Stereospecific synthesis of 2,3-disubstituted 1,4-benzodioxans

The synthesis of cis- and trans-2-methyl-3-phenyl-1,4-benzodioxans 4 and 5 , from 1-phenyl-2-[2-(hydroxy)-phenoxy]propanols threo 2 and erythro 3 are described.     

Delayed fluorescence from the lowest 1B+3u state of anthracene,due to hetero-triplet—triplet annihilation of 3anthracene* and 3xanthone*

The P-type delayed fluorescence (DF) S_i→S_o of aromatic compounds results from the population of excited singlet states S_i by triplet—triplet annihillation (TTA) of molecules in their lowest and metastable triplet state T₁ : T₁ + T₁

S_i + S_o; S_i may be any excited singlet state whose excitation energy E(S_i ? 2 E(T₁). TTA of unlike molecules A and B (hetero-TTA) may lead to excited singlet states either of A or of B. In particular, if E(T_A¹) < E(T₁^B), hetero-TTA may lead to excited singlet states S_k^A which are not accessible by TTA of 2 T₁^A. In the present paper we report the first example of the detection of the DF from a very short-lived upper excited singlet state S_k^A which has been populated by hetero-TTA. The systems investigated are liquid solutions of A = anthracene-h₁₀ or anthracene-d₁₀ or 9,10-dimethylanthracene and B = xanthone in 1,1,2-trichlorotrifluoroethane at 243 K. S_k^A is the lowest ¹B_3U⁺ state (B_b state) of anthracene.     

Synthesis and structural characterization of a new heterobimetallic coordination complex of barium and cobalt for use as a precursor for chemical vapor deposition

Ba(dmae)2 (dmaeH=N,N-dimethylaminoethanol, C4H11NO) reacts with Co(acac)2 (acac=2,4-pentanedionate) to produce the trinuclear coordination complex [Ba2Co(acac)4(dmae)3(dmaeH)] in an 85% yield. Spectroscopic and single-crystal X-ray diffraction experiments indicate that the complex possesses a structure in which two barium atoms and a cobalt atom are bridged by acac and dmae groups. The barium centers are eight and nine coordinate with BaO7N and BaO7N2 coordination spheres while the cobalt is a more regular CoO5N octahedron. This 2:1 heterobimetallic molecular complex was investigated as precursor for the deposition of thin film by AACVD. The film was characterized by SEM and XRD. TGA shows that the complex starts thermal decomposition upon heating in nitrogen atmosphere at 105 degrees C to produce barium cobalt oxide material of a Ba2CoO3 composition with an orthorhombic structure. The synthetic approach detailed here represents a unique route to the formation of a heterobimetallic barium cobalt coordination complex.     

Synthesis of α-trifluoromethyl-α-amino-β-sulfone hydroxamates: novel nanomolar inhibitors of matrix metalloproteinases

The racemic α-trifluoromethyl-α-amino-β-sulfone hydroxamates 1 were synthesized by means of a nucleophilic addition of sulfur-stabilized carbanions to a N-Cbz imine of trifluoropyruvate (4). The free amino derivative 1a was the most potent inhibitor of both MMP-3 (stromelysin-1) and MMP-9 (gelatinase-B), showing an IC₅₀ = 14 nM and 1 nM, respectively, and excellent selectivity versus MMP-1 (>5000-fold difference in inhibitory capacity). The N-Me derivative 1b was the most selective for MMP-3 with respect to MMP-9 (62-fold difference).     

Synthesis and structure of diamido ether uranium(IV) and thorium(IV) halide "ate" complexes and their conversion to salt-free bis(alkyl) complexes

The high-yield synthesis, spectroscopic and structural determination of three new uranium(IV) and thorium(IV)ate complexes supported by three different diamido ether ligands are reported. The reaction of Li2[2,6-iPr2PhN(CH2CH2)]2O (Li2[DIPPNCOCN]) with 1 equiv. of UCl4 in THF generates [DIPPNCOCN]UCl3Li(THF)2(1), while reaction in toluene/ether gives salt-free [DIPPNCOCN]UCl2.1/2C7H8(2), which was identified by paramagnetically shifted 1H NMR. Reaction of 0.5 equiv. of {[tBuNON]UCl2}2([tBuNON]=[(CH3)3CN(Si(CH3)2)]2O2-) with 3.5 equiv. LiI in toluene and a minimal amount of THF results in [tBuNON]UI3Li(THF)2(3) and is very similar in structure to 1. {[MesNON]ThCl3Li(THF)}2(4), a dimeric complex with a Th2Li2Cl6 core, is prepared by reaction of Li2[2,4,6-Me3PhN(Si(CH3)2)]2O (Li2[MesNON]) with ThCl4 in THF. The analogous reaction in toluene did not yield the salt-free complex but rather a sterically crowded diligated compound, [MesNON]2Th (5), which was also structurally characterized. Complex 5 was prepared rationally by reacting 2 equiv. Li2[MesNON] with ThCl4 in toluene. The reaction of 1 and 3 with 2 equiv. of LiCH2Si(CH3)3 generates the stable, salt-free organoactinides [DIPPNCOCN]U(CH2Si(CH3)3)2(6) and [tBuNON]U(CH2Si(CH3)3)2(7). Complex 6 was structurally characterized. These reactions illustrate the viability of ate complexes as useful synthetic precursors.     

Ligand discrimination in the reaction of nitrones with [PtCl2(PhCN)2]. Selective formation of mono-oxadiazoline and mixed bis-oxadiazoline complexes under thermal and microwave conditions

[2+3] Cycloaddition of nitrones to the nitrile ligands in the complexes cis- or trans-[PtCl2(PhCN)2] occurs under ligand differentiation and allows for selective synthesis of complexes of the type cis- or trans-[PtCl2(oxadiazoline)(PhCN)]. Microwave irradiation enhances the reaction rates of the cycloaddition considerably and further favours the selectivity towards the mono-cycloadduct with respect to thermal conditions, because the first cycloaddition is accelerated to a higher extent than the second one. Reaction of the trans-substituted mono-oxadiazoline complexes with a nitrone different from the one used for the first cycloaddition step gives access to mixed bis-oxadiazoline compounds of the composition trans-[PtCl2(oxadiazoline-a)(oxadiazoline-b)]. The corresponding cis-configured complexes, however, do not undergo further cycloaddition. All reactions described occur without isomerisation of the stereochemistry around the platinum center, independently of whether thermal or microwave heating is applied.     

Design and Enantioselective Synthesis of Cashmeran Odorants by Using “Enol Catalysis”

Novel Cashmeran odorants were designed by molecular modeling. Their short syntheses involve a novel asymmetric Brønsted acid catalyzed Michael addition of unactivated α‐substituted ketones. This key transformation was realized by utilizing a new type of enol activation catalysis and affords different cyclic ketones bearing α‐quaternary stereocenters in good to excellent yields and with high enantioselectivity. Subsequent McMurry coupling and Saegusa–Ito oxidation furnished the enantiopure target odorants, one enantiomer of which indeed possesses the typical olfactory aspects of Cashmeran.     

Two 2,6‐Dioxabicyclo[3.3.1]nonan‐3‐ones from Phragmanthera capitata (Spreng.) Balle (Loranthaceae)

Phytochemical investigation of the leaves of Phragmanthera capitata collected on Cassia spectabilis tree led to the isolation of two natural lactones, rel‐(1R,5S,7S)‐7‐[2‐(4‐hydroxyphenyl)ethyl]‐2,6‐dioxabicyclo[3.3.1]nonan‐3‐one ( 1 ) and 4‐{2‐[rel‐(1R,3R,5S)‐7‐oxo‐2,6‐dioxabicyclo[3.3.1]non‐3‐yl]ethyl}phenyl 3,4,5‐trihydroxybenzoate ( 2 ) together with the known compounds betulinic acid ( 3 ), dodoneine ( 4 ), quercetin 3‐O‐α‐L ‐rhamnopyranoside ( 5 ), quercetin 3‐O‐α‐L ‐arabinofuranoside ( 6 ), quercetin ( 7 ), betulin ( 8 ), lupeol ( 9 ), and sitosterol ( 10 ). Their structures were established by means of modern spectroscopic techniques, and the relative configuration of compound 1 was confirmed by X‐ray analysis. Compounds 1 and 2 were tested in vitro for their antiplasmodial activity against the Plasmodium falciparum chloroquine sensitive‐strains NF54 and 3D7. Compound 2 exhibited good antiplasmodial activity against both strains with IC₅₀ of 2.4 and 4.9 μM , respectively, while compound 1 was inactive.     

Determination of 90Sr and 210Pb in deer bone samples by liquid scintillation counting after ion-exchange procedures

This work describes a procedure for the isolation of ⁹⁰Sr and ²¹⁰Pb from deer bones by anion exchange methods and their sequential measurement by LSC. To prevent collection of Pb on the Sr·Spec^® resin we first separated Pb on a Dowex anion exchange column. Sr, which is not held back on the Dowex column, was then purified using Sr·Spec^® resin: first Ca and the Ra isotopes were eluted with 3 M HNO₃ and then Sr was eluted with distilled water. With this 2-steps procedure pure ²¹⁰Pb and ⁹⁰Sr spectra can be achieved. The chemical yield of both steps was determined by ICP-MS. Our ⁹⁰Sr results show satisfying agreement with data obtained by a shorter Sr·Spec^® method and also by the “classical” ⁹⁰Sr determination using fuming nitric acid. Also ²¹⁰Pb results were checked by re-measuring bone samples with already known ²¹⁰Pb activities. Further our method was verified on the reference sample IAEA-A-12.     

Laccase–polyazetidine prepolymer–MWCNT integrated system: Biochemical properties and application to analytical determinations in real samples

Bioelectrochemical properties of Trametes versicolor Laccase (TvL) and Trametes hirsuta Laccase (ThL) immobilized by using polyazetidine prepolymer (PAP) onto multi-walled carbon nanotubes (MWCNTs) screen printed electrode (SPE) surface, have been studied with several redox mediators by cyclic voltammetry (CV). The efficient entrapment of laccase in the PAP layer was confirmed by determination of both kinetic parameters (maximum current and Michaelis–Menten apparent constant) and analytical performances by chronoamperometry. The Laccase-modified MWCNTs electrode provides an effective biosensor for determination of polyphenols and catecholamines in real matrices; performances of the considered biosensors for real samples analysis are also compared and discussed.