An expeditious synthesis of an analogue of (−)-steviamine by way of the 1,3-dipolar cycloaddition of a nitrile oxide with a 1-C-allyl iminosugar

In our continuing effort to develop inhibitors of the mycobacterial galactan biosynthesis, we planned to synthesize original iminosugar-based analogues of UDP-galactofuranose by way of the 1,3-dipolar cycloaddition reaction between a 1-C-allyl iminosugar and a nitrile oxide, followed by the reductive cleavage of the resulting isooxazoline. In initial studies, it was found that this last step led in one pot to a new polyhydroxylated indolizidine derivative closely related to the recently isolated (−)-steviamine, in good yield, by way of a sequence involving at least five individual reactions. The activity of this new compound as a glycosidase inhibitor was evaluated against a panel of glycosidases and compared to (−)-steviamine.     

Influence of reaction conditions on products of the Pictet-Spengler condensation

The Pictet-Spengler reaction with N-protected α-amino aldehydes was found to be very sensitive to reaction conditions. The outcome of the reaction can be controlled mainly by choice of solvent. Tetrahydro-β-carbolines were obtained in apolar solvents, while in polar media octahydro-bipyrroloindoles were the main compounds. Temperature, amount of acid and reaction time also influenced the final results of the PS reaction. Depending on conditions, products with opposite configuration of stereogenic centre, descended from amino aldehydes, were formed as byproducts.     

SEM and TEM analysis of composite of ZrO2-Ti system

3Y-ZrO₂-Ti composites obtained by slip casting method were studied by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Moreover, the Vickers hardness was measured. The experiments show the complex microstructure of composites. The tetragonal zirconium dioxide (t-ZrO₂) and monoclinic zirconium dioxide (m-ZrO₂) as a composite matrix were detected at XRD analysis. SEM observations revealed that Ti -rich phase are uniform distributed in composites. Moreover, the large and very fine precipitations were found. The very fine Ti rich precipitations were located at ZrO₂ grain boundaries as well as in the triple-points. TEM experiments confirmed that in the sintered composites 3Y-ZrO₂ – 10%Ti the uniaxial ZrO₂ grains (100–600 nm), fine monoclinic martensitic plates and fine round monoclinic particles (20–40 nm) of ZrTiO₂ phase were exist. The complex microstructures of 3Y-ZrO₂-Ti composites have a high hardness as a result of existing fine ZrTiO₂ and other Ti oxides precipitations.     

Changes in electronic structure and chemical bonding upon crystallization of the phase change material GeSb2Te4

High-resolution photoelectron spectroscopy of in situ prepared films of GeSb2Te4 reveals significant differences in electronic and chemical structure between the amorphous and the crystalline phase. Evidence for two different chemical environments of Ge and Sb in the amorphous structure is found. This observation can explain the pronounced property contrast between both phases and provides new insight into the formation of the amorphous state.     

Methoxy-Substituted γ-Oxa-ε-Lactones Derived from Flavanones—Comparison of Their Anti-Tumor Activity In Vitro

Background: The study investigated four flavanone-derived γ-oxa-ε-lactones: a parent unsubstituted compound and its three derivatives with the methoxy group in positions 2′, 4′ and 8. Our objective was to find out if the introduction of the methoxy group into the aromatic ring affects in vitro anti-tumor potency of the investigated lactones. Methods: Cytotoxic and pro-apoptotic effects were assessed with cytometric tests with propidium iodide, annexin V, and Western blot techniques. We also investigated potential synergistic potency of the tested lactones and glucocorticoids in canine lymphoma/leukemia cell lines. Results: The tested flavanone-derived lactones showed anti-cancer activity in vitro. Depending on its location, the methoxy group either increased or decreased cytotoxicity of the derivatives as compared with the parent compound. The most potent lactone was the one with the methoxy group at position 4′ of the B ring (compound 3), and the weakest activity was observed when the group was located at C-8 in the A ring. A combination of the lactones with glucocorticoids confirmed their synergy in anti-tumor activity in vitro. Conclusions: Methoxy-substituted flavanone-derived lactones effectively kill canine lymphoma/leukemia cells in vitro and, thanks to their synergistic action with glucocorticoids, may potentially be applied in the treatment of hematopoietic cancers.     

Distigmasterol-Modified Acylglycerols as New Structured Lipids—Synthesis,Identification and Cytotoxicity

Plant sterols, also referred as phytosterols, have been known as bioactive compounds which have cholesterol-lowering properties in human blood. It has been established that a diet rich in plant sterols or their esters alleviates cardiovascular diseases (CVD), and also may inhibit breast, colon and lung carcinogenesis. Phytosterols, in their free and esterified forms, are prone to thermo-oxidative degradation, where time and temperature affect the level of degradation. Looking for new derivatives of phytosterols with high thermo-oxidative stability for application in foods, our idea was to obtain novel structured acylglycerols in which two fatty acid parts are replaced by stigmasterol residues. In this work, asymmetric (1,2- and 2,3-) distigmasterol-modified acylglycerols (dStigMAs) were synthesized by the covalent attachment of stigmasterol residues to sn-1 and sn-2 or sn-2 and sn-3 positions of 3-palmitoyl-sn-glycerol or 1-oleoyl-sn-glycerol, respectively, using a succinate or carbonate linker. The chemical structures of the synthesized compounds were identified by NMR, HR-MS, and IR data. Moreover, the cytotoxicity of the obtained compounds was determined. The dStigMAs possessing a carbonate linker showed potent cytotoxicity to cells isolated from the small intestine and colon epithelium and liver, whereas the opposite results were obtained for compounds containing a succinate linker.