Development and validation studies for determination of phenylpropanoid‐substituted flavan‐3‐ols in semipurified extract of Trichilia catigua by high‐performance liquid chromatography with photodiode array detection

The phenolic compounds are the main phytochemical constituents of the bark of Trichilia catigua and are commonly used for medicinal purposes. An HPLC method for the simultaneous quantification of phenolic compounds (procyanidin B2 (PB2), epicatechin (EPC), chinchonains Ia, Ib, IIa, IIb, catechin, and chrologenic acid) in T. catigua extract was developed and validated. A suitable chromatographic system was selected, which uses a gradient elution with methanol/ACN (75:25), and water both with 0.05% TFA, as mobile phase, column Luna, 280 nm, and flow 0.4 mL/min. Validation of the analytical method was based on the parameters: linearity, precision, LODs and LOQs, accuracy, robustness, and stability. The method showed linearity for PB2 and EPC, in the range 10–120 μg/mL with good correlation coefficients (>0.996). For precision, the repeatability ranged from 1.89 to 3.23%, and the values for accuracy for PB2 and EPC were 95 and 89%, respectively. The LODs and LOQs for PB2 were 1.36 and 4.12 μg/mL, and for EPC were 2.18 and 6.61 μg/mL, respectively. The method was robust under the conditions employed. The proposed method could be employed for quality assessment of T. catigua, as well as pharmaceutical products.     

Isolation and determination of estrogens in water samples by solid‐phase extraction using molecularly imprinted polymers and HPLC

Advanced SPE with molecularly imprinted polymers (MIP) was used in this study. A noncovalent imprinting approach was applied to separate 17β‐estradiol, estriol, and estrone from water samples. Polymer material was prepared by bulk polymerization with methacrylic acid as a functional monomer, divinylbenzene and ethyleneglycol dimethacrylate as crosslinkers, and acetonitrile, acetonitrile/toluene (3:1, v/v) or isooctane/toluene (1:99, v/v) as a porogen. We also prepared an MIP film on a silica gel surface with methacrylic acid and ethyleneglycol dimethacrylate as monomers and acetonitrile as a solvent. Qualitative and quantitative hormone analyses were carried out by HPLC with various detection techniques, including UV/visible spectroscopic detection (diode array detection) and electrochemical detection (CoulArray). The results of the study indicate that MIP technology is an excellent method for the quality control of estrogens in environmental analyses with a low quantification limit for 17β‐estradiol of around 26 (diode array detection) and 0.25 ng/mL (electrochemical detection). The proposed method was found to be suitable for routine determinations of the analyzed compound in environmental laboratories.     

Novel Method for HPLC Analysis of Triterpenic Acids Using 9-Anthryldiazomethane Derivatization and Fluorescence Detection

Triterpenic acids are a group of secondary plant metabolites which are part of the cuticular waxes covering fruits, leaves, and flowers. To date, quantitative analysis of these compounds has often been conducted using high-performance liquid chromatography coupled with spectrophotometric detection or mass spectrometry; however, these methods have some major drawbacks. This paper reports a new method of analysis implementing derivatization with 9-anthryldiazomethane and fluorescence detection. The method consists of the extraction of analytes from a matrix, purification with anion exchanging SPE columns, and an optional step of the alkaline hydrolysis of triterpenic acid esters. The paper also describes a fast and easy method for the synthesis of the derivatization agent. The detection limits of the method presented are approximately 100-fold lower than in a similar method using ultraviolet spectrophotometry as the mode of detection. The recovery and repeatability of the method are at satisfactory levels.     

Properties of monolayers of crown ethers bearing an azo and azoxy group in the macrocycle

Two methods are described for preparing monomolecular layers of crown ethers with an azo or azoxy group in the macrocycle. When the molecules used to build the monolayer are soluble in aqueous solutions, adsorptive preconcentration on mercury electrodes was used to prepare the monolayer coating. The monolayer was electroactive due to the presence of the azo or azoxy unit in the molecules. Monolayers of crown ethers bearing an azo group in the macrocycle were shown to recognize alkali metal cations present in the solution. Changes of the parameters of the voltammetric reduction peaks - peak potential and peak width, served as an indication of specific interactions of the monolayer of 13-membered and 16-membered azocrown ethers with Na⁺ and K⁺ cations, respectively.The monolayers capable of recognizing cations have also been prepared on the aqueous solution-air interface, using the Langmuir technique. In this approach, amphiphilic derivatives of the azocrowns were synthesized and the monolayer has been assembled on the subphase containing metal cations. Binding of the cation by the macrocycle has a stabilizing effect on the monolayer and higher collapse pressures are achieved than on the pure water subphase. The monolayer was transferred from the air-water interface on the solid substrate using the Langmuir-Blodgett technique. Thin mercury film electrodes on the Ag substrate, or An films evaporated on glass slides were employed as the electrode substrates. The former gave monolayer modified electrodes of higher stability.Presented at the Sixth International Seminar on Inclusion Compounds, Istanbul, Turkey, 27–31 August, 1995.     

The synthesis of methyl 2-(benzyloxycarbonyl)amino-3-dimethylaminopropenoate. The synthesis of trisubstituted pyrroles, 3-amino-2H-pyran-2-ones,fused 2H-pyran-2-ones and 4H-pyridin-4-ones

Methyl 2-(benzyloxycarbonyl)aimno-3-dimemylaminopropenoate ( 2 ) was prepared from methyl N-(benzyloxycarbonyl)glycinate ( 1 ) and t-butoxybis(dimethylamino)methane, and used as a reagent for preparation of substituted 3-(benzyloxycarbonyl)amino-4H-quinolizin-4-ones 5 and 6 , ?2H-pyran-2-ones 17–19 , ?2H-1-benzopyran-2-ones 28–31 , and -naphthopyrans 32–35 , ?2H-pyrano[3,2-c]pyridine-2,5-dione 46 , -pyrano-[4,3-b]pyran-2,5-dione 47 , -pyrano[3,2-c]benzopyran-2,5-dione 48 , -pyrano[2,3-c]pyrazol-6-ones 49 and 50 , -pyrano[2,3-d]pyrirnidin-7-ones 51 and 52 derivatives. In the reaction of 2 with 1,3-diketones trisubsti tuted pyrroles 14–16 were formed. Selective removal of benzyloxycarbonyl group was achieved by cat alytic transfer hydrogenation with Pd/C in the presence of cyclohexene to afford free 3-amino compounds 7 , 8 , 20 , 36–38 and 53–57 in yields better than 80%.     

Total Synthesis of Tambromycin by Combining Chemocatalytic and Biocatalytic C−H Functionalization

A combination of genomic and metabolomic approaches recently resulted in the identification of a nonribosomal tetrapeptide tambromycin, which possesses promising antiproliferative activity and several unusual structural features, including a densely substituted indole, a methyloxazoline ring, and an unusual pyrrolidine‐containing amino acid called tambroline. In this work, we identify a concise synthetic route to access tambromycin, which relies on the strategic use of biocatalytic and chemocatalytic C?H functionalization methods to prepare two key precursors to the natural product in an efficient and scalable manner. The success of our study highlights the benefits of applying the principles of biocatalytic retrosynthesis as well as C?H functionalization logic to the synthesis of complex molecular scaffolds.     

Evaluation of gamma irradiation effect on physico-chemical properties of a mixed beverage based in soy milk and grape juice

The effects of the main operation variables on the electrochemical oxidation of simulated tributyl phosphate (TBP) waste by a boron-doped diamond anode are individually studied. The optimum operating conditions are obtained as follows: 4 g L^?1 initial TBP concentration, 180 min degradation time, 40 mA cm^?2 current density, 0.5 mol L^?1 Na₂SO₄ as the supporting electrolyte, and unadjusted pH of the aqueous phase. Under such conditions, a chemical oxygen demand (COD) removal ratio of 82.3% is achieved, and the energy consumption is 26.16 kWh m^?3. A degradation mechanism of TBP is tentatively proposed.     

Elemental Analysis of Phytotherapeutic Products by Inductively Coupled Plasma–Tandem Mass Spectrometry

A procedure for the determination of As, Cd, Cr, Ni, Pb, and V in phytotherapy medicines by inductively coupled plasma–tandem mass spectrometry is reported. The use of tandem mass spectrometry with oxygen into an octopole reaction system at various gas flow rates and the combination of on-mass and mass-shift modes was evaluated. Cadmium, Cr, Ni, and Pb were determined as free atomic ions while As and V were determined as the oxides AsO⁺ and VO⁺ in the same run. Samples were prepared by microwave-assisted digestion with dilute nitric acid and hydrogen peroxide. Two plant-certified reference materials (apple leaves and tomato leaves) were used to check the accuracy. For tandem mass spectrometry with 0.5?mL min^?1 O₂, recoveries in the 85–113% were typically obtained and no statistical differences were observed at the 95% confidence level (t-test) in comparison with the certified values. Using these conditions, the limits of detection for the method were 0.01, 0.0002, 0.008, 0.008, 0.003, and 0.002?µg g^?1 for As, Cd, Cr, Ni, Pb, and V, respectively. The procedure was used for the analysis of four phytotherapic drugs and the determined concentrations were up to 0.168?µg g^?1 As, 0.03?µg g^?1 Cd, 0.82?µg g^?1 Cr, 1.18?µg g^?1 Ni, 0.52?µg g^?1 Pb, and 2.4?µg g^?1 V with average precision values of 8% as the relative standard deviation. The found concentrations were compared with limits proposed in official guidelines and, in most cases, the values were below the maximum limits allowed.