Efficient Antimicrobial Activities of Microwave-Assisted Synthesis of Benzisoxazole Derivatives

Introduction

Microwave assisted synthesis is an eco-friendly and well-organized synthesis of organic compounds in contrast to the conventional process. In this system, reaction takes place more swiftly, securely and with advanced chemical yields and thus, this method becomes greater to the conventional mode.

Benzisoxazole exhibits a remarkable prospective as antimicrobial, anticancer, anti-inflammatory actions. In medicinal chemistry as it relates to the broad and general outline of the different benzisoxazole analogs, their application as beginning building blocks of diverse architectures on scales adequate to drive human drug experiments.^1-5 Heterocyclic molecules such as benzisoxazole derivatives, particularly 3-(piperidin-4-yl)-1,2-benzisoxazole have been extensively used as antipsychotic drugs.⁶ Atypical antipsychotic drugs which are derived from benzisoxazole.⁷ Benzisoxazole derivatives are oxygen, nitrogen holding heterocycles with broad variety of synthetic and pharmaceutical applications, and are renowned for biological activities. The high therapeutic properties of these heterocycles have persuaded the medicinal chemist to synthesize a huge quantity of chemotherapeutic agents.⁸

Isoxazole is a vital heterocyclic core, which is broadly used as many pharmacological properties.^9-12 We herein detail the synthesis of benzisoxazole derivatives from dimedone with the use of microwave irradiation.

Experimental and Materials Method

Dimedone, benzaldehyde and hydroxylamine hydrochloride were provided by Sigma-aldrich (St.Louis, USA). IR spectra were documented in SHIMADZU FT-IR 8400S spectrometer by employing KBr pellets. ¹H NMR (500 MHz)   and ¹³C NMR (400 MHz) spectra recorded on Brucker spectrometer using CDCl₃ solvent. Microwave (Godrej GMS 17M 07 WHGX). Melting point was recorded in Royal Scientific RSW 138 B.

Synthesis of Benzisoxazole Derivatives

5,5-dimethylcyclohexane-1,3-dione (0.001 mm) react with hydroxylamine hydrochloride (0.001 mm) and  benzaldehyde (0.1 mL) under microwave irradiation at a suitable time (Table 1). The development of the reaction was monitored on TLC (Scheme 1). Following the completion of reaction, the reaction combination was quenched in distilled water and the precipitate was formed. It were filtered and dried.

Scheme 1: Synthetic route of benzisoxazole derivatives Click here to View Scheme

Table 1: Melting point, yield and time taken for microwave irradiation of the benzisoxazole derivatives 1-4

Compounds	MP (°C)	Yield (%)	Time (min)
1	158	86	7
2	162	75	9
3	152	78	8
4	144	80	7

Antibacterial Studies

Antibacterial studies, Gram-positive and Gram-negative strains have been used for the studyB. subtilis E. coli, P. aeruginosa, S. aureus, S. pyogenes. Antifungal studies, used following fungal strains, A. flavus, A. niger, P. chryogenum, T. veride, F. oxysporum.

Results and Discussion

IR and NMR Spectrum of Benzisoxazole Derivatives (1-4)

Synthesis of benzisoxazole derivatives (1-4) by utilizing microwave irradiation for suitable time (9 minutes) afforded remarkable yields with absolute transformation of reactants. The foundation of newly synthesized (1-4) was launched by IR and NMR spectroscopy.

3-(2-Chlorophenyl)-6,6-Dimethyl-2,3,6,7-Tetrahydrobenzo[d] Isoxazol-4(5H)-One (1)

FT-IR spectrum the carbonyl (C=O) and N-H stretching frequency were scrutinized in the area of 1688 and 3666-3750 cm^-1. The C-N and aromatic C=C stretching frequency were examined at 2360 and 1548 cm^-1.

Molecular formula for C₁₅H₁₆ClNO₂: ¹H NMR (500 MHz, CDCl₃): d 1.16 (s, 6H), 2.33 (s, 1H), 2.34 (s, 2H), 2.44 (s, 2H), 5.50 (s, 1H), 7.02 (d, J = 3.0 Hz, 3H),7.24 (t, 2H), 7.45 (d, J = 8.0 Hz, 1H). ¹³C NMR (400 MHz, CDCl₃): d 27.67, 31.76, 41.62, 51.16, 59.14, 104.47, 126.99, 128.05, 128.59, 129.35, 142.79, 187.47, 198.93. Theoritical value of MS: m/z. 277.75 [M­+].

3-(4-Chlorophenyl)-6,6-Dimethyl-2,3,6,7-Tetrahydrobenzo[d] Isoxazol-4(5H)-One (2)

FT-IR spectrum the carbonyl (C=O) and N-H stretching frequency were surveyed in the region of 1688 and 3666-3750 cm^-1. The C-N and aromatic C=C stretching frequency were examined at 2360 and 1548 cm^-1.

Molecular formula for C₁₅H₁₆ClNO₂: ¹H NMR (500 MHz, CDCl₃): d 1.16 (s, 6H), 2.33 (s, 1H), 2.40 (s, 2H), 2.44 (s, 2H), 5.10 (s, 1H), 7.01 (d, J = 8.0 Hz, 1H), 7.25 (d, J = 12.0 Hz, 1H), 7.37 (d, J = 7.5 Hz, 1H), 7.45 (d, J = 8.0 Hz, 1H). ¹³C NMR (400 MHz, CDCl₃): d 27.67, 31.76, 41.65, 51.14, 62.47, 104.45, 126.99, 128.59, 133.96, 141.56, 187.40, 198.91. Theoritical value of MS: m/z. 277.75 [M­+].

3-(4-Hydroxyphenyl)-6,6-Dimethyl-2,3,6,7-Tetrahydrobenzo[d] Isoxazol-4(5H)-One (3)

FT-IR spectrum the hydroxyl (–OH), carbonyl (C=O) and N-H stretching frequency were examined in the area of 3852, 1688 and 3666-3750 cm^-1. The C-N and aromatic C=C stretching frequency were detected at 2360 and 1548 cm^-1.

Molecular formula for C₁₅H₁₇NO₃: ¹H NMR (500 MHz, CDCl₃): d 1.14 (s, 3H), 1.29 (s, 3H), 2.25 (s, 1H), 2.37 (s, 2H), 2.49 (s, 2H), 5.56 (s, 1H), 7.02 (d, J = 8.0 Hz, 1H), 7.24 (d, J = 12.0 Hz, 1H), 7.37 (d, J = 7.5 Hz, 1H), 7.45 (d, J = 7.9 Hz, 1H), 11.88 (s, 1H). ¹³C NMR (400 MHz, CDCl₃): d 27.66, 31.76, 41.65, 51.14, 61.47, 104.65, 115.17, 126.99, 135.96, 139.55, 156.59, 187.40, 198.91. Theoritical value of MS: m/z. 259.30 [M­+].

6,6-Dimethyl-3-(3-Nitrophenyl)-2,3,6,7-Tetrahydrobenzo[d] Isoxazol-4(5H)-One (4)

FT-IR spectrum the carbonyl (C=O) and N-H stretching frequency were detected in the area of 1688 and 3666-3750 cm^-1. The C-N and aromatic C=C stretching frequency were detected at 2360 and 1548 cm^-1.

Molecular formula for C₁₅H₁₆N₂O₄: ¹H NMR (500 MHz, CDCl₃): d 1.15 (s, 3H), 1.27 (s, 3H), 2.25 (s, 1H), 2.37 (s, 2H), 2.49 (s, 2H), 5.56 (s, 1H), 7.56 (t, 1H), 7.89 (d, J = 8.0 Hz, 1H), 7.72 (d, J = 7.9 Hz, 1H), 8.43 (s, 1H). ¹³C NMR (400 MHz, CDCl₃): d 27.66, 31.76, 41.65, 51.14, 61.47, 119.32, 121.68, 129.84, 135.96, 147.12, 187.59, 198.91. Theoritical value of MS: m/z. 288.30 [M­+].

Antimicrobial Activities

The preliminary antimicrobial activities of the moieties 1-4 are scrutinized using disc diffusion method. The bacterial strains viz., B. subtilis, E. coli, P. aeruginosa, S. aureus, S. pyogenes are used in this study. Dimethylsulphoxide is used as a control. Streptomycin and Amphotericin B are used as an indication for bacterial and fungal studies correspondingly.

The antibacterial screening studies indicated that the compound having 1, 2, 4 showed outstanding antibacterial against B. subtilis, E. coli, S. pyogenes, but no active against P. aeruginosa and S. aureus. The compound 1 is more active against P. aeruginosa and S. pyogenes (Figure 1). The results are given in Table 2. The antifungal activity screening studies confirmed that the 1, 2, 4 chloro substituted compound showed outstanding activity against A.flavus, P. chryogenum, F. oxysporum and less active against A. niger, T. veride (Figure 2). The result is given in Table 3.

Figure 1: Zone of inhibition of moieties 1-4 against B Click here to View Figure

Figure 2: Zone of inhibition of moieties 1-4 against A Click here to View Figure

Table 2: Antibacterial activity of compounds 1 to 4

S. No.	Bacteria	Zone of inhibition mm in diameter
		1	2	3	4
1	B. subtilis	25	20	20	31
2	E. coli	18	8	–	22
3	P. aeruginosa	26	–	–	–
4	S.  aureus	18	8	–	–
5	S. pyogenes	17	12	–	19

*Streptomycin

Table 3: Antifungal activity of compounds 1 to 4

S. No.	Fungi	Zone of inhibition mm in diameter
		1	2	3	4
1	Aspergillus flavus	14	24	–	26
2	Aspergillus niger	19	18	–	11
3	Penicillim chryogenum	12	23	–	28
4	Trichoderma veride	20	17	–	8
5	Fusarium oxysporum	12	22	–	27

*Amphotericin-B

Conclusion

The depicted synthetic protocol permits for the preparation of a series of benzisoxazole derivativesas new arrangement which can be latently useful in various pharmacological applications. Chief benefits of these original techniques are equipped with effortlessness, high yield in a very tiny reaction time, eco-friendly conditions, very cheap, effortlessly available reagent and simple technique employed.

Acknowledgment

Special thanks to the VN the Director of Collegiate Education, Govt. of Tamilnadu, India, for financial support.  Author is thanks to Research centre, IISc, Bangalore, for providing NMR facility. Thanks to Dr. P. Ramanathan, Assistant Professor, for helping me to complete the bioactivity tests.

Conflict of Interest

No conflict of interest

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