Biopolymeric alginic acid: an efficient recyclable green catalyst for the Friedel–Crafts reaction of indoles with isoquinoline-1,3,4-triones in water

A supramolecular catalyst based on sodium alginate and viologen calix[4]resorcinol for the room temperature hydrolysis of paraoxon

Properties of paraoxon, such as poor water solubility, low rate of natural decomposition, ability to accumulate in soil and wastewater, lead to the fact that paraoxon is found in various agricultural products and textiles. In this regard, the search for effective ways of paraoxon degradation becomes an extremely urgent problem, which can be solved by creating catalysts by mimicking paraxonase. In this work, a complex of physicochemical methods was used to study the supramolecular interactions of sodium alginate, which has a calcium-binding ability similar to paraxonase, with viologen calix[4]resorcinol and to reveal the nature of the intermolecular interactions between them resulting in the spontaneous formation of nanoparticles. Before proceeding to the investigation of the binding ability of obtained nanoparticles to paraoxon, the encapsulating effect of nanoparticles on a number of model substrates of different solubility (doxorubicin hydrochloride, quercetin and oleic acid) was studied. The kinetics of paraoxon hydrolysis reaction using these nanoparticles was studied at room temperature in an aqueous medium by spectrophotometric method. The rate of this reaction increases with increasing concentration of stable nanoparticles having hydrophobic domains that ensure paraoxon immobilization. The results obtained allow considering the supramolecular polysaccharide/calixarene system as an effective biomimetic catalyst.

Facile synthesis of pyrazolopyridine pharmaceuticals under mild conditions using an algin-functionalized silica-based magnetic nanocatalyst (Alg@SBA-15/Fe3O4)†

Pyrazolopyridines are common scaffolds in various bioactive compounds, which have several therapeutic effects and unique pharmacological properties. In this study, we fabricated a novel environmentally friendly silica-based nanocomposite as a multifunctional catalytic system for the synthesis of pyrazolopyridine derivatives. This novel heterogeneous nanocomposite named Alg@SBA-15/Fe₃O₄ (Alg stands for alginic acid), was prepared in several steps. In this regard, SBA-15 was synthesized by the hydrothermal method. Next, it was magnetized by Fe₃O₄ nanoparticles via an in situ co-precipitation process. Then, SBA-15/Fe₃O₄ particles were functionalized with 3-minopropyltriethoxysilane (APTES). Afterward, Alg@SBA-15/Fe₃O₄ was obtained by a nucleophilic substitution reaction between SBA-15/Fe₃O₄–NH₂ and an as-synthesized methyl-esterified alginic. Different analyses such as Fourier-transform infrared (FTIR), energy-dispersive X-ray (EDX) spectroscopy, field-emission scanning-electron microscopy (FESEM), vibrating-sample magnetometer (VSM), X-ray diffraction (XRD), thermogravimetric analysis (TGA), and BET (Brunauer–Emmett–Teller) have been used to confirm the structure of the fabricated catalyst. The magnetic properties of the Alg@SBA-15/Fe₃O₄ catalytic system imparted by Fe₃O₄ MNPs enable it to be conveniently isolated from the reaction mixture by using an external magnet. According to the obtained results, the prepared nanocatalyst has high thermal stability and it lost approximately 26% of its weight up to 800 °C. Interestingly, a small amount of prepared nanocatalyst (0.02 g) has shown excellent catalytic performance in the synthesis of pyrazolopyridine derivatives (90–97%) in a short reaction time (20–30 min) at room temperature which can be attributed to its porous structure and large surface area, and the presence of many acidic and basic functional groups. In general, it can be argued that the Alg@SBA-15/Fe₃O₄ nanocomposite deserves more attention due to its non-toxicity, ease of preparation, good recyclability, and its high catalytic efficiency.

Pyrazolopyridines are common scaffolds in various bioactive compounds, which have several therapeutic effects and unique pharmacological properties.

Removal of Zn(II) and Ni(II) heavy metal ions by new alginic acid-ester derivatives materials

The present work concerns the preparation of new materials based on alginic acid (AA) and diols in a facile and efficient process by improving the adsorption properties of Zn(II) and Ni(II) metal ions on the modified AA. The materials were analysed by zeta potential, thermogravimetric analysis (TGA), derivative thermogravimetry (DTG), in addition to the Fourier Transform InfraRed spectroscopy (FTIR), scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS) before and after the adsorption behaviour was conducted. The results show that the esterification of AA with diols of different lengths significantly improves its adsorption efficiency of Zn(II) and Ni(II) with Q_max up to 200 mg/g and 185.185 mg/g respectively. Equilibrium and kinetic studies showed that the Langmuir and Freundlich adsorption isotherm models fit the experimental data well, and followed a pseudo-first order kinetic model and the particle diffusion model with correlation coefficients R² ≈ 1.

Structures, properties and application of alginic acid: A review

Alginic acid is a natural polysaccharide, which has been widely concerned and applied due to its excellent water solubility, film formation, biodegradability and biocompatibility. This paper briefly describes the source, properties, structure and application of sodium alginate by summarizing and analyzing the current literature. This paper reviews the application of sodium alginate in the fields of food industry, catalyst, health, water treatment, packaging, immobilized cells, and looks forward to its application prospects.

Valorization of Waste: Sustainable Organocatalysts from Renewable Resources

One of the greatest challenges facing our society is to reconcile our need to develop efficient and sophisticated chemical processes with the limited resources of our planet and its restricted ability to adsorb pollution. Organocatalysis has allowed many issues to be addressed in the development of sophisticated, but less polluting, processes. However, minimizing waste also means an efficient utilization of raw and renewable materials. Waste biomass represents an alternative to conventional petroleum-based chemical manufacturing and is a highly attractive renewable resource for the production of chemicals and high-value-added organocatalysts. Recent achievements in the use of renewable biomass feedstocks for the synthesis of organocatalysts are presented. Their application in synthetic methodologies, including multicomponent reactions, which are performed under solvent-free conditions or in eco-friendly reaction media, as well as recycling and reusing the organocatalysts, is illustrated. A few pioneering examples that demonstrate the potential of these promoters in asymmetric synthesis have also been documented. In particular, this review covers examples on the use of hetero- and homogeneous organocatalysts derived from 1) waste biopolymers, such as chitosan, alginic acid, and cellulose; ii) renewable platform molecules, such as levoglucosenone, isosorbide, mannose, d-glucosamine, and lecithin; 3) terpenes and rosin, such as pinane, isosteviol, and abietic acid; and iv) natural proteins (gelatin, bovine tendons, silk fibroin proteins).

Spiro Indane-Based Phosphine-Oxazolines as Highly Efficient P,N Ligands for Enantioselective Pd-Catalyzed Allylic Alkylation of Indoles and Allylic Etherification

A series of indane-based phosphine-oxazoline ligands with a spirocarbon stereogenic center were examined for palladium-catalyzed asymmetric allylic alkylation of indoles. Under optimized conditions, high yields (up to 98%) and enantioselectivities (up to 98% ee) were obtained with a broad scope of indole derivatives. The ligand was determined to be the most efficient P,N-ligand for this reaction. Moreover, the ligand was also efficient for Pd-catalyzed asymmetric allylic etherification with hard aliphatic alcohols as nucleophiles.

Enantioselective synthesis of isoquinoline-1,3(2H,4H)-dione derivatives via a chiral phosphoric acid catalyzed aza-Friedel-Crafts reaction

A highly enantioselective aza-Friedel-Crafts reaction of structurally new ketimines with indoles and pyrrole is developed by using a chiral phosphoric acid as the catalyst. This protocol enables the first enantioselective synthesis of isoquinoline-1,3(2H,4H)-dione derivatives in good to excellent yields (up to 99% yield) and excellent enantioselectivities (up to >99% ee).

Synthesis of α-functionalized α-indol-3-yl carbonyls through direct SN reactions of indol-3-yl α-acyloins

A new and efficient synthesis of α-functionalized α-indol-3-yl ketones from easily available indolyl α-acyloins is reported. This process, catalyzed by Brønsted or Lewis acids, involves an uncommon direct nucleophilic substitution reaction of a secondary α-carbonyl-substituted hydroxyl group. The described methodology allows the introduction of a variety of nucleophiles such as (hetero)arenes, thiophenols, nitroanilines and 1,3-dicarbonyl derivatives. The synthesized α-indol-3-yl carbonyl compounds are important synthetic targets also useful for accessing functionalized tryptophols and furan-3-yl indoles.