Chemo‐ and Regioselective C(sp3)?H Arylation of Unactivated Allylarenes by Deprotonative Cross‐Coupling

The combination of aryl bromides, allylbenzene, base and a palladium catalyst usually results in a Heck reaction. Herein we combine these same reagents, but override the Heck pathway by employing a strong base. In the presence of LiN(SiMe₃)₂, allylbenzene derivatives undergo reversible deprotonation. Transmetalation of the resulting allyllithium intermediate to LPdAr(Br) and reductive elimination provide the 1,1‐diarylprop‐2‐enes, which are not accessible by the Heck reaction. The regioselectivity in this deprotonative cross‐coupling process is catalyst‐controlled and very high.     

Regioselective synthesis of C-2 substituted imidazo[4,5-b]pyridines utilizing palladium catalysed C–N bond forming reactions with enolizable heterocycles

In this Letter we report a rapid and facile access to C2-substituted imidazo[4,5-b]pyridine analogues utilizing palladium mediated Buchwald–Hartwig cross-coupling reactions. The use of enolizable heterocycles as cross-coupling partners resulted in a wide range of imidazo[4,5-b]pyridine analogues which are prone to have medicinal relevance. Xantphos and Pd(OAc)₂ were found to be more effective for the coupling of 2-halo imidazo[4,5-b]pyridines with pyridone nucleophiles. A regioselective approach for the synthesis of 2-substituted 3H-imidazo[4,5-b]pyridine and 1H-imidazo[4,5-b]pyridine is also reported.     

Polyvinylimidazole/sol–gel composite as a novel solid‐phase microextraction coating for the determination of halogenated benzenes from aqueous solutions

A polyvinylimidazole/sol–gel composite is proposed as a novel solid‐phase microextraction fiber to extract five halobenzenes from the headspace of aqueous solutions in combination with gas chromatography with mass spectrometry. The prepared fiber was characterized by scanning electron microscopy and Fourier transform infrared spectroscopy. The obtained results showed that porous polyvinylimidazole/sol–gel composite was chemically deposited on fused silica fiber. The effect of important extraction parameters including extraction temperature, extraction time, and salt content were investigated. The optimum conditions were as follows: extraction temperature 25°C, extraction time 20 min, and salt concentration 30 w/v%. Detection limits and relative standard deviations of the developed method for halogenated benzenes were below 0.1 pg/mL and 15%, respectively. Repeatability of the proposed method, explained by relative standard deviation, varied between 5.48 and 9.15% (n = 5). The limits of detection (S/N = 3) ranged between 0.01 and 0.10 ng/L using gas chromatography with mass spectrometry with selected ion monitoring mode. For real sample analysis, three types of water samples with different matrices (ground, surface, and tap water) were studied. The optimized procedure was applied to extraction and method validation of halogenated benzenes in spiked water samples.     

Synthesis,spectroscopic characterization,X-ray crystal structure,biological screening and catalytic studies of organotin(IV) carboxylates of 3-(4-cyanophenyl) acrylic acid

A series of six organotin(IV) carboxylates [Me₂SnL₂] (1), [n-Bu₂SnL₂] (2), [n-Oct₂SnL₂] (3), [Me₃SnL] (4), n-Bu₃SnL (5) and [Ph₃SnL] (6), where L = 3-(4-cyanophenyl) acrylic acid have been synthesized and characterized by elemental analysis, FT-IR and NMR (¹H, ¹³C). The complex (4) was also analyzed by single crystal X-ray analysis which showed distorted trigonal bipyramidal geometry with polymeric bridging behavior. The complexes 1–6 were screened for antimicrobial activities and cytotoxicity. The results showed significant activity with few exceptions. The catalytic activity of complexes was assessed in transesterification reaction of Brassica campestris oil (triglycerides) to produce biodiesel (fatty acid methyl esters). The results showed that triorganotin(IV) complexes exhibited good catalytic activity than their di-analogues.     

Phenylpropanoids from Tanacetum baltistanicum with Nematocidal and Insecticidal Activities

Chemistry of Natural Compounds - One new and seven known secondary metabolites 1–8 were isolated, and the nematocidal and insecticidal activities of major compounds from Tanacetum...     

Biogenic Synthesis of Gold Nanoparticles on a Green Support as a Reusable Catalyst for the Hydrogenation of Nitroarene and Quinoline

Direct attachment of gold nanoparticles to a green support without the use of an external reducing agent and using it for removing toxic pollutants from wastewater, i. e., reduction of nitroarene to amine, are described. A novel approach involving the reduction of gold by the jute plant (Corchorus genus) stem-based (JPS) support itself to form nanoparticles (AuNPs) to be used as a catalytic system (‘dip-catalyst’) and its catalytic activity for the hydrogenation of series of nitroarenes in aqueous media are presented. AuNPs/JPS catalyst was characterized using SEM, UV-Vis, FTIR, TEM, XPS, and ICP-OES. Confined area elemental mapping exhibits uniform and homogeneous distribution of AuNPs on the support surface. TEM shows multi-faceted AuNPs in the range of 20–30 nm. The reactivity of AuNPs/JPS for the transfer hydrogenation of nitroarene as well as hydrogenation of quinoline under molecular H₂ pressure was evaluated. Sodium borohydride, when used as the hydrogen source, demonstrates a high catalytic efficiency in the transfer hydrogenation reduction of 4-nitrophenol (4-NP). Quinoline is quantitatively and chemoselectively hydrogenated to 1,2,3,4-tetrahydroquinoline (py-THQ) using molecular hydrogen. Reusability studies show that AuNPs are stable on the support surface and their selectivity is not affected.     

Malformin-A1 (MA1) Sensitizes Chemoresistant Ovarian Cancer Cells to Cisplatin-Induced Apoptosis

High-grade epithelial ovarian cancer is a fatal disease in women frequently associated with drug resistance and poor outcomes. We previously demonstrated that a marine-derived compound MalforminA1 (MA1) was cytotoxic for the breast cancer cell line MCF-7. In this study, we aimed to examine the effect of MA1 on human ovarian cancer cells. The potential cytotoxicity of MA1was tested on cisplatin-sensitive (A2780S) and cisplatin-resistant (A2780CP) ovarian cancer cell lines using AlamarBlue assay, Hoechst dye, flow cytometry, Western blot, and RT-qPCR. MA1 had higher cytotoxic activity on A2780S (IC50 = 0.23 µM) and A2780CP (IC50 = 0.34 µM) cell lines when compared to cisplatin (IC50 = 31.4 µM and 76.9 µM, respectively). Flow cytometry analysis confirmed the cytotoxic effect of MA1. The synergistic effect of the two drugs was obvious, since only 13% of A2780S and 7% of A2780CP cells remained alive after 24 h of treatment with both MA1 and cisplatin. Moreover, we examined the expression of bcl2, p53, caspase3/9 genes at RNA and protein levels using RT-qPCR and Western blot, respectively, to figure out the cell death mechanism induced by MA1. A significant down-regulation in bcl2 and p53 genes was observed in treated cells compared to non-treated cells (p < 0.05), suggesting that MA1 may not follow the canonical pathway to induce apoptosis in ovarian cancer cell lines. MalforminA1 showed promising anticancer activity by inducing cytotoxicity in cisplatin-sensitive and cisplatin-resistant cancer cell lines. Interestingly, a synergistic effect was observed when MA1 was combined with cisplatin, leading to it overcoming its resistance to cisplatin.     

Structures and Bioactivities of Steroidal Saponins Isolated from the Genera Dracaena and Sansevieria

The species Dracaena and Sansevieria, that are well-known for different uses in traditional medicines and as indoor ornamental plants with air purifying property, are rich sources of bioactive secondary metabolites. In fact, a wide variety of phytochemical constituents have been isolated so far from about seventeen species. This paper has reviewed the literature of about 180 steroidal saponins, isolated from Dracaena and Sansevieria species, as a basis for further studies. Saponins are among the most characteristic metabolites isolated from the two genera. They show a great variety in structural motifs and a wide range of biological activities, including anti-inflammatory, anti-microbial, anti-proliferative effects and, in most case, remarkable cytotoxic properties.