A New Cyclic Peptide and a New Steroid from the Fungus Penicillium sp. GD6 Isolated from the Mangrove Bruguiera gymnorrhiza

A rare new cyclic tetrapeptide, 5,5′‐epoxy‐MKN‐349A ( 1 ), featured by a MKN‐349A ( 5 ) skeleton and containing an uncommon ether bridge between C(5) and C(5′), and a new steroid, named 11‐O‐acetyl‐NGA0187 ( 2 ), together with two known steroids, 3 and 4 , were isolated from an endophytic fungus Penicillium sp. GD6 associated with the Chinese mangrove Bruguiera gymnorrhiza. The structures of the new compounds were elucidated on the basis of extensive spectroscopic analyses and by comparison with the data of related compounds reported in literature. Neither of the compounds 3 and 4 , isolated in this study, showed obvious bioactivities in the antibacterial bioassay experiments.     

Facile Mechanochemical Synthesis of Nano SnO2/Graphene Composite from Coarse Metallic Sn and Graphite Oxide: An Outstanding Anode Material for Lithium‐Ion Batteries

A facile method for the large‐scale synthesis of SnO₂ nanocrystal/graphene composites by using coarse metallic Sn particles and cheap graphite oxide (GO) as raw materials is demonstrated. This method uses simple ball milling to realize a mechanochemical reaction between Sn particles and GO. After the reaction, the initial coarse Sn particles with sizes of 3–30 μm are converted to SnO₂ nanocrystals (approximately 4 nm) while GO is reduced to graphene. Composite with different grinding times (1 h 20 min, 2 h 20 min or 8 h 20 min, abbreviated to 1, 2 or 8 h below) and raw material ratios (Sn:GO, 1:2, 1:1, 2:1, w/w) are investigated by X‐ray diffraction, X‐ray photoelectron spectroscopy, field‐emission scanning electron microscopy and transmission electron microscopy. The as‐prepared SnO₂/graphene composite with a grinding time of 8 h and raw material ratio of 1:1 forms micrometer‐sized architected chips composed of composite sheets, and demonstrates a high tap density of 1.53 g cm^?3. By using such composites as anode material for LIBs, a high specific capacity of 891 mA h g^?1 is achieved even after 50 cycles at 100 mA g^?1.     

Controllable synthesis of nanosilica surface-grafted PMMA macromonomers via catalytic chain transfer polymerization

Catalytic chain transfer polymerization (CCTP) has emerged as an efficacious method to produce low-molecular weight polymers. In this paper, we reported the first controllable synthesis of nanosilica surface-grafted poly(methyl methacrylate) (PMMA) (SI-PMMA) macromonomers by using bis(aqua)bis((difluoroboryl)-dimethylglyoximato)cobalt(II) (CoBF) as a chain transfer catalyst via CCTP. In a typical run, we firstly prepared functionalized nanosilica by using 3-(trimethoxysilyl)propylmethacrylate (MPS) as the coupling agent, allowing naosilica containing unsaturated double bonds in end groups. Subsequently, SI-PMMA macromonomers were prepared by PMMA surface-grafted onto the functionalized nanosilica via CCTP. The as-prepared products were characterized by Fourier transforms infrared (FT-IR) spectrum, thermogravimetric analysis (TGA), scanning electron microscopy (SEM), Fourier transforms Raman (FT-Raman) spectrum and gel permeation chromatography (GPC). We also investigated the dependence of macromonomers on CoBF concentrations.     

LC Method for Determination and Pharmacokinetic Study of 5,6,7,8,3′,4′-Hexamethoxy-3-sulfonyl Flavone in Rat Plasma

A sensitive, specific and rapid high-performance liquid chromatography method was developed for determination of 5,6,7,8,3′,4′-hexamethoxy-3-sulfonyl flavone in rat plasma. A simple methanol-induced protein precipitation was applied to extract 5,6,7,8,3′,4′-hexamethoxy-3-sulfonyl flavone and Picroside II (the internal standard) from rat plasma. Chromatographic separation was achieved on a Hypersil ODS₂ analytical column (200 mm × 4.6 mm, 5 μm) with acetonitrile–0.04% triethylamine solution (adjusted to pH 5.8 using phosphoric acid) (24:76, v/v) as mobile phase. The calibration curves were linear over the range of 0.2–40 μg mL^?1. Absolute recoveries of 5,6,7,8,3′,4′-hexamethoxy-3-sulfonyl flavone were 82.7–95.9% from rat plasma. The intra- and inter-day relative standard deviation precisions were less than 5 and 9%, respectively. The method was successfully applied to the pharmacokinetic study of 5,6,7,8,3′,4′-hexamethoxy-3-sulfonyl flavone in rats after intravenous administration.     

Coupled Chromatography for Assay of the Venom Proteome of the Snake Agkistrodon acutus: An Effective Strategy for Discovery of Active Components

Two-dimensional liquid chromatography (2D-LC) is an attractive option for proteome profiling because of its advantages in separation and analysis of proteins and peptides of extreme pH and molecular weight. Proteomics, regarded as a promising and high-throughput method for discovery of new active natural products, calls for technical progress in comprehensive separation, especially for peptides, glycoproteins, and hydrophobic proteins, etc. Here, an optimized off-line IEX-RP LC system has been used for separation of all the components of the venom of the five-pace snake (Agkistrodon acutus). Seventy-nine different natural venom components were obtained by use of this system, more than were obtained by two dimensional electrophoresis of the venom. An automated on-line IEX-RP LC system was also developed for heart-cut separation of components of interest. As a result, we discovered a new tripeptide (PGlu-Asn-Trp, MW 429.1) in the venom. This emphasizes the role of 2D-LC in drug discovery.     

A Sensitive LC–ESI–MS–MS Method for the Determination of Huperzine A in Human Plasma: Method and Clinical Applications

A sensitive and specific liquid chromatography–electrospray ionization–tandem mass spectrometry method has been developed and validated for the quantification of huperzine A in human plasma. After the addition of trimetazidine, the internal standard (IS) and sodium hydroxide, plasma samples were extracted using 5 mL ethyl acetate. The compounds were separated on an Agilent Zorbax SB C₁₈ column (100 mm × 2.1 mm ID, dp 3.5 μm) using an elution system of 10 mM ammonium acetate solution–methanol–formic acid (18:82:0.1, v/v) as the mobile phase. The quantification of target compounds was obtained by using multiple reaction monitoring (MRM) transitions: m/z 243.1, 210.1 and 267.2, 166.0 were measured in positive mode for huperzine A and IS. Linearity was established for the range of concentrations 0.01–4.0 ng mL^?1 with a coefficient of correlation (r) of 0.9991. The lower limit of quantification (LLOQ) was identifiable and reproducible at 0.01 ng mL^?1. The method has been successfully applied to study the pharmacokinetics of huperzine A in healthy male Chinese volunteers.     

Enantioselective pinacol coupling reaction of aromatic aldehydes catalyzed by chiral vanadium complexes

The asymmetric pinacol coupling of aromatic aldehydes by chiral salan–vanadium complexes as effective catalysts is reported. Chiral 1,2-diols were obtained with high diastereoselectivities (up to 90/10) and moderate to high enantioselectivities (up to 82% ee). The possible mechanism of the pinacol coupling reaction is also discussed.     

Two-dimensional turbulent flow chromatography coupled on-line to liquid chromatography–mass spectrometry for solution-based ligand screening against multiple proteins

We present herein a novel bioseparation/chemical analysis strategy for protein–ligand screening and affinity ranking in compound mixtures, designed to increase screening rates and improve sensitivity and ruggedness in performance. The strategy is carried out by combining on-line two-dimensional turbulent flow chromatography (2D-TFC) with liquid chromatography–mass spectrometry (LC–MS), and accomplished through the following steps: (1) a reversed-phase TFC stage to separate the protein/ligand complex from the unbound free molecules, (2) an on-line dissociation process to release the bound ligands from the complexes, and (3) a second mixed-mode cation-exchange/reversed-phase TFC stage to trap the bound ligands and to remove the proteins and salts, followed by LC–MS analysis for identification and determination of the binding affinities. The technique can implement an ultra-fast isolation of protein/ligand complex with the retention time of a complex peak in about 5 s, and on-line prepare the “clean” sample to be directly compatible with the LC–MS analysis. The improvement in performance of this 2D-TFC/LC–MS approach over the conventional approach has been demonstrated by determining affinity-selected ligands of the target proteins acetylcholinesterase and butyrylcholinesterase from a small library with known binding affinities and a steroidal alkaloid library composed of structurally similar compounds. Our results show that 2D-TFC/LC–MS is a generic and efficient tool for high-throughput screening of ligands with low-to-high binding affinities, and structure-activity relationship evaluation.     

Tailoring noise frequency spectrum to improve NIR determinations

Near infrared spectroscopy (NIR) contains excessive background noise and weak analytical signals caused by near infrared overtones and combinations. That makes it difficult to achieve quantitative determinations of low concentration samples by NIR. A simple chemometric approach has been established to modify the noise frequency spectrum to improve NIR determinations. The proposed method is to multiply one Savitzky-Golay filtered NIR spectrum with another reference spectrum added with thermal noises before the other Savitzky-Golay filter. Since Savitzky-Golay filter is a kind of low-pass filter and cannot eliminate low frequency components of NIR spectrum, using one step or two consecutive Savitzky-Golay filter procedures cannot improve the determination of NIR greatly. Meanwhile, significant improvement is achieved via the Savitzky-Golay filtered NIR spectrum processed with the multiplication alteration before the other Savitzky-Golay filter. The frequency range of the modified noise spectrum shifts toward higher frequency regime via multiplication operation. So the second Savitzky-Golay filter is able to provide better filtering efficiency to obtain satisfied result. The improvement of NIR determination with tailoring noise frequency spectrum technique was demonstrated by both simulated dataset and two measured NIR spectral datasets. It is expected that noise frequency spectrum technique will be adopted mostly in applications where quantitative determination of low concentration sample is crucial.     

An approach to identifying sequential metabolites of a typical phenylethanoid glycoside, echinacoside, based on liquid chromatography-ion trap-time of flight mass spectrometry analysis

Metabolite identification for the compounds that undergo multiple and sequential metabolism is still a great challenge. Echinacoside (ECH), a typical phenylethanoid glycoside, contains multiple unstable chemical bonds and high reactive functional groups which are susceptible to multiple pathways of degradation and metabolism, leading great difficulties for its metabolite identification. This study proposed a novel approach for rapidly identifying the complicated and unpredictable metabolites of ECH, based on the powerful liquid chromatography hybrid ion trap and time of flight mass spectrometry (LC/MS-IT-TOF) analysis. Four degradation products were rapidly identified via the “fragmentation-degradation” comparisons. Five phase I and phase II metabolites of the degradation products were rapidly characterized via the crossover mass differences comparisons of their quasi-molecular ions with the potential precursors. Four direct phase I and phase II metabolites of the parent compound were identified by the mass differences analysis of the molecular ions between metabolites and the parent compound. Multiple stages of fragmentation patterns were used to confirm the metabolites characterizations. This study provides a novel approach to characterizing the complicated metabolites, and would be widely applicable for the metabolite identification of natural products.