Mononuclear and binuclear manganese(II) complexes with tridentate bis-benzimidazolyl ligands

Summary Manganese(II) complexes of bis(2-benzimidazolylmethyl) ether (DGB), bis(2-benzimidazolylmethyl) sulphide (TGB) and the n-butyl derivative of DGB (BDGB) were prepared and characterised. The solution e.p.r. spectrum of [Mn(TGB)Cl₂] in DMF at 143 K is commensurate with an axially distorted monomeric manganese(II) complex, room temperature magnetic moment (6.04 B.M.) per manganese(II) atom being in the range found for other d⁵ monomeric manganese(II) complexes. The solution e.p.r. spectrum of [Mn(BDGB)Cl₂]-2H₂O in DMF at 143 K indicates the presence of two equivalent manganese(II) ions coupled by an exchange interaction, fostered by bridging chlorides. Evidence for this is provided by a nearly isotropic 11 line hyperfine structure of ⁵⁵Mn, with a coupling constant 45 ± 5G. Contact-shifted ¹H n.m.r. data also supports an exchange coupled dimeric manganese complex. The room temperature magnetic moment, 5.64 B.M., per manganese(II) indicates quenching of the magnetic moment below that of monomeric manganese(II) ion. The [Mn(DGB)Cl₂]·H₂O complex exhibits a magnetic moment of 6.02 B.M. per manganese, indicating a monomeric manganese complex. E.p.r. data of the complex diluted in an analogous Zn-DGB complex (1∶20) correlates well for D = 0.22cm⁻¹ and λ ∼- 0.267. The [Mn(DGB)-(C1O₄)₂] and [Mn(BDGB)(ClO₄)₂] complexes, diluted in analogous Zn-DGB and Zn-BDGB complexes (1∶20), show a strong single e.p.r. line at g _eff ∼- 2. The complexes have low magnetic moments; 4.44 B.M./Mn and 4.39 B.M./Mn, at room temperature.     

Calculation of the minimum energy conformation of acetylcholine using a global optimization technique

The conformational energy of acetylcholine is minimized with respect to the distances between nonbonded atoms with the help of the Bremermann method of unconstrained global optimization. The set of distances for which the energy is the absolute minimum is then used to calculate the coordinates of all the atoms and hence the conformation of the molecule. The simplest type of potential function, namely the classical potential function is chosen for the calculation. The major advantages of this method are (i) that the starting point need not be close to the actual solution, (ii) that it gives the global minimum, irrespective of the starting point, (iii) that it is very general and can be used for any type of potential function, and (iv) that it does not require the computation of gradients. The results obtained are in very good agreement with those of other workers.     

Ligand-free copper nanoparticle promoted N-arylation of azoles with aryl and heteroaryl iodides

A relatively mild, efficient, and inexpensive method for the nucleophilic aromatic substitution of the N–H heterocycles with various aryl and heteroaryl iodides using copper nanoparticles (Cu-NP) is reported. The coupling reaction has been successfully achieved with moderate to good yields.     

Phosphorylation and Thiophosphorylation of 2-Substituted Benzoxazoles and Their Biological Activities

Novel organophosphorus compounds have been conveniently prepared using 2-(2′-hydroxynapthyl)benzoxazole and 2-(2′-aminophenyl)benzoxazole as starting materials. Phosphorylation and thiophosphorylation was performed using different molar ratio (1:1, 1:2 and 1:3) of phosphorus oxychloride/thiophosphoryl chloride and substituted benzoxazole. The toxicity of newly synthesized phosphorylated/thiophosphorylated compounds was tested on Aspergillus niger and Fusarium oxysporium. All were found antifungal agents. Plausible structures have been proposed on the basis of IR, ¹ H NMR, ³¹ P NMR spectral studies.     

Synthesis and Antimicrobial Studies of Organophosphates Derived From 2-(2″-Hydroxynaphthyl)Benzoxazole

Abstract

A series of biologically active phenoxy derivatives of 2-substituted benzoxazole organophosphates have been synthesized by the reaction of O-(naphthyl benzoxazolyl-2-) phosphorodichloridate/phosphorodichloridothioate with phenol/4-chlorophenol/4-nitroph- enol in 1:1 and 1:2 molar ratios. These compounds have been characterized on the basis of elemental analysis, IR, ¹H NMR, ³¹P NMR, and mass spectral studies. The antibacterial activity of these 2-substituted benzoxazole phenoxy derivatives has been evaluated against pathogenic bacteria Staphylococcus aureus (+ve) and Escherichia coli (?ve). The antifungal activity of these 2-substituted benzoxazole phenoxy derivatives has been evaluated against pathogenic fungi Aspergillus niger and Fusarium oxysporium. All compounds were found to have significant antibacterial and antifungal activity.     

Molecular modeling of neurokinin B and tachykinin NK₃ receptor complex

The tachykinin receptor NK? is a member of the rhodopsin family of G-protein coupled receptors. The NK? receptor has been regarded as an important drug target due to diverse physiological functions and its possible role in the pathophysiology of psychiatric disorders, including schizophrenia. The NK3 receptor is primarily activated by the tachykinin peptide hormone neurokinin B (NKB) which is the most potent natural agonist for the NK? receptor. NKB has been reported to play a vital role in the normal human reproduction pathway and in potentially life threatening diseases such as pre-eclampsia and as a neuroprotective agent in the case of neurodegenerative diseases. Agonist binding to the receptor is a critical event in initiating signaling, and therefore a characterization of the structural features of the agonists can reveal the molecular basis of receptor activation and help in rational design of novel therapeutics. In this study a molecular model for the interaction of the primary ligand NKB with its G-protein coupled receptor NK? has been developed. A three-dimensional model for the NK? receptor has been generated by homology modeling using rhodopsin as a template. A knowledge based docking of the NMR derived bioactive conformation of NKB to the receptor has been performed utilizing limited ligand binding data obtained from photoaffinity labeling and site-directed mutagenesis studies. A molecular model for the NKB-NK? receptor complex obtained sheds light on the topographical features of the binding pocket of the receptor and provides insight into the biochemical data currently available for the receptor.     

Synthesis,characterization, and biological activity of organophosphates derived from substituted benzoxazole

The reaction of phosphorus oxychlo‐ ride/phosphorus thiochloride with 2‐(2′‐mercapto‐ phenyl)benzoxazole in 1:1, 1:2, and 1:3 molar ratio in the presence of stoichiometric amounts of triethyl‐ amine has afforded a series of organophosphates. These organophosphates have been characterized by elemental analyses, infrared, ¹H NMR, ³¹P NMR, and mass spectral studies. The antifungal activity of these organophosphates has been evaluated against pathogenic fungi Aspergillus niger and Fusarium oxysporium. The antifungal screening data reveal that these compounds are more fungitoxic than 2‐(2′‐mercaptophenyl) benzoxazole. These organophosphates were also found to be insecticidal when tested against Periplenata americana.© 2009 Wiley Periodicals, Inc. Heteroatom Chem 20:309–315, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20551     

Calculation of the minimum energy conformation of biomolecules by using a global optimization technique. V. Preferred conformations of the thyrotropin-releasing hormone

The preferred conformations of the thyrotropin-releasing hormone (TRH) have been calculated by the global optimization method proposed earlier by us. [G. Subba Rao, R. S. Tyagi, and R. K. Mishra, J. Theor. Biol. 90 , 377 (1981)]. The potential function used comprises the electrostatic, nonbonded, torsional and hydrogen-bonding terms. The results are in good agreement with the crystal structures of TRH. No intramolecular hydrogen bonding is found to occur.     

Binding energy of triton and scattering lengths in neutron-deuteron collision in Faddeev formalism with local potential

A separable representation for the off-shell two-body t-matrix for a local Hulthén potential is presented, in which deuteron states are chosen as the expansion bases. Using the Faddeev equations with these t-matrices as input, the ground state energy of the triton and doublet and quartet scattering lengths in neutron-deuteron scattering, have been computed. The results have been compared with the experimental findings and the theoretical results of Sitenko et al. obtained in the Sturmian function representation with the same Hulthén potential.     

Visible Light-Induced Sulfonylation/Arylation of Styrenes in a Double Radical Three-Component Photoredox Reaction

Simultaneous sulfonylation/arylation of styrene derivatives is achieved in a photoredox-catalyzed three-component reaction using visible light. A broad variety of difunctionalized products is accessible in mostly excellent yields and high diastereoselectivity. The developed reaction is scalable and suitable for the modification of styrene-functionalized biomolecules. Mechanistic investigations suggest the transformation to be operating through a designed sequence of radical formation and radical combination.