A validated, stability-indicating method for the assay of dexamethasone in drug substance and drug product analyses, and the assay of preservatives in drug product

Summary A new high-performance liquid chromatographic (HPLC) procedure for the determination of dexamethasone, imprities, degradation products and product preservatives is described. A three-stage, linear gradient with UV detection at 240 nm allows the alysis of dexamethasone drug substance and dexamethasone in two formulated products, using the same chromatographic system. The Limit of Quantitation (LOQ) of dexamethasone importies in drug substance is 0.05%, and 0.1% for dexamethasone degradation products in formulated products. The method is linear, precise, accurate and robust. Sample preparations are simiple, and are accomplished without the use of an internal standard. Several degradation products of stressed dexamethasone have been identified.     

Natural Products Originated from the Oxidative Coupling of Tyrosine and Tryptophan: Biosynthesis and Bioinspired Synthesis

The oxidative coupling of tyrosine and tryptophan units is a pivotal step in the total synthesis of some peptide-derived marine and terrestrial natural products, such as the diazonamides, azonazine and tryptorubin A. This Minireview details the biosynthesis and bioinspired synthesis of natural products with such structures. A special focus is put on the challenges of the synthesis of these natural products and the innovative solutions adopted by synthetic chemists.     

Detection of new radiolysis products in γ-irradiated,methanolic medazepam by GC-FTIR

Summary A methanolic solution of 2% medazepam was irradiated with a dose of 50 kGy. A capillary gas chromatograph with a Fourier Transformation Infrared Spectrophotometer (FTIR) was used to investigate the radiolysis products in the solution. The changed products found earlier were confirmed and new ones identified. The radiolytic scheme can be improved and enlarged.     

Oxidation of methylbenzimidazoles with ceric ammonium nitrate

A convenient method for the preparation of benzimidazole carboxaldehydes by the oxidation of methylbenzimidazoles with cerie ammonium nitrate is described. A series of methyl, dimethyl, and trimethylbenzimidazoles was treated with ceric ammonium nitrate in sulfuric acid, and the major ethyl acetate soluble products were characterized. In addition to carboxaldehyde products, side reactions yielding benzimidazolediones and nitrobenzimidazoles were also observed.     

A chip-type thin-layer electrochemical cell coupled with capillary electrophoresis for online separation of electrode reaction products

A coupling technique of thin-layer electrolysis with high-performance capillary electrophoresis/UV–vis technique(EC/HPCE/UV–vis) is developed for online separation and determination of electrode reaction products. A chip-type thin-layer electrolytic (CTE) cell was designed and fabricated, which contains a capillary channel and a background electrolyte reservoir, allowing rapid electrolysis, direct sampling and online electrophoretic separation. This chip-type setup was characterized based on an electrophoresis expression of Nernst equation that was applied to the redox equilibrium of o-tolidine at different potentials. The utility of the method was demonstrated by separating and determining the electro-oxidation products of quercetin in different pH media. Two main products were always found in the studied time, potential and pH ranges. The variety of products increased not only with increasing potential but also with increasing pH value, and in total, at least 13 products were observed in the electropherograms. This work illustrates a novel example of capillary electrophoresis used online with thin-layer electrolysis to separate and detect electrode reaction products.     

Facile N-arylation of amines and sulfonamides

[reaction: see text] A facile, transition-metal-free N-arylation procedure for amines and sulfonamides has been developed, which affords good to excellent yields of arylated products under very mild reaction conditions. A methoxy-substituted aryl triflate affords N-arylated products in high yields with excellent regioselectivity. This chemistry tolerates a variety of functional groups.     

Facile O-arylation of phenols and carboxylic acids

[reaction: see text] A facile, transition-metal-free O-arylation procedure for phenols and aromatic carboxylic acids has been developed that affords good to excellent yields of arylated products under very mild reaction conditions. A methoxy-substituted aryl triflate affords O-arylated products in high yields with excellent regioselectivity. This chemistry tolerates a variety of functional groups.     

Reactions of thioquinanthrene with alkanethiolates. The smiles rearrangement of diquinolinyl sulfides

Reactions of thioquinanthrene 1 with alkali metal alkanethiolates in DMSO or DMF at 70° proceeded through a stage of the S→S type of the Smiles rearrangement (3′-quinolinethiolate 2A→ 4′-quinolinethiolate 3A ) to give 4,4′-dialkylthio-3,3′-diquinolinyl sulfides 3 as the final products. When these reactions were carried out at 20° two types of the products were isolated: 3′,4-dialkylthio-3,4′-diquinolinyl sulfides 2 or sulfides 3 depending on the reaction time (1 hour or 7 days). Under acidic conditions 3 ′-quinolinethiolate 2A underwent intramolecular cyclization to dithiin 1 . Reactions of dithiin 1 with sodium alkanethiolates at 20°, realized as a one-pot procedure, led to various 3,4-dialkylthioquinolines 7 . The rearrangement of other 3′-quinolinethiolates 8A and 11A (the products of the reactions of dithiin 1 with sodium sulfide and sodium methoxide) needed higher temperature (140°).     

Chemical studies of the antioxidant mechanism of theaflavins: radical reaction products of theaflavin 3,3′-digallate with hydrogen peroxide

The objective of the current study is to characterize the reaction products of theaflavin 3,3′-digallate, one of the major characteristic polyphenols of black tea, with hydroxyl radicals generated by hydrogen peroxide, with the aim of gaining insights into specific mechanisms of antioxidant reactions in physiological systems. Two major reaction products were isolated and identified using high-field 1D and 2D NMR spectral analysis. Both of them are A-ring fission products. The observation of these compounds indicates that the A ring rather than the benzotropolone moiety is the initial site for formation of reaction products in the hydrogen peroxide oxidant system.     

Thermal decomposition products of polyethylene

Decomposition products of polymers have been determined by many investigators, but the results are often conflicting because of difficulties in analyzing a large number of products. A comprehensive analysis of the volatile thermal decomposition products of high-density polyethylene has been made with the latest techniques in gas chromatography. The formation of products is explained on the basis of free-radical mechanism. The predominant process in the formation of volatiles appears to be intramolecular transfer of radicals, in which isomerization by a coiling mechanism plays an important role in determining the relative quantities of each product.     

Gas chromatographic analysis of the thermal and photochemical reaction products in diethyl ether solutions of nitrogen oxides

Summary When dissolved in diethyl ether, nitrogen dioxide reacts with the solvent, slowly at room temperature, more rapidly on heating of UV irradiation. A complex mixture of products is formed in which further changes are observed after prolonged storge: these are less pronounced if the unreacted nitrogen oxides are removed. A gas chromatographic method was applied for the identification of the majority of products. Irradiation does not change significantly the qualitative and quantitative composition of the reaction products. The reaction is thus the so-called photo-induced process [ΔG<0]. Preliminary suggestions are made concerning the reaction mechanism.     

Oxidative Cyclization of Azo-coupling Products of 3-Isopropenyltropoloneand 3-Cinnamoyltropolone with Bromine

Heterocycle-fusedtroponoidsareakindofcompoundswithphysiologicalactivitysuchasanticancer'.germicide',antiphlogistic',antihypertension'andantidiabetics.Troponoidcompoundscanbesynthesizedinmanyways,amongwhichonewastooxidizethesidechainoftropoloneforcycl...     

Determination of Amikacin Isomers by High Pressure Liquid Chromatography

Abstract

A high-pressure liquid chromatographic (HPLC) method for quantitative monitoring of amikacin isomers is described. Four isomers, BB-K8, BB-K29, BB-K6 and BB-K11 were applied to a silica gel column. While adsorbed, the isomers were derivatized with o-phthalaldehyde and the derivatized products eluted with ethanol. A decrease in the fluorescence of the derivatized products with time was observed. Heating at 50°C for 5 min produced products with stable fluorescence for at least three hours. Using the fluorescent properties of the amikacin derivative for detection, the four isomers of amikacin were separated by reverse phase (HPLC). A linear relationship from 1 to 10 μg/mL was obtained for all four isomers.     

Synthesis of taiwaniaquinoids via Nazarov triflation

A unified approach toward the taiwaniaquinoids that has yielded four natural products is described. A new variant of the Nazarov reaction with concomitant formation of an enol triflate serves as one of the key steps, considerably shortening the synthetic scheme and providing a general entry into this class of bioactive natural products.     

Nickel-catalyzed trans-alkynylboration of alkynes via activation of a boron-chlorine bond

Reaction of (diisopropylamino)chloroboryl ethers of alkynols with alkynylstannanes in the presence of nickel catalysts afforded formal trans-alkynylboration products in good yields. The products were isolated as pinacol boronates after treatment of the crude reaction mixture with acetic anhydride and pinacol in the presence of a base. The trans-alkynylboration products underwent Suzuki-Miyaura coupling reaction with organic halides. A 2-borylalkenylnickel(II) complex, in which the boryl and nickel groups are located in a trans fashion, was isolated in a reaction of the chloroboryl ether with a single equivalent of a nickel(0)-phosphine complex.     

气相色谱-质谱法分析芥子气的氯氨消毒产物

用气相色谱／质谱法分析了芥子气的氯胺Ｔ、氯胺Ｂ的消毒产物。根据消毒剂和消毒产物的性质，研究了不同消毒液样品制备方法。探讨了消毒剂过量和不过量时对消毒反应的影响。     

Synthesis of Novel Hydrophobic Media and Purification of Recombinant HBsAg

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Structures of epicatechin gallate trimer and tetramer produced by enzymatic oxidation

During black tea production, catechins and their galloyl esters are enzymatically oxidized to generate a complex mixture of black tea polyphenols. The role of galloyl ester groups in this process has yet to be determined. Enzymatic oxidation of epicatechin 3-O-gallate (1) yielded two new oxidation products, theaflavate C and bistheaflavate A, along with theaflavate A (2), a known dimer of 1 generated by coupling of the B-ring with the galloyl group. Theaflavate C is a trimer of 1 and possesses two benzotropolone moieties generated by the oxidative coupling of the galloyl groups with the catechol B-rings. Bistheaflavate A was found to be a tetramer produced by intermolecular coupling of two benzotropolone moieties of 2. From the structures of the products, it was deduced that oxidative coupling of galloyl groups resulted in extension of the molecular size of the products in catechin oxidation.     

Determination of short-lived activation products in neutron-irradiated sodium through application of hydrated antimony pentoxide

A method for the determination of short-lived activation products in neutron-irradiated sodium is described. It is based on hydrolysis of sodium with methanol, separation of Na⁺ with specially prepared antimony pentoxide (HAP) possessing very high selectivity and capacity, and subsequent gamma-spectroscopic measurement of the activation products.     

Rhodium-catalyzed enantioselective [2+2+2] cycloaddition of diynes with unfunctionalized alkenes

A chiral rhodium complex catalyzed an enantioselective [2+2+2] cycloaddition of unsymmetrical diynes with norbornene, and tetracyclic products were obtained in good to excellent ee. The cycloaddition of a symmetrical diyne with styrene derivatives as coupling partners gave bicyclic products in good ee.