Synthesis of new 4-pyrrol-1-yl benzoic acid hydrazide analogs and some derived oxadiazole, triazole and pyrrole ring systems: A novel class of potential antibacterial and antitubercular agents

Article abstract of DOI:10.1016/j.ejmech.2007.11.016

In the present study, a novel series of 4-pyrrol-1-yl benzoic acid hydrazide analogs, some derived 5-substituted-2-thiol-1,3,4-oxadiazoles, 5-substituted-4-amino-1,2,4-triazolin-3-thione and 2,5-dimethyl pyrroles have been synthesized in good yields and c

Full text of DOI:10.1016/j.ejmech.2007.11.016

Available online at www.sciencedirect.com
European Journal of Medicinal Chemistry 43 (2008) 1989e1996
http://www.elsevier.com/locate/ejmech
Short communication
Synthesis of new 4-pyrrol-1-yl benzoic acid hydrazide analogs and some
derived oxadiazole, triazole and pyrrole ring systems: A novel class of
potential antibacterial and antitubercular agents
a
b
S.D. Joshi b, H.M. Vagdevi a, , V.P. Vaidya , G.S. Gadaginamath
*
a Department of PG Studies and Research in Chemistry, School of Chemical Sciences, Kuvempu University, Jnana Sahyadri,
Shankaraghatta, Shimoga, Karnataka, India
b Department of Pharmaceutical Chemistry, S.E.T’s College of Pharmacy, S.R. Nagar, Dharwad, Karnataka, India
Received 24 May 2007; received in revised form 14 November 2007; accepted 22 November 2007
Available online 5 December 2007
Abstract
In the present study, a novel series of 4-pyrrol-1-yl benzoic acid hydrazide analogs, some derived 5-substituted-2-thiol-1,3,4-oxadiazoles,
5-substituted-4-amino-1,2,4-triazolin-3-thione and 2,5-dimethyl pyrroles have been synthesized in good yields and characterized by IR,
NMR, mass spectral and elemental analyses. Compounds were evaluated for their preliminary in vitro antibacterial activity against some
Gram-positive and Gram-negative bacteria and compounds were screened for antitubercular activity against Mycobacterium tuberculosis
H37Rv strain by broth dilution assay method. Some compounds showed very good antibacterial and antitubercular activities.
Ó 2007 Elsevier Masson SAS. All rights reserved.
Keywords: Pyrroles; Acid hydrazide derivatives; Antibacterial activity; Antitubercular activity; Broth dilution assay method
1. Introduction
Pyrrole is one of the most ubiquitous heterocycles in the
plant and animal kingdom because of its participation as a sub-
unit of chlorophyll in plant cells and hemin and vitamin B12 in
animal cells.
Pyrrole and its derivatives have shown to possess biological
activities such as antibacterial [2], antitumor [3], analgesics
[4], antitubercular [5,6], anti-inflammatory, and antiallergic
[7]. Several macromolecular antibiotics having pyrrole struc-
ture were isolated from biological sources and their activities
were defined [8,9].
In view of the above-mentioned findings, the purpose of the
present work was to design, synthesize and investigate the in
vitro antibacterial and antitubercular activities of some novel
4-pyrrol-1-yl benzoic acid hydrazide derivatives.
Careful literature survey for functional groups which could
be considered as pharmacophores for the antitubercular activ-
ities revealed that the hydrazone moiety is common among
most of the antitubercular agents such as salinazid and vera-
zide [5,10]. Therefore, the target compounds were rationalized
so as to comprise the hydrazone pharmacophores that are
Tuberculosis (TB) is the leading infectious cause of death
in the world today, with approximately three million patients
deceasing every year. Nearly one-third of the world’s popula-
tion is infected with Mycobacterium tuberculosis and the
World Health Organization (WHO) estimates that about 30
million people will be infected within next 20 years [1]. The
emergence of AIDS, decline of socioeconomic standards and
a reduced emphasis on tuberculosis control programs contrib-
ute to the disease’s resurgence in industrialized countries.
During recent years, M. tuberculosis and microorganisms
increased resistance against drugs. Therefore, there is a need
to develop new, potent, fast-acting antimicrobial and antimy-
cobacterial drugs with low toxicity.
* Corresponding author. Tel.: þ91 9448254093; fax: þ91 828256228.
E-mail address: vagdevihm@gmail.com (H.M. Vagdevi).
0223-5234/$ - see front matter Ó 2007 Elsevier Masson SAS. All rights reserved.
doi:10.1016/j.ejmech.2007.11.016

1990
S.D. Joshi et al. / European Journal of Medicinal Chemistry 43 (2008) 1989e1996
believed to be responsible for the biological significance of
some relevant chemotherapeutic agents. The substitution pat-
tern of such hydrazone derivatives was carefully selected so
as to confer different electronic environment to the molecules.
Several triazole ring systems are associated with diverse
biological activities [11e13] as well as biological activities
of oxadiazole and 3-acetyl-2,5-disubstituted-2,3-dihydro-1,3,
4-oxadiazoline ring systems are well documented [14,15].
Therefore, it was planned to synthesize hybrid compounds
that comprise both the pyrrole and the aforementioned hetero-
cyclic ring systems. Such hybridization was designed in order
to investigate the effect of such structural variation on the
anticipated antitubercular and/or antibacterial activities.
Several Schiff’s bases, hydrazones and hydrazides of isoni-
azid have shown good activity against tubercular, fungal and
bacterial infections [16]. In the quest for biologically more
potent antibacterial and antitubercular compounds, we envi-
sioned to design and synthesize pyrrole substituted hydrazone
derivatives. Antibacterial and antitubercular activity results of
the newly synthesized pyrrole derivatives are discussed in this
paper.
60511), Klebsiella pneumoniae (ATCC 10031), Escherichia
coli (ATCC 10536) and Pseudomonas aeruginosa (ATCC
10145).
MIC of compounds was determined against M. tuberculosis
H37Rv strain by using broth dilution assay method [19,20].
4. Results and discussion
A novel series of 4-pyrrol-1-yl benzoic acid hydrazide
analogs and some derived ring systems have been synthesized
in good yields using the synthetic route outlined in Scheme 1.
1
IR, H NMR, 13C NMR and mass spectral data are in agree-
ment with the proposed structures of all newly synthesized
compounds.
In the IR spectrum of 1 broad stretching bands at around
3335 and 3278 cmꢀ1 were due to amine/amide NH while
strong stretching band at 1610 cmꢀ1 was attributed to amide
1
carbonyl. H NMR spectrum showed a singlet at d 4.51 and
d 9.81 which were accounted for NH2 and NH which vanished
on D2O exchange. The four protons of pyrrole ring appeared
as multiplets between d 6.29 and d 7.47. The four protons of
phenyl moiety resonated as two doublets at d 7.90 and
d 7.67. The mass spectrum of 1 showed a molecular ion
peak at m/z 201 which confirmed its molecular weight.
1H NMR spectrum of 2a showed a singlet at d 2.01 and
d 1.96 which was accounted for two magnetically nonequiva-
lent methyl groups. The 13C NMR data of 2a also supported
the structure via two CH3 and C]N resonances appeared at
d 25.11, d 17.38 and d 158.79, respectively. The mass spec-
trum of 2a showed a molecular ion peak at m/z 241 which
confirmed its molecular weight.
2. Chemistry
The synthetic strategies adopted to obtain the target com-
pounds are depicted in Scheme 1. The key intermediate in
the present study is 4-pyrrol-1-yl benzoic acid hydrazide 1,
it was prepared by hydrazinolysis of the ethyl ester of 4-
pyrrol-1-yl benzoate with hydrazine hydrate. Reacting the
starting compound 1 with acetone resulted in the formation
of the corresponding N0-(propan-2-ylidene)-4-(1H-pyrrol-
1-yl) benzohydrazide 2a. Condensation of 1 with acetophe-
none and benzophenone yielded hydrazone derivatives 2b
and 2c. The preparation of 5-(4-pyrrol-1-yl phenyl)-1,3,4-
oxadiazole-2-thiol 3 was achieved by adopting a simple one-
pot procedure that involves reacting 1 with carbon disulfide
under strong basic conditions followed by acidification with
dilute hydrochloric acid. Hydrazide 1 was converted into the
corresponding potassium dithiocarbazinate, which on cycliza-
tion with hydrazine hydrate afforded 4-amino-5-(4-pyrrol-1-yl
phenyl)-2,4-dihydro-1,2,4-triazole-3-thione 4. Warming 1 with
acetic anhydride afforded N-acetyl-4-pyrrol-1-yl benzoic acid
hydrazide 5. The reaction of 1 with different aldehydes in al-
cohol gave Schiffs bases 6aee. Cyclization of 6a,b with acetic
anhydride afforded 1,3,4-oxadiazole derivatives 7a,b. Further
1 reacted with acetonyl acetone to afford N-(2,5-dimethyl-
pyrrol-1-yl)-4-pyrrol-1-yl benzamide 8.
1
Lack of H NMR resonances observed with NH and NH2
functions in the 1H NMR spectrum of 3 proved that ring
closure starting from 1 resulted in the formation of 1,3,4-
oxadiazole ring. This was further substantiated by the 13C
NMR data of 3 which showed a peak at d 177.53 and
d 159.87 due to C2 and C5 of oxadiazole. Mass spectrum of
3 displayed a molecular ion base peak at m/z 243 which con-
firmed its molecular weight.
The IR spectrum of 4 displayed stretching bands at 3289
1
and 3113 cmꢀ1 due to NH/NH2. H NMR spectrum of this
sample displayed a singlet at d 13.73 and d 5.55 which was
accounted for NH and NH2, respectively. 13C NMR spectrum
of 4 showed signals at d 168.10 and d 149.15 due to C]S of
triazole and C5 carbon of triazole, respectively. The mass spec-
trum of 4 displayed a molecular ion peak at m/z 257 which
confirmed its molecular weight.
1
The three singlets at d 1.93, d 9.91 and d 10.33 in the H
3. Biological activity
NMR spectrum of 5 were assigned to CH3, amide NH and
NH protons, respectively. The structure of 5 was further
confirmed by the 13C NMR data which displayed signals at
d 21.46, d 165.56 and d 169.48 due to CH3, benzamide and
acetyl carbonyl carbons, respectively. The mass spectrum
exhibited the molecular ion peak at m/z 243 which confirmed
its molecular weight.
The standard strains were procured from the American
Type Culture Collection (ATCC) and Gene Bank, Institute of
Microbial Technology, Chandigarh, India. The antibacterial
activity of the synthesized compounds was performed by broth
microdilution method [17,18] against the following standard
bacterial strains: Staphylococcus aureus (ATCC 11632), Strep-
tococcus faecalis (ATCC 14506), Bacillus subtilis (ATCC
Hydrazones 6a,b obtained from hydrazide 1 showed
carbonyl amide stretching at 1650 cmꢀ1 and NeH bands in

S.D. Joshi et al. / European Journal of Medicinal Chemistry 43 (2008) 1989e1996
1991
R
CH3COR
N
CONHN=C
R'
2 a-c
R
R'
CH3
2a
2b
2c
CH3
CH3
C6H5
C6H5
C6H5
N
N
KOH/CS2
C2H5OH
N
N
CONHNH2
SH
O
3
1
KOH/CS2
H
N
N
NH2NH2.H2O
N
S
CH3COCH2CH2COCH3
N
C2H5OH
NH2
4
H3C
CONH N
H3C
(CH3CO)2O
N
N
CONHNHCOCH3
N
5
8
R-CHO
CONHN=CH
R
6 a-d
R
6 C
6 a
6 b
6 e
NO2
N(CH3)2
Cl
6 d
Cl
OH
(CH3CO)2O
COCH3
N
N
N
R
O
7 a-b
R
7 a
Cl
Cl
7 b
Scheme 1.
1
3203e3200 cmꢀ1 region. H NMR and 13C NMR data were
also in agreement with the formation of hydrazones. 1H
NMR spectra of 6a and 6b showed two singlets at d 8.48,
8.04 and at d 11.89, 12.05 which were attributed to the
N]CH and NH protons, respectively.
1650 cmꢀ1 which were attributed to the C]O stretching of
acetyl group. 2,3-Dihydro-1,3,4-oxadiazole derivatives 7a
and 7b obtained from hydrazones 6a and 6b gave the two sin-
1
glets at d 7.19 and d 7.48 in the H NMR spectra which were
attributed to the OeCHReN resonance of the oxadiazolines
ring and two singlets at d 2.27and d 2.21 were assigned to ace-
tyl CH3. The formation of the oxadiazolines was further
IR spectra of 7a,b had different characteristics as they
showed no NH stretching bands and only C]O bands at

1992
S.D. Joshi et al. / European Journal of Medicinal Chemistry 43 (2008) 1989e1996
supported by the 13C NMR data of compounds 7a and 7b.
While N]CH carbon of compounds in hydrazone structures
was observed at d 148.60 and d 143.12 in their 13C NMR spec-
tra, the same carbon atoms (OCHReN) were observed at
d 92.77 and d 89.82 after cyclization of oxadiazoline ring. In
the 13C NMR spectrum of 7a, this signal was observed at
d 92.77 due to the sp3 hybridization.
Further evidence for the formation of 2,3-dihydro-1,3,4-
oxadiazole 7a was obtained by recording the mass spectra.
The mass spectrum of compound 7a showed a molecular ion
peak at m/z 331 which is in conformity with the molecular for-
mula C20H17N3O2.
B. subtilis. The synthesized compounds showed antimicrobial
activity with MIC values between 31.25 and 500 mg/mL
against S. aureus.
Compounds exhibited lower potencies against S. faecalis.
Compound 5 showed moderate bacterial inhibition.
Compounds 7a,b which have 2,3-dihydro-1,3,4-oxadiazole
ring were more active than the starting compounds 6aee
against some of the test microorganisms.
Compounds 6b, 6e, and 7b which are having inductively
electron withdrawing but mesomerically electron donating
substituents on phenyl group were found to be the most active
compounds against the test microorganisms.
The 1H NMR spectrum of 8 showed singlet at d 2.08 due to
methyl protons of pyrrole, while singlet at d 5.72 was due to
two protons of pyrrole. The mass spectrum of 8 showed a mo-
lecular ion peak at m/z 279 which confirmed its molecular
weight.
In order to determine the antimicrobial activity of the
synthesized compounds, three Gram-positive and three
Gram-negative bacteria species were screened using the broth
dilution technique. Antibacterial results of compounds are
given in Table 1.
The investigation of antibacterial screening data revealed
that all the tested compounds showed moderate to good bacte-
rial inhibition.
Compounds showed antimicrobial activity at MIC values of
8e500 mg/mL.
All the compounds exhibited good activity against P.
aeruginosa.
All the compounds showed good activity against E. coli and
moderate activity against K. pneumoniae.
The tested compounds showed activities against mycobac-
teria with MIC values ranging from 16 to 500 mg/mL. MIC
values are reported in Table 2.
From first examination of the antimycobacterial activity
results, it appears that compounds 7a,b, containing the 1,3,4-
oxadiazoline ring and acetyl group, show better activity
against M. tuberculosis H37Rv and compound 3 showed high-
est activity (MIC 16 mg/mL). Due to the better activity against
tested microorganisms and mycobacteria, compound 3 has
been selected for further development and studies to acquire
more information about structureeactivity relationships are
in progress in our laboratories.
Compounds 1 and 3 were found to be more active than
the other compounds at an MIC value of 8 mg/mL against
5. Experimental procedures
Table 1
In vitro antibacterial activity
5.1. Chemical protocols
Compound
MIC values (mg mLꢀ1
Gram-positive organismsa
)
Gram-negative organismsb
Melting points were determined using open capillary tube
method and are uncorrected.
Thin layer chromatography was performed on precoated
Silica Gel 60 F254 plates from Merck and visualized by
Sa
Sf
31.25
Bs
Kp
Ec
Pa
62.5
1
250
250
250
500
250
500
500
250
125
500
250
125
250
8
125
250
125
125
125
125
125
125
125
500
125
125
125
125
125
125
2a
2b
2c
3
125
125
250
62.5
62.5
62.5
8
62.5
62.5
62.5
31.25
Table 2
Primary antitubercular activity screening results of newly synthesized
compounds
31.25
31.25
4
250
250
250
125
500
125
125
125
125
62.5
125
62.5
250
125
62.5
500
500
125
125
62.5
125
5
Compound
MIC values (mg mLꢀ1) of
M. tuberculosis H37Rv
6a
6b
6c
6d
6e
7a
7b
8
62.5
62.5
62.5
500
250
1
2a
125
62.5
62.5
62.5
16
125
2b
2c
62.5
125
62.5
62.5
62.5
31.25
62.5
62.5
31.25
62.5
62.5
62.5
250
62.5
62.5
3
4
62.5
62.5
125
250
<5
<5
125
<5
<5
125
ꢁ1
ꢁ1
CIPc
NORd
a
ꢁ1
ꢁ1
>5
>5
5
6a
ꢁ1
ꢁ1
6b
6c
31.25
62.5
62.5
31.25
31.25
31.25
31.25
0.25
The screening organisms. Gram-positive bacteria: Staphylococcus aureus
(ATCC 11632, Sa), Streptococcus faecalis (ATCC 14506, Sf), Bacillus subtilis
(ATCC 60511, Bs).
6d
6e
b
The screening organisms. Gram-negative bacteria: Klebsiella pneumoniae
(ATCC 10031, Kp), Escherichia coli (ATCC 10536, Ec), Pseudomonas aeru-
ginosa (ATCC 10145, Pa).
7a
7b
8
Isoniazid
c
Reference drugs: ciprofloxacin.
Reference drugs: norfloxacin.
d

S.D. Joshi et al. / European Journal of Medicinal Chemistry 43 (2008) 1989e1996
1993
exposure to iodine vapors. Spectra were obtained as follows:
infra red (IR) spectra were recorded using KBr disk on
5.1.3. Synthesis of N0-(1-methylbenzylidene)-
4-(1H-pyrrol-1-yl) benzohydrazide (2b)
1
a Nicolet MX-1 FTIR spectrophotometer, H NMR and 13C
A mixture of 1 (0.573 g, 0.003 mol) and acetophenone
(0.360 g, 0.003 mol) in ethanol (20 mL) was refluxed for 4 h
in the presence of few drops of acetic acid. The product
formed is filtered, washed with ethanol and recrystallised
from aqueous DMF as yellow crystals in 75% yield. M.p.
234e36 ꢃC.
IR (KBr) nmax, cmꢀ1: 3308 (NH), 1658 (amide C]O).
1H NMR (DMSO-d6, 300 MHz) d: 10.78 (s, 1H, amide NH,
disappeared on D2O exchange), 7.42e7.96 (m, 11H, ArH,
pyrroleeC2 and C5eH ), 6.31 (s, 2H, pyrroleeC3 and
C4eH ), 2.37 (s, 3H, CH3) ppm.
NMR spectra were recorded at 300 MHz on a Bruker spec-
trometer and their chemical shifts are reported in d (parts
per million) units with respect to TMS as internal standard.
Microanalysis for C, H, N was performed in a Heraeus
CHN Rapid Analyzer. The FAB mass spectra were recorded
on Autospec mass spectrometer.
All new compounds yielded spectral data consistent with
the proposed structure and microanalysis within ꢂ0.4% of
the theoretical values.
13C NMR (DMSO-d6, 300 MHz) d: 168.00 (amide C]O),
152.20 (C]NeNH), 144.10 (C4), 131.75 (phenyleC1),
130.69 (C2 and C6), 130.02 (phenyleC4), 129.14 (phenyle
C2 and C6), 128.02 (C1), 126.32 (phenyleC3 and C5),
118.77 (pyrroleeC2 and C5), 111.07 (pyrroleeC3 and C4),
14.10 (CH3) ppm.
5.1.1. Synthesis of 4-pyrrol-1-yl benzoic acid hydrazide (1)
Compound 1 was synthesized by refluxing a mixture of
ethyl 4-pyrrol-1-yl benzoate [21] (3.22 g, 0.015 mol) with
hydrazine hydrate (10 mL) in absolute ethanol (10 mL) for
3 h. The reaction mixture was cooled and crystalline mass ob-
tained was recrystallised from ethanol and obtained as yellow
crystals in 74% yield. M.p. 180e182 ꢃC.
MS m/z: found 303 [Mþ], 304 [M þ 1]; calcd. 303. Anal
C19H17N3O.
IR (KBr) nmax, cmꢀ1: 3335, 3278 (NH/NH2), 1610 (amide
C]O).
5.1.4. Synthesis of N0-(benzhydrylidene)-
1H NMR (DMSO-d6, 300 MHz) d: 9.81 (s, 1H, NH, disap-
peared on D2O exchange), 7.90 (d, J ¼ 8.5 Hz, 2H, C2 and
C6eH ), 7.67 (d, J ¼ 8.5 Hz, 2H, C3 and C5eH ), 7.47 (s, 2H,
pyrroleeC2 and C5eH ), 6.29 (s, 2H, pyrroleeC3 and
C4eH ), 4.51 (s, 2H, NH2, disappeared on D2O exchange) ppm.
13C NMR (DMSO-d6, 300 MHz) d: 165.10 (amide C]O),
141.74 (C4), 129.67 (C1), 128.54 (C2 and C6), 118.96 (C3 and
C5), 118.46 (pyrroleeC2 and C5), 111.01 (pyrroleeC3 and
C4) ppm.
4-(1H-pyrrol-1-yl) benzohydrazide (2c)
A mixture of 1 (0.573 g, 0.003 mol) and benzophenone
(0.546 g, 0.003 mol) in ethanol (20 mL) was refluxed for 6 h
in presence of few drops of acetic acid. The product formed
is filtered, washed with water and recrystallised from ethanol
as orange crystals in 61% yield. M.p. 186e88 ꢃC.
IR (KBr) nmax, cmꢀ1: 3368 (NH), 1674 (amide C]O).
1H NMR (DMSO-d6, 300 MHz) d: 10.10 (s, 1H, amide
NH, disappeared on D2O exchange), 7.40e7.80 (m, 16H,
ArH, pyrroleeC2 and C5eH ), 6.30 (s, 2H, pyrroleeC3 and
C4eH ) ppm.
MS m/z: found 201 [Mþ], 202 [M þ 1]; calcd. 201. Anal
C11H11N3O.
MS m/z: found 365 [Mþ], 366 [M þ 1]; calcd. 365. Anal
C24H19N3O.
5.1.2. Synthesis of N0-(propan-2-ylidene)-4-(1H-pyrrol-1-yl)
benzohydrazide (2a)
5.1.5. Synthesis of 5-(4-pyrrol-1-yl phenyl)-
A solution of 4-pyrrol-1-yl benzoic acid hydrazide 1
(0.95 g, 0.005 mol) in 75 mL of acetone was refluxed for
1 h. Evaporation of solvent furnished a pale yellow solid, re-
crystallised from ethanol and obtained as pale yellow crystals
in 75% yield. M.p. 210e213 ꢃC.
1,3,4-oxadiazole-2-thiol (3)
Acid hydrazide 1 (0.573 g, 0.003 mol) was dissolved in
a solution of potassium hydroxide (0.336 g, 0.006 mol) in wa-
ter (2 mL) and ethanol (20 mL). Carbon disulfide (2 mL) was
then added while stirring and the reaction mixture was heated
under reflux for 8 h. The solvents were removed under reduced
pressure, the residue was treated with water and then filtered.
The filtrate was cooled, neutralized to pH 6 using dilute hydro-
chloric acid and the separated product was filtered, washed
with water, dried and recrystallised from benzene as yellow
crystals in 86% yield. M.p. 208e210 ꢃC.
IR (KBr) nmax, cmꢀ1: 3260 (NH), 1660 (amide C]O).
1H NMR (DMSO-d6, 300 MHz) d: 10.45 (s, 1H, amide NH,
disappeared on D2O exchange), 7.92 (d, J ¼ 8.5 Hz, 2H, C2
and C6eH ), 7.69 (d, J ¼ 8.5 Hz, 2H, C3 and C5eH ), 7.47
(s, 2H, pyrroleeC2 and C5eH ), 6.31 (s, 2H, pyrroleeC3 and
C4eH ), 2.01 (s, 3H, CH3), 1.96 (s, 3H, CH3) ppm.
13C NMR (DMSO-d6, 300 MHz) d: 163.15 (amide C]O),
158.79 (C]NeNH), 142.14 (C4), 128.98 and 130.22 (C2 and
C6), 128.37 (C1), 118.62 (C3 and C5), 118.39 (pyrroleeC2 and
C5), 110.75 (pyrroleeC3 and C4), 25.11 (CH3), 17.38
(CH3) ppm.
IR (KBr) nmax, cmꢀ1: 1617 (C]N), 2773 (SH).
1H NMR (DMSO-d6, 300 MHz) d: 7.92 (d, J ¼ 8.5 Hz, 2H,
C2 and C6eH ), 7.81 (d, J ¼ 8.5 Hz, 2H, C3 and C5eH ), 7.50
(s, 2H, pyrroleeC2 and C5eH ), 6.32 (s, 2H, pyrroleeC3 and
C4eH ), 3.43 (SH merged in HOD peak of DMSO-d6) ppm.
13C NMR (DMSO-d6, 300 MHz) d: 177.53 (oxadiazolee
C2), 159.87 (oxadiazoleeC5), 142.49 (C4), 127.78 (C1),
MS m/z: found 241 [Mþ], 242 [M þ 1]; calcd. 241. Anal
C14H15N3O.

1994
S.D. Joshi et al. / European Journal of Medicinal Chemistry 43 (2008) 1989e1996
127.32 (C2 and C6), 119.42 (C3 and C5), 118.99 and 118.35
(pyrroleeC2 and C5), 111.11 (pyrroleeC3 and C4) ppm.
MS m/z: found 243 [Mþ], 244 [M þ 1]; calcd. 243. Anal
C12H9N3OS.
MS m/z: found 243 [Mþ], 244 [M þ 1]; calcd. 243. Anal
C13H13N3O2.
5.2. General procedure for the synthesis of N0-
(arylidene)-4-(1H-pyrrol-1-yl) benzohydrazides (6aee)
5.1.6. Synthesis of 4-amino-5-(4-pyrrol-1-yl phenyl)-2,
4-dihydro-1,2,4-triazole-3-thione (4)
Equimolar quantity of 4-pyrrol-1-yl-benzoic acid hydrazide
and different aldehydes was refluxed in alcohol for 4 h in the
presence of few drops of glacial acetic acid. Solvent was evap-
orated and the product was poured onto cold water, filtered
and dried. The crude solid was recrystallised in appropriate
solvent systems to give the products.
To a solution of potassium hydroxide (0.37 g, 0.0067 mol)
in absolute ethanol (30 mL), 4-pyrrol-1-yl benzoic acid hydra-
zide 1 (0.578 g, 0.003 mol) and carbon disulphide (0.45 mL,
0.006 mol) were added and the mixture was agitated for
16 h. To the resulting solution anhydrous ether was added
and the precipitated potassium dithiocarbazinate was collected
by filtration, washed with ether and dried under vacuum. The
potassium salt was obtained in quantitative yield and was used
in the next step without further purification.
5.2.1. N0-(Benzylidene)-4-(1H-pyrrol-1-yl)
benzohydrazide (6a)
Recrystallised from aqueous DMF as yellow crystals in
84% yield. M.p. 230e232 ꢃC.
IR (KBr) nmax, cmꢀ1: 3200 (NH), 1650 (amide C]O).
1H NMR (DMSO-d6, 300 MHz) d: 11.89 (s, 1H, NH,
disappeared on D2O exchange), 8.48 (s, 1H, eN]CHeAr),
8.02 (d, 2H, J ¼ 8.5 Hz, C2 and C6eH ), 7.45e7.78
(m, 9H, AreH pyrroleeC2 and C5eH ), 6.32 (s, 2H, pyrro-
leeC3 and C4eH ) ppm.
A suspension of the potassium salt, hydrazine hydrate
(1.5 mL) and water (1.0 mL) was heated under reflux for
5 h. Hydrogen sulphide evolved and homogenous solution
resulted which was diluted with 50 mL water and subsequent
acidification with dilute acetic acid gave a white precipitate
which was filtered, washed with water and recrystallised
from aqueous DMF and obtained as pale yellow crystals in
81% yield. M.p. 250e252 ꢃC.
13C NMR (DMSO-d6, 300 MHz) d: 163.13 (amide C]O),
148.60 (CH]N), 143.13 (C4), 135.22 (phenyleC1), 130.93
(phenyleC4), 130.46 (phenyleC2 and C6), 130.21 (phenyle
C3 and C5), 129.71 (C2 and C6), 127.94 (C1), 119.89 (C3
and C5), 119.36 (pyrroleeC2 and C5), 112.06 (pyrroleeC3
and C4) ppm.
IR (KBr) nmax, cmꢀ1: 3289 (NH), 3113 (NH2).
1H NMR (DMSO-d6, 300 MHz) d: 13.73 (s, 1H, NH, disap-
peared on D2O exchange), 8.14 (d, J ¼ 8.5 Hz, 2H, C2 and
C6eH ), 7.48 (d, J ¼ 8.5 Hz, 2H, C3 and C5eH ), 7.17 (s,
2H, pyrroleeC2 and C5eH ), 6.25 (s, 2H, pyrroleeC3 and
C4eH ), 5.55 (s, 2H, NH2, disappeared on D2O exchange) ppm.
13C NMR (DMSO-d6, 300 MHz) d: 168.10 (triazolee
C]S), 149.15 (triazoleeC5), 142.10 (C4), 130.00 (C2 and
C6), 122.21 (C1), 119.10 (C3 and C5), 118.80 (pyrroleeC2
and C5), 111.01 (pyrroleeC3 & C4) ppm.
MS m/z: found 289 [Mþ], 290 [M þ 1]; calcd. 289. Anal
C18H15N3O.
5.2.2. N0-(2,6-Dichlorobenzylidene)-4-(1H-pyrrol-1-yl)
benzohydrazide (6b)
Recrystallised from aqueous DMF as yellow crystals in
81% yield. M.p. 220e222 ꢃC.
MS m/z: found 257 [Mþ], 258 [M þ 1]; calcd. 257. Anal
C12H11N5S.
IR (KBr) nmax, cmꢀ1: 3203 (NH), 1650 (amide C]O).
1H NMR (DMSO-d6, 300 MHz) d: 12.05 (s, 1H, NH, dis-
appeared on D2O exchange), 8.04 (s, 1H, eN]CHeAr),
7.50e7.79 (m, 9H, AreH pyrroleeC2 and C5eH ), 6.32 (s,
2H, pyrroleeC3 and C4eH ) ppm.
13C NMR (DMSO-d6, 300 MHz) d: 167.28 (amide C]O),
143.12 (CH]N), 142.70 (C4), 134.53 (dichlorophenyleC2
and C6), 133.09 (dichlorophenyleC1), 130.78 (C1), 130.614
(dichlorophenyleC4), 129.78 (dichlorophenyleC3 and C5),
129.63 (C2 and C6), 120.09 (C3 and C5), 118.74 (pyrrolee
C2 and C5), 111.16 (pyrroleeC3 and C4) ppm.
MS m/z: found 358 [Mþ], 359 [M þ 1]; calcd. 358. Anal
C18H13Cl3N3O.
5.1.7. Synthesis of N-acetyl-4-pyrrol-1-yl benzoic acid
hydrazide (5)
Acid hydrazide 1 (0.578 g, 0.003 mol) was warmed with
acetic anhydride (5 mL) for 1 h and then the mixture was
allowed to attain room temperature. The deposited pale yellow
solid was filtered, washed and recrystallised from ethanol and
obtained as yellow crystals in 77% yield. M.p. 232e234 ꢃC.
IR (KBr) nmax, cmꢀ1: 3346, 3325 (NH), 1693 (acetyl
C]O), 1645 (amide C]O).
1H NMR (DMSO-d6, 300 MHz) d: 10.33 (s, 1H, NH, disap-
peared on D2O exchange), 9.91 (s, 1H, amide NH, disappeared
on D2O exchange), 7.96 (d, J ¼ 8.5 Hz, 2H, C2 and C6eH ),
7.73 (d, J ¼ 8.5 Hz, 2H, C3 and C5eH ), 7.49 (s, 2H, pyrro-
leeC2 and C5eH ), 6.30 (s, 2H, pyrroleeC3 and C4eH ),
1.93 (s, 3H, CH3) ppm.
5.2.3. N0-(3-Nitrobenzylidene)-4-(1H-pyrrol-1-yl)
benzohydrazide (6c)
13C NMR (DMSO-d6, 300 MHz) d: 169.48 (acetyleC]O),
165.56 (amideeC]O), 143.09 (C4), 129.98 (C2 and C6),
129.60 (C4), 119.84 (C3 and C5), 119.29 (pyrroleeC2 and
C5), 112.06 (pyrroleeC3 and C4), 21.46 (CH3) ppm.
Recrystallised from aqueous DMF as yellow crystals in
82% yield. M.p. 258e260 ꢃC.
IR (KBr) nmax, cmꢀ1: 3261 (NH), 1660 (amide C]O).

S.D. Joshi et al. / European Journal of Medicinal Chemistry 43 (2008) 1989e1996
1995
1H NMR (DMSO-d6, 300 MHz) d: 12.15 (s, 1H, amide NH,
5.3. General procedure for the synthesis of 3-acetyl-5-
(4-pyrrol-1-yl phenyl)-2-substituted-2,3-dihydro-
1,3,4-oxadiazoles (7a,b)
disappeared on D2O exchange), 8.55 (s, 1H, eN]CHeAr),
7.73e8.27 (m, 8H, ArH ), 7.49 (s, 2H, pyrroleeC2 and
C5eH ), 6.33 (s, 2H, pyrroleeC3 and C4eH ) ppm.
13C NMR (DMSO-d6, 300 MHz) d: 162.57 (amide C]O),
148.05 (CH]N), 145.02 (3-nitro-phenyleC5), 142.39 (C4),
136.14 (3-nitro-phenyleC1), 132.99 (3-nitro-phenyleC2),
129.85 (C2 and C6), 129.33 (3-nitro-phenyleC3), 129.19
(C1), 123.83 (3-nitro-phenyleC6), 120.94 (3-nitro-phenyle
C4), 118.63 (C3 and C5), 118.45 (pyrroleeC2 and C5),
111.01 (pyrroleeC3 and C4) ppm.
A mixture of 6 (0.003 mol) and acetic anhydride (10 mL)
was heated under reflux for 4 h. After the reaction mixture at-
tained room temperature, excess acetic anhydride was decom-
posed by water and the mixture was stirred for further 30 min.
The separated product was filtered, washed with water, dried
and recrystallised in appropriate solvent systems to give the
products.
MS m/z: found 334 [Mþ], 335 [M þ 1]; calcd. 334. Anal
C18H14N4O3.
5.3.1. 3-Acetyl-5-(4-pyrrol-1-yl phenyl)-2-phenyl-
2,3-dihydro-1,3,4-oxadiazole (7a)
Recrystallised from ethanol as pale brown crystals in 60%
yield. M.p. 184e186 ꢃC.
5.2.4. N0-(4-Dimethylaminobenzylidene)-4-(1H-pyrrol-1-yl)
benzohydrazide (6d)
Recrystallised from aqueous DMF as pale yellow crystals
in 72% yield. M.p. 252e254 ꢃC.
IR (KBr) nmax, cmꢀ1: 1660 (acetyl C]O).
1H NMR (DMSO-d6, 300 MHz) d: 7.45e7.86 (m, 11H,
AreH ), 7.19 (oxadiazoleeC2eH ), 6.32 (s, 2H, pyrroleeC3
and C4eH ), 2.27 (s, 3H, CH3) ppm.
IR (KBr) nmax, cmꢀ1: 3184 (NH), 1649 (amide C]O).
1H NMR (DMSO-d6, 300 MHz) d: 11.56 (s, 1H, NH, dis-
appeared on D2O exchange), 8.31 (s, 1H, eN]CHeAr),
7.49e7.99 (m, 8H, AreH ), 6.76 (s, 2H, pyrroleeC2 and
C5eH ), 6.31 (s, 2H, pyrroleeC3 and C4eH ), 2.97 (s, 6H,
2CH3) ppm.
13C NMR (DMSO-d6, 300 MHz) d: 162.89 (amide C]O),
159.49 (CH]N), 148.88 (4-hydroxy phenyleC4), 142.39
(C4), 130.48 (C1), 129.32 (4-hydroxy phenyleC2 and C6),
128.90 (C3 and C5), 125.41 (C2 and C6), 122.10 (4-hydroxy
phenyleC1), 118.74 (pyrroleeC2 and C5), 115.65 (4-hydroxy
phenyleC3 and C5), 111.04 (pyrroleeC3 and C4) ppm.
MS m/z: found 332 [Mþ], 333 [M þ 1]; calcd. 332. Anal
C18H14N4O3.
13C NMR (DMSO-d6, 300 MHz) d: 167.57 (acetyl C]O),
155.13 (oxadiazoleeC5), 143.06 (C4), 137.49 (C1), 130.70
(phenyleC1 at C5 of oxadiazole), 129.65 (phenyleC4 at C5
of oxadiazole), 129.03 (C2 and C6), 127.42 (phenyleC2 and
C6 at C5 of oxadiazole), 121.14 (phenyleC3 and C5 at C5 of
oxadiazole), 120.02 (C3 and C5), 119.83 (pyrroleeC2 and
C5), 112.25 (pyrroleeC3 and C4), 92.77 (oxadiazoleeC2),
22.07 (CH3) ppm.
MS m/z: found 331 [Mþ], 332 [M þ 1]; calcd. 331. Anal
C20H17N3O2.
5.3.2. 3-Acetyl-5-(4-pyrrol-1-yl phenyl)-2-(2,6-dichloro
phenyl)-2,3-dihydro-1,3,4-oxadiazole (7b)
Recrystallised from ethanol as pale brown crystals in 67%
yield. M.p. 188e192 ꢃC.
5.2.5. N0-(4-Hydroxybenzylidene)-4-(1H-pyrrol-1-yl)
benzohydrazide (6e)
Recrystallised from aqueous DMF as pale yellow crystals
in 66% yield. M.p. 264e266 ꢃC.
IR (KBr) nmax, cmꢀ1: 3388 (OH), 3266 (NH), 1650 (amide
C]O).
1H NMR (DMSO-d6, 300 MHz) d: 11.67 (s, 1H, OH ), 9.95
(s, 1H, NH, disappeared on D2O exchange), 8.36 (s, 1H, e
N]CHeAr), 7.98 (d, 2H, J ¼ 8.5 Hz, C2 and C6eH ), 7.73
(d, 2H, J ¼ 8.5 Hz, C3 and C5eH ), 7.50e7.58 (m, 4H, C3
and C5eH and pyrroleeC2 and C5eH ), 6.83 (d, 2H,
J ¼ 8.5 Hz, 4-hydroxy-phenyleC3 and C5eH ), 6.31 (s, 2H,
pyrroleeC3 and C4eH ) ppm.
IR (KBr) nmax, cmꢀ1: 1660 (acetyl C]O).
1H NMR (DMSO-d6, 300 MHz) d: 7.48e8.02 (m, 10H,
AreH, oxadiazoleeC2eH ), 6.31 (s, 2H, pyrroleeC3 and
C4eH ), 2.21 (s, 3H, CH3) ppm.
13C NMR (DMSO-d6, 300 MHz) d: 167.28 (acetyl C]O),
154.81 (oxadiazoleeC5), 143.03 (C4), 134.08 (dichlorophe-
nyleC2 and C6), 133.09 (dichlorophenyleC1), 130.08 (C1),
130.66 (dichlorophenyleC4), 129.97 (dichlorophenyleC3
and C5), 129.00 (C2 and C6), 120.09 (C3 and C5), 119.84
(pyrroleeC2 and C5), 112.22 (pyrroleeC3 and C4), 89.82
(oxadiazoleeC2), 21.80 (CH3) ppm.
MS m/z: found 400 [Mþ], 401 [M þ 1]; calcd. 400. Anal
C20H15Cl2N3O2.
13C NMR (DMSO-d6, 300 MHz) d: 162.10 (amide C]O),
151.76 (CH]N), 148.88 (4-dimethylamino-phenyleC4),
142.27 (C4), 130.26 (C1), 129.39 (4-dimethylamino-phenyle
C2 and C6), 128.66 (C2 and C6), 121.87 (4-dimethylamino-
phenyleC1), 119.23 (C3 and C5), 118.71 (pyrroleeC2 and
C5), 112.04 (4-dimethylamino-phenyleC3 and C5), 111.31
(pyrroleeC3 and C4) ppm.
5.4. N-(2,5-Dimethyl-pyrrol-1-yl)-4-pyrrol-1-yl
benzamide (8)
To a suspension of 4-pyrrol-1-yl benzoic acid hydrazide 1
(0.573 g, 0.003 mol) in ethanol (10 mL) were added acetonyl
acetone (0.684 g, 0.006 mol) and glacial acetic acid (1 mL),
and the reaction mixture was heated on a boiling water bath
for 4 h. The reaction mixture was concentrated to half of
MS m/z: found 305 [Mþ], 306 [M þ 1]; calcd. 305. Anal
C18H15N3O2.

1996
S.D. Joshi et al. / European Journal of Medicinal Chemistry 43 (2008) 1989e1996
original volume and poured into crushed ice (50 g). The sepa-
rated solid was filtered, washed with water, dried and recrys-
tallised from ethanol as brown crystals in 86% yield. M.p.
228e230 ꢃC.
culture and then incubated at 37 ꢃC for 21 days. The growth in
the U-tubes was compared with visibility against positive
control (without drug), negative control (without drug and
inoculum) and with standard isoniazid.
IR (KBr) nmax, cmꢀ1: 3275 (NH), 1660 (amide C]O).
1H NMR (DMSO-d6, 300 MHz) d: 11.27 (s, 1H, NH, disap-
peared on D2O exchange), 8.06 (d, J ¼ 8.5 Hz, 2H, C2 and
C6eH ), 7.80 (d, J ¼ 8.5 Hz, 2H, C3 and C5eH ), 7.52 (s,
2H, pyrroleeC2 and C5eH ), 6.33 (s, 2H, pyrroleeC3 and
C4eH ), 5.72 (s, 2H, dimethyl pyrroleeC3 and C4eH ), 2.08
(s, 6H, pyrrole methyls) ppm.
13C NMR (DMSO-d6, 300 MHz) d: 165.50 (amide C]O),
143.06 (C4), 129.32 (C1), 128.63 (C2 and C6), 127.45
(dimethyl pyrroleeC2 and C5), 119.17 (C3 and C5), 118.74
(pyrroleeC2 and C5), 111.22 (pyrroleeC3 and C4), 103.43
(dimethyl pyrroleeC3 and C4), 11.04 (2CH3) ppm.
MS m/z: found 279 [Mþ], 280 [M þ 1]; calcd. 279. Anal
C17H17N3O.
Acknowledgements
We thank Shri. H.V. Dambal, President, Dr. V.H. Kulkarni,
Principal, S.E.T’s College of Pharmacy, Dharwad, India, for
providing necessary facilities. We are grateful to Dr. K.G.
Bhat, Maratha Mandal’s Dental College, Hospital and Research
Centre, Belgaum, India, for providing the facilities to determine
the antibacterial and antitubercular activities. We also wish to
thank Director, RSIC, Panjab University, Chandigarh, India
and Quest Research and Training Institute (Pvt.) Ltd, Banga-
lore, India for providing IR, NMR and mass spectral data.
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