Alkenenitriles: conjugate additions of alkyl iodides with a silica-supported zinc-copper matrix in water

A new silica-supported zinc-copper matrix reagent promotes the conjugate addition of alkyl iodides to cyclic and acyclic alkenenitriles in water. X-ray diffraction and electron microscopy techniques suggest that the active copper species generated from elemental zinc and copper(I) iodide is finely dispersed, zerovalent copper. Alkyl iodides react with the silica-supported reagent to generate putative radicaloid intermediates that efficiently add to alkenenitriles to provide beta-substituted nitriles. Conjugate additions to acyclic and cyclic 5-7-membered alkenenitriles are most effective for primary alkyliodides, although secondary and tertiary alkyliodides are viable reaction partners. The strategy addresses the challenge of performing conjugate additions to disubstituted alkenenitriles and demonstrates the beneficial role of the silica-supported reagent.     

Nanoscale patterning in mixed fluorocarbon-hydrocarbon phospholipid bilayers

A growing body of literature suggests that fluorocarbons can direct self-assembly within hydrocarbon environments. We report here the fabrication and characterization of supported lipid bilayers (SLBs) composed of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and a synthetic, fluorocarbon-functionalized analogue, 1. AFM investigation of these model membranes reveals an intricate, composition-dependent domain structure consisting of approximately 50 nm stripes interspersed between approximately 1 microm sized domains. Although DSC of 1 showed a phase transition near room temperature, DSC of DPPC:1 mixtures exhibited complex phase behavior suggesting domain segregation. Finally, temperature-dependent AFM of DPPC:1 bilayers shows that, while the stripe structures can be melted above the Tm of 1, the stripes and domains result from immiscibility of the hydrocarbon and fluorocarbon lipid gel phases. Fluorination appears to be a promising strategy for chemical self-assembly in two dimensions. In particular, because no modification is made to the lipid headgroups, it may be useful for nanopatterning biologically relevant ligands on bilayers in vitro or in living cells.     

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.     

1,10-Phenanthrolines with tunable luminescence upon protonation: a spectroscopic and computational study

We have synthesized nine 2,9-aryl-substituted 1,10-phenanthrolines (1-9) with the aim of rationalizing their electronic absorption and luminescence properties in both the basic and acid form. The latter are generated upon addition of trifluoroacetic acid to CH2Cl2 solutions of 1-9 and their formation is unambiguously evidenced by UV-vis absorption and 1H NMR spectroscopy. 1-9 can be subdivided into three groups, depending on their chemical structure and luminescence behavior. 1-3 are symmetrically substituted p-dianisylphenanthrolines which exhibit relatively intense violet fluorescence in CH2Cl2 (lambda(max) ca. 400 nm, Phi(fl) = 0.12-0.33) and are strongly quenched and substantially red-shifted upon protonation (lambda(max) ca. 550 nm, Phi(fl) = 0.010-0.045). 4-5 are 2,6-dimethoxyphenylphenanthrolines with faint luminescence in both the basic and acid form. 6-9 are various unsymmetric aryl-substituted-phenanthrolines and their relatively strong fluorescence (lambda(max) ca. 400 nm, Phi(fl) = 0.08-0.24) is red-shifted and substantially enhanced following protonation (lambda(max) ca. 475 nm, Phi(fl) = 0.16-0.50). The markedly different trends in the electronic absorption and fluorescence spectra are rationalized by means of both time-dependent Hartree-Fock and density functional theory by using hybrid functionals to assign the excited states. Interestingly, protonation of 1-9 also occurs in spin-coated films simply exposed to vapors of acid, and the reaction can be signaled by the color tuning of the emission signal (vapoluminescence). This observation makes substituted phenanthrolines potential candidates as proton sensors also in the solid phase.     

C?C Cross‐Coupling Reactions of O6‐Alkyl‐2‐Haloinosine Derivatives and a One‐Pot Cross‐Coupling/O6‐Deprotection Procedure

Reaction conditions for the C? C cross‐coupling of O⁶‐alkyl‐2‐bromo‐ and 2‐chloroinosine derivatives with aryl‐, hetaryl‐, and alkylboronic acids were studied. Optimization experiments with silyl‐protected 2‐bromo‐O⁶‐methylinosine led to the identification of [PdCl₂(dcpf)]/K₃PO₄ in 1,4‐dioxane as the best conditions for these reactions (dcpf=1,1′‐bis(dicyclohexylphosphino)ferrocene). Attempted O⁶‐demethylation, as well as the replacement of the C‐6 methoxy group by amines, was unsuccessful, which led to the consideration of Pd‐cleavable groups such that C? C cross‐coupling and O⁶‐deprotection could be accomplished in a single step. Thus, inosine 2‐chloro‐O⁶‐allylinosine was chosen as the substrate and, after re‐evaluation of the cross‐coupling conditions with 2‐chloro‐O⁶‐methylinosine as a model substrate, one‐step C? C cross‐coupling/deprotection reactions were performed with the O⁶‐allyl analogue. These reactions are the first such examples of a one‐pot procedure for the modification and deprotection of purine nucleosides under C? C cross‐coupling conditions.     

Synthesis,characterization, antibacterial and antifungal activity of 2‐(aryl)‐3‐(3‐((8‐hydroxyquinolin‐5‐yl)diazenyl)phenyl)thiazolidin‐4‐ones

5‐((3‐Aminophenyl)diazenyl)quinolin‐8‐ol ( 1 ) was synthesized by diazotization reaction and coupled with 8‐hydroxyquinoline moiety. This amine on facile condensation with aromatic aldehydes in presence of glacial acetic acid and ethanol affords anils ( 2 ). These anils on cyclocondensation reaction with thioglycolic acid (i.e., mercaptoacetic acid) yield the titled compound ( 3 ). The structure of the newly synthesized anils ( 2 ) and thiazolidinones ( 3 ) has been confirmed by elemental analysis and spectral analysis. The titled compounds have been screened against different bacterial and fungal strains. J. Heterocyclic Chem., (2011).     

An expeditious one‐pot synthesis of substituted phenylazetidin‐2‐ones in the presence of zeolite

In this study, one‐pot rapid and efficient series of phenylazetidin‐2‐ones were synthesized from N,N‐dimethylaminobenzaldehyde, different substituted aromatic amines and phenylacetyl chloride in the presence of zeolite catalyst under microwave irradiation. We also reported schiff bases (1a–j) by classical and conventional microwave technique. The titled compounds are evaluated for their antimicrobial properties. The activities are due to C?O, C? N, linkages in 2‐azetidinones. All the compounds have shown comparable antibacterial activities. J. Heterocyclic Chem., (2011).     

Design,synthesis and screening of some novel benzoxazole based 1,3,4-oxadiazoles as potential antimicrobial agents

A series of novel 2-(5-substituted-[1,3,4]oxadiazol-2-yl)-benzoxazoles (7a–h) were synthesized in good yields in two different directions by involving benzoxazole-2-carboxylic acid (1) as raw material and benzoxazole-2-carbonyl chloride (2), benzoxazole-2-carboxylic acid methyl ester (3), benzoxazole-2-carboxylic acid hydrazide (4), benzoxazole-2-carboxylic acid N′-acetyl hydrazide (5a–d) and benzoxazole-2-carboxylic acid-ethylidene-hydrazides (6a–d) as reactive intermediates. The chemical structures of all the synthesized compounds were elucidated by their IR, ¹H NMR and ¹³C NMR and mass spectral data. Further, the target compounds were screened for their antimicrobial activity against various Gram-positive and Gram-negative bacteria.     

Antimony Trioxide as an Efficient Lewis Acid Catalyst for the Synthesis of 5-Substituted 1H-Tetrazoles

Sb₂O₃ was found to be effective as a catalyst for a smooth (2 + 3) cycloaddition of sodium azide with nitriles to afford 5-substituted 1H-tetrazoles in good yields.