Synthesis, biology, and modeling of a C-4 carbonyl C,D-seco-taxoid

A C,D-seco-paclitaxel derivative 26 was prepared from taxine and tested for biological activity. Chemical reactivity of the seco-compounds proved to be substantially modified, with respects to taxoids. The corresponding C,D-seco-taxoid does not show tubulin stabilizing activity or cytotoxicity. Explanation of these observations based on molecular modeling is provided.     

A volume microstrip RF coil for MRI microscopy

Quantitative magnetic resonance imaging (MRI) studies of small samples such as a single cell or cell clusters require application of radiofrequency (RF) coils that provide homogenous B₁ field distribution and high signal-to-noise ratio (SNR).We present a novel design of an MRI RF volume microcoil based on a microstrip structure. The coil consists of two parallel microstrip elements conducting RF currents in the opposite directions, thus creating homogenous RF field within the space between the microstrips. The construction of the microcoil is simple, efficient and cost-effective.Theoretical calculations and finite element method simulations were used to optimize the coil geometry to achieve optimal B₁ and SNR distributions within the sample and predict parameters of the coil. The theoretical calculations were confirmed with MR images of a 1-mm-diameter capillary and a plant obtained with the double microstrip RF microcoil at 11.7 T. The in-plane resolution of MR images was 24 μm×24 μm.     

The [4+2]-Cycloaddition of α-Nitrosoalkenes with Thiochalcones as a Prototype of Periselective Hetero-Diels–Alder Reactions—Experimental and Computational Studies

The [4+2]-cycloadditions of α-nitrosoalkenes with thiochalcones occur with high selectivity at the thioketone moiety of the dienophile providing styryl-substituted 4H-1,5,2-oxathiazines in moderate to good yields. Of the eight conceivable hetero-Diels–Alder adducts only this isomer was observed, thus a prototype of a highly periselective and regioselective cycloaddition has been identified. Analysis of crude product mixtures revealed that the α-nitrosoalkene also adds competitively to the thioketone moiety of the thiochalcone dimer affording bis-heterocyclic [4+2]-cycloadducts. The experiments are supported by high-level DFT calculations that were also extended to related hetero-Diels–Alder reactions of other nitroso compounds and thioketones. These calculations reveal that the title cycloadditions are kinetically controlled processes confirming the role of thioketones as superdienophiles. The computational study was also applied to the experimentally studied thiochalcone dimerization, and showed that the 1,2-dithiin and 2H-thiopyran isomers are in equilibrium with the monomer. Again, the DFT calculations indicate kinetic control of this process.     

Mandelic acid derived α-aziridinyl alcohols as highly efficient ligands for asymmetric additions of zinc organyls to aldehydes

A straightforward synthesis of a series of new catalysts containing secondary hydroxyl and aziridine moieties as nucleophilic centers built on the chiral scaffold of (S)-(+)-mandelic acid is described. The new compounds have been tested for the enantioselective addition of diethylzinc and phenylethynylzinc to aryl and alkyl aldehydes, which yielded the corresponding chiral alcohols in high chemical yields (up to 95%) and with excellent ee’s of ca. 90%. The strong influence of the stereogenic center located at the aziridine subunit on the stereochemical outcome is also reported on.     

A convenient procedure for the preparation of Garner’s aldehyde

The palladium/silane reduction of a serine thioester derivative allows for the preparation of enantiomerically pure Garner’s aldehyde from serine, in gram quantities within 24 h.     

New Insights into the Mechanism of Reduction of Tertiary Phosphine Oxides by Means of Phenylsilane

The mechanism of the reduction of phosphine oxides by PhSiH₃ was established on the basis of kinetic measurements and Density Functional Theory (DFT) calculations. In particular, it has been proved that the model reaction between tri‐n‐butylphosphine oxide and phenylsilane occurs via a nonpolar mechanism. The data presented herein allow prediction and verification of the applicability of the new reduction reagents and conditions for industrially attractive processes.     

Reduction of Thiocarbonyl Compounds with Lithium Diisopropylamide

Treatment of 4,4‐disubstituted 2‐phenyl‐1,3‐thiazole‐5(4H)‐thiones with lithium diisopropylamide (LDA; LiNⁱPr₂) in THF at ?78° yielded the corresponding 1,3‐thiazole‐5(4H)‐thioles in moderate yields. Sequential treatment with LDA and MeI under the same conditions led to the 5‐methylsulfanyl derivatives. Similarly, reaction of some cycloalkanethiones as well as diaryl thioketones with LDA and MeI gave cycloalkyl methyl sulfides and diarylmethyl methyl sulfides, respectively. A reaction mechanism via H transfer from LDA to the thiocarbonyl C‐atom via a six‐membered transition state is proposed for this unprecedented reduction of the C?S bond.     

Fully atomistic molecular‐mechanical model of liquid alkane oils: Computational validation

Fully atomistic molecular dynamics simulations were performed on liquid n‐pentane, n‐hexane, and n‐heptane to derive an atomistic model for middle‐chain‐length alkanes. All simulations were based on existing molecular‐mechanical parameters for alkanes. The computational protocol was optimized, for example, in terms of thermo‐ and barostat, to reproduce properly the properties of the liquids. The model was validated by comparison of thermal, structural, and dynamic properties of the normal alkane liquids to experimental data. Two different combinations of temperature and pressure coupling algorithms were tested. A simple differential approach was applied to evaluate fluctuation‐related properties with sufficient accuracy. Analysis of the data reveals a satisfactory representation of the hydrophobic systems behavior. Thermodynamic parameters are close to the experimental values and exhibit correct temperature dependence. The observed intramolecular geometry corresponds to extended conformations domination, whereas the intermolecular structure demonstrates all characteristics of liquid systems. Cavity size distribution function was calculated from coordinates analysis and was applied to study the solubility of gases in hexane and heptane oils. This study provides a platform for further in‐depth research on hydrophobic solutions and multicomponent systems. © 2014 Wiley Periodicals, Inc.     

Reactions of Cycloaliphatic Thioketones and Their Oxo Analogues with Lithiated Methoxyallene: A New Approach to Vinylthiiranes

Admantanethione smoothly reacted with lithiated methoxyallene at low temperatures yielding the expected allenyl‐substituted thiolate, which upon aqueous work‐up underwent spontaneous 1,3‐cyclization to afford a hitherto unknown methoxy‐substituted vinylthiirane derivative. The analogous reaction with adamantanone led to the corresponding allenyl alcohol that can be isolated and—depending on the conditions applied—either be converted into the corresponding vinyloxirane or into the 2,5‐dihydrofuran derivative. Sterically more crowded thioketones were also combined with lithiated methoxyallene, but in these cases competitive 1,5‐cyclization leading to isomeric dihydrothiophene derivatives was observed. DFT calculations of model intermediates and products show distinct energy differences of the sulfur and the corresponding oxygen compounds. Desulfurization of the adamantanethione‐derived vinylthiirane yielded a methoxy‐substituted 1,3‐diene that was studied in cycloadditions with electron‐deficient dienophiles. Whereas in the case of tetracyanoethylene the corresponding cyclobutane derivative was formed, the reaction with nitrosobenzene provided the expected 1,2‐oxazine derivative. By reductive cleavage of the N? O bond this heterocycle was converted into an unsaturated amino alcohol bearing an adamantane moiety.     

Radioactive contamination of the forests of Southern Poland and Finland

Experimental data of caesium and ruthenium radioactivity in chosen parts of forest ecosystems in Finland and Southern Poland are presented and compared. Measurements were performed with a low-background -spectrometer coupled with a Ge/Li/ detector. The maximum caesium-137 activity in litter from Poland is 2.5 kBq, in that from Finland 3.9 kBq, in spruce needles it is 0.4 kBq /Poland/, 0.9 kBq /Finland/ and in fern leaves it is as high as 15.9 kBq per kg of dry mass in one sample from Poland.