Magnetoresistance of Sc3In

The magnetoresistance of the weak itinerant-electron ferromagnet Sc₃In was measured from 1.5 to 40 K in magnetic fields up to 14 T. The measurements were made on three samples containing 24.1, 24.3 and 24.4 at% In with Curie temperatures at H = 0 of T_c(0) = 5.5, 6.0 and 6.3 K, respectively. By assuming that the characteristic spin-fluctuation temperature is equal to T_c(0), the negative magnetoresistance in Sc₃In was systematically and reasonably analyzed in terms of the quenching of spin fluctuations by magnetic fields.     

Photochemical cyclization of some aldehyde thiosemicarbazones

The photochemical behaviour of some substituted aldehyde thiosemicarbazones 1a-k has been investigated in methanol at 254 nm. Thiosemicarbazones of glyoxil methyl ester 1a-f cyclized to furnish the 3-thioxo- 1,2,4-triazin-5-one 2 ring system. The remaining thiosemicarbazones 1g-j gave 1,2,4-triazoline 4 derivatives.     

Short and efficient chemoenzymatic synthesis of goniothalamin

A high-yielding three-step synthesis of goniothalamin involving an enzymatic kinetic resolution in the presence of vinyl acrylate followed by ring-closing metathesis is discussed.     

The radiochemical purity determination of18F preparations

A simple and fast chromatographic method for determining the chemical form of¹⁸F is given.     

Effects of Nonionic Micelles on the Rate of Mononuclear Heterocyclic Rearrangement of (Z)-Phenylhydrazones of 5-Substituted 3-Benzoyl-1,2,4-oxadiazoles

Nonionic Triton X-100 micelles solubilize the otherwise water-insoluble (Z)-phenylhydrazones of some 5-substituted 3-benzoyl-1,2,4-oxadiazoles to an extent suitable for studying the occurrence of a general-base-catalyzed rearrangement in the presence of borate buffers (pH 9.6). The kinetic data, obtained at 40.0 degrees C over a wide range of surfactant concentrations, are found to conform to a reaction scheme which implies partitioning of the substrates and the base between water and the micellar pseudophase. Evidence that both the rate of the rearrangement reactions and the binding of the substrates to the micellar aggregates are primarily governed by the steric requirements of the 5-substituent group is obtained. Copyright 2001 Academic Press.     

Green conditions for the Suzuki reaction using microwave irradiation and a new HNT‐supported ionic liquid‐like phase (HNT‐SILLP) catalyst

A new catalytic system based on modified halloysite nanotubes was employed in the Suzuki reaction under microwave irradiation. A set of solvents, times and bases was screened and the best experimental conditions were obtained when the reactions were carried out for 10 min in water–ethanol at 120 °C in presence of K₂CO₃ as base. Good recyclability was observed. The new catalytic system was employed using either 1 mol% or 0.1 mol%. The palladium catalyst displayed good activity, allowing the synthesis of several biphenyl compounds in high yield working with only 0.1 mol% palladium loading. The application of microwave irradiation decreased the reaction time and also improved conversion with respect to traditional heating. Copyright © 2014 John Wiley & Sons, Ltd.     

Concise Synthesis and Biological Assessment of (+)‐Neopeltolide and a 16‐Member Stereoisomer Library of 8,9‐Dehydroneopeltolide: Identification of Pharmacophoric Elements

We describe herein a concise synthesis of (+)‐neopeltolide, a marine macrolide natural product that elicits a highly potent antiproliferative activity against several human cancer cell lines. Our synthesis exploited the powerful bond‐forming ability and high functional group compatibility of olefin metathesis and esterification reactions to minimize manipulations of oxygen functionalities and to maximize synthetic convergency. Our findings include a chemoselective olefin cross‐metathesis reaction directed by H‐bonding, and a ring‐closing metathesis conducted under non‐high dilution conditions. Moreover, we developed a 16‐member stereoisomer library of 8,9‐dehydroneopeltolide to systematically explore the stereostructure–activity relationships. Assessment of the antiproliferative activity of the stereoisomers against A549 human lung adenocarcinoma, MCF‐7 human breast adenocarcinoma, HT‐1080 human fibrosarcoma, and P388 murine leukemia cell lines has revealed marked differences in potency between the stereoisomers. This study provides comprehensive insights into the structure–activity relationship of this important antiproliferative agent, leading to the identification of the pharmacophoric structural elements and the development of truncated analogues with nanomolar potency.     

A quantitative study of substituent effects on oxidative cyclization of some 2-methylsubstituted aldehydes. Thiosemicarbazones induced by ferric chloride

In order to gain further mechanistical information about the cyclization of thiosemicarbazones and thiosemicarbazone-type substrates induced by metallic salts as oxidizing agents, we performed the synthesis of substrates 1a-s and a kinetic study of the oxidative cyclization of 1 to 5-imino-Δ²-1,3,4-thiadiazole 2 and 1,2,4-triazoline-5-thione 3 derivatives induced by methanolic ferric chloride solutions. The results of cyclization were compared to those of corresponding semicarbazones. The kinetic data were analyzed by means of the Hammett's equation and ρ values discussed.     

Ionic liquids/[bmim][N3] mixtures: promising media for the synthesis of aryl azides by SNAr

The nucleophilic aromatic substitution of some activated aryl or heteroaryl halides has been performed in ionic liquid solution, using the 1-butyl-3-methylimidazolium azide as a nucleophile. The reaction course was studied varying the structures of both substrates and ionic liquids. In particular, in the latter case, the reaction of 2-bromo-5-nitrothiophene was carried out in five different ionic liquids ([bmim][BF 4], [bmim][PF 6], [bmim][NTf 2], [bm 2im][NTf 2], and [bmpyrr][NTf 2]). Finally, for all the substrates considered, a comparison with data obtained in MeOH solution in the presence of NaN 3 was also performed. Data collected indicate that in some cases it is possible to obtain aromatic or heteroaromatic azide derivatives in satisfactory yield by means of a S NAr reaction using [bmim][N 3] as the nucleophile.     

Kemp elimination: a probe reaction to study ionic liquids properties

The amino induced elimination of benzisoxazole into the relevant o-cyanophenolate ion (Kemp elimination) has been studied in [bmim][BF 4] solution at 298 K. To have information about the interactions between reactants and ionic liquid, the reaction has been carried out at different temperatures (293-313 K). Several primary, secondary, and tertiary amines have been used to study the effect of amine structure on the reaction rate. The collected data show that the amine structure seems to have a crucial role in determining the reaction rate. Furthermore, as different cation or anion structures of an ionic liquid can significantly affect its properties, the title reaction has been performed in four different ionic liquids ([bmim][PF6], [bmim][NTf 2], [bm 2im][NTf 2], and [bmpyrr][NTf 2]), using pyrrolidine and piperidine as model amines. An H-donor negative solvent (MeOH and [bmim][NTf 2]) effect on reaction rate was detected. Finally, a narrow range of activation parameters was calculated both for the reaction induced by different amines and for pyrrolidine and piperidine, in the presence of different ILs. This fact suggests the occurrence of an "early" transition state.