Total syntheses of (±)-cis- and (±)-trans-neocnidilides

Total syntheses of two antimicrobial natural products (±)-cis-neocnidilide and (±)-trans-neocnidilide starting from a readily preparable cyclohexa[b]-fused 5-oxabicyclo[2.1.1]hexane derivative are presented. The diastereomeric tetrahydrofuran tricarboxylate epimers obtained from a BF₃·OEt₂ promoted Grob-type fragmentation of the oxa-bicycle derivative were converted into title natural products by employing pyridinium dichromate/acetic anhydride mediated bis-oxidative cleavage reaction.     

Application of butenonyl-C-glucosides in the synthesis of pyrazolinyl-, aminopyrimidinyl- and biphenyl methyl-��-d-C-glucopyranosides

An access to different glycohybrids involving nucleophilic addition of N- and C-nucleophiles to the butenonyl glycosides followed by cyclization and subsequent reactions is reported. In the present communication, three different prototypes, β-D-glucopyranosylmethyl pyrazolines, β-D-glucopyranosylmethyl pyrimidines and β-D-glucopyranosylmethyl biphenyls, were prepared in moderate to good yields.     

1-(1-aryl-3-ethylthiocarbamido)-4-arylaminothiocarbonyl)- piperazines as possible anticonvulsants

Several 1-(1-aryl-3-ethylthiocarbamido)-4-(arylaminothiocarbonyl)piperazines were synthesized as possible anticonvulsants. These 1,4-disubstituted piperazines were characterized by their sharp melting points and elemental and spectral analyses.     

Organoboranes : XXV. Hydridation of dialkylhaloboranes. New practical syntheses of dialkylboranes under mild conditions

Practical methods for the synthesis of dialkylboranes (R₂BH) via the hydridation of dialkylhaloboranes (R₂BX) have been developed. Convenient methods available for the preparation of R₂BX via the hydroboration of alkenes with monohaloborane complexes (H₂BX · SMe₂) make this approach valuable for the preparation of various dialkylboranes, R₂BH, many of which are not available by direct hydroboration of alkenes with borane itself. The suitability of various hydriding agents, such as borane derivatives, complex metal hydrides, and alkoxy metal hydrides, for the hydridation of R₂BX was examined, utilizing B-halo-9-borabicyclo[3.3.1]nonane as a representative dialkylhaloborane. In this case, the unusual stability of the resulting dialkylborane, 9-BBN, permits direct estimation of the reaction products by ¹¹B NMR spectroscopy. The generality of the procedure has been demonstrated.     

Antibunching,sub-poissonian photon statistics and finite bandwidth effects in resonance fluorescence

It is demonstrated that, although the fluorescent photons from a driven two-level atom always exhibit antibunching, they need not obey sub-poissonian statistics. The maximum sub-poissonian excursion of the normalized second factorial moment (〈(Δn)²〉 ? 〈n〉)/〈n〉 occurs in the transient regime where it can approach the value -1. Effect s of finite bandwidth of excitation on photon statistics are also investigated and it is shown that the photon number distribution may be narrower with finite bandwidth excitation than with coherent excitation.     

RP-LC Analysis and Hydrolytic Degradation Profile of Racecadotril

A sensitive, stability-indicating liquid-chromatographic method for analysis of racecadotril in the presence of its degradation products has been developed and validated. Efficient chromatographic separation was achieved on a C₁₈ column with a simple isocratic mobile phase—60:40 methanol–water. Quantification was by photo-diode array (PDA) detection at 220 nm. The linearity of the method was excellent over the range 1–32 μg mL^?1. The method was sensitive, with low limits of detection (20 ng mL^?1) and quantification (100 ng mL^?1). The recovery of the method was consistently good (98.7–100.9%), with low (<1%) intra-day and inter-day relative standard deviation. Robustness studies confirmed that peak area was unaffected by small changes in temperature, and mobile phase composition and flow rate. Both alkaline and acidic hydrolytic degradation were performed in methanolic solution. In alkaline medium the drug was degraded immediately; it was degraded within 90 min in acidic medium. The validated, stability-indicating, method was used for analysis of racecadotril in pharmaceutical dosage form and also to reveal the hydrolytic degradation profile of the racecadotril.     

Approximate Controllability of Fractional Order Semilinear Delay Systems

In this paper, the approximate controllability for a class of semilinear delay control systems of fractional order is proved under the natural assumption that the linear system is approximately controllable. The existence and uniqueness of the mild solution is also proved under suitable assumptions. An example is given to illustrate our main results.     

Four-body interaction energy for compressed solid krypton from quantum theory

The importance of the four-body contribution in compressed solid krypton was first evaluated using the many-body expansion method and the coupled cluster theory with full single and double excitations plus perturbative treatment of triples. All different four-atom clusters existing in the first- and second-nearest neighbor shells of face-centered cubic krypton were considered, and both self-consistent-field Hartree-Fock and correlation parts of the four-body interaction were accurately determined from the ambient conditions up to eightfold volume compression. We find that the four-body interaction energy is negative at compression ratio lower than 2, where the dispersive forces play a dominant role. With increasing the compression, the four-body contribution becomes repulsive and significantly cancels the over-softening effects of the three-body potential. The obtained equation of state (EOS) was compared with the experiments and the density-functional theory calculations. It shows that combination of the four-body effects with two- and three-body interactions leads to an excellent agreement with EOS measurements throughout the whole experimental range 0-130 GPa, and extends the prediction to 300 GPa.     

Characterizing Frictional Contact Loading via Isochromatics

Isochromatic patterns in the vicinity of frictional contacts furnish vital clues for characterizing friction. Though friction effects are evident in a diametrally loaded circular disk, three-point loading provides better results towards highlighting friction. In this paper, a new method of characterizing friction at loading contacts using photoelastic isochromatics patterns is presented. Location of isotropic points (IPs) formed in three-point and four-point loadings of circular disk is used as a main tool to quantify the friction component using theoretical analysis. Bifurcation of isochromatic fringe loops near the distributed loads is explained by the presence of anti-symmetric Hertzian shear traction in addition to Hertzian normal traction. The classical solution by Flamant for point load at the edge of half plane is used to derive stresses in circular disk for all required loading configurations. A semicircualr ring under three-point loading is examined using photoelasticity to understand the isochromatics pattern theoretically by considering normal and shear traction components at loaded regions.