Synthesis and reactions of N-methylbenzylammonium fluorochromate(VI) on silica gel, a selective and efficient heterogeneous oxidant.
N-Methylbenzylammonium fluorochromate(VI) (MBAFC) is easily synthesized by addition of N-methylbenzylamine to an aqueous solution of CrO3 and HF. MBAFC shows selectivity in the oxidation of aryl alcohols to their corresponding aldehydes and ketones under mild conditions. The durability, ease of work up and efficiency of MBAFC are considerably increased upon its absorption on silica gel.
Merrifield resin supported peroxomolybdenum(VI) compounds: recoverable heterogeneous catalysts for the efficient, selective and mild oxidation of organic sulfides with H2O2
We have generated new heterogeneous catalysts by immobilizing dioxomonoperoxomolybdenum(VI) on amino acid functionalized Merrifield resin, which exhibit excellent activity, stability and selectivity for the oxidation of thioethers and dibenzothiophene (DBT) to the corresponding sulfoxides or sulfones by H2O2 at ambient temperature. The synthetic protocols are high-yielding, halogen-free, environmentally clean and safe, and operationally simple. The catalysts, [MoO2(O2)(L)2]2−-MR [L = valine (MRVMo) or alanine (MRAMo) and MR = Merrifield resin] were prepared by reacting H2MoO4 with 30% H2O2 and the respective amino acid functionalized resin, at near neutral pH. The compounds were characterized by elemental analysis, spectral studies (FTIR, Raman, 13C NMR and 95Mo NMR, diffuse reflectance UV-Vis and XPS), SEM, EDX, XRD, Brunauer–Emmett–Teller (BET) and TGA-DTG analysis. The easy recyclability of the catalysts for several catalytic cycles without change in activity and selectivity, their complete chemoselectivity towards the sulfur group of substrates bearing other oxidation prone functional groups, are important “green” attributes of these catalysts.
Correlation between oxysterol binding to a cytosolic binding protein and potency in the repression of hydroxymethylglutaryl coenzyme A reductase.
Support for the role of a cytosolic oxysterol-binding protein in the regulation of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase was obtained by correlating the relative binding affinities of a wide range of oxysterols to their potency in suppressing HMG-CoA reductase activity in mouse fibroblast cell cultures. Forty-seven oxysterols encompassing a 100-fold range of activity in both assays were tested and the two parameters were closely correlated for 35 of the sterols. Twelve sterols showed poor binding when compared to their ability to suppress HMG-CoA reductase activity in cell cultures. Among these were seven sterols with a ketone function at C-3. For this group, the discrepancy could be explained by their rapid conversion within cells to the 3 beta-hydroxy derivatives which have a much higher affinity for the binding protein. One sterol with 3-keto-4-ene grouping was not reduced to its 3 beta-hydroxy derivative in cells and thereby showed no discrepancy in the two assays. The remaining five sterols exhibiting discordant activities in the two tests contained 4,4-dimethyl moieties and were relatively weak suppressors of HMG-CoA reductase activity. Cellular metabolism of these sterols was not detected. Possible reasons for their apparent inactivity in the binding assay are discussed.