Design, synthesis, and evaluation of curcumin analogues as potential inhibitors of bacterial sialidase

Half-Curcuminoids Encapsulated in Alginate-Glucosamine Hydrogel Matrices as Bioactive Delivery Systems

The therapeutic effects of curcumin and its derivatives, based on research in recent years, are limited by their low bioavailability. To improve bioavailability and develop the medical field of application, different delivery systems have been developed that are adapted to certain environments or the proposed target type. This study presents some half-curcuminoids prepared by the condensation of acetylacetone with 4-hydroxybenzaldehyde (C1), 4-hydroxy-3-methoxybenzaldehyde (C2), 4-acetamidobenzaldehyde (C3), or 4-diethylaminobenzaldehyde (C4), at microwaves as a simple, solvent-free, and eco-friendly method. The four compounds obtained were characterized in terms of morphostructural and photophysical properties. Following the predictions of theoretical studies on the biological activities related to the molecular structure, in vitro tests were performed for compounds C1-C3 to evaluate the antitumor properties and for C4's possible applications in the treatment of neurological diseases. The four compounds were encapsulated in two types of hydrogel matrices. First, the alginate-glucosamine network was generated and then the curcumin analogs were loaded (G1, G3, G5-G7, and G9). The second type of hydrogels was obtained by loading the active compound together with the generation of the hydrogel carrier matrices, by simply dissolving (G4 and G10) or by chemically binding half-curcuminoid derivatives to glucosamine (G2 and G8). Thus, two types of curcumin analog delivery systems were obtained, which could be applied in various types of medical treatments.

The role of sialidases in the pathogenesis of bacterial vaginosis and their use as a promising pharmacological target in bacterial vaginosis

Bacterial vaginosis (BV) is an infection of the genital tract characterized by disturbance of the normally Lactobacilli-dominated vaginal flora due to the overgrowth of Gardnerella and other anaerobic bacteria. Gardnerella vaginalis, an anaerobic pathogen and the major pathogen of BV, produces sialidases that cleave terminal sialic acid residues off of human glycans. By desialylation, sialidases not only alter the function of sialic acid-containing glycoconjugates but also play a vital role in the attachment, colonization and spread of many other vaginal pathogens. With known pathogenic effects, excellent performance of sialidase-based diagnostic tests, and promising therapeutic potentials of sialidase inhibitors, sialidases could be used as a biomarker of BV. This review explores the sources of sialidases and their role in vaginal dysbiosis, in aims to better understand their participation in the pathogenesis of BV and their value in the diagnosis and treatment of BV.

Synthesis and studies of new purines/pyrimidine derivatives as multi-targeted agents involving various receptor sites in the immune system

Pro-inflammation, which is developed due to the increased production of cytokines, mainly interleukin-6 (IL-6), during the working of immune system pathways, becomes a major concern these days for many researchers. So, it is desired to design, screen, and synthesize new molecules with multi-parametric features showing their efficacy for Toll-like receptors (TLRs) and inhibiting the disease-causing receptor sites like viral infections, cancers, etc. along with controlling inflammation, fever, and other side effects during such pathways. Further, looking at the literature, curcumin a multi-targeted agent is showing its efficiency toward various receptor sites involved in many diseases as mentioned above. This fascinated us to build up new molecules which behave like curcumin with minimum side effects. In silico studies, involving ADMET studies, toxicological data, and docking analyses, of newly synthesized compounds (3-5) along with tautomers of curcumin i.e., (1-2), and some reported compounds like 9 and 10 have been studied in detail. Great emphasis has been made on analyzing binding energies, protein-ligand structural interactions, stabilization of newly synthesized molecules against various selected receptor sites using such computational tools. Compound 3 is the most efficient multifunctional agent, which has shown its potential toward most of the receptor sites in docking analysis. It has also responded well in Molecular dynamics (MD) simulation toward 5ZLN, 4RJ3, 4YO9, 4YOJ, and 1I1R sites. Finally, studies were extended to understand in vitro anti-inflammatory activity for particularly compound 3 in comparison to diclofenac and curcumin, which signifies the efficiency of compound 3.

Recent advances in the discovery of plant-derived antimicrobial natural products to combat antimicrobial resistant pathogens: insights from 2018-2022

Covering: 2018 to 2022Antimicrobial resistance (AMR) poses a significant global health threat. There is a rising demand for innovative drug scaffolds and new targets to combat multidrug-resistant bacteria. Before the advent of antibiotics, infections were treated with plants chosen from traditional medicine practices. Of Earth's 374 000 plant species, approximately 9% have been used medicinally, but most species remain to be investigated. This review illuminates discoveries of antimicrobial natural products from plants covering 2018 to 2022. It highlights plant-derived natural products with antibacterial, antivirulence, and antibiofilm activity documented in lab studies. Additionally, this review examines the development of novel derivatives from well-studied parent natural products, as natural product derivatives have often served as scaffolds for anti-infective agents.

Sialidase Inhibitors with Different Mechanisms

Sialidases, or neuraminidases, are enzymes that catalyze the hydrolysis of sialic acid (Sia)-containing molecules, mostly removal of the terminal Sia (desialylation). By desialylation, sialidase can modulate the functionality of the target compound and is thus often involved in biological pathways. Inhibition of sialidases with inhibitors is an important approach for understanding sialidase function and the underlying mechanisms and could serve as a therapeutic approach as well. Transition-state analogues, such as anti-influenza drugs oseltamivir and zanamivir, are major sialidase inhibitors. In addition, difluoro-sialic acids were developed as mechanism-based sialidase inhibitors. Further, fluorinated quinone methide-based suicide substrates were reported. Sialidase product analogue inhibitors were also explored. Finally, natural products have shown competitive inhibiton against viral, bacterial, and human sialidases. This Perspective describes sialidase inhibitors with different mechanisms and their activities and future potential, which include transition-state analogue inhibitors, mechanism-based inhibitors, suicide substrate inhibitors, product analogue inhibitors, and natural product inhibitors.

Investigation of Antistress and Antidepressant Activities of Synthetic Curcumin Analogues: Behavioral and Biomarker Approach

Depression is a serious psychiatric disorder that affects millions of individuals all over the world, thus demanding special attention from researchers in order to investigate its effective remedies. Curcumin, along with its synthetic derivatives, is recognized for its incredible pharmacological activities. In this study, methyl, methoxy and chloro-substituent synthetic curcumin analogues C1-C3 were respectively tested for free radical-scavenging activity. Behavioral studies were performed using chemical-induced and swimming endurance tests as stress models, and forced swim tests (FSTs) and tail suspension tests (TSTs) as depression mice models. Biochemical examinations were performed after a scopolamine-induced stress model by decapitating the mice, and brain tissues were isolated for biochemical assessment of catalase (CAT), superoxide dismutase (SOD), glutathione (GSH), and malondialdehyde (MDA). The curcumin analogue C2 exhibited higher DPPH (2,2-diphenyl-1-picrylhydrazyl) and ABTS (2,2'-azinobis-3-ethylbenzothiazo-line-6-sulphonate) free radical-scavenging potential, having IC50 values of 45.18 µg/mL and 62.31 µg/mL, respectively, in comparison with reference curcumin and tocopherol. In the chemical-induced test, C2 (80.17%), C3 (72.79%) and C1 (51.85%) revealed higher antistress responses by significantly reducing the number of writhes, whereas the immobility time was significantly reduced by C2 and C3 in the swimming endurance test, indicating excellent antistress potential. Similarly, C2 and C3 significantly reduced the immobility times in FST and TST, demonstrating their antidepressant properties. The biomarkers study revealed that these compounds significantly enhanced hippocampus CAT, SOD and GSH, and reduced MDA levels in the scopolamine-induced stress mice model. These findings suggest the potential of curcumin analogues (C2 and C3) as antistress and antidepressant agents.

An In Vitro and In Silico Study of Antioxidant Properties of Curcuminoid N-alkylpyridinium Salts: Initial Assessment of Their Antitumoral Properties

In this work, we report the synthesis of curcuminoids with ionic liquid characteristics, obtained by incorporating alkyl-substituted pyridinium moiety rather than one phenyl group through a two-step process. The antioxidant capacity of the obtained compounds was evaluated in vitro by 1,1-diphenyl-picrylhydrazyl (DPPH) free radical scavenging and ferric reducing antioxidant power (FRAP) assays, showing that some derivatives are more potent than curcumin. Pyridine curcuminoids (group 4) and curcuminoid N-alkylpyridinium salts with two methoxyl groups in the phenyl ring (group 7), presented the best antioxidant capacity. The experimental results were rationalized by density functional theory (DFT) calculations of the bond dissociation enthalpy (BDE) for O–H in each compound. The computational calculations allowed for insight into the structural–antioxidant properties relationship in these series of compounds. BDEs, obtained in the gas phase and water, showed a notable impact of water solvation on the stabilization of some radicals. The lower values of BDEs in the water solution correspond to the structurally related compounds curcuminoid-pyridine 4c and curcuminoid pyridinium salt 7a, which is consistent with the experimental results. Additionally, an assessment of cell viability and cell migration assays was performed for human colon cancer (HT29), human breast cancer (MCF7) cells, in addition to NIH3T3 murine fibroblast, as a model of non-cancer cell type. These compounds mainly cause inhibition of the cell migration observed in MCF7 cancer cells without affecting the non-tumoral NIH3T3 cell line: Neither in viability nor in migration.

Improved Synthesis of Asymmetric Curcuminoids and Their Assessment as Antioxidants

In this paper, the syntheses of twelve asymmetric curcumin analogs using Pabon's method are reported. Generally, the previously reported yields of asymmetric curcuminoids, such as 9a (53%), 9c (38%), and 9k (38%), have been moderate or low. Herein, we propose that the low yields were due to the presence of water and n-BuNH₂ in the reaction media. To prove this formulated hypothesis, we have demonstrated that the yields can be improved by adding molecular sieves (MS) (4 Å) to the reaction mixture, thus reducing the interference of water. Therefore, improved yields (41-76%) were obtained, except for 9b (36.7%), 9g (34%), and 9l (39.5%). Furthermore, compounds 9b, 9d, 9e, 9f, 9g, 9h, 9i, 9j, and 9l are reported herein for the first time. The structures of these synthetic compounds were determined by spectroscopic and mass spectrometry analyses. The free radical scavenging ability of these synthetic asymmetric curcuminoids was evaluated and compared to that of the positive control butylated hydroxytoluene (BHT). Among the synthesized asymmetric curcuminoids, compounds 9a (IC₅₀ = 37.57 ± 0.89 μM) and 9e (IC₅₀ = 37.17 ± 1.76 μM) possessed effective 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging abilities, and compounds 9h (IC₅₀ = 11.36 ± 0.65 μM) and 9i (IC₅₀ = 10.91 ± 0.77 μM) displayed potent 2,2'-azinobis-(3-ethylbenzthiazoline-6-sulphonate) (ABTS) radical scavenging abilities comparable to that of curcumin (IC₅₀ = 10.14 ± 1.04 μM). Furthermore, all the synthetic asymmetric curcuminoids were more active than BHT.

Styryl Group, a Friend or Foe in Medicinal Chemistry

The styryl (Ph-CH=CH-R) group is widely represented in medicinally important compounds, including drugs, clinical candidates, and molecular probes as it positively impacts the lipophilicity, oral absorption, and biological activity. The analysis of matched molecular pairs (styryl vs. phenethyl, phenyl, methyl, H) for the biological activity indicates the superiority aspect of styryl compounds. However, the Michael acceptor site in the styryl group makes it amenable to the nucleophilic attack by biological nucleophiles and transformation to the toxic metabolites. One of the downsides of styryl compounds is isomerization that impacts the molecular conformation and directly affects biological activity. The impact of cis-trans isomerism and isosteric replacements on biological activity is exemplified. We also discuss the styryl group-bearing drugs, clinical candidates, and fluorescent probes. Overall, the present review reveals the utility of the styryl group in medicinal chemistry and drug discovery.

Sialidase and Sialyltransferase Inhibitors: Targeting Pathogenicity and Disease

Sialidases (SAs) and sialyltransferases (STs), the enzymes responsible for removing and adding sialic acid to other glycans, play essential roles in viruses, bacteria, parasites, and humans. Sialic acid is often the terminal sugar on glycans protruding from the cell surface in humans and is an important component for recognition and cell function. Pathogens have evolved to exploit this and use sialic acid to either “cloak” themselves, ensuring they remain undetected, or as a mechanism to enable release of virus progeny. The development of inhibitors against SAs and STs therefore provides the opportunity to target a range of diseases. Inhibitors targeting viral, bacterial, or parasitic enzymes can directly target their pathogenicity in humans. Excellent examples of this can be found with the anti-influenza drugs Zanamivir (Relenza™, GlaxoSmithKline) and Oseltamivir (Tamiflu™, Roche and Gilead), which have been used in the clinic for over two decades. However, the development of resistance against these drugs means there is an ongoing need for novel potent and specific inhibitors. Humans possess 20 STs and four SAs that play essential roles in cellular function, but have also been implicated in cancer progression, as glycans on many cancer cells are found to be hyper-sialylated. Whilst much remains unknown about how STs function in relation to disease, it is clear that specific inhibitors of them can serve both as tools to gain a better understanding of their activity and form the basis for development of anti-cancer drugs. Here we review the recent developments in the design of SA and ST inhibitors against pathogens and humans.

Recent progress in chemical approaches for the development of novel neuraminidase inhibitors

Influenza virus is the main cause of an infectious disease called influenza affecting the respiratory system including the throat, nose and lungs. Neuraminidase inhibitors are reagents used to block the enzyme called neuraminidase to prevent the influenza infection from spreading. Neuraminidase inhibitors are widely used in the treatment of influenza infection, but still there is a need to develop more potent agents for the more effective treatment of influenza. Complications of the influenza disease lead to death, and one of these complications is drug resistance; hence, there is an urgent need to develop more effective agents. This review focuses on the recent advances in chemical synthesis pathways used for the development of new neuraminidase agents along with the medicinal aspects of chemically modified molecules, including the structure-activity relationship, which provides further rational designs of more active small molecules.

Synthesis, crystal structure, Hirshfeld surface and interaction energies analysis of 5-methyl-1,3-bis(3-nitrobenzyl)pyrimidine-2,4(1H,3H)-dione

The title compound 5-methyl-1,3-bis(3-nitrobenzyl)pyrimidine-2,4(1H,3H)-dione was obtained by reaction of thymine with 3-nitrobenzylbromide in the presence of cesium carbonate. Characterization of the product was achieved by NMR spectroscopy and its stability was probed in basic condition using UV-Visible analysis. Furthermore, the molecular structure was confirmed by X-ray diffraction analysis. The compound crystallizes in orthorhombic Pna21 space group with unit cell parameters a = 14.9594 (15) Å, b = 25.711 (3) Å, c = 4.5004 (4) Å, V = 1731.0 (3) Å3 and Z = 4. The crystal packing of the title compound is stabilized by intermolecular hydrogen bond, π···π and C−H···π stacking interactions. The intermolecular interactions were furthermore analyzed through the mapping of different Hirshfeld surfaces. The two-dimensional fingerprint revealed that the most important contributions to these surfaces come from O···H (37.1%), H···H (24%) and H···C/C···H (22.6%) interactions. The interaction energies stabilizing the crystal packing were calculated and were presented graphically as framework energy diagrams. Finally, the energy-framework analysis reveals that π···π and C−H···π interactions energies are mainly dispersive and are the most important forces in the crystal.

Diversity of sialidases found in the human body - A review

Sialidases are enzymes essential for numerous organisms including humans. Hydrolytic sialidases (EC 3.2.1.18), trans-sialidases and anhydrosialidases (intramolecular trans-sialidases, EC 4.2.2.15) are glycoside hydrolase enzymes that cleave the glycosidic linkage and release sialic acid residues from sialyl substrates. The paper summarizes diverse sialidases present in the human body and their potential impact on development of antiviral compounds - inhibitors of viral neuraminidases. It includes a brief overview of catalytic mechanisms of action of sialidases and describes the origin of sialidases in the human body. This is followed by description of the structure and function of sialidase families with a special focus on the GH33 and GH34 families. Various effects of sialidases on human body are also briefly described. Modulation of sialidase activity may be considered a useful tool for effective treatment of various diseases. In some cases, it is desired to completely suppress the activity of sialidases by suitable inhibitors. Specific sialidase inhibitors are useful for the treatment of influenza, epilepsy, Alzheimer's disease, diabetes, different types of cancer, or heart defects. Challenges and future directions are shortly depicted in the final part of the paper.

Sialidases From Clostridium perfringens and Their Inhibitors

Clostridium perfringens is an important human and animal pathogen that is the primary causative agent of necrotizing enteritis and enterotoxemia in many types of animals; it causes traumatic gas gangrene in humans and animals and is associated with cases of food poisoning in humans. C. perfringens produces a variety of toxins as well as many enzymes, including three sialidases, NanH, NanI, and NanJ. Sialidases could be important virulence factors that promote the pathogenesis of C. perfringens. Among them, NanI promotes the colonization of C. perfringens in the intestinal tract and enhances the cytotoxic activity and association of several major C. perfringens toxins with host cells. In recent years, studies on the structure and functions of sialidases have yielded interesting results, and the functions of sialic acid and sialidases in bacterial pathogenesis have become a hot research topic. An in-depth understanding and additional studies of sialidases will further elucidate mechanisms of C. perfringens pathogenesis and could promote the development and clinical applications of sialidase inhibitors. This article reviews the structural characteristics, expression regulation, roles of sialidases in C. perfringens pathogenesis, and effects of their inhibitors.

Computational elucidation of the binding mechanisms of curcumin analogues as bacterial RecA inhibitors

Antimicrobial resistance (AMR) presents as a serious threat to global public health, which urgently demands action to develop alternative antimicrobial strategies with minimized selective pressure. The bacterial SOS response regulator RecA has emerged as a promising target in the exploration of new classes of antibiotic adjuvants, as RecA has been implicated in bacterial mutagenesis and thus AMR development through its critical roles in error-prone DNA repair. The natural product curcumin has been reported to be an effective RecA inhibitor in several Gram-negative bacteria, but details on the underlying mechanisms are wanting. In order to bridge the gap in how curcumin operates as a RecA inhibitor, we used computational approaches to model interactions between RecA protein and curcumin analogues. We first identified potential binding sites on E. coli RecA protein and classified them into four major binding pockets based on biological literature and computational findings from multiple in silico calculations. In docking analysis, curcumin-thalidomide hybrids were predicted to be superior binders of RecA compared with bis-(arylmethylidene)acetone curcumin analogues, which was further confirmed by MMGBSA calculations. Overall, this work provides mechanistic insights into bacterial RecA protein as a target for curcumin-like compounds and offers a theoretical basis for rational design and development of future antibiotic adjuvants.