Rajiv Trivedi

The medicinal chemistry of ferrocene has gained its momentum after the discovery of biological activities of ferrocifen and ferroquine. These ferrocenyl drugs have been designed by replacing the aromatic moiety of the organic drugs, tamoxifen and chloroquine respectively, with a ferrocenyl unit. The promising biological activities of these ferrocenyl drugs have paved a path to explore the medicinal applications of several ferrocenyl conjugates. In these conjugates, the ferrocenyl moiety has played a vital role in enhancing or imparting the anticancer activity to the molecule. The ferrocenyl conjugates induce the cytotoxicity by generating reactive oxygen species and thereby damaging the DNA. In medicinal chemistry, the five membered nitrogen heterocycles (azoles) play a significant role due to their rigid ring structure and hydrogen bonding ability with the biomolecules. Several potent drug candidates with azole groups have been in use as chemotherapeutics. Considering the importance of ferrocenyl moiety and azole groups, several ferrocenyl azole conjugates have been synthesized and screened for their biological activities. Hence, in the view of a wide scope in the development of potent drugs based on ferrocenyl azole conjugates, herein we present the details of synthesis and the anticancer activities of ferrocenyl compounds bearing azole groups such as imidazole, triazoles, thiazole and isoxazoles.

Fluoride ion plays a pivotal role in a range of biological and chemical applications however excessive exposure can cause severe kidney and gastric problems. A simple and selective molecular sensor, 4,5-di(thien-2-yl)-2-(4-(1,2,2-triphenylvinyl)-phenyl)-1H-imidazole, DTITPE, has been synthesized for the detection of fluoride ions, with detection limits of 1.37 × 10⁻⁷ M and 2.67 × 10⁻¹³ M, determined by UV-vis. and fluorescence spectroscopy, respectively. The variation in the optical properties of the molecular sensor in the presence of fluoride ions was explained by an intermolecular charge transfer (ICT) process between the bis(thienyl) and tetraphenylethylene (TPE) moieties upon the formation of a N-H---F⁻ hydrogen bond of the imidazole proton. The sensing mechanism exhibited by DTITPE for fluoride ions was confirmed by ¹H NMR spectroscopic studies and density functional theory (DFT) calculations. Test strips coated with the molecular sensor can detect fluoride ions in THF, undergoing a color change from white to yellow, which can be observed with the naked eye, showcasing their potential real-world application.

Functional materials composed of Boron‐chalcogenophene conjugates have emerged as promising ensemble featuring commendable optoelectronic properties. This review describes the categories, synthetic routes and optoelectronic applications of a range of boron‐chalcogenophene conjugates. Conjugation and linking of different types of tri‐ and tetra‐coordinated boron moieties with chalcogenophenes have remained an important strategy for constructing a range of functional materials. Synthetic protocols have been devised to efficiently prepare such chemically robust conjugates, often exhibiting a myriad of photophysical properties, redox capabilities and also solid‐state behaviors. Tin‐boron and silicon‐boron exchange protocols have been efficiently adapted to access these boron‐chalcogenophenes. Few other commonly used methods namely, hydroboration of alkynes as well as electrophilic borylations are also mentioned. The chemical and electronic properties of such boron‐chalcogenophene conjugates are directly influenced by the strong Lewis acid character of trivalent boranes which can further alter the intra‐ and inter‐ molecular Lewis acid‐base interactions. Apart from the synthetic protocols, recent advances in the application of these boron‐chalcogenophene conjugates towards analyte sensing, organic electronics, molecular switches and several other aspects will be discussed in this review.

Correction for ‘Bacterial biosynthesis of nanosilver: a green catalyst for the synthesis of (amino pyrazolo)-(phenyl)methyl naphth-2-ol derivatives and their antimicrobial potential’ by Ganji Praveena et al., New J. Chem., 2020, 44, 13046–13061, DOI: 10.1039/D0NJ01924K.

Over the past few decades, the use of silver nanoparticles in various fields like medicine, agriculture and the food industry has emerged as an interesting and exciting approach. In addition to these, recently, silver nanoparticles have also demonstrated their catalytic properties in various applications like synthesis of pharmaceutical compounds and natural products. The use of silver nanoparticles as catalysts has gained more importance due to their stability, unique reactivity and recyclability. In the present study, heterogeneous silver nanoparticles, produced from isolated strain Streptomyces sp. RAB 10, were used as catalysts in a three-component reaction of aryl aldehydes, 5-amino-3-methyl pyrazole and β-naphthol for the synthesis of naphthalene-2-derivatives in aqueous media. The synthesized compounds were characterized using ¹H NMR, ¹³C NMR, mass spectroscopy and FT-IR. Some of the advantages of the multi-component one-pot protocol used in the study include shorter reaction time, good yield, ease of recoverability and reuse of the silver nanoparticles as catalysts. One of the important features of this methodology is the synthesis of a novel product with two reactive functional groups (hydroxy and free amine), which opens up avenues for the synthesis of a new array of compounds. The biosynthesised AgNPs as well as the naphthalene-2-derivatives exhibited moderate to good anti-microbial activity.

A series of eight novel ferrocene–oxime ether benzyl 1H-1,2,3 triazole hybrids 5a–h were designed and synthesized by employing Cu(I) catalyzed azide–alkyne [3+2] cycloaddition (CuAAC) between ferrocenecarboxaldehyde oxime O-propargyl ether and benzyl azides. The alkyne, ferrocenecarboxaldehyde oxime O-propargyl ether 3, was synthesized by converting ferrocenecarboxaldehyde 1 into ferrocenecarboxaldehyde oxime 2 with subsequent O-propargylation. All the ferrocenyl triazole derivatives are remarkably stable crystalline solids and were obtained in good yields. All the products were well characterized by means of various analytical and spectroscopic techniques. The electrochemical behavior of the synthesized ferrocene–oxime ether benzyl triazole hybrids was investigated. Further, the structure of one of the triazoles 5a was unambiguously established by means of single-crystal X-ray diffraction study. All the triazole compounds have been screened for in vitro antimicrobial activity against two Gram-positive (Bacillus subtilis and Staphylococcus aureus) and two Gram-negative bacteria (Escherichia coli and Klebsiella pneumoniae), and one fungal (Candida albicans) microorganism. All the ferrocene–oxime ether benzyl 1H-1,2,3 triazole hybrids have shown moderate to good inhibitory activity against most of the tested bacterial and fungal strains in comparison with standard drugs.

A series of bioactive, triazole‐linked benzyl, aryl, sugar and aliphatic conjugates of 3‐ferrocenylidene‐oxindole have been synthesized. A facile 1,3‐dipolar‐Huisgen coupling reaction of the respective azides with the 3‐ferrocenylidene‐oxindole N‐propargyl moiety (3) gave the corresponding conjugates (5a–n). All the newly synthesized compounds (5a–n) were characterized by ¹H‐NMR, ¹³C‐NMR, HRMS, Fourier transform‐infrared spectroscopy and elemental analysis. The UV–Vis and electrochemical studies of these compounds were performed in dimethylsulfoxide solutions. The structure of compound (3) was determined by single crystal X‐ray diffraction study. These compounds exhibited moderate to good antimicrobial activity against Gram‐positive and Gram‐negative strains.

A highly selective isophorone‐boronate ester based chemosensor, (1), having a dicyanovinyl moiety as a convenient colorimetric probe, has been designed. Different types of anionic analyte such as CH₃COO⁻, ClO₄⁻, Cl⁻, F⁻, PF₆⁻, Br⁻ and HSO₄⁻ were tested and among them only highly nucleophilic F⁻ anion displayed significant response towards the sensor. Addition of the fluoride anion across the boron atom disrupts the π‐conjugation thereby shifts the absorption wavelength towards the redshift region due to the decrease in the HOMO‐LUMO energy gap and a colour change from yellow to blue is observed under visible light condition. The detection limit of this probe was calculated to be 3.25 × 10^—8 M for fluoride anion. The binding constants and the detection limits of the sensor were calculated using absorption titration studies. The silica gel TLC strips dip‐coated by the chemosensor (1) revealed a colour change from yellow to brick red to naked eye.

A copper catalyzed Chan–Lam type N-arylation protocol has been applied to achieve moderate to good yields of N-arylated ferrocenyl 2,4 thiazolidinedione conjugates. A general and mild strategy has been developed for the cross-coupling of aryl boronic acids and ferrocenyl 2,4 thiazolidinedione conjugates. This coupling was achieved through the use of copper(II) acetate and screened for different bases, solvents and a variety of arylboronic acids including electron-withdrawing and electron-donating groups. All the new compounds were obtained as red crystalline solids. The solid state structure of (3b) was established by single crystal X-ray diffraction analysis. All the compounds were fully characterized by ¹H and ¹³C NMR, FT-IR, ESI-mass, UV-Visible and fluorescence spectroscopies. Electrochemical studies (CV) showed reversible one-electron oxidation and the conjugates were found to be stable in organic solvents. Furthermore, these ferrocenyl 2,4-thiazolidinedione conjugates (3b, 3f, 3i, 3k, and 3l) exhibited good to moderate antidiabetic activities.

A new series of ferrocenyl sugar–triazole conjugates, derived from d‐xylose, d‐ribose and d‐galactose, linked by a 2,4‐thiazolidinedione moiety, has been prepared. Facile 1,3‐dipolar‐Huisgen coupling reactions of the respective sugar azides with the ferrocenyl 2,4‐thiazolidinedione alkyne units give the corresponding conjugates. These conjugates have been characterized by various spectroscopic techniques, including UV/Vis spectroscopy. The electrochemical analysis exhibits one‐electron reversible oxidation behaviour, except for 5c and 5f, which exhibit quasireversible behaviour. Single‐crystal X‐ray diffraction studies of two of the compounds (2 and 3) are performed to determine their structures. The 2,4‐thiazolidinedione linked ferrocenyl sugar–triazole conjugates exhibit moderate‐to‐good antibacterial and antidiabetic activities.