Expanding the Myxochelin Natural Product Family by Nicotinic Acid Containing Congeners.

Myxobacteria represent a viable source of chemically diverse and biologically active secondary metabolites. The myxochelins are a well-studied family of catecholate-type siderophores produced by various myxobacterial strains. Here, we report the discovery, isolation, and structure elucidation of three new myxochelins N1-N3 from the terrestrial myxobacterium Corallococcus sp. MCy9049, featuring an unusual nicotinic acid moiety. Precursor-directed biosynthesis (PDB) experiments and total synthesis were performed in order to confirm structures, improve access to pure compounds for bioactivity testing, and to devise a biosynthesis proposal. The combined evaluation of metabolome and genome data covering myxobacteria supports the notion that the new myxochelin congeners reported here are in fact frequent side products of the known myxochelin A biosynthetic pathway in myxobacteria.

Chitosan tailor-made membranes as biopolymeric support for electromembrane extraction.

A chitosan membrane composed by 60% (w/w) chitosan and 40% (w/w) Aliquat®336 has been proposed as a new biopolymeric support for electromembrane extraction. The new support has been characterized by Scanning Electron Microscopy, resulting a 30-35 µm thickness. Amoxicillin, nicotinic acid, hippuric acid, salicylic acid, anthranilic acid, ketoprofen, naproxen and ibuprofen have been successfully extracted using the proposed support. Better enrichment factors were obtained for the acidic polar analytes than for the non-steroidal anti-inflammatory compounds (ranging from 118 for hippuric acid and 20 for ibuprofen). Electromembrane extraction was developed applying a DC voltage of 100 V, 1-octanol as supported liquid membrane and 20 min of extraction. The target analytes have also been satisfactorily extracted from human urine samples, providing high extraction efficiencies. The chitosan membrane is presented as a promising alternative for supporting liquid membrane compared to commonly used materials for this purpose.

Use of Polymer Inclusion Membranes (PIMs) as support for electromembrane extraction of non-steroidal anti-inflammatory drugs and highly polar acidic drugs.

The use of polymer inclusion membranes (PIMs) as support of 1-octanol liquid membrane in electromembrane extraction (EME) procedure is proposed. Synthesis of PIMs were optimized to a composition of 29% (w/w) of cellulose triacetate as base polymer and 71% (w/w) of Aliquat®336 as cationic carrier. Flat PIMs of 25µm thickness and 6mm diameter were used. EME protocol was implemented for the simultaneous extraction of four non-steroidal anti-inflammatory drugs (NSAIDs) (salicylic acid, ketoprofen, naproxen and ibuprofen) and four highly polar acidic drugs (anthranilic acid, nicotinic acid, amoxicillin and hippuric acid). Posterior HPLC separation of the extracted analytes was developed with diode array detection. Recoveries in the 81-34% range were obtained. EME procedure was applied to human urine samples.

New nanostructured support for carrier-mediated electromembrane extraction of high polar compounds.

A new support has been proposed to be used for carrier-mediated electromembrane extraction purposes. The new support (Tiss®-OH) is a 100µm thickness sheet nanofiber membrane manufactured by electrospinning and composed by acrylic nanofibers. It has been used in an electromembrane extraction (EME) combined with a HPLC procedure using diode array detection. The proposed method has been used for the extraction of four high polarity acidic compounds: nicotinic acid, amoxicillin, hippuric acid and salicylic acid. Analytes were extracted from an aqueous sample solution (pH 4) (donor phase) using a Tiss®-OH sheet that supports a 5% (w/v) Aliquat®336 in 1-octanol liquid membrane. Aqueous solution (pH 6) was used as acceptor phase. The electrical field was generated from a d.c. electrical current of 100V through two spiral shaped platinum wires placed into donor and acceptor phases. Analytes were extracted in 10min with recoveries in the 60-85% range. The proposed EME procedure has been successfully applied to the determination of the target analytes in human urine samples.

Structure and antibacterial property of a new diterpenoid from Euphorbia helioscopia.

The present study was designed to isolate and evaluate the antibacterial activity of the compounds from the whole plant of Euphorbia helioscopia L.. Various chromatographic techniques were used to isolate and purify the compound. The structure of the compound was elucidated on basis of spectral data ((1)H NMR, (13)C NMR, (1)H-(1)H COSY, HSQC, HMBC, NOESY, IR, and HR-ESI-MS). A new jatrophone-type diterpenoid (14α,15ß-diacetoxy-3ß-benzoyloxy-7ß-nicotinoyloxy-9-oxo-jatropha-5E,11E-diene), named euphoheliosnoid E (1), was isolated from the whole plant of E. helioscopia L. Compound 1 showed significant anti-microbial activity against oral pathogens.

The relative importance of the adsorption and partitioning mechanisms in hydrophilic interaction liquid chromatography.

We propose an original model of effective diffusion along packed beds of mesoporous particles for HILIC developed by combining Torquatos model for heterogeneous beds (external eluent+particles), Landauers model for porous particles (solid skeleton+internal eluent), and the time-averaged model for the internal eluent (bulk phase+diffuse water (W) layer+rigid W layer). The new model allows to determine the analyte concentration in rigid and diffuse W layer from the experimentally determined retention factor and intra-particle diffusivity and thus to distinguish the retentive contributions from adsorption and partitioning. We apply the model to investigate the separation of toluene (TO, as a non-retained compound), nortriptyline (NT), cytosine (CYT), and niacin (NA) on an organic ethyl/inorganic silica hybrid adsorbent. Elution conditions are varied through the choice of a third solvent (W, ethanol, tetrahydrofuran (THF), acetonitrile (ACN), or n-hexane) in a mobile phase (MP) of ACN/aqueous acetate buffer (pH 5)/third solvent (90/5/5, v/v/v). Whereas NA and CYT retention factors increase monotonously from W to n-hexane as third solvent, NT retention reaches its maximum with polar aprotic third solvents. The involved equilibrium constants for adsorption and partitioning, however, do not follow the same trends as the overall retention factors. NT retention is dominated by partitioning and NA retention by adsorption, while CYT retention is controlled by adsorption rather than partitioning. Our results reveal that the relative importance of adsorption and partitioning mechanisms depends in a complex way from analyte properties and experimental parameters and cannot be predicted generally.

[Secondary Metabolites from Penicillium raistrickii].

OBJECTIVE: To investigate the secondary metabolites from Penicillium raistrickii. METHODS: Compounds were isolated and purified by normal and reverse phase silica gel, Sephadex LH-20 gel column chromatography and RP-HPLC. Their structures were established by means of spectral techniques and physicochemical properties. RESULTS: Twelve compounds were identified as pestafolide A(II), 3-methoxy-4-methyl-2,4-dien-pentanoic acid (2),p-hydroxy phenylacetamide (3),2-(2-hydroxy propanamido) benzamide (4), nicotinic acid (5), thymine (6), uracil (7) cyclo (Gly-Ala) (8), (22E,24R)-3ß,5α,9α-trihydroxy ergosta-7,22-diene-6-one (9), cerevisterol (10), ergosterol (11) and ergosterol peroxide (12). CONCLUSION: All compounds are isolated from Penicillium raistrickii for the first time.

Lipoproteínas de alta densidad y reducción de riesgo cardiovascular: ¿promesas o realidades? / High-density lipoprotein and cardiovascular risk reduction: promises and realities

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[Study on the chemical constituents of endophytic fungus Fimetariella rabenhorstii isolated from Aquilaria sinensis].

OBJECTIVE: To study the chemical constituents of endophytic fungus Fimetariella rabenhorsti isolated from Aquilaria sinensis. METHODS: Chemical constituents of the fungus were isolated and purified by column chromatography and their structures were elucidated on the basis of spectral data. RESULTS: Five compounds were isolated and identified as 4-hydroxy-phenylethyl alcohol (1),nicotinic acid (2), D-galacitol(3), 2-anilino-1,4-naphthoquinone (4), N-phenylacetamide (5). CONCLUSION: Compounds 1-5 are isolated from the genus Fimetariella for the first time, compound 5 is rare in natural products.

Imitation of biomembranes on the basis of cholic acid and endogenic thermostable protein complex in biopartitioning micellar chromatography.

The structure of biomembranes was imitated by introducing nonionic surfactant polyoxyethylene (23) dodecylether, cholic acid and endogenic thermostable protein complex (14-65 kDa) into the mobile phase. The influence of concentration of these additives on the retention of the model compounds was studied. The competing interaction of cholic acid and endogenic thermostable protein complex in the lipid bilayer model was revealed on the basis of chromatographic data. The values of efficiency of the chromatographic column regarding solutes were increased by addition of endogenic thermostable protein complex to the mobile phase containing Brij-35 and cholic acid.

[Studies on the chemical constituents from aerial parts of Gynura divaricata].

OBJECTIVE: To study the chemical constituents from aerial parts of Gynura divaricata. METHODS: The constituents were isolated on silica gel column chromatography, preparative TLC and Sephadex LH-20 column chromatography, identified by physicochemical properties and the structures were elucidated by spectral analysis. RESULTS: 10 compounds were isolated and identified as 2-(1', 2', 3', 4'-tetrahydroxybutyl)-6-(2", 3", 4"-trihydroxybutyl)-pyrazine (1), 2-(1', 2', 3', 4'-tetrahydroxybutyl)-5-(2", 3", 4"-trihydroxybutyl) -pyrazine (2), nicotinic acid (3), 5-hydroxy-picolinic acid(4), methyl-5-hydroxy-2- pyridinecarboxylate (5), adenosine (6), uridine (7), stigmasterol-5-O- beta-D-glucoside (8), dibutyl terephthalate (9), methyl chlorogenate (10). CONCLUSION: Compounds 1, 2, 5, 9, 10 are obtained from this genus for the first time, Compounds 3, 4 are obtained from this plant for the first time.

Chip electrophoresis with mass spectrometric detection in record speed.

We demonstrate that the combination of high speed separations on chip with a fast mass spectrometer enables electrophoretic separations with full mass spectra registration within a second. This was accomplished by coupling a microfluidic glass chip with an integrated nanospray emitter to a fast time of flight mass spectrometer working at 100 Hz for data acquisition. Applying field strengths up to 5800 V cm(-1) we achieved separations of model analytes such as pharmaceuticals and peptides with subsequent acquisition of full mass spectra within one second or slightly more.

[Study on the chemical constitutes of submerged cultivation mycelium of Cordyceps jiangxiensis].

OBJECTIVE: In an effort to investigate the chemical constitutes of submerged cultivation mycelium of Cordyceps jiangxiensis anamorph. METHODS: The mycelia of C. jiangxiensis anamorph produced by submerged cultivation technique were separated and purified using various chromatographic techniques such as repeated liquid column chromatography, preparative thin layer chromatography etc. , and then the chemical structures of compounds obtained were elucidated on the basis of physicochemical analysis and spectroscopic techniques such as 1H-NMR, 13C-NMR and MS. RESULTS: Nine compounds were obtained from the petroleum ether and ethyl acetate extractive fractions of mycelial methanol extract, and were identified as follows: uracil (I), adenine (II), adenosine (III), uridine (IV), 3'-methoxyuridine (V), succinic acid (VI), nicotinic acid (VII), 1-monostearin (VIII), tetracosanoic acid (IX). CONCLUSION: Chemical constitutes of C. jiangxiensis anamorph are systematically separated for the first time, and compounds V, VII, VIII, and IX obtained are separated from Cordyceps species firstly.

Optimization of subcritical fluid extraction of bioactive compounds using Hansen solubility parameters.

Process engineering operations in food and nutraceutical industries pertaining to the design of extraction of value-added products from biomass using pressurized liquids involve a careful selection of the solvent and optimal temperature conditions to achieve maximum yield. Complex molecular structure and limited physical property data in the literature of biological solutes extracted from biomass compounds have necessitated the process modeling of such operations. In this study, we have applied the Hansen 3-dimensional solubility parameter concept to optimize the extraction of molecularly complex solutes using subcritical fluid solvents. Hansen solubility spheres characterized by the relative energy differences (RED) have been used to characterize and quantify the solute-subcritical solvent interactions as a function of temperature. The solvent power of subcritical water and compressed hydroethanolic mixtures above their boiling points has been characterized using the above-mentioned method. The use of group contribution methods in collaboration with computerized algorithms to plot the Hansen spheres provides a quantitative prediction tool for optimizing the design of extraction conditions. The method can be used to estimate conditions for solute-solvent miscibility, an optimum temperature range for conducting extractions under pressurized conditions, and approximate extraction conditions of solutes from natural matrices.

Characteristics of the adsorption mechanism of acido-basic compounds with two pKa in reversed-phase liquid chromatography.

Overloaded band profiles of phthalic acid, nicotinic acid, and sodium nicotinate eluted with a methanol-aqueous buffer solution were recorded at the exit of a 150 mm x4.6mm column packed with 3.5 microm X-Bridge-C(18) porous particles. The WSpHs of the mobile phase was adjusted at different values, with addition of hydrochloric acid (WSpH approximately 1.37), phosphate (WSpH approximately 2.01, 2.85, and 7.32), formate (WSpH approximately 3.61), acetate (WSpH approximately 4.41 and 5.15), or succinate buffers (WSpH approximately 6.11). The ionic strengths of all the buffers were fixed at 0.1M by adding the necessary amount of potassium chloride when necessary. The compositions of the solutions at equilibrium were solved by using the extended Debye-Hückel theory, which estimates the activity coefficients of the ions in the bulk phase. The adsorption of the samples onto X-Bridge-C(18) assumed a simple bi-Langmuir isotherm for the neutral species (or zwitterion) and a Langmuir isotherm for the ionizable species. Competition for adsorption between the neutral and the ionic species was neglected. The band profiles were calculated based on the equilibrium-dispersive model of chromatography. An excellent agreement was observed between the experimental and the calculated band profiles for all buffer solutions. This work validates the adsorption mechanism assumed in earlier work for neutral and ionizable species. It is consistent with the neutral species adsorbing weakly (due to dispersive interactions) onto and/or into the C(18)-bonded layer (large number of sites) while the singly charged species adsorb strongly onto the few residual accessible silanol groups (due to charge-dipole interactions). Doubly charged species are not retained and are probably excluded from the pores of the hydrophobic stationary phase.

Isolation and characterization of xanthine oxidase inhibitory constituents of Pyrenacantha staudtii.

Six compounds have been isolated from the leaves of Pyrenacantha staudtii, two of which are new compounds. The new compounds have been characterized as kaempherol 3-O-beta-rhamnopyranosyl (1-->6)-beta-D-glucopyranoside (1) and 4-beta-glucopyranosyl-(2-furyl)-5-methy-1,2-glucopyranoside phenylmethanone (2). The known compounds are 3-pyridinecarboxylic acid (3), beta-sitosterol (4), sitosterol 3-O-beta-glucopyranoside (5) and taraxerol (6). Their structures were determined by spectroscopic and chemical evidences. The two new compounds together with 3-pyridinecarboxylic acid showed significant in vitro xanthine oxidase inhibitory activity. To the best of our knowledge, this is the first report of these compounds from this plant.

Preparation and characterization of temperature-responsive capillary electrochromatographic column using poly(N-isopropylacrylamide).

Poly(N-isopropylacrylamide) is a temperature-responsive polymer, which is hydrophilic at low temperature but hydrophobic at high temperature. Using this characteristic, the polymer was bonded to the inner surface of fused-silica capillary to prepare a temperature-responsive column to study the separation behavior in electrochromatography.

Analysis of substances to be used as internal standards in MEKC.

The use of internal standards (ISs) improves the quantitative performance of CE. However, ISs chosen for use in CZE often cannot be used for micellar EKC (MEKC). Therefore 22 substances were investigated as potential ISs in MEKC. These substances were selected based upon a literature search. The substances were investigated using a method similar to the standard operating conditions for MEKC as recommended by S. Terabe. Furthermore, the migration time and the corrected migration time (k(S)) were determined for each substance to establish the migration position relative to other peaks in the electropherograms. A combination of eight substances, selected according to the obtained results (t(m) = 4 up to 12 min), was tested for practical benefit and applicability. The peak area precision was in the range of 0.8 and 1.2% (n = 60), and the peaks were well shaped for all the investigated substances. The selected substances covered a wide migration time window and therefore they can be regarded as suitable for future analysis at any required migration position.

Enantiomeric separation of imidazolinone herbicides using chiral high-performance liquid chromatography.

Chiral high-performance liquid chromatography (HPLC) is one of the most powerful tools to prepare enantiopure standards of chiral compounds. In this study, the enantiomeric separation of imidazolinone herbicides, i.e., imazethapyr, imazapyr, and imazaquin, was investigated using chiral HPLC. The enantioselectivity of Chiralpak AS, Chiralpak AD, Chiralcel OD, and Chiralcel OJ columns for the three analytes was compared under similar chromatographic conditions. Chiralcel OJ column showed the best chiral resolving capacity among the test columns. The resolved enantiomers were distinguished by their signs of circular dichroism detected at 275 nm and their structures confirmed with LC-mass spectrometric analysis. Factors affecting the chiral separation of imidazolinones on Chiralcel OJ column were characterized. Ethanol acted as a better polar modifier than the other alcohols including 2-propanol, 1-butanol, and 1-pentanol. Although the acidic modifier in the mobile phase did not influence chiral recognition, it was necessary for reducing the retention time of enantiomers and suppressing their peak tailing. Thermodynamic evaluation suggests that enantiomeric separation of imidazolinones on Chiralcel OJ column is an enthalpy-driven process from 10 to 40 degrees C. This study also shows that small amounts of pure enantiomers of imidazolinones may be obtained by using the analytical chiral HPLC approach.