Aqueous phase synthesis, crystal structure and antimicrobial activity of 4-(substituted phenylazo)-3-methyl-4H-isoxazol-5-one azo dyes

Article abstract of DOI:10.4314/bcse.v32i2.6

3-Methyl-4H-isoxazol-5-one was synthesized at room temperature by simple stirring method from ethyl acetoacetate and hydroxylamine hydrochloride in aqueous medium and coupled with diazotized substituted amine to form series of 4-(substituted phenylazo)-3-methyl-4H-isoxazol-5-ones through green chemistry. All the compounds formed were characterized by IR, ¹H and ¹³C NMR spectroscopy, MS and elemental analysis. Crystal structure of novel 4-(4-fluorophenylazo)-3-methyl-4H-isoxazol-5-one was determined by the X-ray diffraction. Antibacterial and antifungal activity was studied against Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, Staphylococcus pyogenus and Candida albicans, Aspergillus niger, Aspergillus clavatus, respectively. All synthesized compounds were found to be active against a gram-positive bacterium Staphylococcus aureus. Two compounds showed antifungal activity against Candida albicans close to standard greseofulvin.

Full text of DOI:10.4314/bcse.v32i2.6

Bull. Chem. Soc. Ethiop. 2018, 32(2), 249-257.
 2018 Chemical Society of Ethiopia and The Authors
DOI: https://dx.doi.org/10.4314/bcse.v32i2.6
ISSN 1011-3924
Printed in Ethiopia
AQUEOUS PHASE SYNTHESIS, CRYSTAL STRUCTURE AND ANTIMICROBIAL
ACTIVITY OF 4-(SUBSTITUTED PHENYLAZO)-3-METHYL-4H-ISOXAZOL-5-ONE
AZO DYES
Anita R. Banpurkar1*, Sachin S. Wazalwar1 and Franc Perdih2
1Department of Applied Chemistry, Rajiv Gandhi College of Engineering, Research &
Technology, Chandrapur, MS, India-442403
2Faculty of Chemistry and Chemical Technology, University of Ljubljana, SI-1000 Ljubljana,
Slovenia
(Received January 3, 2018; Revised February 16, 2018; Accepted June 11, 2018)
ABSTRACT. 3-Methyl-4H-isoxazol-5-one was synthesized at room temperature by simple stirring method from
ethyl acetoacetate and hydroxylamine hydrochloride in aqueous medium and coupled with diazotized substituted
amine to form series of 4-(substituted phenylazo)-3-methyl-4H-isoxazol-5-ones through green chemistry. All the
compounds formed were characterized by IR, 1H and 13C NMR spectroscopy, MS and elemental analysis. Crystal
structure of novel 4-(4-fluorophenylazo)-3-methyl-4H-isoxazol-5-one was determined by the X-ray diffraction.
Antibacterial and antifungal activity was studied against Escherichia coli, Pseudomonas aeruginosa,
Staphylococcus aureus, Staphylococcus pyogenus and Candida albicans, Aspergillus niger, Aspergillus clavatus,
respectively. All synthesized compounds were found to be active against
a gram-positive bacterium
Staphylococcus aureus. Two compounds showed antifungal activity against Candida albicans close to standard
greseofulvin.
KEY WORDS: Azo dyes, Substituted amines, Antibacterial and antifungal activity, X-ray diffraction,
Spectroscopy, Green chemistry
INTRODUCTION
Azo dyes are the most widely used class of coloring materials because of their fruitful
applications in various fields of science and technology [1-3] and also for their interesting
structural and physicochemical properties [4-6]. Azo dyes are synthesized by diazotization of
aromatic amines and coupling reagent, which include one or more azo groups (–N=N–) attached
to one or more aromatic moieties [7]. Currently, heteroarylazoisoxazol compounds have
received the attention of many research groups [8] because of their wide spread potential
applications in fields of catalysis [9], cancer treatment and as antibacterial and antiviral agents,
agricultural fungicides as well as other biological uses [10-12]. Intramolecular N–H∙∙∙O
hydrogen bonding study assisted by resonance for 1-ketone-2-arylhydrazones derivatives
suggest that heterocyclic five member ring introduces geometrical constraint which hinders the
strengthening of hydrogen bond [13]. Tautomerism and spectroscopic properties of some
heteroarylazoisoxazolone dyes were studied earlier [14]. With these objects in view we focus on
the synthesis and antimicrobial activity of 4-(substituted phenylazo)-3-methyl-4H-isoxazol-5-
one azo dyes.
EXPERIMENTAL
All the starting materials and solvents were purchased from commercial sources and were used
without further purification. Melting points were determined in open capillaries using electro
thermal melting point apparatus and are uncorrected. Progress of reactions was monitored by
TLC. Infrared (IR) spectra (4000–600 cm–1) of the samples were recorded using a Perkin–Elmer
Spectrum 100, equipped with a Specac Golden Gate Diamond ATR as a solid sample support.
__________
*Corresponding author. E-mail: anitabanpurkar1@gmail.com
This work is licensed under the Creative Commons Attribution 4.0 International License

250
Anita R. Banpurkar et al.
1H NMR spectra were recorded with a Bruker Avance III 500 nuclear magnetic resonance
spectrometer with TMS as internal reference. 13C NMR spectra were recorded with a Bruker
Avance III 500 spectrometer at 125 MHz and were referenced against the central line of the
solvent signal (CDCl3 triplet at 77.0 ppm or DMSO-d6 septet at 39.5 ppm). MS spectra were
recorded with an Agilent 6624 Accurate Mass TOF LC/MS instrument (ESI ionization).
Single-crystal X-ray diffraction data for 6c∙0.3H2O were collected on an Agilent
Technologies SuperNova Dual diffractometer with the Atlas detector using monochromated
Mo-Kα radiation (λ = 0.71073 Å) at room temperature. The data were processed using CrysAlis
Pro. [15]. The structure was solved by direct methods using the program Superflip [16] and
refined on F2 using full-matrix least-squares procedures using SHELXL2014 [17]. All non-
hydrogen atoms were refined anisotropically. Hydrogen atoms were readily located in a
difference Fourier maps and were subsequently treated as riding atoms in geometrically
idealized positions, with C–H = 0.93 (aromatic) or 0.96 Å (CH3), N–H = 0.86 Å and with
Uiso(H) = kUeq(C or N), where k = 1.5 for methyl groups, which were permitted to rotate but not
to tilt, and 1.2 for all other H atoms. The water H-atoms were refined with a distance restraint
and with Uiso(H) = 1.5Ueq(O). Initially, the occupation factor for a water solvate molecule was
refined, but was set as fixed at 0.30 in the final stage of the refinement. Structure was refined as
a twin. Crystallographic data are listed in Table 1.
Determination of minimal inhibition concentrations by micro broth dilution for antibacterial
and antifungal activity
All the synthesized drugs were used for antibacterial test procedures. All necessary controls like
drug control, vehicle control, agar control, organism control, known antibacterial drugs control,
all MTCC cultures were tested against above mentioned known and unknown drugs. Mueller
Hinton broth was used as nutrient medium to grow and dilute the drug suspension for the test
bacteria. Inoculum size for test strain was adjusted to 108Cfu [Colony Forming Unit] per
milliliter by comparing the turbidity. Common standard strains were used for screening of
antibacterial and antifungal activities: The strains were procured from Institute of Microbial
Technology, Chandigarh: E. coli (MTCC443), P. aeruginosa (MTCC1688), S. aureus
(MTCC96), S. pyogenus (MTCC442), C. albicans (MTCC227), A. niger (MTCC282), A.
clavatus (MTCC1323). DMSO was used as diluents / vehicle to get desired concentration of
drugs to test upon standard bacterial strains.
The main advantage of the ‘Broth Dilution Method’ for minimal inhibition concentration
(MIC) determination lies in the fact that it can readily be converted to determine the MIC as
well [18-22]. Serial dilutions were prepared in primary and secondary screening. The control
tube containing no antibiotic is immediately sub cultured (before inoculation) by spreading a
loopful evenly over a quarter of plate of medium suitable for the growth of the test organism and
o
put for incubation at 37 C overnight. The tubes are then incubated overnight. The MIC of the
control organism is read to check the accuracy of the drug concentrations. The lowest
concentration inhibiting growth of the organism is recorded as the MIC. The amount of growth
from the control tube before incubation is compared [23].
Each synthesized drug was diluted obtaining 2000 μg/mL concentration, as a stock solution.
In primary screening 1000, 500, and 250 μg/mL concentrations of the synthesized drugs were
taken. The active synthesized drugs found in this primary screening were further tested in a
second set of dilution against all microorganisms. The drugs found active in primary screening
were similarly diluted to obtain 200, 100, 50, 25, 12.5, 6.250 μg/mL end concentrations. The
highest dilution showing at least 99% inhibition zone is taken as MIC.
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Synthesis of 4-(substituted phenylazo)-3-methyl-4H-isoxazol-5-one azo dyes
251
General procedure for synthesis of 3-methyl-4-H-isoxazol-5-one
Hydroxylamine hydrochloride (1.041 g, 15 mmol) was dissolved in 20 mL of water and cooled
to about 10 oC, added ethyl acetoacetate (1.95 g, 15 mmol). The mixture was shaken thoroughly
in absence of any catalyst till the appearance of pale yellow color solution of 3-methyl-4H-
isoxazol-5-one [24].
General procedure for synthesis of 4-(substituted phenylazo)-3-methyl-4H-isoxazol-5-one azo
dyes
Substituted amine 4a–e (15 mmol) were dissolved in dilute HCl (1.5 mL in 15 mL water) and
cooled in an ice bath to 0–5 oC. The reaction mixture was added to the solution of sodium nitrite
(1.043 g, 15 mmol in 15 mL of water) and 0.01 M HCl (15 mL) at about 0–5 oC with continuous
stirring to give yellow colored solution 5a–e. To this solution, equimolar amount of cooled 3-
methyl-4H-isoxazol-5-one solution was added in ice bath with continuous stirring for 30 min to
get yellow orange colored precipitate. The pH of reaction mixture was maintained between 5
and 6. The reaction mixture was kept overnight at about 15 oC for the completion of the reaction.
The precipitate obtained 6a–e was washed with cold water, dried and recrystallized using
ethanol. Crystals of 6c suitable for single crystal XRD analysis were obtained by slow
evaporation of ethanol and chloroform (1:1 v/v) solvent mixture.
Spectral data
3-Methyl-4-phenylazo-4H-isoxazol-5-one (6a). Yellow solid, yield: 2.45 g (85%), m.p.: 170 oC,
Rf 0.214 (EtOH). Elemental analysis: found %, C 59.26; H 4.42; N 20.73; C10H9N3O2 (203.20
g/mol). Calculated, % C 59.11; H 4.46; N 20.68;MS (ESI+) m/z: 204.0767 (MH+), HRMS:
found, m/z: 204.0768; C10H9N3O2 calculated, m/z: 204.0767. IR (cm–1): 3209 (NH), 1708 (C=O),
1
1570 (CH=N), 1482 (C=C), 1277 (C–O); H NMR (500 MHz, CDCl3, δ ppm): 2.26 (s, 3H,
3-CH3), 7.37–7.19 (m, 5H, Ar-H), 12.60 (s, 1H, -NH); 13C NMR, δ ppm, CDCl3: 10.3, 116.1,
121.1, 126.7, 129.8, 140.4, 159.4, 164.9.
4-(4-Chloro-phenylazo)-3-methyl-4H-isoxazol-5-one (6b). Yellow solid, yield: 2.79 g (82%),
o
m.p.: 155 C, Rf 0.224 (EtOH). Elemental analysis: found %, C 50.57; H 3.47; N 17.31;
C10H8ClN3O2 (237.64 g/mol). Calculated, % C 50.54; H 3.39; N 17.68. MS (ESI+) m/z:
238.0377 (MH+), HRMS: found, m/z: 238.0378; C10H9N3O2 calculated, m/z: 238.0377. IR (cm–
1
1): 3204 (NH), 1739 (C=O), 1554 (CH=N), 1477 (C=C), 1220 (C–O). H NMR (500 MHz,
CDCl3, δ ppm): 2.26 (s, 3H, -CH3 isoxazol), 7.35–7.28 (m, 4H, Ar-H), 12.57 (s, 1H, -NH), 13C
NMR (125 MHz, CDCl3, δ ppm): 10.3, 117.2, 130.0, 132.0, 139.0, 159.3, 164.8.
4-(4-Fluorophenylazo)-3-methyl-4H-isoxazol-5-one (6c). Orange yellow solid, yield: 2.60 g
(83%), m.p.: 160 oC, Rf 0.217 (EtOH). Elemental analysis: found %, C 54.60; H 3.25; N 18.80;
C10H8FN3O2 (221.19 g/mol). Calculated, % C 54.30; H 3.65; N 19.00. MS, (ESI+) m/z:
222.0671 (MH+), HRMS: found, m/z: 222.0673; C10H8FN3O2 calculated, m/z: 222.0671. IR
1
(cm–1): 3199 (NH), 1714 (C=O), 1565 (CH=N), 1493 (C=C), 1215 (C–O). H NMR (500 MHz,
CDCl3, δ ppm): 2.26 (s, 3H, -CH3isoxazol), 7.09–7.06 (m, 2H, Ar-H), 7.35–7.32 (m, 2H, Ar-H),
12.62 (s, 1H, -NH). 13C NMR (125 MHz, CDCl3, δ ppm): 10.2, 116.7, 136.7, 159.3, 160.1,
162.1, 164.0.
4-(3-Methyl-5-oxo-4,5-dihydroisoxazol-4-ylazo)benzenesulfonamide (6d). Orange yellow solid,
yield 3.20 g (79%), m.p. 240 oC, Rf 0.260 (EtOH). Elemental analysis found, %: C 42.40; H
3.41; N 19.40; C10H10N4O4S (282.28 g/mol). Calculated, % C 42.55; H 3.57; N, 19.85.MS,
(ESI+) m/z: 283.0491 (MH+), HRMS: found, m/z: 283.0495; C10H10N4O4S calculated, m/z:
Bull. Chem. Soc. Ethiop. 2018, 32(2)

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Anita R. Banpurkar et al.
1
283.0491. IR (cm–1): 3317 (NH), 1719 (C=O), 1570 (CH=N), 1482 (C=C), 1246 (C–O). H
NMR (500 MHz, CDCl3, δ ppm): 2.29 (s, 3H, -CH3 isoxazol), 4.71 (s, 2H, -NH2), 7.46–7.44 (d,
2H, Ar-H), 7.94–7.92 (d, 2H, Ar-H), 12.56 (s, 1H, -NH). 13C NMR (125 MHz, DMSO, δ ppm):
10.6, 117.2, 122.7, 127.5, 141.2, 144.4, 160.5, 162.4.
4-(3-Acetylphenylazo)-3-methyl-4H-isoxazol-5-one (6e). Orange solid, yield: 2.76 g (79%),
o
m.p.: 210 C, Rf 0.251 (EtOH). Elemental analysis found, %: C 59.42; H 3.20; N 16.77;
C12H11N3O3 (245.23 g/mol). Calculated, % C 58.77; H 4.52; N 17.17, MS, (ESI+) m/z:
246.0871 (MH+), HRMS: found, m/z: 246.0873; C12H11N3O3 calculated, m/z: 246.0871. IR
1
(cm–1): 3204 (NH), 1734 (C=O), 1549 (CH=N), 1431 (C=C), 1272 (C–O). H NMR (500 MHz,
CDCl3, δ ppm): 2.29 (s, 3H, -CH3 isoxazol), 2.51 (s, 3H, -COCH3), 7.92–7.47 (m, 4H, Ar-H),
12.63 (s, 1H, -NH). 13C NMR (125 MHz, CDCl3, δ ppm): 10.3, 26.7, 115.3, 120.2, 126.3, 130.2,
138.6, 140.9, 159.4, 164.7, 196.9.
RESULTS AND DISCUSSION
A series of 4-(substituted phenylazo)-3-methyl-4-H-isoxazol-5-one azo dyes were obtained from
easily available, economically feasible chemicals like ethyl acetoacetate, hydroxylamine
hydrochloride and some substituted amines by environmentally benign, green route in aqueous
medium without using any catalyst. In the first step the reaction of ethyl acetoacetate (1) and
hydroxylamine hydrochloride (2) resulted in the formation of oxime, which on further ring
closure formed 3-methyl-4H-isoxazol-5-one (3) (Scheme 1). Electron withdrawing effect of N
atom in 3-methyl-4H-isoxazol-5-one along with electron donating effect of O atom and presence
of electron releasing methyl and keto groups makes it more reactive [15]. In the second step
diazotization of substituted amine 4a–e was carried out in the presence of sodium nitrite and
hydrochloric acidwhich then coupled with active hydrogen atom of isoxazol nucleus under cold
condition to give desired product (Scheme 1).
NH2
O
O
O
R
1
4(a-e)
NH2OH.HCl
2
0-5o
C
N
aN
O
,H
Cl
2
N
+N
Cl-
O
N
O
O
H
Stirring
0-5oC
N
N
N
R
O
R
3
5(a-e)
6(a-e)
a: R = H, b: R = 4-Cl, c: R = 4-F, d: R = 4-SO2NH2, e: R = 3-COCH3
Scheme 1: Synthesis of 4-(substituted phenylazo)-3-methyl-4H-isoxazol-5-one azo dyes.
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Synthesis of 4-(substituted phenylazo)-3-methyl-4H-isoxazol-5-one azo dyes
253
All compounds 6a–e show singlet for NH proton in the range of 12.50–12.60 ppm.
Multiplets for aromatic ring were observed between 7–8 ppm. A singlet for three protons in the
range of 2.26–2.29 is attributed to CH3 group of isoxazol. Compound 6d shows a singlet for two
protons of NH2 group related to sulphanilamide moiety at 4.71 ppm and compound 6e show a
singlet for three protons related to COCH3 group at 2.51 ppm. 13C NMR study of 6a–e shows a
singlet at about 10.24–10.56 ppm for CH3 group of isoxazol, about 160–165 ppm for C=O group
of isoxazol, compound 6e shows singlet at 197 ppm for C=O group of acetophenone and at 26
ppm for CH3 group of acetophenone. The IR spectrum of compound 6a–e showed characteristic
(-NH) absorption band in the region 3024-3317 cm-1, (C=O) absorption band in the region
1708-1739 cm-1 and (CH=N) absorption band in the region 1550-1570 cm-1 (Figure 1).
Figure 1. IR spectra of 6a–e.
Figure 2. Molecular structure and atom numbering scheme for 6c. Elipsoid Probability are
drawn at the 50% level and hydrogen bonding of C4–H4A∙∙∙O2 and C10–H10∙∙∙O1 is
indicated by blue dashed lines.
Single-crystal X-ray structures of 4-(4-fluorophenylazo)-3-methyl-4H-isoxazol-5-one
(6c∙0.3H2O) was determined (Figure 2, Table 1). Table 3 and 4 describes significant bond
distances and bond angles. All the bond lengths and bond angles of compounds are within
normal ranges for this type of structure as reported earlier [13]. Molecule 6c is almost planar,
maximum deviation from the mean plane described by all atoms of 6c is –0.132(3) Å for atom
C10. The dihedral angle between the isoxazolone and phenyl rings is 7.81(18)o. In the crystal
structure bond distances indicates that the isoxazolone ring contains one double bond, i.e.
C1-N1. Also, atoms C2 and N2 are connected through double bond and intramolecular
N3–H3∙∙∙O2 hydrogen bonding is present between NH group and the carbonyl group of the
isoxazole ring. A water solvate molecule present in the crystal lattice with 30% occupancy
Bull. Chem. Soc. Ethiop. 2018, 32(2)

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Anita R. Banpurkar et al.
forms O3–H3A∙∙∙O2 hydrogen bond with two adjacent molecules of 6c. Furthermore, molecules
are linked into chains via C4–H4A···O2 interactions between methyl group of isoxazole ring
and carbonyl oxygen atom of isoxazole moiety of the adjacent molecule and C10–H10···O1
interactions between the phenyl moiety and the oxygen atom of isoxazole moiety of the adjacent
molecule (Figure 3).
Figure 3. Chain formation generated by C4–H4A∙∙∙O2 and C10–H10∙∙∙O1 interactions.
Hydrogen-bonds are indicated by blue dashed lines.
Table 1. Crystallographic data for 4-(4-fluorophenylazo)-3-methyl-4H-isoxazol-5-one (6c∙0.3H2O).
Compound code
CCDC number
Molecular formula
Molecular weight
Crystal System
Space group
Unit cell dimensions (Å)
a
6c∙0.3H2O
1561281
C10H8.6FN3O2.3
226.60
Orthorhombic
Fdd2
24.2754(17)
24.5121(17)
6.8469(5)
16
4074.2(5)
1.478
b
c
Z
V (Å3)
Dcalc (g cm–3)
μ (mm–1)
0.120
F(000)
1872
Reflections collected
Parameters
8741
155
1.069
0.0407, 0.0939
0.0560, 0.1023
–0.172, 0.13
Goodness-of-fit on F2
R1, wR2 [I > 2σ(I)]a
R1, wR2 (all data)b
Δρmin, Δρmax (e Å–3)
Table 2. Hydrogen bond geometry of 6c (Å and °).
D–H···A
D–H (Å) H∙∙∙A (Å) D···A (Å) D–H∙∙∙A (°) Symmetry code
N3–H3∙∙∙O2
O3–H3A∙∙∙O2
C4–H4A∙∙∙O2
C10–H10∙∙∙O1
0.86
0.82(2)
0.96
2.23
2.20(3)
2.56
2.882(3)
3.007(4)
3.371(4)
3.379(3)
132.4
169(8)
142.8
149.4
x, y, z
x, y, z
–x + 3/4, y – 1/4, z + 1/4
–x + 3/4, y + 1/4, z – 1/4
0.93
2.55
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Synthesis of 4-(substituted phenylazo)-3-methyl-4H-isoxazol-5-one azo dyes
Table 3. Significant bond distances.
255
Sr. No.
Bond
F1 C8
O1 C3
O1 N1
O2 C3
N1 C1
N2 N3
N2 C2
N3 C5
Distance (Å)
1.363(3)
1.359(3)
1.470(3)
1.213(4)
1.292(3)
1.306(3)
1.311(3)
1.412(3)
1
2
3
4
5
6
7
8
Table 4. Significant bond angles.
Sr. No.
1
2
3
4
5
6
7
8
Bond
Angle (°)
109.2(2)
106.6(2)
118.4(2)
120.0(2)
111.9(3)
120.9(3)
127.2(2)
125.2(2)
129.1(2)
105.6(2)
122.1(3)
131.1(3)
106.7(2)
C3 O1 N1
C1 N1 O1
N3 N2 C2
N2 N3 C5
N1 C1 C2
N1 C1 C4
C2 C1 C4
N2 C2 C1
N2 C2 C3
C1 C2 C3
O2 C3 O1
O2 C3 C2
O1 C3 C2
9
10
11
12
13
All synthesized compounds 6a–e were screened for antibacterial and antifungal study
against E. coli, P. aeruginosa, S. aureus and S. pyogenus as bacterial strain and C. albicans, A.
niger, A. clavatus as fungal strain. All synthesized compounds 6a–e showed antibacterial
activity against S. aureus. Compound 6c and 6e showed antibacterial activity against E. coli
whereas compound 6b showed antibacterial activity against S. pyogenus close to activity of
standard ampicillin (Table 5). It was found that compounds 6b and 6e show antifungal activity
against C. albicans close to standard greseofulvin (Table 6).
Table 5. Antibacterial activity study of 6a–e with standard drugs.
Minimal inhibition concentration (μg/mL)
Entry Compound
E. coli
(MTCC443)
125
200
62.5
200
100
0.05
100
P. aeruginosa
(MTCC1688)
S.
aureus S. pyogenus
(MTCC96)
100
200
200
100
250
0.25
250
50
(MTCC442)
125
100
200
200
250
0.5
100
1
6a
200
500
250
250
250
1
-
50
25
10
2
6b
3
6c
4
6d
5
6e
9
Gentamycin
Ampicillin
Chloramphenicol 50
Ciprofloxacin
Norfloxain
10
11
12
13
50
50
10
25
10
50
10
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Anita R. Banpurkar et al.
Table 6. Antifungal activity study of 6a–e with standard drugs.
Minimal inhibition concentration (μg/mL)
C. albicans (MTCC227) A. niger (MTCC282) A. clavatus (MTCC1323)
Entry Compound
1
2
3
4
5
9
10
6a
6b
6c
6d
1000
500
1000
1000
500
>1000
>1000
1000
500
>1000
100
>1000
>1000
1000
500
>1000
100
6e
Nystatin
Griseofulvin
100
500
100
100
CONCLUSION
The method of synthesis of 6a–e is aqueous phased, environmentally friendly and gives product
easily in good yield without using any hazardous chemicals. Spectroscopic study of 6a–e and X-
ray crystallographic study of 6c shows azo dye formation with tautemerism to retain aromaticity
of isoxazole ring. All synthesized compounds showed antibacterial activity against S. aureus
close to standard ampicillin. Compounds 6c and 6e showed antibacterial activity against E. coli
close to ampicillin and 6b and 6e showed antifungal activity against C. albicans close to
gresiofulvin. The crystal structure of 6c shows hydrogen bonding interaction with water
molecule. Oxygen atom attached to isoxazole ring shows intermolecular as well as
intramolecular hydrogen bonding.
ACKNOWLEDGMENTS
The authors are thankful to Microcare Laboratory and Tuberculosis Centre, Surat for providing
antibacterial and antifungal activity. Financial support from the Slovenian Research Agency
(ARRS) through project P1-0175 is gratefully acknowledged. We thank the EN-FIST Centre of
Excellence, Ljubljana, Slovenia, for using SuperNova diffractometer.
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