Tripodal imidazole frameworks: Reversible vapour sorption both with and without significant structural changes

A series of tripodal imidazole frameworks (TIFs) are reported based on a tripodal, cavity-containing tris(imidazole) derivative. In the case of [Co(3)Cl(6)(1)(2)]·n(solvent) (TIF-1) which possesses a doubly interpenetrated framework structure, the material exhibits rigid, permanent porosity and selectively absorbs CO(2). The non-interpenetrated [Co(1)(2)(H(2)O)(2)]Cl(2)·4H(2)O (TIF-2) also absorbs gases and vapours fully reversibly exhibiting a reversible phase change in the process and considerable conditioning and hysteresis. The very highly hydrated [Co(1)(2)]Cl(2)·22H(2)O (TIF-3) irreversibly dehydrates to the layered structure [Co(1)(2)]Cl(2)·H(2)O (TIF-4). A nickel analogue [Ni(1)(2)]Cl(2)·22H(2)O (TIF-5) closely related to TIF-3 is also reported along with two isostructural, non-porous materials [MCl(2)(1)] (M = Mn, TIF-6; M = Cd, TIF-7) based on d(5) and d(10) Mn(II) and Cd(II). Some of the materials may be prepared by mechanochemical as well as solution based methods. We liken TIF-1 to a gas cylinder, TIF-2 to a sponge and TIF-3 to a fragile soda can that is crushed on emptying to give TIF-4.     

Chelating effect as a driving force for the selective formation of heteroligated Pt(II) complexes with bidentate phosphino-chalcoether ligands

The halide-induced ligand rearrangement reaction (HILR) has been employed to provide selective and exclusive in situ formation of heteroligated Rh(I), Pd(II), and Pt(II) complexes with bidentate phosphino-chalcoether ligands. To gain insights on the nature of this unique reaction, we explored this process via the stepwise addition of bidentate phosphino-chalcoether (P, X; X = S or Se) and relevant monodentate phosphine ligands with a Pt(II) metal precursor. The corresponding monoligated complexes were obtained in quantitative yields by reacting 1 equiv of a P, X bidentate ligand with Pt(II) and were fully characterized via single crystal X-ray diffraction studies and heteronuclear ((31)P, (77)Se, and (195)Pt) NMR spectroscopy in solution. These species were further reacted with a second equivalent of either a bidentate ligand or the monodentate ethyl diphenylphosphine ligand, resulting in the clean formation of the heteroligated species or, in the case of the monodentate ligand with an electron-withdrawing bidentate ligand, a mixture of products. On the basis of competitive exchange reactions between these heteroligated, homoligated, and monoligated complexes, we conclude that ligand chelation plays a crucial role in the Pt(II) HILR. The in situ preferable formation of the stable monoligated complex allows for ligand sorting to occur in these systems. In all cases where the heteroligated product results, the driving force to these species is ligand chelation.     

A total synthesis of (±)-α-cyclopiazonic acid using a cationic cascade as a key step

The indole alkaloid α-cyclopiazonic acid 1 has been synthesised by a route, which features at its core an acid-catalysed cationic cascade cyclisation terminated by a sulfonamide group.     

Ion Mobility Mass Spectrometry for Extracting Spectra <Emphasis Type="Italic">of N</Emphasis>-Glycans Directly from Incubation Mixtures Following Glycan Release: Application to Glycans from Engineered Glycoforms of Intact,Folded HIV gp120

The analysis of glycosylation from native biological sources is often frustrated by the low abundances of available material. Here, ion mobility combined with electrospray ionization mass spectrometry have been used to extract the spectra of N-glycans released with PNGase F from a serial titration of recombinantly expressed envelope glycoprotein, gp120, from the human immunodeficiency virus (HIV). Analysis was also performed on gp120 expressed in the α-mannosidase inhibitor, and in a matched mammalian cell line deficient in GlcNAc transferase I. Without ion mobility separation, ESI spectra frequently contained no observable ions from the glycans whereas ions from other compounds such as detergents and residual buffer salts were abundant. After ion mobility separation on a Waters T-wave ion mobility mass spectrometer, the N-glycans fell into a unique region of the ion mobility/m/z plot allowing their profiles to be extracted with good signal:noise ratios. This method allowed N-glycan profiles to be extracted from crude incubation mixtures with no clean-up even in the presence of surfactants such as NP40. Furthermore, this technique allowed clear profiles to be obtained from sub-microgram amounts of glycoprotein. Glycan profiles were similar to those generated by MALDI-TOF MS although they were more susceptible to double charging and fragmentation. Structural analysis could be accomplished by MS/MS experiments in either positive or negative ion mode but negative ion mode gave the most informative spectra and provided a reliable approach to the analysis of glycans from small amounts of glycoprotein.     

Lamellar crystalline self-assembly behaviour and solid lipid nanoparticles of a palmityl prodrug analogue of Capecitabine--a chemotherapy agent

An amphiphile prodrug, 5′-deoxy-5-fluoro-N⁴-(palmityloxycarbonyl) cytidine or 5′-deoxy-5-fluoro-N⁴-(hexadecanaloxycarbonyl) cytidine (5-FCPal), consisting of the same head group as the commercially available chemotherapeutic agent Capecitabine, linked to a palmityl hydrocarbon chain via a carbamate bond is reported. Thermal analysis of this prodrug indicates that it melts at ∼115 °C followed quickly by degradation beginning at ∼120 °C. The neat solid 5-FCPal amphiphile acquires a lamellar crystalline arrangement with a d-spacing of 28.6 ± 0.3 Å, indicating interdigitation of the hydrocarbon chains. Under aqueous conditions, solid 5-FCPal is non-swelling and no lyotropic liquid crystalline phase formation is observed. In order to assess the in vitro toxicity and in vivo efficacy in colloidal form, solid lipid nanoparticles (SLNs) with an average size of ∼700 nm were produced via high pressure homogenization. The in vitro toxicity of the 5-FCPal SLNs against several different cancer and normal cell types was assessed over a 48 h period, and IC₅₀ values were comparable to those observed for Capecitabine. The in vivo efficacy of the 5-FCPal SLNs was then assessed against the highly aggressive mouse 4T1 breast cancer model. To do so, the prodrug SLNs were administered orally at 3 different dosages (0.1, 0.25, 0.5 mmol/mouse/day) and compared to Capecitabine delivered at the same dosages. After 21 days of receiving the treatments, the 0.5 mmol dose of 5-FCPal exhibited the smallest average tumour volume. Since 5-FCPal is activated in a similar manner to Capecitabine via a 3 step enzymatic pathway with the final step occurring preferentially at the tumour site, formulation of the prodrug into SLNs combines the advantage of selective, localized activation with the sustained release properties of nanostructured amphiphile self-assembly and multiple payload materials thereby potentially creating a more effective anticancer agent.     

Ir(PCy3)2(H)2(H2B-NMe2)]+ as a latent source of aminoborane: probing the role of metal in the dehydrocoupling of H3B⋅NMe2H and retrodimerisation of [H2BNMe2]2

The Ir^III fragment {Ir(PCy₃)₂(H)₂}⁺ has been used to probe the role of the metal centre in the catalytic dehydrocoupling of H₃B?NMe₂H ( A ) to ultimately give dimeric aminoborane [H₂BNMe₂]₂ ( D ). Addition of A to [Ir(PCy₃)₂(H)₂(H₂)₂][BAr^F₄] ( 1 ; Ar^F=(C₆H₃(CF₃)₂), gives the amine‐borane complex [Ir(PCy₃)₂(H)₂(H₃B?NMe₂H)][BAr^F₄] ( 2 a ), which slowly dehydrogenates to afford the aminoborane complex [Ir(PCy₃)₂(H)₂(H₂B? NMe₂)][BAr^F₄] ( 3 ). DFT calculations have been used to probe the mechanism of dehydrogenation and show a pathway featuring sequential BH activation/H₂ loss/NH activation. Addition of D to 1 results in retrodimerisation of D to afford 3 . DFT calculations indicate that this involves metal trapping of the monomer–dimer equilibrium, 2 H₂BNMe₂ ? [H₂BNMe₂]₂. Ruthenium and rhodium analogues also promote this reaction. Addition of MeCN to 3 affords [Ir(PCy₃)₂(H)₂(NCMe)₂][BAr^F₄] ( 6 ) liberating H₂B? NMe₂ ( B ), which then dimerises to give D . This is shown to be a second‐order process. It also allows on‐ and off‐metal coupling processes to be probed. Addition of MeCN to 3 followed by A gives D with no amine‐borane intermediates observed. Addition of A to 3 results in the formation of significant amounts of oligomeric H₃B?NMe₂BH₂?NMe₂H ( C ), which ultimately was converted to D . These results indicate that the metal is involved in both the dehydrogenation of A , to give B , and the oligomerisation reaction to afford C . A mechanism is suggested for this latter process. The reactivity of oligomer C with the Ir complexes is also reported. Addition of excess C to 1 promotes its transformation into D , with 3 observed as the final organometallic product, suggesting a B? N bond cleavage mechanism. Complex 6 does not react with C , but in combination with B oligomer C is consumed to eventually give D , suggesting an additional role for free aminoborane in the formation of D from C .     

Bis(phosphinic)diamido yttrium amide, alkoxide, and aryloxide complexes: an evaluation of lactide ring-opening polymerization initiator efficiency

The synthesis and characterization of a series of bis(phosphinic)diamido yttrium alkoxide, amide, and aryloxide initiators are reported. The new complexes are characterized using multinuclear nuclear magnetic resonance (NMR) spectroscopy, elemental analysis, and, in some cases, X-ray crystallography. The alkoxide complexes are all dimeric in both the solid state and in solution, as are the amide complexes substituted with iso-propyl or phenyl groups on the phosphorus atoms. On the other hand, increasing the steric hindrance of the phosphorus substituents (tert-butyl), enables isolation of mononuclear yttrium amide complexes with either 2,2-dimethylpropylene or ethylene diamido ligand backbones. The complex of 2,6-di-tert-butyl-4-methylphenoxide is also mononuclear. All the new complexes are efficient initiators for rac-lactide ring-opening polymerization. The polymerization kinetics are compared and pseudo first order rate constants, k(obs), determined. The polymerization control is also discussed, by monitoring the number-averaged molecular weight, M(n), and polydispersity index, PDI, obtained using gel permeation chromatography (GPC). The alkoxide complexes are the most efficient initiators, showing very high rates and good polymerization control, behavior consistent with rapid rates of initiation. The phenoxide and amide complexes are less efficient as manifest by nonlinear regions in the kinetic plots, lower values for k(obs), and reduced polymerization control. One of the mononuclear yttrium amide complexes shows heteroselectivity in the polymerization of rac-lactide; however, this effect is reduced on changing the initiating group to phenoxide or on changing the ancillary ligand diamido backbone group.     

Interplay of symmetries of block polymers and confining geometries

The morphologies that block polymers exhibit under various types of confinement are reviewed with emphasis on experimental results and theoretical predictions. Confining geometries in all three dimensions are considered and special attention is paid to cylindrical and spherical boundary conditions. Past experimental techniques and theoretical understanding are discussed and an outlook for future advances due to the possibility for novel, well ordered and aligned morphologies to occur when polymers are confined between surfaces of varying distance, curvature, and surface chemistry is provided. Confinement creates new morphologies which are not present in the bulk, indicating that the confined thermodynamic boundary conditions result in phase behavior that is distinct from the bulk and that there is the possibility for new phases and order-order transitions to be discovered as future researchers impose new types of confinement and explore a greater range of block polymer architecture, composition and molecular weights. The article concludes with a brief introduction of interference lithography, which can be used to form arbitrary and novel boundary conditions, and a perspective on the future outlook of the phase behavior of confined block polymers.     

Modifications to the Vilsmeier‐Haack formylation of 1,4‐dimethylcarbazole and its application to the synthesis of ellipticines

An improved method for the preparation of 3‐formyl‐1,4‐dimethylcarbazole, a key intermediate in the synthesis of ellipticine, is presented. Conditions of the Vilsmeier‐Haack reaction have been modified to facilitate the production of 3‐formyl‐1,4‐dimethylcarbazole as a major product leading to an overall improvement in yield of ellipticine from 3% to 14%. This approach was also applied to the synthesis of 6‐methylellipticine and 9‐methoxyellipticine. J. Heterocyclic Chem., (2011).     

Consecutive three-component synthesis of 3-(hetero)aryl-1H-pyrazoles with propynal diethylacetal as a three-carbon building block

A novel consecutive three-component synthesis of 3-(hetero)aryl-1H-pyrazoles via room temperature Sonogashira arylation of propynal diethylacetal used as a propargyl aldehyde synthetic equivalent has been disclosed. The final acetal cleavage-cyclocondensation with hydrazine hydrochloride at 80 °C rapidly furnishes the title compounds in a one-pot fashion.