Keeping in view the structural requirements suggested in the pharmacophore model for anticonvulsant activity, a new series of 3-(2-(substitutedbenzylidene)hydrazinyl)-
Epilepsy is one of the most prevalent noncommunicable neurological conditions. It is a main cause of disability and mortality [
Benzothiazole scaffold is amongst the commonly occurring heterocyclic nuclei in many marine as well as natural plant products. It is a promising bicyclic ring system with multiple biological applications [
In view of these facts and as a part of our continuing studies in the area of anticonvulsant agents, it was thought of interest to synthesize some newer derivatives of benzothiazole as anticonvulsant agents. A pharmacophore model along with physicochemical determination provides a useful tool for designing prototypic molecules and explanation of probable interactions. In terms of interaction at binding site, the titled compounds have common structural features such as aromatic hydrophobic aryl ring (A), NH–C=O as hydrogen bonding domain (HBD), nitrogen atom as electron donor (D), and phenyl as distal aryl ring (C) [
The entire chemicals used in the synthesis were procured from E. Merck and S. D. Fine Chemicals. A Thin layer chromatography (TLC) was performed with Silica gel 60 F254 TLC aluminium sheet (Merck) using toluene : ethyl acetate : formic acid (5 : 4 : 1) and benzene : acetone (9 : 1) as eluents. Ashless Whatmann number 1 filter paper was used for vacuum filtration. Melting points were determined by using open capillary tubes in a Hicon melting point apparatus (Hicon, India) and are uncorrected. The purity of the compounds was confirmed through elemental analysis. The elemental analyses (C, H, N, and S) of all compounds were performed on the CHNS Elimentar (Analysen systime, GmbH) Germany Vario EL III and results were within ±0.4% of the theoretical values. Fourier transform infrared (FT-IR) spectra were recorded in KBr pellets on a Shimadzu FT-IR spectrometer. 1HNMR and 13CNMR spectra in DMSO-
The anticonvulsant activity was carried out on male albino mice (20–25 g) as experimental animals. The animals were housed under standard conditions and allowed free access to standard pellet diet and water. The pharmacological testing of all the final compounds was performed according to the standard protocol given by epilepsy branch of the National Institute of Neurological Disorders and Stroke (NINDS) following the protocol adopted by the Antiepileptic Drug Development (ADD) program. Phase I pharmacological screening comprised MES, scPTZ, and neurotoxicity. Compounds were administered intraperitoneally as a solution in polyethylene glycol (PEG). The most active compounds were evaluated quantitatively in phase II screening in which the ED50 and TD50 of the compounds were determined. These compounds were also tested for their median hypnotic dose (HD50) and median lethal dose (LD50) in phase III screening. To compare the bioavailability of the active compounds, the ED50 and TD50 values of the synthesized compounds were also determined after oral administration in phase IV screening.
This test was performed using the rotarod method. At 30 min after the administration of the compounds, the animals were tested on a knurled plastic rod of diameter 3.2 cm rotating at 10 rpm for 1 min. Neurotoxicity was indicated by the inability of an animal to maintain equilibrium in each of three trials.
To find out the toxic effects, if any, of the synthesized compounds on liver, the test compounds were administered to mice. After 24 hours, serum samples were taken for estimation of serum glutamate oxaloacetate transaminase (SGOT), serum glutamate pyruvate transaminase (SGPT), alkaline phosphatase (ALP), albumin, and bilirubin using commercially available kits.
A series of new benzothiazole derivatives were synthesized in satisfactory yields (65–80%) as demonstrated in Scheme
Physicochemical parameters of the synthesized compounds (
Compound | R | R′ | Molecular formula |
|
|
M.P (°C) |
|
---|---|---|---|---|---|---|---|
|
Cl | H | C17H15ClN4OS | 4.32 | 4.14 | 192–194 | 0.42 |
|
F | H | C17H15FN4OS | 3.92 | 3.57 | 188–190 | 0.35 |
|
CH3 | H | C18H18N4OS | 4.24 | 3.92 | 130–132 | 0.81 |
|
OCH3 | H | C18H18N4O2S | 3.63 | 3.72 | 202–204 | 0.32 |
|
Cl | 2-OH | C17H15ClN4O2S | 3.93 | 4.73 | 198–200 | 0.59 |
|
F | 2-OH | C17H15FN4O2S | 3.53 | 3.53 | 164–166 | 0.44 |
|
CH3 | 2-OH | C18H18N4O2S | 3.86 | 4.46 | 180–182 | 0.61 |
|
OCH3 | 2-OH | C18H18N4O3S | 3.24 | 4.32 | 110–112 | 0.78 |
|
Cl | 4-OH | C17H15ClN4O2S | 3.95 | 4.76 | 210–212 | 0.31 |
|
F | 4-OH | C17H15FN4O2S | 3.59 | 3.61 | 201–203 | 0.48 |
|
CH3 | 4-OH | C18H18N4O2S | 3.89 | 3.97 | 185–187 | 0.62 |
|
OCH3 | 4-OH | C18H18N4O3S | 3.24 | 4.32 | 117–119 | 0.57 |
|
Cl | 4-CH3 | C18H17ClN4OS | 4.8 | 4.61 | 175-176 | 0.65 |
|
F | 4-CH3 | C18H17FN4OS | 4.44 | 4.06 | 190–192 | 0.4 |
|
CH3 | 4-CH3 | C19H20N4OS | 4.73 | 4.44 | 205-206 | 0.71 |
|
OCH3 | 4-CH3 | C19H20N4O2S | 4.12 | 4.22 | 200-201 | 0.6 |
|
Cl | 4-OCH3 | C18H17ClN4O2S | 4.19 | 4.42 | 140–142 | 0.55 |
|
F | 4-OCH3 | C18H17FN4O2S | 3.79 | 3.85 | 169–171 | 0.43 |
|
CH3 | 4-OCH3 | C19H20N4O2S | 4.12 | 4.20 | 161–163 | 0.38 |
|
OCH3 | 4-OCH3 | C19H20N4O3S | 4.75 | 4.41 | 215–217 | 0.54 |
Solvent of crystallization-ethanol.
Synthetic route to the titled compounds (
The synthesized benzothiazole derivatives showed (N–H), (C=O), and (C=N) stretching bands in the region of 3355–3316 cm−1, 1747–1640 cm−1, and 1615–1569 cm−1, respectively, in their IR spectrum, while, in their 1H NMR spectra, these compounds exhibited multiplets for (Ar–H) in the regions of
A pragmatic approach to synthesize new series of benzothiazole derivatives in satisfactory yields was illustrated in Scheme
Phase I anticonvulsant evaluation of the synthesized compounds (
Compound | Intraperitoneal injection in mice | |||||
---|---|---|---|---|---|---|
MES | scPTZ | Neurotoxicity screen | ||||
0.5 h | 4.0 h | 0.5 h | 4.0 h | 0.5 h | 4.0 h | |
|
100 | 100 | 100 | 300 | — | — |
|
300 | — | — | — | — | 300 |
|
— | 300 | 100 | — | — | — |
|
100 | 300 | 300 | — | — | — |
|
300 | — | 300 | — | — | — |
|
100 | 300 | 300 | — | — | — |
|
300 | — | — | — | — | — |
|
30 | 100 | 100 | — | — | — |
|
100 | — | 100 | 300 | 300 | — |
|
300 | — | 300 | 300 | — | 300 |
|
100 | 300 | — | — | — | — |
|
— | 300 | — | — | — | — |
|
— | — | 300 | — | — | — |
|
100 | — | 300 | — | — | 300 |
|
100 | 300 | — | — | 300 | — |
|
30 | 30 | 100 | — | — | 300 |
|
300 | 300 | — | — | — | — |
|
300 | — | 300 | — | 300 | — |
|
100 | 300 | — | — | — | — |
|
100 | — | 300 | 300 | — | — |
PHY | 30 | 30 | — | — | 100 | 100 |
CBZ |
30 | 100 | 100 | 300 | 100 | 300 |
Number of animals in each group (
The synthesized compounds challenged the scPTZ test to predict their potential against seizure threshold. Compounds
In the neurotoxicity screen, most of the compounds did not show any neurotoxicity. Compounds
In phase II anticonvulsant screening, the most active compounds
Phase II quantitative anticonvulsant evaluation of selected active compounds.
Compound |
|
|
PIc | ||
---|---|---|---|---|---|
MES | scPTZ | MES | ScPTZ | ||
|
27.9 ± 1.43d | 188.6 ± 9.23 | 378.5 ± 17.09 | 13.5 | 2.0 |
|
28.4 ± 0.88 | 89.1 ± 7.72 | 287.1 ± 22.13 | 10.1 | 3.2 |
PHY | 9.5 ± 0.77 | >300 | 65.5 ± 12.06 | 6.9 | <0.22 |
CBZ | 15.8 ± 1.02 | >100 | 71.6 ± 12.07 | 8.1 | <0.22 |
Number of animals used = 08; solvent used: polyethylene glycol (0.1 mL, i.p.),
bTD50 median toxic dose eliciting minimal neurological toxicity in 50% animals.
cPI = protective index (TD50/ED50). dData in parentheses are the 95% confidence limits.
In phase III screening, the toxicity profile of compounds
Phase III quantitative toxicity profile of selected compounds.
Compound |
|
|
HD50/ED50 | |
---|---|---|---|---|
MES | PTZ | |||
|
642.2 (609.7–689.6)c | 865.9 (821.1–902.7) | 23.01 | 3.41 |
|
712.3 (664.9–768.2) | 650.5 (609.1–697.5) | 25.07 | 8.00 |
PHY | 182.4 (169.3–94.2) | 224.8 (201.3–249.2) | 19.15 | >0.06 |
c95% confidence interval in parenthesis.
In phase IV anticonvulsant screening, the selected compounds
Phase IV quantitative anticonvulsant evaluation of selected active compounds after oral administration.
Compound | TPEa (h) |
|
|
PId |
---|---|---|---|---|
|
2 | 39.8 (33.1–44.5)e | 456.3 (419.2–502.2) | 11.4 |
|
2 | 48.5 (41.3–54.6) | 689.1 (643.8–720.4) | 14.2 |
PHY | 2 | 9.16 (7.9–11.4) | 87.6 (78.3–98.4) | 9.56 |
bED50 median effective dose eliciting anticonvulsant protection in 50% animals.
cTD50 median toxic dose eliciting minimal neurological toxicity in 50% animals.
dPI (protective index) was determined by TD50/ED50.
e95% confidence interval in parenthesis.
Phenytoin is a probable cause of acetaminophen hepatotoxicity [
Enzyme estimation of the selected compounds.
Compound | SGOTa level |
SGPTb level |
Alkaline phosphatase |
Albumin |
Bilirubin (mg/dL) |
---|---|---|---|---|---|
Control |
|
|
|
|
|
|
84.9 ± 2.21 | 25.81 ± 1.65 | 14.98 ± 0.87 | 1.46 ± 0.09 | 1.49 ± 0.07 |
|
85.6 ± 1.76 | 25.94 ± 1.56 | 11.56 ± 0.36 | 1.58 ± 0.06 | 1.55 ± 0.03 |
PHY | 86.3 ± 4.12 | 26.91 ± 2.20 | 13.98 ± 0.72 | 1.52 ± 0.02 | 1.57 ± 0.02 |
Number of animals tested (
Hepatic enzymes estimations after treatment with different test compounds. Number of animals tested (
High power photomicrograph of portal triad area of liver tissue from animals treated with (a) control, (b) compound (
In the present study, a series of 3-[2-(2-substituted benzylidene)hydrazinyl]-
The authors declare that there is no conflict of interests regarding the publication of this paper.
One of the authors (Ruhi Ali) is thankful to the University Grants Commission, Ministry of Human Resource Development, and Government of India for financial support.