Glycosyl Hemiacetals Research Articles

Benzene-1,3-disulfonyl Fluoride Mediated Synthesis of Glycosyl Fluorides from Glycosyl Hemiacetals.

We developed an efficient method for synthesizing glycosyl fluorides from glycosyl hemiacetals using benzene-1,3-disulfonyl fluoride (S2) as the fluorinating agent in combination with the base DBU (1,8-diazabicyclo[5.4.0]undec-7-ene) under mild conditions. This approach enabled the successful synthesis of 17 glycosyl fluorides with various functional groups, including disaccharides and deoxysulfates, with yields of up to 99%. The utility of these synthesized glycosyl fluorides was further demonstrated in the synthesis of important O- and C-glycosides.

Mild method for the synthesis of α-glycosyl chlorides: A convenient protocol for quick one-pot glycosylation

A simple and efficient protocol for the preparation of α-glycosyl chlorides within 15–30 min is described which employs a stable, cheap, and commercially available Trichloroisocyanuric acid (TCCA) as non-toxic chlorinating agent along with PPh3. This process involved a wide range of substrate scope and is well-suited with labile hydroxyl protecting groups such as benzyl, acetyl, benzoyl, isopropylidene, benzylidene, and TBDPS (tert-butyldiphenylsilyl) groups. This process is operationally simple, mild conditions and obtained good yields with excellent α selectivity. Moreover, a multi-catalyst one-pot glycosylation can be carried out to transform the glycosyl hemiacetals directly to a various O-glycosides in high overall yields without the need for separation or purification of the α-glycosyl chloride donors.

Stereoselective Synthesis of β-glycosyl Esters via 1-Hydroxybenzotriazole Mediated Acylation of Glycosyl Hemiacetals.

Highly stereoselective access to β-glycosyl esters was disclosed, employing 1-hydroxybenzotriazole (HOBt) mediated esterification of glycosyl hemiacetals in the presence of EDCI and 1,4-diazabicyclo[2.2.2]octane (DABCO). Mechanistic studies indicated a dynamic kinetic acylation pathway. In addition, a stereoretentive esterification of glycosyl hemiacetals with tert-butyloxycarbonyl ortho-hexynylbenzoate and DMAP was also reported.

Stereoselective β-mannosylations and β-rhamnosylations from glycosyl hemiacetals mediated by lithium iodide

Stereoselective β-mannosylation is one of the most challenging problems in the synthesis of oligosaccharides. Herein, a highly selective synthesis of β-mannosides and β-rhamnosides from glycosyl hemi-acetals is reported, following a one-pot chlorination, iodination, glycosylation sequence employing cheap oxalyl chloride, phosphine oxide and LiI. The present protocol works excellently with a wide range of glycosyl acceptors and with armed glycosyl donors. The method doesn't require conformationally restricted donors or directing groups; it is proposed that the high β-selectivities observed are achieved via an SN2-type reaction of α-glycosyl iodide promoted by lithium iodide.

A dehydrative glycosylation protocol mediated by nonafluorobutanesulfonyl fluoride (NfF)

A new dehydrative glycosylation protocol that proceeds through selective activation of glycosyl hemiacetals with nonafluorobutanesulfonyl fluoride (NfF) has been disclosed. Contrary to the major classical glycosylation reactions that proceed under acidic or neutral conditions, the present glycosylation reaction proceeds under mild basic conditions. In the absence of an external acceptor, self-condensation of the glycosyl hemiacetal occurs, providing the corresponding symmetrical 1,1′-disaccharides in high yields.

Synthesis of glycosyl chlorides using catalytic Appel conditions.

The stereoselective synthesis of glycosyl chlorides using catalytic Appel conditions is described. Good yields of α-glycosyl chlorides were obtained using a range of glycosyl hemiacetals, oxalyl chloride and 5 mol% Ph3PO. For 2-deoxysugars treatment of the corresponding hemiacetals with oxalyl chloride without phosphine oxide catalyst also gave good yields of glycosyl chloride. The method is operationaly simple and the 5 mol% phosphine oxide by-product can be removed easily. Alternatively a one-pot, multi-catalyst glycosylation can be carried out to transform the glycosyl hemiacetal directly to a glycoside.

Copper-mediated anomeric O-arylation with organoboron reagents.

Copper-mediated couplings of arylboroxines with glycosyl hemiacetals furnish O-aryl glycosides via Csp2-O bond formation. The method enables the anomeric O-arylation of protected pyranose and furanose derivatives, and is tolerant of functionalized arylboroxine partners. Whereas mixtures of anomers are formed from glucopyranose, galactopyranose and arabinofuranose hemiacetals, the α-anomer is generated selectively from mannopyranose and mannofuranose-derived substrates.

Sequential Dy(OTf)3 -Catalyzed Solvent-Free Per-O-Acetylation and Regioselective Anomeric De-O-Acetylation of Carbohydrates.

Dysprosium(III) trifluoromethanesulfonate-catalyzed per-O-acetylation and regioselective anomeric de-O-acetylation of carbohydrates can be tuned by adjusting the reaction medium. In this study, the per-O-acetylation of unprotected sugars by using a near-stoichiometric amount of acetic anhydride under solvent-free conditions resulted in the exclusive formation of acetylated saccharides as anomeric mixtures, whereas anomeric de-O-acetylation in methanol resulted in a moderate-to-excellent yield. Reactions with various unprotected monosaccharides or disaccharides followed by a semi-one-pot sequential conversion into the corresponding acetylated glycosyl hemiacetal also resulted in high yields. Furthermore, the obtained hemiacetals could be successfully transformed into trichloroimidates after Dy(OTf)3 -catalyzed glycosylation.

Borinic Acid Catalyzed Stereo- and Regioselective Couplings of Glycosyl Methanesulfonates

In the presence of a diarylborinic acid catalyst, glycosyl methanesulfonates engage in regio- and stereoselective couplings with partially protected pyranoside and furanoside acceptors. The methanesulfonate donors are prepared in situ from glycosyl hemiacetals, and are coupled under mild, operationally simple conditions (amine base, organoboron catalyst, room temperature). The borinic acid catalyst not only influences site-selectivity via activation of 1,2- or 1,3-diol motifs, but also has a pronounced effect on the stereochemical outcome: 1,2-trans-linked disaccharides are obtained selectively in the absence of neighboring group participation. Reaction progress kinetic analysis was used to obtain insight into the mechanism of glycosylation, both in the presence of catalyst and in its absence, while rates of interconversion of methanesulfonate anomers were determined by NMR exchange spectroscopy (EXSY). Together, the results suggest that although the uncatalyzed and catalyzed reactions give rise to opposite stereochemical outcomes, both proceed by associative mechanisms.

Appel-reagent-mediated transformation of glycosyl hemiacetal derivatives into thioglycosides and glycosyl thiols.

A series of glycosyl hemiacetal derivatives have been transformed into thioglycosides and glycosyl thiols in a one-pot two-step reaction sequence mediated by Appel reagent (carbon tetrabromide and triphenylphosphine). 1,2-trans-Thioglycosides and β-glycosyl thiol derivatives were stereoselectively formed by the reaction of the in situ generated glycosyl bromides with thiols and sodium carbonotrithioate. The reaction conditions are reasonably simple and yields were very good.

ChemInform Abstract: N‐Bromosuccinimide‐Mediated Conversion of Allyl Glycosides to Glycosyl Hemiacetals.

AbstractThe hydrolysis of differentially functionalized allyl glycosides to their corresponding glycosyl hemiacetal derivatives under mild and metal‐free conditions proceeds exceptionally fast and is compatible with most of the functional groups used in oligosaccharide synthesis.

ChemInform Abstract: Synthesis of Glycosyl Esters and Glycosyl Hemiacetals from Methylthioglycosides.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

N-Bromosuccinimide-Mediated Conversion of Allyl Glycosides to Glycosyl Hemiacetals

A novel reaction condition has been developed for the hydrolysis of differentially functionalized allyl glycosides to their corresponding glycosyl hemiacetal derivatives in the presence of N-bromosuccinimide (NBS). The reaction condition is exceptionally fast, mild, and compatible with most of the functional groups used in the oligosaccharide synthesis, and yields were excellent.

Mild and Efficient Hydrolysis of Thioglycosides to Glycosyl Hemiacetals Using N‐Iodosaccharin.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Chloramine-T-mediated chemoselective hydrolysis of thioglycosides into glycosyl hemiacetals under neutral conditions

A metal-free, mild, efficient and chemoselective hydrolysis of several thioalkylglycosides ( 1 ) into their corresponding 1-hydroxy sugars ( 2 ) using sodium N-chloro- p-toluenesulfonamide trihydrate (chloramine-T) without affecting other functional groups is reported.

Synthesis of Glycosyl Esters and Glycosyl Hemiacetals From Methylthioglycosides

ABSTRACT Glycosyl esters constitute a widespread family of natural products such as anti-tumor agents,1 antibiotics,2 terpenoid glycosides,3 plant pigments4 and other substances.5 It has been shown that aromatic carboxylic acids are metabolized by humans as glycosyl esters,6 and D-glucopyranosyl fatty acid esters were found to inhibit the growth of leukemia cells7 and plant growth.8 The synthesis of a prodrug in the g form of a glycosyl ester has been reported.9 In synthetic chemistry glycosyl acetates are frequently used glycosyl donors in Lewis-acid catalyzed glycosylation reactions10 and other transformations.11