Journal of Chemistry

Volume 2013 (2013), Article ID 637205, 7 pages

http://dx.doi.org/10.1155/2013/637205

Research Article

Synthesis and Antidepressant Activity of Some New 5-(1H-Indol-3-yl)-3-(substituted aryl)-4,5-dihydroisoxazoline Derivatives

Pravin O. Patil and Sanjay B. Bari

Department of Pharmaceutical Chemistry, R. C. Patel Institute of Pharmaceutical Education and Research, Shirpur, Maharashtra, Dhule 425405, India

Received 20 June 2012; Revised 28 July 2012; Accepted 13 August 2012

Academic Editor: Volker Boehm

Copyright © 2013 Pravin O. Patil and Sanjay B. Bari. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract.

The present study refers to the synthesis of new antidepressant candidates using the indole scaffold. In an attempt to identify potential lead antidepressant agents, a number of indole molecules, incorporating isoxazoline, were synthesized by microwave-assisted synthesis. The antidepressant activity of the synthesized compounds (3a–3n) was evaluated by forced swim test in mice and their locomotor activity was assessed using actophotometry. The present paper showed significant antidepressant activity for all compounds of the series and no significant change in locomotor activity of mice. Compounds 3d and 3j were found to be potent molecules of this series, when compared with the reference drugs imipramine and fluoxetine. It clearly demonstrated that replacement of aromatic core by appropriate heterocycles such as pyridine and pyrrole on the 5-(1H-Indol-3-yl)-3-(Phenyl)-4,5-dihydroisoxazoline (3a) would generate more potent derivatives. Thus, these compounds can serve as potential leads for further antidepressant studies.

1. Introduction

Depression is a prevalent psychiatric disorder with estimates reaching as high as 21% of the world population. The World Health Organization (WHO) predicts that it will be the second leading cause of death by the year 2020 due to complications arising from stress and the cardiovascular system [1]. Although a broad range of antidepressants are available today, a significant proportion of these patients will not respond to treatment or will show only partial response [2]. Clinically used antidepressants have several limitations and side effects which demand continuous development of novel, efficient, and safe drugs for the treatment of depression.

In an attempt to synthesize and evaluate new compounds as antidepressant, we report, herein, synthesis and biological evaluation of a number of indole derivatives bearing isoxazolines. The indole framework is a medicinally relevant scaffold and has become widely identified as a privileged structure or pharmacophore due to its different pharmacological actions [3–5].

Literature survey also suggests the potential of the indolyl isoxazoline derivatives as anti-inflammatory [6] and antimicrobial agents [7, 8]. Compounds containing the isoxazole nucleus have been reported to possess diverse pharmacological activities [9–12]. The indole moiety is present in approved as well as experimental drugs [13–16] and the isoxazoline moiety in experimental drugs [17, 18].

Amongst the various methods available for the synthesis of isoxazolines, Tiwari et al. reported synthesis of quinoline isoxazolines under ultrasound irradiation [19]. Panda et al. reported synthesis of indolyl isoxazole [20], whereas Kidwai et al. reported the first solid-phase regioselective synthesis of isoxazole [21]. The microwave-assisted synthesis was found advantageous over conventional reactions [22, 23].

Therefore, in the present investigation, it was envisaged that if these two pharmacophores are linked together this would generate new molecular templates (Figure 1), which are likely to exhibit antidepressant-like action in animal models.

Figure 1: General structure of proposed scaffold as antidepressant agents.

2. Results and Discussion

2.1. Chemistry

In the present work, the title compounds, (3a–3n), were synthesized by utilizing the reaction sequence shown in Scheme 1. Thus, indole (1a) reacted with DMF in the presence of phosphorus oxychloride (POCl₃) to produce 3-formylindole (1b) [24], which further reacted with substituted aryl ketones using piperidine as a base in ethylene glycol under microwave irradiation conditions to yield (2a–2n) [25]. The reaction of equimolar quantities of 2a–2n with hydroxylamine hydrochloride under microwave irradiation resulted in the formation of the target derivatives 3a–3n (Table 1). The structures of the final compounds were confirmed by ¹H NMR, ¹³C NMR, IR, mass spectrometry, and elemental (C, H, N) analysis.

Table 1: Data of 5-(1H-Indol-3-yl)-3-(substituted aryl)-4,5-dihydroisoxazoline derivatives 3a–3n produced via Scheme 1.

Compound
Ar
Yield (%)a
m.p. (°C) [lit. m.p.]

3a

87.6
61–164

3b

81.7
167-168 (167) [26]

3c

84.3
178-179

3d

74.1
198-199

3e

71.9
201–203

3f

81.2
206–208

3g

76.4
171–176

3h

74.6
207-208

3i

70.6
164–167

3j

75.1
183-184

3k

78.9
174–176

3l

77.3
181–183

3m

72.9
191–193

3n

80.6
194–197

All yields refer to products purified by column chromatography.

Scheme 1: Synthetic route for the synthesis of target compounds (3a–3n). Reagents and conditions: (a) DMF, POCl₃; (b) piperidine, ethylene glycol, mw, 420 W, 10 min, target temperature 100°C; (c) hydroxylamine hydrochloride, EtOH, AcOH, mw, 455 W, 35 min, target temperature 95–98°C.

The IR spectra of the compounds 3a–3n revealed absorption bands in the region of 1630–1550 cm⁻¹ corresponding to C=N stretching. Absence of carbonyl (C=O) peak around 1710–1650 cm⁻¹ reveals the formation of indolyl isoxazolines. In the ¹H NMR spectrum, C4 (Ha, Hb) and C5 (Hx) protons of isoxazolines ring resonated as a pair of doublets at 3.50–3.70 (δ ppm), 3.70–3.85 (δ ppm), and 5.50–5.65 (δ ppm). These splittings are owing to vicinal coupling with the two magnetically nonequivalent C4 methylene protons of the ring.

2.2. Antidepressant Activity

The compounds 3a–3n were evaluated for antidepressant activity by forced swim test (FST) in mice at dose of 100 mg/kg and compared with the standard drugs imipramine (20 mg/kg) and fluoxetine (20 mg/kg). There were no mortality and noticeable behavioural changes in acute oral toxicity for all the groups tested. The synthesized compounds were found to be safe upto 2000 mg/kg body weight. Initially, dose-dependent study of compound 3a at different doses (25, 50, 100, and 200 mg/kg, i.p.) were performed to ensure the maximum effective dose for new synthesized compounds as antidepressant in FST. From this study, we found that 100 mg/kg is the maximum effective dose and therefore was selected for further pilot study of antidepressant-like effects of compounds 3b-3n in FST. Antidepressant activity was assessed as mean immobility time in seconds, and data has been presented as mean ± S.E.M as shown in (Table 2).

Table 2: Effect of 5-(1H-Indol-3-yl)-3-(substituted aryl)-4,5-dihydroisoxazoline series of compounds in forced swim test and locomotor activity.

Sr. no.
Compounds
Duration of immobilitya (sec.)

(mean ± SEM)
Percentage decrease in immobility duration

(% DID)
Locomotor activity scores for 10 minutes (sec.)

(mean ± SEM)

1
3a
35.7 ± 4.3***
62.2
470 ± 16.0ns

2
3b
56.3 ± 2.0***
40.4
490 ± 9.0ns

3
3c
26.2 ± 2.8***
72.3
480 ± 17.0ns

4
3d
11.3 ± 0.5***
88.0
480 ± 13.0ns

5
3e
23.7 ± 1.1***
75.0
460 ±13.0ns

6
3f
40.2 ± 4.1***
57.5
450 ± 14.0ns

7
3g
50.7 ± 4.2***
46.4
430 ± 29.0ns

8
3h
27.5 ± 0.9***
70.9
410 ± 28.0ns

9
3i
68.5 ± 4.6***
27.5
470 ± 18.0ns

10
3j
12.5 ± 0.9***
86.8
470 ± 8.4ns

11
3k
72.5 ± 4.5***
23.3
450 ± 17.0ns

12
3l
54.3 ± 4.4***
42.5
460 ± 17.0ns

13
3m
33.2 ± 5.7***
64.9
410 ± 26.0ns

14
3n
29.3 ± 2.1***
69.0
460 ± 17.0ns

15
Vehicle
94.5 ± 3.3
0.0
510 ± 15

16
Imipramine (20 mg/kg)
23.2 ± 0.9***
75.5
490 ± 14ns

17
Fluoxetine (20 mg/kg)
21.3 ± 0.6***
77.4
470 ± 11ns

aData analyzed by one-way ANOVA followed by Dunnett’s test. n = 6; dose = 100 mg/kg. Values are represented as mean ± S.E.M. Values are significant at ***P < 0.001, compared with control group. ns: not significant (P < 0.05) as compared to vehicle-treated group.

Results of FST revealed that all compounds exhibited significant antidepressant activity as becomes evident from their decrease in duration of immobility (DID) values compared to the control group and high %DID values. Compounds 3d and 3j were found to be the most potent derivatives from the series, at the same time, 3a and 3f showed moderate activity. Further, in order to compare the antidepressant effect of active compounds 3d and 3j with that of the standard drugs, a separate study was carried out by employing doses of 20 mg/kg i.p. of 3d, 3j, imipramine and fluoxetine; the results are presented in Figure 2.

Figure 2: Effect of treatment with 3d and 3j (20 mg/kg, i.p.), imipramine (20 mg/kg, i.p.), and fluoxetine (20 mg/kg, i.p.) on the immobility time in forced swim test. (Values are represented as mean ± S.E.M. . Values are significant at ***, compared with control group.)

Compounds 3d and 3j at the dose of 20 mg/kg i.p exhibited significant antidepressant activity compared with imipramine and fluoxetine. The preliminary SAR of indolyl isoxazolines suggested that replacement of the phenyl ring by the heterocycles pyridine, pyrrole, and so forth. led to an increase of antidepressant activity (3d, 3e, and 3j). Compounds bearing electron-withdrawing groups (F, Br, and Cl) on the para position of the aromatic core showed good antidepressant activity (3c, 3h, 3m, 3n), whereas electron-releasing groups (CH₃, OH, and OCH₃) at para as well as ortho position of the aromatic nucleus caused decrease in antidepressant activity (3b, 3g, 3i, 3k, 3l). Therefore, such compounds would represent a useful matrix for the development of a new class of clinically useful antidepressant agents and deserve further investigation and derivatization.

2.3. Locomotor Activity

The antidepressant activities of isoxazolines seem not to be associated with any motor effects, since they did not show significant () change in locomotor function of mice as compared to vehicle-treated group (Table 2) indicating that the new compounds have no excitatory or inhibitory action on central nervous system, which eliminated the probability of false-positive results in forced swimming test.

3. Conclusion

In summary, we developed a practical, fast, ecofriendly, and cost effective procedure for the synthesis of new 5-(1H-Indol-3-yl)-3-(4-substituted aryl)-4,5-dihydroisoxazoline derivatives under microwave irradiation. The remarkable advantages offered by microwave-assisted reactions over the conventional syntheses are the reduced reaction times, high purity, and better yields of the products. All synthesized compounds were evaluated for antidepressant activity in FST. Among all the derivatives tested in the present study, compounds 3d and 3j exhibited promising antidepressant activity comparable to that of the imipramine and fluoxetine. It was clearly demonstrated that the introduction of the appropriate heterocyclic ring on the basic scaffold led to potent derivatives. Hence, the present compounds can act as potential leads for further antidepressant studies.

4. Experimental

4.1. General Remarks

All solvents and reagents were used as obtained from commercial sources without further purification. Melting points were recorded and are uncorrected on an Elico Melting Point Apparatus using open capillary tube. All microwave-assisted reactions were performed using a scientific microwave oven (catalyst electromagnetic system) with a power of 800 W specially designed for organic synthesis. Thin-layer chromatography (TLC) was performed on precoated plates SiO₂ (silica gel 60, F 254, Merck) to monitor the progress of the reaction and purity of the compounds, spots being visualized under iodine vapors or UV-light. Silica gel (60–120 mesh size, Merck) was used for column chromatography. All NMR spectra were recorded on a Bruker Avance III, 400 MHz spectrometer with CDCl₃/DMSO as solvent using tetramethyl silane (TMS) as internal reference standard; chemical shifts are reported in ppm (δ). IR spectra of compounds were recorded on a Shimadzu IR 48 spectrophotometer with DRS technology. Mass spectra were recorded on a 410 Prostar Binary LC with 500 MS IT PDA detectors with direct infusion mass with ESI and APCI Negative and Positive mode ionization. Elemental analyses were performed on a Vario-EL III CHNOS elemental analyzer.

General Procedure for Synthesis of 5-(1H-Indol-3-yl)-3-(substituted aryl)-4,5-dihydroisoxazoline Derivatives (3a–3n). To a mixture of 1-(1H-indol-3-yl)-3-(substituted aryl)-prop-1-en-3-ones (1 mmoL) and hydroxylamine hydrochloride (1 mmol) in 20 mL EtOH was added a catalytic amount of acetic acid in 100 mL round bottom flask and subjected to microwave irradiation at 455 watt for specified time to attain the set temperature of 95–98°C. Most of the chalcone was consumed at this time (monitored by TLC); the reaction mixture was cooled to room temperature and was poured into crushed ice. The precipitate was separated by filtration and washed with water to get the desired products, which were purified by column chromatography (Chloroform/Acetone 18 : 1 as eluant). Physical data and percentage yields of all the synthesized compounds are represented in (Table 1).

5-(1H-Indol-3-yl)-3-(phenyl)-4,5-dihydroisoxazoline (3a). Yield: 87.64%, yellow solid; reaction time: 36 minutes; m.p.: 161–164°C; IR (KBr): cm⁻¹ 3315 (N–H), 1620 (C=C), 1548 (C=N); ¹H NMR (400 MHz CDCl₃, ppm) 6.02–6.07 (dd, 1H), 3.55–3.62 (dd, 1H), 3.69–3.70 (dd, 1H), 7.09–7.76 (m, 10H), 8.175 (brs, 1H). ¹³C NMR (100 MHz CDCl₃, ppm): 41, 73.0, 156.6, 130.02, 128.8, 129.9, 126.7, 111.4, 125.2, 136.9, 111.5, 120.5, 119.4, 120.2, 122.6, MS: m/z with +ve mode: 263.2 (), 264.1 (M+1). Anal. Calcd. for C₁₇H₁₄N₂O: C, 77.84; H, 5.38; N, 10.68. Found: C, 77.71; H, 5.58; N, 10.59%.

5-(1H-Indol-3-yl)-3-(4-methylphenyl)-4,5-dihydroisoxazoline (3b) . Yield: 81.71%; yellow solid; reaction time: 37 minutes; m.p.: 167-168°C; IR (KBr): cm⁻¹ 3408 (N–H), 1608 (C=C), 1630 (C=N); ¹H NMR (400 MHz CDCl₃, ppm) 2.39 (s, 3H), 5.99–6.04 (dd, 1H), 3.53–3.60 (dd, 1H), 3.68–3.74 (dd, 1H), 7.09–7.64 (m, 9H), 8.15 (brs, 1H). ¹³C NMR (100 MHz CDCl₃, ppm): 19.4, 39.0, 71.2, 154.5, 127.4, 124.6, 125, 138.2, 117.2, 123.1, 134.8, 109.5, 120.5, 113.4, 118.0, 127.4, MS: m/z with +ve mode: 277.2 (), 278.1 (M+1). Anal. Calcd. for C₁₈H₁₆N₂O: C, 78.24; H, 5.84; N, 10.14. Found: C, 78.17; H, 5.93; N, 9.38%.

5-(1H-Indol-3-yl)-3-(4-chlorophenyl)-4,5-dihydroisoxazoline (3c). Yield: 93.98%, yellow solid; reaction time: 34 minutes; m.p.: 178–179°C; IR (KBr): cm⁻¹ 3417 (N–H), 1618 (C=C), 1591 (C=N); ¹H NMR (400 MHz CDCl₃, ppm) 6.03–6.08 (dd, 1H), 3.27–3.59 (dd, 1H), 3.52–3.59 (dd, 1H), 7.10–7.68 (m, 9H), 8.15 (brs, 1H). ¹³C NMR (100 MHz CDCl₃, ppm): 40.8, 77.9, 156.2, 128.4, 127.9, 129, 136.9, 115.3, 125, 135.97, 111.5, 122.5, 119.3, 115.5, 126.7, MS: m/z with +ve mode: 297.2 (), 298.1 (M+1). Anal. Calcd. for C₁₇H₁₃ClN₂O: C, 68.81; H, 4.42; N, 9.44. Found: C, 68.53; H, 4.32; N, 9.40%.

5-(1H-Indol-3-yl)-3-(2-pyridyl)-4,5-dihydroisoxazoline (3d). Yield: 74.12%, yellow solid; reaction time: 41 minutes; m.p.: 198-199°C; IR (KBr): cm⁻¹ 3205 (N–H), 1598 (C=C), 1622 (C=N); ¹H NMR (400 MHz, DMSO, ppm) 6.01–6.98 (dd, 1H), 3.63–3.69 (dd, 1H), 3.79–3.87 (dd, 1H), 6.98–8.94 (m, 9H), 11.17 (brs, 1H). ¹³C NMR (100 MHz DMSO, ppm): 40.7, 77.5, 154.7, 123.9, 147.5, 136.8, 125.8, 150.7, 113.4, 125.3, 133.7, 111.8, 121.5, 119, 118.8, 124.2, MS: m/z with +ve mode: 265.14 (), Anal. Calcd. for C₁₆H₁₃N₃O: C, 72.99; H, 4.98; N, 15.96. Found: C, 72.91; H, 5.02; N, 15.79%.

5-(1H-Indol-3-yl)-3-(2-thienyl)-4,5-dihydroisoxazoline (3e). Yield: 71.88%, yellow solid; reaction time: 37 minutes; m.p.:194–197°C; IR (KBr): cm⁻¹ 3217 (N–H), 1623 (C=C), 1568(C=N); ¹H NMR (400 MHz CDCl₃, ppm) 6.03–6.06 (dd, 1H), 3.52–3.59 (dd, 1H), 3.67–3.74 (dd, 1H), 6.08–7.68 (m, 9H), 8.150 (brs, 1H). ¹³C NMR (100 MHz CDCl₃, ppm): 40.6, 78, 155.5, 128.4, 127.9, 129, 136.9, 115.3, 125.1, 136, 111.6, 122.7, 122.4, 119.2, 115.3, MS: m/z with +ve mode: 308.1 (), Anal. Calcd. for C₁₇H₁₃N₃O₃: C, 66.44; H, 4.26; N, 13.67. Found: C, 66.47; H, 4.41; N, 13.54%.

5-(1H-Indol-3-yl)-3-(2-naphthyl)-4,5-dihydroisoxazoline (3f). Yield: 81.24%, light yellow solid; reaction time: 34 minutes; m.p.: 206–208°C; IR (KBr): cm⁻¹ 3253 (N–H), 1618 (C=C), 1582 (C=N); ¹H NMR (400 MHz CDCl₃, ppm) 6.02–6.07 (dd, 1H), 3.55–3.62 (dd, 1H), 3.68–3.71 (dd, 1H), 7.02–7.78 (m, 12H), 8.17 (brs, 1H). ¹³C NMR (100 MHz CDCl₃, ppm): 41, 73, 156.6, 130, 128.8, 129.9, 126.7, 111.4, 125.1, 136.9, 111.5, 120.5, 119.3, 120.1, 122.6, MS: m/z with +ve mode: 313.21 (), Anal. Calcd. for C₂₁H₁₆N₂O: C, 80.75; H, 5.16; N, 8.97. Found: C, 80.62; H, 5.04; N, 9.01%.

5-(1H-Indol-3-yl)-3-(4-methoxyphenyl)-4,5-dihydroisoxazoline (3g). Yield: 84.57%, yellow solid; reaction time: 40 minutes; m.p.: 171–174°C; IR (KBr): cm⁻¹ 3258 (N–H), 1602 (C=C), 1612 (C=N); ¹H NMR (400 MHz CDCl₃, ppm) 3.79 (s, 3H), 5.92–6.01 (dd, 1H), 3.59–3.61 (dd, 1H), 3.63–3.78 (dd, 1H), 7.11–7.61 (m, 9H), 8.16 (brs, 1H). ¹³C NMR (100 MHz CDCl₃, ppm): 39, 55.6, 71.3, 153.6, 127.4, 124.75, 124.9, 138.1, 117.7, 123.1, 134.8, 109.2, 120.1, 113, 118.4, 127.1, MS: m/z with +ve mode: 293.31 (), Anal. Calcd. for C₁₈H₁₆N₂O₂: C, 73.95; H, 5.52; N, 9.58. Found: C, 73.91; H, 5.37; N, 9.46%.

5-(1H-Indol-3-yl)-3-(4-fluorophenyl)-4,5-dihydroisoxazoline (3h). Yield: 74.62%, yellow solid; reaction time: 34 minutes; m.p.: 207-208°C; IR (KBr): cm⁻¹ 3256 (N–H), 1608 (C=C), 1583 (C=N); ¹H NMR (400 MHz CDCl₃, ppm) 6.03–6.05 (dd, 1H), 3.53–3.59 (dd, 1H), 3.67–3.74 (dd, 1H), 6.09–7.67 (m, 9H), 8.154 (brs, 1H). ¹³C NMR (100 MHz CDCl₃, ppm): 40.5, 77.8, 156.1, 128.5, 127.9, 129.1, 136.8, 115.3, 125.1, 135.9, 111.7, 122.5, 122.8, 120.5, 119.3, MS: m/z with +ve mode: 297.32 (), Anal. Calcd. for C₁₈H₁₇FN₂O: C, 72.85; H, 4.67; N, 9.99. Found: C, 72.93; H, 4.41; N, 9.78%.

5-(1H-Indol-3-yl)-3-(2-hydroxyphenyl)-4,5-dihydroisoxazoline (3i). Yield: 70.62%, light yellow solid; reaction time: 36 minutes; m.p.: 164–167°C; IR (KBr): cm⁻¹ 3272 (N–H), 3336 (OH), 1618 (C=C), 1591 (C=N); ¹H NMR (400 MHz CDCl₃, ppm) 11.81 (s, 1H), 6.03–6.08 (dd, 1H), 3.53–3.59 (dd, 1H), 3.61–3.74 (dd, 1H), 6.07–7.67 (m, 9H), 8.14 (brs, 1H). ¹³C NMR: 41.2, 77.8, 153.7, 127.3, 127.5, 128, 135.8, 115.4, 124.2, 135.8, 111, 122, 122.1, 119.4, 115.5, MS: m/z with +ve mode: 279.17 (), Anal. Calcd. for C₁₇H₁₄N₂O₂: C, 73.37; H, 5.07; N, 10.07. Found: C, 73.19; H, 5.21; N, 10.29%.

5-(1H-Indol-3-yl)-3-(2-pyrolyl)-4,5-dihydroisoxazoline (3j). Yield: 75.12%, yellow solid; reaction time: 37 minutes; m.p.: 183-184°C; IR (KBr): cm⁻¹ 3278 (N–H), 1618 (C=C), 1589 (C=N); ¹H NMR (400 MHz CDCl₃, ppm) 13.06 (s, 1H), 5.97–6.06 (dd, 1H), 3.51–3.62 (dd, 1H), 3.66–3.76 (dd, 1H), 7.09–7.67 (m, 8H), 8.14 (brs, 1H). ¹³C NMR: 40.7, 77.4, 154.6, 123, 147.2, 136.6, 125.7, 151.3, 113.6, 133.5, 111.5, 121.2, 119.7, 118.3, 123.2, MS: m/z with +ve mode: 252.1 (), Anal. Calcd. for C₁₅H₁₃N₃O: C, 71.70; H, 5.21; N, 16.72. Found: C, 71.57; H, 5.46; N, 16.84%.

5-(1H-Indol-3-yl)-3-(4-hydroxyphenyl)-4,5-dihydroisoxazoline (3k). Yield: 75.92%, yellow solid; reaction time: 34 minutes; m.p.:174–176°C; IR (KBr): cm⁻¹ 3248 (N–H), 3317 (OH), 1622 (C=C), 1579 (C=N); ¹H NMR (400 MHz CDCl₃, ppm) 11.83 (s, 1H), 6.04–6.08 (dd, 1H), 3.51–3.57 (dd, 1H), 3.69–3.71 (dd, 1H), 6.09–7.64 (m, 9H), 8.15 (brs, 1H). ¹³C NMR: 40.5, 77.9, 154.5, 127.3, 127.9, 129, 135.4, 115.6, 125.4, 136.9, 111.51, 122, 122.4, 118.2, 115.7, MS: m/z with +ve mode: 279.21 (), Anal. Calcd. for C₁₇H₁₄N₂O₂: C, 73.37; H, 5.07; N, 10.07. Found: C, 73.27; H, 5.18; N, 10.34%.

5-(1H-Indol-3-yl)-3-(2-methylphenyl)-4,5-dihydroisoxazoline (3l). Yield: 77.32%; light yellow solid; reaction time: 37 minutes; m.p.: 167-168°C; IR (KBr): cm⁻¹ 3408 (N–H), 1608 (C=C), 1630 (C=N); ¹H NMR (400 MHz CDCl₃, ppm) 2.39 (s, 3H), 5.99–6.04 (dd, 1H), 3.53–3.60 (dd, 1H), 3.68–3.74 (dd, 1H), 7.09–7.64 (m, 9H), 8.15 (brs, 1H). ¹³C NMR (100 MHz CDCl₃, ppm): 19.4, 39, 71.2, 154.5, 127.4, 124.6, 125, 138.2, 117.8, 123.1, 134.8, 109.5, 120.5, 113.4, 118, 127.4, MS: m/z with +ve mode: 277.2 (), 278.1 (M+1). Anal. Calcd. for C₁₈H₁₆N₂O: C, 78.24; H, 5.84; N, 10.14. Found: C, 78.17; H, 5.93; N, 9.38%.

5-(1H-Indol-3-yl)-3-(4-bromophenyl)-4,5-dihydroisoxazoline (3m). Yield: 77.32%, yellow solid; reaction time: 36 minutes; m.p.: 191–193°C; IR (KBr): cm⁻¹ 3317 (N–H), 1614 (C=C), 1576 (C=N); ¹H NMR (400 MHz CDCl₃, ppm) 6.03–6.06 (dd, 1H), 3.53–3.58 (dd, 1H), 3.68–3.73 (dd, 1H), 6.08–7.68 (m, 9H), 8.157 (brs, 1H). ¹³C NMR (100 MHz CDCl₃, ppm): 40.5, 77.9, 155.5, 128.6, 127.9, 129, 136.9, 115.3, 125.2, 136, 111.6, 122.6, 122.7, 120.2, 119.3, MS: m/z with +ve mode: 342.14 (), Anal. Calcd. for C₁₈H₁₇BrN₂O: C, 59.84; H, 3.84; N, 8.21. Found: C, 59.67; H, 3.79; N, 8.13%.

5-(1H-Indol-3-yl)-3-(4-nitrophenyl)-4,5-dihydroisoxazoline (3n). Yield: 80.62%; light red solid; reaction time: 34 minutes; m.p.: 194–197°C; IR (KBr): cm⁻¹ 3217 (N–H), 1623 (C=C), 1568 (C=N); ¹H NMR (400 MHz CDCl₃, ppm) 6.03–6.06 (dd, 1H), 3.52–3.59 (dd, 1H), 3.67–3.74 (dd, 1H), 6.08–7.68 (m, 9H), 8.150 (brs, 1H). ¹³C NMR (100 MHz CDCl₃, ppm): 40.6, 78, 155.5, 128.4, 127.9, 129, 136.9, 115.3, 125.2, 136, 111.6, 122.7, 122.5, 119.3, 115.3, MS: m/z with +ve mode: 308.1 (), Anal. Calcd. for C₁₇H₁₃N₃O₃: C, 66.44; H, 4.26; N, 13.67. Found: C, 66.47; H, 4.41; N, 13.54%.

4.2. Antidepressant Activity

The Porsolt forced swimming test (behavioral despair test) was employed. Adult male albino Swiss-Webster ( g) mice were used with free access to food and water. They were housed in a group of six. The approval of the Institutional Animal Ethical Committee (IAEC) of R. C. Patel Institute of Pharmaceutical Education and Research, Shirpur (Maharashtra, India) was taken prior to the start of experiments. All the synthesized compounds (3a–3n) were screened for antidepressant activity using a Porsolt forced swimming (behavioral despair) test [27]. Acute oral toxicity of synthesized compounds was determined by OECD guideline no. 425 (up and down procedure). LD₅₀ was calculated as per OECD guidelines 425 [28].

The synthesized compounds (100 mg/kg), imipramine (20 mg/kg), and fluoxetine (20 mg/kg) suspended in aqueous tween 80 (0.5%), were injected as intraperitonealy (ip) (). After 1/2 hr, the mouse was dropped into the glass cylindrical container (diameter 10 cm, height 25 cm), containing approximately 20 cm of water at °C temperature. Water was replaced between every trial. Each mouse left for 6 minute at the end of the first 2 min; the animals showing initial vigorous struggling were immobile. The immobility times of each mouse were measured over the period of 4 min. Each mouse was judged immobile when it ceased struggling and remained floating motionless in the water, making only those movements necessary to keep its head above water. Conventional antidepressants decreased the immobility time in this test. Statistical analysis was performed by one-way ANOVA followed by Dunnett’s test to evaluate the results. Percentage decrease in immobility duration (%DID) for test and standard drugs was calculated using following formula:

where is the duration of immobility in control group and is the duration of immobility in test group. All the results of the antidepressant activity are given in (Table 2).

4.3. Locomotor Activity

Most of drugs acting on CNS influence the locomotor activities in man and animals. In other words, locomotor activity can be index of wakefulness (alertness) of mental activity [29]. Hence, locomotor activities of animals treated with synthesized compounds were measured using actophotometer (Spacelab, India) to examine the possible effect on locomotor activity. In brief, test animals were placed individually, in square arena of actophotometer for ten minutes, and locomotor activity was recorded (digitally displayed). The arena was cleaned with dilute alcohol and dried between trials [30]. All the results of the locomotor activity are given in Table 2.

Acknowledgments

The authors are thankful to Dr. S. J. Surana, Principal of the institute that provided research facilities to carry out the work. The authors gratefully acknowledge SAIF, IIT, Powai, and STIC, Cochin University, Cochin, for spectral data.

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