Synthesis of novel 4-nitropyrrole-based semicarbazide and thiosemicarbazide hybrids with antimicrobial and anti-tubercular activity

Article abstract of DOI:10.1016/j.bmcl.2014.05.018

We report the synthesis and screening of forty novel 4-nitropyrrole- semicarbazide conjugates inspired from the reported bio-potential of bromopyrrole alkaloids and semicarbazide derivatives for antimicrobial activity. Herein, hybrids 5k-5o, 5r, 5s and 5t

Full text of DOI:10.1016/j.bmcl.2014.05.018

Accepted Manuscript
Synthesis of novel 4-nitropyrrole-based semicarbazide and thiosemicarbazide
hybrids with antimicrobial and anti-tubercular activity
Rajesh A. Rane, Shital S. Naphade, Pavan Kumar Bangalore, Mahesh B. Palkar,
Mahamadhanif S. Shaikh, Rajshekhar Karpoormath
PII:
S0960-894X(14)00505-8
DOI:
http://dx.doi.org/10.1016/j.bmcl.2014.05.018
BMCL 21631
Reference:
Bioorganic & Medicinal Chemistry Letters
To appear in:
Received Date:
Revised Date:
Accepted Date:
18 March 2014
30 April 2014
5 May 2014
Please cite this article as: Rane, R.A., Naphade, S.S., Bangalore, P.K., Palkar, M.B., Shaikh, M.S., Karpoormath,
R., Synthesis of novel 4-nitropyrrole-based semicarbazide and thiosemicarbazide hybrids with antimicrobial and
anti-tubercular activity, Bioorganic & Medicinal Chemistry Letters (2014), doi: http://dx.doi.org/10.1016/j.bmcl.
2014.05.018
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Synthesis of novel 4-nitropyrrole-based semicarbazide and thiosemicarbazide hybrids
with antimicrobial and anti-tubercular activity
Rajesh A. Ranea, Shital S. Naphadeb, Pavan Kumar Bangalorec, Mahesh B. Palkara,
Mahamadhanif S. Shaikha and Rajshekhar Karpoormatha*
a Discipline of Pharmaceutical Sciences, College of Health Sciences, University of KwaZulu-
Natal, Durban 4001, South Africa.
bPiramal Health Care Ltd, Goregaon, Mumbai, India.
cS. P. P. School of Pharmacy and Technology Management, NMIMS University, Vile Parle,
Mumbai 400056, India.
To receive all correspondence: Rajshekhar Karpoormath: Tel: +27 (0) 312607179, E-mail:
karpoormath@ukzn.ac.za
Abstract
We report the synthesis and screening of forty novel 4-nitropyrrole-semicarbazide conjugates
inspired from the reported bio-potential of bromopyrrole alkaloids and semicarbazide
derivatives for antimicrobial activity. Herein, hybrids 5k-5o, 5r-5s and 5t displayed four-fold
increased activity (MIC = 0.39 µg/mL) against E. coli compared to standard ciprofloxacin.
Eight hybrids, 5k-5o and 5r-5t displayed equal antibacterial activity (MIC = 1.56 µg/mL)
against K. pneumonia compared to standard Ciprofloxacin. Hybrid, 5k -5o (MIC = 0.195
µg/mL) displayed highly potent antibacterial activity against MSSA as compared to standard
Ciprofloxacin. Eight-fold superior activity was observed for four hybrids 5k-5m and 5o (MIC
= 0.39 µg/mL) against MRSA. Further, nine hybrids displayed four-fold superior antifungal
activity (MIC = 0.78 µg/mL) compared to standard Amphotericin B. Encouraging MICs of
these hybrids recognize them as promising leads for development of potential antimicrobial
drugs.
Keywords: 4-Nitropyrrole, semicarbazides, thiosemicarbazides, antimicrobial agent, anti-
tubercular agent

Bacterial resistance to antibacterial agents or antibiotics is of grave concern in the medical
community as many species of bacteria have evolved resistance to certain antibiotics and
synthetic agents. Therefore, there is a rapidly growing global crisis in the clinical
management of life-threatening infectious disease caused by multidrug-resistant strains of the
Gram-positive pathogens Streptococcus, Enterococcus, and Staphylococcus as well as the
Gram-negative pathogens Escherichia, Salmonella, and certain Pseudomonas strains.
Especially, the emergence of multidrug-resistant strains of gram-positive bacterial pathogens
such as methicillin-resistant Staphylococcus aureus (MRSA) and Staphylococcus epidermis
and vancomycin-resistant Enterococcus is a primarily alarming problem of ever-increasing
significance.This increased resistance demands for the discovery and development of novel
antimicrobial leads with high efficacy.1-3
Over the years, molecular hybrid-based approachs4 had been exploited by researchers to
discover some promising chemical architectures, displaying significant medicinal profiles.
Using this approach, we have reported molecular hybridization assisted design, synthesis and
evaluation of natural pyrrole alkaloids-inspired conjugates with antimicrobial and anticancer
properties.5-7 Our recent exploration of this approach led to synthesis of 1,3,4-oxadiazole-4-
nitropyrrole hybrids7. The synthesized conjugates were tested for their antimicrobial and anti-
tubercular activity. These hybrids showed promising antibacterial activity against
Staphylococcus aureus, Bacillus subtilis, Escherichia coli, Methicillin-resistant
Staphylococcus aureus and Methicillin-sensitive Staphylococcus aureus. Herein, three
hybrids demonstrated promising anti-tubercular activity at MIC value less than 1.0 µg/mL
against Mycobacterium tuberculosis H37RV. Likewise, equal antifungal activity (MIC = 1.56
µg/mL) compared to standard Amphotericin-B was displayed by most of the hybrids. The
promising antibacterial, antifungal and anti-tubercular results along with their non-toxicity
profile for mammalian cells indicates that integration of 4-nitropyrrole feature with 1,3,4-
oxadiazole was favourable for antimicrobial activity. Further from the literature reports it is
known that 4-nitropyrrole-based natural products and their derivatives have shown potent
antimicrobial activities8-12 (Figure 1).
The bio-potential of semicarbazides and thiosemicarbazide derivatives as antibacterial,
antifungal and anti-tubercular agents have been well documented in literature (Figure 1).13-19
Semicarbazides are biologically active and nontoxic compounds due to the presence of ureido
unit (–NH-CO-NH–), which acts as pseudodipeptide motif. Considering the biological
importance of substituted semicarbazides/thiosemicarbazides and 4-nitropyrrole templates, an
attempt was made to design a series of novel antimicrobial conjugates incorporating these

features (Figure 2). In this communication we report the synthesis and in vitro screening of
semicarbazide and thiosemicarbazide hybrids for their antibacterial, antifungal and anti-
tubercular activities against Escherichia coli (ATCC- 25922), Klebsiella pneumoniae
(recultured), Methicillin-resistant Staphylococcus aureus ((MRSA; ATCC 43866) ,
Methicillin-sensitive Staphylococcus aureus (MSSA; ATCC 35556) and Mycobacterium
tuberculosis H37RV. We also reviewed the effect of N-methylation of pyrrole core on
antimicrobial activity. These hybrids were further evaluated for their toxicity profile on
mammalian cell using VERO cell lines.
The target semicarbazide and thiosemicarbazide hybrids were synthesized as illustrated in
Scheme 1. Initial key intermediates 1, 2 and 3 were synthesized as per previously reported
reaction scheme by our group.7 Acetylation of pyrrole/N-methylpyrrole using
trichloroacetylchloride gave 2-trichloroacetylpyrrole/N-methyl-2-trichloroacetylpyrrole 1a
and 1b in good yield. The acetylated products 1a and 1b underwent reaction with fuming
nitric acid in acetic anhydride resulting in to compounds 2a and 2b (4-nitro-1H-2-
trichloroacetylpyrrole). The obtained nitrated products were reacted with excess of hydrazine
hydrate in absolute alcohol to give hydrazide derivatives 3a and 3b.7 Equivalent amounts of
arylisocyanates/arylisothiocyanates were added to the hydrazide compounds 3a and 3b in
absolute alcohol under reflux conditions to obtain the desired compounds 4 a-t and 5 a-t.20
The synthesized (thio)semicarbazides exhibited encouraging antibacterial, antifungal and
anti-tubercular activities as shown in Table 1. Moderate to excellent antibacterial activity
(MIC = 0.39 – 6.25 µg/mL) was exhibited by synthesized hybrids against Gram-negative
bacterium E. coli. Among the thiosemicarbazides, eight hybrids (5k-5o and 5r-5t) displayed
four-fold increased antibacterial activity (MIC = 0.39 µg/mL) followed by 5p (MIC = 0.78
µg/mL) with two-fold superior activity against E. coli compared to standard ciprofloxacin
(MIC = 1.56 µg/mL). Presence of halogen on phenyl ring at ring B in hybrids 5m-5o is
beneficial for antibacterial activity against Gram-negative bacterium E. coli. N-methylation of
pyrrole core is more favored for antibacterial activity against E. coli than pyrrole-NH-free
(5c-5e; MIC = 1.56 µg/mL). Hybrids 5l and 5t highlight the benefit of having methoxy group
on phenyl ring at ring B for antibacterial activity against E. coli. Superior activity shown by
hybrids with pyrrole-N-CH3 substitution (5b and 5j) compared to their NH-free analogs (5l
and 5t) point out the favorable effect of N-methylation of pyrrole core for antibacterial
activity against E. coli. All the pyrrole-NH-free analogs (5a-5i and 5j) demonstrated similar
antibacterial activity (MIC 1.56 µg/mL) compared to standard ciprofloxacin against E. coli

except 5f and 5g. The semicarbazide analogs (4a-4t) exhibited less antibacterial potency
(MIC = 1.56 - 6.25 µg/mL) compared to thiosemicarbazides against E.coli. The
thiosemicarbazides and N-methylated semicarbazides displayed superior antibacterial activity
than their NH-free analogs.
From the forty tested hybrids, most of the compounds displayed moderate to good
antibacterial activity (MIC = 1.56 - 6.25 µg/mL) against K. pneumoniae compared to standard
ciprofloxacin (MIC = 1.56 µg/mL). The semicarbazide analogs (4a-4t) demonstrated two to
three-fold less activity against K. pneumoniae compared to standard ciprofloxacin. However,
eight thiosemicarbazide hybrids 5k-5o and 5r-5t showed identical antibacterial activity (MIC
= 1.56 µg/mL) against K. pneumoniae compared to standard Ciprofloxacin. This indicated
that the thio-analogs, thiosemicarbazides are more favored than semicarbazides for activity
against K. pneumoniae. Further, biological data also revealed that N-methylation of the
pyrrole core is more favored than pyrrole-NH-free for antibacterial activity against K.
pneumoniae.
Synthesized semicarbazide and thiosemicarbazide hybrids exhibited moderate to excellent
antibacterial activity against Methicillin Susceptible Staphylococcus aureus (MSSA) (MIC =
0.195 - 3.125 µg/mL). Seventeen of the twenty semicarbazide analogs 4a-4t displayed equal
antibacterial activity against MSSA (MIC = 1.56 µg/mL) while the hybrids 4e, 4h and 4p
exhibited two fold less antibacterial potency (MIC = 3.125 µg/mL) against MSSA compared
to standard Ciprofloxacin. However thiosemicarbazide analogs showed moderate to excellent
antibacterial activity against MSSA (MIC = 0.195 – 3.125 µg/mL). Among these, four
hybrids 5k, 5l, 5m and 5o significantly displayed an eight-fold antibacterial activity (MIC =
0.195 µg/mL) against MSSA as compared to standard Ciprofloxacin. MICs of hybrids 5m
(MIC = 0.195 µg/mL) and 5n (MIC = 0.39 µg/mL) indicated that presence of halogen atom at
para-position on the phenyl ring is more favored than at ortho- for antibacterial activity
against MSSA. Further, antibacterial activity of hybrid 5l (MIC = 0.195 µg/mL) and 5t (MIC
= 0.78 µg/mL) revealed that the presence methoxy group at para-position on phenyl ring
enhanced the activity. However, substituting more than one methoxy group on phenyl ring
decreased activity against MSSA compared to para-methoxyphenyl- substituted analog.
Four-fold superior activity was observed for hybrids 5n, 5r and 5s (MIC = 0.39 µg/mL)
against MSSA compared to standard Ciprofloxacin. Eight semicarbazide hybrids 5a-5f, 5h
and 5i displayed equal antibacterial activity (MIC = 1.56 µg/mL) against MSSA. Analysis of

the anti-MSSA activity revealed that pyrrole-NH-free thiosemicarbazides were less potent
compared to pyrrole-N-methylated analogs against MSSA. Overall, thiosemicarbazide
hybrids are more favored for anti-MSSA activity than semicarbazides.
In case of Methicillin Resistant Staphylococcus aureus (MRSA) the synthesized
semicarbazides and thiosemicarbazides displayed moderate to excellent antibacterial activity
(MIC = 0.39 - 6.25 µg/mL) compared to standard ciprofloxacin (MIC = 3.125 µg/mL). The
semicarbazides showed moderate antibacterial activity (MIC = 3.125 – 6.25 µg/mL) against
MRSA. Unlike semicarbazide hybrids, thiosemicarbazides demonstrated moderate to
excellent activity (MIC = 0.78 – 3.125 µg/mL) against MRSA strain. Eight of the synthesized
hybrids 5a-5f, 5h and 5i (MIC = 3.125 µg/mL), displayed an equal antibacterial activity
against MRSA compared to standard ciprofloxacin. Eight-fold superior potency was observed
for hybrids 5k-5m and 5o (MIC = 0.39 µg/mL) against MRSA. Presence of halogen atom
like fluorine or chlorine at para-position on phenyl ring at ring B was highly favored for the
antibacterial activity against MRSA. Likewise, presence of methoxy group on phenyl ring
was preferred for antibacterial activity as indicated by the MICs of hybrids 5l (MIC = 0.39
µg/mL) and 5t (MIC = 1.56 µg/mL). This also showed that presence of three methoxy groups
on phenyl ring is less favored for anti-MRSA activity compared to one on para-substition.
Four-fold greater activity was observed for four hybrids 5n, 5p, 5r and 5t (MIC = 0.78
µg/mL) against MRSA. Substitution of the fluorine atom at para-postion on phenyl ring (5m,
MIC = 0.39 µg/mL) was more preferred for anti-MRSA activity than at ortho-position (5n,
MIC = 0.78 µg/mL). Hybrid 5p (MIC = 0.78 µg/mL) with ethyl linker has shown four-fold
higher anti-MRSA activity compared to standard Ciprofloxacin indicating beneficial effect of
linker between the aryl ring and thiosemicarbazide group for anti-MRSA activity. Overall
thiosemicarbazides are more active against MRSA than semicarbazides. The N-methylation
of pyrrole core among the thiosemicarbazide hybrid was more beneficial for anti-MRSA
activity.
Analysis of the biological data of the hybrids
4
a-t and
5
a-t
revealed that N-methylation of pyrrole core was beneficial for anti-fungal activity against C.
albicans. All the synthesized hybrids displayed moderate to excellent antifungal activity
(MIC = 0.78 - 3.125 µg/mL) against C. albicans compared to standard Amphotericin-B (MIC
= 3.125 µg/mL). From the semicarbazide analogs (4a-4t), all pyrrole-N-methylated hybrids
exhibited either identical or to two-fold greater antifungal activity (MIC = 1.56 - 3.125
µg/mL) against C.albicans. All the pyrrole-NH-free semicarbazides displayed equal

antifungal activity (MIC = 3.125 µg/mL). For thiosemicarbazides (5a-5t), all pyrrole-N-
methylated hybrids significantly displayed four-fold superior antifungal activity (MIC = 0.78
µg/mL) except 5q (MIC = 1.56 µg/mL), which exhibited two-fold superior activity against
C.albicans. Hence thiosemicarbazides motif and N-methylation on pyrrole core are more
favored features for antifungal activity against C.albicans.
The synthesized hybrids showed moderate to good anti-tubercular activity (MIC = 0.5 - 59.2
µg/mL) against Mycobacterium tuberculosis H37RV using REMA method. Hybrid 5a
displayed the highest anti-tubercular activity (MIC = 0.50 µg/mL), significantly very close to
the activity of standard Isoniazid (MIC = 0.40 µg/mL). Substitution of nitro group on phenyl
ring at para-position was highly favored for anti-tubercular activity against M. tuberculosis.
Anti-tubercular activity of hybrid 5a also revealed that pyrrole-NH-free core is beneficial for
activity against M. tuberculosis. Hybrid 5k demonstrated less anti-tubercular activity (MIC =
53.8 µg/mL) compared to its N-methylated analog 5a indicating that pyrrole-N-methylation is
not favored for activity against M. tuberculosis. Similarly hybrid 5c (MIC = 0.56 µg/mL)
exhibited potent anti-tubercular activity close to that of standard isoniazid. Presence of
halogen atom at para-position on phenyl ring was also highly favored for anti-tubercular
activity. This observation was supported by comparing the anti-tubercular activities of
hybrids 5c (MIC = 0.56 µg/mL) and 5d (MIC = 0.82 µg/mL), where in para substitution on
phenyl ring with fluorine (5d) decreased anti-tubercular activity compared to ortho-position
(5c). Further chloro analog 5e (MIC = 1.3 µg/mL) of hybrid 5c showed decreased anti-
tubercular activity than later indicating that substituting at para-position on phenyl ring with
fluorine is more favored than chlorine for activity against M. tuberculosis. Hybrid compounds
5a (MIC = 0.50 µg/mL), 5c (MIC = 0.56 µg/mL) and 5i (MIC = 0.67 µg/mL) have exhibited
promising anti-tubercular activity compared to standard Isoniazid. The presence of 4-
nitrophenyl substitution at ring B was favored for activity against M. tuberculosis as
displayed by the good activity of hybrid 4c (MIC = 0.80 µg/mL). In comparison the activity
of hybrid 4c (MIC = 0.80 µg/mL) and 5a (MIC = 0.50 µg/mL) revealed that
thiosemicarbazide motif was more preferential for anti-tubercular activity than
semicarbazide. The anti-tubercular activity of hybrid 5d (MIC = 0.82 µg/mL) was almost
identical to that of 4c. It was also observed that heterocyclic furfuryl- substitution at ring B in
hybrid 4i (MIC = 0.92 µg/mL) favored for anti-tubercular activity against M. tuberculosis.
Likewise, potent anti-tubercular activity was observed for hybrids 4d (MIC = 1.1 µg/mL), 5b
MIC = 1.3 µg/mL) and 5e (MIC = 1.3 µg/mL). In summary thiosemicarbazide analogs are

more potent than semicarbazides and N-methylation of the pyrrole core has negative effect on
the anti-tubercular activity.
The synthesized analogs were further studied for their mammalian toxicity (IC50) using
VERO cell lines at concentrations of 62.0 and 62.5 µg/mL. Viability was assessed, after 72
hours, by the conversion of MTT into formazan product using Promega Cell Titre 96 non-
radioactive cell proliferation assay22. All the hybrids were found to be non-toxic and the data
is tabulated in Table 1. The standard INH toxicity has been taken as >454.7 which was
reported previously.23 It can be safely deduced that these synthetic compounds have shown
toxicity profiles on-par with standard INH cell toxicity (>454) and are safe to use for further
studies.
In conclusion, we have synthesized forty novel 4-nitroopyrrole-semicarbazide conjugates
based on the reported bio-prospective of bromopyrrole alkaloids and semicarbazide
derivatives, with the objective of evaluating their antimicrobial properties against Escherichia
coli, Klebsiella pneumoniae, Methicillin-resistant Staphylococcus aureus, Methicillin-
sensitive Staphylococcus aureus and Mycobacterium tuberculosis. The structure activity
relational studies give us glimpse that N-alkylation of pyrrole core has shown superior
antibacterial and antifungal activity. On the contrary, hybrids with pyrrole-NH-free displayed
superior activity against Mycobacterium tuberculosis compared to its N-methylated analogs.
All the tested microbes showed more sensitivity towards thiosemicabazide analogs than
semicarbazides. In general, presence of substitutions like halogen atom on phenyl ring at ring
B is beneficial for antimicrobial activity. Hybrids 5k, 5l, 5m, 5n, 5o, 5r, 5s and 5t displayed
four-fold increased activity (MIC = 0.39 µg/mL) against E. coli compared to standard
ciprofloxacin. Eight hybrids 5k-5o and 5r-5t displayed equal antibacterial activity (MIC =
1.56 µg/mL) against K. pneumonia compared to standard Ciprofloxacin. Further five
thiosemicarbazide 5k-5o (MIC = 0.195 µg/mL) displayed highly potent antibacterial activity
against MSSA compared to standard Ciprofloxacin. It was observed that hybrids 5k-5m and
5o (MIC = 0.39 µg/mL) displayed eight-fold increase in potency against MRSA. Nine
pyrrole-N-methylated hybrids significantly displayed four-fold superior antifungal activity
(MIC = 0.78 µg/mL) than standard Amphotericin B. Excellent MICs shown by these hybrids
identify them as promising leads for development of novel antibacterial and antifungal drugs.
Further potent activity displayed by five hybrids 5a, 5c, 5i, 5d, and 4c with MICs of 0.50,

0.56, 0.67, 0.82 and 0.80 µg/mL respectively; against Mycobacterium tuberculosis H37RV
recognize them as future anti-tubercular lead candidates.
Acknowledgements
The authors sincerely thank College of Health Science, University of KwaZulu-Natal,
Durban, South Africa for funding this project and Professor R.S. Gaud for providing facility
at SPP SPTM, NMIMS, Mumbai to carry out these experiments.
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Scheme 1: Synthesis of 2-(N-(arylaminocarbonyl)-hydrazinocarbonyl)-4-nitro-1H-pyrrol (4)
and 2-(N-(arylaminothiocarbonyl)-hydrazinocarbonyl)-4-nitro-1H-pyrrol (5)
O2N
O2N
Fuming HNO3
ClCOCCl3
N2H4, RT
H
CCl3
CCl3
N
N
N
N
R
N
NH2
Acetic anhy.
-10 0C, 2h
Abs. alc, 2h
R
R
Anh. ether
K2CO3
R
O
O
O
1
2
R=H/CH3
3
1a-R=H
1b-R=CH3
2a-R=H
2b-R=CH3
3a-R=H
3b-R=CH3
4a - phenyl
5a - 4-nitrophenyl
5b - 4-methoxyphenyl
5c - 4-fluorophenyl
5d - 2-fluorophenyl
5e - 4-chlorophenyl
5f - pheneth-2-yl
5g - benzyl
4b - 4-methoxyphenyl
4c - 4-nitrophenyl
4d - 4-bromophenyl
4e - 4-chlorophenyl
4f - 2,5-dimethoxyphenyl
4g - benzyl
Abs. alc
Reflux
Ar-NCO or
Ar-NCS
TEA, 4-5h
O2N
4h - pheneth-2-yl
4i - furfuryl
4j - cyclopentyl
5h - cyclohexyl
5i - o-tolyl
X
H
Ar
N
5j - 3,4,5-trimethoxyphenyl
5k - 4-nitrophenyl
5l - 4-methoxyphenyl
5m - 4-fluorophenyl
5n - 2-fluorophenyl
5o - 4-chlorophenyl
5p - pheneth-2-yl
5q - benzyl
N
N
N
R
H
H
4k - phenyl
O
4l - 4-methoxyphenyl
4m - 4-nitrophenyl
4n - 4-bromophenyl
4o - 4-chlorophenyl
4p - 2,5-dimethoxyphenyl
4q - benzyl
4r - pheneth-2-yl
4s - furfuryl
4t - cyclopentyl
4/5
Ar = aryl/heteroaryl
4(a-j) - R=H, X=O
4(k-t) - R=CH3, X=O
5(a-j) - R=H, X=S
5(k-t) - R=CH3, X=S
5r - cyclohexyl
5s - o-tolyl
5t - 3,4,5-trimethoxyphenyl

Fig 1: Literature reports for semicarbazide and thiosemicarbazide analogs with their
biological activities
Fig 2. Design of (thio)-semicarbazides of 4-nitropyrrole using molecular hybridization
method.

Table 1: Antimicrobial results (MIC in µg/mL) of synthesized semicarbazide (4) and
Thiosemicarabazide (5) derivatives
Compound
E.colia K.pneumoniaea
MSSA
MRSA
C.albicansb
Antitubercular
activityc
40.6
2.5
IC50
(µM)d
357.0
400.6
211.3
377.9
218.2
332.8
348.0
220.3
442.8
231.0
305.8
328.0
401.7
602.3
289.5
429.2
304.1
633.0
481.5
271.4
528.9
331.0
331.3
471.2
190.6
281.0
396.7
204.1
461.9
328.1
395.0
183.5
662.4
293.1
210.3
403.5
239.0
352.4
470.6
392.1
NT
4a
4b
3.125
3.125
3.125
3.125
3.125
3.125
6.25
6.25
3.125
3.125
1.56
1.56
1.56
1.56
1.56
1.56
3.125
3.125
1.56
1.56
1.56
1.56
1.56
1.56
1.56
3.125
3.125
1.56
1.56
1.56
0.39
0.39
0.39
0.39
0.39
0.78
1.56
0.39
0.39
0.39
1.56
NT
3.125
3.125
3.125
3.125
3.125
3.125
6.25
1.56
1.56
1.56
1.56
3.125
1.56
1.56
3.125
1.56
1.56
1.56
1.56
1.56
1.56
1.56
3.125
1.56
1.56
1.56
1.56
1.56
1.56
1.56
1.56
1.56
1.56
3.125
1.56
1.56
3.125
0.195
0.195
0.195
0.39
0.195
0.39
0.78
0.39
0.39
0.78
1.56
NT
3.125
3.125
3.125
3.125
6.25
3.125
3.125
3.125
3.125
3.125
3.125
3.125
3.125
3.125
3.125
1.56
4c
0.80
1.1
4d
4e
2.0
4f
4g
3.125
3.125
6.25
14.5
15.2
10.3
0.92
12.5
59.2
26.1
11.9
7.8
4h
4i
6.25
3.125
3.125
3.125
3.125
3.125
3.125
3.125
6.25
3.125
3.125
3.125
3.125
3.125
3.125
3.125
6.25
4j
4k
4l
4m
1.56
1.56
4n
1.56
4o
4p
1.56
1.56
30.5
42.4
51.9
42.1
17.0
38.7
0.50
1.3
4q
3.125
6.25
3.125
3.125
3.125
3.125
3.125
3.125
3.125
3.125
3.125
3.125
6.25
1.56
4r
4s
1.56
1.56
3.125
3.125
3.125
3.125
3.125
3.125
3.125
6.25
4t
5a
1.56
3.125
3.125
3.125
3.125
3.125
3.125
3.125
3.125
3.125
3.125
0.78
5b
5c
0.56
0.82
1.3
5d
5e
5f
5g
3.9
7.3
6.25
5h
3.125
3.125
3.125
1.56
3.125
3.125
6.25
2.8
5i
0.67
2.7
5j
5k
0.39
53.8
19.4
6.7
5l
5m
1.56
1.56
0.39
0.39
0.78
0.78
5n
1.56
0.78
0.78
3.2
5o
1.56
0.39
0.78
16.3
23.0
31.9
27.5
11.9
21.5
NT
5p
5q
3.125
3.125
1.56
0.78
1.56
0.78
1.56
5r
0.78
0.78
5s
5t
1.56
0.78
0.78
1.56
1.56
1.56
3.125
NT
0.78
NT
Ciproflixacin
Amphoterecin-
B
NT
3.125
NT
NT
Isoniazide
NT
NT
NT
NT
NT
0.40
NT
a - MIC values are determined by broth dilution method (two fold dilution). b - MIC values are
determined by agar dilution method (two fold dilution).
c - MIC values are determined by Resazurin micro titer assay (REMA). d – Mammalian toxicity testing
using VERO cell lines.

Graphical Abstract
Synthesis of novel 4-nitropyrrole-based semicarbazide and thiosemicarbazide hybrids
with antimicrobial and anti-tubercular activity
Rajesh A. Ranea*, Shital S. Naphadeb, Pavan Kumar Bangalorec, Mahesh B. Palkara,
Mahamadhanif S. Shaikha and Rajshekhar Karpoormatha*
A series of forty novel semicarbazide and thiosemicarbazide hybrids with 4-nitropyrrole were
synthesized and evaluated for antibacterial, antifungal and anti-tubercular activities.
O2N
Pyrrole core
X
R=H/CH3
H
Ring B
Ar = aryl/heteroaryl
Ar
N
N
N
N
R
H
H
O
(thio)semicarbazide; X = O/S