Reductive coupling of polyfunctionalized organobismuth and organolead arylating reagents in the synthesis of benzopyran derivatives

Benzopyran derivatives were synthesized in good yields by the reactions of tris[2-(chloromethyl)phenyl]bismuth diacetate and 2-(halomethyl)aryllead triacetates with phenols and naturally occurring 4-hydroxycoumarins in the presence of bases according to a three-step one-pot procedure. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2520–2529, November, 2005.     

Uniform convexity properties of norms on a super-reflexive Banach space

We study uniform convexity and smoothness properties satisfied by all the equivalent norms of a super-reflexive Banach space. We give some applications concerning quasi-transitive Banach spaces, and the uniform approximation property.     

Interactions between poloxamers in aqueous solutions: micellization and gelation studied by differential scanning calorimetry, small angle X-ray scattering, and rheology

Poloxamers F88 (EO97PO39EO97) and P85 (EO27PO39EO27) are triblock copolymers of ethylene oxide (EO) and propylene oxide (PO), which have the same hydrophobic PO block. We studied aqueous solutions of these two copolymers by the conjoint use of differential scanning calorimetry (DSC), rheology, and small-angle X-ray scattering (SAXS). The results showed that the temperature-induced micellization of aqueous solutions of F88 and P85 was a progressive process followed by gelation for sufficiently concentrated samples. Gelation was due to the ordered packing of micelles under a hexagonal compact (HC) structure for P85 and a body-centered cubic (BCC) phase for F88. Importantly, the phase diagram of F88/P85 mixtures in water was elucidated and showed the destabilization of the HC phase upon addition of small amounts of F88.     

EPR, NMR, and Thermodynamic Evidences for Forced Nuclear Spin–Electron Spin Interactions in the Case of 1-Phenyl-2-Methylpropyl-1,1-Dimethyl-2-Nitroxide (TIPNO) Attached to Permethylated β-Cyclodextrin

In a recent paper (Bardelang et al. in J Org Chem 71:7657–7667, 2006), the deep inclusion of the TIPNO (1-phenyl-2-methylpropyl-1,1-dimethylethyl-2-nitroxide) free radical attached to a permethylated β-cyclodextrin (TRIMEB) into its cavity was questioned. In the present paper it is shown that the results of X-band and W-band electron paramagnetic resonance (EPR) and ¹H nuclear magnetic resonance (NMR) studies of the TIPNO–TRIMEB in the presence of competitors of complexation (1-adamantanol, methyl orange and 1-adamantylamine) are consistent with a situation where the nitroxide is capping the small cavity entrance. The inclusion of the incoming guest was proven by ¹H NMR, whereas no changes in EPR spectra were noticed whatever the competitors’ concentrations. These observations are rationalized in terms of an equilibrium between a nitroxide-capped cyclodextrin (weak complex) and a non-self included form, both species involving competitors’ inclusion without significant EPR spectral changes. These results not only confirm our preliminary findings, but also point out to the peculiar role of the cyclodextrin methoxy crown of the primary rim stabilizing the appended guest by means of weak interactions.     

Persilylated phosphoranyl radicals: the first persistent noncyclic phosphoranyl radicals

Persistent noncyclic phosphoranyl radicals have been prepared and observed by electron paramagnetic resonance (EPR) for the first time. They were obtained by UV-photolysis of a solution containing a bis(trialkylsilyl) peroxide (R = Me, Et) and a tris(trialkylsilyl) phosphite (R = Me, Et, iPr). EPR parameters (a(P) approximately 100 mT) are typical of phosphoranyl radicals exhibiting a trigonal-bipyramidal structure, with the odd electron in an equatorial site. Analysis of the pseudo-first-order decay shows that these phosphoranyl radicals decay by S(H)2 homolytic substitution on the bis(trialkylsilyl) peroxide and by loss of a trialkylsilyloxyl radical (alpha-scission reaction). Both the S(H)2 and alpha-scission reactions depend on the steric bulk of the alkyl groups, that is, the bulkier the alkyl group, the slower the S(H)2 and alpha-scission reactions.     

Compactness of composition operators on a Hilbert space of Dirichlet series

In this paper new L_α^p→L_β^q estimates are proved for translation-invariant Radon transforms along curves for α?β and p<q. For a fixed α and β, if p is sufficiently close to 2 the best possible q is obtained, up to ε. The method is related to that of [5].     

Synthesis and biological evaluation of isoflavone analogues from Dalbergia oliveri

Mucronulatol 1 and violanone 2 isolated from Dalbergia oliveri Gamble, and the corresponding isoflavone 3 were prepared by ligand coupling reactions involving organolead reagent. Biological studies have shown a significant cytotoxic effect against an HBL100 leukemia cell line only for isoflavan 1 with an IC₅₀ value amounting to 5.7 μM. All the drugs modestly inhibit the in vitro microtubule assembly, independently of the cytotoxic ability. Natural compounds 1 and 2 have no antibacterial activity, but are potent inhibitors of the Fusarium oxysporum phytopathogenic fungal growth.     

Nitroxide bound beta-cyclodextrin: is there an inclusion complex?

236CDTIPNO, a derivative of the persistent free radical TIPNO (1,1-dimethylethyl 2-methyl-1-phenylpropyl nitroxide) covalently bound to a permethylated-beta-cyclodextrin, was prepared. Self-association of 236CDTIPNO in water was proved by solvent- and competition-dependent EPR spectroscopy experiments with 2,6-di-O-Me-beta-cyclodextrin (DIMEB) and permethylated-beta-cyclodextrin (TRIMEB) as external hosts competing for accommodation of the TIPNO moiety. Temperature-dependent EPR spectra were simulated with a novel two-dimensional (field-temperature) EPR simulation program that afforded a full determination of the thermodynamic parameters characterizing the rate constants of the self-inclusion reaction derived from Arrhenius and Eyring models. This method allows separating the line broadening effects due to relaxation from a chemical exchange, even if only the fast exchange regime is accessible experimentally. The activation parameters for the forward and backward steps were consistent with an equilibrium between a nonassociated form and a weakly associated form, with activation free enthalpies for each reaction of around 34 kJ.mol(-)(1).