Stereoselectivity control by oxaspiro rings during Diels-Alder cycloadditions to cross-conjugated cyclohexadienones: the syn oxygen phenomenon

The diastereofacial selectivity operating in Diels-Alder additions involving spirocyclic cross-conjugated cyclohexadienones with dienes of varying reactivity has been investigated. The study has included the ether series 1a-c as well as the lactone/ketone pair 2a/2b. In all cases, the preferred [4+2] cycloaddition pathway consisted of bonding from that pi-surface syn to the oxygen atom. 4-Substituted-4-methyl-2,5-cyclohexadienones (monocyclic systems) were also examined and found to undergo bond formation preferentially from the face bearing the more electron-withdrawing of the two groups at the 4 position. Kinetic parameters were determined for the cycloaddition of 1a and 2a to cyclopentadiene. The rate acceleration profile of solvents was in the order CF(3)CH(2)OH > CH(3)CN approximately CH(2)Cl(2) for the production of 9a from 1a and CF(3)CH(2)OH > CH(2)Cl(2) > CH(3)CN for the production of 21a from 2a, respectively. This spread in polarity had no major impact on product distribution, a phenomenon also reflected in the behavior of 4-substituted-4-methyl-2,5-cyclohexadienones under comparable conditions. Theoretical assessment of these experimental facts was undertaken at the HF/6-31G level. The facial selectivity is understandable in terms of the secondary interaction between the HOMO of the diene and LUMO of the dienophile as well as the effective hyperconjugation between the newly forming bond and the 4-anti-C-C sigma-orbital due to the more electron-donating bond, as defined by the Cieplak model.     

A new route to pyridine derivatives by the reaction of tris(isopropylthio)cyclopropenylium perchlorate with α-lithiated isocyanides

The reaction of tris(isopropylthio)cyclopropenylium perchlorate ( 1 ) with α-lithiated tosylmethyl, benzyl and benzoylmethyl isocyanides 2a-c in dry tetrahydrofuran gave the pyridine derivatives 3a-c respectively.     

A comparison of the analysis of covariance (ANCOVA) and range-based approaches for assessing batch-to-batch variability of the stability of pharmaceutical products

Stability data were generated by the Monte Carlo method, and batch-to-batch variability was evaluated by analysis of differences in slope and intercept according to the analysis of covariance (ANCOVA) approach recommended in the FDA Guidance. Using the same generated data, batch-to-batch variability was also evaluated by assessing the equivalence of shelf lives estimated for individual batches based on the range (Range-based approach) in order to compare the ability of the two approaches to detect stability differences among batches. The results of the study indicated that the Range-based approach can detect a 30% difference in the slope of degradation curves among batches with a similar beta error as the ANCOVA approach, provided that degradation data are obtained with assay errors below 0.5. The range-based approach appears to be useful as an alternative method to ANCOVA, if it is modified such that the variance of estimates is taken into account.     

Application of sucrose fatty acid ester to reverse micellar extraction of lysozyme

Reverse micellar extraction of lysozyme has been carried out using an organic solution containing a mixture of monoester and polyester of sucrose fatty acid ester. The forward extraction of lysozyme from the feed aqueous phase to the reverse micellar organic phase of the mixture of monoester and polyester of sucrose fatty acid ester at pH 7.2 was strongly dependent upon the weight fraction of monoester, while any amount of lysozyme was not extracted only by using monoester or polyester. The forward extraction ratio dramatically increased with an increase in the concentration of fatty acid ester, and was high around neutral pH and at low ionic strength. The backward extraction of lysozyme from the reverse micellar organic phase to the recovery aqueous phase exhibited high efficiency at acidic pH value or at high ionic strength. The addition of sucrose into the recovery aqueous phase promoted the backward extraction ratio, and caused the activity of lysozyme recovered from the reverse micellar phase to be retained perfectly.     

Separation and spectrophotometric determination of uranium(VI) by extraction with tri-n-octylphosphine oxide and benzophenone

Uranium(VI) is separated by extraction from nitric acid medium into a molten mixture of tri-n-octylphosphine oxide and benzophenone at about 50°. The organic phase solidifies on cooling and is separated and dissolved in ethanol. The uranium(VI) in this solution is then determined spectrophotometrically with 1-(2-pyridylazo)-2-naphthol.     

Crossover from dilute to majority spin freezing in two leg ladder system Sr(Cu,Zn)2O3

The two-dimensional electron gas (2DEG) in moderate magnetic fields in ultraclean AlAs-GaAs heterojunctions exhibits transport anomalies suggestive of a compressible anisotropic metallic state. Using scaling arguments and Monte Carlo simulations, we develop an order parameter theory of an electron nematic phase. The observed temperature dependence of the resistivity anisotropy behaves like the orientational order parameter if the transition to the nematic state occurs at a finite temperature T(c) approximately 65 mK, and is slightly rounded by a small background microscopic anisotropy. We propose a light scattering experiment to measure the critical susceptibility.     

Attenuation of second sound in superfluid 3He-A1

The attenuation of second sound (spin-entropy) wave in the superfluid A1 phase has been measured in magnetic fields up to 11 T and to sufficiently high frequency to observe the bulk attenuation proportional to the square of frequency. The measured attenuation coefficient is compared with the existing theories of hydrodynamics and dissipative coefficients. The resulting "excess" attenuation is discussed in terms of the temperature dependent spin diffusion coefficient in the superfluid.     

Phellifuropyranone A: a new furopyranone compound isolated from fruit bodies of wild Phellinus linteus

A new furopyranone, phellifuropyranone A, was isolated from fruit bodies of wild Phellinus linteus as well as phelligridin G, and their chemical structures were determined by various spectroscopic methods including measurement of NMR spectra. Phellifuropyranone A together with meshimakobnol A and meshimakobnol B showed antiproliferative activity against mouse melanoma cells and human lung cancer cells in vitro.