Solvent effect in the chromatographic enantioseparation of 1,1′-bi-2-naphthol on a polysaccharide-based chiral stationary phase

Enantioseparation of 1,1′-bi-2-naphthol (BINOL) was performed on a polysaccharide-based chiral stationary phase, Chiralcel OD-H, under normal-phase mode. The effects of polar modifier in the mobile phase on the retention, enantioseparation and elution order were investigated in detail. Solvent-induced reversal of elution order for BINOL was observed. When linear alcohols were adopted, R-BINOL was always eluted first. S-BINOL was eluted first when 2-propanol was used as a polar modifier. Enantioseparation could not be obtained when sec-butyl alcohol or tert-butyl alcohol was used as a polar modifier. When isoamyl alcohol or cyclohexanol was used as a polar modifier, favorable enantioseparation was obtained as with 1-pentanol or 1-hexanol; also, R-BINOL was the first-eluted enantiomer. It is worth emphasizing that significantly better enantioseparation was obtained when higher alcohols were used as polar modifier of the mobile phase. A nonlinear characteristic for the ln α against 1/T plots was universally observed in this study though the ln k against 1/T plots exhibited a linear feature. Associated with the obtained thermodynamic parameters, some interesting inferences about chiral recognition mechanism were proposed.     

Microwave-assisted synthesis of pyridylpyrroles from N-acylated amino acids

A small library of 3- and 4-pyridyl-substituted pyrroles was prepared from N-acylated amino acids. Nicotinoyl or isonicotinoyl chloride was used for the N-acylation of benzyl esters of amino acids. Debenzylation by palladium-catalyzed hydrogenation gave N-acylated amino acids. Dehydration of the acylated amino acids gave cyclic intermediates, münchnones or azlactones, which were treated in situ with alkynes in 1,3-dipolar cycloadditions. The starting materials were prepared in a parallel fashion, and microwave irradiation was used to facilitate the cycloaddition reactions. The regiochemistry of the cycloaddition was studied.     

Solvent effect on the synthesis of monodisperse amine-capped Au nanoparticles

A remarkable solvent effect in a single-phase synthesis of monodisperse amine-capped Au nanoparticles is demonstrated.Oleylamine-capped Au nanoparticles were prepared via the reduction of HAuCU by an amine-borane complex in the presence of oleylamine in an organic solvent.When linear or planar hydrocarbon(e.g.,n-hexane,n-octane,1-octadecylene,benzene,and toluene) was used as the solvent, high-quality monodisperse Au nanoparticles with tunable sizes were obtained.However,Au nanoparticles with poor size dispersity were obtained when tetralin,chloroform or cyclohexane was used as the solvent.The revealed solvent effect allows the controlled synthesis of monodisperse Au nanoparticles with tunable size of 3-10 nm.     

New selective O-debenzylation of phenol with Mg/MeOH

Carboxylate-benzyl and nitro-benzyl groups used in phenols protection were selectively debenzylated with 3-25 equiv of Mg in methanol at room temperature. Good yields of the desired phenols were obtained within 3-10 h from a wide variety of O-(carboxylate-benzyl)- or O-(nitro-benzyl)-phenols. Selective O-debenzylation was possible in the presence of O-(carboxylate-benzyl)- or O-(nitro-benzyl)-phenols with Mg/MeOH.     

Rearrangement of azoxybenzocrowns into chromophoric hydroxyazobenzocrowns and the use of hydroxyazobenzocrowns for the synthesis of ionophoric biscrown compounds

The Wallach rearrangement was used as a method for preparing p-hydroxyazobenzocrown ethers starting from different azoxybenzocrowns as substrates. Synthesis of a series of p-hydroxyazobenzocrowns under modified conditions and characterization of the obtained products are presented. o-Hydroxyazobenzocrowns were identified among the products of the photochemical rearrangement of azoxybenzocrowns. Novel biscrowns were synthesized from p-hydroxyazobenzocrown ethers. The synthesized host molecules, differing in the size of the macrocycles and in the substituents in the aromatic rings, have the same dioxymethylene linkers. They were used as potential sodium or potassium ionophores in classic and miniature (screen-printed) ion-selective electrodes. The properties (tautomerism, acid–base equilibrium) of newly prepared o-hydroxyazobenzocrown ethers and their p-substituted analogs were studied using spectroscopic methods and compared.     

What to sacrifice? Fusions of cofactor regenerating enzymes with Baeyer-Villiger monooxygenases and alcohol dehydrogenases for self-sufficient redox biocatalysis

A collection of fusion biocatalysts has been generated that can be used for self-sufficient oxygenations or ketone reductions. These biocatalysts were created by fusing a Baeyer-Villiger monooxygenase (cyclohexanone monooxygenase from Thermocrispum municipale: TmCHMO) or an alcohol dehydrogenase (alcohol dehydrogenase from Lactobacillus brevis: LbADH) with three different cofactor regeneration enzymes (formate dehydrogenase from Burkholderia stabilis: BsFDH; glucose dehydrogenase from Sulfolobus tokodaii: StGDH, and phosphite dehydrogenase from Pseudomonas stutzeri: PsPTDH). Their tolerance against various organic solvents, including a deep eutectic solvent, and their activity and selectivity with a variety of substrates have been studied. Excellent conversions and enantioselectivities were obtained, demonstrating that these engineered fusion enzymes can be used as biocatalysts for the synthesis of (chiral) valuable compounds.     

Gamma-ray irradiation and characterization of synthesized bidentate and tetradentate Schiff base ligands and their complexes with some transition metal ions

Salen ligands are essential for coordinating a diverse group of metals in their respective oxidation states. This creates significant complexes of salen metals that are used in different fields. Condensation of ehylenediamine (en) with p-methoxybenzaldehyde (L¹) or o-hydroxyacetophenone (L²) with a ratio 1: 2 (en: p-methoxybenzaldehyde or o-hydroxyacetophenone) or by the interaction of o-phenylenediamine (phen) with o-hydroxybenzaldehyde (L³) or p-hydroxybenzaldehyde (L⁴) with a ratio 1: 2 (phen: o-hydroxybenzaldehyde or p-hydroxybenzaldehyde) has been used to prepare four symmetrical Schiff bases (L¹-L⁴). The UV–vis spectroscopy has been used to investigate the diverse electronic transitions associated with the Schiff bases molecules as well as how these transitions are impacted by diverse polarities of solvents. Elemental analysis, FT-IR, UV–vis spectra, molar conductivity, and ¹H NMR have been used to characterise all the compounds obtained in this process. The continuous variation applied alongside molar ratio spectral methods showed the formation of different complexes arising from the reaction of the ligand (L^1-L⁴) with the metal ions Mn(II), Fe(III) and Cu(II) is 1: 1 and/ or 1: 2 (M: L). A series of universal buffer solutions (20 % ethanol v/v) with varying pH values were used in spectrophotometry to determine the acid dissociation constants of the L² and L⁴ ligands. Gamma radiation was applied to examine the compounds’ irradiation stability. Additionally, the absorptions of the main functional groups were screened using FT-IR spectra before and after Gamma irradiation. The results show that all the compounds are stable after irradiation process; therefore, it could be used as enhancing agents in cancer therapy.     

A simple,efficient, regioselective and one-pot preparation of N-hydroxy- and N–O-protected hydroxyindoles via cycloaddition of nitrosoarenes with alkynes. Synthetic scope,applications and novel by-products

The thermal reaction between nitrosoarenes and alkynes under alkylating conditions produces N-alkoxyindoles as the major products in moderate to good yields and excellent regioselectivity. Various electrophiles are used affording different N–O-protected hydroxyindoles in a multi-component fashion. Privileged acetylenic substrates used in reactions with substituted nitrosoarenes are arylalkynes or propiolates. Potentially bioactive compounds and other classes of highly functionalizable indole products were prepared. Reactions between o-carbomethoxy-nitrosoarenes and arylacetylenes provided tricyclic compounds containing an acylaziridine indoline skeleton.     

Submicro methods for the analysis of organic compounds : The determination of hydroxyl groups

Various procedures were examined for the determination of organic hydroxyl groups. Conventional acetylation methods could not be used on the submicro scale, but the spectrophotometric method based on esterification with 3,5-dinitrobenzoyl chloride followed by extraction of the ester and colour development with alkaline acetone proved reasonably satisfactory for aliphatic alcohols. Acidic hydroxyl groups e.g. in phenolic compounds, were titrated accurately with 0.01 M tetrabutylammonium hydroxide in benzene-methanol solution in a pyridine medium ; visual end-points or potentiometricend-points with glass-silver or glass-in-stream platinum electrode pairs were used depending on the strength of the acidic group. Some differentiating titrations were possible. A general submicro bromination method for phenols was not feasible.     

A new application of Baylis–Hillman alcohols to a diastereoselective synthesis of 3-nitrothietanes

Three key reactions, the generation of a nucleophile, an thia-Michael addition and an intramolecular cyclisation, were used to achieve an efficient one-pot diastereoseletive synthesis of 3-nitrothietanes. Thus, Baylis–Hillman alcohols and their aldehydes were reacted with either O,O-diethyl hydrogen phosphorodithioate or O,O-diethyl hydrogen phosphorodithioate in combination with a task-specific ionic liquid [bmim]X–Y to afford the corresponding 2,3-di- or 2,3,4-trisubstituted thietanes, respectively. The reaction is high yielding and proceeds with complete diastereoselectivity in favour of the trans isomers.     

A mixed anhydride approach to the preparation of sulfinate esters and allylic sulfones: Trimethylacetic p-toluenesulfinic anhydride

A reagent combination of toluenesulfinic acid and trimethylacetyl chloride affords a putative trimethylacetic p-toluenesulfinic anhydride. This reagent has been used to prepare a series of sulfinate esters from primary and secondary alcohols. In addition, the reagent was used to convert Baylis-Hillman substrates into allylic sulfones. Attempts to use the reagent to convert amines to sulfinamides were unsuccessful. In contrast, the use of 2-pyrrolidinone afforded N-p-toluenesulfinyl pyrrolidinone in 64% yield. The use of a chiral 4-benzyl-1,3-oxazolidinone or 4-benzyl-1,3-oxazolidine-2-thione led to the isolation of S-p-tolyl p-toluenethiosulfonate.     

Study of [EMim][ESO4] ionic liquid as solvent in the liquid-liquid extraction of xylenes from their mixtures with hexane

The aim of this work is to determine if the ionic liquid 1-ethyl-3-methylimidazolium ethylsulfate is a good solvent for the separation of xylenes and hexane by liquid extraction. With this purpose, liquid-liquid equilibrium (LLE) data for the ternary systems {hexane + o-xylene, or m-xylene, or p-xylene + 1-ethyl-3-methylimidazolium ethylsulfate} were determined at T = 298.15 K and atmospheric pressure. Selectivity and solute distribution ratio, derived from the experimental equilibrium data, were calculated and used to determine if this ionic liquid can be used as a potential solvent for the extraction of xylenes from their mixtures with hexane. The experimental LLE data for the ternary systems were correlated using the NRTL and UNIQUAC models.     

Ozonolysis of 18α-Oleanane triterpenoid with an alkenenitrile moiety in the five-membered ring A

A novel synthetic protocol of ozonolytic cleavage of 18α-oleanane triterpenoid with the five-membered α,β-alkenenitrile moiety dissolved in dichloromethane to selectively synthesize a 1,3-secotriterpene derivative with 78% yield was developed. Spontaneous condensations of the synthesized 19β,28-epoxy-1,3-seco-2-nor-18α-olean-3-al-1-oic acid followed by formation of unsubstituted 1,3- and 1,4-lactones were registered in reactions with sodium borohydride as a reducing reagent or oxalyl chloride as an activating agent, respectively. α-Methoxy- and α-ethoxy-substituted 1,3-lactones were obtained when the polar protic solvents methanol or ethanol were used for the ozonolysis of the alkenenitrile. Experiments on ozonolysis were carried out in combination with reduction with dimethyl sulfide. Ozonolysis of alkenenitrile in dichloromethane without reductive treatment was found out to have resulted in stable triterpene ozonide.     

Enantioselective Michael addition of aldehydes to maleimides organocatalysed by chiral 1,2-diamines: an experimental and theoretical study

Simple and commercially available chiral 1,2-diamines were used as organocatalysts for the enantioselective conjugate addition of aldehydes, including α,α-disubstituted, to maleimides. The reaction was carried out in the presence of hexanedioic acid as an additive in aqueous solvents at room temperature. By employing (1S,2S)- and (1R,2R)-cyclohexane-1,2-diamine as organocatalysts, the corresponding Michael adducts bearing new stereocenters were obtained in high or quantitative yields with enantioselectivities of up to 92%, whereas the use of (1S,2S)-1,2-diphenylethane-1,2-diamine gave a much lower ee. Theoretical calculations were used to justify the observed sense of the stereoinduction.     

Evaluation of the influence of proline, hydroxyproline or pyrrolidine in the presence of sodium nitrite on N-nitrosamine formation when heating cured meat

N-nitrosamines are meant to be probable or possible carcinogenic components, possibly formed out of a reaction between nitrite and N-containing substances such as amino acids and secondary amines. Nitrite is often used for processing meat products because of its colouring and antimicrobial properties.During this experimental setup, the influence of proline, hydroxyproline or pyrrolidine on N-nitrosamine formation in meat samples was evaluated. The N-nitrosamines concentrations were measured with gas chromatography-thermal energy analyzer. Only the concentrations of N-nitrosodimethylamine and N-nitrosopyrrolidine were found above the limit of detection in a number of tested experimental conditions. The concentration of these two N-nitrosamines was modelled as a function of temperature and nitrite concentration for different situations (presence or absence of added natural N-containing meat components). It could be concluded that proline and pyrrolidine promoted the formation of N-nitrosopyrrolidine. It could also be confirmed that the higher the temperature of the meat processing procedure and the higher the sodium nitrite amounts added, the higher were the yields of the respective N-nitrosamines.     

Synthesis of diarylamines in the benzo[b]thiophene series bearing electron donating or withdrawing groups by Buchwald-Hartwig C-N coupling

Diarylamines in the benzo[b]thiophene series bearing electron donating or withdrawing groups, were prepared by Buchwald-Hartwig C-N coupling in moderate to high yields. The conditions used were Pd(OAc)₂ (3 mol%), BINAP as ligand (4 mol%) and Cs₂CO₃ as base (1.4 equiv.), in toluene at 100°C, being 6-bromo or amino benzo[b]thiophenes coupled, respectively, with substituted anilines or phenylbromides. The 6-aminobenzo[b]thiophene derivatives were also prepared by palladium catalyzed C-N coupling of the corresponding 6-bromo compounds with benzophenone imine, followed by acidic hydrolysis of the imino derivatives. When 4-nitrobromobenzene and 4-bromobenzonitrile were used as coupling components, triarylamines were also isolated in small amounts. The presence of a fluorine atom on the phenylbromide highly increases the diarylamine yields.     

Indole 3-alkylation/vinylation under catalysis of the guanidinium ionic liquids

Two ionic liquids, N,N,N,N-tetramethylguanidinium trifluoroacetate (TMGT) and the unprecedented N,N,N,N-tetramethylguanidinium triflate (TMGT_f), were used as catalyst solvents in condensations between indoles and arylaldehydes or 1,3-diketones providing a simple and efficient method for synthesis of bis(3-indolyl)methanes or casually 3-alkenylindoles due to stereoelectronic concerns of reactants. The ionic liquids are easily separated and reused for several times.     

Application of probabilistic neural networks in qualitative analysis of near infrared spectra: determination of producing area and variety of loquats

Near infrared (NIR) spectra of a sample can be treated as a signature, allowing samples to be grouped on basis of their spectral similarities. Near infrared spectroscopy (NIRS) combined with probabilistic neural networks (PNN) have been used to discriminate producing area and variety of loquats. Two varieties of loquats (‘Dahongpao’ and ‘Jiajiaozhong’) picked from two producing areas of ‘Tangxi’ and ‘Cunan’ in Zhejiang province were analyzed in this study. Principal component analysis (PCA) was applied before PNN modeling and the results indicated that the dimension of the vast spectral data can be effectively reduced. For each model, half samples were used to train the network and the remaining half were used to test the network. The results of the PCA-PNN models for discriminating the variety of samples from the same producing area or for discriminating the producing area of the same variety samples were much better than those of the PCA-PNN models for discriminating variety or producing area of all loquat samples. The results of this study show that NIRS combined with PCA-PNN is a feasible way for qualitative analysis of discriminating fruit producing areas and varieties.     

Investigation of flavonoid profile of Scutellaria bacalensis Georgi by high performance liquid chromatography with diode array detection and electrospray ion trap mass spectrometry

Scutellaria baicalensis Georgi is a well-known medicinal plant widely used in China and other East Asian countries. High performance liquid chromatography combined with diode array detection and electrospray ion trap mass spectrometry was used to determine the flavonoid profile of S. baicalensis. Under the optimized experiment conditions, 32 flavonoids were clearly detected. Eighteen main ones were doubtless identified by comparing their retention time, UV and MS (MSⁿ) data with isolated or commercial standards. The UV characteristics of these 18 known standards were studied in detail. The rules summarized provided valuable indications for the subsequent on-line identification processes. By interpreting both the MS and the UV data in detail, other 13 minor flavonoids in S. baicalensis were on-line identified successfully.     

Discrimination and classification techniques applied on Mallotus and Phyllanthus high performance liquid chromatography fingerprints

Mallotus and Phyllanthus genera, both containing several species commonly used as traditional medicines around the world, are the subjects of this discrimination and classification study. The objective of this study was to compare different discrimination and classification techniques to distinguish the two genera (Mallotus and Phyllanthus) on the one hand, and the six species (Mallotus apelta, Mallotus paniculatus, Phyllanthus emblica, Phyllanthus reticulatus, Phyllanthus urinaria L. and Phyllanthus amarus), on the other. Fingerprints of 36 samples from the 6 species were developed using reversed-phase high-performance liquid chromatography with ultraviolet detection (RP-HPLC-UV). After fingerprint data pretreatment, first an exploratory data analysis was performed using Principal Component Analysis (PCA), revealing two outlying samples, which were excluded from the calibration set used to develop the discrimination and classification models. Models were built by means of Linear Discriminant Analysis (LDA), Quadratic Discriminant Analysis (QDA), Classification and Regression Trees (CART) and Soft Independent Modeling of Class Analogy (SIMCA). Application of the models on the total data set (outliers included) confirmed a possible labeling issue for the outliers. LDA, QDA and CART, independently of the pretreatment, or SIMCA after “normalization and column centering (N_CC)” or after “Standard Normal Variate transformation and column centering (SNV_CC)” were found best to discriminate the two genera, while LDA after column centering (CC), N_CC or SNV_CC; QDA after SNV_CC; and SIMCA after N_CC or after SNV_CC best distinguished between the 6 species. As classification technique, SIMCA after N_CC or after SNV_CC results in the best overall sensitivity and specificity.