Comprehensive Comparison of Bioactive N-Glycans among Seven Species of Livestock and Poultry Plasma Using a Relative Quantification Strategy.

Glycans have been proven to play special roles in keeping human health as a class of nutritional and bioactive ingredients in many food materials. However, their broad use in the food industry is hindered by the lack of comprehensive analytical methods for high-quality food glycomics studies and large-quantity raw materials for their production. This study focuses on structural identification and quantitative comparison of bioactive N-glycans in seven species of livestock and poultry plasma as potential natural glycan resources by a novel comprehensive relative quantification strategy based on stable isotope labeling with nondeuterated and deuterated 4-methyl-1-(2-hydrazino-2-oxoethyl)-pyridinium bromide (d0/d7-HMP) in combination with linkage-specific derivatization of sialic acid residues. Methodological validation of the method in terms of detection sensitivity, signal resolution, quantification linearity, precision, and accuracy on model neutral and complicated sialylated glycans demonstrated its advantages over the existing methods. Based on this method, a series of bioactive N-glycans were found in seven species of livestock and poultry plasma, and their differences in structure, abundance percentages, and relative contents of N-glycans were revealed, demonstrating their excellent applicability for comprehensive food glycomics analysis and great exploitation potential of these plasma samples as large-quantity raw materials in producing bioactive N-glycans for application in food and pharmaceutical industries.

Strategy for Isolation, Preparation, and Structural Analysis of Chondroitin Sulfate Oligosaccharides from Natural Sources.

The structure of chondroitin sulfate oligosaccharides (CSOs), especially their sulfation pattern, has been found to be closely related with many biological pathways and diseases. However, detailed functional analysis such as their interaction with glycan binding proteins (GBPs) has been lagging, presumably due to the unavailability of well-defined, diverse structures. Besides challenging chemical and enzymatic synthesis, this is also due to the challenges in their purification at the isomer level and structural analysis owing to their instability, structural complexity, and low mass spectrometry detection sensitivity. Herein, we first used recycling preparative HPLC to separate and purify shark CS tetrasaccharide component labeled by a bifunctional fluorescent linker 2-amino-N-(2-aminoethyl)benzamide (AEAB) at the isomer level. Then, each isomer was derivatized through a multistage procedure including N-acetylation, carboxyl amidation, permethylation, and desulfation with silylating reagent. Structural analysis of each derivatized isomer was performed with ESI-MSn in positive ion mode. A total of 16 isomers of CSO-AEAB were isolated, with a minimum mass component of 0.007 mg and a maximum mass component of 17.53 mg, of which 10 isomers (>90 µg) were structurally analyzed. This preparation and structure analysis of CSOs lay the foundation for further study of the structure-activity relationship of CSOs.

Stereoselective Synthesis of (E)-3-Alkylideneoxindoles via Gold(I)-Catalyzed Cross-Coupling of 3-Diazooxindoles with Diazoesters.

A versatile gold(I)-catalyzed cross-coupling reaction of 3-diazooxindoles with diazoesters has been presented, affording (E)-3-alkylideneoxindoles stereoselectively. Density functional theory calculations rationalized the chemo- and stereoselectivity of the reaction, which was in good agreement with experimental observations. In addition, (E)-3-alkylideneoxindoles were converted into their (Z)-isomers under UV-irradiation facilely, indicating the great advantage of this approach in stereoselective synthesis of both (E)- and (Z)-3-alkylideneoxindoles.

Oxidant and Transition-Metal-Free Photoinduced Direct Oxidative Annulation of 1-Aryl-2-(furan/thiophen-2-yl)butane-1,3-diones.

A photoinduced direct oxidative annulation of 1-aryl-2-(furan/thiophen-2-yl)butane-1,3-diones and ethyl-2-(furan-2-yl)-3-oxo-3-(aryl-2-yl)propanoates in EtOH without the need for any transition metals and oxidants provided access to highly functionalized polyheterocyclic 1-(5-hydroxynaphtho[2,1-b]furan-4-yl)ethanones and 1-(5-hydroxyfuran/thieno/pyrrolo[3,2-e]benzofuran-4-yl)ethanones. The phenomenon of excited-state intramolecular proton transfer (ESIPT) was observed for both 1-(5-hydroxynaphtho[2,1-b]furan-4-yl)ethanone and 1-(5-hydroxy furan/thieno/pyrrolo[3,2-e]benzofuran-4-yl)ethanone analogues.

Synthesis of 2,5-Dihydrofurans via a Gold(I)-Catalyzed Formal [4 + 1] Cycloaddition of α-Diazoesters and Propargyl Alcohols.

A gold(I)-catalyzed formal [4 + 1] cycloaddition of α-diazoesters and propargyl alcohols is disclosed, offering access to a variety of 2,5-dihydrofurans. The reaction shows a broad substrate scope and functional group tolerance. Preliminary mechanistic investigation indicates that this reaction most likely occurs through a 5-endo-dig cyclization of an α-hydroxy allene intermediate.