Stereoselective total synthesis of (+)-cardiobutanolide

Stereoselective synthesis of styryllactone (+)-cardiobutanolide was accomplished in good overall yield from d-(-)-tartaric acid. Key features of the synthesis include the elaboration of a gamma-hydroxy butyramide obtained from the dimethylamide of tartaric acid, involving a combination of the addition of 1,3-dithian-2-yllithium and stereoselective reduction.     

Catalytic asymmetric syntheses of tyrosine surrogates

Amino acid esters 5-11 as tyrosine mimics have been synthesized in excellent enantioselectivity (up to 99.6% ee) and in good overall chemical yields. The key step in the sequence was the Burk's [Rh(COD)(2R,5R)-Et-DuPhos]BF4-catalyzed asymmetric hydrogenation of enamides with a variety of reactive functional groups.     

Stereoselective total synthesis of bioactive styryllactones (+)-goniofufurone, (+)7-epi-goniofufurone, (+)-goniopypyrone, (+)-goniotriol, (+)-altholactone, and (-)-etharvensin

Stereoselective total synthesis of biologically active styryllactones 7-epi-goniofufurone, goniofufurone, goniopypyrone, goniotriol, altholactone, and etharvensin was achieved in high overall yields from a common intermediate derived from d-(-)-tartaric acid. It is based on the utility of a masked tetrol, comprising an alkene tether and four contiguous hydroxy groups. The pivotal reaction sequence involves hydroxy-directed lactonization via the oxidation of alkene, and subsequent elaboration to styryllactones. The masked tetrol was prepared by the extension of gamma-phenyl-gamma-hydroxy butyramide, readily obtained from the bis-dimethylamide of tartaric acid, employing a combination of selective Grignard additions and a stereoselective reduction.     

UV excited green luminescence of SrAl<Subscript>2</Subscript>O<Subscript>4</Subscript>:Eu<Superscript>2+</Superscript>, Dy<Superscript>3+</Superscript> nanophosphor

Eu, Dy co-doped strontium aluminate nanophosphors were prepared by the combustion synthesis method. Their structure and morphology were investigated by X-ray diffraction (XRD), scanning electron microscopy, transmission electron microscopy (TEM), and Fourier transform infrared spectroscopy. According to the XRD and the TEM analysis, the average crystallite size was found to be in the nanometer range. The phase structure of the prepared nanophosphor is consistent with a standard monoclinic phase with a space group P2₁. The prepared SrAl₂O₄:Eu²⁺, Dy³⁺ nanophosphor emitted green light with a peak at 510 nm showing blue shift, which is due to the reduction in the particle size. Two distinct peaks were observed in the ML intensity versus time curve. The two peaks in ML indicate the presence of charge transfer in an ML process.     

Calculating distribution coefficients based on multi-scale free energy simulations: an evaluation of MM and QM/MM explicit solvent simulations of water-cyclohexane transfer in the SAMPL5 challenge

One of the central aspects of biomolecular recognition is the hydrophobic effect, which is experimentally evaluated by measuring the distribution coefficients of compounds between polar and apolar phases. We use our predictions of the distribution coefficients between water and cyclohexane from the SAMPL5 challenge to estimate the hydrophobicity of different explicit solvent simulation techniques. Based on molecular dynamics trajectories with the CHARMM General Force Field, we compare pure molecular mechanics (MM) with quantum-mechanical (QM) calculations based on QM/MM schemes that treat the solvent at the MM level. We perform QM/MM with both density functional theory (BLYP) and semi-empirical methods (OM1, OM2, OM3, PM3). The calculations also serve to test the sensitivity of partition coefficients to solute polarizability as well as the interplay of the quantum-mechanical region with the fixed-charge molecular mechanics environment. Our results indicate that QM/MM with both BLYP and OM2 outperforms pure MM. However, this observation is limited to a subset of cases where convergence of the free energy can be achieved.     

Remarkable Anion‐Dependent Spin‐State Switching in Diiron(III) μ‐Hydroxo Bisporphyrins: What Role Do Counterions Play?

Addition of 2,4,6‐trinitrophenol (HTNP) to an ethene‐bridged diiron(III) μ‐oxo bisporphyrin ( 1 ) in CH₂Cl₂ initially leads to the formation of diiron(III) μ‐hydroxo bisporphyrin ( 2? TNP) with a phenolate counterion that, after further addition of HTNP or dissolution in a nonpolar solvent, converts to a diiron(III) complex with axial phenoxide coordination ( 3? (TNP)₂). The progress of the reaction from μ‐oxo to μ‐hydroxo to axially ligated complex has been monitored in solution by using ¹H NMR spectroscopy because their signals appear in three different and distinct spectral regions. The X‐ray structure of 2? TNP revealed that the nearly planar TNP counterion fits perfectly within the bisporphyrin cavity to form a strong hydrogen bond with the μ‐hydroxo group, which thus stabilizes the two equivalent iron centers. In contrast, such counterions as I₅, I₃, BF₄, SbF₆, and PF₆ are found to be tightly associated with one of the porphyrin rings and, therefore, stabilize two different spin states of iron in one molecule. A spectroscopic investigation of 2? TNP has revealed the presence of two equivalent iron centers with a high‐spin state (S=5/2) in the solid state that converts to intermediate spin (S=3/2) in solution. An extensive computational study by using a range of DFT methods was performed on 2? TNP and 2 ⁺, and clearly supports the experimentally observed spin flip triggered by hydrogen‐bonding interactions. The counterion is shown to perturb the spin‐state ordering through, for example, hydrogen‐bonding interactions, switched positions between counterion and axial ligand, ion‐pair interactions, and charge polarization. The present investigation thus provides a clear rationalization of the unusual counterion‐specific spin states observed in the μ‐hydroxo bisporphyrins that have so far remained the most outstanding issue.     

Novel 7‐Nitro‐1‐(Piperidin‐4‐yl)‐4,5‐Dihydro‐[1,2,4] Triazolo[4,3‐a]Quinoline‐Sulphonamide Derivatives as Antimicrobial Agents: Design,Synthesis, and Bio‐Activity

In attempt to search for more potent antimicrobial agents, a series of 7‐nitro‐1‐(piperidin‐4‐yl)‐4,5‐dihydro‐[1,2,4]triazolo[4,3‐a]quinoline‐derived sulphonamides were synthesized. Their structures were established by elemental analyses, IR, and NMR (¹H and ¹³C) spectral data. The antibacterial activity of the obtained compounds was investigated against different Gram‐negative (Escherichia coli and Pseudomonas aeruginosa) and Gram‐positive (Bacillus subtilis and Staphylococcus aureus) bacteria and antifungal activity against two fungal strains (Aspergillus niger and Aspergillus clavatus) using disk diffusion method at various concentrations (20, 40, 60, and 80 μg/mL). The study reveals that most of the title compounds showed significant antibacterial and fungal activity when compared with their respective standards streptomycin and griseofulvin.     

Electronic structure and conformational analysis of P218: An antimalarial drug candidate

P218 is one of the very important and recent lead compounds for antimalarial research. The 3D structural and electronic details of P218 are not available. In this article, quantum chemical studies to understand the possible 3D structures of P218 are reported and compared with 3D structures from the active site cavities of hDHFR and PfDHFR. The neutral P218, can adopt open chain as well as cyclic arrangements. Under implicit solvent condition a zwitterionic‐cyclic conformer is found to be quite possible. Microsolvation studies using explicit water molecules indicate that one water molecule may bridge the two ends of zwitterionic‐cyclic P218. It was observed that the protonation occurs preferentially at N¹ position of the 2,4‐diaminopyrimidine ring, with a proton affinity of 274.49 kcal/mol (implicit solvent phase) and 236.35 kcal/mol (gas phase). A dimer of P218 may be zwitterionic dimer, the dimer formation can release upto ～28.60 kcal/mol (implicit solvent phase).     

Iron(III) metallomesogen of [N2O2] donor Schiff base ligand containing 4-substituted alkoxy chains

Two new square pyramidal iron(III)-complexes of ‘salen’-type Schiff base ligands containing 4-substituted long alkoxy arms on the aromatic rings, [Fe(4-C₁₆H₃₃O)₂salcn)]Cl and [Fe(4-C₁₆H₃₃O)₂salophen)]Cl {salcn = N,N?-cyclohexanebis(salicylideneiminato) and salophen = N,N?-phenylenebis(salicylideneiminato)}, have been successfully synthesised, and their mesomorphic property investigated. The ligands and complexes were characterised by elemental analyses, UV–Vis, FT-IR, ESI–MS, ¹H and ¹³C NMR (for ligands only). The phase behaviour of the iron(III) complexes were ascertained by differential scanning calorimetry, polarising optical microscopy and variable temperature PXRD study. Ligands are non-mesomorphic, however, mesomorphism got induced upon complexation with the iron(III) centre. X-ray diffraction study revealed a layer-like arrangement of the five coordinated mesomorphic iron(III) complexes. The mesophase is stable over a wide range of temperature. The density functional theory calculations were carried out using Gaussian 09 program at B3LYP level using unrestricted 6–31G (d, p) basis set to obtain the optimised geometry of the iron(III) complexes.