Suzuki–Miyaura coupling of quinazolines containing an unprotected NH2 group: Synthesis and biological testing of quinazoline derivatives

A robust approach to 4-amino quinazoline bi-aryl compounds was developed through Suzuki–Miyaura coupling reaction of quinazoline containing an unprotected NH₂ group and arylboronic acids. Pd(dcpf)Cl₂ was found to be an efficient catalyst for the reaction. All the compounds were evaluated for antimicrobial activity against gram-positive and gram-negative bacteria and fungi. One of the compounds, 3l, found to be more active against Candida albicans than the standard Miconazole.     

Towards nanotubular structures with large voids: dynamic heteroleptic oligophenanthroline metallonanoscaffolds and their solution-state properties

The assembly of a rigid macrocycle with two exotopic phenanthroline binding sites in combination with linear bis- or trisphenanthrolines and copper(I) ions is used to generate nanoscale double and triple deckers, the latter showing a tubular structure. With supramolecular chemistry expanding to dynamic, large cavity, nanoscale structures, it becomes increasingly important to use robust assembly protocols as well as reliable characterization techniques. To fully elucidate and to describe the dynamic nature of metallonanoscaffolds with large voids, we applied a battery of both direct and indirect solution-state characterization methods. These methods along with the conventional direct methods provide a very useful tool for characterizing tubular nanoscaffold aggregates.     

Kinetics and mechanism of certain benzoylation reactions under Vilsmeier–Haack conditions using benzamide and oxychloride in acetonitrile medium

Vilsmeier–Haack (VH) benzoylation reactions with benzaldehydes and acetophenones in acetonitrile medium obeyed second‐order reaction kinetics. Under kinetic conditions, the reactions afforded benzoyl derivatives irrespective of the nature of oxychloride (POCl₃ or SOCl₂) used for the preparation of VH reagent along with benzamide. The present finding is advantageous to understand the nature of reactive species as well as the mechanism of benzoylation. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 45: 69–80, 2013     

Metal-driven and covalent synthesis of supramolecular grids from racks: a convergent approach to heterometallic and heteroleptic nanostructures

Supramolecular nanogrids were prepared from dynamic supramolecular racks through the coupling of terminal alkynes using either a covalent (with CuCl/O(2)) or a coordinative (with [trans-(PEt(3))(2)PtCl(2)]) approach. Because of the rapid equilibration of the racks (as tested by exchange reactions), oligomeric adducts potentially formed in the coupling process will selectively furnish the nanogrids through an entropically driven self-repair mechanism. To ascertain the structural assignment, the nanogrids were also synthesized by an independent strategy.     

Model system for cell adhesion mediated by weak carbohydrate-carbohydrate interactions

The multivalent carbohydrate-carbohydrate interaction between membrane-anchored epitopes derived from the marine sponge Microciona prolifera has been explored by colloidal probe microscopy. An in situ coupling of sulfated and non-sulfated disaccharides to membrane-coated surfaces was employed to mimic native cell-cell contacts.The dynamic strength of the homomeric self-association was measured as a function of calcium ions and loading rate. A deterministic model was used to estimate the basic energy landscape and number of participating bonds in the contact zone.     

Conformations of dibenzylideneacetone: An IR spectroscopic study

The conformational analysis of dibenzylideneacetone has been carried out using IR spectroscopy. Appearance of a triplet C=O band is attributed to the coexistence of three conformers viz s-cis, cis, s-cis, trans and nonplanar s-trans, trans in contrast to the earlier findings which showed the existence of only two conformers. The relative proportions of the conformers are in the order s-cis, trans> nonplanar s-trans, trans> s-cis, cis in less polar solvents and nonplanar s-trans, trans> s-cis, trans> s-cis, cis in more polar solvents.     

Structure and thermotropic phase behavior of fluorinated phospholipid bilayers: a combined attenuated total reflection FTIR spectroscopy and imaging ellipsometry study

Lipid bilayers consisting of lipids with terminally perfluoroalkylated chains have remarkable properties. They exhibit increased stability and phase-separated nanoscale patterns in mixtures with nonfluorinated lipids. In order to understand the bilayer properties that are responsible for this behavior, we have analyzed the structure of solid-supported bilayers composed of 1,2-dipalmitoyl- sn-glycero-3-phosphocholine (DPPC) and of a DPPC analogue with 6 terminal perfluorinated methylene units (F6-DPPC). Polarized attenuated total reflection Fourier-transform infrared spectroscopy indicates that for F6-DPPC, the tilt of the lipid acyl chains to the bilayer normal is increased to 39 degrees as compared to 21 degrees for native DPPC, for both lipids in the gel phase. This substantial increase of the tilt angle is responsible for a decrease of the bilayer thickness from 5.4 nm for DPPC to 4.5 nm for F6-DPPC, as revealed by temperature-controlled imaging ellipsometry on microstructured lipid bilayers and solution atomic force microscopy. During the main phase transition from the gel to the fluid phase, both the relative bilayer thickness change and the relative area change are substantially smaller for F6-DPPC than for DPPC. In light of these structural and thermotropic data, we propose a model in which the higher acyl-chain tilt angle in F6-DPPC is the result of a conformational rearrangement to minimize unfavorable fluorocarbon-hydrocarbon interactions in the center of the bilayer due to chain staggering.     

Efficient Synthesis of Novel 3-[5-(1H-Benzimidazol-2-Ylmethanesulfonyl)-4-Phenyl-4H-(1,2,4)Triazol-3-Yl]-1H-(1,8)Naphthyridin-4-One Derivatives

Abstract

of 1,4-dihydro-4-oxo-1,8-naphthyridine-3-carbohydrazide (4) with substituted phenyl isothiocyanates (5) in ethanol under reflux for 30 min gave thiosemicarbazide derivatives 6, which on cyclization in 2N NaOH under refluxing conditions for 1 h resulted in 3-(5-mercapto- 4-phenyl-4H-1,2,4-triazol-3-yl)-1,8-naphthyridin-4(1H)-one (7). Alternatively, 7 could also be prepared from following sequence of reactions, i.e., 4 → 8 → 7. In another sequence of reactions, condensation of 7 with chloroacetic acid in dimethylformamide (DMF) and K₂CO₃ as a mild base at 120 °C for 2 h resulted in 2-((5-(1,4-dihydro-4-oxo-1,8-naphthyridin-3-yl)-4-phenyl-4H-1,2,4-triazol-3-yl)sulfanyl)acetic acid (10). The latter, on reaction with substituted o-phenylenediamine (11) in 6N HCl for 4 h yielded 3-(5-((1H-benzo[d]imidazol-2-yl)methylthio)-4-phenyl-4H-1,2,4-triazol-3-yl)-1,8-naphthyridin-4(1H)-one (12). Alternatively, 12 could also be prepared by reacting 7 with 13 in DMF and K₂CO₃ as a mild base at 120 °C for 2 h, followed by oxidation with H₂O₂ resulting in the corresponding sulfonyl derivatives 14.     

Novel phenanthroline ligands and their kinetically locked copper(I) complexes with unexpected photophysical properties

The new, sterically encumbered phenanthroline ligands 1a,b, both characterized by the presence of bulky aryl substituents (3,5-di-tert-butyl-4-methoxyphenyl, 2,4,6-trimethylphenyl) in the 2,9-position, were prepared along with their homoleptic [Cu(1a,b)2]+ and heteroleptic complexes [Cu(1a,b)(phen)]+ (phen = parent 1,10-phenanthroline). Due to the pronounced steric shielding, particularly effective in ligand 1a, the formation of the homoleptic complex [Cu(1a)2]+ becomes very slow (5 days). Once formed, the homoleptic complexes [Cu(1a,b)2]+ do not exchange ligands even with phen added in excess because they are kinetically locked due to the large tert-butylphenyl substituents at the phenanthroline unit. The electronic absorption spectra of the homoleptic complexes [Cu(1a)2]+ and [Cu(1b)2]+ evidence a strongly different ground state geometry of the two compounds, the former being substantially more distorted. This trend is also observed in the excited-state geometry, as derived by emission spectra and lifetimes in CH2Cl2 solution. The less distorted [Cu(1b)2]+, compared to [Cu(1a)2]+, is characterized by a 15- and over 100-fold stronger emission at 298 and 77 K, respectively. Noticeably, the excited-state lifetime of [Cu(1a)2]+ in solution is unaffected by the presence of molecular oxygen and only slightly shortened in nucleophilic solvents. This unusual behavior supports the idea of a complex characterized by a "locked" coordination environment.     

Supramolecular effects on the potential of redox units-nanoscaffolds internally functionalised with ferrocene units

Redox-active nanoscale racks and nanoladders were prepared as proof of principle in a directional heteroleptic approach towards internally functionalised aggregates. Using the HETTAP concept, zinc(ii) phenanthroline terpyridine nanoladder and nanorack structures with internal ferrocene units were prepared. Proximal effects exerted by the ferrocene units in the nanoladders could be read out by comparison of their redox potentials with those of nanorack R1 and of the parent ligand. The increasing compression of the ferrocene units when going from the larger nanoladder L1 to the smaller aggregate L2 manifested itself in an enlarged anodic shift. Thus, the redox potential series (vs. DMFc: E(1/2) = 0.462 V for R1, 0.480 V for L1 and 0.491 V for L2) reveals convincingly the supramolecular effect on a redox transition. At cathodic potentials the zinc(II) phenanthroline terpyridine complexes were decomposed due to a reduction of the ligands, as could be detected from an evaluation of the ferrocene redox potential.