Anomeric Position Of Carbohydrates Research Articles

Synthesis of New Glycosylamine Derivatives based on Carbohydrates

Background: Glycosylamine play an important role in living organisms. Most plants store their chemical resources in the form of inactive glycosides, which are broken down and con-verted into sugar in the body of herbivores by hydrolyzing enzymes. Glycosylamine are obtained from the secondary metabolism of plants and consist of two parts. One part of it contains sugar like glucose and is inactive in most substances, and has a good effect on the solubility of the glycosyla-mine derivatives and its absorption and even its transfer from one organ to another. The therapeutic effect is related to the second part, which is called aglycan (or aglucan). Glycosylamine derivatives form a large group of valuable medicinal substances, which at the same time include some of the most dangerous and toxic substances in nature. These substances are present in many groups of flowering plants. Glycosides are made in different ways in different metabolic pathways. These materials have a complex and special chemical structure and leave special effects on the human body. Glycosylamine derivatives are called O-glycosid, N-glycosid, S-glycosid in terms of atoms coupling to anomeric carbon. Carbohydrate esterification reaction to prepare new glycosylamine derivatives is one of the most important carbohydrate reactions. The anomeric position of carbohy-drates with strong leaving groups is very important for the preparation of glycosides. Preparation of glycosylamine derivatives based on acetylated carbohydrates is the main purpose of this article. Dif-ferent carbohydrates were acetylated under mild conditions and high yields. The anomeric position was deacetylated by a magnesium oxide heterogeneous catalyst in methanol solvent. In order to pre-pare new glycosides acetylated/ deacytylated carbohydrate reacted with N-Methyl-(naphtha-2-ylmethoxy)amine. The final product was identified by various spectroscopic methods. Methods: Anhydrous sodium acetate (4 g) and α-D-glucose (28 mg, 5 g) were mixed. The mixture was transferred to a 200 ml Round-bottom flask . Acetic acid (260 mg, 25 ml) was added to the reaction mixture. The reaction mixture was heated in a boiling water bath for 2 h until complete dissolution of the glucose. Then 100 ml of ice was added. After 1 hour, White crystals formed and were washed with cold water. And then 1 mol of glucose pentaacetate per 50 ml of methanol was dissolved by a magnetic stirrer. After thatMgO (0.2gr) was added to the reaction mixture. The re-action mixture was refluxed at room temperature within 4-5 hours. After 5 hours, the solvent was removed and separated by chromatography. It is then washed with hexane and crystallized by ether-hexane. And the final step reacted with N-Methyl- (naphtha-2-ylmethoxy) amine in order to prepare new glycosylamine derivatives. Results: Magnesium oxide in methanol solvent is one of the best effective catalysts in the deacetyla-tion of the anomer position of acetylated carbohydrates. It is done under ambient temperature and in very easy conditions and makes carbohydrates susceptible to extensive chemical reactions. One of these reactions is the formation of glycosides. Various carbohydrates are acetylated by acetic anhy-dride in the presence of sodium acetate, and the anomeric position is deacetylated by a heterogeneous catalyst. In order to prepare N-glycoside, the glycosides are reacted with N-alkoxy N-methylglycosyl amine. The final products are identified by various spectroscopic methods. Conclusion: Glucose, mannose, for example, were acetylated by acetic anhydride in the presence of sodium acetate. And the anomeric position of pentaacetate glucose was selectively deacetylated with magnesium oxide in a methanol solvent. Then, the reaction for the preparation of glycosylamine de-rivatives was carried out under very mild and easy conditions. The aminoglycosides synthesized in this article are used as raw materials for the synthesis of a wide range of antibacterials.

Inside Cover Picture

In this work, a structurally novel leaving group of 8‐phenylethynyl‐1‐naphthoate is disclosed. This leaving group can not only promote the efficient glycosylation reactions under the mild condition of gold(I)‐catalysis, but also possess the unprecedent character of base‐stability at anomeric position of carbohydrates. The X‐ray diffraction analysis of the leaving group reveals the congested environment between the ester and the alkyne that accounts for the base‐tolerant character. More details are discussed in the article by Zhu et al. on page 1305–1312.image

An Anomeric Base‐Tolerant Ester of 8‐Alkynyl‐1‐naphthoate for Gold(I)‐Catalyzed Glycosylation Reaction

Comprehensive SummaryGiven the extreme complexity and diversity of carbohydrates, efficient approaches to the homogeneous oligosaccharide remain limited. Chemical synthesis represents one of the most reliable methods to access homogeneous samples, which mainly relies on the key glycosylation reaction. Consistent with enormous efforts to develop leaving groups for establishing robust glycosylation protocols, we herein disclose a structurally novel leaving group of 8‐phenylethynyl‐1‐naphthoate that is able to enable efficient glycosylation reactions under the extremely mild condition of gold(I)‐catalysis. Notably, the anomeric naphthoate possesses the unprecedent character of base‐stability in sharp contrast to the conventional ester groups at anomeric position of carbohydrates, which endows high compatibility with a variety of chemical transformations. Furthermore, the present glycosylation protocol with 8‐phenylethynyl‐ 1‐naphthoate as leaving group is able to realize minimally protected glycosylation processes. Mechanistic studies reveal a unique structure of 8‐phenylethynyl‐1‐naphthoate that accounts for the reason for these characteristics.

Selective Anomeric Deacetylation of Per-Acetylated Carbohydrates Using (i-Pr)3Sn(OEt) and Synthesis of New Derivatives

In this study natural carbohydrates such as glucose, galactose, xylose, fructose andlactose, are acetylated by acetic anhydride and sodium acetate catalyst. Anomeric configuration is deacetylated by (i-Pr)3Sn(OEt)as a catalyst, an easy synthetic regioselective deacetylation of full acetylated carbohydrates using (i--Pr)3Sn(OEt) is described. The acetylated carbohydrates reacted with HBr (solution in AcOH, 32 wt.%) for the bromination of anomeric position. The synthesis oxazaphosphorine, and bromo hexa alkyl Methylsulfonate derivatives from anomeric position of carbohydrates was reacted. FT IR, 1H, 13C NMR, 31PNMR spectroscopy techniques were employed to examine the synthesized compounds.

Catalyst‐Free Synthesis of Alkylpolyglycosides Induced by High‐Frequency Ultrasound

AbstractInvited for this month′s cover is the group of François Jérôme at the University of Poitiers. The image shows that the anomeric position of carbohydrates was successfully activated by high frequency ultrasound, without any catalyst or protective agent. The Communication itself is available at 10.1002/cssc.201801137.

Gram-Scale Quaternarization of the Anomeric Position of Carbohydrates: Dramatic Effects of Molecular Sieves on Rhodium(II)-Mediated Decomposi­tion of Diazo Sugars

The optimization of rhodium(II) carbene mediated quaternarization of the anomeric position of carbohydrates is reported. Preparation of ketopyranosides in good and reliable yields requires reverse addition of the substrate to a highly diluted suspension of the catalyst in refluxing 1,2-dichloroethane, as well as addition of a carefully controlled amount of molecular sieves, and vigorous stirring. Following these optimized reaction conditions, functionalization of the anomeric position of carbohydrates can finally be performed on a preparative scale.

Sugar amino acids at the anomeric position of carbohydrates: synthesis of spirocyclic amino acids of 6-deoxy- l-lyxofuranose

Two anomeric spirodiketopiperazines and one spirohydantoin of 6-deoxy- l-lyxofuranose have been prepared from l-fucono-δ-lactone via ring contraction to the corresponding tetrahydrofuran carboxylate and anomeric functionalization including regioselective bromination and azide displacement.

A new route to C-glycosyl compounds. Wittig-type reaction promoted by zinc

In recent years, methods for the preparation of C-glycosyl compounds have become increasingly important in synthetic organic chemistry. These compounds are useful as subunits for the synthesis of biological active products’ and as potential enzyme inhibitors’. Significant attention has been focused on the development of new routes to prepare functionalized C-glycosyl compounds that are synthetic precursors of more complex C-glycosyl compounds. The starting materials can be furanose or pyranose carbohydrates, the main problem being the stereoselective introduction of a functionalized carbon atom at C-l. A widely used procedure to obtain carbon-carbon bonding at the anomeric position of carbohydrates was first reported by Zhdanov ef al. 3 This two-step procedure involves the formation of an unsaturated, open-chain intermediate, followed by a cyclization leading to the expected C-glycosyl compound. The first step is a Wittig reaction with protected furanose and pyranose hemiacetals. When stabilized ylides are used4, subsequent cyclization of the unsaturated intermediate may occur by treatment with bases or, sometimes, spontaneously. But when the Wittig reaction takes place with unstabilized ylides, the cyclization can be obtained by the iodoor mercuro-cyclization process’. It should be noted that C-glycosyl compounds can be synthesized in the same way when phosphonates are used instead of phosphorane$. Lastly, although stereoselective routes exist for both C-aand /I-glycosyl compounds, they mainly lack a general application. Stereoselectivity indeed depends on carbohydrate structures, ylides, and solvents. In the case of 2,3,4,6-tetra-O-benzyl-a,/?-D-glucopyranose (l), Nicotra et al.’ have observed an abnormal reaction of (carbethoxymethylene)triphenylphosphorane leading solely to a diene. The same elimination by Wittig reaction was observed for 3,4,6-tri-O-acetyl-2-O-benzyl-a&D-glucopyranose and partial elimination for 2,3,4,6-tetra-U-acetyl-a&D-glucopyranose. These abnormal reactions led Allevi et af.6 to use a Wittig-Horner reaction with 1 and sodium triethylphosphonoacetate