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Xanthine oxidase inhibitory properties of 1,2,3,4-tetrahydroisoquinoline derivatives.

  • Faculty of Medicine, University of Niš, 18000 Niš, Serbia
Original article
UDC: 577.152.1:547.833
Mihajlo Gajić1, Budimir S. Ilić2, Bojan P. Bondž3, Zdravko Džambaski3, Ana Filipović3,
Gordana Kocić4, Andrija Šmelcerović2
Xanthine oxidase (XO) is a versatile metalloflavoprotein enzyme that is best known for
its rate-limiting role in the purine degradation pathway. Therapeutic inhibition of XO is based on
its role in a variety of diseases that is attributed either to the hyperproduction of uric acid, or
the hyperproduction of reactive oxygen species. Herein, we report the assessment of XO
inhibitory properties of 24 1,2,3,4-tetrahydroisoquinoline derivatives, among which compound
16 exhibited IC50 value of 135.72 ± 2.71 µM. The interaction of compound 16 with XO enzyme
was simulated using the Site Finder module, molecular docking and molecular dynamics.
Molecular modeling suggests that interactions with Met 1038, Gln 1040, Thr 1077, Gln 1194
and Val 1259 are an important factor for inhibitor affinity toward the XO enzyme. Our proposed
binding model might be beneficial for the discovery of new active 1,2,3,4-tetrahydroisoquino-
line-based inhibitors of XO enzyme.
Acta Medica Medianae 2021;60(1):48-55.
Key words: xanthine oxidase inhibition, 1,2,3,4-tetrahydroisoquinolines, molecular
docking, molecular dynamic simulation
1University of Niš, Faculty of Medicine, Department of
Pharmacy, Niš, Serbia
2University of Niš, Faculty of Medicine, Department of
Chemistry, Niš, Serbia
3University of Belgrade, Institute of Chemistry, Technology and
Metallurgy, Belgrade, Serbia
4University of Niš, Faculty of Medicine, Department of
Biochemistry, Niš, Serbia
Contact: Andrija Šmelcerović
48 Dr Zoran Djindjić Blvd., 18000 Niš, Serbia
Xanthine oxidoreductase (XOR) is a versatile
molybdopterin-containing flavoprotein enzyme that
exists in two interconvertible forms, xanthine oxi-
dase (XO) and xanthine dehydrogenase (XDH) (1).
The enzyme is best known for its rate-limiting role in
the purine degradation pathway, where it catalyzes
oxidative hydroxylation of hypoxanthine and xan-
thine, subsequently producing uric acid (2, 3). Dehy-
drogenase form is predominant in healthy tissues,
while conversion to XO occurs in pathological con-
ditions, after XDH proteolysis or oxidation of some of
its sulfhydryl residues (1). Superoxide anion radical
and hydrogen peroxide that are generated as the
byproducts of enzyme activity are responsible for
oxidative stress which usually accompanies elevated
XO activity. The role of XO in diseases is attributed
either to the hyperproduction of uric acid, or the
hyperproduction of reactive oxygen species. There-
fore, pharmacological inhibition of xanthine oxidase
is proven to be invaluable for the treatment of
hyperuricemia and gout in the first place, but might
also be beneficial for plethora of conditions, such as
cholecystitis, hemorrhagic shock, ischemia-reperfu-
sion injuries, hypercholesterolemia and carcinogene-
sis (4).
Given the broad therapeutic potential of XO
inhibitors, the aim of the current study was to
assess a group of 24 1,2,3,4-tetrahydroisoquinoline
derivatives for potential inhibitory properties against
XO and to perform molecular docking and molecular
dynamics simulation on active compounds, in order
to elucidate key structural features responsible for
XO inhibitory activity.
Materials and methods
The synthesis of 24 1,2,3,4-tetrahydroiso-
quinoline derivatives was preformed according to the
description in our previous study (5).
Xanthine oxidase inhibitory properties of 1,2,3,4-tetrahydroisoquinoline... Mihajlo Gajić et al.
Evaluation of xanthine oxidase inhibition
Compounds were studied for inhibitory pro-
perties against bovine milk xanthine oxidase. Spec-
trophotometric measurement of uric acid formation
at 293 nm was used for in vitro evaluation of en-
zyme inhibition, as described in our previous studies
(6, 7). Initially, all compounds were assayed at a
concentration of 150 µM, while those inhibiting more
than 50% of enzyme activity were subsequently
tested in a broader concentration range to allow for
IC50 determination. Allopurinol was used as a posi-
tive control. All experiments were performed in tri-
plicate and averaged.
Ligand preparation
Examined inhibitor was generated using the
builder panel in the Molecular Operating Environ-
ment (MOE) 2019.0101 software (8). Using the MOE
LigX module, partial atomic charges were ascribed
and possible ionization states were generated at a
pH of 7.0. The MMFF94x force field was used for
optimization and the resulting structure was used for
modeling studies. Conformational search was carried
out by MOE LowModelMD method which performs
molecular dynamic perturbations along with low
frequency vibrational modes with energy window of
7 kcal/mol, and conformational limits of 1000.
Receptor preparation
The X-ray crystallographic structure of XO
enzyme (PDB code: 1N5X), retrieved from the Pro-
tein Data Bank, was prepared using the Structure
Preparation process in MOE. After the correction, hy-
drogens were added and partial charges (Gasteiger
methodology) were calculated. Energy minimization
(AMBER14:EHT, RMS gradient: 0.100) was perfor-
Binding site selection
The Site Finder module of the MOE was used
to identify possible ligand-binding sites within the
optimized structure of XO enzyme. Hydrophobic or
hydrophilic alpha spheres served as probes denoting
zones of tight atom packing. These alpha spheres
were utilized to define and rank potential ligand-
binding sites according to their propensity for ligand
binding (PLB) score, which was based on the amino
acid composition of the pocket (9).
Docking protocol
The molecular docking study was performed
using the MOE to understand the ligand/protein
interactions in detail. The default Triangle Matcher
placement method was used for the induced fit
docking. GBVI/WSA dG scoring function which esti-
mates the free energy of binding of the ligand from
a given pose was used to rank the final poses. The
ligand/protein complex with lowest relative binding
free energy (ΔG) score was selected for further
Molecular dynamics simulation
The molecular dynamics simulation of com-
pound 16 on XO enzyme, was carried out using the
Desmond Molecular Dynamics System (Desmond)
2018.4 software (10). The structure of the added
water was based on the simple point charge (SPC)
solvent model. The system was neutralized with Na+
ions to balance the net charge of the whole simula-
tion box to neutral. The final system contained ap-
proximately 123,000 atoms. The system was passed
through a 6-step relaxation protocol before molecu-
lar dynamics simulations. The relaxed system was
simulated for 10 ns, using a normal pressure tempe-
rature (NPT) ensemble with a NoséHoover thermo-
stat at 300 K and MartynaTobiasKlein barostat at
1.01325 bar pressure. Atomic coordinate data and
system energies were recorded every 1 ps. The root
mean square deviation (RMSD) and root mean
square fluctuation (RMSF) of the inhibitor/XO en-
zyme complex were analyzed with respect to the
simulation time.
Results and discussion
Previously synthetized 1,2,3,4-tetrahydroiso-
quinoline derivatives (5) were assayed for potential
in vitro XO inhibitory properties. Among 24 tested
compounds (Table 1), IC50 value below 150 µM was
observed only in the case of 16 (135.72 ± 2.71 µM).
Analysis of structural features of active compound
16 and its closest inactive analog 17 indicate to 7,8-
dimethoxy substitution on 1,2,3,4-tetrahydroiso-
quinoline core as a probable cause for the lack of XO
inhibitory properties of 17. Identified active com-
pound 2-(4-fluorophenyl)-1,2,3,4-tetrahydroisoquino-
line-1-carbonitrile (16) was subjected to docking
studies and molecular dynamics simulation with the
goal to provide insight into the key structural featu-
res required for its XO inhibitory activity.
By combining a novel and highly effective
algorithm for rapid binding-site evaluation with
easy-to-use property visualization tools, Site Finder
provides researchers with efficient means to identify
and characterize binding sites (9). The results from
the Site Finder analysis highlighted that catalytic
residues like Gln 767, Glu 802, Arg 880, Phe 914,
Phe 1009 and Glu 1261 (11, 12) constituted the top-
ranked binding pocket of XO enzyme (Table 2,
Figure 1).
The intermolecular contacts between exam-
ined inhibitor and XO enzyme were analyzed using
the ligand interaction diagram of MOE suite (Table 3,
Figure 2). It illustrates the existence of hydrogen
bond and pi-H interactions. Additionally, the bond
distances, bond energy and binding free energy be-
tween the inhibitor and receptor atoms were also
examined (Table 3). The molecular docking high-
lighted the importance of Met 1038, Gln 1040, Thr
1077, Gln 1194 and Val 1259 in the formation of
inhibitor/XO enzyme complex (Table 3, Figure 2).
Observed interactions between 16 and non-catalytic
Acta Medica Medianae 2021, Vol.60(1) Xanthine oxidase inhibitory properties of 1,2,3,4-tetrahydroisoquinoline...
residues (Table 3, Figure 2), are similar to molecular
interplay involving non-purine XO inhibitors (13-16).
Some of recently synthesized pyrazole derivatives
were found to inhibit XO enzyme via Met 1038, Gln
1040 and Gln 1194 residues (13). Furthermore,
inhibitory effect of verbascoside on XO activity, can
be attributed to the formation of hydrogen bond
with Gln 1194 residue (14). Moreover, molecular
simulation revealed that newly synthesized hesperi-
din derivatives interacted with XO residues Met
1038, Gln 1040, Thr 1077, Gln 1194 and Val 1259
(15). Additionally, molecular docking revealed that
1,4-dicaffeoylquinic acid interacted with XO enzyme
via Gln 1040 and Thr 1077 residues (16).
Table 1. In vitro XO inhibitory activity of 1,2,3,4-tetrahydroisoquinolines
IC50 values (µM) ± SD
> 150
> 150
> 150
> 150
> 150
> 150
> 150
> 150
> 150
> 150
> 150
> 150
> 150
> 150
> 150
135.72 ± 2.71
> 150
> 150
> 150
> 150
> 150
> 150
> 150
> 150
Xanthine oxidase inhibitory properties of 1,2,3,4-tetrahydroisoquinoline... Mihajlo Gajić et al.
Table 2. Summary of the top five inhibitor-binding sites in XO
Gln 112, Cys 150, Gln 767, Gly 796, Gly 797, Phe 798, Gly
799, Glu 802, Leu 873, Ser 876, Arg 880, Ala 910, Phe 911,
Arg 912, Gly 913, Phe 914, Phe 1005, Ser 1008, Phe 1009,
Thr 1010, Val 1011, Leu 1014, Met 1038, Gly 1039, Gln 1040,
Gly 1041, Leu 1042, Lys 1045, Pro 1076, Thr 1077, Ala 1078,
Ala 1079, Ser 1080, Val 1081, Ser 1082, Thr 1083, Ile 1190,
Asp 1191, Gln 1194, Gly 1197, Lys 1257, Ala 1258, Val 1259,
Gly 1260, Glu 1261
Cys 662, Val 663, Ile 696, Thr 697, Ile 698, Glu 699, Tyr 735,
Gly 738, Gln 739, Asp 740, His 741, Asp 832, Met 833, Leu
834, Ile 835, Thr 836, Gly 837, Gly 838, Arg 839, Pro 841, Asn
866, Asn 904, Leu 905, Ser 906, Asn 908, Leu 1211, Tyr
1213, Ser 1214, Pro 1215, Gly 1217, Ser 1218, Leu 1219, Thr
1221, Arg 1222
His 614, Asp 651, Glu 652, Thr 653, Thr 661, Cys 662, Val
663, Gly 664, His 665, Ile 666, Pro 693, Ala 694, Ile 695, Ser
706, Tyr 708, Arg 804, Leu 807, Leu 834, Ile 835, Thr 836,
Gly 837, Gly 868, Asn 869, Ser 870, Arg 871, Lys 902, Thr
903, Asn 904, Ser 906, Ser 907
Gln 62, Ile 66, His 67, Phe 68, Ser 69, Ser 123, Thr 126, Leu
127, Asn 130, Gln 131, Glu 137, Glu 138, Asp 141, Ala 142,
Gln 144, Ala 304, Ser 306, Ser 307, Glu 309, Lys 310, Leu
313, Arg 328, Leu 331, Glu 332, Leu 334, Arg 335, Trp 336,
Lys 340, Gln 341, Lys 343, Ser 344, Leu 548, Gln 550, Lys
Leu 952, Asn 956, Gln 957, Arg 958, Leu 959, Glu 960, Gly
961, Ser 963, Pro 1136, Asn 1137, Leu 1138, Asn 1148, Phe
1150, His 1151, Tyr 1152, Phe 1153, Tyr 1155, Asp 1181, Gly
1183, Cys 1247, Pro 1248, Asn 1249, Lys 1250, Lys 1251, Lys
Figure 1. The top ranked XO binding site, represented by a grey-red surface map
Acta Medica Medianae 2021, Vol.60(1) Xanthine oxidase inhibitory properties of 1,2,3,4-tetrahydroisoquinoline...
Table 3. Summary of the 16 interactions with protein residues in XO
ΔG binding
Met 1038
Gln 1194
Thr 1077
Gln 1040
Val 1259
Figure 2. 3D/2D view of compound 16 (A, B) bound in the active site of XO.
The polar part of the active site is shown as a pink surface, hydrophobic part as a green surface,
while the solvent exposed part is shown as a red surface.
The study was further extended to assess the
stability of 16/XO enzyme complex through the
molecular dynamics simulation. The RMSD and RMSF
plots for XO enzyme and examined inhibitor showed
that docking complex was stable during entire simu-
lation period (Figures 3-4). The RMSD for Cα, side
chains and heavy atoms remained within the limit of
2 Å. The similar situation was noted for RMSF
values. The obtained results indicated small struc-
tural rearrangements, less conformational changes
and confirmed stability of 16/XO enzyme complex
Figure 3. RMSD (A) and RMSF (B) plot of XO, obtained during the course of 10 ns molecular dynamics simulation
Xanthine oxidase inhibitory properties of 1,2,3,4-tetrahydroisoquinoline... Mihajlo Gajić et al.
Figure 4. RMSD (A) and RMSF (B) plot of compound 16,
obtained during the course of 10 ns molecular dynamics simulation
A series of 24 1,2,3,4-tetrahydroisoquinoline
derivatives were screened for potential XO inhibitory
properties. Among them, only compound 16 (IC50 =
135.72 ± 2.71 µM) exhibited IC50 value below 150
µM, and was further subjected to molecular docking
and molecular dynamic simulation. Molecular model-
ing suggests that interactions with Met 1038, Gln
1040, Thr 1077, Gln 1194 and Val 1259 are an
important factor for inhibitor affinity toward the XO
enzyme. Observed interactions with non-catalytic
residues, might be beneficial for the discovery of
new active 1,2,3,4-tetrahydroisoquinoline-based in-
hibitors of XO enzyme.
The financial support of this work by the
Ministry of Education, Science and Technological
Development of the Republic of Serbia (Grant
numbers 451-03-68/2020-14/200113 and 451-03-
68/2020-14/200026) and the Faculty of Medicine of
the University of Niš (Internal project No. 40) are
gratefully acknowledged. The authors would like to
thank D. E. Shaw Research, for providing us the
Desmond software package free of cost for this
Acta Medica Medianae 2021, Vol.60(1) Xanthine oxidase inhibitory properties of 1,2,3,4-tetrahydroisoquinoline...
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Xanthine oxidase inhibitory properties of 1,2,3,4-tetrahydroisoquinoline... Mihajlo Gajić et al.
Originalni rad
UDC: 577.152.1:547.833
Mihajlo Gajić1, Budimir S. Ilić2, Bojan P. Bondž3, Zdravko Džambaski3, Ana Filipović3,
Gordana Kocić4, Andrija Šmelcerović2
1Univerzitet u Nišu, Medicinski fakultet, Katedra za farmaciju, Niš, Srbija
2Univerzitet u Nišu, Medicinski fakultet, Katedra za hemiju, Niš, Srbija
3Univerzitet u Beogradu, Institut za hemiju, tehnologiju i metalurgiju, Beograd, Srbija
4Univerzitet u Nišu, Medicinski fakultet, Katedra za biohemiju, Niš, Srbija
Kontakt: Andrija Šmelcerović
Bulevar dr Zorana Đinđa 48, 18000 Niš, Srbija
Ksantin oksidaza (XO) je metaloflavoproteinski enzim, koji je najpoznatiji po svojoj
ulozi ograničavanja brzine razgradnje purinskih nukleotida. Terapijska inhibicija XO zasniva se
na njenoj ulozi u brojnim bolestima, koje su povezane bilo sa hiperprodukcijom mokraćne
kiseline ili hiperprodukcijom reaktivnih kiseoničnih vrsta. U ovom radu izvršeno je ispitivanje
sposobnosti inhibicije XO 24 derivata 1,2,3,4-tetrahidroizohinolina, od kojih je jedinjenje 16
pokazalo IC50 vrednost od 135,72 µM ± 2,71 µM. Interakcija jedinjenja 16 sa XO enzimom
simulirana je korišćenjem Site Finder modula molekularnog dokinga i molekularne dinamike.
Molekulsko modelovanje ukazuje na to da su interakcije sa Met 1038, Gln 1040, Thr 1077,
Gln 1194 i Val 1259 važan faktor postojanja afiniteta inhibitora prema XO enzimu. Naš
predloženi model vezivanja mogao bi biti od značaja za razvoj novih aktivnih inhibitora XO
zasnovanih na 1,2,3,4-tetrahidroizohinolinskom heterociklusu.
Acta Medica Medianae 2021;60(1):48-55.
Ključne reči: inhibicija ksantin oksidaze, 1,2,3,4-tetrahidroizohinolini, molekularni
doking, simulacija molekularne dinamike
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Full-text available
Xanthine oxidase (XO), a versatile metalloflavoprotein enzyme, catalyzes the oxidative hydroxylation of hypoxanthine and xanthine to uric acid in purine catabolism while simultaneously producing reactive oxygen species. Both lead to the gout-causing hyperuricemia and oxidative damage of the tissues where overactivity of XO is present. Over the past years, significant progress and efforts towards the discovery and development of new XO inhibitors have been made and we believe that not only experts in the field, but also general readership would benefit from a review that addresses this topic. Accordingly, the aim of this article was to overview and select the most potent recently reported XO inhibitors and to compare their structures, mechanisms of action, potency and effectiveness of their inhibitory activity, in silico calculated physico-chemical properties as well as predicted pharmacokinetics and toxicity. Derivatives of imidazole, 1,3-thiazole and pyrimidine proved to be more potent than febuxostat while also displaying/possessing favorable predicted physico-chemical, pharmacokinetic and toxicological properties. Although being structurally similar to febuxostat, these optimized inhibitors bear some structural freshness and could be adopted as hits for hit-to-lead development and further evaluation by in vivo studies towards novel drug candidates, and represent valuable model structures for design of novel XO inhibitors.
Full-text available
Thirty 2-amino-5-alkylidene-thiazol-4-ones were assayed for inhibitory activity against commercial enzyme xanthine oxidase (XO) in vitro and XO in rat liver homogenate as well as for anti-inflammatory response on human peripheral blood mononuclear cells (PBMCs). 4-((2-Benzylamino-4-oxothiazol-5(4H)-ylidene)-methyl)benzonitrile showed the most potent inhibitory effect against commercial XO (IC50=17.16μg/mL) as well as against rat liver XO (IC50=24.50μg/mL). All compounds containing the 4-cyanobenzylidene group or (indol-3-yl)methylene group at the position 5 of thiazol-4-one moiety were moderately potent inhibitors of commercial XO. The assayed compounds were docked into the crystal structures of XO enzyme complexes with three diverse inhibitors (PDB codes: 1FIQ, 1VDV, and 1V97) using OEDocking software. Our results strongly point to a correlation between the data on inhibitory activity against commercial XO and data on antioxidant activity of studied compounds, screened using a lipid peroxidation (LP) method. 2-(Benzylamino)-5-((thiophen-2-yl)methylene)thiazol-4(5H)-one showed the highest anti-inflammatory response on PBMCs, exerted most probably through the NF-κB inhibition. Studied 2-amino-5-alkylidene-thiazol-4-ones obey the "Rule of five" and meet all criteria for good solubility and permeability. Copyright © 2015. Published by Elsevier Ireland Ltd.
Xanthine oxidase (XOD) is a key enzyme in the production of uric acid, related to the occurrence of hyperuricemia. In this study, the inhibitory mechanism of 1,4-dicaffeoylquinic acid (1,4-diCQA) on XOD was investigated. Kinetic analysis showed that 1,4-diCQA inhibited XOD (IC50: 7.36 ± 0.63 μM) in a reversible competitive mode. Fluorescence spectra revealed that hydrogen bonds and van der Waals forces played main roles in the binding of XOD and 1,4-diCQA. Circular dichroism showed that the contents of α-helix, β-turn and random coil of XOD decreased while the β-sheet content increased with the addition of 1,4-diCQA. Molecular docking revealed that 1,4-diCQA interacted with the active site of XOD via the key amino acid residues of Gln112, Gln1040, Thr1077, Ser1080, Ser1082 and Asp1084. These findings provide the mechanism of 1,4-diCQA on inhibiting XOD and further the application of 1,4-diCQA in preventing hyperuricemia.
Multiple-targeting compounds might reduce complex polypharmacy of multifactorial diseases, such as diabetes, and contribute to the greater therapeutic success. Targeting reactive oxygen species-producing enzymes, as xanthine oxidase (XO), might suppress progression of diabetes-associated vascular complications. In this study a small series of benzimidazole derivatives (1-9) was evaluated for inhibitory activity against dipeptidyl peptidase-4 (DPP-4) and XO. One 1,3-disubstituted-benzimidazole-2-imine (5) and 1,3-thiazolo[3,2-a]benzimidazolone derivative (8) were shown as effective dual DPP-4 and XO inhibitors, with IC50 values lower than 200 μM, and predicted binding modes with both target enzymes. Both selected dual inhibitors (compounds 5 and 8) did not show cytotoxicity to a greater extent on Caco-2 cells even at concentration of 250 μM. These structures represent new non-purine scaffolds bearing two therapeutic functionalities, being DPP-4 and XO inhibitors, more favorable in comparison to DPP-4 inhibitors with DPP-4 as a single target due to pleiotropic effects of XO inhibition.
Organocatalyzed Mannich reaction of unsubstituted and N-Aryl-substituted tetrahydroisoquinolines (THIQs) and Strecker reaction of several N-Aryl-substituted THIQs through dehydrogenative sp3 C−H bond functionalization (Cross dehydrogenative coupling) promoted by organic singleelectron oxidants DDQ and IBX is presented. Oxidative C-H Functionalization/Mannich reaction of less reactive N-Aryl substituted pirrolidines is achieved via metal catalyzed photoredox catalysis. Operationally simple procedures provide desired products in effective and time preserving manner.
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.
Docking has become an indispensable approach in drug discovery research to predict the binding mode of a ligand. One great challenge in docking is to efficiently refine the correct pose from various putative docking poses through score functions. We recently examined the stability of self-docking poses under molecular dynamics (MD) simulations and showed that equilibrium MD simulations have some capability to discriminate between correct and decoy poses. Here, we have extended our previous work to cross-docking studies for practical applications. Three target proteins (thrombin, heat shock protein 90-alpha, and cyclin-dependent kinase 2) of pharmaceutical interest were selected. Three comparable poses (one correct pose and two decoys) for each ligand were then selected from the docking poses. To obtain the docking poses for the three target proteins, we used three different protocols; namely, normal docking, induced fit docking (IFD), and IFD against the homology model. Finally, five parallel MD equilibrium runs were performed on each pose for the statistical analysis. The results showed that the correct poses were generally more stable than the decoy poses under MD. The discrimination capability of MD depends on the strategy. The safest way was to judge a pose as being stable if any one run among five parallel runs was stable under MD. In this case, 95% of the correct poses were retained under MD, and about 25–44% of the decoys could be excluded by the simulations for all cases. On the other hand, if we judge a pose as being stable when any two or three runs were stable, with the risk of incorrectly excluding some correct poses, approximately 31–53% or 39–56% of the two decoys could be excluded by MD, respectively. Our results suggest that simple equilibrium simulations can serve as an effective filter to exclude decoy poses that cannot be distinguished by docking scores from the computationally expensive free-energy calculations.
Introduction: Xanthine oxidase (XO) is a versatile molybdoflavoprotein, widely distributed, occurring in milk, kidney, lung, heart, and vascular endothelium. Catalysis by XO to produce uric acid and reactive oxygen species leads to many diseases. Anti hyperuricemic therapy by xanthine oxidase inhibitors has been mainly employed for the treatment of gout. Area covered: This review covers the patent literature (2011-2015) and also presents the interesting strategies/rational approaches employed for the design of xanthine oxidase inhibitors reported recently. Expert opinion: Recent literature indicates that various non purine scaffolds have been extensively investigated for xanthine oxidase inhibition. The significant potential endowed by heteroaryl based compounds, in particularly fused heterocycles clearly highlights their clinical promise and the need for detailed investigation. Studies by various research groups have also revealed that the flavone framework is open for isosteric replacements and structural modifications for yielding potent non purine xanthine oxidase inhibitors. In addition, various plant extracts recently reported to possess significant xanthine oxidase inhibitory potential presents enough promise to initiate a screening program for the identification of other plant extracts and phytoconstituents possessing inhibitory potential towards the enzyme.
Non-purine derivatives have been shown to be promising novel drug candidates as xanthine oxidase inhibitors. Based on three-dimensional quantitative structure-activity relationship (3D-QSAR) methods including comparative molecular field analysis (CoMFA) and comparative molecular similarity indices analysis (CoMSIA), two 3D-QSAR models for a series of non-purine xanthine oxidase (XO) inhibitors were established, and their reliability was supported by statistical parameters. Combined 3D-QSAR modeling and the results of molecular docking between non-purine xanthine oxidase inhibitors and XO, the main factors that influenced activity of inhibitors were investigated, and the obtained results could explain known experimental facts. Furthermore, several new potential inhibitors with higher activity predicted were designed, which based on our analyses, and were supported by the simulation of molecular docking. This study provided some useful information for the development of non-purine xanthine oxidase inhibitors with novel structures.