis to produce the cyclized products. The functional group transformations of the resulting bicyclic compounds furnished diverse polyhydroxylated alkaloids in good yields.

The Heck coupling of aryl iodides with pyranoid glycals using a catalytic amount of Pd(OAc)(2) to form pyranoid aryl C-glycosides has been achieved. The reaction takes place smoothly in the presence of Ag(2)CO(3) and Cu(OAc)(2) (or DMSO) in acetonitrile. This arylation process, which occurs in a highly regio- and stereo-selective manner, provides a simple, mild, and efficient approach to the synthesis of aryl 2-deoxy-C-glycopyranosides.

Oxidative Heck-type C-glycosylations of glycals with various arylboronic acids using Pd(OAc)(2) as catalyst in the presence of oxidant were developed. The corresponding ketone, enol ether, and enone types of C-glycosides were predictably obtained with benzoquinone (BQ), Cu(OAc)(2)/O(2), and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) as oxidants, respectively. This method provides a simple, mild, and stereoselective synthesis of aryl 2-deoxy-C-glycosides.

The reaction of 4, 6-O-benzylidene-d-pyranosides with a stoichiometric amount of TsCl, AcCl, and BzCl in the presence of silver(I) oxide and a catalytic amount of potassium iodide led to monosubstituted derivatives in high regioselectivity and in good yields., (Copyright 2004 American Chemical Society)

A new glycosylation method promoted by visible light with 3,5-dimethoxyphenyl glycoside as the donor was developed. This protocol delivers both O-glycosides and N-glycosides in moderate to excellent yields using a wide range of O-nucleophiles and nucleobases as the glycosyl acceptors. [ABSTRACT FROM AUTHOR]

A stereoselective Koenigs-Knorr glycosylation reaction under the catalysis of urea is described. This method is characterized by urea-mediated hydrogen-bond activation and subsequent glycosylation with glycosyl chlorides or bromides. Excellent yields and high anomeric selectivity can be achieved in most cases. Moreover, the low a-stereoselectivity of glycosylations observed when using perbenzylated glucosyl donors can be greatly improved by the addition of tri-(2,4,6-trimethoxyphenyl) phosphine (TTMPP). [ABSTRACT FROM AUTHOR]

A mild method for the synthesis of α-C-glycosides by the samarium diiodide mediated coupling reactions of glycosyl 2-pyridyl sulfones with different α,β-unsaturated carbonyl compounds has been developed. This method allows the use of less amount of substrates. [ABSTRACT FROM AUTHOR]

Abstract: The repeating GalpNAc-α-(1→4)-GalpNAc unit is part of a series of essential structures that can be found in many important biomolecules such as the glycoproteins and the O-antigenic polysaccharides of clinically important bacterial strains. In this paper, we describe an exclusive α-selective glycosylation reaction, using a 4,6-di-O-tert-butyldimethylsilyl-N-acetyloxazolidinone-protected thioglycoside as the glycosyl donor, under pre-activation conditions, with only half amount of the promoter, providing the product GalpNAc-α-(1→4)-GalpNAc in high isolated yield. This reaction can be also applied to increasing the length of the repeating structure, which is of significant use in further synthesis of branched or linear oligosaccharides. [ABSTRACT FROM AUTHOR]

A general approach to the synthesis of diverse heteroaryl-C-Δ1,2-glycosides has been developed by employing the Pd(OAc)2/CuI cocatalyzed direct cross-coupling of five-membered nitrogen heterocycles with 1-iodoglycals in a C-H activation manner. Using this method, 27 examples of heteroaryl-C-Δ1,2-glycosides, containing indoles, thiazoles, benzothiazoles, imidazoles, benzimidazoles, and benzoxazoles as aglycones were obtained in 43-99% yield. [ABSTRACT FROM AUTHOR]

A new "ring-opening--ring closure" strategy for the synthesis of aryl-C-glycosides was described. This strategy exploited the nickel-catalyzed regioselective β-O elimination of glycals by reactions with various aryl boronic acids or potassium aryltrifluoroborates to yield the ring-opened products, which underwent the Lewis acid, protonic acid, PhSeCl, or NBS mediated ring closure reactions to afford diverse aryl-C-glycosides. After Lewis acids and protonic adds were screened, it was found that, starting from the ring-opened substrates, the Ph3PHBr or Sc(OTf)3 mediated ring closure reaction provided α- or α-preferred aryl-C-Δ2,3-glycosides, respectively. Furthermore, β-D-phenyl-C-glycosides were successfully prepared via the PhSeCl-mediated cydization reaction, whereas the α-n-phenyl-C-glycoside was obtained via the NBS-mediated cydization reaction. After removal of the 2-substituted functionalities by Bu3SnH/AIBN, the synthesis of 2-deoxy-aryl-C-gIycosides was ultimately realized in a stereoselective manner. [ABSTRACT FROM AUTHOR]

Highlights: [•] o-Methylphenylthioglycosides were used as blocks in preactivation protocol. [•] The aglycon transfer was avoided. [•] The efficiency of glycosyl coupling reactions was enhanced. [•] The thioglycosides were efficiently employed in one-pot oligosaccharide assembly. [ABSTRACT FROM AUTHOR]

A monoselective synthesis of aryl-C-Δ1,2-glycosides from 1-iodoglycals via palladium-catalyzed ortho-C-H activation of N-quinolyl benzamides has been developed. An amino acid derivative was used as a crucial ligand to improve the yield and monoselectivity of the coupling reaction. The utility of this protocol was demonstrated by a concise synthesis of key moieties of some natural products. [ABSTRACT FROM AUTHOR]

A glycosylcoupling reaction via photoinduced direct activationof thioglycosides and subsequent O-glycosylationin the absence of photosensitizer was developed for the first time.This reaction underwent a selectively homolytic cleavage of a C–Sbond to generate a glycosyl radical, which was oxidized to an oxacarbeniumion by Cu(OTf)2, and a sequential O-glycosylation.A wide range of glycosides were synthesized in moderate to excellentyield using sugars, amino acids, or cholesterol as the acceptors. [ABSTRACT FROM AUTHOR]

2-Pyridyl glycosides have been identified to be powerful glycosyl donors for the preactivation-based oligosaccharide synthesis. By using stoichiometric amount of Tf 2 O, the 2-pyridyl glycosides were pre-activated, which subsequently underwent glycosylation reactions smoothly to produce the coupled products in high yields. Furthermore, the 2-pyridyl glycosides were applied to the efficient oligosaccharide assembly by the preactivation-based one-pot oligosaccharide synthesis protocol. [ABSTRACT FROM AUTHOR]

A new efficient pre-activation method for the highly α-stereoselective glycosylation of 2-deoxysugars and 2,6-dideoxysugars has been developed using 2-deoxy- and 2,6-dideoxythioglycosides as glycosyl donors. The approach allows a wide range of glycosyl acceptors and donors to be used; the α-selectivity is very good to excellent. [ABSTRACT FROM AUTHOR]

A general and efficient approach to the synthesis of various C -acyl glycosides has been developed via Pd 2 (dba) 3 /CuTC co-catalyzed cross-coupling reaction of glycosyl carbothioates with arylboronic acids. The reaction showed a broad substrate scope and 25 examples were exhibited in 61%–97% isolated yields. Furthermore, this reaction was applied to the gram-scale preparation of C -acyl glycosides. The coupled products can be further transformed into diverse biologically useful compounds, as exemplified by the synthesis of protected sergliflozin-A mimics. Image 1 [ABSTRACT FROM AUTHOR]

Activation of thioglycosides upon UV irradiation followed by cupric triflate oxidation leads to the in situ formation of an oxacarbenium ion which is able to undergo glycosylation reactions with a wide variety of substrates such as sugars, amino acids, terpenes, and sterols. [ABSTRACT FROM AUTHOR]