Highly atom-economic one-pot formation of three different C-P bonds: general synthesis of acyclic tertiary phosphine sulfides

The reaction of benzothiadiphosphole 1 with an equimolar mixture of R1MgBr and R2MgBr gave intermediate A', which, after only 4-5 min, was treated with an equimolar amount of R3MgBr, giving the asymmetric phosphine PR1R2R3 in 45% overall yield (75-80% yield when R1 = R2 and 85-90% yield when R1 = R2 = R3) and the byproduct 6 in 90% yield. The treatment of 6 with PCl3 quantitatively regenerates the starting reagent 1. Treatment of the phosphines with elemental sulfur gave the corresponding sulfides.     

Total synthesis of (+)-crocacin D

[structure: see text] The total synthesis of (+)-crocacin D is described. The convergent asymmetric synthesis relies on the use of a Stille cross-coupling between an (E)-vinyl stannane with an (E)-vinyl iodide to establish the (E,E)-dienamide moiety followed by a mild and efficient copper-catalyzed coupling between (+)-crocacin C and a (Z)-vinyl iodide to establish the challenging (Z)-enamide function.     

ESR and ENDOR Investigations on Various <Emphasis Type="Italic">Wurster</Emphasis>’s Radical Cations in Solution. Experimental Results,Theoretical <Emphasis Type="Italic">Ab Initio</Emphasis>, and DFT Calculations

Summary. ESR and ENDOR spectra are reported of several symmetrical substituted N,N,N,N-tetraalkyl-p-phenylenediamine radical cations in solution. Different N,N-alkyl substituted para-phenylenediamines, like the ethyl, n-propyl, and iso-propyl derivative are compared with the parent N,N,N,N-tetramethyl-p-phenylenediamine (Wursters Blue Cation). N,N,N,N-Tetrabenzyl-p-phenylenediamine, 1,4-dipyrrolidinylbenzene, and N,N-bis[4-(dimethylamino)phenyl]piperazine are additionally investigated. Experimental and calculated hyperfine coupling constants are compared. Characteristic UV-VIS data and redox potentials in acetonitrile are reported, together with the syntheses of the compounds.     

Cardanol as a replacement for cholesterol into the lipid bilayer of POPC liposomes

Large unilamellar liposomes were prepared by hydration of 1-palmitoyl-2-oleylphosphatydilcholine (POPC) films and subsequent extrusion of the obtained liposomal suspension. Inclusion of cholesterol and cardanol brings about a stabilization of the membranes of the liposomes, as determined by their rates of release of entrapped 5(6)-carboxyfluorescein. The liposome breakdown was promoted by a non-ionic surfactant (Triton X-100) and the kinetic measurements were carried out by fluorimetry in water at 25 degrees C. Morphological analyses of giant POPC liposomes in the presence and in the absence of both guests were also performed. The results obtained suggest the use of cardanol (an easy available natural product) as a replacement for cholesterol as a new possibility for stabilizing liposomes in drug targetting.     

Advances in the universal NMR database approach. 2'-substituted taxanes as probes for an improved protocol of diastereomeric differentiation

[structure: see text] The configuration of the alpha-substituted alpha-hydroxy-beta-aminoester moiety in a series of 2'-substituted taxanes was analyzed according to the recently proposed Universal NMR Database (UDB) approach. A critical analysis of the results showed that modifications regarding chemical shift adjustment (so as to render the shifts virtually connectivity independent) were necessary to get consistent stereoassignments in this set of compounds. On this basis, a modified UDB-based strategy, especially tailored to the configurational assignment of densely substituted diastereomeric fragments, is proposed.     

Quantitative Analysis of Protein–Protein Interactions by Native Page/Fluorimaging

We have developed a new quantitative native PAGE mobility shift assay, which allows for the measurement of binding affinities for interacting protein pairs, one of which is fluorescently labelled. We have used it to examine recognition of the Simian virus 40 (SV40) large tumour T-antigen (T-ag) nuclear localisation sequence (NLS) by members of the importin (Imp) superfamily of nuclear transport proteins. We demonstrate that the T-ag NLS binds to the Imp α/β heterodimer in NLS-dependent manner, determining that it binds with eight-fold higher affinity (340 nM), when compared to Imp α alone, consistent with autoinhibition of Imp αwhen not complexed with Imp β. The mobility shift assay is able to detect nM binding affinities, making it a sensitive and useful tool to analyse protein–protein interactions in solution.     

Radially symmetric weak solutions for a quasilinear wave equation in two space dimensions

We prove the convergence of the radially symmetric solutions to the Cauchy problem for the viscoelasticity equations

     

Vibration Frequencies of Mg3Al2Si3O12 Pyrope. An ab initio study with the CRYSTAL code

The vibrational spectrum of Mg(3)Al(2)Si(3)O(12) pyrope is calculated at the Gamma point by using the periodic ab initio CRYSTAL program that adopts an all-electron Gaussian-type basis set and the B3LYP Hamiltonian. The full set of frequencies (17 IR active, 25 RAMAN active, 55 silent modes) is calculated. The effect of the basis set and of the computational parameters on the calculated frequencies is discussed. It is shown that the mean absolute difference with respect to the experimental IR and RAMAN data is as small as 6 and 8 cm(-1), respectively. The IR and RAMAN modes are fully characterized by various tools such as isotopic substitution, direct inspection of the eigenvectors, and graphical representation. The present calculation permits to clarify some of the assignment and interpretation problems raised by experiment and previous simulations with force fields.     

Orbital interactions and their effects on 13C NMR chemical shifts for 4,6-disubstituted-2,2-dimethyl-1,3-dioxanes. A theoretical study

A theoretical study is employed to describe the orbital interactions involved in the conformers' stability, the energies for the stereoelectronic interactions, and the corresponding effects of these interactions on the molecular structure (bond lengths) for cis- and trans-4,6-disubstituted-2,2-dimethyl-1,3-dioxanes. For cis-4,6-disubstituted-2,2-dimethyl-1,3-dioxanes, two LPO --> sigma*C(2)-Me(8) interactions are extremely important and the energies involved in these interactions are in the range 6.81-7.58 kcal mol(-1) for the LP(O)(1) --> sigma*C(2)-Me(8) and 7.58-7.71 kcal mol(-1) for the LP(O)(3) --> sigma*C(2)-Me(8) interaction. These two LP(O) --> sigma*C(2)-Me(8) interactions cause an upfield shift, indicating an increased shielding (increased electron density) of the ketal carbon C(2) as well as the axial Me(8) group in the chair conformation. These LP(O) --> sigma*C(2)-Me(8) hyperconjugative anomeric type interactions can explain the 13C NMR chemical shifts at 19 ppm for the axial methyl group "Me(8)" and 98.5 ppm for the ketal carbon "C(2)". The observed results for the trans derivatives showed that for compounds 2a-c (R = -CN, -C[triple bond]CH, and -CHO, respectively) the chair conformation is predominant, whereas for 2d,f-h [-CH3, -Ph, -C6H4(p-NO2), -C6H4(p-OCH3), respectively] the twist-boat is the most stable compound and for 2e [-C(CH3)3] is the only form.     

Supramolecular assemblies of DNA with neutral nucleoside amphiphiles

A neutral uridine-based amphiphile is described which condenses plasmid DNA. AFM studies show that the three distinct structural components of the amphiphile (i.e, nucleobase, alkyl chains, and poly(ethylene glycol)) are required for the formation of DNA-amphiphile supramolecular assemblies on a mica surface.