Synthesis, photophysical property study of novel fluorescent 4-(1,3-benzoxazol-2-yl)-2-phenylnaphtho[1,2-d][1,3]oxazole derivatives and their antimicrobial activity

Article abstract of DOI:10.1007/s12039-012-0324-3

A series of 4-(1,3-benzoxazol-2-yl)-2-phenylnaphtho[1,2-d][1,3]oxazole derivatives have been synthesized from intermediate 1-amino-3-(1,3-benzoxazol-2- yl)naphthalen-2-ol. This intermediate was obtained by coupling 3-(1,3-benzoxazol-2-yl)naphthalen-2-ol with 4-sulphobenzenediazonium chloride followed by reduction with sodium dithionate in water at pH 8-9. 3-(1,3-benzoxazol-2-yl)naphthalen-2-ol was synthesized from 3- hydroxynaphthalene-2-carboxylic acid and 2-amino phenol in the presence of PCl₃ in chlorobenzene at 130-135 C. All these compounds were characterized by FT-IR, ¹H NMR, mass spectral and elemental analysis. The synthesized compounds are fluorescent which absorbs in the range of 296 to 332 nm while emits in the ranges of 368 to 404 nm with excellent quantum yield. All compounds were evaluated for in vitro antibacterial activities against Escherichia coli and Staphylococcus aureus strains and in vitro antifungal activity against Candida albicans and Aspergillus niger strains by using serial dilution method.

Full text of DOI:10.1007/s12039-012-0324-3

c
J. Chem. Sci. Vol. 125, No. 1, January 2013, pp. 141–151. ꢀ Indian Academy of Sciences.
Synthesis, photophysical property study of novel fluorescent
4-(1,3-benzoxazol-2-yl)-2-phenylnaphtho[1,2-d][1,3]oxazole
derivatives and their antimicrobial activity
KIRAN R PHATANGARE, BHUSHAN N BORSE, VIKAS S PADALKAR, VIKAS S PATIL,
VINOD D GUPTA, PRASHANT G UMAPE and N SEKAR∗
Department of Intermediate and Dyestuff Technology, Institute of Chemical Technology (Formerly UDCT),
NP Marg, Matunga, Mumbai 400 019, India
e-mail: n.sekar@ictmumbai.edu.in, nethi.sekar@gmail.com
MS received 23 December 2011; revised 28 July 2012; accepted 10 August 2012
Abstract. A series of 4-(1,3-benzoxazol-2-yl)-2-phenylnaphtho[1,2-d][1,3]oxazole derivatives have been
synthesized from intermediate 1-amino-3-(1,3-benzoxazol-2-yl)naphthalen-2-ol. This intermediate was
obtained by coupling 3-(1,3-benzoxazol-2-yl)naphthalen-2-ol with 4-sulphobenzenediazonium chloride fol-
lowed by reduction with sodium dithionate in water at pH 8–9. 3-(1,3-benzoxazol-2-yl)naphthalen-2-ol was
synthesized from 3-hydroxynaphthalene-2-carboxylic acid and 2-amino phenol in the presence of PCl3 in
chlorobenzene at 130–135◦C. All these compounds were characterized by FT-IR, 1H NMR, mass spectral and
elemental analysis. The synthesized compounds are fluorescent which absorbs in the range of 296 to 332 nm
while emits in the ranges of 368 to 404 nm with excellent quantum yield. All compounds were evaluated for in
vitro antibacterial activities against Escherichia coli and Staphylococcus aureus strains and in vitro antifungal
activity against Candida albicans and Aspergillus niger strains by using serial dilution method.
Keywords. Heterocyclic synthesis; benzoxazole; naphthoxazole; fluorescence; photophysical properties;
antibacterial activity; antifungal activity.
1. Introduction
The excellent photophysical properties like broad
spectral windows, high molar absorptivity values and
reasonably good fluorescence quantum efficiency have
made them to be of use as fluorescent probe and sensing
materials.14 In material chemistry, benzoxazoles find
applications as laser dyes and photochromatic agents.15
Some of the phenylaminonaphtho[1,2-d]oxazol-2-yl-
type compounds were reported as a sensor for water
in organic solvents by photo-induced electron transfer
(PET).16
There are reports available describing the synthesis
and biological activity of naphtho[1,2-d][1,3]oxazole5
and benzoxazole17 separately. However, there are no
reports available describing synthesis and biological
activity of benzoxazole derivatives incorporated with
naphthoxazole heterocycles in a single moiety. There-
fore, as a part of ongoing research work on synthesis of
biologically important fused heterocycles,18 we report
here the synthesis of novel 4-(1,3-benzoxazol-2-yl)-2-
phenylnaphtho[1,2-d][1,3]oxazole derivatives and their
antimicrobial activity study.
Benzoxazoles and naphthoxazoles are important class
of heterocyclic compounds because of their wide spec-
trum of biological and photochromatic activities. 2-
Substituted naphthoxazole is a major subunit occur-
ring in a number of biologically active compounds1 and
natural products.2 They find extensive use as fluores-
cent probes3 and as intermediates for dyes.4 Ortho-
substituted naphthoxazole derivatives show promising
inhibitory activity for protein tyrosine phosphatase-1B
(PTB-1B) and in vivo antidiabetic activity in SLM,
STZ-S and db/db mice models.5–7
A number of benzoxazole and naphthoxazole deriva-
tives possessing antifungal,8 antiinflammatory,9 anti-
tumour10 and antiHIV11 activities have been reported.
Some of the benzoxazole derivatives exhibit diverse
chemotherapeutic activity including anticancer agent12
NSC-693638 and antibacterial agents;13 some exam-
ples are UK-1, MUK-1 and DMUK-1 (figure 1).
The synthesized derivatives are the structural ana-
logues of bis(benzoxazole) natural product UK-1
(scheme 1), a secondary metabolite with interesting
biological activity. This UK-1 was also found to be
∗For correspondence
141

142
Kiran R Phatangare et al.
2. Experimental
O
OR1
OR2
All commercial reagents were used as received with-
out purification and all solvents were reagent grade.
The reaction was monitored by TLC using 0.25 mm E-
Merck silica gel 60 F254 precoated plates, which were
visualized with UV light. Melting points were mea-
sured on standard melting point apparatus from Sunder
Industrial Product, Mumbai and were uncorrected. The
FT-IR spectra were recorded on a Perkin Elmer 257
O
N
N
O
N
NH
N
N
O
CH3
NSC 693638
UK-1 (R1 = Me, R2 = H)
MUK-1 (R1 = Me, R2 = Me)
DMUK-1 (R1 = H, R2 = H)
1
spectrometer using KBr discs. H NMR spectra were
Figure 1. Various bioactive molecules containing benzoxa-
recorded on a Varian Cary Eclipse Australia, MR-
300 MHz, USA instrument using TMS as an internal
standard. Mass spectra were recorded on Finnigan Mass
spectrometer. The absorption spectra of the compounds
were recorded on a Spectronic Genesys 2 UV-Visible
spectrophotometer; UV-Visible emission spectra were
recorded on JASCO – FP 1520. Simultaneous DSC-
TGA measurements were performed on simultaneous
DSC-TGA Waters (India) Pvt. Ltd.
zole.
fluorescent, on excitation at 335 nm, it emits at 530 nm.
It binds to double strand DNA 10 times more tightly in
the presence of Mg2+ than in its absence. The decrease
in emission intensity is the detection tool for its binding
with DNA strand. It is also used as inhibitor of human
topoisomerase II.19 It shows wide spectrum of potential
anticancer activity against leukemia, lymphoma, and
certain solid tumour derived cell lines.20 The benzoxa-
zole derivatives are used as fluorescent probes21,22 and
sensors for the detection of different metal ions.23,24
In this study, one of the 1,3-benzoxazole ring of UK-1
is replaced by naphtho[1,2-d][1,3]oxazole ring and
studied for their biological activities.
2.1 Experimental procedure for the synthesis
of 3-(1,3-benzoxazol-2-yl)naphthalen-2-ol (3)
A mixture of 2-aminophenol 2 (1.09 g, 0.01 mol)
and 3-hydroxynaphthalene-2-carboxylic acid 1 (1.88 g,
0.01 mol) was refluxed (133–135◦C) in chlorobenzene
OH
OH
HO
a
+
O
COOH
H2N
N
3
1
2
HO3S
HO3S
b
+
Cl-
NH2
N2
5
4
SO3H
HO3S
NH2
+
OH
Cl-
N2
N
d
N
3
O
OH
c
N
O
N
6
7
Scheme 1. Synthesis of 1-amino-3-(1,3 benzoxazol-2-yl)naphthalene-2-
ol (7). Reagents and conditions: (a) PCl3, Chlorobenzene, Reflux (133–
135◦C), 4 h, 80%; (b) NaNO2, HCl, 0–5◦C, 45 min, 98%; (c) Methanol:
Water, pH 8–9, 0–5◦C (80: 20) 3 h, 90%; (d) Na2S2O4, NaOH, H2O, 90◦C,
1.5 h, 66%.

Experimental procedure for the synthesis of 3-(1,3-benzoxazol-2-yl)naphthalen-2-ol (3)
143
(10 mL) in the presence of PCl3 (2 g, 1.3 mL, 0.01 mol) robenzene (130–133◦C) (6 mL) up to the completion
for 4 h. After completion of reaction, the solid product of reaction (16–18 h) and was confirmed by TLC.
was precipitated out and was filtered to get crude pro- After cooling the reaction mass, solid product was fil-
duct 3 (yield 80%) which was further recrystalized form tered out and recrystalized from chloroform to afford
ethanol.
corresponding compounds 8–11 in 57–65% yield.
2.5 General experimental procedure for the synthesis
of 4-(1,3-benzoxazol-2-yl)-2-phenylnaphtho[1,2-
d][1,3]oxazole derivatives from intermediate 7
and substituted aromatic aldehydes (8–11)
2.2 Experimental procedure for the synthesis
of 4-{[3-(1,3-benzoxazol-2-yl)-2-hydroxynaphthalen-
1-yl]diazenyl}benzenesulphonic acid (6)
1-Amino-3-(1,3-benzoxazol-2-yl) naphthalen-2-ol 7
(0.010 mol) and corresponding aromatic substituted
aldehydes (0.010 mol) were heated in dimethylsulphox-
ide (6 mL) at 158–160◦C up to the completion of reac-
tion (10–12 h), confirmed by TLC. After cooling the
reaction mass, solid product was filtered out and recrys-
talized form chloroform to afford corresponding com-
pounds 8–11 in 62–72% yield.
Sulphanilic acid 4 (2.07 g, 0.012 mol) was dissolved
in water (10 mL) containing sodium carbonate of
(0.62 g) at 50–55◦C. A solution NaNO2 (0.84 g,
0.012 mol) in water (10 mL) was added to sulphanilic
acid solution in water and then this mixture was added
slowly to the conc. HCl (4 mL) at 0–5◦C for 30 min
and further stirred at this temperature for 1.5 h to
get 4-sulphobenzenediazonium chloride salt 5. This
was further coupled with the 3-(1,3-benzoxazol-2-
yl)naphthalene-2-ol 3 (2.61 g, 0.010 mol) at 0–5◦C at
pH 8–9 for 3 h and then at room temperature for 1 h in
methanol:water mixture (80:20). Then reaction mixture
was neutralized with acetic acid (9–10 mL) at pH 7,
methanol was removed under reduced pressure and then
filtered out to afford 4-{[3-(1,3-benzoxazol-2-yl)-2-
hydroxynaphthalen-1-yl]diazenyl}benzenesulphonic acid
6 (yield 90%).
2.6 Experimental procedure for the synthesis of
4-(1,3-benzoxazol-2-yl)-2-methylnaphtho [1,2-d] [1,3]
oxazole (12)
1-Amino-3-(1,3-benzoxazol-2-yl)naphthalen-2-ol (1.38 g,
0.005 mol) 7 was refluxed in the presence of acetic
anhydride (5 mL) up to completion of reaction (30 min)
which was confirmed by TLC. Reaction mass was
cooled and slowly poured on crushed ice with efficient
stirring. Solid product was filtered out and recrysta-
lized form ethyl alcohol to afford compound 12 in 73%
yields.
2.3 Experimental procedure for the synthesis
of 1-amino-3-(1,3-benzoxazol-2-yl)naphthalen-2-ol (7)
The azo compound 6 (4.45 g, 0.010 mol) was heated
in water containing NaOH (3.51 g, 0.088) at 50◦C
and sodium dithionate (3.78 g, 0.025 mol) was added
at 90◦C in portions over period of 1 h. The mixture
was heated at 90◦C at pH 8–9 until the colour of
azo get disappeared (1.5 h). The progress of the reac-
tion was monitored by TLC. After completion of reac-
tion, the reaction mass was neutralized up to pH 7,
filtered and washed well with water 2–3 times and
dried well to afford crude 1-amino-3-(1,3-benzoxazol-
2-yl)naphthalen-2-ol 7 in 66% yield. Crude product was
recrystalized in ethyl alcohol.
2.7 Spectral data of compounds (7–12)
2.7a 1-Amino-3-(1,3-benzoxazol-2-yl)naphthalen-2-ol
(7): Mp: 206–208◦C. FT-IR (KBr): 3510, 3452, 3357
(-NH2, -OH), 3028 (Aromatic -CH Stretching), 1615,
1585, 1477, (C=C, C=N ring stretching), 1222, 1132
(C–O stretching), 750 (Aromatic -CH out of plane
1
bending) cm−1. H NMR: (DMSO-d6)δ = 6.98 (d,
J = 7.9 Hz, 1H, Ar-H), 7.30–7.43 (dd, J = 7.8, 8.2,
1.8 Hz, 5H, Ar-H), 7.58 (d, J = 8.2, 1.9 Hz, 1H,
Ar-H), 7.93 (d, J = 8.5, 1.6 Hz, 1H, Ar-H), 8.83 (s,
1H, Ar-H), 9.96 (s, 2H, -NH2), 10.12 (s, 1H, -OH)
ppm. MS (m/z): 277.1 (M+1, 98%), 276.1 (M+, 26%),
275.1 (22%), 250.1 (89%) 248.2 (65%), 232.2 (23%)
124 (24%). Anal. Calcd. for C17H12N2O2: C, 73.90; H,
4.38; N, 10.14. Found: C, 73.87; H, 4.48; N, 10.03.
2.4 General experimental procedure for the synthesis
of 4-(1,3-benzoxazol-2-yl)-2-phenylnaphtho[1,2-
d][1,3]oxazole derivatives from intermediate 7
and substituted aromatic acids (8–11)
2.7b 4-(1,3-Benzoxazol-2-yl)-2-phenylnaphtho[1,2-d]
[1,3]oxazole (8): Mp: 210–212◦C. FT-IR (KBr):
3040 (Aromatic -CH streching), 1615, 1576 (C=C,
1-Amino-3-(1,3-benzoxazol-2-yl) naphthalen-2-ol 7
(0.010 mol), corresponding substituted aromatic acid
(0.010 mol) and PCl3 (0.015 mol) were refluxed in chlo-

144
Kiran R Phatangare et al.
C=N ring stretching), 1217, 1126 (C–O stretching), stretching), 780, 695 (Aromatic -CH out of plane bend-
1
740, 695 (Aromatic -CH out of plane bending vibra- ing vibration) cm−1. H NMR: (DMSO-d6)δ = 7.10–
tion) cm−1. 1H NMR: (CDCl3) δ = 7.43–7.46 (m, J = 7.26 (m, J = 8.4, 8.6, 2.2 Hz, 4H, Ar-H), 7.41–7.47 (m,
8.2, 2.1 Hz, 2H, Ar–H), 7.59–7.66 (m, J = 8.4, 1.8 Hz, J = 8.9, 7.1, 1.5 Hz, 4H, Ar-H), 7.52–7.78 (m, J = 8.5,
4H, Ar–H), 7.73–7.84, (m, J = 8.7, 7.3, 0.2 Hz, 2H, 7.2, 1.8 Hz, 4H, Ar-H), 7.90 (m, J = 2.1, 0.9 Hz, 1H,
Ar–H), 7.94 (dd, J = 7.2, 2.1 Hz, 1H, Ar–H), 8.12 Ar-H), 8.08–8.12 (d, J = 8.1, 1.8 Hz, 2H, Ar-H), 8.22
(d, J = 8.4 Hz, 1H, Ar–H), 8.48 (dd, J = 8.1, 1.8, (d, J = 6.9, 0.9 Hz, 1H, Ar-H), 8.60 (d, J = 8.4 Hz,
3 Hz, 2H, Ar–H), 8.64 (d, J = 8.1 Hz, 1H, Ar–H), 8.75 1H, Ar-H), 8.74 (s, 1H, Ar-H) ppm. MS (m/z): 455.3
(s, 1H, Ar–H) ppm. MS (m/z): 363.3 (M+1, 100%), (M+1, 99%), 454.1 (M+, 57%), 362 (47%), 250 (38%),
277.3 (54%), 251.6 (48%), 233.1 (37%). Anal. Calcd. 232 (41%). Anal. Calcd. for C30H18N2O3: C, 79.28; H,
for C24H14N2O2: C, 79.55; H, 3.89; N, 7.73. Found: C, 3.99; N, 6.16. Found: C, 79.35; H, 3.89; N, 6.11.
79.51; H, 3.92, N, 7.70.
2.7e 4-[4-(1,3-Benzoxazol-2-yl)naphtho [1,2-d][1,3]
oxazol-2-yl]phenol (11): Mp: 272–275◦C. FT-IR
2.7c 4-(1,3-Benzoxazol-2-yl)-2-(4-nitrophenyl)
naphtho[1,2-d][1,3]oxazole (9): Mp: >300◦C. FT-
(KBr): 3365, 3352 (O–H), 3045 (-CH streching), 1626,
IR (KBr): 3042 (Aromatic -CH streching), 1624, 1575
1575 (C=C, C=N ring stretching), 1215, 1122 (C–O
(C=C, C=N ring stretching), 1538, 1330 (-NO2) 1210,
stretching), 845, 730 (Aromatic -CH out of plane bend-
1
ing vibration) cm−1. H NMR: (DMSO-d6)δ = 6.90
1126 (C–O stretching), 835, 740 (Aromatic -CH out of
plane bending vibration) cm−1. 1H NMR: (CDCl3)δ =
7.43–7.49 (m, J = 9.9, 9.3 Hz, 2H, Ar–H), 7.64–7.82
(m, J = 7.8, 7.9 Hz, 3H, Ar-H), 7.94 (t, J = 9.3,
1.5 Hz, 1H, Ar-H), 8.11 (d, J = 8.1, 1.8 Hz, 1H, Ar-H),
8.43–8.46 (d, J = 9 Hz, 2H, Ar-H), 8.59–8.65 (t, J =
9.0, 7.2 Hz, 3H, Ar-H), 8.79 (s, 1H, Ar-H), ppm. MS
(m/z): 408.2 (M+1, 99%), 407.3 (M+, 21%), 378.1
(23%), 362.2 (90%), 350.2 (12%), 301.1 (19%). Anal.
Calcd. for C24H13N3O4: C, 70.76; H, 3.22; N, 10.31;
Found: C, 70.71; H, 3.26; N, 10.39.
(t, J = 7.8, 1.4 Hz, 1H, Ar-H), 7.00 (d, J = 7.9 Hz,
1H, Ar-H), 7.10–7.18 (t, J = 10.8, 7.8 Hz, 2H, Ar–
H), 7.38–7.48, (m, J = 7.2, 1.8 Hz, 2H, Ar–H), 7.58
(d, 7.4 Hz, 1H, Ar–H), 7.68 (m, J = 8.2, 1.8 Hz,
1H, Ar–H), 7.90–8.02 (dd, J = 9.2, 1.2 Hz, 2H, Ar–
H), 8.36 (dd, J = 8.1, 1.5 Hz, 1H, Ar–H), 8.72 (d,
J = 8.2 Hz, 1H, Ar–H), 8.84 (s, 1H, Ar–H), 10.48 (s
1H, Ar-OH) ppm. 1H NMR (D2O Exchange of Comp
11): (DMSO-d6) δ = 4.81 (s, 1H, H-OD), 6.90 (t,
J = 7.8, 1.4 Hz, 1H, Ar–H), 7.00 (d, J = 7.9 Hz,
1H, Ar–H), 7.10–7.18 (t, J = 10.8, 7.8 Hz, 2H, Ar–
H), 7.38–7.48 (m, J = 7.2, 1.8 Hz, 2H, Ar–H), 7.58
(d, J = 7.4 Hz, 1H, Ar-H), 7.68 (m, J = 8.2, 1.8 Hz,
1H, Ar-H), 7.90–8.02 (dd, J = 9.2, 1.2 Hz, 2H, Ar-
H), 8.36 (dd, J = 8.1, 1.5 Hz, 1H, Ar-H), 8.72 (d,
2.7d 4-(1,3-Benzoxazol-2-yl)-2-(3-phenoxyophenyl)
naphtho[1,2-d][1,3]oxazole (10): Mp: 160–162◦C.
FT-IR (KBr): 3065 (Aromatic -CH streching), 1628,
1565 (C=C, C=N ring stretching), 1214, 1134 (C–O
Scheme 2. Synthesis of 4-(1,3-benzoxazol-2-yl)-2-phenylnaphtho[1,2-
d][1,3]oxazole derivatives (8–12). Reaction conditions: (a) Chlorobenzene,
PCl3 130–133◦C, 16–18 h (57–65%); (b) DMSO, 158–160◦C, 10–12 h
(62–72%); (c) 100–104◦C, 1–1.5 h (73%).

Experimental procedure for the synthesis of 3-(1,3-benzoxazol-2-yl)naphthalen-2-ol (3)
145
J = 8.2 Hz, 1H, Ar–H), 8.84 (s, 1H, Ar–H), ppm. 7.35–7.43 (m, J = 7.8, 6.9, 1.4 Hz, 2H, Ar-H), 7.52–
MS (m/z): 379.6 (M+1, 91%), 378 (M+, 51%), 362.2 7.78 (m, J = 8.8, 7.6, 2.2 Hz, 5H, Ar-H), 8.12 (d, J =
(58%), 350.2 (52%), 277.2 (16%), 261.1 (27%), 250.6 8.1 Hz, 1H), 8.96 (s, 1H, Ar-H) ppm. MS (m/z): 301.7
(76%), 232.2 (37%). Anal. Calcd. for C24H14N2O3: C, (M+1, 100%), 300.2 (M+, 51%), 260.1 (16%), 250.2
76.18; H, 3.73; N, 7.40; Found: C, 76.69; H, 3.82; (89%), 232.2 (32%). Anal. Calcd. for C19H12N2O2:
N, 7.56.
C, 75.99; H, 4.03; N, 9.33; Found: C, 75.89; H, 4.12;
N, 9.26.
2.7f 4-(1,3-Benzoxazol-2-yl)-2-methylnaphtho[1,2-
d][1,3]oxazole (12): Mp: 190–192◦C. FT-IR (KBr):
3055 (Aromatic -CH streching), 1616, 1555 (C=C,
C=N ring stretching), 1205, 1110 (C-O stretching),
740 (Aromatic C-H out of plane bending vibration)
3. Results and discussion
The synthetic scheme for the preparation of 4-(1,3-
benzoxazol-2-yl)-2-phenylnaphtho[1,2-d][1,3]oxazole
1
cm−1. H NMR: (DMSO-d6)δ = 2.64 (s, 3H, -CH3),
Table 1. Synthesis of 4-(1,3-benzoxazol-2-yl)naphtho[1,2-d][1,3]oxazole derivatives from intermediate 7 and substituted
aromatic aldehydesa.
Sr. No.
Substituted aromatic aldehydes
Product
Time (h)
Yieldb (%)
1
10
68
2
3
12
11
72
69
4
10.5
62
aSolvent: DMSO, Temp: 158–160◦C, Time: 10–12 h.
bIsolated yield

146
Kiran R Phatangare et al.
The series of 4-(1,3-benzoxazol-2-yl)-2-phenylnaphtho
derivatives is shown in schemes 1 and 2. 3-(1,3-
Benzoxazol-2-yl) naphthalen-2-ol 3 was prepared by [1,2-d][1,3]oxazole derivatives were synthesized by
reported procedure from 3-hydroxynaphthalene-2- three different routes from intermediate 1-amino-3-
carboxylic acid 1 and 2-aminophenol 2 in the presence (1,3-benzoxazol-2-yl) naphthalen-2-ol 7 as shown in
of PCl3 in chlorobenzene at 130–135◦C.25 Sulphanilic scheme 2. Compound 7 on treatment with different aro-
acid was diazotized to get 4-sulphobenzenediazonium matic acids in the presence of phosphorus trichloride
chloride 5, which was further coupled with 3 to get azo (PCl3) in chlorobenzene at reflux temperature (130–
compound 6. This azo compound 6 was reduced by 133◦C) for 15–18 h or with different aromatic alde-
using sodium dithionate at pH 8–9 to get 1-amino-3- hydes in dimethylsulphoxide at 158–160◦C for 10–
(1,3-benzoxazol-2-yl)naphthalene-2-ol 726 (scheme 1) 12 h gives 4-(1,3-benzoxazol-2-yl)naphtho[1,2-d][1,3]
1
which was confirmed by FT-IR, H-NMR, mass spec- oxazole derivatives 8–11. Substituted aromatic alde-
tral analysis and its M+1 peak was found to be at 277.1.
hyde gives product with good yield in short reaction
Table 2. Synthesis of 4-(1,3-benzoxazol-2-yl)naphtho[1,2-d][1,3]oxazole derivatives from intermediate 7 and substituted
aromatic carboxylic acidsc.
Sr. No.
Substituted aromatic acids
Product
Time (h)
Yieldd (%)
1
18
62
2
3
16 65
16.5
63
4
16
57
cSolvent: Chlorobenzene, Reagent: PCl3 Temp: 130–133◦C, Time: 16–18 h.
dIsolated yield

Experimental procedure for the synthesis of 3-(1,3-benzoxazol-2-yl)naphthalen-2-ol (3)
147
(a)
(b)
Figure 2. Day light and UV light photographs of the molecules in DMF. (a)
Day light photograph and (b) UV-light photograph.
time (table 1) as compared to substituted aromatic acids 3.3 Preparation of the plates
(table 2).
Plates were prepared under aseptic conditions. A ste-
rile 96 well plate was labelled. A volume of 100 μL of
test material in 10% (v/v) DMSO (usually a stock con-
centration of 4 mg/ml) was pipetted into the first row of
the plate. To all other wells 50 μL of nutrient broth was
added. Serial dilutions were performed using a mul-
tichannel pipette. Tips were discarded after use such
that each well had 50 μL of the test material in seri-
ally descending concentrations. To each well, 10 μL of
resazurin indicator solution was added. Using a pipette
30 μL of 3.3 × strength isosensitized broth added to
each well to ensure that the final volume was single
strength of the nutrient broth. Finally, 10 μL of bacterial
suspension (5 × 106 cfu/ mL) was added to each well to
achieve a concentration of 5 × 105 cfu/ mL. Each plate
was wrapped loosely with cling film to ensure that bac-
teria did not become dehydrated. Each plate had a set
of controls: a column with a broad-spectrum antibiotic
as positive control, a column with all solutions with the
exception of the test compound, and a column with all
solutions with the exception of the bacterial solution,
adding 10 μL of nutrient broth instead. The plates were
Treatment of 7 with acetic anhydride at reflux
temperature furnishes 4-(1,3-benzoxazol-2-yl)-2-
methylnaphtho[1,2-d][1,3]oxazole 12. All synthesized
1
compounds were confirmed by FT-IR, H NMR and
mass spectral analysis. FT-IR spectra of compound 9
shows peak at 1538 and 1330 cm−1 clearly indicates the
presence of –NO2 group in the structure. Compound
11 shows distinct peak for –OH in FTIR at 3352–
3365 cm−1 and phenolic –OH signal at 10.48 δ ppm in
1H-NMR and was confirmed by D2O exchange. The
phenolic –OH peaks were disappeared in D2O exchange
with additional peak at 4.80–4.82 δ ppm. Mass spectral
data for compounds 9 and 12 show M+1 peak at 408.2
and 301.1, respectively which are in well agreement
with their molecular weight.
3.1 Biological activity
All compounds were evaluated for in vitro antibacterial
activities against E. coli and S. aureus strains and in
vitro antifungal activity against C. albicans and A. niger
strains by using serial dilution method.
2
Absorption in DMF
3.2 General
8
1.6
9
Incubator at 37◦C; pipettes of various sizes (Gilson);
sterile tips, 100, 200, 500, and 1000 μL; sterile normal
saline; sterile isosensitest agar (Southern Group Lab-
oratory, SGL); antibiotic solutions (Sigma–Aldrich);
sterile solution of 10% (v/v) DMSO in water (Sigma–
Aldrich) were used. Isosensitest medium was used
throughout the assay, as it is pH buffered. Although
NCCLS recommends the use of Mueller Hinton me-
dium for susceptibility testing,27 the isosensitest me-
dium had comparable results for most of the tested
bacterial strains.28
10
1.2
11
0.8
12
0.4
0
290
310
330
350
370
390
Wavelength (nm)
Figure 3. Absorption of compounds 8–12 in DMF.

148
Kiran R Phatangare et al.
Table 4. Quantum yield of compounds
1000
Emission in DMF
8–12 in DMF.
8
800
600
400
200
0
Compound No
Quantum yield
9
8
9
10
11
12
0.206
0.129
0.308
0.047
0.274
10
11
12
Absorption λmax and emission λmax were
measured in nm.
Samples were prepared in DMF.
Analyses were carried out at room
temperature
330
350
370
390
410
430
450
470
490
Wavelength (nm)
Figure 4. Emission of compounds 8–12 in DMF.
4-OH phenyl ring to benzoxazole ring via fused naph-
thoxazole ring system and electron withdrawing ability
of –NO2 in compound 9 (table 3)
prepared in triplicate, and placed in an incubator set at
37◦C for 18–24 h. The colour change was assessed visu-
ally. Any colour changes from purple to pink or colour-
less were recorded as positive. The lowest concentra-
tion at which colour change occurred was taken as the
MIC value. The average of three values was calculated
and that was the MIC for the test material and bacterial
or fungal strain.29
An effective compound for the biological application
should have good fluorescent intensity, high quantum
yield and high photostability. Quantum yield of all
compounds were recorded by using tinopal as a refe-
rence standard. Absorption and emission characteristics
of standard as well as unknown samples were measured
at different concentration of unknown samples and
standard at (2, 4, 6, 8 and 10 ppm level). Absorbance
intensity values were plotted against emission intensity
values. A linear plot was obtained. Gradients were
calculated for each unknown compound and for stan-
dard. All the measurements were done by keeping the
parameters such as solvent and slit width constant.
Relative quantum yield of all synthesized compounds
8–12 were calculated by using the formula 1.30
3.4 Photophysical properties
All synthesized compounds are fluorescent (figure 2b)
and were studied for their photophysical properties.
Their absorption and emission properties were recorded
in DMF. All these compounds absorb from 296 to
332 nm (figure 3) and emit from 368 to 404 nm
(figure 4) with good Stokes shift ranges from 39 to
108 nm. Out of these compounds, compound 8 shows
good Stokes shift with 108 nm. As compared to com-
pound 9, compound 11 shows larger Stokes shift, this
property attributed due to electron donating ability of
–OH in compound 11 for easy flow of electron from
Formula 1: Relative fluorescence quantum yield
ꢀ
ꢁ
ꢂ ꢀ
ꢁ
ꢂ
ꢀX = ꢀST GradX GradST ηX2 ηS2T
,
where
ꢀX:
ꢀST:
Quantum yield of unknown sample
Quantum yield of standard used
Gradient of unknown sample
GradX:
Table 3. Absorption and emission at 1 × 10−6 M concen-
tration of compounds 8–12 in DMF.
GradST: Gradient of standard used
Absorption
λmax(nm)
Emission
λmax(nm)
Stokes shift
(nm)
Table 5. Thermal gravimetric analysis
(TGA) of compound 8–12.
Compounds
8
9
10
11
12
296
332
320
326
320
404
371
368
404
384
108
39
48
78
64
Compound
TGA
8
9
10
11
12
222 (97.50%)
223 (98.41%)
236 (98.34%)
216 (99.67%)
255 (98.12%)
Absorption λmax and emission λmax were measured in nm.
Samples were prepared in DMF.
Analyses were carried out at room temperature
TGA was measured in ◦C

Experimental procedure for the synthesis of 3-(1,3-benzoxazol-2-yl)naphthalen-2-ol (3)
149
Figure 5. TGA curves of compound 8–12.
Refractive index of solvent for standard was determined for the compounds. The MIC (μg/mL)
ηX2 :
sample
values recorded in table 6 indicate that most of the
tested compounds showed variable inhibitory growth
effects against tested bacterial and fungal strains.
Antimicrobial data were compared with standard drug
Streptomycin and Fluconazole.
The MIC values from table 6 reveals that com-
pound 10, 11 and 12 showed good to moderate activity
against E. coli and S. aureus. Compound 8 shows activ-
ity against S. aureus while compound 9 showed good
activity against E. coli.
ηS2T:
Refractive index of solvent for sample.
The fluorescence quantum yields of all compounds
were recorded in DMF at room temperature as shown
in table 4. Quantum yields of all compounds are found
to be good and ranges from 0.047 to 0.308 (table 4).
3.5 Thermal stability
To investigate the thermal stability of synthesized
compounds 8–12 the thermal stability studies have been
carried out using thermo gravimetric analysis (TGA)
technique. The thermal gravimetric analysis has been
carried out in the temperature range of 50–600◦C under
nitrogen atmosphere. TGA result in table indicates that
the naphthoxazole ring skeleton is 98% stable up to
216◦C (compound 11). Above this temperature all com-
pounds start to decompose and show the major loss in
weight. The compound 12 shows the highest thermal
stability up to 255◦C (98.12%). The comparison of Td
(decomposition temperature) showed that the thermal
stability of the compound 8–12 decreases in the order
12 > 10 > 9 > 8 > 11 as shown in table 5. TGA
analysis curve of the compounds 8–12 is as shown in
figure 5.
As compared to the antibacterial activity all synthe-
sized compounds (8–12) showed good antifungal acti-
vity against antifungal strains C. albicans and A. niger.
Results mentioned in table 6 showed that compounds
Table 6. Antibacterial and antifungal activities of newly
synthesized compounds indicated by MIC (μg/mL) using the
modified resazurin assay.
Compounds
Bacterial strain
Fungal strain
E. coli S. aureus C. albicans A. niger
8
9
10
11
625
156.2
156.2
156.2
156.2
125
156.2
625
156.2
156.2
156.2
125
156.2
78
312.5
78
156.2
–
125
78
78
312.5
78
156.2
–
125
12
Streptomycin
Fluconazole
–
–
3.6 Antimicrobial activity
Antimicrobial activities were expressed in MIC.
MIC: Minimal inhibitory concentration values.
Bacterial strain: E. coli; S. aureus.
Fungal Strain: C. albicans; A. niger.
Solvent used: DMSO (Dimethyl sulphoxide).
The novel compounds 8–14 were evaluated for their
in vitro antibacterial activity against E. coli and S.
aureus strains and in vitro antifungal activity against C.
albicans and A. niger strains by using serial dilution
Standard: Bacterial strain: Streptomycin- 125 μg/mL, Fungal
method. The minimum inhibitory concentration (MIC) strains: Fluconazole- 125 μg/mL.

150
Kiran R Phatangare et al.
8, 9, 11 and 12 showed good inhibition of growth in
case of C. albicans as well as A. niger while compound
10 showed moderate activity against both antifun-
gal strain. Electron donating and electron withdrawing
groups present on phenyl ring does not affect the growth
inhibitory activity against tested bacterial and fungal
strains.
In general, most of the tested compounds revealed
better activity against the antibacterial strain (E. coli,
S. aureus) and antifungal strain (C. albicans, A.
niger). Novel compounds are reactive against fun-
gal strain as compared to bacterial strain tested over
microorganisms.
3. Tanaka K, Kumagai T, Aoki H, Deguchi M and Iwata S
2001 J. Org. Chem. 66 7328
4. Abbady M A 1966 Preparation and application of
some new naphthoxazole dyes. M. Sc. Thesis, Assiut
University Assiut, Egypt
5. Kumar A, Ahmad P, Maurya R A, Singh A B and
Srivastava A K 2009 Eur. J. Med. Chem. 44 109
6. Malamas M S, Sredy J, Katz Moxham A, Xu W X,
Mcdevitt R, Adedayo F O, Sawiciki D R, Seetaller L,
Sullivan L and Taylor J R 2000 J. Med. Chem. 43
1293
7. Malamas M S, Sredy J, Gunavan I, Mihan B, Sawichi
D R, Seestaller L, Sullivan D and Flam B R 2000 J. Med.
Chem. 43 995
8. Ertan T, Yildiz I, Tekiner-Gulbas B, Bolelli K, Temiz-
Arpaci O, Yalcin I, Aki E, Ozkan S and Kaynak F 2009
Eur. J. Med. Chem. 44 501
9. Dunwell D W and Delme 1977 Eur. J. Med. Chem. 20
797
4. Conclusion
10. White A W, Curtin N J, Eastman B W, Golding B T,
Hostomsky Z, Kyle S, Li J, Maegley K A, Skalitzky D J,
Webber S E, Yu X H and Griffin R 2004 J. Bioorg. Med.
Chem. Lett. 14 2433
11. Novelli F, Tasso B, Sparatore F and Sparatore A 1997
Farmaco 52 499
12. (a) McKee M L and Kerwin S M 2008 Bioorg. Med.
Chem. 16 1775; (b) Oksuzoglu E, Temiz-Arpaci O,
Tekiner-Gulbas B, Eroglu H, Sen G, Alper S, Yildiz I,
Diril N, Aki-Sener E and Yalcin I 2008 Med. Chem. Res.
16 1
13. Sun L Q, Chen J, Bruce M, Deskus J A, Epperson J R,
Takaki K, Johnson V G, Iben L, Mahle C D, Ryan E and
Xu C 2004 Bioorg Med. Chem. Lett. 14 3799
14. (a) Costa S P G, Oliveira E, Lodeiro C and Raposo
M M 2007 Sensors 7 2096; (b) Shamsipur M, Poursaberi
T, Karami A R, Hosseini M, Momeni A, Alizadeh N,
Yousefi M and Ganjali M R 2004 Anal. Chim. Acta. 501
55; (c) Zang X B, Peng J, He C L, Shen G L and Yu R Q
2006 Anal. Chim. Acta. 567 189
We have designed and synthesized a series of
novel 4-(1,3-benzoxazol-2-yl)-2-phenylnaphtho[1,2-
d]1,3]oxazole derivatives. The photophysical property
study shows that all are fluorescent and absorbs from
296 to 332 nm while emits in the ranges of 368 to
404 nm with excellent quantum yield. These novel com-
pounds were evaluated for in vitro antibacterial activity
against E. coli and S. aureus and antifungal activity
against C. albicans and A. niger using serial dilution
technique. The synthesized compounds show good
antifungal activity than that of antibacterial. All synthe-
1
sized compounds were confirmed by FT-IR, H NMR
and mass spectral analysis. We believe that the insights
gained in this study would be useful for the develop-
ment of potential drug candidates derived from naphtho
[1,2-d] [1,3] oxazole derivatives in the development of
novel antiinfective agents.
15. (a) Heathcock C H 1991 In: Comprehensive organic
synthesis B M Trost, and I Flemming (eds) New York:
Pergamon Press Vol 2; (b) Varga A, Aki Sxener E, Yalcin
I, Temiz Arpaci O, Tekiner Gulbasx B, Cherepnev G and
Molnar J 2005 In Vivo 19 1087
16. Yousuke O, Haruka E and Katsuhira Y 2009 Dyes
Pigments 82 58
Acknowledgements
The authors are thankful to sophisticated analytical
instrument facility (SAIF), Indian Institute of Techno-
1
logy (IIT) Mumbai for providing the H NMR and
17. Ooyama Y, Nonami K, Watanabe S and Yoshida K 2008
Dyes Pigments 77 315
Mass facility. One of the authors KRP is thankful
to the University Grants Commission (UGC)-SAP for
financial support.
18. (a) Padalkar V S, Borse B N, Gupta V D, Phatangare
K R, Patil V S and Sekar N 2011 J. Het. Chem. (Arti-
cle Accepted, Manuscript ID: JHET-11–0566.R1); (b)
Padalkar V S, Borse B N, Gupta V D, Phatangare K R,
Patil V S, Umape P G and Sekar N 2011 Arab. J. Chem
(Article Accepted, doi:10.1016/j.arabjc.2011.12.006)
19. Reynolds M b, DeLuca M R and Kerwin S M 1999
Bioorg. Chem. 27 326
20. Devinder K, Melissa R J, Michael B R and Sean M K
2002 Bioorg. Med. Chem. 10 3997
21. Xu Y and Pang Y 2010 Chem. Commun. 46 4070
22. Kim T I, Kang H J, Han G, Chung S J and Kim Y 2009
Chem. Commun. 45 5895
References
1. (a) Devinder K, Jacob M R, Reynolds M B and
Kerwin S M 2002 Biorg. Med. Chem. 10 3997; (b) Sato
Y, Yamada M, Yoshida S, Soneda T, Ishikawa M, Nizato
T, Suzuki K and Konno F 1998 J. Med. Chem. 41 3015;
(c) Katz L 1953 J. Am. Chem. Soc. 75 712
2. (a) Rodriguez A D, Ramirez C, Rodriguez I I and
Gonzalez E 1999 Org. Lett. 1 527; (b) Kobayashi J,
Madono T and Shigemori H 1995 Tetrahedron Lett. 36
5589
23. Chen W, Wright B D and Pang Y 2012 Chem. Commun.
48 3824

Experimental procedure for the synthesis of 3-(1,3-benzoxazol-2-yl)naphthalen-2-ol (3)
151
24. Yan L, Ye Z, Peng C and Zhang S 2012 Tetrahedron 68
2725
25. Matsui, Kuroda 1967 Kogyo Kagaku Zasshi 70 2325
26. Rangnekar D W and Rajadhyaksha D D 1986 Dyes
Pigments 7 365
M7-A4. 2000 National Committee for Clinical Labora-
tory Standards, PA: Wayne
28. Koeth L M, King A, Knight May J, Miller Phillips I and
Poupard J A 2000 J. Antimicrob. Chemother. 46 369
29. Sarker S D, Nahar L and Kumarasamy Y 2007 Methods
42 321
27. National Committee for Clinical Laboratory Standards.
Methods for dilution antimicrobial susceptibility tests 30. Padalkar V S, Tathe A B, Gupta V D, Patil V S,
for bacteria that grow aerobically. Approved standard Phatangare K R and Sekar N 2012 J. Fluoresc. 22 311