Design, synthesis, and biological evaluation of N-(3-cyano-1H-indol-5/6-yl)-6-oxo-1,6-dihydropyrimidine-4-carboxamides and 5-(6-oxo-1,6-dihydropyrimidin-2-yl)-1H-indole-3-carbonitriles as novel xanthine oxidase inhibitors

Design, synthesis and biological evaluation of 2-[1-(pyridin-2-ylmethyl)-1H-pyrazole-3-carboxamido]benzoic acids as promising urate transporter 1 inhibitors with potential nephroprotective efficacy for the treatment of hyperuricemic nephropathy

Hyperuricemic nephropathy (HN) is considered an important risk factor for mortality in patients with hyperuricemia. Reducing serum uric acid (UA) levels and mitigating kidney injury are essential components in the treatment of HN. Thus, UA-lowering drugs that can also protect the kidneys are urgently needed. We identified a urate transporter 1 (URAT-1) inhibitor, T29, with cytoprotective efficacy through screening an internal library against hyperuricemia using a UA-induced HK-2 cell injury model. A bioisosteric strategy was then employed to replace the indole core of T29 with pyrazole moieties; this resulted in a series of 2-[1-(pyridin-2-ylmethyl)-1H-pyrazole-3-carboxamido]benzoic acids. Among them, compound 18 demonstrated the best cytoprotective efficacy (cell viability = 92.2 % vs. model = 31.5 %), and the IC50 value of compound 18 against URAT-1 was 3.36 μM; both of these values exceeded T29. In an HN mice model induced by a 0.75 % adenine diet and intraperitoneal injection of potassium oxonate (400 mg/kg), compound 18 significantly reduced the serum UA levels by inhibiting URAT-1 activity. Furthermore, compound 18 improved kidney function by lowering serum creatinine (CRE) and urea nitrogen (BUN) levels while attenuating tubular dilation and inflammatory cell infiltration in the kidneys. Additionally, it suppressed the release of the proinflammatory cytokines IL-1β and TNF-α and reduced kidney fibrosis by downregulating the expression of α-SMA and TGF-β. In conclusion, compound 18 ameliorated HN by inhibiting URAT-1, alleviating immune-inflammatory responses and mitigating fibrosis; the results from this study demonstrate its potential as a therapeutic agent for HN.

A patent review of xanthine oxidase inhibitors (2021-present)

INTRODUCTION

Xanthine oxidase (XO) catalyzes the oxidation of both hypoxanthine and xanthine in the last two steps of the purine metabolic pathway, serving as a rate-limiting enzyme for uric acid production as well as a key target for the treatment of gout and other hyperuricemia-related conditions.

AREAS COVERED

This paper reviews XO inhibitors in patents from 2021 to the present. We summarize in detail the structural classes and characteristics, in vitro and in vivo biological results, and structure‒activity relationships of synthetic inhibitors, as well as the sources, specific structures, research methods, and biological activities of XO inhibitors from natural products.

EXPERT OPINION

(1) Benefiting from the discovery of many high-affinity inhibitors, the binding modes of small molecules in the active pocket of XO have been further elucidated, and this information will contribute to future development; (2) natural products remain one of the important sources in the discovery of XO inhibitors; (3) with a deeper exploration of XO and URAT1 targets, XO/URAT1 dual target inhibitors may be a future research hotspot; and (4) the search for high-affinity, small-molecule scaffolds remains a key challenge and an important direction for the future development.

Recent Progress and Future Perspectives on Anti-Hyperuricemic Agents

Increased biosynthesis or underexcretion of uric acid (UA or urate) in the body ultimately leads to the development of hyperuricemia. Epidemiological studies indicate that hyperuricemia is closely associated with the occurrence of various diseases such as gout and cardiovascular diseases. Currently, the first-line therapeutic medications used to reduce UA levels primarily include xanthine oxidase (XO) inhibitors, which limit UA production, and urate transporter 1 (URAT1) inhibitors, which decrease urate reabsorption and enhance urate excretion. Despite significant progress in urate-lowering therapies, long-term use of these drugs can cause hepatorenal toxicity as well as cardiovascular complications. Therefore, there is an urgent need for novel anti-hyperuricemic agents with better efficacy and lower toxicity. This perspective mainly focuses on the current research progress and design strategy of anti-hyperuricemic agents, particularly those targeting XO and URAT1. It is our hope that this perspective will provide insights into the challenges and opportunities for anti-hyperuricemic drug discovery.

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.

Discovery of a Potent and Orally Bioavailable Xanthine Oxidase/Urate Transporter 1 Dual Inhibitor as a Potential Treatment for Hyperuricemia and Gout

The main uric acid-lowering agents in clinical use for hyperuricemia and gout are xanthine oxidase (XO) inhibitors or urate transporter 1 (URAT1) inhibitors. While these therapies can partially control the disease, they have various limitations. The development of XO/URAT1 dual inhibitors offers the potential to enhance therapeutic potency and reduce toxicity compared with single-target inhibitors. Through scaffold hopping from the XO inhibitor febuxostat (2) and the URAT1 inhibitor probenecid (3), followed by structure-activity relationship (SAR) studies, we identified compound 27 as a potent dual inhibitor of XO and URAT1. Compound 27 demonstrated significant dual inhibition in vitro (XO IC50 = 35 nM; URAT1 IC50 = 31 nM) and exhibited favorable pharmacology and pharmacokinetic (PK) profiles in multiple species including monkeys. Furthermore, toxicity studies in rats and monkeys revealed general safety profiles, supporting that compound 27 emerges as a promising novel drug candidate with potent XO/URAT1 dual inhibition for the treatment of gout.

A comprehensive review of synthetic and semisynthetic xanthine oxidase inhibitors: identification of potential leads based on in-silico computed ADME characteristics

Xanthine oxidase (XO) inhibitors, both synthetic and semisynthetic, have been developed extensively over the past few decades. The increased level of XO is not only the major cause of gout but is also responsible for various conditions associated with hyperuricemia, such as cardiovascular disorders, chronic kidney disorders, diabetes, Alzheimer's disease and chronic wounds. Marketed available XO inhibitors (allopurinol, febuxostat, and topiroxostat) are used to treat hyperuricemia but they are associated with fatal side effects, which pose serious problems for the healthcare system, rising the need for new, more potent, safer compounds. This review summarizes recent findings on XO and describes their design, synthesis, biological significance in the development of anti-hyperuricemic drugs with ADME profile, structure activity relationship (SAR) and molecular docking studies. The results might help medicinal chemists to develop more efficacious XO inhibitors.

Indole-3-Lactic Acid Derived from Lacticaseibacillus paracasei Inhibits Helicobacter pylori Infection via Destruction of Bacteria Cells, Protection of Gastric Mucosa Epithelial Cells, and Alleviation of Inflammation

Indole-3-lactic acid (ILA) has exhibited antimicrobial properties. However, its role in inhibiting Helicobacter pylori infection remains elusive. This study investigated the inhibitory effect of ILA produced by Lacticaseibacillus paracasei on H. pylori, which was further confirmed by cell and animal experiments. 5 mg/mL ILA was sufficient to directly inhibit the growth of H. pylori in vitro, with a urease inhibitory activity reaching 60.94 ± 1.03%, and the cell morphology and structure were destroyed. ILA inhibited 56.5% adhesion of H. pylori to GES-1 and significantly reduced the number of apoptotic cells. Furthermore, ILA suppresses H. pylori colonization by approximately 38% to 63%, reduced inflammation and oxidative stress in H. pylori-infected mice, and enhanced the enrichment and variety of gut microbiota, notably fostering the growth of beneficial bacteria such as Lactobacillus and Bifidobacterium strains. The results support that ILA derived from Lactobacillus can be applicated as a novel prebiotic in anti-H. pylori functional foods.

Heterocyclic compounds as xanthine oxidase inhibitors for the management of hyperuricemia: synthetic strategies, structure-activity relationship and molecular docking studies (2018-2024)

Hyperuricemia is characterized by higher-than-normal levels of uric acid in the bloodstream. This condition can increase the likelihood of developing gout, a form of arthritis triggered by the deposition of urate crystals in the joints, leading to inflammation and pain. An essential part of purine metabolism is played by the enzyme xanthine oxidase (XO), which transforms xanthine and hypoxanthine into uric acid. Despite its vital role, diseases such as gout have been associated with elevated uric acid levels, which are linked to increased XO activity. To manage hyperuricemia, this study focuses on potential nitrogen based heterocyclic compounds that may serve as XO inhibitors which may lower uric acid levels and prevent hyperuricemia. Xanthine oxidase inhibitors are a class of medications used to treat conditions like gout by reducing the production of uric acid. The present study demonstrates numerous compounds, particularly nitrogen containing heterocyclic compounds including their synthesis, structure-activity relationship, and molecular docking studies. This paper also contains drugs undergoing clinical studies and the xanthine oxidase inhibitors that have been approved by the FDA.

Design, synthesis, and biological evaluation of 5-(1H-indol-5-yl)isoxazole-3-carboxylic acids as novel xanthine oxidase inhibitors

Xanthine oxidase (XO) is a key enzyme for the production of uric acid in the human body. XO inhibitors (XOIs) are clinically used for the treatment of hyperuricemia and gout, as they can effectively inhibit the production of uric acid. Previous studies indicated that both indole and isoxazole derivatives have good inhibitory effects against XO. Here, we designed and synthesized a novel series of N-5-(1H-indol-5-yl)isoxazole-3-carboxylic acids according to bioisosteric replacement and hybridization strategies. Among the obtained target compounds, compound 6c showed the best inhibitory activity against XO with an IC50 value of 0.13 μM, which was 22-fold higher than that of the classical antigout drug allopurinol (IC50 = 2.93 μM). Structure-activity relationship analysis indicated that the hydrophobic group on the nitrogen atom of the indole ring is essential for the inhibitory potencies of target compounds against XO. Enzyme kinetic studies proved that compound 6c acted as a mixed-type XOI. Molecular docking studies showed that the target compound 6c could not only retain the key interactions similar to febuxostat at the XO binding site but also generate some new interactions, such as two hydrogen bonds between the oxygen atom of the isoxazole ring and the amino acid residues Ser876 and Thr1010. These results indicated that 5-(1H-indol-5-yl)isoxazole-3-carboxylic acid might be an efficacious scaffold for designing novel XOIs and compound 6c has the potential to be used as a lead for further the development of novel anti-gout candidates.

Discovery of a Novel Thienopyrimidine Compound as a Urate Transporter 1 and Glucose Transporter 9 Dual Inhibitor with Improved Efficacy and Favorable Druggability

Gout and hyperuricemia are metabolic diseases characterized with high serum uric acid (SUA) levels that significantly impact human health. Lesinurad, a uricosuric agent, is limited to concurrent use with xanthine oxidase inhibitors (XOIs) in clinical practice due to its restricted efficacy and potential nephrotoxicity. Herein, extensive structural modifications of lesinurad were conducted through scaffold hopping and substituent modification strategies, affording 54 novel derivatives containing pyrimidine-fused cyclic structures. Notably, the thienopyrimidine compound 29 demonstrated a remarkable 2-fold increase in SUA-lowering in vivo activity compared to lesinurad, while exhibiting potent inhibitory activity against the urate transporter 1 (URAT1, IC50 = 2.01 μM) and glucose transporter 9 (GLUT9, IC50 = 18.21 μM). Furthermore, it possessed a lower effective dosage of 0.5 mg/kg, favorable safety profile without any apparent acute toxicity at doses of 1000 mg/kg, and improved pharmacokinetic properties. Overall, we have discovered an efficacious URAT1/GLUT9 dual inhibitor for inhibiting urate reabsorption with favorable pharmacokinetic profiles.

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.

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.

Identification of 5-[5-cyano-1-(pyridin-2-ylmethyl)-1H-indole-3-carboxamido] thiazole-4-carboxylic acid as a promising dual inhibitor of urate transporter 1 and xanthine oxidase

In combination with allopurinol, tranilast is used as an urate transporter 1 (URAT1) inhibitor for the treatment of hyperuricemia, but its structure-activity relationship concerning URAT1 inhibitory activity is rarely studied. In this paper, analogs 1-30 were designed and synthesized using scaffold hopping strategy on the basis of tranilast and the privileged scaffold indole. Then, URAT1 activity was evaluated using ¹⁴C-uric acid uptake assay with HEK293-URAT1 overexpressing cells. Compared with tranilast (inhibitory rate = 44.9% at 10 μM), most compounds displayed apparent inhibitory effects, ranging from 40.0% to 81.0% at 10 μM on URAT1. Surprisingly, along with the bringing in of a cyano group at the 5-position of indole ring, compounds 26 and 28-30 exerted xanthine oxidase (XO) inhibitory activity. In particular, compound 29 presented potency on URAT1 (48.0% at 10 μM) and XO (IC₅₀ = 1.01 μM). Molecular simulation analysis revealed that the basic structure of compound 29 had an affinity with URAT1, and XO. Furthermore, compound 29 demonstrated a significant hypouricemic effect in a potassium oxonate-induced hyperuricemia rat model at an oral dose of 10 mg/kg during in vivo tests. In summary, tranilast analog 29 was identified as a potent dual-target inhibitor of URAT1 and XO, and a promising lead compound for further investigation.

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.

Chalcone derivatives as xanthine oxidase inhibitors: synthesis, binding mode investigation, biological evaluation, and ADMET prediction

Xanthine oxidase (XO) is a crucial target for the treatment of hyperuricemia and gout. A series of derivatives based on natural 3,4-dihydroxychalcone, obtained from Carthamus tinctorious and Licorice, were designed and synthesized. Nine derivatives (9a-e, 10b,c, and 15a,b) exhibited apparent XO inhibitory activity in vitro (IC₅₀ values varied from 0.121 to 7.086 μM), 15b presented the most potent inhibitory activity (IC₅₀ = 0.121 µM), which was 27.47-fold higher than that of allopurinol (IC₅₀ = 3.324 µM). The SAR analysis indicated that introducing hydroxyl groups at 3'/4'/5'-position on ring A was more beneficial to the inhibition of XO than at 2'/6'-position; the removal of 3‑hydroxyl group on ring B could weaken the inhibitory potency of hydroxychalcones on XO, but it was beneficial to the XO inhibitory potency of methoxychalcones. Molecule modeling studies afforded insights into the binding mode of 15b with XO and supported the findings of SAR analysis. Additionally, kinetics studies demonstrated that 15b presented a reversible and competitive XO inhibitor, which spontaneously combined with XO through hydrophobic force, and finally changed the secondary conformation of XO. Furthermore, the acute hyperuricemia model was employed to investigate the hypouricemic effect of 15b, which could effectively reduce the serum uric acid levels of rats at an oral dose of 10 mg/kg. ADMET prediction suggested that compound 15b possessed good pharmacokinetic properties. Briefly, compound 15b emerges as an interesting XO inhibitor for the treatment of hyperuricemia and gout with beneficial effects on serum uric acid levels regulating. Meanwhile, the XO inhibitors with chalcone skeleton will deserve further attention and discussion.

An Overview of the Biological Evaluation of Selected Nitrogen-Containing Heterocycle Medicinal Chemistry Compounds

Heterocyclic compounds are a class of compounds of natural origin with favorable properties and hence have major pharmaceutical significance. They have an exceptional adroitness favoring their use as diverse smart biomimetics, in addition to possessing an active pharmacophore in a complex structure. This has made them an indispensable motif in the drug discovery field. Heterocyclic compounds are usually classified according to the ring size, type, and the number of heteroatoms present in the ring. Among different heterocyclic ring systems, nitrogen heterocyclic compounds are more abundant in nature. They also have considerable pharmacological significance. This review highlights recent pioneering studies in the biological assessment of nitrogen-containing compounds, namely: triazoles, tetrazoles, imidazole/benzimidazoles, pyrimidines, and quinolines. It explores publications between April 2020 and February 2022 and will benefit researchers in medicinal chemistry and pharmacology. The present work is organized based on the size of the heterocyclic ring.

Intramolecular hydrogen bond interruption and scaffold hopping of TMC-5 led to 2-(4-alkoxy-3-cyanophenyl)pyrimidine-4/5-carboxylic acids and 6-(4-alkoxy-3-cyanophenyl)-1,2-dihydro-3H-pyrazolo[3,4-d]pyrimidin-3-ones as potent pyrimidine-based xanthine oxidase inhibitors

Many pyrimidine-based xanthine oxidase (XO) inhibitors with diverse chemotypes have been reported recently. Our previous study revealed that 2-(4-alkoxy-3-cyano)phenyl-6-imino-1,6-dihydropyrimidine-5-carboxylic acid derivatives exhibited remarkable XO inhibitory potency. Notably, an intramolecular hydrogen bond (IMHB) formed between amino and carboxylic groups could be observed. With the hope to expand the structure-activity relationships (SARs) and obtain potential pyrimidine-based XO inhibitors, IMHB interruption and scaffold hopping were carried out on these compounds to design 2-(4-alkoxy-3-cyanophenyl)pyrimidine-4/5-carboxylic acids (11a-11n and 15a-15j) and 6-(4-alkoxy-3-cyanophenyl)-1,2-dihydro-3H-pyrazolo[3,4-d]pyrimidin-3-ones (19a-19j). Among them, compound 19a (IC₅₀ = 0.039 μM) was identified as the most promising compound with substantially higher in vitro inhibitory potency than allopurinol (IC₅₀ = 7.590 μM) and comparable to febuxostat (IC₅₀ = 0.028 μM). The SAR analysis revealed that interrupting the IMHB through the removal of the amino group could damage the XO inhibitory potency; pyrimidine-4-carboxylic acid moiety was more beneficial for the XO inhibitory potency than the pyrimidine-5-carboxylic acid moiety. Additionally, enzyme kinetics studies suggested that compounds 11a, 15a and 19a acted as mixed-type inhibitors for XO and the removal of 6-position amino group resulted in a weakened affinity to the free enzyme, but an enhanced binding to the enzyme-substrate complex. Molecular modeling provided a reasonable explanation for the SARs observed in this study. Furthermore, in vivo hypouricemic effects demonstrated that compounds 15a and 19a could effectively reduce serum uric acid levels at an oral dose of 10 mg/kg, with 19a demonstrating a stronger effect than 15a. Therefore, our study proved that 6-(4-alkoxy-3-cyanophenyl)-1,2-dihydro-3H-pyrazolo[3,4-d]pyrimidin-3-ones were potent pyrimidine-based XO inhibitors and compound 19a required further structural optimization as a potential and efficacious agents for the treatment of hyperuricemia and gout.