Reaction Of Glycals Research Articles

Suzuki‐Miyaura Reaction of Glycals with Base‐Labile Protecting Groups as a New Route to Glycoporphyrins

AbstractGlycoporphyrins are considered promising photosensitisers of new generation. Herein, we describe a metal‐catalysed synthetic method towards porphyrin‐carbohydrate C−C conjugates. The protocol of Suzuki‐Miyaura reaction has been developed and it was compatible with peracetylated 2‐iodoglycals. The utility of the reaction was exemplified on 15 different (C‐2)‐arylated sugar derivatives. Then it was applied on more challenging starting materials, namely, porphyrin boronates in which we addressed the issues of difficult transmetalation step usually observed on palladium‐catalysed processes of porphyrin derivatives. The efficiency of the protocol was finally applied to synthesize the library of glycoporphyrins proving the versatile character of this strategy. Finally, the methodology was transferred onto A4‐type porphyrin to efficiently obtain an interesting example of a multivalent glycoconjugate.

Suzuki‐Miyaura Reaction of Glycals with Base‐Labile Protecting Groups as a New Route to Glycoporphyrins.

Suzuki‐Miyaura Reaction of Glycals with Base‐Labile Protecting Groups as a New Route to Glycoporphyrins.

Zinc tetrafluoroborate catalyzed α-stereoselective synthesis of pseudoglycals: efficient synthesis of digitoxin α-L-amicetose.

We report here an efficient, fast, and cost-effective strategy for synthesizing pseudoglycals by the reaction of glycals with alcohols or nucleophiles using zinc tetrafluoroborate. This mild, transition metal-free approach allowed the α-selective synthesis of pseudoglycals using a wide range of acceptors containing various protecting groups/functionalities. This method is exemplified by the synthesis of digitoxin α-L-amicetose, a known potential cardiac glycoside anticancer agent. The improved 3-step synthesis from L-rhamnal afforded an overall yield of 54%, thus representing a significant improvement over the previous method.

Regio and Stereoselective One-Pot Synthesis of 2-Deoxy-3-thio Pyranoses and Their O-Glycosides from Glycals.

A reaction of glycals with two different types of nucleophiles in the presence of SnCl4 enabled one-pot rapid access to 2-deoxy-3-thio pyranoses and their O-glycosides. The process involves thioaryl substitution at C-3 with stereoretention and α-selective O-glycosylation at C-1 from d-glycals, thus combining two reactions with three interventions. The present methodology features an attractive three-component coupling (1:1.2:1.5 ratio) with operational simplicity at 0 °C in 10-20 min. This stereoselective one-pot 1,3-difunctionalization approach of glycals is compatible with wide range of primary and secondary alcohols affording products in good to excellent yields. This methodology was successfully extended toward disaccharide synthesis. Several control experiments suggested a plausible reaction mechanism and rationale behind regio and stereoselectivity. The reaction strategy possesses an intrinsic ability for the synthesis of various natural products and drug molecules.

Further Investigation of the 2‐Azido‐phenylselenylation of Glycals

AbstractDerivatives of 2‐azido‐2‐deoxysugars are widely applied as precursor of 2‐amino‐2‐deoxysugars in the synthesis of various oligosaccharides of bacterial, fungal and mammalian origin. Heterogeneous or homogeneous azidophenylselenylation (APS) of glycals, i. e., reaction of glycals with Ph2Se2, PhI(OAc)2 and NaN3 or TMSN3 as azide radical donors, is a straightforward way to phenyl 2‐azido‐2‐deoxy‐1‐selenoglycosides that can be directly used as glycosyl donors. However, heterogeneous APS is characterized by insufficient reproducibility and scalability. We have studied the effect of reaction conditions on the product distribution in heterogeneous APS of 3,4,6‐tri‐O‐acetyl‐d‐galactal and found the conditions that enabled reliable preparation of crystalline phenyl 2‐azido‐2‐deoxy‐1‐seleno‐α‐d‐galactopyranoside triacetate in yield of 58 % on the 3.7 mmol scale. APS of 3,4,6‐tri‐O‐acetyl‐d‐glucal under those conditions produced a ∼1 : 1 mixture of phenyl 2‐azido‐2‐deoxy‐1‐seleno‐α‐d‐gluco‐ and mannopyranosides in total yield of 78 %. Acetoxyphenylselenylation of differently protected galactals and 3,4,6‐tri‐O‐acetyl‐d‐glucal under the action of Ph2Se2 and PhI(OAc)2 has been shown to be a convenient method for the synthesis of 1‐O‐acetyl‐2‐seleno‐2‐deoxy derivatives, valuable intermediates in chemistry of 2‐deoxysugars. 2‐Seleno‐2‐deoxy sugars were characterized in detail by NMR data including 77Se chemical shifts and nJSe−H coupling constant values.

Solvent Free Stereoselective Iodoacetoxylation of Alkenes and Glycals Using N-Iodosuccinimide and Acetic Anhydride

The reactions of glycals with N-iodosuccinimide and acetic anhydride under solvent free conditions provide 2-deoxy-2-iodo-α-mannopyranosyl acetates with good stereoselectivity. The developed process is in accordance with principles of green chemistry and addresses the shortage of such methods for the regioselective iodo acetoxylation of alkenes.

One-Pot Regioselective and Stereoselective Synthesis of C-Glycosyl Amides from Glycals Using Vinyl Azides as Glycosyl Acceptors.

The reaction of glycals containing good leaving groups with aromatic vinyl azides to give α- C-glycosyl amides in good yields is described. Various vinyl azides with different groups undergo the reaction smoothly. In these reactions, an iminodiazonium intermediate is generated by the attack of the vinyl azide onto the glycal under Lewis acid conditions. This undergoes Schmidt-type denitrogenative 1,2-migration to form a nitrilium ion, which, upon hydrolysis, gives the desired C-glycosyl amide.

Reaction of Glycals with Organic Peroxides: Synthesis of 2-iodo, 2-Deoxy and 2,3-Unsaturated Glycosides

Reaction of Glycals with Organic Peroxides: Synthesis of 2-iodo, 2-Deoxy and 2,3-Unsaturated Glycosides

Tuning the Bioactivity of Tensioactive Deoxy Glycosides to Structure: Antibacterial Activity Versus Selective Cholinesterase Inhibition Rationalized by Molecular Docking

AbstractNew octyl/dodecyl 2,6‐dideoxy‐D‐arabino‐hexopyranosides have been synthesized by a simple but efficient methodology based on the reaction of glycals with alcohols catalysed by triphenylphosphane hydrobromide, deprotection, regioselective tosylation and reduction. Their surface‐active properties were evaluated in terms of adsorption and aggregation parameters and compared with those of 2‐deoxy‐D‐glycosides and 2,6‐dideoxy‐L‐glycosides. Deoxygenation at the 6‐position led to a decrease in the critical micelle concentration, and an increase in the adsorption efficiency (pC20) promoting aggregation more efficiently than adsorption. With regard to the antibacterial activity, dodecyl 2,6‐dideoxy‐α‐L‐arabino‐hexopyranoside was the most active compound towards Bacillus anthracis (MIC 25 μM), whereas its enantiomer exhibited a MIC value of 50 μM. Both 2,6‐dideoxy glycosides were active towards Bacillus cereus, Bacillus subtilis, Enterococcus faecalis and Listeria monocytogenes. In contrast, none of the 2‐deoxy glycosides was significantly active. These results and the data on surface activity suggest that aggregation is a key issue for antimicrobial activity. Beyond infection, Alzheimer's disease also threatens elderly populations. In the search for butyrylcholinesterase (BChE) selective inhibition, 2‐deoxy glycosides were screened in vitro by using Ellman's assay. Octyl 2‐deoxy‐α‐D‐glycoside was found to be a BChE selective inhibitor promoting competitive inhibition. Docking studies supported these results as they pinpoint the importance of the primary OH group in stabilizing the BChE inhibitor complex. A size‐exclusion mechanism for inhibition has been proposed based on the fact that acetylcholinesterase (AChE) exhibits several bulky residues that hinder access to the active‐site cavity. This work shows how the deoxygenation pattern, configuration and functionality of the anomeric centre can tune physical and surface properties as well as the bioactivity of these multifunctional and stereochemically rich molecules.

ChemInform Abstract: Palladium‐Catalyzed Direct Cross‐Coupling Reaction of Glycals with Activated Alkenes.

AbstractThe procedure provides an efficient access to 2‐alkenylated glycals as exclusive (E) isomers and subunits of various pyran‐containing natural substances.

ChemInform Abstract: Vilsmeier-Haack Reaction of Glycals (I). A Short Route to C-2-Formyl Glycals (III).

ChemInform Abstract: Vilsmeier-Haack Reaction of Glycals (I). A Short Route to C-2-Formyl Glycals (III).

ChemInform Abstract: Synthesis of 2-Deoxyglycopyranosyl Thioureas from Glycals.

Instituto de Biotecnologia, Facultad de Ciencias, Universidad de Granada, 18071 Granada, SpainFax+34(958)243186; E-mail: fsantoyo@goliat.ugr.esReceived 11 June 1999; revised 16 September 1999Abstract: The reaction of glycals with phenylselenenyl chloridefollowed by treatment with KNCS lead to 2-deoxy-2-phenylseleno-glycopyranosyl isotiocyanates which were further transformed into2-deoxyglycopyranosyl thioureas.Key words: glycals, 2-deoxysugars, thioureas, isothiocyanates,phenylselenenyl chloride

Regioselective Synthesis of Phosphonylated Sugars from Reactions of Glycals with Diphenylphosphenium Cation.

Reaction of methyl 4,6‐di‐O‐acetyl‐2,3‐dideoxy‐d‐erythro‐hex‐2‐enopyranoside 1 with two equivalents of diphenylphosphenium cation at 0°C gave the 1‐phosphonylated 2‐enopyranosides 3α and 3β as major products. Similarly, reaction of diphenylphosphenium cation with tri‐O‐acetylglycal afforded the same products in a similar ratio. In contrast, a reaction with tri‐O‐benzylglucal at reflux temperature of dichloromethane afforded the 3‐phosphonylated sugar 13 as a major product. These reactions may proceed via stable allyl cations.

Regioselective Synthesis of Phosphonylated Sugars from Reactions of Glycals with Diphenylphosphenium Cation

Reaction of methyl 4,6‐di‐O‐acetyl‐2,3‐dideoxy‐d‐erythro‐hex‐2‐enopyranoside 1 with two equivalents of diphenylphosphenium cation at 0°C gave the 1‐phosphonylated 2‐enopyranosides 3α and 3β as major products. Similarly, reaction of diphenylphosphenium cation with tri‐O‐acetylglycal afforded the same products in a similar ratio. In contrast, a reaction with tri‐O‐benzylglucal at reflux temperature of dichloromethane afforded the 3‐phosphonylated sugar 13 as a major product. These reactions may proceed via stable allyl cations.

Synthesis of 2-Deoxyglycopyranosyl Thioureas from Glycals

Instituto de Biotecnologia, Facultad de Ciencias, Universidad de Granada, 18071 Granada, SpainFax+34(958)243186; E-mail: fsantoyo@goliat.ugr.esReceived 11 June 1999; revised 16 September 1999Abstract: The reaction of glycals with phenylselenenyl chloridefollowed by treatment with KNCS lead to 2-deoxy-2-phenylseleno-glycopyranosyl isotiocyanates which were further transformed into2-deoxyglycopyranosyl thioureas.Key words: glycals, 2-deoxysugars, thioureas, isothiocyanates,phenylselenenyl chloride

Iodoacetoxylation of glycals using cerium(IV) ammonium nitrate, sodium iodide, and acetic acid: stereoselective synthesis of 2-deoxy-2-iodo-alpha-mannopyranosyl acetates.

[formula: see text] The reactions of glycals with ceric(IV) ammonium nitrate and sodium iodide in the presence of acetic acid provides 2-deoxy-2-iodo-alpha-mannopyranosyl acetates with good stereoselectivity. In the majority of the cases examined, the selectivity was considerably better than that from reactions using N-iodosuccinimide and HOAc.

Iodoalkoxylation of 1,5-anhydro-2-deoxy-hex-1-enitols (glycals)

Exclusive trans-addition is observed in the iodoalkoxylation of the 6-membered cyclic enol ethers 3,4-di- O-acetyl- l-rhamnal ( 1), 3,4-di- O-acetyl- l-fucal ( 2), and related glycal derivatives. The main products from 1 and from 3,4,6-tri- O-acetyl- d-glucal ( 3) thus had the α- manno configuration. Similarly, α- talo products were obtained from 2 in 87–93% yield. The product distribution is not affected by the electronegativity of the 5-substituent. It is concluded that steric factors in the glycal and the nucleophile affect only the step of trans-diaxial opening of the intermediate iodonium ion. Enhanced yields of the desired trans-diaxial products were observed in reactions of glycals having the lyxo configuration when the reactions were conducted in tetrahydrofuran or methanol.

Reaction of glycals with pyridinium poly(hydrogen fluoride) giving ferrier rearranged sugar fluorides

Treatment of certain glycals with pyridinium poly(hydrogen fluoride) afford Ferrier rearranged fluorides, which have been characterized by their 19F n.m.r. spectra and the preparation of derivatives.

Additions and Corrections - Reaction of Glycals with Trifluoroacetic Anhydride and Ammonium Nitrate: A Novel Cleavage Reaction of Glycals.

Additions and Corrections - Reaction of Glycals with Trifluoroacetic Anhydride and Ammonium Nitrate: A Novel Cleavage Reaction of Glycals.

ChemInform Abstract: Factors Affecting the Purity of 2‐Deoxy‐2‐fluoro‐D‐glucose Synthesized from the Reactions of Glycals with Acetyl Hypofluorite.

AbstractDurch die Reaktion der Glycal‐Derivate (Ia)‐(Id) mit gasförmigem Acetylhypofluorit (II) und anschließende Hydrolyse erhält man die 2‐Desoxy‐2‐fluorglucose (III).