INTRODUCTION:

Epilepsy is a most common non-communicable primary neurological disease where the activity of the nerve cell is agitated in the brain which causes seizures.¹ According to World Health Organization (WHO), epilepsy is one of the oldest disorders present in humans. More than 50 million² people worldwide are affected by epilepsy. Epilepsy is a disorder where a person experiences intermittent seizures,³ usually unprovoked and stereotyped which result from the abnormal,⁴ paroxysmal electric discharge of cerebral cortex neurons. Seizures may differ from muscle twitching to chronic and elongated convulsions.

The frequency can vary from several months to a few days.⁵Two groups of seizures are named partial and generalized. Epilepsy can be caused by a hereditary disorder or a traumatic brain injury. Abnormal behaviour, symptoms, sensation, and also chances of unconsciousness may occur during seizures. Medication can cure convulsions; surgery and dietarychanges are also the treatments in some cases.

Newer antiepileptic drugs (AED) are being developed for years because patients may become resistant to AEDs.⁶Hence there is a need for the newer AEDs without pharmacokinetic drug interactions, drugs with minimal adverse effects,⁷ and drugs with different mechanisms of action for synergistic combination therapy. The majority of existing AEDs suffer from toxicity issues. Nausea, diplopia, dizziness, headache,⁸ tiredness, and ataxia are some of the most prevalent dose-related adverse effects of AEDs. But less than 70% of patients who take the anticonvulsants now prescribed for this illness see a reduction in the severity and frequency of their seizures.⁹

Thiophene is a five-membered monocyclic heterocyclic compound with sulfur (S) at 1^st position with the molecular formula C₄H₄S. It is chemically called as thiacyclopentadiene.¹⁰ Thiophene has gained interest from early dye chemistry to moderndrug design. Thiophene derivatives are extensively used due to their wide therapeutic applications. Fused heteroaromatic compounds are widely employed than the monocyclic compound. Newer heterocyclic compounds can be synthesized by fusing thiophene¹¹ and heterocyclic systems.Anti-inflammatory, anti-psychotic, anti-arrhythmic, anti-anxiety,¹² anti-fungal, antioxidant, estrogen receptor regulating, anti-mitotic, anti-microbial, kinases inhibiting, and anti-cancer activities are found in the thiophene moiety.

Benzothiazepines are seven-membered heterocyclic ring with nitrogen and sulfur. Benzothiazepines are an important compound because of their pharmacological properties and have become an interesting concept since 1,5-benzothiazepines show antifungal, antibacterial, analgesic¹³, and anticonvulsant activity1,5-Benzothiazepines are a widely recognized type of benzo-condensed compound that belongs to the group of benzothiazepines, which also includes 1,4-thiazepines and three other conceivable benzo-condensed variations: 1,4-, 4,1-, and 1,5-benzothiazepines.¹⁴ 1, 5- benzothiazepines are gaining more interest due to their broad range of chemotherapeutic¹⁵ applications like anticonvulsive. The first clinically used 1,5-benzothiazepine molecule is diltiazem for its cardiovascular activity, followed by clentiazem. Some of the other clinical used drugs for CNS disorders are thiazesim, clothiapine, and quetiapine.¹⁶

MATERIAL AND METHODS:

The proposed compounds underwent in silico analysis using Maestro 12.3 on a Dell Inc. 27" workstation with an Intel Core i7-7700 CPU running at 3.60 GHz x8, 8GB of RAM, a 1000 GB hard drive, and Linux -x86 64 as the operating system.

Molecular Docking:

2 D designs of the ligands were drawn using chemdraw tool where the canonical SMILES were generated and imported to the Schrodinger. The minimum energy confomers of all ligands were done by LigPrep tool.The CryoEM structure of human full-length alpha1beta3gamma2L GABA(A)R in complex with diazepam (Valium), GABA and megabody Mb38 (PDB ID: 6HUP) with resolution of 3.58°A as protein was imported from RCSB Protein data bank. Protein preparation was done using protein preparation wizard tool were refined, and optimization will be carried.¹⁷ Receptor grid was generated based on the ligand similarity and surrounding the active binding pocket of the protein. Docking of these ligands by extra precision (XP) mode was evaluated by diazepam.

Prime MM-GBSA:

Molecular mechanics-generalized born surface area (MM-GBSA) determines the receptor-ligand complex's binding free energy. Schrodinger's Prime module (Schrodinger 2020-4: Prime), which costs $60 and computes the total free energy in ΔG bind (kcal/mol), taking into account molecular mechanics energies, solvation models for polar and nonpolar solvation.¹⁸

Insilico ADMET property:

Absorption, distribution, metabolism, and distribution of the designed were estimated by Qikprop tool in Schrodinger application.¹⁹

Pharmacophore Modelling:

Modern technology called pharmacophore modelling is used to locate and exact potential interactions between a multiple-ligand complex. Pharmacophore model were generated using the phase application of Schrödinger software. Pharmacophore-based screening has become one of the key aspects in computer aided drug design. A set of pharmacophore properties was used to create the pharmacophore model, which generated sites for each molecule. A set of points in 3D space is used to depict each structure, and these points correspond to numerous chemical characteristics that may facilitate its pharmacological activity.²⁰

RESULTS:

Table 1: Docking studies of compounds with 6HUP

Compound score	Docking score	glide evdw	glide ecoul	glide energy
TB-A4	-8.354	-22.669	-5.459	-28.128
TB-A5	-8.022	-20.471	-6.848	-27.319
TB-A2	-3.611	-18.384	1.361	-17.023
TB-A6	-2.912	-18.624	-0.331	-18.955
TB-A1	-2.641	-13.219	-0.694	-13.913
TB-A11	-2.635	-19.048	1.167	-17.882
TB-A13	-2.322	-12.862	2.327	-10.535
TB-B4	-2.301	-25.479	-0.044	-25.522
TB-A10	-2.132	-18.132	0.939	-17.193
TB-A9	-2.036	-23.626	1.693	-21.933
Diazepam	-7.297	-42.217	-1.412	-43.629

Glide score, glide score; Glide EvdW, glide van der Waals energy; Glide ecoul, glide Coulomb energy; Glide energy, glide energy

Table 2: Molecular docking interaction with 6HUP

Compound code	Hydrphobic bonding	Polar interaction	Hydrogen bond	Negative charge
TB-A1	Met E:283, Phe E: 438, Leu E:285, Met E:286, Phe E;289, Val E:290, Leu L:232, ProD :233, Met D:236
TB-A2	Phe E:438, Met E:283, Met E:286, Phe E:286, Val E: 290, Leu D:232, Pro D:233, Met D:236, Ile D:228
TB-A4	Leu D: 269, Leu D: 240, Met E:286, Leu E:285, Phe E: 289, Val E: 290, Leu D:232, Pro D:233, Met D:236, Ile D:228	Thr D: 265, Asn E:265, Thr D: 237, Thr E: 262	Thr D: 237	Asp E:282
TB-A5	Leu D: 269, Leu D:240, Leu E: 285, Met E: 286, Met D: 236, Phe E: 289, Val E: 290, Pro D: 233, Leu D: 232, Ile D:228	Thr D: 265, Asn E:265, Thr D: 237, Thr E: 262		Asp E:282
TB-A6	Leu D: 232, Pro D:233, Ile D: 228, Met D: 236, Val E: 290, Phe E: 289, Met E; 286, Leu E; 285, Met E; 283	Asn E; 265	Ile D:228
TB-A9	Leu D: 232, Pro D:233, Ile D: 228, Met D: 236, Val E: 290, Phe E: 289, Met E; 286, Met E; 283, Phe E:438
TB-A10	Leu D: 232, Pro D:233, Ile D: 228, Met D: 236, Val E: 290, Phe E: 289, Met E; 286, Met E; 283, Phe E:438
TB-A11	Leu D: 232, Pro D:233, Ile D: 228, Met D: 236, Val E: 290, Phe E: 289, Met E; 286, Met E; 283, Phe E:438
TB-A13	Leu D: 232, Pro D:233, Ile D: 228, Met D: 236, Val E: 290, Phe E: 289, Met E; 286, Met E; 283, Phe E:438
TB-B4	Leu E: 294, Val E: 290, Phe E: 438, Met E: 286, Met E: 283, Met D: 236, Leu D:232, Leu E: 297, Met D: 236

Figure 1: 2Dand3DinteractionofcompoundTB-A4with6HUP

Figure 2: 2Dand3DinteractionofcompoundTB-A5with6HUP

Table 3:Binding free energy calculation

Compound code	MMGBSA ΔG Bind	MMGBSA ΔG Bind Coulomb	MMGBSA ΔG Bind Covalent	MMGBSA ΔG Bind Hbond	MMGBSA ΔG Bind Lipo	MMGBSA ΔG Bind Packing	MMGBSA ΔG Bind Solv GB	MMGBSA ΔG Bind vdW
TB-A4	-83.57	0.54	9.48	-0.06	-70.39	-1.48	15.30	-36.96
TB-A5	-83.75	-9.15	8.38	-0.27	-65.78	-1.84	15.14	-30.23
Diazepam	-82.97	-3.97	0.41	0.00	-43.29	-2.80	12.69	-46.01
TB-A2	-62.15	1.71	5.96	-0.01	-59.07	0.00	6.68	-17.41
TB-A6	-51.90	-2.14	12.46	-0.26	-51.14	-0.00	6.54	-17.35
TB-A1	-51.21	-3.15	7.17	-0.00	-47.81	-0.14	7.30	-14.58
TB-A11	-64.01	2.17	4.93	-0.01	-59.13	-0.00	6.22	-18.19
TB-A13	-63.84	2.36	5.95	-0.01	-60.24	0.00	6.70	-18.60
TB-B4	-52.81	-3.02	0.11	0.00	-33.11	-0.00	9.69	-26.48
TB-A10	-58.57	1.30	5.74	-0.01	-55.17	0.00	7.22	-17.65
TB-A9	-59.40	10.07	8.35	-0.01	-53.21	0.00	-1.30	-23.30

Table 4: Insilico ADMET Screening

Compound code	Qlog BB	QPPCaco	QPlogKhsa	Percent human oral absorption	#metab	CNS
TB-A13	-0.252	131.966	0.976	90.175	2	1
TB-A11	-0.115	134.574	1.064	92.429	2	1
TB-A10	-0.296	132.059	0.902	88.702	2	1
TB-A9	-1.389	18.091	0.818	68.018	3	-2
TB-A6	-0.796	508.372	0.889	100	3	-1
TB-A5	-1.328	154.092	0.661	87.828	3	-2
TB-B4	-1.375	176.854	1.082	96.118	3	-2
TB-A4	-1.423	152.53	0.681	88.108	4	-2
TB-A2	-0.259	134.637	0.946	89.532	2	1
TB-A1	-0.568	508.054	0.98	100	2	0
Diazepam	0.199	2684.726	0.149	100	1	1

Table 5: Lipinski’s Rule of Five

Compound code	Molecular weight	Donor HB	Accpt HB	QPlogPo/w	RuleOfFive
TB-A13	389.901	1.5	3.5	4.317	0
TB-A11	424.347	1.5	3.5	4.676	0
TB-A10	373.447	1.5	3.5	4.065	0
TB-A9	400.454	1.5	4.5	3.171	0
TB-A6	403.516	1.5	4.25	4.609	0
TB-A5	389.489	2.5	4.25	3.711	0
TB-B4	481.586	2.5	5	4.943	0
TB-A4	419.515	2.5	5	3.772	0
TB-A2	389.901	1.5	3.5	4.181	0
TB-A1	407.935	1.5	3.5	4.984	0
Diazepam	284.744	0	4	2.992	0

Figure 3: Pharmacophore modeling of compounds a) TB-A5, b) TB-A4

Table 6: solvent accessible surface area of the compound

Compound code	SASA	FOSA	FISA	PISA	volume
TB-A13	653.195	90.321	134.17	329.757	1161.424
TB-A11	664.4	91.163	133.274	289.845	1193.499
TB-A10	639.506	91.068	134.138	338.966	1133.899
TB-A9	662.448	86.318	225.176	322.744	1187.616
TB-A6	662.718	144.025	136.003	316.321	1196.057
TB-A5	641.876	56.909	190.67	326.679	1141.882
TB-B4	733.594	90.051	184.36	390.629	1366.017
TB-A4	668.941	136.719	191.136	283.852	1212.338
TB-A2	640.19	91.056	133.253	337.391	1149.225
TB-A1	653.148	56.93	136.032	321.028	1162.835
Diazepam	523.093	121.519	59.791	270.205	896.098

Table 7: Structure and compound codes

Compound code	Structure	Compound code	Structure
TB-A1		TB-A6
TB-A2		TB-A9
TB-A4		TB-A10
TB-B4		TB-A11
TB-A5		TB-A13

DISCUSSION:

Molecular Docking:

All the designed compounds show moderate docking scores and good hydrophobic interaction with the protein. The major protein interaction types are hydrogen bonding and polar interaction, which are provided in the interaction diagram Figure 1 and Table 2. The docking scores ranged from -2.036 kcal/mol to -8.354 kcal/mol. Out of which 2 compounds showed higher docking scores compared to the standard drug. Compound A4 showed a docking score of -8.354 with hydrophilicinteractions at Leu D: 269, Leu D: 240, Met E:286, Leu E:285, Phe E: 289, Val E: 290, Leu D:232, Pro D:233, Met D:236, Ile D:228, polar interaction Thr D: 265, Asn E:265, Thr D: 237, Thr E: 262, hydrogen bonds at Thr D: 237. Compound TB-A5 has a docking score of -8.022, hydrophobic interaction at LEU D: 269, Leu D:240, Leu E: 285, Met E: 286, Met D: 236, Phe E: 289, Val E: 290, Pro D: 233, Leu D: 232, Ile D:228 and polar interactions at Thr D: 265, Asn E:265, Thr D: 237, Thr E: 262.

Apart from docking scores, glide energy, glide van der Waals energy (glide evdw), and glide coulomd energy (glide ecoul) are also provided in Table 1.

Binding free energy calculation:

MMGBSA calculated the binding free energy of the receptor-ligand complexes. The scores from mmgbsa data depicts that the compound A4 and A5 show greater Δ G Bind for GABA_Areceptor with values -83.57 and -83.75, respectively. The non polar solvation (ΔG Bind Lipo) for A4 is -70.39 and ΔG Bind vdW is -36.96. ΔG Bind Lipo and ΔG Bind vdW for A5 are -65.78 and -30.23as shown intable 3.

Insilico ADMET (Absorption, distribution, metabolism, excretion, toxicity):

The bioavailability of the drug becomes a major factor indicating the drug's safety and efficacy, which in turn depends on ADME properties. Hence, ADMET prediction was calculated for the designed compounds using QikProp tool. Predicted ADMET for all the ligands are listed in Table 5.most of the compounds show good oral absorption. Compounds A1, A6, A7, A8 have 100% oral absorption when compared to others.

Blood-brain barrier (BBB) penetration prediction:

Log BB indicates the penetration of compounds to central nervous system. Here, all the designed compounds show good blood brain barrier penetration as compared to the standard. The expected BB penetration values lies from 2 to -2. When considering the top docking score compounds which comparatively lesser penetration rate as that of others.

Plasma-protein binding Prediction:

Plasma protein binding of the compound to the receptor indicates the degree to which the compounds attach to proteins within the blood. It is represented by the term QPlogKhsa binding to the human serum albumin from -1.5 to 1.5. in the present case all the compounds are within the range. But as compared to the standard compound the values are slightly high.

Metabolism prediction:

Metabolism predictionindicates the number of metabolisms undergone by the compound. The usual range is 1-8. In the present context all the compound’s metabolism rate lies in the given range.

Lipinski’s Rule of five (RO5):

The designed compounds show desired physicochemical properties. As per the R05, where the Molecular weight of all the compounds are ≤ 500 Daltons, No more than 5 hydrogen bond donors (the total number of nitrogen–hydrogen and oxygen–hydrogen bonds), A calculated octanol-water partition coefficient (Clog P) of no more than 5 and a maximum of 10 hydrogen bond acceptors (all nitrogen or oxygen atoms) (table 4).Thus, all the ligand molecules obey Lipinski’s Rule of Five.

Pharmacophore modeling:

Pharmacophore validation is helpful to assess the potential characteristics of both active and inactive drugs. All the designed compounds were subjected for pharmacophore modeling by using phase application. The distance and angle between each pharmacophoric feature of compounds A4 and A5 are depicted in figure 1 & 2. Pharmacophoric features such as Donor (D5), Hydrophobic (H8, H10), and Aromatic rings (R11, R13) are present. The distance from H10-H8 is 3.97, and R13- R11 is 5.76 in compound A4. And the angle corresponding to this distance is 54.33 ⁰ and 111.7 ⁰respectively. Similarly, the hydrophobic feature (H8,10), with a distance of, R12-R13 is 6.38 and the distance between a hydrophobic feature and an aromatic ring is 4.28 in the case of compound A5.

Prediction of solvent-accessible surface area (SASA, FOSA, FISA):

The solvent-accessible surface area or the accessible surface area indicates the surface area of the compound available for the solvent. The value of SASA should lie in the range of 300.0–1000.0 Å2, FOSA 0.0-750.0, FISA 7.0 – 330.0 and PISA 0.0 – 450.0. All the designed compounds are also within this specified range shown in table 6.

CONCLUSION:

In the present context the aim was to design molecules which incorporate 2 different rings. As we were concerned with thiophene and 1,5-benzothiazepine as anticonvulsant drug, it was a successful attempt of deriving a molecule which incorporated both the rings. Based on the prior knowledge from the literature, we have confirmed that the thiophene and 1,5-benzothiazepine were potent antiepileptic dug moieties. The design of 26 compounds with different substituted benzaldehyde were underwent the docking studies using human full length alpha1beta3gamma2L GABA(A)R in complex with diazepam (Valium), GABA and megabody Mb38 (PDB ID: 6HUP). Out of which the 10 best score compounds are selected. Most of the compounds had high hydrophobic interaction and can penetrate the blood brain barrier. Compound TB-A4 and TB-A5 showed better docking scores than the standard drug diazepam. Pharmacophore modeling of the compounds were revealed the active and inactive features of the compound responsible for the pharmacological activity. And all the compound obeyed Lipinski’s Rule of Five. Since all the parameter of a molecule satisfies the condition there is further scope for the study to improve their efficacy.

Therefore, this study could result in molecules with maximum antiepileptic activity as far as docking studies are concerned. To the best of our knowledge, this is the first time thiophene and 1,5-benzothiazepine molecule have been incorporated into a single structure. Henceforth structural studies and pharmacological activity will be confirmed by synthetic methods and invivo study.

ACKNOWLEDGEMENT:

The authors are thankful to Nitte (Deemed to be University) for providing the necessary facilities to carry out this research.

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Received on 29.04.2023 Modified on 21.07.2023

Research J. Pharm. and Tech 2024; 17(5):2114-2120.

DOI: 10.52711/0974-360X.2024.00335