Rajesh K. Pandey

Role of mixed metal oxides in catalysis science—versatile applications in organic synthesis

A variety of mixed metal oxides (MMOs), containing alkali, alkaline, rare earth and noble metals, and their applications are presented. In this mini review, we summarize versatile applications of mixed metal oxides in organic synthesis. A variety of reactions such as reduction, oxidation, multicomponent, Mannich, alkylation, condensation, deprotection, cycloaddition, hydroxylation, dehydration, dehydrogenation, transesterification, reactions involving biomimetic oxygen-evolving catalysts and other important C–C bond forming reactions are well presented on the surface of mixed metal oxides under a variety of reaction conditions. The scope of MMOs in important organic reactions, industrial applications, and green chemistry and recent applications of MMOs are well presented in this review.

Synthesis and characterization of versatile MgO–ZrO2 mixed metal oxide nanoparticles and their applications

A heterogeneous, versatile nano-magnesia-zirconia or MgO–ZrO2 (MZ) catalyst was prepared by an ultra dilution method. The as-synthesised catalyst was characterized by several analytical techniques such as XRD, particle size analysis, BET surface area, thermogravimetric analysis (TGA), differential thermal analysis (DTA), FT-IR spectroscopy, SEM (scanning electron microscope), TEM (transmission electron microscope) and XPS (X-ray fluorescence spectroscopy). The surface area is found to be 268 m2 g−1. The catalytic activity of MZ was tested for various important organic reactions such as cross-aldol condensation, N-benzyloxycarbonylation of amines, reduction of aromatic nitrocompounds, and synthesis of 1,5-benzodiazepines. It has been observed that for all reactions MZ shows a good catalytic activity. All corresponding products were obtained in good to excellent yield under mild conditions. The MgO-ZrO2 catalyst can be prepared from inexpensive precursors, has high surface area, and is reusable and recyclable for all reactions.

Reactivity of (2-alkenyl-3-pentene-1,5-diyl)iron complexes: preparation of functionalized vinylcyclopropanes and cycloheptadienes

The reactivity of (2-alkenyl-3-pentene-1,5-diyl)iron complexes toward olefin metathesis, cycloaddition, and mild oxidations (MnO 2 or mCPBA) was examined. Cycloaddition reactions were observed to occur with modest diastereoselectivity (33-63% de). Decomplexation of the (3-pentenediyl) ligand may be accomplished by oxidation with either CAN or alkaline hydrogen peroxide to afford vinylcyclopropanecarboxylates or divinylcyclopropanecarboxylates. Reduction of the latter, followed by Cope rearrangement generates cycloheptadienylmethanols. These studies demonstrate that (2-alkenyl-3-pentene-1,5-diyl)iron complexes can serve as organometallic scaffolds for the preparation of a wide variety of structural motifs containing up to 5 contiguous stereocenters.

Probing the human estrogen receptor-α binding requirements for phenolic mono- and di-hydroxyl compounds: a combined synthesis, binding and docking study.

Various estrogen analogs were synthesized and tested for binding to human ERα using a fluorescence polarization displacement assay. Binding affinity and orientation were also predicted using docking calculations. Docking was able to accurately predict relative binding affinity and orientation for estradiol, but only if a tightly bound water molecule bridging Arg394/Glu353 is present. Di-hydroxyl compounds sometimes bind in two orientations, which are flipped in terms of relative positioning of their hydroxyl groups. Di-hydroxyl compounds were predicted to bind with their aliphatic hydroxyl group interacting with His524 in ERα. One nonsteroid-based dihdroxyl compound was 1000-fold specific for ERβ over ERα, and was also 25-fold specific for agonist ERβ versus antagonist activity. Docking predictions suggest this specificity may be due to interaction of the aliphatic hydroxyl with His475 in the agonist form of ERβ, versus with Thr299 in the antagonist form. But, the presence of this aliphatic hydroxyl is not required in all compounds, since mono-hydroxyl (phenolic) compounds bind ERα with high affinity, via hydroxyl hydrogen bonding interactions with the ERα Arg394/Glu353/water triad, and van der Waals interactions with the rest of the molecule.

A-C Estrogens as Potent and Selective Estrogen Receptor-beta Agonists (SERBAs) to Enhance Memory Consolidation under Low-estrogen Conditions

Estrogen receptor-beta (ERβ) is a drug target for memory consolidation in postmenopausal women. Herein is reported a series of potent and selective ERβ agonists (SERBAs) with in vivo efficacy that are A-C estrogens, lacking the B and D estrogen rings. The most potent and selective A-C estrogen is selective for activating ER relative to seven other nuclear hormone receptors, with a surprising 750-fold selectivity for the β over α isoform and with EC50s of 20-30 nM in cell-based and direct binding assays. Comparison of potency in different assays suggests that the ER isoform selectivity is related to the compounds ability to drive the productive conformational change needed to activate transcription. The compound also shows in vivo efficacy after microinfusion into the dorsal hippocampus and after intraperitoneal injection (0.5 mg/kg) or oral gavage (0.5 mg/kg). This simple yet novel A-C estrogen is selective, brain penetrant, and facilitates memory consolidation.