Design, synthesis and biological evaluation of N-(4-alkoxy-3-cyanophenyl)isonicotinamide/nicotinamide derivatives as novel xanthine oxidase inhibitors

Discovery of 4-(isopentyloxy)-3-nitrobenzamide derivatives as xanthine oxidase inhibitors through a non-anthraquinone exploration

In our previous study, we reported a series of N-(9,10-anthraquinone-2-carbonyl) amino acid derivatives as novel inhibitors of xanthine oxidase (XO). Recognizing the suboptimal drug-like properties associated with the anthraquinone moiety, we embarked on a nonanthraquinone medicinal chemistry exploration in the current investigation. Through systematic structure-activity relationship (SAR) studies, we identified a series of 4-(isopentyloxy)-3-nitrobenzamide derivatives exhibiting excellent in vitro potency against XO. The optimized compound, 4-isopentyloxy-N-(1H-pyrazol-3-yl)-3-nitrobenzamide (6k), demonstrated exceptional in vitro potency with an IC50 value of 0.13 μM. Compound 6k showed favorable drug-like characteristics with ligand efficiency (LE) and lipophilic ligand efficiency (LLE) values of 0.41 and 3.73, respectively. In comparison to the initial compound 1d, 6k exhibited a substantial 24-fold improvement in IC50, along with a 1.6-fold enhancement in LE and a 3.7-fold increase in LLE. Molecular modeling studies provided insights into the strong interactions of 6k with critical amino acid residues within the active site. Furthermore, in vivo hypouricemic investigations convincingly demonstrated that 6k significantly reduced serum uric acid levels in rats. The MTT results revealed that compound 6k is nontoxic to healthy cells. The gastric and intestinal stability assay demonstrated that compound 6k exhibits good stability in the gastric and intestinal environments. In conclusion, compound 6k emerges as a promising lead compound, showcasing both exceptional in vitro potency and favorable drug-like characteristics, thereby warranting further exploration.

Identification of natural xanthine oxidase inhibitors: Virtual screening, anti-xanthine oxidase activity, and interaction mechanism

Xanthine oxidase (XO) is a crucial target for hyperuricemia treatment(s). Naturally occurred XO inhibitors with minimal toxicity and high efficacy have attracted researchers' attention. With the goal of quickly identifying natural XO inhibitors, an integrated computational screening strategy was constructed by molecular docking and calculating the free energy of binding. Twenty-seven hits were achieved from a database containing 19,377 natural molecules. This includes fourteen known XO inhibitors and four firstly-reported inhibitors (isolicoflavonol, 5,7-dihydroxycoumarin, parvifolol D and clauszoline M, IC50 < 40 μM). Iolicoflavonol (hit 8, IC50 = 8.45 ± 0.68 μM) and 5,7-dihydroxycoumarin (hit 25, IC50 = 10.91 ± 0.71 μM) displayed the great potency as mixed-type inhibitors. Docking study and molecular dynamics simulation revealed that both hits could interact with XO's primarily active site residues ARG880, MOS1328, and ASN768 of XO. Fluorescence spectroscopy studies showed that hit 8 bound to the active cavity region of XO, causing changes in XO's conformation and hydrophobicity. Hits 8 and 25 exhibit favorable Absorption, Distribution, Metabolism, and Excretion (ADME) properties. Additionally, no cytotoxicity against human liver cells was observed at their median inhibition concentrations against XO. Therefore, the present study offers isolicoflavonol and 5,7-dihydroxycoumarin with the potential to be disease-modifying agents for hyperuricemia.

Recent Advances in Xanthine Oxidase Inhibitors

Uric acid is a product of purine nucleotide metabolism, and high concentrations of uric acid can lead to hyperuricemia, gout and other related diseases. Xanthine oxidase, the only enzyme that catalyzes xanthine and hypoxanthine into uric acid, has become a target for drug development against hyperuricemia and gout. Inhibition of xanthine oxidase can reduce the production of uric acid, so xanthine oxidase inhibitors are used to treat hyperuricemia and related diseases, including gout. In recent years, researchers have obtained new xanthine oxidase inhibitors through drug design, synthesis, or separation of natural products. This paper summarizes the research on xanthine oxidase inhibitors since 2015, mainly including natural products, pyrimidine derivatives, triazole derivatives, isonicotinamide derivatives, chalcone derivatives, furan derivatives, coumarin derivatives, pyrazole derivatives, and imidazole derivatives, hoping to provide valuable information for the research and development of novel xanthine oxidase inhibitors.

Past, present and future of xanthine oxidase inhibitors: design strategies, structural and pharmacological insights, patents and clinical trials

Xanthine oxidase, a molybdo-flavoenzyme, and an isoform of xanthine dehydrogenase both exist as xanthine oxidoreductase and are responsible for purine catabolism. Xanthine oxidase is more involved in pathological conditions when extensively modulated. Elevation of xanthine oxidase is not only the prime cause of gout but is also responsible for various hyperuricemia associated pathological conditions like diabetes, chronic wounds, cardiovascular disorders, Alzheimer's disease, etc. Currently available xanthine oxidase inhibitors in clinical practice (allopurinol, febuxostat and topiroxostat) suffer from fatal side effects that pose a serious problem to the healthcare system, raising global emergency to develop novel, potent and safer xanthine oxidase inhibitors. This review will provide key and systematic information about: a. design strategies (inspired from both marketed drugs in clinical practice and natural products), structural insights and pharmacological output (xanthine oxidase inhibition and associated activities) of various pre-clinical candidates reported by various research groups across the globe in the past two decades; b. patented xanthine oxidase inhibitors published in the last three decades and c. clinical trials and their outcomes on approved drug candidates. Information generated in this review has suggested fragment-based drug design (FBDD) and molecular hybridization techniques to be most suitable for development of desired xanthine oxidase inhibitors as one provides high selectivity toward the enzyme and the other imparts multifunctional properties to the structure and both may possess capabilities to surpass the limitations of currently available clinical drugs. All in combination will exclusively update researchers working on xanthine oxidase inhibitors and allied areas and potentially help in designing rational, novel, potent and safer xanthine oxidase inhibitors that can effectively tackle xanthine oxidase related disease conditions and disorders.

Agents for the Treatment of Gout: Current Advances and Future Perspectives

Gout is characterized by hyperuricemia and the deposition of monosodium urate (MSU) crystals around joints. Despite the availability of several drugs on the market, its treatment remains challenging owing to the notable side effects, such as hepatorenal toxicity and cardiovascular complications, that are associated with most existing agents. This perspective aims to summarize the current research progress in the development of antigout agents, particularly focusing on xanthine oxidase (XO) and urate anion transporter 1 (URAT1) inhibitors from a medicinal chemistry viewpoint and their preliminary structure-activity relationships (SARs). This perspective provides valuable insights and theoretical guidance to medicinal chemists for the discovery of antigout agents with novel chemical structures, better efficiency, and lower toxicity.

A New Avenue for Enhanced Treatment of Hyperuricemia and Oxidative Stress: Design, Synthesis and Biological Evaluation of Some Novel Mutual Prodrugs Involving Febuxostat Conjugated with Different Antioxidants

Febuxostat (FEB) is the first non-purine xanthine oxidase inhibitor (XOI) used for the treatment of hyperuricemia and gout. The oxidative stress induced by reactive oxygen species (ROS) which accompany purine metabolism by XO, could contribute to cellular damage and several pathological conditions. In this view, the present work addresses the evaluation of combining the hypouricemic effect of FEB and the free radical scavenging potential of various natural antioxidants in a single chemical entity by implementing the "mutual prodrug" strategy. Accordingly, a series of five ester prodrugs containing FEB together with different naturally occurring antioxidants namely, thioctic acid (4), thymol (5), menthol (6), vanillin (7), and guaiacol (8) was synthesized. Prominently, all the chemically conjugated prodrugs (4 - 8) revealed an obvious increase in the hypouricemic and antioxidant potentials when compared with their corresponding promoieties and physical mixtures. Moreover, they showed a potential protective effect against CCl4-induced hepatotoxicity and oxidative stress, together with no cytotoxicity on normal breast cells (MCF10A). Furthermore, the in vitro chemical and enzymatic stability studies of the prodrugs (4 - 8) using a developed HPLC method, verified their stability in different pHs, and rapid hydrolysis in rabbit plasma and liver homogenate to their parent metabolites. Moreover, the prodrugs (4 - 8) showed higher lipophilicity and lower aqueous solubility when compared to the parent drugs. Finally, the obtained merits from the implementation of the mutual prodrug strategy would encourage further application in the development of promising candidates with high therapeutic efficacy and improved safety profiles.

Design, synthesis and structure-activity relationship of N-phenyl aromatic amide derivatives as novel xanthine oxidase inhibitors

Our previous studies suggested that N-phenyl aromatic amides are a class of promising xanthine oxidase (XO) inhibitor chemotypes. In this effort, several series of N-phenyl aromatic amide derivatives (4a-h, 5-9, 12i-w, 13n, 13o, 13r, 13s, 13t and 13u) were designed and synthesized to carry out an extensive structure-activity relationship (SAR). The investigation provided some valuable SAR information and identified N-(3-(1H-imidazol-1-yl)-4-((2-methylbenzyl)oxy)phenyl)-1H-imidazole-4-carboxamide (12r, IC₅₀ = 0.028 µM) as the most potent XO inhibitor with close in vitro potency to that of topiroxostat (IC₅₀ = 0.017 µM). Molecular docking and molecular dynamics simulation rationalized the binding affinity through a series of strong interactions with the residues Glu1261, Asn768, Thr1010, Arg880, Glu802, etc. In vivo hypouricemic studies also suggested that the uric acid lowering effect of compound 12r was improved compared with the lead g25 (30.61 % vs 22.4 % reduction in uric acid levels at 1 h; 25.91 % vs 21.7 % reduction in AUC of uric acid) . Pharmacokinetic studies revealed that compound 12r presented a short t_1/2 of 0.25 h after oral administration. In addition, 12r has non-cytotoxicity against normal cell HK-2. This work may provide some insights for further development of novel amide-based XO inhibitors.

Ten Years Milestones in Xanthine Oxidase Inhibitors Discovery: Febuxostat-Based Inhibitors Trends, Bifunctional Derivatives, and Automatized Screening Assays

Xanthine oxidase (XO) is an enzyme involved in the oxidative process of hypoxanthine and xanthine to uric acid (UA). This process also produces reactive oxygen species (ROS) as byproducts. Both UA and ROS are dangerous for human health, and some health conditions trigger upregulation of XO activity, which results in many diseases (cancer, atherosclerosis, hepatitis, gout, and others) given the worsened scenario of ROS and UA overproduction. So, XO became an attractive target to produce and discover novel selective drugs based on febuxostat, the most recent XO inhibitor out of only two approved by FDA. Under this context, high-performance liquid chromatography (HPLC) and capillary electrophoresis (CE) have been successfully applied to rapidly and easily screen for bioactive compounds, isolated or in complex natural matrixes, that act as enzyme inhibitors through the use of an immobilized enzyme reactor (IMER). This article’s goal is to present advances comprising febuxostat-based XO inhibitors as a new trend, bifunctional moieties capable of inhibiting XO and modulating ROS activity, and in-flow techniques employing an IMER in HPLC and CE to screen for synthetic and natural compounds that act as XO inhibitors.

Synthetic heterocyclic derivatives as promising xanthine oxidase inhibitors: An overview

Inhibition of xanthine oxidase is an effective and most prominent therapeutic approach for the management of gout. Discovery of its association in the pathophysiology of diabetes, cardiovascular disorders, etc., widened its therapeutic horizons. Limited drug candidates in clinical practice along with side effects forced researchers to develop more efficacious and safer xanthine oxidase inhibitors for the management of gout and other disorders associated with xanthine oxidase hyperactivity. In this regard, this review focus on: (a) Various drug candidates in clinical practice and under clinical trials, (b) Development of various heterocyclic motifs as xanthine oxidase inhibitors in last two decades and (c) Various patented synthetic xanthine oxidase inhibitors.

Design, synthesis and biological evaluation of N-(4-alkoxy-3-(1H-tetrazol-1-yl)phenyl) heterocyclic aromatic amide derivatives as xanthine oxidase inhibitors

Xanthine oxidase (XO) is a flavoprotein that exists in various organisms and can catalyze the uric acid formation in the human body. Based on the amide framework of N-(4-((3-cyanobenzyl)oxy)-3-(1H-tetrazol-1-yl)phenyl)isonicotinamide (compound 1) reported in our previous work, a series of N-(4-alkoxy-3-(1H-tetrazol-1-yl)phenyl) heterocyclic aromatic amide derivatives were designed, synthesized and evaluated as novel amide-based XO inhibitors. Structure-activity relationship campaign identified the most promising compound g25 (IC₅₀ = 0.022 μM), which possesses a special 1H-imidazole-5-carboxamide scaffold and presented comparable XO inhibitory potency to topiroxostat (IC₅₀ = 0.017 μM). Enzyme kinetic studies revealed that compound g25 acted as a mixed-type XO inhibitor. Molecular docking and molecular dynamics indicated that imidazole NH of g25 formed two stable hydrogen bonds with Glu1261 residue of XO that provided a vital contribution for the binding affinity. In addition, in vivo activity evaluation demonstrated that compound g25 exhibited obviously hypouricemic effect on a potassium oxonate induced hyperuricemic rat model.

Amide-based xanthine oxidase inhibitors bearing an N-(1-alkyl-3-cyano-1H-indol-5-yl) moiety: Design, synthesis and structure-activity relationship investigation

Our previous work identified a promising isonicotinamide based xanthine oxidase (XO) inhibitor, N-(3-cyano-4-((2-cyanobenzyl)oxy)phenyl)isonicotinamide (1), and concluded that amide is an effective linker in exploring the XO inhibitor chemical space that is completely different from the five-membered ring framework of febuxostat and topiroxostat. Indole, an endogenous bioactive substance and a popular drug construction fragment, was involved in the structural optimization campaign of the present effort. After the installation of some functional groups, N-(1-alkyl-3-cyano-1H-indol-5-yl) was generated and employed to mend the missing H-bond interaction between the 3'-cyano of 1 and Asn768 residue of XO by shortening their distance. In this context, eight kinds of heterocyclic aromatic amide chemotypes were rationally designed and synthesized to investigate the structure-activity relationship (SAR) of amide-based XO inhibitors. The optimized compound a6 (IC₅₀ = 0.018 μM) exhibits 17.2-fold improved potency than the initial compound 1 (IC₅₀ = 0.31 μM). Its potency is comparable to that of topiroxostat (IC₅₀ = 0.013 μM). Molecular docking and molecular dynamics studies proved the existence of the stable H-bond between the cyano group and the Asn768 residue. Moreover, oral administration of a6 (11.8 mg/kg) could effectively reduce serum uric acid levels in an acute hyperuricemia rat model. Liver microsomal stability assay illustrated that compound a6 possesses well metabolic stability in rat liver microsomes. However, the in vivo potency of a6 was much lower than that of topiroxostat, which may be explained by the poor absorption found in the parallel artificial membrane permeability assay (PAMPA). In addition, 6a has non-cytotoxicity against normal cell lines MCF10A and 16HBE. Taken together, this work culminated in the identification of compound 6a as an excellent lead for further exploration of amide-based XO inhibitors.

N-(3-cyano-1H-indol-5-yl)isonicotinamide and N-(3-cyano-1H-indol-5-yl)-1H-benzo[d]imidazole-5-carboxamide derivatives: Novel amide-based xanthine oxidase inhibitors

Our previous work demonstrated that amide is an efficient linker to explore chemical space of xanthine oxidase (XO) inhibitors that are entirely different from febuxostat and topiroxostat. In this effort, with 3-cyano-1H-indol-5-yl as a key moiety, two series of amide-based XO inhibitors, N-(3-cyano-1H-indol-5-yl)isonicotinamides (2a-w) and N-(3-cyano-1H-indol-5-yl)-1H-benzo[d]imidazole-5-carboxamides (3a-i), were designed and synthesized. The structure-activity relationship investigation identified N-(3-cyano-1-cyclopentyl-1H-indol-5-yl)-1H-benzo[d]imidazole-5-carboxamide (3i, IC50 = 0.62 μM) as the most promising compound, with 14.4-fold higher in vitro inhibitory potency than allopurinol (IC50 = 8.91 μM). Molecular simulations provided reasonable interaction modes for the representative compounds. Furthermore, in vivo activity evaluation demonstrated that compound 3i (oral dose of 12.8 mg/kg) has obviously hypouricemic effect on a potassium oxonate induced hyperuricemic rat model. Cytotoxicity assay and ADME prediction also supported that 3i is an excellent lead for further exploration of amide-based XO inhibitors.

Synthesis, inhibition properties against xanthine oxidase and molecular docking studies of dimethyl N-benzyl-1H-1,2,3-triazole-4,5-dicarboxylate and (N-benzyl-1H-1,2,3-triazole-4,5-diyl)dimethanol derivatives

This study focused on synthesis various dimethyl N-benzyl-1H-1,2,3-triazole-4,5-dicarboxylate and (N-benzyl-1H-1,2,3-triazole-4,5-diyl)dimethanol derivatives under the conditions of green chemistry without the use of solvent and catalysts. Their inhibition properties were also investigated on xanthine oxidase (XO) activity. All dimethanol and dicarboxylate derivatives exhibited significant inhibition activities with IC₅₀ values ranging from 0.71 to 2.25 μM. Especially, (1-(3-bromobenzyl)-1H-1,2,3-triazole-4,5-diyl)dimethanol (5c) and dimethyl 1-(4-chlorobenzyl)-1H-1,2,3-triazole-4,5-dicarboxylate (6 g) compounds were found to be the most promising derivatives on the XO enzyme inhibition with IC₅₀ values 0.71 and 0.73 μM, respectively. Moreover, the double docking procedure was to evaluate compound modes of inhibition and their interactions with the protein (XO) at atomic level. Surprisingly, the docking results showed a good correlation with IC₅₀ [correlation coefficient (R² = 0.7455)]. Also, the docking results exhibited that the 5c, 6f and 6 g have lowest docking scores -4.790, -4.755, and -4.730, respectively. These data were in agreement with the IC₅₀ values. These results give promising beginning stages to assist in the improvement of novel and powerful inhibitor against XO.

Computationally exploring novel xanthine oxidase inhibitors using docking-based 3D-QSAR, molecular dynamics, and virtual screening

Computationally exploring novel potential xanthine oxidase inhibitors using a systematic modeling study.

Design, synthesis and biological evaluation of N-(3-(1H-tetrazol-1-yl)phenyl)isonicotinamide derivatives as novel xanthine oxidase inhibitors

In our previous study, we reported a series of N-phenylisonicotinamide derivatives as novel xanthine oxidase (XO) inhibitors and identified N-(3-cyano-4-((2-cyanobenzyl)oxy)phenyl)isonicotinamide (compound 1) as the most potent one with an IC₅₀ value of 0.312 μM. To further optimize the structure and improve the potency, a structure-based drug design (SBDD) strategy was performed to construct the missing H-bond between the small molecule and the Asn768 residue of XO. We introduced a tetrazole moiety at the 3'-position of the phenyl to serve as an H-bond acceptor and obtained a series of N-(3-(1H-tetrazol-1-yl)phenyl)isonicotinamide derivatives (2a-t and 6-8). Besides, to investigate the influence of the amide-reversal, some N-(pyridin-4-yl)-3-(1H-tetrazol-1-yl)benzamide derivatives (3c, 3e, 3i, 3k and 3u) were also synthesized and evaluated. Biological evaluation and structure-activity relationship analysis demonstrated that the 3'-(1H-tetrazol-1-yl) moiety was an excellent fragment for the N-phenylisonicotinamide scaffold; a substituted benzyloxy, especially, an m-cyanobenzyloxy (e.g., 2s), linking at the 4'-position was welcome for the potency; and the amide-reversal could damage the potency, so maintenance of the N-phenylisonicotinamide scaffold was essential. In summary, starting from compound 1, the SBDD effort successfully identified a promising XO inhibitor 2s (IC₅₀ = 0.031 μM), with a 10-fold gain in potency. Its potency was very close to the positive control topiroxostat (IC₅₀ = 0.021 μM). A Lineweaver-Burk plot indicated that compound 2s acted as a mixed-type XO inhibitor. Molecular docking and molecular dynamics simulations revealed that the tetrazole moiety could occupy the Asn768-sub-pocket with N-4 atom accepting an H-bond from the Asn768 residue, as expected.

Inhibitors of Xanthine Oxidase: Scaffold Diversity and Structure-Based Drug Design

Xanthine oxidase (XO) is the enzyme responsible for the catabolism of purines and their conversion into uric acid. XO is thus the target for the treatment of hyperuricemia and gout. For more than 50 years the only XO inhibitor drug available on the market was the purine analogue allopurinol. In the last decade there has been a resurgence in the search for new inhibitors of XO, as the activity of XO and hyperuricemia have also been associated with a variety of conditions such as diabetes, hypertension, and other cardiovascular diseases. In recent years the non-purine inhibitor febuxostat was approved in Europe and the USA for the treatment of hyperuricemia. This drug was followed by another XO inhibitor called topiroxostat. This review discusses the molecular structures and activities of the multiple classes of inhibitors that have been developed since the discovery of allopurinol, with a brief review of the molecular interactions between inhibitors and XO active site residues for the most important molecules. The challenges ahead for the discovery of new inhibitors of XO with novel chemical structures are discussed.

Design, synthesis and biological evaluation of 1-hydroxy-2-phenyl-4-pyridyl-1H-imidazole derivatives as xanthine oxidase inhibitors

In our previous study, we reported a series of 1-hydroxy-2-phenyl-1H-imidazole-5-carboxylic acid derivatives that presented excellent in vitro xanthine oxidase inhibitory potency. As a continuation study, a series of 1-hydroxy-2-phenyl-1H-imidazole derivatives containing a pyridine moiety (4a-g and 5a-g) at the 4-position was designed and synthesized. Evaluation of in vitro xanthine oxidase inhibition demonstrated that the 4a-g series was more potent than the 5a-g series. Compound 4f was the most promising derivative in the series with an IC₅₀ value of 0.64 μM. A Lineweaver-Burk plot revealed that compound 4f acted as a mixed-type xanthine oxidase inhibitor. An iso-pentyloxy group at the 4'-position improved the inhibitory potency. More interestingly, structure-activity relationship analysis indicated that the pyridine para-N atom played a crucial role in the inhibition. Molecular modeling provided a reasonable explanation for the structure-activity relationships observed in this study. In addition, a three dimensional quantitative structure-activity relationships model which possessed reasonable statistics (q² = 0.885 and r² = 0.993) was conducted to further understand the structural basis of these compounds as xanthine oxidase inhibitors. These compounds, especially compound 4f, have good potential for further investigations.