Unprotected Carbohydrates Research Articles

ChemInform Abstract: Simple One‐Pot Regioselective 6‐O‐Phosphorylation of Carbohydrates and Trehalose Desymmetrization.

AbstractThe presented protocol gives selective access to 6‐phosphorylated monosaccharides and disaccharides in a two step one‐pot procedure from unprotected carbohydrates or glycosides in good yields.

Organocatalyzed cascade reactions of carbohydrates – a direct access to C-glycosides

An organocatalyzed transformation to elongate unprotected carbohydrates is described. This operationally simple methodology is based on a Knoevenagel-oxa-Michael cascade. This reaction is catalyzed by proline and DBU. Products were obtained with exceptional high degrees of stereoselectivity.

ChemInform Abstract: Organocatalyzed Knoevenagel‐Addition — Simple Access to Carbon Chain‐Elongated Branched Carbohydrates.

AbstractA chain‐elongation of terminal protected and unprotected carbohydrates via a Knoevenagel‐addition process of 3‐keto‐esters is presented.

Yarrowia lipolytica dehydrogenase/reductase: An enzyme tolerant for lipophilic compounds and carbohydrate substrates

Yarrowia lipolytica short chain dehydrogenase/reductase (YlSDR) was expressed in Escherichia coli, purified and characterized in vitro. The substrate scope for YlSDR mediated oxidation was investigated with alcohols and unprotected carbohydrates spectrophotometrically, revealing a preference for secondary compared to primary alcohols. In reduction direction, YlSDR was highly active on ribulose and fructose, suggesting that the enzyme is a mannitol-2-dehydrogenase. In order to explore substrate tolerance especially for space-demanding, lipophilic protecting groups, 5-O-trityl-d-ribitol and 5-O-trityl-α,β-d-ribose were investigated as substrates: YlSDR oxidized 5-O-trityl-d-ribitol and 5-O-trityl-α,β-d-ribose and reduced the latter at the expense of NADP(H).

Organocatalyzed Knoevenagel-addition—simple access to carbon chain-elongated branched carbohydrates

Chain elongations of unprotected carbohydrates via a Knoevenagel-addition are described. The reactions were carried out in the presence of catalytic amounts of tertiary amines. The C–C bond formation processes yielded high syn-stereoselectivities. Additionally, through an asymmetric induction controlled by the configuration of the deployed carbohydrates pyranoid or furanoid products were formed. Yields were strongly increased by the use of 5-protected carbohydrates in these transformations.

Solid phase synthesis of glycopeptides using Shoda's activation of unprotected carbohydrates

An expedient and simple protocol to access S-linked glycopeptides by Fmoc SPPS using unprotected carbohydrates is reported. The utility of the method was demonstrated with the solid phase synthesis of a MUC1 fragment (20 mer) containing two glycosylation sites that were substituted with S-linked glycans.

ChemInform Abstract: A Novel Protocol for the Regioselective Bromination of Primary Alcohols in Unprotected Carbohydrates or Glycosides.

The regioselective and efficient bromination of primary hydroxyl groups in unprotected carbohydrates or glycosides is successfully achieved by using (chloro-phenylthio-methylene)dimethylammoniumchloride (CPMA) in the presence of tetrabutylammonium bromide (TBAB) in dry DMF.

Protective group-free synthesis of 3,4-dihydroxytetrahydrofurans from carbohydrates: formal total synthesis of sphydrofuran

Carbohydrates are taking a more prominent role in chemistry as an environmentally benign chemical feedstock. However, major efforts are still required to convert unprotected carbohydrates into high-value building blocks. We have investigated the protective group-free Wittig reaction and subsequential acid catalyzed intramolecular cyclization of unprotected carbohydrates to obtain 3,4-dihydroxytetrafurans. In this process, we have found that, when using Lewis acids and poly-alcohol substrates, additional attention should always be given to the catalytic nature of the acid as it might involve its ligands instead of the metal. Furthermore, we illustrate the viability of the concept by a straightforward formal total synthesis of the natural product sphydrofuran from d-xylose.

Synthesis of imidazo[2,1-b]thiazoles linked to an unprotected carbohydrate moiety

Two series of imidazo[2,1-b]thiazoles substituted on C-3 or C-5 with an unprotected carbohydrate moiety were synthesized. Different protective groups for position 3 of the carbohydrate moiety were tested (acetyl, tert-butyldimethylsilyl (TBDMS), and p-methoxybenzyl (PMB)) and the latter turn out to be the best strategy to obtain the desired products. Full deprotection of the carbohydrate was performed successfully in only one step.

A Novel Protocol for the Regioselective Bromination of Primary Alcohols in Unprotected Carbohydrates or Glycosides

AbstractThe regioselective and efficient bromination of primary hydroxyl groups in unprotected carbohydrates or glycosides is successfully achieved by using (chloro‐phenylthio‐methylene)dimethylammoniumchloride (CPMA) in the presence of tetrabutylammonium bromide (TBAB) in dry DMF.

Stereoselective amine-catalyzed carbohydrate chain elongation

Aldol additions of unprotected carbohydrates to 1.3-dicarbonyl compounds have been described. This transformation is based on a dual activation by tertiary amines and 2-hydroxypyridine.

Synthesis of Urea and Carbamate Glycosides Employing Unprotected Carbohydrates

Synthesis of Urea and Carbamate Glycosides Employing Unprotected Carbohydrates

Synthesis of Urea and Carbamate Glycosides Employing Unprotected Carbohydrates

A study of methods for the synthesis of urea and carbamate glycosides,starting with unprotective carbohydrates, led to the preparationof amino acid-carbohydrate conjugates in aqueous -media.

ChemInform Abstract: Knoevenagel Reaction of Unprotected Sugars

AbstractReview: 122 refs.

Asymmetrically substituted calix[4]pyrrole with chiral substituents

We have prepared first calix[4]pyrrole containing unprotected carbohydrate moiety directly linked to meso-position of oligopyrrole by stable "C-glycosidic" bond. Basic examination of its superassembly capability is presented.

ChemInform Abstract: A Simple Stereoselective One-Pot Synthesis of C-Nucleosides by 1,3- Dipolar Cycloaddition of Chiral Azomethine Imines Prepared in situ.

The NH,NH-dihydrocycloadduct 1 (6-chloro-9,9-dimethyl-7,8-dihydro-9H-pyrazolo[4,3-d]tetrazolo[1,5-b]-pyridazine) obtained by the cycloaddition of 2-diazopropane to 6-chlorotetrazolo[1,5-b]pyridazine, is transformed with protected or unprotected carbohydrates 2, 5, 7,9, 11, 13 and 15 in the presence of methyl acrylate (3) into the corresponding C-nucleosides 4, 6, 8, 10, 12, 14 and 16. In this one-pot synthesis two new chiral centers are formed stereoselectively, dependent on the chirality at C-atom next to aldehydo group in the carbohydrate

Direct azidation of unprotected carbohydrates under Mitsunobu conditions using hydrazoic acid

A single step procedure for the direct and regioselective synthesis of carbohydrate azides from unprotected sugars using hydrazoic acid under Mitsunobu conditions is reported. A series of mono-, di-, or triazido polyhydroxylated systems are described.

Patterned Immobilization of Unprotected Carbohydrates on an Aminooxy Polymer-Grafted Solid Surface

Abstract We describe a graft-type modification of a solid surface to be able to immobilize unprotected carbohydrates with a desired pattern. Water soluble carbohydrate-trapping polymers were grown from a solid surface through surface-initiated polymerization. The polymerization of an N-tert-butonyloxycarbonyl (N-Boc)-protected aminooxy monomer 3 was carried out from the immobilized initiator on silicon or glass surfaces. The N-Boc protecting group was then removed in an acidic solution to generate an aminooxy group, which reacts with free carbohydrates through oxime bonds on immersion of the plate in a carbohydrate solution. Sugar attachment on the surface polymer was confirmed by using infrared reflection absorption spectroscopy (IR-RAS) and fluorescent images after sugar-specific binding of fluorescein-labeled lectin proteins. The polymer was also grafted in a desired pattern by partial UV-irradiation over a photomask, giving a new material to create carbohydrates arrays.

Direct Azidation of Unprotected Carbohydrates with PPh3/CBr4/NaN3. Modulation of the Degree of Substitution.

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.

Benzylsulfanyloxazolines in Palladium‐Catalyzed Cross‐Coupling Reactions: A Novel Approach to Chiral Oxazolines.

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.