A divergent approach to highly substituted benzothiepinones and to 2,3-dihydrothieno[2,3-b]thiopyran-4-ones

The radical addition-transfer of S-(2-fluoro-phenacyl)xanthates can be used to construct rapidly benzothiepinones, including libraries of complex aza-bridged derivatives, and highly functionalized 2,3-dihydrothieno[2,3-b]thiopyran-4-ones.     

Synthesis and characterization of an amethyrin-uranyl complex displaying aromatic character

Abstract

The reaction between amethyrin and non-aqueous uranyl silylamide (UO₂[N(SiMe₃)₂]₂) under anaerobic conditions affords a bench-stable uranyl complex. UV–vis spectroscopy, cyclic voltammetry, as well as proton NMR spectroscopic analyses provide support for the conclusion that all six pyrrole subunits participate in coordination of the uranyl dication and that, upon complexation, the amethyrin-core undergoes a 2-electron oxidation to yield a formal 22 π-electron aromatic species.     

Synthesis and properties of carbamate‐ and amine‐containing poly(phenylacetylenes)

The 3‐ and 4‐aminophenylacetylenes protected by t‐butoxycarbonyl (t‐Boc) and 9‐fluorenylmethoxycarbonyl (Fmoc) groups ( 3a – 6a ) were synthesized and polymerized using [(nbd)RhCl]₂ ( 1 ) and [(nbd)Rh⁺‐η⁶‐PhB^?Ph₃] ( 2 ) catalysts. The t‐Boc‐containing polymers [poly( 3a ) and poly( 4a )] were obtained in high yield (82–91%). Among the Fmoc‐protected monomers, the para‐derivative polymerized well [poly( 6a ); yield = 85–94%], whereas its meta‐substituted analogue did not afford high molecular weight polymer in good yield [poly( 5a ); yield = 10–15%]. The use of KN(SiMe₃)₂ as a cocatalyst in conjunction with 1 led to a dramatic increase in the molecular weight of the polymers. The acid‐ and base‐catalyzed removal of the t‐Boc and the Fmoc groups, respectively, generated primary amine‐containing polymers [poly( 3b )–poly( 6b )] which cannot be obtained directly by the polymerization of the corresponding monomers. The solubility characteristics of the polymers bearing protected amino groups were quite different from those of the unprotected ones, the former being soluble in polar solvents, whereas the latter displayed poor solubility even in polar protic or highly polar aprotic solvents. The attempts to accomplish the free‐standing membrane fabrication by solution casting were successful only for poly( 3a ), and an augmentation in the gas permeability and CO₂/N₂ permselectivity was discerned in comparison with the unsubstituted poly(phenylacetylene) and poly(m‐t‐butyldimethylsiloxyphenylacetylene). © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1853–1863, 2009     

Longitudinal distribution of trace elements in the atmosphere of an industrial area from neutron activation analysis

Industrial units play a significant role in atmospheric pollution. Industrial exhausts deteriorate the atmospheric quality causing unhygienic environment for the people working in the vicinity. This work presents a study of the longitudinal distribution of trace elements of the Sheikhupura industrial area. Three kinds of distribution patterns were observed and are discussed in detail. The results are based on the neutron activation analysis of 16 trace elements.     

Hydrogen bond formation to cyclic and acyclic polyethers

Equilibrium constants and enthalpies of hydrogen-bond formation of mcresol to various cyclic (crown) and acyclic polyethers have been determined in benzene solvent. Equilibrium constants indicated no evidence for an operative macrocyclic effect; the relationship between the increasing size of the equilibrium constant and the number of ether oxygens was rationalized with a simple statistical thermodynamic model. Enthalpies of interactions ranged between –19 and –23 kJ-mol^–1. In agreement with PCILO calculations, enthalpies of interaction were essentially independent of the number of oxygen atoms in the ether; no significant difference in enthalpies of interaction between cyclic and acyclic ethers was found.     

Thiol–Ene “Click” Reaction Triggered by Neutral Ionic Liquid: The “Ambiphilic” Character of [hmim]Br in the Regioselective Nucleophilic Hydrothiolation

Thiol–ene “click” chemistry has emerged as a powerful strategy to construct carbon–heteroatom (C? S) bonds, which generally results in the formation of two regioisomers. To this end, the neutral ionic liquid [hmim]Br has been explored as a solvent cum catalyst for the synthesis of linear thioethers from activated and inactivated styrene derivatives or secondary benzyl alcohols and thiols without the requirement of using a metal complex, base, or free radical initiator. Furthermore, detailed mechanistic investigations using ¹H NMR spectroscopy and quadrupole time‐of‐flight electrospray ionization mass spectrometry (Q‐TOF ESI‐MS) revealed that the “ambiphilic” character of the ionic liquid promotes the nucleophilic addition of thiol to styrene through an anti‐Markovnikov pathway. The catalyst recyclability and the extension of the methodology for thiol–yne click chemistry are additional benefits. A competitive study among thiophenol, styrene, and phenyl acetylene revealed that the rate of reaction is in the order of thiol–yne>thiol–ene>dimerization of thiol in [hmim]Br.     

In vitro anti-oxidant potential of new metabolites from Hypericum oblongifolium (Guttiferae)

Phytochemical investigations on Hypericum oblongifolium led to the isolation of a flavone named folicitin (1) and a bicyclic conjugated lactone, folenolide (2) from the ethyl acetate fraction of methanolic extract. Both metabolites were characterised as new compounds based on detailed spectroscopic analyses. In vitro anti-oxidant potential of both the compounds was evaluated by the DPPH radical scavenging assay. Compound 1 exhibited significant antioxidant activity while compound 2 was found inactive.     

Rapid preparative isolation of erythrocentaurin from Enicostemma littorale by medium‐pressure liquid chromatography,its estimation by high‐pressure thin‐layer chromatography,and its α‐amylase inhibitory activity

Erythrocentaurin is a relatively simple natural product present among the members of Gentianaceae. A preparative method for the isolation of erythrocentaurin from the ethyl acetate fraction of Enicostemma littorale using medium‐pressure liquid chromatography has been reported. The method consisted of a simple step gradient from 10 to 20% ethyl acetate in n‐hexane. Using a 70 × 460 mm Si60 column, this method is capable of processing 20 g of material in <3 h (purity ≈ 97%). The recovery of erythrocentaurin was 87.77%. Estimation of erythrocentaurin in extracts and fractions based on high‐pressure thin‐layer chromatography was carried out on silica gel 60 F₂₅₄ plates with toluene/ethyl acetate/formic acid (80:18:2 v/v/v) as the mobile phase. The densitometric analysis was performed at 230 nm. A well‐separated compact band of erythrocentaurin appeared at R_f 0.54 ± 0.04. The analytical method showed good linearity in the concentration range of 200–1500 ng/band with a correlation coefficient of 0.99417. The limits of detection and quantification were found to be ≈60 and ≈180 ng/band, respectively. Erythrocentaurin exhibited a concentration‐dependent α‐amylase inhibition (IC₅₀ 1.67 ± 0.28 mg/mL). The outcome of the study should be considered for pharmacokinetic and biotransformation studies involving E. littorale.     

Evaluation of the effect of Ramadan fasting on fat-soluble antioxidants and markers of oxidative stress in healthy Pakistani subjects

The aim of this study is to evaluate the effect of Ramadan fasting on the fat-soluble antioxidants [all-trans-retinol (vitamin A) and α-tocopherol (vitamin E)] in healthy Pakistani subjects. Thirty (30) healthy male volunteers (aged 30–50 years) with Ramadan fasting have participated in the study. Blood sampling from these subjects was conducted 1 day before and on 15th and 28th days of Ramadan. The serum levels of vitamin A and vitamin E were measured using liquid chromatography linked with UV–visible (HPLC–UV). The comparison between the samples taken at different times was made by Minitab software applying two samples and paired t-test at (p?<?0.05) as significant. No significant changes have been found in the levels of all-trans-retinol before and during Ramadan values. The levels of α-tocopherol on 28th Ramadan have been decreased significantly when compared with its values before Ramadan (p?<?0.0001). It is concluded that there is nonsignificant change in the levels of vitamin A during the month of Ramadan while the levels of α-tocopherol have been decreased significantly on the 28th day of Ramadan. It is therefore suggested that the fasting of Ramadan has effect on the levels of α-tocopherol and food-based interventions might be necessary to modify the diet during Ramadan.