Jubi John

Catalytic oxidation of silanes by carbon nanotube-gold nanohybrids.

The selective oxidation of silanes has attracted wide interest as silanols are key synthons for the production of siliconcontaining materials and nucleophilic partners in organometallic cross-coupling reactions. Silanes are classically converted into silanols using strong oxidizing agents such as osmium tetroxide, permanganate, ozone, peracids, or peroxides. However, under these reaction conditions, significant amounts of siloxanes and toxic by-products are formed. To overcome these drawbacks, catalytic systems involving water and oxygen have been recently devised. They offer the advantage of cleanly producing silanols along with hydrogen gas as the only by-product. While initial catalytic silane oxidation studies relied on homogeneous transition metals, heterogeneous catalytic systems have emerged as very promising alternatives. 10] Indeed, the latter are more efficient (high conversion rate), recyclable, selective (little to no siloxane by-product formation), and usually operate under milder conditions. Amongst heterogeneous catalysts for silane oxidation, recent elegant examples include nanoporous gold by Asao, Yamamoto, and co-workers, and hydroxyapatite-supported silver or gold nanoparticles by Kaneda and co-workers. Herein we report an alternative strategy which has led to the discovery of the most efficient catalytic system to date for silane oxidation. Our approach involves layer-by-layer (LBL) assembly of gold nanoparticles on carbon nanotubes (CNTs). Nanotubes provide high specific surface area and excellent nanoparticle (NP) dispersion. In addition, nanotubes are electronically active and stabilization of transient higher oxidation states of gold are anticipated by collaborative interactions with the metal. To the best of our knowledge, this is the first report on silane oxidation by CNTsupported catalysts. The preparation of the CNT–gold nanohybrid (see the Supporting Information for details) started with aqueous selfassembly of amphiphilic nitrilotriacetic diyne lipids (DANTA) on multiwalled carbon nanotubes (Figure 1) to

A metal-free three-component reaction for the regioselective synthesis of 1,4,5-trisubstituted 1,2,3-triazoles.

A metal-free three-component reaction to synthesize 1,4,5-trisubstituted 1,2,3-triazoles from readily available building blocks, such as aldehydes, nitroalkanes, and organic azides, is described. The process is enabled by an organocatalyzed Knoevenagel condensation of the formyl group with the nitro compound, which is followed by the 1,3-dipolar cycloaddition of the azide to the activated alkene. The reaction features an excellent substrate scope, and the products are obtained with high yield and regioselectivity. This method can be utilized for the synthesis of fused triazole heterocycles and materials with several triazole moieties.

Tumor-targeted polydiacetylene micelles for in vivo imaging and drug delivery.

In vivo tumor targeting and drug delivery properties of small polymerized polydiacetylene (PDA) micelles (∼10 nm) is investigated in a murine MDA-MB-231 xenograft model of breast cancer. Three micelles with different surface coatings are synthesized and tested for their ability to passively target tumor through the enhanced permeability and retention effect. After injection (24 h), fluorescence diffuse optical tomographic imaging indicates a tumor uptake of nearly 3% of the injected dose for the micelles with a 2 kDa poly(ethylene glycol) (PEG)-coating (PDA-PEG2000). The uptake of PDA micelles in tumors is confirmed by co-localization with [(18) F]-fluorodeoxyglucose (FDG) positron emission tomography. Although FDG has a higher diffusion rate in tumors, 40 ± 19% of the retained micelles is co-registered with the tumor volume visualized by FDG. Finally, PDA-PEG2000 micelles are loaded with the hydrophobic anticancer drug paclitaxel and used in vivo to inhibit tumor growth. These findings demonstrate the potential of PDA-PEG2000 micelles for both in vivo tumor imaging and drug delivery applications.

Palladium catalyzed tandem ring opening-ring closing reaction of diazabicyclic alkenes: a facile one pot strategy for cyclopentannulation of heterocycles.

A novel palladium catalyzed protocol for the synthesis of cyclopentene fused heterocycles from diazabicyclic alkenes and ortho-functionalized aryliodides has been elaborated. The reaction can be tuned toward the formation of either 3,4-disubstituted cyclopentenes or cyclopentene fused heterocycles by careful manipulation of the reaction parameters. A number of cyclopentene fused benzofurans and indole derivatives were prepared in excellent yield by utilizing the developed methodology.

Advances in carbon nanotube-noble metal catalyzed organic transformations

Abstract This review article is dealing with heterogeneous catalysis applied to synthetic chemistry using various carbon nanotube-supported noble metals (e.g., ruthenium, rhodium, palladium, silver, osmium, iridium, platinum, and gold).

Iodine assisted palladium catalyzed ring opening of bicyclic hydrazines with organoboronic acids: stereoselective synthesis of functionalized cyclopentenes and alkylidene cyclopentenes

A novel reactivity of organoboronic acids with bicyclic hydrazines leading to the stereoselective formation of trans-vicinal disubstituted cyclopentenes in good to excellent yield is discussed. The reaction of cyclopentadiene and fulvene derived azabicyclic alkenes with organoboronic acids afforded the trans-3,4-disubstituted cyclopentenes and alkylidene cyclopentenes in good to excellent yields. The products, having a broad range of substituents, are important intermediates in the synthesis of a number of pharmaceutically important molecules.

Palladium catalyzed reaction of ortho-functionalized aryl iodides with bicyclic hydrazines: facile route toward heteroannulated cyclopentenes and azabicycles

Abstract A palladium catalyzed tandem protocol for the synthesis of cyclopentene fused heterocycles from diazabicyclic alkenes and ortho -functionalized aryl iodides has been elaborated. This tandem protocol was utilized for the synthesis of a number of cyclopentene fused dihydrobenzofurans and indolines. The reaction can be tuned toward the formation of either 3,4-disubstituted cyclopentenes or cyclopentene fused heterocycles by careful manipulation of the reaction parameters. The reaction was also extended to bicyclic alkenes derived from fulvene, which resulted in the heteroannulation of the azabicyclic system.

Alpha-carboxy nucleoside phosphonates as universal nucleoside triphosphate mimics

Significance The polymerization of nucleotides by DNA polymerases occurs through a common mechanism based on similar highly conserved amino acid motifs and the universal role of the coordination of Mg2+ by three dNTP phosphate oxygens. Based on these universal principles, we aimed at designing a dNTP mimic that could interact with a broad variety of DNA polymerases and should consist of three major indispensable entities: a nucleobase for Watson–Crick base-pairing, an enzymatically and chemically stable triphosphate replacement that can efficiently coordinate the Mg2+ cation, and a variable linker moiety between the nucleobase and the modified phosphate. The resulting α-carboxy nucleoside phosphonates (α-CNPs) were structurally, kinetically, and biochemically investigated, and the novel dNTP mimics were successfully validated in several DNA polymerase models. Polymerases have a structurally highly conserved negatively charged amino acid motif that is strictly required for Mg2+ cation-dependent catalytic incorporation of (d)NTP nucleotides into nucleic acids. Based on these characteristics, a nucleoside monophosphonate scaffold, α-carboxy nucleoside phosphonate (α-CNP), was designed that is recognized by a variety of polymerases. Kinetic, biochemical, and crystallographic studies with HIV-1 reverse transcriptase revealed that α-CNPs mimic the dNTP binding through a carboxylate oxygen, two phosphonate oxygens, and base-pairing with the template. In particular, the carboxyl oxygen of the α-CNP acts as the potential equivalent of the α-phosphate oxygen of dNTPs and two oxygens of the phosphonate group of the α-CNP chelate Mg2+, mimicking the chelation by the β- and γ-phosphate oxygens of dNTPs. α-CNPs (i) do not require metabolic activation (phosphorylation), (ii) bind directly to the substrate-binding site, (iii) chelate one of the two active site Mg2+ ions, and (iv) reversibly inhibit the polymerase catalytic activity without being incorporated into nucleic acids. In addition, α-CNPs were also found to selectively interact with regulatory (i.e., allosteric) Mg2+-dNTP-binding sites of nucleos(t)ide-metabolizing enzymes susceptible to metabolic regulation. α-CNPs represent an entirely novel and broad technological platform for the development of specific substrate active- or regulatory-site inhibitors with therapeutic potential.

An exclusive approach to 3,4-disubstituted cyclopentenes and alkylidene cyclopentenes via the palladium catalyzed ring opening of azabicyclic olefins with aryl halides

A simple and efficient method for the stereoselective ring opening of bicyclic hydrazines with various aryl halides under palladium catalysis has been elaborated. The reactions afforded trans-3,4-disubstituted cyclopentenes or alkylidene cyclopentenes in good to excellent yields. By taking advantage of multiple points of functionalization in the synthesized trans-3-phenyl-4-hydrazino-cyclopentene, we have synthesized the antidepressant Cypenamine (trans-2-phenylcyclopentylamine).

Iodine assisted modified Suzuki type reaction of bicyclic hydrazines: stereoselective synthesis of functionalized cyclopentenes

Bicyclic hydrazines undergo a facile palladium/iodine mediated stereoselective ring opening on reaction with organoboronic acids affording trans-3,4-disubstituted hydrazino cyclopentenes in good to excellent yield.