Green synthesis and characterization of silver nanoparticles (Ag NPs) from extract of plant Radix Puerariae: An efficient and recyclable catalyst for the construction of pyrimido[1,2-b]indazole derivatives under solvent-free conditions

Divergent synthesis of pyrrolidone fused pyrimido[1,2-b]indazole through selective trapping of an enone intermediate by 1H-indazol-3-amine

An oxidant-controlled divergent synthesis of a pyrrolidone fused pyrimido[1,2-b]indazole skeleton was developed through selective cyclization of an in situ generated enone intermediate and 1H-indazol-3-amine. The one-pot, metal-free process formed three C-N bonds, one C-C bond, and a tetrasubstituted carbon stereocenter containing a hydroxyl group. This method not only allowed for the synthesis of over 60 new pyrrolidone fused pyrimido[1,2-b]indazole derivatives, but was also compatible with the transformation of complex active molecules and the derivation of target products. Significantly, product 4q exhibited aggregation-induced emission (AIE) characteristics without any further modification.

Assessment of the Effect of Surface Modification of Metal Oxides on Silver Nanoparticles: Optical Properties and Potential Toxicity

Silver nanoparticles (AgNPs) have garnered significant interest due to their distinctive properties and potential applications. Traditional fabrication methods for nanoparticles often involve high-energy physical conditions and the use of toxic solvents. Various green synthesis approaches have been developed to circumvent these issues and produce environmentally benign nanoparticles. Our study focuses on the green synthesis of AgNPs using L-ascorbic acid and explores the modification of their properties to enhance antibacterial and anticancer effects. This is achieved by coating the nanoparticles with Zinc oxide (ZnO) and Silica oxide (SiO2), which alters their optical properties in the visible spectrum. The synthesized formulations-AgNPs, zinc oxide-silver nanoparticles (Ag@ZnO), and silica oxide-silver nanoparticles (Ag@SiO2) core/shell nanoparticles-were characterized using a suite of physicochemical techniques, including Transmission Electron Microscopy (TEM), Dynamic Light Scattering (DLS), Zeta potential measurement, UV-Vis spectroscopy, Refractive Index Measurements, and Optical Anisotropy Assessment. TEM imaging revealed particle sizes of 11 nm for AgNPs, 8 nm for Ag@ZnO, and 400 nm for Ag@SiO2. The Zeta potential values for Ag@ZnO and Ag@SiO2 were measured at -17.0 ± 5 mV and -65.0 ± 8 mV, respectively. UV-Vis absorption spectra were recorded for all formulations in the 320 nm to 600 nm wavelength range. The refractive index of AgNPs at 404.7 nm was 1.34572, with slight shifts observed for Ag@ZnO and Ag@SiO2 to 1.34326 and 1.37378, respectively. The cytotoxicity of the nanocomposites against breast cancer cell lines (MCF-7) was assessed using the MTT assay. The results indicated that AgNPs and Ag@ZnO exhibited potent therapeutic effects, with IC50 values of 494.00 µg/mL and 430.00 µg/mL, respectively, compared to 4247.20 µg/mL for Ag@SiO2. Additionally, the antibacterial efficacy of AgNPs was significantly enhanced under visible light irradiation. Ag@ZnO demonstrated substantial antibacterial activity both with and without light exposure, while the Ag@SiO2 nanocomposites significantly reduced the inherent antibacterial activity of silver. Conversely, the Ag@ZnO nanocomposites displayed pronounced antibacterial and anticancer activities. The findings suggest that silver-based nanocomposites, particularly Ag@ZnO, could be practical tools in water treatment and the pharmaceutical industry due to their enhanced therapeutic properties.

I2-DMSO-Mediated Construction of 2,3- and 2,4-Disubstituted Pyrimido[1,2-b]indazole Skeletons

An efficient synthetic method for constructing 2,3- and 2,4-disubstituted pyrimidio[1,2-b]indazole skeletons through I2-DMSO-mediated and substrate-controlled regioselective [4 + 2] cyclization is reported. The reaction conditions are mild, its operation is simple, and the substrate scope is wide. More than 60 pyrimidio[1,2-b]indazole derivatives have been synthesized, providing a new methodology for constructing related molecules and potentially enriching bioactive-molecule libraries.

Transition-Metal Catalyzed Synthesis of Pyrimidines: Recent Advances, Mechanism, Scope and Future Perspectives

Pyrimidine is a pharmacologically important moiety that exhibits diverse biological activities. This review reflects the growing significance of transition metal-catalyzed reactions for the synthesis of pyrimidines (with no discussion being made on the transition metal-catalyzed functionalization of pyrimidines). The effect of different catalysts on the selectivity/yields of pyrimidines and catalyst recyclability (wherever applicable) are described, together with attempts to illustrate the role of the catalyst through mechanisms. Although several methods have been researched for synthesizing this privileged scaffold, there has been a considerable push to expand transition metal-catalyzed, sustainable, efficient and selective synthetic strategies leading to pyrimidines. The aim of the authors with this update (2017-2023) is to drive the designing of new transition metal-mediated protocols for pyrimidine synthesis.

One-pot green synthesis of silver nanoparticles using brittle star Ophiocoma scolopendrina: Assessing biological potentialities of antibacterial, antioxidant, anti-diabetic and catalytic degradation of organic dyes

In the current study, aqueous extract of O. scolopendrina (OSE) was used to synthesize AgNPs in a simple and environmentally friendly manner. The biosynthesized OSE-AgNPs were also assessed for its catalytic, antibacterial, anti-diabetic, antioxidant and dye degradation properties. The techniques like UV-visible spectroscopic examinations, TEM, SEM, TGA, zeta potential and FT-IR were used in the characterization investigations. The bioproduction of OSE-AgNPs was preliminary confirmed by UV-visible spectroscopic based investigation followed by microscopic visualization. The synthesized OSE-AgNPs exhibited a reddish brown colour and nearly spherical forms with sizes between 5 and 50 nm quantified by TEM and SEM. The attendance of functional groups like -OH and -NH present in OSE caps on the AgNPs surface was confirmed by FTIR analysis. Interestingly, in the presence of OSE-AgNPs, the degradation of dyes (CV, 95% and EY, 96% in 15 min) were noticeably accelerated. Further, OSE-AgNPs demonstrated substantial antibacterial activity; robust antioxidant properties andnotable anti-diabetic activities. This is the first account on the biosynthetic process of AgNPs using the aqueous extract of O. scolopendrina.

Recent advances in 3-aminoindazoles as versatile synthons for the synthesis of nitrogen heterocycles

Nitrogen-based heterocycles are an important class of structural scaffolds distributed in biologically active natural products, medicinal chemistry, and agrochemicals. Hence, there is increasing interest in the development of novel synthetic strategies for the construction of these privileged structural motifs. Recently, 3-aminoindazoles have emerged as versatile synthons participating in a variety of condensation annulation, denitrogenative transannulation and rearrangement ring expansion reactions, which provide efficient synthetic routes for the formation of nitrogen heterocycles. This review systematically highlights for the first time the most recent advances in 3-aminoindazoles to provide a deep understanding of using 3-aminoindazoles as versatile synthons in organic transformations for synthetic and medicinal chemists.

Antimicrobial Activities against Opportunistic Pathogenic Bacteria Using Green Synthesized Silver Nanoparticles in Plant and Lichen Enzyme-Assisted Extracts

Enzyme-assisted extraction is a valuable tool for mild and environmentally-friendly extraction conditions to release bioactive compounds and sugars, essential for silver nanoparticle (AgNP) green synthesis as capping and reducing agents. In this research, plant and fungal kingdoms were selected to obtain the enzyme-assisted extracts, using green synthesized AgNPs. For the synthesis, pseudo-cereal Fagopyrum esculentum (F. esculentum) and lichen Certaria islandica (C. islandica) extracts were used as environmentally-friendly agents under heating in an aqueous solution. Raw and enzyme-assisted extracts of AgNPs were characterized by physicochemical, phytochemical, and morphological characteristics through scanning and transmission electron microscopy (SEM and TEM), as well as Fourier transform infrared spectroscopy (FTIR). The synthesized nanoparticles were spherical in shape and well dispersed, with average sizes ranging from 10 to 50 nm. This study determined the total phenolic content (TPC) and in vitro antioxidant activity in both materials by applying standard methods. The results showed that TPC, ABTS^•+, FRAP, and DPPH^• radical scavenging activities varied greatly in samples. The AgNPs derived from enzymatic hydrolyzed aqueous extracts C. islandica and F. esculentum exhibited higher antibacterial activity against the tested bacterial pathogens than their respective crude extracts. Results indicate that the extracts’ biomolecules covering the AgNPs may enhance the biological activity of silver nanoparticles and enzyme assistance as a sustainable additive to technological processes to achieve higher yields and necessary media components.

Recent advances on botanical biosynthesis of nanoparticles for catalytic, water treatment and agricultural applications: A review

Green synthesis of nanoparticles using plant extracts minimizes the usage of toxic chemicals or energy. Here, we concentrate on the green synthesis of nanoparticles using natural compounds from plant extracts and their applications in catalysis, water treatment and agriculture. Polyphenols, flavonoid, rutin, quercetin, myricetin, kaempferol, coumarin, and gallic acid in the plant extracts engage in the reduction and stabilization of green nanoparticles. Ten types of nanoparticles involving Ag, Au, Cu, Pt, CuO, ZnO, MgO, TiO₂, Fe₃O₄, and ZrO₂ with emphasis on their formation mechanism are illuminated. We find that green nanoparticles serve as excellent, and recyclable catalysts for reduction of nitrophenols and synthesis of organic compounds with high yields of 83-100% and at least 5 recycles. Many emerging pollutants such as synthetic dyes, antibiotics, heavy metal and oils are effectively mitigated (90-100%) using green nanoparticles. In agriculture, green nanoparticles efficiently immobilize toxic compounds in soil. They are also sufficient nanopesticides to kill harmful larvae, and nanoinsecticides against dangerous vectors of pathogens. As potential nanofertilizers and nanoagrochemicals, green nanoparticles will open a revolution in green agriculture for sustainable development.

Plant-Mediated Green Synthesis of Ag NPs and Their Possible Applications: A Critical Review

The potential applications of Ag NPs are exciting and beneficial in a variety of fields; however, there is less awareness of the new risks posed by inappropriate disposal of Ag NPs. The Ag NPs have medicinal, plasmonic, and catalytic properties. The Ag NPs can be prepared via physical, chemical, or biological routes, and the selection of any specific route depends largely on the end-use. The downside of a physical and chemical approach is that it requires a wide space, high temperature, high temperature for a longer time to preserve the thermal stability of synthesized Ag NPs, and the use of toxic chemicals. Although these methods produce nanoparticles with high purity and well-defined morphology, it is critical to develop cost-effective, energy-efficient, and facile route, such as green synthesis; it suggests the desirable use of renewable resources by avoiding the use of additional solvents and toxic reagents in order to achieve the ultimate goal. However, each method has its pros and cons. The synthesized Ag NPs obtained using the green approach have larger biocompatibility and are less toxic towards the biotic systems. However, identifying the phytoconstituents that are responsible for nanoparticle synthesis is difficult and has been reported as a suitable candidate for biological application. The concentration of the effective bioreducing phytoconstituents plays a crucial role in deciding the morphology of the nanoparticle. Besides these reaction times, temperature, pH, and concentration of silver salt are some of the key factors that determine the morphology. Hence, careful optimization in the methodology is required as different morphologies have different properties and usage. It is due to which the development of methods to prepare nanoparticles effectively using various plant extracts is gaining rapid momentum in recent days. To make sense of what involves in the bioreduction of silver salt and to isolate the secondary metabolites from plants are yet challenging. This review focuses on the contribution of plant-mediated Ag NPs in different applications and their toxicity in the aquatic system.

Formation, antimicrobial activity, and biomedical performance of plant-based nanoparticles: a review

Because many engineered nanoparticles are toxic, there is a need for methods to fabricate safe nanoparticles such as plant-based nanoparticles. Indeed, plant extracts contain flavonoids, amino acids, proteins, polysaccharides, enzymes, polyphenols, steroids, and reducing sugars that facilitate the reduction, formation, and stabilization of nanoparticles. Moreover, synthesizing nanoparticles from plant extracts is fast, safe, and cost-effective because it does not consume much energy, and non-toxic derivatives are generated. These nanoparticles have diverse and unique properties of interest for applications in many fields. Here, we review the synthesis of metal/metal oxide nanoparticles with plant extracts. These nanoparticles display antibacterial, antifungal, anticancer, and antioxidant properties. Plant-based nanoparticles are also useful for medical diagnosis and drug delivery.

A review of the phytochemical mediated synthesis of AgNP (silver nanoparticle): the wonder particle of the past decade

Silver nanoparticle (AgNP) has been one of the most commonly used nanoparticles since the past decade for a wide range of applications, including environmental, agricultural, and medical fields, due to their unique physicochemical properties and ease of synthesis. Though chemical and physical methods of fabricating AgNPs have been quite popular, they posed various environmental problems. As a result, the bioinspired route of AgNP synthesis emerged as the preferred pathway for synthesis. This review focuses extensively on the biosynthesis of AgNP-mediated through different plant species worldwide in the past 10 years. The most popularly utilized application areas have been highlighted with their in-depth mechanistic approach in this review, along with the discussion on the different phytochemicals playing an important role in the bio-reduction of silver ions. In addition to this, the environmental factors which govern their synthesis and stability have been reviewed. The paper systematically analyses the trend of research on AgNP biosynthesis throughout the world through bibliometric analysis. Apart from this, the feasibility analysis of the plant-mediated synthesis of nanoparticles and their applications have been intrigued considering the perspectives of engineering, economic, and environmental limitations. Thus, the review is not only a comprehensive summary of the achievements and current status of plant-mediated biosynthesis but also provides insight into emerging future research frontier.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13204-021-02135-5.

Ag-Catalyzed Multicomponent Synthesis of Heterocyclic Compounds: A Review

The investigation of the procedures for the multi-component synthesis of heterocycles has attracted the interest of organic and medicinal chemists. The use of heterogeneous catalysts, especially transition metal catalysts in organic synthesis, can provide a new, improved alternative to traditional methods in modern synthetic chemistry. The main focus is on the utilization of silver as a catalyst for the multi-component synthesis of heterocyclic compounds. The present review describes some important reported studies for the period of 2010 to 2020. Conclusion: The present review addresses some of the important reported studies on multi-component synthesis of heterocycles in the period of 2010-2020. These approaches were performed under classical and nonclassical conditions, using Ag salts, Ag NPs, Ag on the support, Ag as co-catalysts with other transition metals, ionic liquids, acidic or basic materials. Most of the reported reactions were performed under solvent-free conditions or in green solvents and the utilized catalysts were mostly recyclable. The main aim of the present review is to provide the organic chemists with the most appropriate procedures in the multi-component synthesis of desired heterocycles using silver catalysts.

Indoleninyl-substituted pyrimido[1,2-b]indazoles via a facile condensation reaction

A new series of pyrimido[1,2-b]indazoles bearing indolenine moieties was synthesized through a simple condensation reaction with up to 94% yield. The present method features the versatile formation of a pyrimidine ring with a broad range of substrates, great functional group compatibility and facile synthetic operation. The work offers opportunities in drug development as well as in materials science.

Pyrimido[1,2-b]indazole derivatives: Selective inhibitors of human monoamine oxidase B with neuroprotective activity

Structurally diverse heterotricyclic compounds are recognized as monoamine oxidase (MAO) inhibitors and thus represent an appealing scaffold in development and optimization of novel MAO inhibitors. Herein we explored the chemical space of pyrimido[1,2-b]indazoles as MAO inhibitors by preparing a small library of (hetero)aryl derivatives. An efficient synthetic strategy was developed starting from commercially available 1H-indazol-3-amines, which were converted to various 3-bromoheterotricyclic derivatives and further functionalized via Suzuki-Miyaura coupling reaction. Derivatives 4a-t selectively inhibited human MAO-B isoform in a reversible and competitive manner as confirmed by kinetic experiments and docking studies. Selected derivatives were not cytotoxic to neuroblastoma SH-SY5Y cells. Moreover, analogue 4i protected human neuroblastoma SH-SY5Y cells against 6-hydroxydopamine-induced cell death, which confirms the applicability of the pyrimido[1,2-b]indazoles as potential antiparkinsonian agents.

Valorisation of Fruits, their Juices and Residues into Valuable (Nano)materials for Applications in Chemical Catalysis and Environment

One of the most abundant wastes from all around the world is nutrient resources. Among them, fruits, their extracts, and residues comprise a major portion, which contain many valuable components that get lost during disposal or become burden on the shrinking landfills. These concerns are addressed by seeking sustainable processing methods that would have a minimal environmental impact. The crops contain renewable chemicals which are useful for catalysis, wastewater treatment, or preparation of nanomaterials; there has been an upsurge for the industrial applications of (nano)materials as their environmental and catalytic appliances is a fascinating subject to design cheaper and safer catalytic systems. Due to the excellent chemical properties of the fruit extracts, they have garnered attention as cost-effective catalysts and support materials. This review focuses on the preparation of (nano)materials and their catalytic and environmental applications and highlights the potential appliances and industrial benefits derived from these low-cost renewable and sustainable greener sources thus essentially converting waste into wealth.

A decennary update on applications of metal nanoparticles (MNPs) in the synthesis of nitrogen- and oxygen-containing heterocyclic scaffolds

Heterocycles have been found to be of much importance as several nitrogen- and oxygen-containing heterocycle compounds exist amongst the various USFDA-approved drugs. Because of the advancement of nanotechnology, nanocatalysis has found abundant applications in the synthesis of heterocyclic compounds. Numerous nanoparticles (NPs) have been utilized for several organic transformations, which led us to make dedicated efforts for the complete coverage of applications of metal nanoparticles (MNPs) in the synthesis of heterocyclic scaffolds reported from 2010 to 2019. Our emphasize during the coverage of catalyzed reactions of the various MNPs such as Ag, Au, Co, Cu, Fe, Ni, Pd, Pt, Rh, Ru, Si, Ti, and Zn has not only been on nanoparticles catalyzed synthetic transformations for the synthesis of heterocyclic scaffolds, but also provide an inherent framework for the reader to select a suitable catalytic system of interest for the synthesis of desired heterocyclic scaffold.

Catalyst-Free One-Pot Synthesis of Densely Substituted Pyrazole-Pyrazines as Anti-Colorectal Cancer Agents

The first catalyst-free post-Ugi cascade methodology was developed for expeditious access to structurally diverse and complex pyrazole-pyrazines in one-pot. This novel cascade reaction features an intramolecular N2-arylation of pyrazoles with allenes at the C-β position of triple bond. Screening in the colorectal cancer cell lines HCT116 and SW620 validated the feasibility of the methodology for generating bioactive compounds. The lead compound 7h which is active against HCT116 and SW620 with IC₅₀ of 1.3 and 1.8 µM, respectively, can be synthesized and purified in a gram process synthetic scale in 7 hours. The mechanical studies indicated that compound 7h can induce cell cycle arrest in the G2/M phase and inhibit proliferation and viability in human colon cancer cells. Overall, compound 7h is represented as a promising starting point for the development of new anti-colorectal cancer drugs.

New efficient synthesis of benzofuro[2,3-b]pyrroles utilizing a reactive nitrilium trapping approach by an acid-promoted cascade addition/cyclization sequence

The first p-TSA·H₂O-catalyzed highly efficient one-pot cascade reaction for the synthesis of novel fused tricyclic benzofuro[2,3-b]pyrroles has been discovered.

Phyto-Nanocatalysts: Green Synthesis, Characterization, and Applications

Catalysis represents the cornerstone of chemistry, since catalytic processes are ubiquitous in almost all chemical processes developed for obtaining consumer goods. Nanocatalysis represents nowadays an innovative approach to obtain better properties for the catalysts: stable activity, good selectivity, easy to recover, and the possibility to be reused. Over the last few years, for the obtaining of new catalysts, classical methods—based on potential hazardous reagents—have been replaced with new methods emerged by replacing those reagents with plant extracts obtained in different conditions. Due to being diversified in morphology and chemical composition, these materials have different properties and applications, representing a promising area of research. In this context, the present review focuses on the metallic nanocatalysts’ importance, different methods of synthesis with emphasis to the natural compounds used as support, characterization techniques, parameters involved in tailoring the composition, size and shape of nanoparticles and applications in catalysis. This review presents some examples of green nanocatalysts, grouped considering their nature (mono- and bi-metallic nanoparticles, metallic oxides, sulfides, chlorides, and other complex catalysts).

Green syntheses of silver nanoparticle decorated reduced graphene oxide using l-methionine as a reducing and stabilizing agent for enhanced catalytic hydrogenation of 4-nitrophenol and antibacterial activity

Herein, we have reported a facile and green synthesis approach of Ag NP decorated reduced graphene oxide (RGO) through an in situ self-assembly method in the presence of l-methionine (l-Met) as reducing and stabilizing agent. The electronic properties, crystal structure, and morphology of the as-synthesized RGO–Ag nanocomposite were investigated by UV-Visible (UV-Vis) spectroscopy, Fourier transform-infrared (FTIR), X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) techniques. UV-Vis and FTIR show the effective reduction of GO and the formation of Ag NPs using l-Met. FESEM, TEM, and XRD analysis show the successful impregnation of Ag NPs into RGO with a 23 nm average crystallite size. The RGO–Ag nanocomposite with NaBH₄ shows a fast-catalytic reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AMP). The enhanced catalytic activity of RGO–Ag nanocomposites can be attributed to the synergistic effect of improved adsorption capacity and the absence of agglomeration of Ag nanoparticles. Moreover, RGO–Ag showed strong antibacterial activity against B. subtilis and E. coli.

Herein, we have reported a facile and green synthesis approach of Ag NP decorated reduced graphene oxide (RGO) through an in situ self-assembly method in the presence of l-methionine (l-Met) as reducing and stabilizing agent.

Palladium-catalyzed direct C–H nitration and intramolecular C–H functionalization for the synthesis of 3-nitro-1-(phenylsulfonyl)-1H-indazole derivatives

Various 3-nitro-1-(phenylsulfonyl)-1H-indazole derivatives have been obtained in moderate to high yields using palladium catalysis.

Aminoazole-Based Diversity-Oriented Synthesis of Heterocycles

The comprehensive review contains the analysis of literature data concerning reactions of heterocyclization of aminoazoles and demonstrates the application of these types of transformations in diversity-oriented synthesis. The review is oriented to wide range of chemists working in the field of organic synthesis and both experimental and theoretical studies of nitrogen-containing heterocycles.