Osmium (VI) catalyzed chemoselective oxidation of allylic and benzylic alcohols

A mild and highly chemoselective approach to oxidation of allylic, electron rich/deficient benzylic, and heterocyclic alcohols employing catalytic quantities of K₂[OsO₂(OH)₄] (3 mol %) and chloramine-T (50 mol %) is described. The protocol offers short reaction times (25 min–2 h), controlled oxidation, and tolerance to a variety of substrates. A systematic mechanistic study based on the LC-ESI-MS/MS reveals the presence of imidotriooxoosmium species which further reacts with alcohol to give the oxidized product.     

Enoxacin trihydrate

The structure of the title compound, 1‐ethyl‐6‐fluoro‐1,4‐di­hydro‐4‐oxo‐7‐(piperazin‐4‐ium‐1‐yl)‐1,8‐naphthyridine‐3‐carb­oxylate trihydrate, C₁₅H₁₇FN₄O₃·3H₂O, has a zwitterion of enoxacin and three water mol­ecules in the asymmetric unit. The zwitterions form sheets lying parallel to each other and are hydrogen bonded in a head‐to‐tail manner. The crystal structure is stabilized by the involvement of O and H atoms from all the water mol­ecules in strong hydrogen bonds. The naphthyridine ring system is essentially planar, with the carboxyl­ate group lying out of this plane at an angle of 26.13 (6)° and the ethyl group oriented at approximately right angles to this plane. The piperazinium ring adopts a chair conformation.     

Preconcentration and speciation of chromium in water samples by atomic absorption spectrometry after cloud-point extraction.

A rapid, sensitive and accurate atomic absorption method for Cr(III) and Cr(VI) ions was developed based on the cloud-point extraction (CPE) technique. Cr(III) reacts with a new Schiff's base ligand to form the hydrophobic complex, which is subsequently entrapped in the surfactant micelles. The Cr(VI) assay is based on its reduction to Cr(III) by the addition of concentrated H2SO4 and ethanol to the sample solution. The condensed surfactant phase containing the metal chelates is introduced into an atomic absorption spectrometer. The relative standard deviations were 2.1% for both species and the limits of detection were around 0.17 microg l(-1).     

具有三阶非调和修正项时非线性弹性波动方程的对称解

应用Lie对称法,当弹性能具有三阶非调和修正项时,分析纵向变形的非线性弹性波动方程.通过不同对称下的恒等条件,寻找对称代数,并将它简化为二阶常微分方程.对该简化的常微分方程作进一步分析后,获得若干个显式的精确解.分析Apostol的研究成果(Apostol B F.on a non-linear wave equation in elasticity.Phys Lett A,2003,318(6):545-552)发现,非调和修正项通常导致解在有限时间内具有时间相关奇异性.除了得到时间相关奇异性的解外,还得到无法显示时间相关奇异性的解.     

Some Diels–Alder adducts of 6-vinyl-1-oxa-4-thiaspiro[4.5]dec-6-ene

6-Vinyl-1-oxa-4-thia­spiro­[4.5]­dec-6-ene has been reacted with dienophiles, such as N-phenyl­male­imide (NPM), N-methyl­triazoline-2,5-dione (MTAD) and di­methyl­acetyl­ene di­carboxyl­ate (DMAD), to assess the 1,3-diastereofacial selection caused by the acetal function. In each case, a mixture of two diastereoisomers was produced. The crystal structures of the products of the addition of NPM and MTAD syn to the acetal oxy­gen, 2-phenyl-2,3,3a,4,5,5a,6,7,8,9,9a,9b-dodeca­hydro-1H-benz­[e]­iso­indole-6-spiro-2′-[1′,3′]­oxa­thiol­ane-1,3-dione, C₂₀H₂₁NO₃S, (IIa), and 2-methyl-5,7,8,9,10,10a-hexa­hydro-1H-1,2,4-triazolo­[1,2-a]­cinnoline-7-spiro-2′-[1′,3′]­oxa­thiol­ane-1,3-dione, C₁₃H₁₇N₃O₃S, (IIIa), respectively, and the product of the addition of DMAD syn to the acetal sulfur, di­methyl 1,2,3,4,4a,7-hexa­hydro­naphthalene-1-spiro-2′-[1′,3′]­oxa­thiol­ane-5,6-di­carboxyl­ate, C₁₆H₂₀O₅S, (IVb), have been determined. All three structures are composed of independent mol­ecules separated by normal van der Waals distances. The 1-oxa-4-thia heterocyclic ring has an envelope conformation in the three structures and the S—Csp³ bond distances differ significantly from each other, as observed in comparable structures; the remaining molecular dimensions are as expected.     

Short and efficient diastereoselective synthesis of pyrrolidinone-containing dipeptide analogues

The pyrrolidine-2,4-diones have been identified as a convenient starting point for the synthesis of peptide analogues. Herein we describe an optimized two-step reductive amination procedure, which provides a small library of pyrrolidinone-containing dipeptide analogues in high yield and excellent diastereoselectivity.     

Assembly of a planar, tricyclic B4N8 framework with s-indacene structure

A neutral, formally 16pi-electron, tricyclic tetrahydrazidotetraborane was obtained in a two-step procedure involving self-assembly of a dilithiodiborate with B(4)N(8) framework and subsequent oxidation of the phenylborate moieties to boranes and biphenyl using Fe(II) as an oxidant.     

Development of a simple and sensitive high-performance liquid chromatography method for determination of glucosamine in pharmaceutical formulations

A column high-performance liquid chromatography (HPLC) method was developed for the determination of glucosamine in dosage forms. Glucosamine was derivatized by addition of a solution containing orthophthaldialdehyde. The HPLC separation was achieved on a Spherimage 80 ODS2 column (250 x 4 mm id, 5 microm particle size) using an isocratic mobile phase containing phosphate buffer-methanol (90 + 10, v/v, pH 6.50) and methanol-tetrahydrofuran (97 + 3, v/v) in proportions of 85 + 15 at a flow rate of 1 mL/min, followed by fluorescence detection. The method was validated for specificity, linearity, accuracy, precision, limit of detection (LOD), and limit of quantitation (LOQ). The detector response for glucosamine HCI was linear over the concentration range of 0.1-20 microg/mL with a correlation coefficient of 0.9980. The accuracy was between 99.4 and 100.8%. The LOD and the LOQ were 0.009 and 0.027 microg/mL, respectively. The method was applied to determination of glucosamine in solid dosage forms.