A novel and efficient direct aldol condensation from ketones and aromatic aldehydes catalyzed by proline-TEA through a new pathway

A novel and efficient direct aldol condensation from various ketones and a wide range of aldehydes was catalyzed by l-proline-TEA (triethylamine) in MeOH at room temperature, affording the corresponding (E)-α,β-unsaturated ketones in excellent yields. By using the method, some complicated (E)-α,β-unsaturated ketone C-glycosides were obtained from unmodified ketone C-glycosides and aldehydes. This reaction proceeds through a new pathway, in which the specific intermediate was captured and identified.     

Stereoselective Synthesis of C-Glycosides by Suzuki Cross-coupling Reaction

Carbohydrates and their conjugates have been recognized to play a wide variety of metabolic roles in numerous biological processes.[1] Various modified sugars and analogues have been recently synthesized for further investigation of glycosidase reactions and for the development of specific glycosidase inhibitors.[2] As one of the most important carbohydrate mimics, C-glycosides have attracted great attention due to their stability to chemical or enzymatic hydrolysis of the glycosidic linkage. A number of methodologies for the preparation of C-glycosides have been extensively investigated.[3] We have recently reported the syntheses of novel C-glycosyl amino acids and amino-C-disaccharides possessing a ketose form via the stereoselective 1,3-dipolar cycloaddition of exo-methylenesugars (1) and nitrones.[4,5] As a continuation of our research on the synthesis of C-glycosides using exo-methylenesugar as the precursor, we wish to describe here a stereoselective synthesis of C-glycosides by Suzuki cross-coupling reaction.     

对氯醌基碳糖苷的高区域选择性合成方法

本文报道了两条温和、高效、实用的实验室合成对氯代醌基碳糖苷化合物的方法：其一是以芳香碳糖苷1a (1b)为初始原料,在硝酸铵催化下,与N-氯代丁二酰亚胺(NCS)反应获得对氯代芳香碳苷2a (2b),继而经硝酸铈铵(CAN)氧化,得到氯代醌基糖苷3a (3b),总收率为88% (84％);另一路线是通过三甲基氯硅烷在三氟化硼•乙醚作用下对苯醌碳苷4a (4b)的催化加成和水解反应,获得对氯代氢醌基碳苷5a (5b),总收率为82% (76%), 而它与氯代醌基糖苷3a (3b)可以通过氧化与还原反应得以相互转化。     

Access to L- and D-iminosugar C-glycosides from a D-gluco-derived 6-azidolactol exploiting a ring isomerization/alkylation strategy

A flexible synthetic access to six-membered L- and D-iminosugar C-glycosides is reported starting from the easily available 6-azido-6-deoxy-2,3,4-tri-O-benzyl-D-glucopyranose precursor. This methodology involves a highly diastereoselective tandem ring enlargement/alkylation and a stereocontrolled ring contraction. It allows an efficient synthesis of iminosugar C-glycosides displaying structural diversity at both C-1 and C-6.     

Tactics and strategies for the synthesis of iminosugar C-glycosides: a review

Three decades after their first synthesis, iminosugar C-glycosides have become an important class of iminosugars with promising biological and therapeutic properties. The purpose of this review is to provide an overview of the versatile strategies that have been developed to synthesize this family of stable imino-analogues of glycosides and glycoconjugates. Some guidelines and predictive stereoselective models are presented to facilitate the design of synthetic strategies toward iminosugar C-glycosides of defined configuration.     

Two novel C-glycosides of aureolic acid repress transcription of the MDR1 gene

In the search for compounds which repress MDR1 gene expression, two novel aryl C-glycosides were isolated from a broth of Streptomyces sp. They had the characteristic structure of a dideoxy-carbohydrate (oliose or olivose) linked directly to chromomycinone, an aglycone of aureolic acids. Further investigation revealed that they were artifacts yielded from an aureolic acid, mithramycin. Acid and methanol were necessary to yield the C-glycosides. This reaction would contribute to the design of useful aryl C-glycosides.     

TESOTf-induced rearrangement of quinols. Efficient construction of the fully functionalized carbon skeleton of the griseusins by a divergent-reconvergent approach

[reaction: see text] The "reverse polarity" or "umpolung" strategy for the total synthesis of aryl C-glycosides was developed in the context of the antibiotic (-)-griseusin B. Although a key reaction in a model sequence for the total synthesis produced two structurally divergent products, both were converted to the same advanced model intermediate that contains the complete carbon skeleton and (except for the extraneous oxygen substituent in the model series) the functional group pattern of the griseusins.     

Stereoselective, electrophilic α-C-sialidation

5-N-Acetyl-5-N,4-O-oxazolidinone protected α- and β-sialyl phosphates react with allyltributylstannane and a variety of trimethylsilyl enol ethers to give α-sialyl C-glycosides in high yield and excellent selectivity. Elimination to give the 2,3-glycal is minimized by the presence of the oxazolidinone ring. The oxazolidinone ring can be subsequently cleaved under mild conditions at room temperature leaving in place the native acetamide group.     

C-glycosides. 3. 1,3-dipolar cycloaddition on nitrile and nitrilimine oxides

1.3-dipolar cycloaddition of alkenes (or alkynes) on sugars-nitriloxides and nitrilimines led respectively to 3-glycosyl-isoxazolines (or isoxazoles) and 3-glycosyl-pyrazolines (or pyrazoles). 5-glycosyl-isoxazolines were similarly prepared from arylnitriloxides and α- or ω-unsaturated sugars. These new C-glycosides are potential antiviral and anti-tumor agents.     

[2,3]-Wittig rearrangement approach to iminosugar C-glycosides: 5-epi-ethylfagomine, 2-epi-5-deoxyadenophorine and formal synthesis of indolizidine 167B and 209D

A new strategy for the synthesis of 1,2-dideoxy iminosugar C-glycosides and indolizidines involving highly stereoselective [2,3]-Wittig rearrangement from Garner aldehyde has been developed. This rearrangement yielded an optically pure, highly functionalized key intermediate, which has been further utilized for the synthesis of 5-epi-ethylfagomine, 2-epi-5-deoxyadenophorine, and 5-hydroxymethyl indolizidine.     

新型碳苷糖类维生素D_2衍生物的合成

以D-葡萄糖为原料,经碳苷化反应,酰化反应和脯氨酸-DIPEA催化的aldol反应制得2个碳苷糖[1-(4'-羟基苯基)-4-C-β-四乙酰基葡萄糖基-3-烯-2-酮(5a)和1-(3-羟基苯基)-4-C-β-四乙酰基葡萄糖基-3-烯-2-酮(5b)];5与琥珀酸维生素D2经Steglich酯化反应合成了2个新型碳苷糖类维生素D2衍生物,其结构经1H NMR,13C NMR和HR-ESI-MS表征。     

TLC separation and identification of some flavonoid C-glycosides

Summary TLC on silica gel plates provides a method for the quantitative separation and identification of isomeric C-glycosides.     

Ultrasound-assisted synthesis of C-glycosides

A significant rate enhancement was observed in the preparation of allyl and allenyl-C-glycosides from glycosyl acetate or methyl O-glycoside precursors when ultrasound irradiation was employed as an energy source. The C-glycosides were obtained in 77-96% yields in <20 min using TMSOTf as promoter. These results show that sonication provides rapid and efficient access to useful C-glycoside-based building blocks.     

A bifunctional anthraquinone synthon

Commercially available anthrarufin has been converted into a bifunctional reagent which will be useful for the preparation of anthraquinone C-glycosides.     

2,3-Anhydrosugars in glycoside bond synthesis: application to furanosyl azides and C-glycosides

The preparation of 2-deoxy-2-thiotolylfuranosyl azides and C-glycosides from a 2,3-anhydrosugar thioglycoside with the d-lyxo stereochemistry is described. The reaction is performed by treatment of the thioglycoside with a trimethylsilylated nucleophile in the presence of BF₃·OEt₂. This approach provides a convenient route to the preparation of the corresponding 2-deoxy-furanosyl azides and C-glycosides. In contrast, the use of an isomeric substrate, with the 2,3-anhydro-d-ribo stereochemistry, gave these products in low to modest yield.     

Schoepfin A, B, C: three new chalcone C-glycosides from Schoepfia chinensis

Three new chalcone C-glycosides named schoepfin A, B, C (1-3), together with three known compounds 4,2',4'-trihydroxy-3'-C-beta-D-glucosylchalcone (4), nothofagin (5) and hemiphloin (6) were isolated from ethanolic extract of the bark of Schoepfia chinensis Gardn. et Champ (Olacaceae). Their structures were determined mainly by spectroscopic techniques including 2D-NMR (HMBC, HMQC) and MS experiments.     

Phosphomolybdic acid supported on silica gel: a mild, efficient and reusable catalyst for the synthesis of 2,3-unsaturated glycopyranosides by Ferrier rearrangement

A simple, mild, efficient and environmentally benign method for the synthesis of 2,3-unsaturated allyl C-glycosides and O- and S-glycosides is described using phosphomolybdic acid supported on silica gel as a reusable catalyst with high α-selectivity.     

中药紫花地丁黄酮碳苷类化学成分的超高效液相色谱-电喷雾离子源-四极杆飞行时间串联质谱研究

采用超高效液相色谱-电喷雾离子源-四极杆飞行时间串联质谱(UPLC-ESI-QTOF-MS/MS)方法,以中药紫花地丁中分离得到的5个黄酮碳苷化合物为对照品,研究了黄酮二糖碳苷类化合物在ESI-QTOF-MS/MS质谱中的裂解规律。研究进一步证实了文献报道的黄酮二糖碳苷C-6位取代糖基较C-8位糖更易优先发生裂解;但同时发现结构中如果含有不稳定构象的糖基取代时,该规律不再适用。通过对照品的质谱裂解规律,并结合文献和高分辨质谱数据,成功表征和鉴定了紫花地丁中21个黄酮二糖碳苷类以及4个黄酮氧苷类成分。该方法能快速、灵敏、准确地对中药中微量黄酮碳苷类成分的结构进行表征和鉴定。     

Solid-phase chemoenzymatic synthesis of C-sialosides

The chemoenzymatic regioselective acylation of Neu5Ac followed by SmI2-mediated C-glycosylation on a solid support is described for five C-glycosides. This method should facilitate the construction of combinatorial libraries of inhibitors of neuraminidase activity and hemagglutinin interaction as potential antiviral agents.     

Olefin addition to acetylated glycals. A new route to C-glycosides.

Olefins react with glycals in the presence of Lewis acids providing a new route to C-glycosides.