Stereoselective synthesis of beta-substituted phenylalanine-beta-phenylisoserine-derived tripeptides using N-cinnamoyl-L-proline as template: synthesis of structural analogues of HIV protease inhibitors

N-Cinnamoyl-L-proline can be used as a template on which beta-substituted phenylalanine and beta-phenylisoserine residues can be synthesized leading to tripeptide derivatives as structural analogues of HIV protease inhibitors.     

The first total synthesis of lipid II: the final monomeric intermediate in bacterial cell wall biosynthesis

Bacterial peptidoglycan is composed of a network of beta-[1,4]-linked glyan strands that are cross-linked through pendant peptide chains. The final product, the murein sacculus, is a single, covalently closed macromolecule that precisely defines the size and shape of the bacterial cell. The recent increase in bacterial resistance to cell wall active agents has led to a resurgence of activity directed toward improving our understanding of the resistance mechanisms at the molecular level. The biosynthetic enzymes and their natural substrates can be invaluable tools in this endeavor. While modern experimental techniques have led to isolation and purification of the biosynthetic enzymes utilized in peptidoglycan biosynthesis, securing useful quantities of their requisite substrates from natural substrates has remained problematic. In an effort to address this issue, we report the first total synthesis of lipid II (4), the final monomeric intermediate utilized by Gram positive bacteria for peptidoglycan biosynthesis.     

Metformin and glitazones: does similarity in biomolecular mechanism originate from tautomerism in these drugs?

This theoretical study attempts to find out similarity between metformin and glitazone class of antidiabetic drugs. It was found that some tautomeric forms of both metformin and thiazolidinedione ring of glitazones have similar molecular electrostatic potential (MESP) surface and may bind to a common complementary surface. Complexation and docking studies were also carried out in order to support this hypothesis. Copyright © 2007 John Wiley & Sons, Ltd.     

Kinetic studies on the reduction of a nickel (III) oxime-imine complex by sulphur(IV) and selenium(IV)

The kinetics of the reduction of [Ni^III(L¹)]²⁺ (where HL¹ = 15-amino-3-methyl-4,7,10,13-tetraazapentadec-3-en-2-one oxime) by sulphur(IV) and selenium (IV) over the regions pH 2.50–8.02 and 2.01–4.00 respectively have been investigated at 30°C. Attempts were made to evaluate the reactivity of all the reacting species, of sulphur(IV) and selenium(IV) by considering suitable pH ranges. The oxidation of SC₂·H₂O and HSO ₃ ⁻ is proposed to proceed through the formation of a hydrogen-bonded adduct. The reaction with SO ₃ ²⁻ seems to follow a direct outer-sphere route which is well supported by Marcus crossrelation calculation. The oxidation of HSeO _l3 ⁻ is ≈ 10³ times slower than that of H₂SeO₃. The kinetic data indicate that the oxidation of sulphur(IV) by [Ni^IIIL¹)]²⁺ is much more favourable as compared to the corresponding oxidation of selenium(IV).     

Three symbol partially balanced arrays

Summary Two methods of construction of partially balanced arrays of strength two and three are presented.     

Viscous fluid motion around the Kerr-Newman black hole

In some recent papers, it has been shown that electrovac spacetimes may sometimes be interpreted as space-time filled with a viscous fluid—one such spacetime being the Kerr-Newman metric. Here the possible fluid motion in that case is studied in some detail and some interesting features of the motion in the black hole region are pointed out.     

Crystal and molecular structure of hexahydropyridine (piperidine) hydrochloride

The structure of hexahydro pyridine (piperidine), a compound of psychobiological importance, has been determined in the form of its hydrochloride by the heavy-atom technique, using three-dimensional X-ray data. Hexahydro pyridine hydrochloride, (C₅H₅N)H₆.HC1, crystallizes in the orthorhombic space groupPbcm with four molecules per unit cell of dimensionsa = 9.68(2),b = 7.30(3),c = 9.67(2) Å. The positions of the hydrogen atoms were located from a difference-Fourier synthesis. The structure was refined by the full-matrix least-squares method, using anisotropic temperature factors, leading to the finalR-value of 0.094. The hexahydro pyridine ring has a chair conformation. The crystallographic mirror plane atz = 1/4 coincides with the molecular mirror plane passing through the C1, N and C(3) atoms of the molecule in such a way that C(1)′ and C(2)′ are the mirror images of C(1) and C(2). The dihedral angles which plane I, containing C(1), C(2), C(2)′ and C(1)′, makes with plane II, containing C(2), C(3) and C(2)′, and planeIII, containing C(1), N and C(1)′, are 120.47 and 116∶42 °, respectively. The molecules are held together by a network of hydrogen bonds of type N⁺ —H ... C1^? in thexy-plane, and by van der Waals forces in thez-direction. Both the hydrogen atoms in the NH ₂ ⁺ group of the molecule take part in the formation of hydrogen bonds.     

Parallel organization of contralateral and ipsilateral prefrontal cortical projections in the rhesus monkey

Background  

The neocortical commissures have a fundamental role in functional integration across the cerebral hemispheres. We investigated whether commissural projections in prefrontal cortices are organized according to the same or different rules as those within the same hemisphere, by quantitatively comparing density, topography, and laminar origin of contralateral and ipsilateral projections, labeled after unilateral injection of retrograde tracers in prefrontal areas.     

Absorption spectrometric study of charge transfer complex formation between 4-acetamidophenol (paracetamol) and a series of quinones including vitamin K3

The formation of charge transfer (CT) complexes of 4-acetamidophenol (commonly called 'paracetamol') and a series of quinones (including Vitamin K3) has been studied spectrophotometrically in ethanol medium. The vertical ionisation potential of paracetamol and the degrees of charge transfer of the complexes in their ground state has been estimated from the trends in the charge transfer bands. The oscillator and transition dipole strengths of the complexes have been determined from the CT absorption spectra at 298 K. The complexes have been found by Job's method of continuous variation to have the uncommon 2:1 (paracetamol:quinone) stoichiometry in each case. The enthalpies and entropies of formation of the complexes have been obtained by determining their formation constants at five different temperatures.     

Unprecedented low Cu-N(azide)-Cu angles in end-on double azido bridged copper(II) complex

A rare asymmetric end-on double azido-bridged copper(II) complex has been synthesized and characterized structurally and magnetically. The Cu-N(azide)-Cu angle in this complex is calculated to be 89.1 degrees. This is unusually low in comparison to the same angle in other end-on azido-bridged binuclear complexes reported so far. Though a strong ferromagnetic interaction between the metal centers is expected in the complex, the coupling has actually been found to be antiferromagnetic, instead.