Suzuki-miyaura cross-coupling of 1,1-dichloro-1-alkenes with 9-alkyl-9-BBN

We addressed an unexplored application of the Suzuki-Miyaura protocol to the cross-coupling of 1,1-dichloro-1-alkenes with 9-alkyl-9-BBN. The use of bisphosphine ligands with a large P-Pd-P bite angle allowed us to synthesize Z-chlorinated internal alkenes in good yields resulting from a selective monocoupling process, a recurrent challenge with 1,1-dichloro-1-alkenes. Moreover, these monochlorinated olefins could be further transformed providing stereospecifically trisubstituted olefins.     

Modified Julia fluoroolefination: selective preparation of fluoroalkenoates

The modified Julia olefination reaction has been applied to develop a stereoselective synthesis of fluoroalkenoate derivatives from a fluorobenzothiazolyl sulfone and aldehydes or a ketone. The olefination reaction can be achieved by using a variety of bases. DBU and DBU in the presence of MgBr2 were found to be the most efficient systems to prepare either (Z)- or (E)-alkenoates in moderate to excellent stereoselectivity.     

Stereocontrolled synthesis of enantiomeric imidazolopiperidinoses and imidazoloazepanoses using Wittig/dihydroxylation reactions

A new route for the synthesis of imidazolosugars—6-deoxyimidazolopiperidinoses 1 and 2 and 7-deoxyimidazoloazepanoses 3 and 4 in two enantiomerical forms—is reported. The new synthetic approach is based on two key reactions: (i) stereocontrolled Wittig Z-olefination of an imidazolecarbaldehyde with phosphoranes containing one chiral centre, obtained from (S)- and (R)-1,2,4-butantriol; (ii) diastereoselective cis-dihydroxylation of previously obtained olefins. All synthesised imidazolosugars were evaluated as potential inhibitors of glycosidases.     

First example of an Ugi type reaction on phenylsulfinimine-avermectin B1 derivatives

A short synthesis of 4″-(S)-4″-deoxy-4″-trifluoroacetylamino-4″-alkylcarbamoyl-avermectin B₁4 has been developed through the diastereoselective Ugi reaction to an phenylsulfinimide intermediate.     

Changing the oxothiomolybdate ring from an anionic to a cationic receptor

The ionic recognition properties of neutral oxothiomolybdenum wheels can be changed from anionic to cationic through ionization of the internal aquo ligands. In the solid state, [Mo8O8S8(OH)10(H2O)]2- (1) interacts with two Cs+ cations to give a close supramolecular host-guest arrangement. Such interactions appear to be maintained in solution as a labile association.     

Capillary pumps for autonomous capillary systems

Autonomous capillary systems (CSs), where liquids are displaced by means of capillarity, are efficient, fast and convenient platforms for many bioanalytical applications. The proper functioning of these microfluidic devices requires displacing accurate volumes of liquids with precise flow rates. In this work, we show how to design capillary pumps for controlling the flow properties of CSs. The capillary pumps comprise microstructures of various shapes with dimensions from 15-250 microm, which are positioned in the capillary pumps to encode a desired capillary pressure. The capillary pumps are designed to have a small flow resistance and are preceded by a constricted microchannel, which acts as a flow resistance. Therefore, both the capillary pump and the flow resistance define the flow rate in the CS, and flow rates from 0.2-3.7 nL s(-1) were achieved. The placement and the shape of the microstructures in the capillary pumps are used to tailor the filling front of liquids in the capillary pumps to obtain a reliable filling behaviour and to minimize the risk of entrapping air. The filling front can, for example, be oriented vertically or tilted to the main axis of the capillary pump. We also show how capillary pumps having different hydrodynamic properties can be connected to program a sequence of slow and fast flow rates in a CS.     

Host-guest adaptability within oxothiomolybdenum wheels: structures, studies in solution and DFT calculations

The formation of host-guest cyclic architectures, built up through the self-condensation process of [Mo(2)O(2)S(2)](2+) oxothiocations around linear dicarboxylate ions such as adipate (Adip(2-)), suberate (Sub(2-)) and azelaate (Azel(2-)) anions is reported. The complexes [Mo(12)Adip](2-), [Mo(12)Sub](2-) and [Mo(14)Azel](2-) have been characterized in the solid state by X-ray diffraction and in solution by (1)H NMR in different solvents (D(2)O, DMF, DMSO and CD(3)CN). The host-guest dynamics appear to be dependent on the nature of the system and are mainly governed by mutual adaptability between the host and the guest. (1)H NMR DOSY experiments show systematic differences, either positive or negative between the experimental and calculated molecular weights which appear to be correlated with the charge of the anion. The relative stabilities of the twelve-membered rings containing the Adip(2-), Pim(2-) (pimelate) or Sub(2-) anions were determined experimentally and decrease according to the order [Mo(12)Adip](2-) > [Mo(12)Pim](2-) > [Mo(12)Sub](2-). The host-guest adaptability depends on the length of the carbon chain and gives rise to selective encapsulation processes. Finally, theoretical DFT investigations in the gas phase yielded conformations whose symmetry and geometrical parameters proved consistent with X-ray structures and (1)H NMR spectra recorded in DMSO or DMF. Energy calculation highlights the high flexibility of the ring showing that only 3.1 kJ mol(-1) accompanies the conformational change from circular to elliptical. The host-guest bond energy (Delta E) calculated for the Mo(12)-based clusters is consistent with the experimental stability scale, major variations being due to some constraints undergone by the central alkyl chain.     

The heteropolytungstate core {BW13O46}11- derived as monomer, dimer, and trimer

A study of the borotungstate system has led to the characterization of new, original compounds based on the unconventional Keggin derivative [H(3)BW(13)O(46)](8-) ion (denoted as 1). [H(3)BW(14)O(48)](6-) (2) and the dimer [H(6)B(2)W(26)O(90)](12-) (3) crystallize as mixed cesium/ammonium salts and have been characterized by single-crystal X-ray diffraction analysis. Anion 2 reveals an unusual arrangement, consisting of an outer {W(3)O(9)} core grafted onto the monovacant [BW(11)O(39)](9-) Keggin moiety and exhibits an unprecedented distorted square-pyramidal arrangement for a cis-{WO(2)} core. Elemental analysis, supported by bond distance analysis, is consistent with the presence of three protons distributed over the terminal oxygens of the outer {W(3)O(7)} capping fragment. The [H(6)B(2)W(26)O(90)](12-) ion (3) is formally derived from the direct condensation of two [H(3)BW(13)O(46)](8-) subunits. The cisoid arrangement of the two [BW(11)O(39)](9-) subunits, coupled with the antiparallel arrangement of the two quasi-linear O=W...O=W-OH2 chains within the central {W(4)O(12)} connecting group, breaks any symmetry, thereby resulting in a chiral compound. Polarography and pH-metric titrations reveal the formation of the monomeric precursor [H(3)BW(13)O(46)](8-) (anion 1) under stoichiometric conditions. (183)W NMR analysis of 2 and 3 in solution gives complex spectra, consistent with the presence of equilibria between several species. In the frame of this study, we also report on a structural re-investigation of the [H(6)B(3)W(39)O(132)](15-) ion (4) based on reliable results obtained in the solid state by means of single-crystal X-ray diffraction analysis, and in solution by means of 1D and 2D COSY (183)W NMR. X-ray diffraction analysis revealed the presence of three attached aquo ligands on the central {W(6)O(15)} connecting core, generating three O=W...O=W-OH2 quasi-linear chains, which are responsible for the chirality of the trimeric assembly. This structural arrangement accounts for the 39-line (183)W solution spectrum. The 2D COSY spectrum permits reliable assignments of the six strongly shielded resonances (around -250 and -400 ppm) to the six central W atoms, as well as additional assignments. The origin of such strong shielding for these particular W atoms is discussed on the basis of previously published results. Infrared data for compounds 1, 3, and 4 are also presented.     

Investigating the in vitro metabolism of fipexide: characterization of reactive metabolites using liquid chromatography/mass spectrometry

The in vitro metabolism of the nootropic drug fipexide was studied using different liquid chromatography/mass spectrometry (LC/MS) techniques. This drug has been withdrawn from the market due to toxic effects. No previous reports have investigated the possible involvement of reactive metabolites in the toxicity of fipexide. The hydrolysis of this drug leads to the formation of two potentially toxic species, 3,4-methylenedioxybenzylpiperazine (MDBP) and 4-chlorophenoxyacetic acid (4-CPA). Here, we investigate the in vitro metabolism of fipexide in human, rat, mouse and dog, as well as of MDBP and 4-CPA in human and rat, while focusing on the formation of reactive metabolites. A combination of LC/MS analyses on a hybrid quadrupole-linear ion trap instrument and accurate mass data from QqTOF measurements was employed for the characterization of these metabolites. Microsomal metabolites of fipexide were MDBP, 4-CPA, fipexide N-oxide or hydroxyl, demethylenated fipexide and other minor ones, all of which were investigated by tandem mass spectrometry. Reactive metabolites were detected using several trapping procedures with small molecules such as glutathione, its ethyl ester derivative and N-acetylcysteine. The demethylenated metabolite, a catechol, formed its corresponding ortho-quinone, which readily reacts with these nucleophiles. MDBP was studied in a similar manner, due to its ability to form an analogous catechol. Because of its acidic nature, 4-CPA was assessed for possible acylglucuronide and acyl-CoA thioester metabolites, which could also be involved in bioactivation pathways. Several important metabolites were identified as potential mediators of toxicity via protein binding.     

Tuning the polarization along linear polyaromatic strands for rationally inducing mesomorphism in lanthanide nitrate complexes

The opposite orientation of the ester spacers in the rodlike ligands L 4C12 (benzimidazole-OOC-phenyl) and L 5C12 (benzimidazole-COO-phenyl) drastically changes the electronic structure of the aromatic systems, without affecting their meridional tricoordination to trivalent lanthanides, Ln(III), and their thermotropic liquid crystalline (i.e., mesomorphic) behaviors. However, the rich mesomorphism exhibited by the complexes [Ln(L 4C12)(NO3)3] (Ln=La-Lu) vanishes in [Ln(L 5C12)(NO3)3], despite superimposable molecular structures and comparable photophysical properties. Density functional theory (DFT) and time-dependant DFT calculations performed in the gas phase show that the inversion of the ester spacers has considerable effects on the electronic structure and polarization of the aromatic groups along the strands, which control residual intermolecular interactions responsible for the formation of thermotropic liquid-crystalline phases. As a rule of thumb, an alternation of electron-poor and electron-rich aromatic rings favors intermolecular interactions between the rigid cores and consequently mesomorphism, a situation encountered for L 4C12, L 5C12, [Ln(L 4C12)(NO3)3], but not for [Ln(L 5C12)(NO3)3]. The intercalation of an additional electron-rich diphenol ring on going from [Ln(L 5C12)(NO3)3] to [Ln(L 6C12)(NO3)3] restores mesomorphism despite an unfavorable orientation of the ester spacers, in agreement with our simple predictive model.