Synthesis and antimicrobial properties of 1,3,4-oxadiazole analogs containing dibenzosuberane moiety

Article abstract of DOI:10.5935/0103-5053.20130275

A series of ten novel 1,3,4-oxadiazole analogs containing dibenzosuberane moiety were synthesized using linear as well as convergent synthesis approach. All the compounds were characterized by mass spectrometry, infrared (IR), ¹H and ¹³C nuclear magnetic resonance (¹H NMR and ¹³C NMR) spectroscopies and elemental analysis. These compounds were evaluated for antibacterial and antifungal activities. Among ten analogs, four compounds, namely, 8a, 8d, 8e and 8j were found to be highly active antibacterial and antifungal agents.

Full text of DOI:10.5935/0103-5053.20130275

http://dx.doi.org/10.5935/0103-5053.20130275
J. Braz. Chem. Soc., Vol. 25, No. 1, 104-111, 2014.
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Article
A
Synthesis and Antimicrobial Properties of 1,3,4-Oxadiazole Analogs Containing
Dibenzosuberane Moiety
Manjunath Moger,a,b Vijay Satam,a Darshan Raj C. Govindaraju,c Paniraj A. S.,a
Vadiraj S. Gopinath,a Rama Mohan Hindupura and Hari N. Pati*,a
aAdvinus Therapeutics Ltd., 21 & 22, Phase II, Peenya Industrial Area, Bangalore 560058, Karnataka, India
bDepartment of Chemistry, Mangalore University, Mangalagangotri 574199, Karnataka, India
cDepartment of Bio-Medicinal Research, Vidya Herbs Pvt. Ltd., Bangalore 562106, Karnataka, India
Uma série de dez novos análogos de 1,3,4-oxadiazóis contendo uma parte dibenzosuberano
foram sintetizados usando tanto uma aproximação de síntese linear, quanto convergente. Todos os
compostos foram caracterizados por espectrometria de massas, espectroscopias no infravermelho
(IR), de ressonância magnética nuclear de 1H (1H NMR ) e 13C (13C NMR) e análise elementar.
As atividades bactericidas e antifúngicas destes compostos foram avaliadas, determinando-se
que entre estes, quatro derivados, especificamente 8a, 8d, 8e e 8j, foram altamente bactericidas
e antifúngicos.
A series of ten novel 1,3,4-oxadiazole analogs containing dibenzosuberane moiety were
synthesized using linear as well as convergent synthesis approach. All the compounds were
characterized by mass spectrometry, infrared (IR), 1H and 13C nuclear magnetic resonance (1H NMR
and 13C NMR) spectroscopies and elemental analysis. These compounds were evaluated for
antibacterial and antifungal activities. Among ten analogs, four compounds, namely, 8a, 8d, 8e
and 8j were found to be highly active antibacterial and antifungal agents.
Keywords: dibenzosuberane, 1,3,4-oxadiazole, antibacterial, antifungal
Introduction
pharmaceutical intermediate, dibenzazepine, makes
dibenzosuberane an attractive drug scaffold.
The rigid, tricyclic framework of dibenzosuberane
(10,11-dihydro-5H-dibenzo[a,d]cycloheptene, (A),
Figure 1) constitutes an integral part of the structure of
molecules that are known to be effective for the treatment
of depressive disorders.1 Analogs of dibenzosuberane such
as amitriptyline2 ((B), Figure 1) and nortriptyline3 ((C),
Figure 1) are well known tricyclic antidepressants which are
used as first line medicines in the treatment of migraines,
tension headaches, anxiety, psychosis, aggression and
violent behavior. Derivative of dibenzosuberane, 1,1a,6,10b-
tetrahydrodibenzo[a,e]cyclopropa[c]cycloheptene ((D),
Figure 1), obtained on annellation of a cyclopropyl ring to
the dibenzosuberane framework, has been incorporated in
the structure of potent multiple drug resistance modulators.4
Easy access and close structural resemblance to popular
Figure 1. Structures of dibenzosuberane (A), amitriptyline (B),
nortriptyline (C), 1,1a,6,10b-tetrahydrodibenzo[a,e]cyclopropa[c]
cycloheptene (D), 2,5-disubstituted-1,3,4-oxadiazole (E) and
1,3,4-oxadiazole analogs containing dibenzosuberane unit (8a-8j).
*e-mail: hari.pati@advinus.com

Vol. 25, No. 1, 2014
Moger et al.
105
2,5-Disubstituted-1,3,4-oxadiazoles ((E), Figure 1)
are known to exhibit a broad range of potent biological
activities.A number of 1,3,4-oxadiazoles having appropriate
substituents at 2 and 5 position are widely used as
antimicrobial,5 anti-HIV,6 analgesic,7 antiinflammatory,8,9
anticonvulsant,10,11 and antitumor12,13 agents. We envisaged
that attachment of dibenzosuberane framework to versatile
1,3,4-oxadiazole ring would produce synergistic effect
and lead to novel hybrid molecules that may possess
interesting biological activities. To validate this hypothesis,
a series of ten novel hybrid molecules (8a-8j, Figure 1)
in which a derivative of dibenzosuberane, 1,1-difluoro-
1a,10b-dihydrodibenzo[a,e]cyclopropa[c]cycloheptane,
was linked to 2-methyl-5-(substituted-phenyl)-1,3,4-
oxadiazole ring were synthesized.All ten novel compounds
were characterized by mass spectrometry, IR and NMR
spectroscopy and elemental analysis and evaluated for
antimicrobial properties. The study revealed that a number
of novel dibenzosuberane containing 1,3,4-oxadiazole
analogs possessed excellent antibacterial as well as
antifungal activity.
approach as depicted in Scheme 2. 2-Chloromethyl-
5-(substituted-phenyl)-1,3,4-oxadiazoles15 (12a-12j)
needed for the convergent synthesis route were
prepared by reacting appropriately substituted benzoic
acids (9a-9j) with hydrazine hydrate in the presence of
ethyl chloroformate in DCM to obtain corresponding
hydrazides (10a-10j) which were further reacted with
chloroacetyl chloride in ethyl acetate under reflux to afford
corresponding N’-(2-chloroacetyl)-substituted-phenyl
hydrazides (11a-11j). Compounds (11a-11j) thus obtained
were cyclized in phosphorus oxychloride at 80 °C to yield
corresponding 2-chloromethyl-5-(substituted-phenyl)-
1,3,4-oxadiazoles (12a-12j). Coupling of compound 314
with suitable 2-chloromethyl-5-(substituted-phenyl)-1,3,4-
oxadiazole (12a-12j) in DMF in the presence of sodium
hydride gave desired dibenzosuberane containing analogs
of 1,3,4-oxadiazole (8a-8j) in good to very good (60-77%)
yield. All the compounds were purified by column
chromatography using silica gel and gradient (0-50%)
ethyl acetate in hexane as the eluent and characterized by
1H NMR, 13C NMR, IR spectroscopy, mass spectrometry
and elemental analysis.
Results and Discussion
Antibacterial and antifungal activity of 1,3,4-oxadiazole
Synthesis of novel 1,3,4-oxadiazole analogs containing
analogs containing dibenzosuberane unit (8a-8j)
dibenzosuberane moiety (8a-8j)
With a range of target molecules at hand, their
antibacterial activity against four bacterial strains namely,
Staphylococcus aureus, Escherichia coli, Pseudomonas
aeroginosa and Klebsiella pneumonia was determined
using disc diffusion method16,17 and compared with
well-known antibacterial drug, nitrofurazone. The
minimum inhibitory concentration (MIC, µg mL-1) was
determined for each compound in triplicate experiments,
the values were averaged and are presented in Table 1.
Among ten analogs, four analogs 8a, 8d, 8e and 8j showed
very good activity against all the bacterial stains. Except
three compounds 8g, 8h and 8i remaining all compounds
were found to be active against Staphylococcus aureus.
Out of ten analogs, two analogs 8b and 8h were found
to be inactive against Escherichia coli. Eight analogs
namely, 8a, 8b, 8d, 8e, 8f, 8g, 8h, and 8j showed very
good activity against Pseudomonas aeroginosa. Two
analogs 8f and 8i were found to be inactive against
Klebsiella pneumonia. The values presented in Table 1
reveal that type of substituent on the phenyl ring directly
attached to 1,3,4-oxadiazole ring has a significant impact
on the antibacterial activity of these novel analogs.
In particular, electron donating methoxy substituent
decreases the activity to a greater extent. Halogen
substituent, especially fluorine, at the para position on
In order to synthesize novel 1,3,4-oxadiazole analogs
containing dibenzosuberane unit (8a-8j), first, we
adopted linear strategy as disclosed in Scheme 1.
Dibenzosuberenone 1 was heated with sodium
chlorodifluoroacetate in triglyme at 180-190 °C to obtain
1,1-difluoro-1a,10b-dihydrodibenzo[a,e]cyclopropa[c]
cyclohepten-6-one 2.Compound 2on reduction with sodium
borohydride in methanol at 0-5 °C afforded corresponding
alcohol 314 which on treatment with ethyl bromoacetate in
presence of sodium hydride in DMF gave compound 4.
The reaction of compound 4 with hydrazine hydrate in
ethanol under reflux yielded hydrazide 5. Interestingly,
cyclization reaction of hydrazide 5 with benzoic acid in
phosphorous oxychloride to construct 1,3,4-oxadiazole
framework did not give corresponding dibenzosuberane-
1,3,4-oxadiazole analog 8a.Alternatively, hydrazide 5 was
treated with benzaldehyde (6) in ethanol under reflux to
obtain corresponding N’-benzylidenehydrazide (7) which
was cyclized using chloramine-T in ethanol at 60 °C to
afford desired analog (8a). Although, the compound was
isolated in good purity, yield of the final cyclization reaction
did not exceed 15%.
Lower yield in the linear synthesis strategy (Scheme 1)
prompted us to explore alternate convergent synthesis

106
Synthesis and Antimicrobial Properties of 1,3,4-Oxadiazole Analogs
J. Braz. Chem. Soc.
Scheme 1. Linear synthesis pathway of 1,3,4-oxadiazole analogs containing dibenzosuberane unit.
Scheme 2. Convergent synthesis pathway of 1,3,4-oxadiazole analogs containing dibenzosuberane unit.
phenyl ring result in higher antibacterial activity (e.g.,
compounds 8e, 8f and 8j). However, fluorine atom at meta
position in combination with chlorine at para position of
the phenyl ring diminishes antibacterial activity to a great
extent (compound 8i). Interestingly, compound 8a, devoid
of any substitution on the phenyl ring, showed remarkable
activity against all four bacterial strains. Compounds 8a, 8d,
8e, and 8j showed uniform activity against gram-positive
(Staphylococcus aureus) and gram-negative (Escherichia
coli, Pseudomonas aeroginosa and Klebsiella pneumoniae)
bacterial strains. Compound 8g was found to be inactive
against gram-positive bacteria and moderately active

Vol. 25, No. 1, 2014
Moger et al.
107
Table 1. Antibacterial activity of analogs (8a-8j)
Antibacterial activity
Minimum Inhibitory Concentration (MIC) and zone of inhibitiona
Compound
Staphylococcus aureus
6.25 (18)
Escherichia coli
12.5 (21)
50 (14)
Pseudomonas aeroginosa
6.25 (23)
12.5 (11)
100 (16)
Klebsiella pneumoniae
6.25 (16)
12.5 (18)
12.5 (16)
12.5 (18)
12.5 (19)
50 (11)
8a
8b
12.5 (17)
6.25 (20)
12.5 (18)
6.25 (18)
6.25 (23)
100 (26)
50 (11)
8c
12.5 (17)
12.5 (32)
6.25 (20)
12.5 (18)
12.5 (24)
100 (09)
12.5 (21)
6.25 (22)
< 6.25 (30)
00
8d
12.5 (21)
6.25 (14)
12.5 (16)
12.25 (15)
6.25 (12)
100 (16)
8e
8f
8g
12.5 (13)
12.5 (17)
100 (13)
8h
8i
50 (15)
8j
12.5 (26)
< 6.25 (32)
00
6.25 (20)
< 6.25 (36)
00
6.25 (25)
< 6.25 (32)
00
Nitrofurazone
DMSO (1%) Solvent control
aZone of inhibition in mm is given in parenthesis; MIC is expressed in µg mL-1 (MIC for the standard drug, nitrofurazone, is reported earlier19); standard
drug used: nitrofurazone;solvent control: 1% DMSO.
against gram-negative bacteria. In general, all compounds
showed broad spectrum of activity against both gram-
positive and gram-negative bacterial strains.
compounds 8a, 8b, 8d, 8e, 8h and 8j displayed very
good activity against all four fungal strains. Compounds
8c and 8i showed activity against all strains except
Trichophyton mentagrophyte and Penicillium marneffei,
respectively. While compound 8f was found to be active
against two strains namely, Penicillium marneffei and
Trichophyton mentagrophyte, compound 8g showed
activity against Trichophyton mentagrophytes and
Aspergillus fumigatus. The values presented in the
Table 2 reveal interesting trends in antifungal activity
of compounds depending on substitution pattern on the
phenyl ring attached to 1,3,4-oxadiazole ring. Alkyl
substituents on the phenyl ring, as in the case of compounds
8b and 8d impart good antifungal activity against all four
Allcompoundswerealsoassessedforantifungalactivity
against Penicillium marneffei (recultured), Trichophyton
mentagrophytes (recultured), Aspergillus flovus (NCIM
No. 524) and Aspergillus fumigatus (NCIM No.
902). The compounds were dissolved in DMSO and
antifungal activity was determined using serial dilution
method.18 For comparison, well-known antifungal drug
Amphotericin B was used as a standard. The minimum
inhibitory concentration (MIC, µg mL-1) was determined
for each compound in triplicate experiments; the
values were averaged and are presented in Table 2. Six
Table 2. Antifungal activity of analogs (8a-8j)
Antifungal activity
Minimum Inhibitory Concentration (MIC) and zone of inhibitiona
Compound
Penicillium marneffei
12.5 (10)
12.5 (12)
6.25 (11)
12.5 (16)
6.25 (16)
6.25 (14)
R
Trichophyton mentagrophyte
12.5 (13)
12.5 (11)
R
Aspergillus flovus
6.25 (11)
12.5 (12)
12.5 (09)
12.5 (12)
6.25 (12)
R
Aspergillus fumigatus
6.25 (16)
12.5 (18)
12.5 (11)
12.5 (13)
12.5 (14)
R
8a
8b
8c
8d
12.5 (16)
6.25 (12)
12.5 (14)
12.5 (13)
12.5 (13)
6.25 (10)
6.25 (12)
< 6.25 (38)
00
8e
8f
8g
R
12.5 (14)
12.5 (12)
6.25 (12)
6.25 (13)
< 6.25 (24)
00
8h
6.25 (12)
R
12.5 (12)
12.5 (14)
6.25 (12)
< 6.25 (29)
00
8i
8j
12.5 (13)
< 6.25 (33)
00
Amphotericin B
DMSO (1%) Solvent control
aZone of inhibition in mm is given in parenthesis; MIC is expressed in µg mL-1 (MIC for the standard drug, amphotericin B, is reported earlier19); standard
drug used: amphotericin B; solvent control: 1% DMSO; R: resistant.

108
Synthesis and Antimicrobial Properties of 1,3,4-Oxadiazole Analogs
J. Braz. Chem. Soc.
strains. Electron withdrawing fluorine substituent at para
position of the phenyl ring, as in the case of compounds
8e and 8j, resulted in remarkably high antifungal activity
against all strains. Presence of chlorine substituent at
the para position of the phenyl ring (compound 8f)
caused diminished activity against Aspergillus flovus and
Aspergillus fumigatus. Interestingly, this trend was reversed
by introduction of fluorine substituent at meta position
next to chloro group (compound 8i). Presence of electron
donating methoxy group on the phenyl ring caused good
to very good antifungal activity (compound 8c and 8h).
However, compound 8c having para-methoxy substituent
showed resistance to Trichophyton mentagrophyte
strain. The compound 8a having no substitution on the
phenyl ring attached to 1,3,4-oxadiazole ring showed
good antifungal activity against Penicillium marneffei
and Trichophyton mentagrophyte and very good activity
against Aspergillus flovus and Aspergillus fumigatus.
Phenyl substitution at para position of the phenyl ring
(compound 8g) caused resistance for Penicillium marneffei
and Aspergillus flovus strains.
the reactions were monitored by thin layer chromatography
(TLC) using precoated silica 60 F254, 0.25 mm aluminum
plates (Merck). The crude compounds were purified by
column chromatography using silica gel (100-200) and
gradient (0-50%) ethyl acetate in hexane as the eluent
system.
Synthesis
General procedure for the preparation of 1,3,4-oxadiazole
analogs containing dibenzosuberane moiety (8a-8j)
A solution of compound 314 (200 mg, 0.77 mmol) in
DMF (5.0 mL) was cooled to 0-5 °C. Sodium hydride
(60%, 47.0 mg, 1.16 mmol) was added to it and stirred
for 15 min. To the reaction mixture was added suitably
substituted 2-chloromethyl-5-phenyl-1,3,4-oxadiazole15
(12a-12j, Scheme 2) (0.85 mmol, 1.1 eq) at 0-5 °C and
stirred for 1.0 h. Progress of the reaction was monitored by
TLC. Upon completion, the reaction mixture was poured
on crushed ice. The precipitated solid was filtered, washed
with water and dried. The crude product was purified by
column chromatography using silica gel (100-200) and
gradient (0-50%) ethyl acetate in hexane as the eluent.
Conclusions
A series of ten novel 1,3,4-oxadiazole analogs containing
dibenzosuberane moiety (8a-8j) having various substituents
on the phenyl ring attached to 1,3,4-oxadiazole ring were
synthesized and well characterized. All the analogs were
investigated for antibacterial and antifungal activities. In
general, all compounds showed moderate-to-good activity
against the bacterial and fungal strains used in this study.
Four compounds 8a, 8d, 8e and 8j were uniformly active
against all bacterial as well as fungal strains used for the
study. para-Fluoro substitution on the phenyl ring attached
to 1,3,4-oxadiazole framework causes marked increase in
both antibacterial as well as antifungal activities of the
novel molecules.
1,1-Difluoro-1,1a,6,10b-tetrahydro-(1a,6,10b)-dibenzo[a,e]
cyclopropa[c]cyclohepten-6-yloxymethyl-5-phenyl-[1,3,4]-
oxadiazole (8a)
White solid; yield 77%; mp 183-185 °C; IR (KBr)
1
n
max/cm-1: 3011, 1456, 1169, 747; H NMR (400 MHz,
DMSO-d6) d 3.53 (d, 2H, J 13.6 Hz), 5.09 (s, 2H), 6.55 (s,
1H), 7.20-7.27 (m, 6H), 7.45 (d, 2H, J 7.2 Hz), 7.60-7.66
(m, 3H), 8.01-8.03 (m, 2H); 13C NMR (100 MHz,
DMSO-d6) d 27.3, 61.7, 77.8, 122.5, 123.6, 126.8, 127.1,
127.8, 128.3, 129.9, 131.8, 132.6, 142.7, 163.7, 165.1; MS
(ESI) m/z: 417.1 [M + H]+; anal. calcd. for C25H18F2N2O5: C,
72.11; H, 4.36; F, 9.12; N, 6.73; O, 7.68; found: C, 72.13;
H, 4.31; F, 9.14; N, 6.68; O, 7.62.
Experimental
1,1-Difluoro-1,1a,6,10b-tetrahydro-(1a,6,10b)-dibenzo
[a,e]cyclopropa[c]cyclohepten-6-yloxymethyl-5-(4-methyl-
phenyl)-[1,3,4]-oxadiazole (8b)
Material and methods
Off white solid; yield 76%; mp 218-220 °C; IR (KBr)
1
All chemicals used for the synthesis were of reagent
grade and procured from Sigma-Aldrich, Bangalore, India.
1H and 13C NMR spectra were recorded on AS 400 MHz
Varian NMR spectrometer using TMS as an internal
standard. IR spectra were recorded by using Perkin-Elmer
Spectrum 100 Series FT-IR spectrometer. Mass spectra
were recorded on Agilent 1200 Series LC/MSD VL
system. Melting points were determined by using Büchi
melting point B-545 instrument and are uncorrected. All
n
max/cm-1: 3011, 1495, 1169, 747; H NMR (400 MHz,
DMSO-d6) d 2.4 (s, 3H), 3.52 (d, 2H, J 13.6 Hz), 5.07 (s,
2H), 6.54 (s, 1H), 7.23-7.26 (m, 6H), 7.41 (m, 4H), 7.88
(d, 2H, J 8.4 Hz); 13C NMR (100 MHz, DMSO-d6) d 26.3,
32.2, 66.5, 82.5, 125.5, 127.3, 131.3, 131.8, 132.5, 133.1,
135.2, 136.6, 147.5, 147.6, 168.2, 169.9; MS (ESI) m/z:
431.1 [M + H]+; anal. calcd. for C26H20F2N2O2: C, 72.55;
H, 4.68; F, 8.83; N, 6.51; O, 7.43; found: C, 72.51; H, 4.60;
F, 8.85; N, 6.47; O, 7.41.

Vol. 25, No. 1, 2014
Moger et al.
109
1,1-Difluoro-1,1a,6,10b-tetrahydro-(1a,6,10b)-dibenzo [a,e]
cyclopropa[c]cyclohepten-6-yloxymethyl-5-(4-methoxy-
phenyl)-[1,3,4]-oxadiazole (8c)
128.9, 130.1, 131.8, 137.4, 142.7, 163.9, 164.3; MS (ESI)
m/z: 451.0 [M + H]+; anal. calcd. for C25H17ClF2N2O2: C,
66.60; H, 3.80; Cl, 7.86; F, 8.43; N, 6.21; O, 7.10; found:
C, 66.66; H, 3.77; Cl, 7.80; F, 8.47; N, 6.18; O, 7.06.
White solid; yield 65%; mp 165-168 °C; IR (KBr)
n
max/cm-1: 3012, 1613, 1496, 1260, 746; 1H NMR (400 MHz,
DMSO-d6) d 3.53 (d, 2H, J 13.6 Hz), 3.86 (s, 3H), 5.06 (s,
2H), 6.54 (s, 1H), 7.15 (d, 2H, J 8.8 Hz), 7.23-7.27 (m, 6H),
7.44 (d, 2H, J 6.4 Hz), 7.93-7.97 (m, 2H); 13C NMR (100
MHz, DMSO-d6) d 27.3, 55.9, 61.7, 77.7, 115.4, 115.9,
122.5, 126.8, 127.8, 128.3, 128.9, 131.8,142.7, 162.6,
163.1, 165.1; MS (ESI) m/z: 447.1 [M + H]+; anal. calcd.
C26H20F2N2O3: C, 69.12; H, 3.94; F, 13.12; N, 6.45; O,
7.37; found: C, 69.15; H, 3.91; F, 13.09; N, 6.41; O, 7.30.
1,1-Difluoro-1,1a,6,10b-tetrahydro-(1a,6,10b)-dibenzo
[a,e]cyclopropa[c]cyclohepten-6-yloxymethyl-5-(4-phenyl-
phenyl)-[1,3,4]-oxadiazole (8g)
White solid; yield 70%; mp 241-244 °C; IR (KBr)
1
n
max/cm-1 3011, 1455, 1169, 747; H NMR (400 MHz,
DMSO-d6) d 3.54 (d, 2H, J 13.6 Hz), 5.11 (s, 1H), 6.56 (s,
1H), 7.22-7.27 (m, 6H), 7.44-7.55 (m, 5H), 7.77 (d, 2H,
J 7.2 Hz), 7.92 (d, 2H, J 8.4 Hz), 8.09 (d, 2H, J 8.4 Hz); MS
(ESI) m/z: 493.0 [M + H]+; anal. calcd. for C31H22F2N2O2: C,
75.60; H, 4.50; F, 7.71; N, 5.69; O, 6.50; found: C, 75.65;
H, 4.47; F, 7.76; N, 5.63; O, 6.55.
1,1-Difluoro-1,1a,6,10b-tetrahydro-(1a,6,10b)-dibenzo[a,e]
cyclopropa[c]cyclohepten-6-yloxymethyl-5-(4-tert-
butylphenyl)-[1,3,4]-oxadiazole (8d)
White solid; yield 73%; mp 157-160 °C; IR (KBr)
1,1-Difluoro-1,1a,6,10b-tetrahydro-(1a,6,10b)-dibenzo[a,e]
cyclopropa[c]cyclohepten-6-yloxymethyl-5-(3,4-dimethoxy-
phenyl)-[1,3,4]-oxadiazole (8h)
1
n
max/cm-1: 2960, 1460, 1165, 749; H NMR (400 MHz,
DMSO-d6) d 1.32 (s, 9H), 3.53 (d, 2H, J 13.2 Hz), 5.08 (s,
2H), 6.54 (s, 1H), 7.21-7.27 (m, 6H), 7.44 (d, 2H, J 6.8 Hz),
7.63 (d, 2H, J 8.8 Hz), 7.92 (d, 2H, J 10.4 Hz); 13C NMR
(100 MHz, DMSO-d6) d 27.3, 31.2, 35.3, 61.7, 77.7, 120.8,
122.5, 126.7, 126.9, 127.8, 128.3, 131.9, 142.7, 155.6,
163.5, 165.1; MS (ESI) m/z: 473.2 [M + H]+; anal. calcd.
for C29H26F2N2O2: C, 73.71; H, 5.55; F, 8.04; N, 5.93; O,
6.77; found: C, 73.75; H, 5.51; F, 8.10; N, 5.90; O, 6.77.
White solid; yield 60%; mp 205-208 °C; IR (KBr)
n
max/cm-1: 3011, 1607, 1500, 1170, 748; 1H NMR (400 MHz,
DMSO-d6) d 3.53 (d, 2H, J 13.2 Hz), 3.85 (s, 6H), 5.07
(s, 2H), 6.54 (s, 1H ), 7.16-7.27 (m, 7H), 7.44-7.48 (m,
3H), 7.57 (dd, 1H, J 2.0, 8.0 Hz, ); 13C NMR (100 MHz,
DMSO-d6) d 27.4, 56.1, 61.7, 77.7, 109.5, 112.5, 115.8,
120.6, 122.5, 126.7, 127.8, 128.3, 131.9, 142.7, 149.5,
152.4, 163.2, 165.1; MS (ESI) m/z: 477.1 [M + H]+; anal.
calcd. C27H22F2N2O4: C, 68.06; H, 4.65; F, 7.97; N, 5.88; O,
13.43; found: C, 68.02; H, 4.60; F, 7.92; N, 5.72; O, 13.41.
1,1-Difluoro-1,1a,6,10b-tetrahydro-(1a,6,10b)-dibenzo[a,e]
cyclopropa[c]cyclohepten-6-yloxymethyl-5-(4-fluorophenyl)-
[1,3,4]-oxadiazole (8e)
White solid; yield 62%; mp 220-223 °C; IR (KBr)
1,1-Difluoro-1,1a,6,10b-tetrahydro-(1a,6,10b)-dibenzo[a,e]
cyclopropa[c]cyclohepten-6-yloxymethyl-5-(4-chloro-3-
fluorophenyl)-[1,3,4]-oxadiazole (8i)
n
max/cm-1: 3011, 1607, 1496, 1168, 746; 1H NMR (400 MHz,
DMSO-d6) d 3.53 (d, 2H, J 13.2 Hz), 5.08 (s, 2H), 6.54 (s,
1H), 7.20-7.27 (m, 6H), 7.44-7.49 (m, 4H), 8.06-8.09 (m,
2H); 13C NMR (100 MHz, DMSO-d6) d 27.3, 61.7, 77.8,
117.1, 117.3, 120.3, 122.5, 126.8, 127.80, 128.3, 129.8,
129.9, 131.9,142.7, 163.7, 164.3; MS (ESI) m/z: 435.1 [M
+ H]+; anal. calcd. for C25H17F3N2O2: C 69.95; H, 4.52; F,
8.51; N, 6.27; O, 10.75; found: C, 69.93; H, 4.47; F, 8.49;
N, 6.21; O, 10.72.
Off white solid; yield 60%; mp 207-210 °C; IR (KBr)
1
n
max/cm-1: 3010, 1608, 1497, 1168, 746; H NMR (400
MHz, DMSO-d6) d 3.52 (d, 2H, J 13.2 Hz), 5.09 (s, 2H),
6.54 (s, 1H), 7.23-7.27 (m, 6H), 7.43 (d, 2H, J 6.4 Hz),
7.86 (d, 2H, J 3.6 Hz), 8.01 (d, 1H, J 8.8 Hz); MS (ESI)
m/z: 469.0 [M + H]+; anal. calcd. for C25H16ClF3N2O2: C,
64.04; H, 3.44; Cl, 7.56; F, 12.16; N, 5.97; O, 6.82; found:
C, 64.07; H, 3.40; Cl, 7.51; F, 12.11; N, 5.99; O, 6.85.
1,1-Difluoro-1,1a,6,10b-tetrahydro-(1a,6,10b)-
dibenzo[a,e]cyclopropa[c]cyclohepten-6-yloxymethyl-5-(4-
chlorophenyl)-[1,3,4]-oxadiazole (8f)
1,1-Difluoro-1,1a,6,10b-tetrahydro-(1a,6,10b)-dibenzo[a,e]
cyclopropa[c]cyclohepten-6-yloxymethyl-5-(4-fluoro-2-
trifluoromethylphenyl)-[1,3,4]-oxadiazole (8j)
White solid; yield 70%; mp 212-214 °C; IR (KBr)
n
max/cm-1: 3006, 1607, 1458, 1166, 747; 1H NMR (400 MHz,
Off white solid; yield 60%; mp 153-155 °C; IR
1
DMSO-d6) d 3.53 (d, 2H, J 13.2 Hz), 5.09 (s, 2H), 6.55
(s, 1H), 7.22-7.27 (m, 6H), 7.44 (d, 2H, J 6.4 Hz), 7.69 (d,
2H, J 8.4 Hz), 8.01 (d, 2H, J 8.8 Hz); 13C NMR (100 MHz,
DMSO-d6) d 27.4, 61.7, 77.8, 122.5, 126.8, 127.8, 128.3,
(KBr) nmax/cm-1: 3011, 2932, 1479, 1168, 748; H NMR
(400 MHz, DMSO-d6) d 3.51 (d, 2H, J 13.2 Hz), 5.10 (s,
2H), 6.54 (s, 1H), 7.21-7.27 (m, 6H), 7.42-7.49 (m, 2H),
7.77-7.86 (m, 1H), 7.99 (dd, 1H, J 2.4, 8.8 Hz), 8.12-8.15

110
Synthesis and Antimicrobial Properties of 1,3,4-Oxadiazole Analogs
J. Braz. Chem. Soc.
(m, 1H); 13C NMR (100 MHz, DMSO-d6) d 27.3, 61.5,
77.7, 115.9, 116.2, 118.4, 120.8, 121.1, 122.4, 126.8,
127.8, 128.2, 128.3, 131.9, 135.4, 135.5, 142.6, 162.5,
162.7, 164.7; MS (ESI) m/z: 503.1 [M + H]+; anal. calcd.
for C26H16F6N2O2: C, 62.16; H, 3.21; F, 22.69; N, 5.58; O,
6.37; found: C, 62.10; H, 3.24; F, 22.63; N, 5.52; O, 6.30.
mentagrophytes (recultured), Aspergillus flovus (NCIM No.
524) and Aspergillus fumigatus (NCIM No. 902) using serial
dilution method.18 Sabouraud’s agar media was prepared
by dissolving peptone (1.0 g), D-glucose (4.0 g) and agar
(2.0 g) in distilled water (100 mL) and adjusting the pH to
5.7. Normal saline was used to make a suspension of spores
of fungal strain for lawning. A loopful of particular fungal
strain was transferred to 3.0 mL saline to get a suspension
of corresponding species. A 20.0 mL of agar media was
poured into each of the Petri dishes. Excess of suspension
was decanted and the plates were dried by placing in an
incubator at 37 °C for 1.0 h. Using an agar punch wells were
made on these seeded agar plates and 10 mg mL-1 of the test
compounds in 1% DMSO were added into each labeled well.
A control was also prepared for the plates in the same way
using 1% DMSO. The Petri dishes were prepared in triplicate
and maintained at 37 °C for 3-4 days. Antifungal activity
was determined by measuring the diameter of the inhibition
zone. Zone of inhibition (inhibition halos) was calculated as
average of three repeated experimental data. Compounds
which inhibited fungal growth (more than 3 mm zone of
inhibition) were considered as active. MIC was determined
for compounds which showed positive activity. Activity
of each compound was compared with amphotericin B as
standard. The minimum inhibitory concentration (MIC) for
the amphotericin Bin 1% DMSO was more than 1.0 mg mL-1
against the tested species.19 One percent DMSO was used as
solvent control; the data is illustrated in Table 2.
Biological assays
The bacterial strains were collected from patients with
different infectious status who had not been administered
any antibacterial drugs for at least two weeks with the
suggestions of an authorized physician and authenticated
by a microbiologist at Kiran Diagnostic Health Center,
Chitradurga, Karnataka (India). Fungal strains were taken
from Dept. of Post Graduate Studies and Research in
Microbiology, Tumkur University, Tumkur, Karnataka
(India).
Antibacterial activity
The newly synthesized compounds were screened for
their antibacterial activity against Staphylococcus aureus,
Escherichia coli, Pseudomonas aeroginosa and Klebsiella
pneumoniae strains by disc diffusion method.16,17 The
discs measuring 6.25 mm in diameter were punched from
Whatman No. 1 filter paper. Batches of 100 discs were
dispensed to each screw capped bottles and sterilized by dry
heat at 140 °C for an hour. The test compounds were prepared
with different concentrations using DMSO. One milliliter
containing 100 times the amount of chemical required in
each disc was added to each bottle which contained 100 discs.
The discs of each concentration were placed in triplicate in
nutrient agar medium seeded with fresh bacteria separately.
The incubation was carried out at 37.8 °C for 24 h. The
minimum inhibitory concentration (MIC) was noted. For
comparison, nitrofurazone was used as a drug standard.
Solvent and growth controls were kept. Antibacterial
activity was determined by measuring the diameter of the
inhibition zone. Zone of inhibition (inhibition halos) was
calculated as average of three repeated experimental data.
Compounds which inhibited bacteria growth (more than
3 mm zone of inhibition) were considered as active. MIC
was determined for compounds which showed positive
activity. The minimum inhibitory concentration (MIC) for
the nitrofurazonein 1% DMSO was more than 1.0 mg mL-1
against the tested species.19 One percent DMSO was used as
solvent control; the data is illustrated in Table 1.
Supplementary Information
1H NMR, 13C NMR, IR and mass spectra of compounds
are available free of charge at http://jbcs.sbq.org.br as a
PDF file.
Acknowledgements
Authors are grateful to Advinus Therapeutics Ltd.,
Bangalore, India for invaluable support throughout
this research work. Authors also thank Department of
Chemistry, Mangalore University, India.
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Mol. Pharm. Fast Forward 2011, 79, 672.
Antifungal activity
3. Wilens, T. E.; Biederman, J.; Geist, D. E.; Steingard, R.;
Spencer, T.; J. Am. Acad. Child and Adolescent Psych. 1993,
32, 343.
Antifungal activity of the compounds was determined
against Penicillium marneffei (recultured), Trichophyton

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4. Pfister, J. R.; Makra, F.; Muehldorf, A. V.; Nelson, J. T.; Slate,
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Med. Chem. Lett. 2009, 19, 1807.
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US pat. 6,570,016 2003.
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N. S.; Eur. J. Med. Chem. 2010, 45, 5225.
Armstrong, J. D.; Org. Lett. 2005, 7, 1039.
16. Collins, A. H.; Microbiological Methods, 2nd ed; Butterworth:
London, 1976.
9. Palusa, S. K.; Udupi, R. H.; Himabindu, V.; Sridhara, A. M.;
Org. Commun. 2011, 4, 82.
17. Arthington, B.A.; Motley, M.; Warnock, D. W.; Morrison, C. J.;
Clin. J. Microbiol. 2000, 38, 2254.
10. Kashaw, S. K.; Gupta, V.; Kashav, V; Mishra, P.; Stables, J. P.;
Jain, N. K.; Med. Chem. Res. 2010, 19, 250.
18. Cruickshank, R.; Duguid, J. P.; Marmion, B. P.; Swain, R. H.A.;
Medical Microbiology, Vol. 2, 12th ed.; Churchill Livingstone:
London, 1975, p. 196.
11. Zarghi, A.; Tabatabai, S. A.; Faizi, M.; Ahadian, A.;
Navabi, P.; Zanganeh,V.; Shafiee,A.; Bioorg. Med. Chem. Lett.
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19. Sarojini, B. K.; Krishna, B. G.; Darshanraj, C. G.; Bharath,
B. R.; Majunatha, H.; Eur. J. Med. Chem. 2010, 45, 3490.
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Submitted: September 17, 2013
Published online: November 22, 2013

J. Braz. Chem. Soc., Vol. 25, No. 1, S1-S20, 2014.
Printed in Brazil - ©2014 Sociedade Brasileira de Química
0103 - 5053 $6.00+0.00
Supplementary Information
SI
Synthesis and Antimicrobial Properties of 1,3,4-Oxadiazole Analogs Containing
Dibenzosuberane Moiety
Manjunath Moger,a,b Vijay Satam,a Darshan Raj C. Govindaraju,c Paniraj A. S.,a
Vadiraj S. Gopinath,a Rama Mohan Hindupura and Hari N. Pati*,a
aAdvinus Therapeutics Ltd., 21 & 22, Phase II, Peenya Industrial Area, Bangalore 560058, Karnataka, India
bDepartment of Chemistry, Mangalore University, Mangalagangotri 574199, Karnataka, India
cDepartment of Bio-Medicinal Research, Vidya Herbs Pvt. Ltd., Bangalore 562106, Karnataka, India
Figure S1. 1H NMR spectrum (400 MHz, DMSO-d6) of compound 8a.
*e-mail: hari.pati@advinus.com

S2
Synthesis and Antimicrobial Properties of 1,3,4-Oxadiazole Analogs
J. Braz. Chem. Soc.
Figure S2. 13C NMR spectrum (100 MHz, DMSO-d6) of compound 8a.
Figure S3. Mass spectrum of compound 8a.

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Figure S4. FT-IR (KBr) spectrum of compound 8a.
Figure S5. 1H NMR spectrum (400 MHz, DMSO-d6) of compound 8b.

S4
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J. Braz. Chem. Soc.
Figure S6. 13C NMR spectrum (100 MHz, DMSO-d6) of compound 8b.
Figure S7. Mass spectrum of compound 8b.

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Figure S8. FT-IR (KBr) spectrum of compound 8b.
Figure S9. 1H NMR spectrum (400 MHz, DMSO-d6) of compound 8c.

S6
Synthesis and Antimicrobial Properties of 1,3,4-Oxadiazole Analogs
J. Braz. Chem. Soc.
Figure S10. 13C NMR spectrum (100 MHz, DMSO-d6) of compound 8c.
Figure S11. Mass spectrum of compound 8c.

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Figure S12. FT-IR (KBr) spectrum of compound 8c.
Figure S13. 1H NMR spectrum (400 MHz, DMSO-d6) of compound 8d.

S8
Synthesis and Antimicrobial Properties of 1,3,4-Oxadiazole Analogs
J. Braz. Chem. Soc.
Figure S14. 13C NMR spectrum (100 MHz, DMSO-d6) of compound 8d.
Figure S15. Mass spectrum of compound 8d.

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Figure S16. FT-IR (KBr) spectrum of compound 8d.
Figure S17. 1H NMR spectrum (400 MHz, DMSO-d6) of compound 8e.

S10
Synthesis and Antimicrobial Properties of 1,3,4-Oxadiazole Analogs
J. Braz. Chem. Soc.
Figure S18. 13C NMR spectrum (100 MHz, DMSO-d6) of compound 8e.
Figure S19. Mass spectrum of compound 8e.

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Figure S20. FT-IR (KBr) spectrum of compound 8e.
Figure S21. 1H NMR spectrum (400 MHz, DMSO-d6) of compound 8f.

S12
Synthesis and Antimicrobial Properties of 1,3,4-Oxadiazole Analogs
J. Braz. Chem. Soc.
Figure S22. 13C NMR spectrum (100 MHz, DMSO-d6) of compound 8f.
Figure S23. Mass spectrum of compound 8f.

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Figure S24. FT-IR (KBr) spectrum of compound 8f.
Figure S25. 1H NMR spectrum (400 MHz, DMSO-d6) of compound 8g.

S14
Synthesis and Antimicrobial Properties of 1,3,4-Oxadiazole Analogs
J. Braz. Chem. Soc.
Figure S26. Mass spectrum of compound 8g.
Figure S27. FT-IR (KBr) spectrum of compound 8g.

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Figure S28. 1H NMR spectrum (400 MHz, DMSO-d6) of compound 8h.
Figure S29. 13C NMR spectrum (100 MHz, DMSO-d6) of compound 8h.

S16
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J. Braz. Chem. Soc.
Figure S30. Mass spectrum of compound 8h.
Figure S31. FT-IR (KBr) spectrum of compound 8h.

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Figure S32. 1H NMR spectrum (400 MHz, DMSO-d6) of compound 8i.
Figure S33. Mass spectrum of compound 8i.

S18
Synthesis and Antimicrobial Properties of 1,3,4-Oxadiazole Analogs
J. Braz. Chem. Soc.
Figure S34. FT-IR (KBr) spectrum of compound 8i.
Figure S35. 1H NMR spectrum (400 MHz, DMSO-d6) of compound 8j.

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Figure S36. 13C NMR spectrum (100 MHz, DMSO-d6) of compound 8j.
Figure S37. Mass spectrum of compound 8j.

S20
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Figure S38. FT-IR (KBr) spectrum of compound 8j.