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Synthesis and biological activities of Bis alkyl 1,3,4-oxadiazole incorporated azo dye derivatives
⁎Corresponding author. Tel.: +91 (0)8282 256308 (O); fax: +91 (0)8282 256255. jkeshavyya@gmail.com (J. Keshavayya)
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Received: ,
Accepted: ,
This article was originally published by Elsevier and was migrated to Scientific Scholar after the change of Publisher.
Peer review under responsibility of King Saud University.
Abstract
3,5-Bis(alkyl-1,3,4-oxadiazole-2-yl azo dyes were synthesized by a multi-step reaction sequence. Structures of newly synthesized compounds were characterized and confirmed by IR, NMR, and Mass spectral studies. The synthesized compounds were screened for their antimicrobial and in vitro antioxidant properties. The results of this investigation revealed that the newly synthesized compounds are potent antibacterial and antioxidant agents. All the synthesized compounds exhibit significant biological activity and certainly hold a greater promise for discovering potent biologically active molecules.
Keywords
Bis(alkyl-1,3,4-oxadiazole)azo dye
8-Hydroxy quinoline
Anti-microbial activity
In vitro antioxidant activity
1 Introduction
In recent years, fungal and bacterial infections have become an important complication and a major cause of morbidity and mortality. The growing incidence of fungal and bacterial resistance to existing antibiotics poses a serious medical problem in treating pathogenic infections. Several five-membered hetero cyclic drugs possess diverse biological effects. Nitrogen and oxygen containing five membered azoles are important bioactive agents, due to their vast pharmacological and industrial applications. Synthesis of such heterocyclic compounds is of pharmaceutical importance and a foremost task for chemists. 1,3,4-Oxadiazole derivatives are heterocyclic compounds which exhibit remarkable pharmacological activities. It has been known that the activity of azo linkage increases with the incorporation of a suitable heterocyclic moiety. Heterocyclic azo compounds are well known for their medicinal importance and are recognized for their use as antineoplastics (Child et al., 1977), antidiabetics (Garg and Praksh, 1972), antiseptics (Browing et al., 1926), anti-inflammatory, antibacterial (Khedr et al., 2011; Nikhil et al., 2011) and other useful chemotherapeutic agents (Bae et al., 2003; Sanjay et al., 2007). Azo dyes are used as hypnotic drugs for the nervous system, in detecting cancer as chemotherapeutic agents and are involved in the structure of nucleic acids in living cells (Zeynel et al., 2008). Azo dyes are known to be involved in a number of biological reactions such as inhibition of DNA, RNA, protein synthesis, carcinogenesis and nitrogen fixation (Browing et al., 1926; Rajendra et al., 1998). Evans blue and Congo red are being studied as HIV inhibitors. This effect is believed to be caused by binding of azo dyes to both protease and reverse transcriptase of this dreadful virus (Fatma and Eser, 2007). 1,2,3-Oxadiazoles can also act as HIV integrase inhibitors (Sicardi et al., 1980).
1,3,4-Oxadiazoles are five membered heterocyclic compounds having significant position in synthetic and medicinal chemistries due to their wide array of biological activities such as anti fungal (Parkash et al., 2010) antimicrobial (Sridhara et al., 2010), anti-inflammatory, analgesic (Akhter et al., 2009; Idrees et al., 2009; Tozcoparan et al., 2000), hypolipidemic (Jayashankar et al., 2009) anti tubercular (Kumar et al., 2010; Kucukguzel et al., 2002), anti-convulsant (Singh and Pankaj, 2010; Bhat et al., 2010), and cytotoxic agents (Padmavathi et al., 2009), also as prostaglandin receptor antagonists (George et al., 2000) and anti oxidant agent (Abdu Musad et al., 2011; Bondock et al., 2009).
In view of the above mentioned findings and our previous findings on synthesis and pharmacological activities of heterocyclic compounds (Keshavayya et al., 2011a,b, 2006, 2007), in the present study we made an efficient attempt to synthesize alkyl bis 1,3,4-oxadiazole substituted azo dyes coupled with quinoline, possessing potent biological activities. Structures of the synthesized compounds were confirmed by 1H NMR, IR and Mass spectral studies. Synthesized compounds were screened for their antimicrobial and in vitro antioxidant properties.
2 Results and discussion
As depicted in Scheme 1, 1,3,4-oxadiazole azo dye derivatives were synthesized by a multi-step reaction sequence. 1,3,4-Oxadiazoles were prepared by reacting 5-nitro bis iso-phthalic dihydrazide with appropriate long chain fatty acids in the presence of phosphorous oxychloride gives 5-nitro alkyl bis 1,3,4-oxadiazoles in good yields. 5-Nitro alkyl bis 1,3,4-oxadiazoles were allowed to react with Zn/HCl using ethanol as a solvent to convert the nitro group to amine. The newly synthesized amine group was diazotized and coupled with 8-hydroxy quinoline to obtain bis alkyl 1,3,4-oxadiazole substituted azo dye 4 (a–f). The synthesized compounds were recrystallized using methanol. The purity of the compounds was checked by TLC. The structures of the newly synthesized compounds were characterized by 1H NMR, IR and Mass spectra studies. The synthesized compounds were found in good agreement with the spectral data. The elemental analysis results were matched within ±0.4% of the theoretical values.
The IR spectra of 1 showed an absorption peak at 3336.4 cm−1 due to hydrazide, a peak at 1507.1 cm−1 due to NO2 and a peak at 1633.3 cm−1 due to C⚌O absorption. These spectral data of synthesized 5-nitro, iso-phthalic dihydrazide stand in good agreement with those reported in the literature (Palekar et al., 2009). The IR spectrum of the compound 2 showed absorption peak at 1561.4 cm−1 due to C⚌N stretching vibration. The absence of C⚌O peak at 1633.3 cm−1 and NHNH2 at 3336.4 cm−1 confirms the formation of oxadiazoles. The 1H NMR spectrum revealed a singlet at δ 13–16 due to —OH protons, δ 2–3 due to long chain aliphatic protons and δ 6–8 due to aromatic proton. The IR spectrum of compounds 4 a–f showing an absorption peak at 3300–3400 cm−1, was attributed to —OH, at 1600–1700 cm−1, due to N⚌N, absorption at 1500–1600 and C⚌N at 2921 (aliphatic chain). The IR, 1H NMR and mass spectral data were found in good agreement with the newly synthesized compounds.
3 Pharmacology
Azoles exert antifungal activity through inhibition based on the structure of the active site of oxadiazoles and extensive investigation of the structure–activity relationships (SAR) of azole has revealed that the oxadiazole ring, having oxygen, nitrogen and the hydroxyl group was the pharmacophore of antifungal agents [41].
3.1 Evaluation of minimal inhibitory concentrations (MICs)
Evaluation of MIC values of all the compounds 4a–f was carried out using concentrations ranging from 2.5 to 20 mg/mL. Compound 4c showed significant inhibition at 2.5 mg/mL against Pseudomonas aureginosa, Escherichia coli, and Candida parapsilosis. While, compounds 4a and 4d showed maximum inhibitory activity against P. aureginosa and C. parapsilosis at MIC 2.5 mg/mL, lowest MIC was shown by compound 4c. Compounds 4b, 4c and 4d demonstrated efficient MIC when compared to other test compounds. Results of MIC are depicted in Table 1.
5a4
5b2
5c1
5d3
5e5
5f6
Staphylococcus aureus
20
10
05
10
20
20
Pseudomonas aureginosa
10
05
05
10
10
10
Bacillus subtilis
10
10
2.5
05
20
20
Escherichia coli
10
05
2.5
05
10
–
Candida albicans
05
2.5
2.5
05
10
20
Candida parapsilosis
–
05
05
10
10
–
3.2 Antimicrobial screening
All synthesized compounds having heterocyclic system containing bridgehead nitrogen and oxygen atoms possess enhanced antimicrobial activity. Among the synthesized compounds 4c having moderate aliphatic chain length showed significant results in inhibiting Staphylococcus aureus and Bacillus subtilis growth with 21.83 ± 0.88 mm and 24.33 ± 1.01 mm zones of inhibition respectively when compared to other compounds. Compounds 4b and 4a against P. aureginosa produced 21.01 ± 0.56 mm and 17.69 ± 0.33 mm zones of inhibition respectively; this was comparable to the effect of the standard used. Whereas compound 4d was significant and showed 17.5 ± 1.2 mm. Test compounds other than 4c showed moderate effect when compared to the standard drug ampicillin against E. coli. Compound 4c showed significant inhibition against Candida albicans and C. parapsilosis with 25.67 ± 0.58 mm and 17.33 ± 1.01 mm zones of inhibition respectively when compared to other compounds but less efficient than the standard drug fluconazole. Evaluation of antimicrobial activity revealed that the all the synthesized compounds were effective in inhibiting the bacterial and fungal growth but with some exceptions. Among all the compounds tested, compounds 4b, 4d, and 4a showed significant antimicrobial activity when compared to other compounds. Specifically, compound 4c was more efficient than other compounds but less potent than standard drug ampicillin. Results of in vitro antimicrobial activity are depicted in Table 2. The value of each constituents consisted of ± S.E.M. of 03 replicates. ND – Not Defined.
Compounds
Zone of inhibition (mm)
Staphylococcus aureus
Bacillus subtilis
Escherichia coli
Pseudomonas aeruginosa
Candida albicans
Candida parapsilosis
ATCC 25923
ATCC 6633
ATCC 25922
ATCC 27853
ATCC 10231
ATCC 90018
4a
10.33 ± 1.12
16.67 ± 0.95
17.88 ± 1.53
17.69 ± 0.33
19.13 ± 0.33
ND
4b
17 ± 1.53
17.67 ± 0.88
18.83 ± 1.4
21.01 ± 0.56
22.33 ± 0.67
18.01 ± 0.33
4c
21.83 ± 0.88
24.33 ± 1.01
23 ± 0.33
20 ± 0.33
25.67 ± 0.58
17.33 ± 1.01
4d
17.33 ± 0.67
18.83 ± 0.33
18.33 ± 0.88
17.5 ± 1.2
18.98 ± 1.17
16.98 ± 1.13
4e
12.28 ± 0.88
11.67 ± 0.33
17.17 ± 1.45
15.11 ± 0.33
16.33 ± 1.86
15.17 ± 1.52
4f
10.33 ± 0.67
9.67 ± 1.01
13.67 ± 0.95
ND
11.33 ± 1.2
ND
Ampicillin
17 ± 1.53
20.67 ± 0.33
14.33 ± 1.45
19.67 ± 0.88
–
–
Fluconazole
–
–
–
–
19.3 ± 0.33
18.83 ± 1.13
3.3 In vitroantioxidant screening
The free radical scavenging activity of test samples 4a–f was measured by DPPH method according to Brand-Williams et al. All the synthesized compounds having electron donating groups like oxygen and nitrogen, exhibited free radical scavenging capacity in comparison with the standard Butylated Hydroxytoulene (BHT). DPPH assay was carried out for compounds 4a–f at different concentrations from 50 to 100 μM concentration. Among the tested compounds, 4b and 4c showed significant DPPH scavenging activity (>70%) at concentration 100 μM whereas other test compounds were less potent than the standard BHT (Fig. 1). The variation exhibited in DPPH scavenging capacity could be attributed to the effect of different substitutions and results are presented in Table 3.
DPPH radical scavenging activity.
Concentration in μM
4a
4b
4c
4d
4e
4f
BHT
50
40.17
43.11
49.16
42.13
34.24
26.33
75.13
100
51.19
69.89
73.67
59.13
49.33
46.03
90.02
4 Experimental
All analytical grade chemicals were used directly. Melting point of the synthesized compounds was determined in a scientific melting point apparatus and uncorrected. The progress of reaction was monitored by TLC using silica gel coated plates (0.5 mm thickness, Merck) and spots were visualized under UV radiation. Synthesized compounds were recrystallized using suitable solvent system. Infra-red spectra were recorded on a Perkin Elmer-spectrum RX-1model spectrophotometer using KBr pellets. NMR spectra were recorded by a Bruker DRX 400 MHz spectrometer and acquired on a Bruker Avance-2 model spectrophotometer using DMSO as a solvent and TMS as an internal reference. The crude compounds were purified by recrystallization method.
4.1 Synthesis of aryl 3-nitro iso-phthalic acid dihydrazide (1)
The 3-nitro iso-phthalic acid dihydrazide (1) was synthesized by adopting reported method. Hydrazine hydrate (0.2 mmol) was added drop-wise to the solution of iso-phthalic ester (0.1 mmol) in 30 mL of dried ethanol with vigorous stirring. The resulting mixture was refluxed for 4–6 h. The progress of the reaction was monitored by TLC with the solvent system petroleum ether: ethyl acetate (1:1) as the mobile phase and visualized under UV light. The excess ethanol was distilled out and the contents were cooled at room temperature. The yellow solid mass formed was filtered and washed thoroughly using brine solution and the resultant was dried.
4.2 General procedure for the synthesis of 2, 2′-(5-nitrobenzene-1, 3-diyl) bis (5-alkyl-1,3,4-oxadiazole) (2)
A suspension of 5-nitrobenzene-1,3-dicarbohydrazide (1 mmol) and the appropriate long chain fatty acids (2 mmol) in POCl3 (10 ml) were refluxed for 6–8 h. The progress of the reaction was monitored on TLC by using silica gel plates using petroleum ether and ethyl acetate (7:3) as the eluting system and visualized in UV light. The reaction mixture was allowed to cool to room temperature and slowly poured over crushed ice kept overnight. The solid thus, separated out was neutralized with anhydrous sodium bicarbonate, filtered, washed with water and recrystallized using ethanol.
4.3 General procedure for the synthesis of 3,5-bis(alkyl-1,3,4-oxadiazol-2-yl)aniline
A suspension of nitro compound (1 mmol) and SnCl22H2O (5 mmol) was dissolved in 0.02 M methanolic HCl solution and refluxed for 3–4 h at 70–80 °C under nitrogen atmosphere. The reaction mixture was concentrated under reduced pressure, diluted with ethyl acetate, and washed with aq. NaHCO3 and water. The organic layer was dried over anhydrous sodium sulphate, concentrated, and then recrystallized from methanol.
4.4 General procedure for the synthesis of 3,5-bis(alkyl-1,3,4-oxadiazol-2-yl azo dye (4a–f)
The newly synthesized amine (1 mmol) was taken in HCl and cooled to 0–5 °C, NaNO2 dissolved in a suitable solvent (1.25 mmol) was added dropwise with constant stirring without allowing the temperature to rise above 10 °C to get a diazonium salt. After complete addition the reaction mixture was adjusted to pH 5–6, the coupling compound (1 mmol) was dissolved in a suitable solvent and cooled to 0–5 °C and this solution was added to the above mixture gradually without allowing the temperature rise above 0–5 °C. After complete addition, the reaction mixture was stirred for 1–2 h for the completion of reaction. The dye obtained was filtered and thoroughly washed with water, dried and recrystallized using methanol that afforded a red coloured dye, a red colour solid with 83% yield, m.p. 168–169 °C.
4.5 Spectral data of synthesized compound
4.5.1 3,5-Bis(alkyl-1,3,4-oxadiazol-2-yl azo dye (4a)
This dye was isolated as red colour solid with 83% yield, m.p. 168–169 °C; IR (Vmax, cm−1) = 2849 (C—H), 1630 (C⚌N), 1507 (NO2), 2921 (aliphatic chain), 1H NMR (CDCl3) (δ ppm) = 0.92 (t, 6H, aliphatic CH3), 1.27 (Br, S, 12H, CH2), 1.33 (m, 4H, Ar–H), 1.6 (t, 4H, CH2) 2.54 (m, 4H, CH2), 8.76 (d, 1H, Ar–H), 8.07 (d, 2H, Ar–H), 7.95 (d, 1H, Ar–H), 7.92 (s, 1H, Ar–H), 7.83 (d, 1H, Ar–H), 7.32 (d, 1H, Ar–H), 7.18 (t, 1H, Ar–H), 14.63 (s, 1H, OH) .MS m/z 582.27 (M+) 13C NMR (CDCl3) (δ ppm) = 14.6, 23.1, 26.0–32.4 (aliphatic-C), 118.6, 118.3, 121.3, 123.8, 127.4, 131.4, 134.6, 134.5, 137.8, 143.1, 150.6, 150.8, 153.2. (Ar–C), 162.6 (C5 of oxadiazole), 168.8 (C2 of oxadiazole). Anal. Calcd. For C33H39N7O3; C, 68.14; H, 6.76; N, 16.86. Found; C, 68.23; H, 6.59; N, 16.91.
4.5.2 3,5-Bis(alkyl-1,3,4-oxadiazol-2-yl azo dye (4b)
This dye was isolated as red colour solid with 78% yield, m.p. 175–176 °C; IR (Vmax, cm−1) = 2849 (C—H), 1630 (C⚌N), 1507 (NO2), 2921 (aliphatic chain), 1H NMR (CDCl3) (δ ppm) = 0.94 (t, 6H, aliphatic CH3), 1.29 (m, 20H, CH2) 1.34 (m, 4H, CH2) 1.63 (m, 4H, CH2), 2.59 (t, 4H, CH2) 8.76 (d, 1H, Ar–H), 8.12 (d, 2H, Ar–H), 7.97 (d, 1H, Ar–H), 7.93 (s, 1H, Ar–H), 7.82 (d, 1H, ArH), 7.31 (d, 1H, Ar–H), 7.15 (t, 1H, Ar–H). 14.7 (s, 1H, OH) .MS m/z = 638.46 (M+) 13C NMR (CDCl3) (δ ppm) = 14.8, 23.3, 26.0–32.6 (aliphatic-C), 118.4, 118.7, 121.7, 123.5, 127.1, 131.8, 133.2, 134.3, 138.2, 143.7, 150.2, 151.3, 153.7. (Ar–C), 162.2 (C5 of oxadiazole), 169.2 (C2 of oxadiazole). Anal. Calcd. For C37H47N7O3; C, 69.67; H, 7.43; N, 15.37. Found; C, 68.92; H, 7.53; N, 15.58.
4.5.3 3,5-Bis(alkyl-1,3,4-oxadiazol-2-yl azo dye (4c)
IR (Vmax, cm−1) = 2849 (C—H), 1630 (C⚌N), 1507 (NO2), 2921 (aliphatic chain) 1H NMR (CDCl3) (δ ppm) = 15.2 (s, 1H), 0.95 (t, 6H, aliphatic CH3), 1.26 (m, 28H, CH2) 1.31 (m, 4H, CH2) 1.64 (m, 4H, CH2), 2.58 (t, 4H, CH2) 8.79 (d, 1H, Ar–H), 8.11 (d, 2H, Ar–H), 7.95 (d, 1H, Ar–H), 7.90 (s, 1H, Ar–H), 7.85 (d, 1H, Ar–H), 7.29 (d, 1H, Ar–H), 7.18 (t, 1H, Ar–H). 24.7 (s, 1H, OH). 13C NMR (CDCl3) (δ ppm) = 14.3, 23.2, 29.8, 30.0, 30.2, 32.2, 32.5 (aliphatic-C), 118.6, 118.4, 121.3, 123.6, 127.7, 131.4, 134.5, 135.3, 137.3, 143.4, 150.7, 150.4, 153.7. (Ar–C), 162.4 (C5 of oxadiazole), 169.1 (C2 of oxadiazole). MS m/z = 694.17(M+). Anal. Calcd. For C41H55N7O3; C, 70.96; H, 7.99; N, 14.13. Found; C, 69.98; H, 7.74; N, 16.15.
4.5.4 3,5-Bis(alkyl-1,3,4-oxadiazol-2-yl azo dye (4d)
This dye was isolated as red colour solid with 86% yield, m.p. 188–189 °C; IR (Vmax, cm−1) = 2849 (C—H), 1630 (C⚌N), 1507 (NO2), 2921 (aliphatic chain) 1H NMR (CDCl3) (δ ppm) = 15.4 (s, 1H), 0.97 (t, 6H, aliphatic CH3), 1.28 (m, 36H, CH2) 1.33 (m, 4H, CH2) 1.624 (m, 4H, CH2), 2.56 (t, 4H, CH2) 8.72 (d, 1H, Ar–H), 8.32 (d, 2H, Ar–H), 7.98 (d, 1H, Ar–H), 7.91 (s, 1H, Ar–H), 7.82 (d, 1H, Ar–H), 7.27 (d, 1H, Ar–H), 7.14 (t, 1H, Ar–H). MS m/z = 751.23 (M+) Anal. Calcd. For C45H63N7O3; C, 72.06; H, 8.47; N, 13.307. Found; C, 71.52; H, 7.98; N, 14.16.
4.5.5 3,5-Bis(alkyl-1,3,4-oxadiazol-2-yl azo dye (4e)
This dye was isolated as red colour solid with 77% yield, m.p. 192–193 °C; IR (Vmax, cm−1) = 2849 (C—H), 1630 (C⚌N), 1507 (NO2), 2921 (aliphatic chain) 1H NMR (CDCl3) (δ ppm) = 15.8 (s, 1H), 0.93 (t, 6H, aliphatic CH3), 1.24 (m, 44H, CH2) 1.36 (m, 4H, CH2) 1.63 (m, 4H, CH2), 2.58 (t, 4H, CH2) 8.76 (d, 1H, Ar–H), 8.34 (d, 2H, Ar–H), 7.93 (d, 1H, Ar–H), 7.96 (s, 1H, Ar–H), 7.84 (d, 1H, Ar–H), 7.29 (d, 1H, Ar–H), 7.16 (t, 1H, Ar–H). MS m/z = 806.35 (M+) Anal. Calcd. For C49H71N7O3; C, 73.01; H, 8.88; N, 12.16. Found; C, 74.19; H, 8.62; N, 15.89.
4.5.6 3,5-Bis(alkyl-1,3,4-oxadiazol-2-yl azo dye (4f)
This dye was isolated as red colour solid with 84% yield, m.p. 198–199 °C; IR (Vmax, cm−1) = 2849 (C—H), 1630 (C⚌N), 1507 (NO2), 2921 (aliphatic chain) 1H NMR (CDCl3) (δ ppm) = 14.3 (s, 1H), 0.98 (t, 6H, aliphatic CH3), 1.25 (m, 52H, CH2) 1.36 (m, 4H, CH2) 1.68 (m, 4H, CH2), 2.52 (t, 4H, CH2) 8.79 (d, 1H, Ar–H), 8.38 (d, 2H, Ar–H), 7.96 (d, 1H, Ar–H), 7.92 (s, 1H, Ar–H), 7.87 (d, 1H, Ar–H), 7.31 (d, 1H, Ar–H), 7.12 (t, 1H, Ar–H). MS m/z = 862.97 (M+) Anal. Calcd. For C53H79N7O3; C, 73.83; H, 9.32; N, 11.37. Found; C, 73.62; H, 9.52; N, 11.85.
4.6 Determination of minimal inhibitory concentrations (MIC)
The agar dilution susceptibility test was performed based on the modified method of NCCLS, 2003 and CLSI, 2009 to determine the MIC of the synthesized compounds. The test compounds (4a–g) dissolved in sterilized 5% DMSO (400 mg/mL concentration) were taken as standard stock. A series of two fold dilutions of each compound in the final concentrations of 40, 20, 10, 5, and 2.5 mg/mL were prepared in nutrient agar for bacteria and potato dextrose agar for fungi. After solidification, the plates were spotted with 100 μL of overnight grown bacterial cultures approximately containing 1 × 104 CFU/mL. The test was carried out in triplicates. The plates of bacterial culture were incubated at 37 °C for 18–24 h and fungal cultures were incubated at 24 °C for 24–48 h. After incubation, the MIC was determined.
4.7 Antimicrobial activity
The antimicrobial activity of newly synthesized compounds 4a–f was determined by well plate method in nutrient agar (antibacterial activity) (Lehrer et al., 1991) and Sabouraud dextrose agar (antifungal activity). The in vitro antibacterial activity was carried out against 24 h old cultures of bacterial strains and 72 h old cultures of fungal strains. In this work, E. coli, S. aureus, B. subtilis, Salmonella typhi, were used to investigate the antibacterial activities and Pseudomonas Aeruginosa, C. albicans, C. parapsilosis, were used to investigate the antifungal activities.
The test compounds were dissolved in dimethyl sulphoxide (DMSO) at concentration of 100 and 50 mg/mL. Approximately 1 cm3 of a 24 h broth culture was placed in sterile petri dishes. Molten nutrient agar kept at 45 °C was then poured into the Petri dishes and allowed to solidify. Six millimetre diameter holes were then punched carefully using a sterile cork borer and completely filled with the test solutions. The plates were incubated for 24 h at 37 °C. The inhibition zone was observed and documented after 24 h for bacterial culture and 72 h for fungal cultures. The clear zone around the holes in each plate was measured as zone of inhibition in mm. Experiments were triplicates and standard deviation was calculated. The zone of inhibition of antifungal activity was determined after 72 h culture. The results were compared with Fluconazole.
4.8 In vitroantioxidant screening
The free radical scavenging activity of synthesized 4a–g was measured by DPPH (2,2-diphenyl 1-picrylhydrazyl) using the method proposed by Brand-Williams et al. (1995). The reaction mixture of the synthesized compounds viz. 4a–g at different concentrations ranging from 25 to 100 μg aliquots was taken and the volume was made up to 3 mL by using methanol, to this 1 mL of 0.1 mM solution of DPPH in methanol was added and kept in the dark for 30 min at room temperature, O.D was measured at 517 nm and the inhibition concentration was calculated using the formula given below. 3 mL of methanol and 1 mL of DPPH were used as controls.
% of inhibition = [(A°–A1)/A°] × 100.
A° = the absorbance of the control at 517 nm,
A1 = the absorbance of the compound 4a–g at 517 nm.
5 Conclusion
This investigation proposes a convenient, economical, cheaper and useful method for the synthesis of 3,5-bis(alkyl-1,3,4-oxadiazol-2-yl) azo dyes, coupled with quinoline, which are biologically active molecules possessing antimicrobial and in vitro antioxidant properties. These new classes of heterocycles, exhibit a significant antimicrobial and antioxidant activities. 1,3,4-Oxodiazole azo dye coupled with 8-hydroxy quinoline showed active antioxidant capacity than 1,3,4-oxodiazole azo dye coupled with naphthols. The preliminary antimicrobial activity studies revealed that the azo dye having 1,3,4-oxodiazole moiety exhibited a potential antimicrobial activity. Hence, it can be concluded that, this new class of compounds certainly holds a greater promise in discovering a potent antimicrobial and antioxidant agent.
Acknowledgements
The authors are grateful to the Kuvempu University, authors remain thankful to the UGC, New Delhi for providing financial support, and are also thankful to the Indian Institute of Science, Bangalore and the Karnataka University, Dharwad for providing spectral data.
Reference
- Bio. Org. & Med. Chem. Lett.. 2011;21:3536-3540.
- Eur. J. Med. Chem.. 2009;44:2372-2378.
- Dyes Pig.. 2003;57:121.
- Der Pharma Chemica.. 2010;1:2.
- Eur. J. Med. Chem.. 2009;44:4813.
- LWT-Food Sci. Technol.. 1995;28:25-30.
- J. Stor.. 1926;10:293-325.
- Chem. Abstr.. 1977;87:6031.
- Acta Chim. Slov.. 2007;54:242-247.
- Med. Chem.. 1972;15:435-436.
- Bioorg. Chem.. 2000;28:140.
- Eur. J. Med. Chem.. 2009;44:3973-3980.
- Eur. J. Med. Chem.. 2009;44:3898-3902.
- Chin. J. Chem.. 2011;29:1124-1132.
- Eur. J. Med. Chem.. 2002;37:197.
- Eur. J. Med. Chem.. 2010;45:2063-2074.
- J. Immunol. Meth.. 1991;137:167-173.
- Int. J. Pharm. Tech. Res.. 2011;3:540-548.
- Eur. J. Med. Chem.. 2009;44:2106-2112.
- Eur. J. Med. Chem.. 2009;44:5112-5116.
- Eur. J. Med. Chem.. 2010;10:1016.
- Croatica Chemica Acta. 1998;71:715-726.
- Saudi Pharm. J.. 2007;15:48-54.
- J. Med. Chem.. 1980;23:1139.
- Der Chemica Sinica. 2010;1:118.
- Eur. J. Med. Chem.. 2000;35:743.
Further reading
- Int. J. Appl. Biol. Pharma. Tech.. 2011;2:332-338.
- Eur. J. Med. Chem.. 2006;41:1048-1058.
- Eur. J. Med. Chem.. 2007;42:823-840.
- Cent. Eur. J. Chem.. 2008;6(1):81-88.
- Int. Res. J. Pure & Appl. Chem.. 2011;1(3):119-129.
- Der Chemica Sinica. 2011;2:106-114.
- Eur. J. Med. Chem.. 2010;45:4983-4989.
