Potent Xanthine Oxidase Inhibitor Research Articles

Hydralazine improves ischemia-induced neovasculogenesis via xanthine-oxidase inhibition in chronic renal insufficiency

Oxidative stress is related to the progression of renal diseases and modulation of oxidative stress can lead to a reduction in vascular events in patients with chronic renal insufficiency (CRI). Indoxyl sulfate (IS) and xanthine oxidase (XO) are related to impaired neovasculogenesis in CRI. Hydralazine is suggested for blood pressure control in CRI. This study aimed to investigate whether hydralazine could improve ischemia-induced neovasculogenesis in CRI animals by reducing reactive oxygen species (ROS) levels. Mice underwent subtotal nephrectomy or sham surgery. Nitrendipine, probenecid, and allopurinol were used to reduce blood pressure, uric acid (UA), and XO activity levels, respectively, for comparison. Blood pressure, XO activity and UA levels that were increased after subtotal nephrectomy were reduced by hydralazine treatment. Allopurinol decreased blood XO activity and UA levels. Only hydralazine and allopurinol increased the number of circulating endothelial progenitor cells (EPCs) and improved neovasculogenesis in CRI mice. IS activated XO mRNA and ROS and inhibited the functions of EPCs and endothelial cells, which could be reversed by hydralazine. However, no additional beneficial effects were observed when XO was inhibited with both hydralazine and siRNA. In conclusion, hydralazine, as a potential XO inhibitor, not only reduced blood pressure and UA levels but also increased the number of circulating EPCs and improved neovasculogenesis in CRI animals. Hydralazine directly inhibited IS-induced ROS and XO activation in EPCs and endothelial cells, and restored their functions in vitro. Future studies should evaluate whether hydralazine could provide additional vascular protection in patients with CRI.

Targeting the subpocket in xanthine oxidase: Design, synthesis, and biological evaluation of 2-[4-alkoxy-3-(1H-tetrazol-1-yl) phenyl]-6-oxo-1,6-dihydropyrimidine-5-carboxylic acid derivatives

Xanthine oxidase is an important target for the treatment of hyperuricemia, gout and other related diseases. Analysis of the high-resolution structure of xanthine oxidase with febuxostat identified the existence of a subpocket formed by the residues Leu648, Asn768, Lys771, Leu1014 and Pro1076. In this study, we designed and synthesized a series of 2-[4-alkoxy-3-(1H-tetrazol-1-yl) phenyl]-6-oxo-1,6-dihydropyrimidine-5-carboxylic acid derivatives (8a-8z) with a tetrazole group targeting this subpocket of the xanthine oxidase active site, and they were further evaluated for their inhibitory potency against xanthine oxidase in vitro. The results showed that all the tested compounds (8a-8z) exhibited an apparent xanthine oxidase inhibitory potency, with IC50 values ranging from 0.0288 μM to 0.629 μM. Among them, compound 8u emerged as the most potent xanthine oxidase inhibitor, with an IC50 value of 0.0288 μM, which was comparable to febuxostat (IC50 = 0.0236 μM). The structure-activity relationship results revealed that the hydrophobic group at the 4′-position was indispensable for the inhibitory potency in vitro against xanthine oxidase. A Lineweaver-Burk plot revealed that the representative compound 8u acted as a mixed-type inhibitor for xanthine oxidase. Furthermore, molecular modeling studies were performed to gain insights into the binding mode of 8u with xanthine oxidase and suggested that the tetrazole group of the phenyl unit was accommodated in the subpocket, as expected. Moreover, a potassium oxonate-induced hyperuricemia model in rats was chosen to further confirm the hypouricemic effect of compound 8u, and the result demonstrated that compound 8u could effectively reduce serum uric acid levels at an oral dose of 5 mg/kg. In addition, acute oral toxicity study in mice indicated that compound 8u was nontoxic and tolerated at a dose up to 2000 mg/kg. Thus, compound 8u could be a potential and efficacious agent in treatment of hyperuricemia with low toxicity.

Design, synthesis and biological evaluation of 2-(4-alkoxy-3-cyano)phenyl-6-oxo-1,6-dihydropyrimidine-5-carboxylic acid derivatives as novel 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 (XO) inhibitory potency. To further investigate the structure-activity relationships of these compounds, the imidazole ring was transformed to a pyrimidine ring to design 2-(4-alkoxy-3-cyano)phenyl-6-oxo-1,6-dihydropyrimidine-5-carboxylic acids (8a-8j), 2-(4-alkoxy-3-cyano)phenyl-4-methyl-6-oxo-1,6-dihydropyrimidine-5-carboxylic acids (9c, 9e, 9j, 9l) and 2-(4-alkoxy-3-cyano)phenyl-6-imino-1,6-dihydropyrimidine-5-carboxylic acids (10c, 10e, 10j, 10l). These compounds exhibited remarkable in vitro XO inhibitory potency with IC50 values ranging from 0.0181 μM to 0.5677 μM. Specifically, compounds 10c and 10e, with IC50 values of 0.0240 μM and 0.0181 μM, respectively, emerged as the most potent XO inhibitors, and their potencies were comparable to that of febuxostat. Structure-activity relationship analysis revealed that the methyl group at 4-position of pyrimidine ring could damage the potency, and the XO inhibitory potency was maintained when carbonyl group was changed to an imino group. Lineweaver-Burk plot analysis revealed that the representative compound 10c acted as a mixed-type inhibitor. A potassium oxonate induced hyperuricemia model in rats was chosen to further confirm the hypouricemic effect of compound 10c, and the results showed that compound 10c (5 mg/kg) was able to significantly lower the serum uric acid level. Furthermore, in acute oral toxicity study, no sign of toxicity was observed when the mice were administered with a single 2000 mg/kg oral dose of compound 10c. These results suggested that compound 10c was a potent and promising uric acid-lowing agent for the treatment of hyperuricemia.

Screening, and identification of the binding position, of xanthine oxidase inhibitors in the roots of Lindera reflexa Hemsl using ultrafiltration LC-MS combined with enzyme blocking.

A method based on enzyme blocking combined with ultrafiltration liquid chromatography-mass spectrometry (LC-MS) has been developed to identify xanthine oxidase (XOD) inhibitors in the roots of Lindera reflexa Hemsl (LR) and determine their binding positions. Allopurinol and febuxostat, known XOD inhibitors, which occupy different binding positions in XOD, were used as blockers and pre-incubated with XOD. Then the LR extract was incubated without XOD, and with XOD, allopurinol-blocked XOD and febuxostat-blocked XOD before ultrafiltration LC-MS was performed. By comparing the chromatographic profiles of the incubation samples, not only the ligands, but also the binding position of these ligands with XOD could be determined. Finally, three compounds, pinosylvin, pinocembrin and methoxy-5-hydroxy-trans-stilbene, were identified as potential XOD inhibitors and the binding modes of these three compounds were shown to be similar to those of febuxostat. To verify the XOD inhibitory activity of the screened compounds, the microplate method and molecular docking in silico were used to evaluate the enzyme inhibitory activities and the binding positions with XOD. The results showed that the developed method could screen for XOD ligands in LR extracts and also determine the binding positions of the ligands. To our knowledge, this is the first report of the XOD inhibitory activity of these three compounds.

Mechanistic approach towards interaction of newly synthesized Hesperidin derivatives against xanthine oxidase

Xanthine oxidase is an important enzyme of purine catabolism pathway and has been associated directly in pathogenesis of gout and indirectly in many pathological conditions like cancer, diabetes and metabolic syndrome. In this research Hesperidin, a bioactive flavonoid was explored to determine the capability of itself and its derivatives to inhibit xanthine oxidase. The design and synthesis of Hesperidin derivatives hybridized with hydrazines to form hydrazides and anilines was performed with the help of molecular docking. The synthesized compounds were evaluated for their antioxidant and xanthine oxidase inhibitory potential. The enzyme kinetic studies performed on newly synthesized derivatives showed a potential inhibitory effect on XO ability in competitive manner with IC50 value ranging from 00.263 μM - 14.870 μM and 3HDa1 was revealed as most active derivative. Molecular simulation revealed that new Hesperidin derivatives interacted with the amino acid residues PHE798, GLN1194, ARG912, THR585, SER1080 and MET1038 positioned inside the binding site of XO. Results of antioxidant activity revealed that all the derivatives showed very good antioxidant potential. Taking advantage of molecular docking, this hybridization of two natural constituent could lead to desirable xanthine oxidase inhibitors with improved activity.

In Silico Design and Synthesis of Targeted Curcumin Derivatives as Xanthine Oxidase Inhibitors.

Curcumin is a well-known pharmacophore and some of its derivatives are shown to target xanthine oxidase (XO) to alleviate disorders caused by the excess production of uric acid. Curcumin based derivatives were designed, synthesized and evaluated for their antioxidant and xanthine oxidase inhibitory potential. In this report, we designed and synthesized two series of curcumin derivatives modified by inserting pyrazole and pyrimidine ring to central keto group. The synthesized compounds were evaluated for their antioxidant and xanthine oxidase inhibitory potential. Results showed that pyrazole analogues of curcumin produced excellent XO inhibitory potency with the IC50 values varying from 06.255 µM to 10.503 µM. Among pyrimidine derivatives compound CU3a1 having ortho nitro substitution exhibited more potent xanthine oxidase inhibitory activity than any other curcumin derivative of this series. Curcumin derivatives CU5b1, CU5b2, CU5b3, and CU3a1 showed a potent inhibitory activity against xanthine oxidase along with good antioxidant potential.

Knoevenagel/Tandem Knoevenagel and Michael Adducts of Cyclohexane-1,3-dione and Aryl Aldehydes: Synthesis, DFT Studies, Xanthine Oxidase Inhibitory Potential, and Molecular Modeling

Xanthine oxidase (XO) plays a crucial role in the formation of uric acid by oxidative hydroxylation of purines. Herein, we report the design and synthesis of Knoevenagel/tandem Knoevenagel and Michael adducts of cyclohexane-1,3-dione and aryl aldehydes as nonpurine XO inhibitors derived from naturally occurring scaffolds. Density functional theory calculations highlighted the reaction pathways and reasoned the formation of tandem Knoevenagel and Michael adducts. The synthetics were assessed for their XO inhibitory potential, and among them, four compounds (1b, 1g, 2b, and 3a) were found to possess best IC50 values in the range of 3.66–4.98 μM. Interestingly, Knoevenagel adducts exhibited a competitive-type inhibition, whereas tandem Knoevenagel and Michael adducts produced a noncompetitive mode of inhibition. The compounds were capable of reducing the H2O2 levels induced by XO, both in normal and cancer cells with no significant cytotoxicity. Molecular modeling studies highlighted the role of interactions...

Effect of febuxostat on biochemical parameters of hyperlipidemia induced by a high-fat diet in rabbits

Febuxostat, a highly potent xanthine oxidase inhibitor with an antioxidant effect, inhibits elevated xanthine oxidase, leading to reduction of reactive oxygen species and oxidative stress, the main causes of vascular inflammation in hyperlipidemia. The aim of this study was to test the potential antioxidant and anti-inflammatory effects of febuxostat and (or) stopping a high-fat diet on the biochemical parameters in rabbits with hyperlipidemia induced by a high-fat diet. Male New Zealand rabbits were distributed into 3 groups: a normal control group fed standard chow for 12 weeks and 2 other groups fed a high-fat diet with 1% cholesterol for 8 weeks, and then shifted to standard chow for 4 weeks. During the last 4 weeks, one high-fat diet group received 0.5% carboxymethyl cellulose, whereas the other group was treated with febuxostat (2 mg/kg per day p.o.). Febuxostat significantly lowered low-density lipoprotein cholesterol ("bad" cholesterol) compared to the untreated group (high-fat diet group). Febuxostat also displayed a potent anti-inflammatory and antioxidant activity by decreasing serum levels of lipid peroxidation index, proinflammatory cytokines, and enhancing antioxidant enzyme activity. Stopping the hyperlipidemic diet in the high-fat diet group did not show improvement. These findings indicate the antioxidant and anti-inflammatory effects of febuxostat that may be common mechanisms of the anti-hyperlipidemic effect of this drug. Stopping a hyperlipidemic diet without treatment is not sufficient once injury has occurred.

Discovery of 2-phenylthiazole-4-carboxylic acid, a novel and potent scaffold as xanthine oxidase inhibitors

The xanthine oxidase (XO) plays an important role in producing uric acid, and therefore XO inhibitors are considered as one of the promising therapies for hyperuricemia and gout. We have previously reported a series of XO inhibitors with pyrazole scaffold to extend the chemical space of current XO inhibitors. Herein, we describe further structural optimization to explore the optimal heterocycle by replacing the thiazole ring of Febuxostat with 5 heterocycle scaffolds unexplored in this field. All of these efforts resulted in the identification of compound 8, a potent XO inhibitor (IC50 = 48.6 nM) with novel 2-phenylthiazole-4-carboxylic acid scaffold. Moreover, lead compound 8 exhibited hypouricemic effect in potassium oxonate-hypoxanthine-induced hyperuricemic mice. These results promote the understanding of ligand-receptor interaction and might help to design more promising XO inhibitors.

Benzoflavone derivatives as potent antihyperuricemic agents.

Two series of benzoflavone derivatives were rationally designed, synthesized and evaluated for their xanthine oxidase (XO) inhibitory potential. Among both series, eight compounds (NF-2, NF-4, NF-9, NF-12, NF-16, NF-25, NF-28, and NF-32) were found to exert significant XO inhibition with IC50 values lower than 10 μM. Enzyme kinetic studies revealed that the most potent benzoflavone derivatives (NF-4 and NF-28) are mixed type inhibitors of the XO enzyme. Molecular modeling studies were also performed to investigate the binding interactions of these molecules (NF-4 and NF-28) with the amino acid residues present in the active site of the enzyme. Docking results confirmed that their favorable binding conformations in the active site of XO can completely block the catalytic activity of the enzyme. Benzoflavone derivatives exhibiting potent XO enzyme inhibition also showed promising results in a hyperuricemic mice model when tested in vivo.

Standardization and xanthine oxidase inhibitory potential of Zanthoxylum armatum fruits

Ethnopharmacological relevanceTejovati (Zanthoxylum armatum DC; Family- Rutaceae) popularly known as toothache tree is widely distributed in sub-tropical Himalaya region. Traditionally, The Southeast Asian population of Indo-Nepal origin uses it to treat asthma, gout, pain, and inflammation. The Ayurvedic action of the plant includes the balancing of Vata-Kapha in the body. Which lead to various ailments related to the circulation of blood and water, digestion, immunity, and skin. Therefore, in-vitro xanthine oxidase (XO) inhibition potential of the extract could be worth to explore prospect in the prevention/treatment of gouty affections of the joints and other diseases. Aim of studyAnti-inflammatory and antioxidant potential of Z. armatum fruit (ZAF) has been reported. To date, no scientific study to validate the claim for gout treatment/management has been attempted so far. The present study deals with the xanthine oxidase inhibitory potential of a various extract of ZAF and marker-based high-performance liquid chromatography (HPLC) standardization of most active fraction. Materials and methodsLiquid-liquid partioning of crude methanol extract of the ZAF followed by repeated column chromatography of most active fraction has resulted in the isolation of seven compounds. Five distinct groups of compounds were isolated, purified, and identified. We have investigated the therapeutic action of ZAF in the management of gout through in-vitro assay of XO, a key enzyme involved in gout pathogenesis. ResultsPhytochemical investigation of ZAF has resulted in the isolation of seven compounds of diverse nature. It is noteworthy to mention that out of seven, five compounds have shown the xanthine oxidase inhibitory action. The ethyl acetate fraction was most potent to inhibit XO. The XO inhibitory activity (IC50 values) of isolated marker chemical was ranging from 5.62 to 41.21 µM. Three compounds viz. acetyl phenyl acetate (ZA-2), prudomestin (ZA-6), and tambulin (ZA-7) showed the most potent XO inhibitory activity (IC50 ≈ 6 µM) comparable with a positive control (Allopurinol, IC50, 3.38 µM). This is the first validated HPLC-PDA method for simultaneous analysis and accurate quantification of seven compounds (phenolic acid, acetyl phenyl acetate, xylopyranoside, diphenyl ether and three flavones) in ZAF as well as their distribution in other tissues of the plant. ConclusionMost potent three chemicals (ZA-2, 6 and 7) could be considered as bioactive to ensure the robust quality of the enriched fraction of ZAF with defined XO inhibition potential. Therefore, either single purified component or their enriched fraction could be a better choice for the management of gout than the crude extract of ZAF. Developed HPLC method is suitable for quality assurance analysis and process control of ZAF derived product intended for gout management. XO inhibitory potential exhibited by the characterized compounds validate the traditional use of this ZAF for the treatment of gout. Further, a detailed study is required to assess the effect of ZAF chemicals on serum uric acid and mechanism of XO inhibition.

Quantitative Prediction of Thiazole Derivatives as Potent Xanthine Oxidase Inhibitors

AbstractIn humans, xanthine oxidase (XO) is a critical rate‐limiting enzyme in biosynthesis of uric acid. Moreover, XO is the most promising target to control uric acid levels and the treat of hyperuricemia and gout. However, XO inhibitors can effectively treat gout through the inhibition of urate synthesis, and by impairing the conversion of hypoxanthine and xanthine to uric acid. In this paper, four different quantitative structure‐activity relationship (QSAR) models of 80 thiazole derivatives were constructed to comprehend chemical‐biological interactions and predict their bioactivities using GA‐MLR (Genetic Algorithm‐Multiple Linear Regression), HQSAR (Hologram Quantitative Structure Activity Relationship), Topomer CoMFA (Comparative Molecular Field Analysis) and CoMSIA (Comparative Molecular Similarity Indices Analysis) methods. Furthermore, R2 and Q2 of the obtained GA‐MLR, HQSAR, Topomer CoMFA and CoMSIA models are 0.956 and 0.911, 0.932 and 0.876, 0.946 and 0.917, 0.964 and 0.877, respectively. In addition, the external predictive values of the GA‐MLR, HQSAR, Topomer CoMFA and CoMSIA models are 0.963, 0.936, 0.973 and 0.934, respectively. Therefore, all QSAR models exhibited good prediction performances, which can be used to quantitatively evaluate bioactivity and screen new XO inhibitors. Moreover, topological charge index, atomic electronegativity and polarizability, atomic van der Waals volumes and hydrophobic van der Waals surface area are very relevant to bioactivity of thiazole derivatives.

Screening of xanthine oxidase inhibitor from selected edible plants and hypouricemic effect of Rhizoma Alpiniae Officinarum extract on hyperuricemic rats

This study was aimed at screening a potential anti-hyperuricemia agent with dual xanthine oxidase (XOD) inhibitory effect (XOI) and antioxidant activity from edible plants with health-promoting effects using non-targeted chemometric analysis (hierarchical cluster analysis and principal component analysis), evaluating its in vivo hypouricemic effect and mechanism, and identifying the key XOD inhibitor using ultrafiltration UPLC-MS/MS. Rhizoma Alpiniae Officinarum extract (GE), which has high contents of total phenolics and flavonoids, as well as dual XOI and antioxidant activity, showed significant hypouricemic and renal protective effects on hyperuricemic rats through inhibiting XOD activity, alleviating oxidative stress, down-regulating URAT1 and GLUT9 protein expression, and reducing urea nitrogen and creatinine levels. GE could be a dual-acting agent with XOI and uricosuric effect for preventing and treating hyperuricemia. Four flavonoids and eight diarylheptanoids were identified as potential XOD inhibitors from GE. Galangin, kaempferide and 3-methoxyl-galangin contributing to 70.1% of XOI were the key XOD inhibitors.

Research on XOD captured components in Lagotis brevituba based on UPLC-Q-TOF-MS and molecular docking technology

Potential xanthine oxidase (XOD) inhibitors in Lagotis brevituba were captured by using affinity and ultrafiltration. The structures of the captured components were identified by ultra-performance liquid chromatography coupled with Q-TOF mass spectrometry (UPLC-Q-TOF-MS). The binding intensity and binding mechanism between the captured components and XOD were analyzed by using molecular docking software Autodock 4.2. A total of 17 compounds were identified, including 9 flavonoids, 5 phenolic acids and 3 triterpenes. Molecular docking results showed that all the captured components could be spontaneously bound with XOD mainly via hydrogen bond, Van der Waals' force and hydrophobic interaction. From the perspective of binding energy and scoring function, the collected fractions all had potential prospects for XOD inhibitors, and the flavonoid luteolin-3',7 glucuronide had the best effect. The results also showed that affinity and ultrafiltration, ultra-performance liquid chromatography-mass spectrometry (UPLC-MS) and molecular docking technology can provide a powerful tool for the analysis of XOD inhibitor components in natural products.

In vivo anti-hyperuricemic and xanthine oxidase inhibitory properties of tuna protein hydrolysates and its isolated fractions

This study follows recent attempts to discover natural xanthine oxidase (XO) inhibitors from foods, focusing herein on under-researched fish proteins. The anti-hyperuricemic function of tuna flesh hydrolysate (TPH) produced using Alcalase 2.4L was confirmed in potassium oxonate-induced hyperuricemic rats. TPH was separated using 80 wt% aqueous ethanol. The ethanol-soluble fraction (ESF) abundant in small peptides (<1000 Da) afforded the highest XO inhibition. Separation of ESF by Sephadex G-15 and UPLC/MS/MS revealed 13 di-/tri-peptides (12 are newly identified XO inhibitors). Their XO inhibitory activities were assessed using corresponding synthetic peptides via an improved HPLC method. Results indicate that Phe-containing peptides were more potent XO inhibitors than Trp-containing peptides, with Phe-His having the highest XO inhibitory activity (IC50 = 25.7 mM). Molecular docking studies revealed the importance of two hydrogen bonds and one π-π stacking interaction with Phe-914 in XO for XO-peptide inhibitor binding. Phe-containing di-/tri-peptides could be potent XO inhibitors against hyperuricemia.

Design, synthesis and bioevaluation of 2-mercapto-6-phenylpyrimidine-4-carboxylic acid derivatives as potent xanthine oxidase inhibitors

A series of 2-mercapto-6-phenylpyrimidine-4-carboxylic acid derivatives (7a‒c, 8a‒e, 9a‒e and 10a‒e) as novel xanthine oxidase inhibitors were designed based on molecular docking, and synthesized by a new method using ketoenol acids and thiourea as the starting materials. In vitro activity assay indicated that most of the designed compounds displayed submicromolar inhibitory potency. Specifically, compound 9b had the most potent enzyme inhibitory activity with the IC50 at 0.132 μM. Steady-state enzyme kinetics indicated that 9b behaved as a mixed-type inhibitor for XO.

The possible mechanism of hydroxytyrosol on reducing uric acid levels

In this study, the inhibitory effect of hydroxytyrosol against xanthine oxidase (XOD) by in vivo animal model and in vitro inhibition assay was analysed. The results showed that hydroxytyrosol could reduce uric acid in rat serum, inhibit XOD activity in rat liver, and adjust the mRNA transcription of the renal uric acid transporters URAT1, GLUT9, OAT1, UAT and ABCG2 towards normal in the transcription level. Hydroxytyrosol was observed as an inhibitor of XOD activity, which’s IC50 value of restraining XOD activity was 8.75 mM. Circular dichroism (CD) spectroscopy indicated that the secondary structures of XOD were changed after incubation with hydroxytyrosol. The docking simulation showed that hydroxytyrosol could enter into the active site of XOD and form hydrogen bonds with amino acid residues (such as ARG880, GLU1261 and THR1010). The results suggested that hydroxytyrosol could be a potential XOD inhibitor for hyperuricaemia treatment.

Modeling the Transition State Structures of the Reductive-Half Reaction Active Site of Xanthine Oxidase Bound to Guanine Analogues: A Density Functional Theory Approach

Modeling and characterization the transition state structure of enzyme catalyzed reactions is essential. A DFT method employing B3LYP level of theory with 6-31G (d',p') basis set for non-metals and LanL2DZ basis set for molybdenum have been used. The bond orders of chemical fragments were calculated using AOmix softaware. The effect of chalcogen replacement, amine group and methyl group in the parent structure of xanthine bound to xanthine oxidase active site were compared. The transition state structure of model substrates (2AX, 2A6TP, 2A6SP and 2A6MP) bound to the truncated form of XO active site has been confirmed by the presence of one negative imaginary frequencies (s-1) (-60), (-140), (-230) and (-270), respectively. The corresponding normalized energy barriers (kcal/mol) from pre-transition state to the transition state, respectively, are (13.869), (21.753), (23.109) and (0.212). In this work, 2A6SP and 2A6TP substrates were found to be potential xanthine oxidase inhibitors. The large bond distances and minimum bond order for CRH-HRH bond, and small bond distances and maximum bond order for SMo-HRH bond at the transition state for chalcogen replaced 2AX confirms early transition state structure. Methyl substituted 2AX analog found to have post transition state structure. A potential xanthine oxidase inhibitor can be designed from purine family enzymes using DFT approach.

Synthesis, structure-activity relationships, and mechanistic studies of 5-arylazo-tropolone derivatives as novel xanthine oxidase (XO) inhibitors

Xanthine oxidase (XO) is an enzyme that contains molybdenum at the active site and catalyzes the oxidation of purine bases to uric acid. Even though XO inhibitors are widely used for the treatment of hyperuricemia and gout, only very few such compounds are clinically used as drugs for the treatment of these diseases. Given the unique physicochemical properties of tropolone, i.e., its chelating effect and the pKa value that is similar to that of carboxylic acid, we have synthesized 22 5-arylazotropolone derivatives as potential XO inhibitors. In vitro enzyme-inhibitory assays for XO revealed that 3-nitro derivative 1j showed the most potent XO inhibitory activity, which is by one order of magnitude more potent than allopurinol. An enzyme-kinetic study revealed that 1j inhibited the production of uric acid by XO both competitively and non-competitively. A docking-simulation study of 1j with XO suggested that the carbonyl and hydroxyl groups of the tropolone ring interact with the hydroxy group that acts as a ligand for molybdenum and the amino acid residues around the active site of XO.

The influence of febuxostat on coronary artery endothelial dysfunction in patients with coronary artery disease: A phase 4 randomized, placebo-controlled, double-blind, crossover trial

The xanthine oxidase (XO) system is a significant source of vascular oxidative stress, which is believed to impair endothelial function, an important contributor to atherosclerotic disease. We tested whether febuxostat, a potent XO inhibitor, improves coronary endothelial function (CEF) in patients with stable coronary artery disease (CAD) in a single-center, randomized, placebo-controlled, double-blind crossover trial. CEF was measured using noninvasive magnetic resonance imaging (MRI) assessment of changes in 30 patients with stable CAD and baseline impaired CEF. Patients received either febuxostat or placebo for 6 weeks and then were crossed over to the alternative for an additional 6 weeks. MRI-detected changes in coronary flow and in coronary cross-sectional area from rest to isometric handgrip exercise, a known endothelial-dependent stressor, were measured at the end of each 6 week period. Mean serum urate levels were lower at the end of the 6-week febuxostat period (2.9±0.8mg/dL) than at the end of the 6-week placebo period (5.9±0.04, P<.001). However, there were no significant differences in any of the CEF parameters measured at the end of the febuxostat and placebo periods. In summary, although XO inhibition with febuxostat was well tolerated and lowered serum urate, it did not improve the primary end point of the study, CEF measured using MRI after 6 weeks of treatment. In conclusion, these findings suggest that short-term inhibition of XO does not significantly improve impaired CEF in patients with stable CAD.