Solvent-Free Synthesis of DecylD-Glycopyranosides Under Focused Microwave Irradiation

Ionic Liquid Catalyzed Per-O-Acetylation and Benzylidene Ring-Opening Reaction

Tunable aryl imidazolium ionic liquids acting as Brønsted acid ionic liquids were found to be efficient catalysts for per-O-acetylation and reductive ring opening of benzylidene acetals. This method requires a truly catalytic amount of the least expensive available ionic liquids that are water-stable and reusable and also stable at room temperature. The reactions were obtained in one hour with good to excellent yields. These reactions can form C−O and C−H bonds with a high atom economy. Furthermore, the ionic liquid is an anomeric selective catalyst in per-O-acetylation and reductive ring opening of benzylidene acetals of sugar moieties.

Biogenic CuFe2O4 magnetic nanoparticles as a green, reusable and excellent nanocatalyst for acetylation reactions under solvent-free conditions

A convenient green method has been developed for the synthesis of biogenic CuFe₂O₄ magnetic nanoparticles using tea extracts within a very short reaction time.

TMSBr-mediated solvent- and work-up-free synthesis of α-2-deoxyglycosides from glycals

The thio-additions of glycals were efficiently promoted by a stoichiometric amount of trimethylsilyl bromide (TMSBr) to produce S-2-deoxyglycosides under solvent-free conditions in good to excellent yields. In addition, with triphenylphosphine oxide as an additive, the TMSBr-mediated direct glycosylations of glycals with a large range of alcohols were highly α-selective.

Efficient one-pot per-O-acetylation–thioglycosidation of native sugars, 4,6-O-arylidenation and one-pot 4,6-O-benzylidenation–acetylation of S-/O-glycosides catalyzed by Mg(OTf)2

Sequential one-pot per-O-acetylation–S-/O-glycosidation under neat condition, regioselective 4,6-O-arylidenation and sequential one-pot benzylidenation–acetylation of Mg(OTf)₂as non-hygroscopic, recyclable catalyst are reported.

Acyl transfer reactions of carbohydrates, alcohols, phenols, thiols and thiophenols under green reaction conditions

Acyl transfer reactions of various carbohydrates, alcohols, phenols, thiols and thiophenols were achieved at room temperature in high yields and catalytic efficiency in the presence of methane sulfonic acid, a green organic acid, under solvent-free conditions over short time periods.

Cu(ClO4)2·6H2O catalyzed solvent free per-O-acetylation and sequential one-pot conversions of sugars to thioglycosides

The solvent free per-O-acetylation of various reducing and non-reducing sugars has been carried out using stoichiometric amounts of acetic anhydride and copper(ii) perchlorate hexahydrate as the catalyst.

Development of Highly PotentD-Glucosamine-Based Chiral Fluorescent Labeling Reagents and a Microwave-Assisted β-Selective Glycosidation of a Methyl Glycoside Reagent

We synthesized new chiral fluorescence labeling reagents having a 2,3-anthracenedicarboximide group from D-glucosamine, and it was possible to introduce target alcohols at the anomeric positions of the reagents with beta-selectivity by glycosidations. Especially, it was possible to use methyl glycoside reagent as a glycosyl donor with a Lewis acid and microwave irradiation, and it gave selectively beta-glycoside while the reaction without microwave irradiation gave alpha- and beta-mixed glycosides. Those reagents showed very high chiral discrimination ability, and they made it possible to separate the eight stereoisomers of 4,8,12,16-tetramethylheptadecanol by HPLC after derivatizations.

Microwave-assisted syntheses of nucleosides and their precursors

In recent decades, nucleosides analogs have been the cornerstone in the treatment of various diseases, such as AIDS, herpes and hepatitis. More than 40 modified nucleosides are officially approved by the US FDA and represent the major compound class for inhibition of viral replication. By comparison with traditional conditions, microwave irradiation offers a powerful tool that can increase yields and decrease reaction time, with simple manipulation and an environmentally friendly way. Here, we report the latest progress in nucleoside synthesis using microwave irradiation.

Indium triflate catalyzed peracetylation of carbohydrates

Peracetylation is a very common protection strategy that is widely implemented in carbohydrate synthesis. Here, a method for the peracetylation of carbohydrates using catalytic In(OTf)(3) in neat acetic anhydride is reported. In(OTf)(3) has low toxicity and is mild and water tolerant, and the reactions are high yielding and efficient. Details regarding the scope and mechanism of the reaction are briefly discussed.

Synthesis and antiviral evaluation of AZT analogues with A spacer arm between glucidic and base moieties. Part II

This article describes the synthesis of a series of AZT analogues bearing an acyclic chain between the sugar and the base moieties is described. These new compounds were readily obtained using microwave irradiation. The compounds were characterized by (1)H NMR and IR spectroscopy. Antiviral (HIV-1) properties of these compounds were examined.

Acylation of carbohydrates over Al2O3: preparation of partially and fully acylated carbohydrate derivatives and acetylated glycosyl chlorides

Selective and per-O-acylation of carbohydrate derivatives using acyl chlorides and Al2O3, a solid support reagent, is reported. This protocol does not require the addition of any base or activator. This methodology has been further extended to the selective acylation of carbohydrate diols and the one-pot preparation of acetylated glycosyl chlorides direct from free reducing sugars. The yields obtained in most of the cases are excellent.

Practical Synthesis of Shi's Diester Fructose Derivative for Catalytic Asymmetric Epoxidation of Alkenes

[reaction: see text] A practical synthesis of Shi's diester 3 for catalytic asymmetric epoxidations has been developed. The catalyst has been prepared in multigram quantities from D-fructose in four steps with a 66% overall yield. Efficiency, cost, and selectivity aspects of the reagents involved for its preparation have been taken care of during its preparation. The workup procedures have been simplified to the bare minimum, rendering a very practical preparation method. The well-known high efficiency of this catalyst 3 in the epoxidation of alpha,beta-unsaturated carbonyl compounds has also proved to be high in unfunctionalized alkenes.

New dinucleoside analogues via cross-coupling metathesis

Synthesis of 3'-3', 5-5', and 3'-5' dimeric thymidine, linked by an olefinic chain between glycosidic moieties is described. Cross metathesis reaction of 3' or 5' O-allyl analogues of thymidine led to the expected 3'-3' and 5'-5' dimeric compounds, respectively. In order to obtain the 3'-5' dimer, 5'-O-allyl and 3'-O-allyl monomers were first linked by their free 3' OH and 5' OH groups through a glutaryl spacer; ring closing metathesis was then operated upon this temporary dimer, followed by glutaryl removal.

InCl3 as a powerful catalyst for the acetylation of carbohydrate alcohols under microwave irradiation

Indium(III) chloride catalyzed microwave assisted acetylation of different carbohydrates is an efficient synthesis of per-O-acetyl derivatives and provides the products in good to excellent yields.

Synthesis and antiviral evaluation of D4T analogues with a spacer arm between glucidic and base moieties

The synthesis of a series of d4T analogues bearing an acyclic chains between the sugar and the base moities, is described. New compounds were obtained readily using microwave irradiation and selective deprotection of sugar part. The compounds were characterized by 1H NMR and IR spectroscopy. Antiviral (HIV-1) properties of these compounds were examined.

HClO4–SiO2 catalyzed per-O-acetylation of carbohydrates

An efficient per-O-acetylation of carbohydrates catalyzed by HClO4-SiO2 is reported using a stoichiometric quantity of acetic anhydride avoiding the use of pyridine and excess acetic anhydride under solvent-free conditions.

Reconsidering glycosylations at high temperature: precise microwave heating

Current methods for glycosylation of complex alcohols, e.g. with glycosyl trichloroacetimidates, generally occur in the presence of a strong Lewis acid 'promoter', and at sub-ambient temperatures. However, the older literature reports high-temperature glycosylations, especially of phenols. We have described an efficient method for glycosylation of alcohols under neutral conditions, using as anomeric leaving group methyl 3,5-dinitrosalicylate (DISAL). Only a very few reports have described the use of microwaves to promote glycosylations, mainly of simple alcohols. Here we describe fast, high-temperature glycosylations using precise microwave heating in the synthesis of oligosaccharides, with both DISAL and widely used trichloroacetimidate glycosyl donors in the absence of strong Lewis acids. Also, we have applied microwave heating as a general protocol for evaluating new, potential glycosyl donors.

Preparation of low-molecular-weight and high-sulfate-content chitosans under microwave radiation and their potential antioxidant activity in vitro

In the present paper microwave radiation has been used to introduce N-sulfo and O-sulfo groups into chitosan with a high degree of substitution and low-molecular weight. The sulfation of chitosan was performed in microwave ovens. It was found that microwave heating is a convenient way to obtain a wide range of products of different degrees of substitution and molecular weight only by changing reaction time or/and radiation power. Moreover, microwave radiation accelerated the degradation of sulfated chitosan, and the molecular weight of sulfated chitosan was considerably lower than that obtained by traditional heating. There are no differences in the chemical structure of sulfated chitosan obtained by microwave and by conventional technology. FTIR and 13C NMR spectral analyses demonstrated that a significantly shorter time is required to obtain a satisfactory degree of substitution and molecular weight by microwave radiation than by conventional technology. In this present paper, we also determined antioxidant activity of low-molecular-weight and high-sulfate-content chitosans (LCTS). The results showed LCTS could scavenge superoxide and hydroxyl radical. Its IC50 is 0.025 and 1.32 mg/mL, respectively. It is a potential antioxidant in vitro.

Selective oxidation of glycosyl sulfides to sulfoxides using magnesium monoperoxyphthalate and microwave irradiation

A protocol that uses moist magnesium monoperoxyphthalate (MMPP) as an oxidant under microwave irradiation rapidly yields a variety of glycosyl sulfoxides from corresponding sulfides in high yields with high selectivity.