Synthesis and antimycobacterial evaluation of pyridinyl- and pyrazinylhydrazone derivatives

Article abstract of DOI:10.1007/s00044-020-02592-7

Bioisosteric replacements are often tried goaling to affect the lipophilicity, polarity, and aqueous solubility of the substances, as a way to obtain therapeutically improved medicines. Also, hydrazonyl compounds are described with a wide range of pharmac

Full text of DOI:10.1007/s00044-020-02592-7

MEDICINAL
CHEMISTRY
RESEARCH
Medicinal Chemistry Research
https://doi.org/10.1007/s00044-020-02592-7
ORIGINAL RESEARCH
Synthesis and antimycobacterial evaluation of pyridinyl- and
pyrazinylhydrazone derivatives
Alessandra C. Pinheiro1 Thaís C. M. Nogueira Gabriela E. Pereira Cristina Lourenço Marcus V. N. de Souza
1 ●
1 ●
2 ●
1
●
Received: 26 March 2020 / Accepted: 17 June 2020
©
Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract
Bioisosteric replacements are often tried goaling to affect the lipophilicity, polarity, and aqueous solubility of the
substances, as a way to obtain therapeutically improved medicines. Also, hydrazonyl compounds are described with a
wide range of pharmacological activities, having also recognized activities in antimycobacterial field. In this study,
twenty-seven pyrimidinyl and pyrazinyl derivatives have been synthesized and evaluated for their antimycobacterial
activity against M. tuberculosis ATTC 27294. The componds were obtained by the reaction of 2-hydrazinylpyridine,
4
-hydrazinylpyridine, or 2-hydrazinylpyrazine with appropriated aromatic or heteroaromatic aldehydes. Antimyco-
bacterial activity of the compounds was determined according to MTT assay. The most active compound, a
-hydroxyl-5-nitrophenyl-4-pyridinylhydrazone derivative, showed good biodisponibility and nonmutagenic or
2
tumorigenic profiles in preliminaries in silico studies, and exceptional in vitro activity, being compared with the
reference drug ethambutol. This study supports that pyrimidinyl and pyrazinyl derivatives may be used for the
development of new tuberculostatic agents.
●
●
●
●
Keywords Tuberculosis Heterocyclic Pyridinyl Pyrazinyl Hydrazones
Introduction
therapeutically improved medicines (Dua et al. 2011). In
order to obtain these products, modern synthetic meth-
odologies are available, allowing rapid access to a wide
variety of functionalized heterocyclic compounds of cri-
tical importance to the medicinal chemist (Taylor et al.
2016; Khanna et al. 2018; El-Sayed et al. 2018; Przybylski
et al. 2018; Brahmachari 2018).
Hydrazonyl compounds are also described with a wide
range of pharmacological activities, such as antibacterial,
antifungal, anticonvulsant, anti-inflammatory, antimalarial,
antileishmanial, and antineoplastic, having also recognized
activities in antimycobacterial field (Rollas and Küçükgüzel
Heterocycles’ ring structures are composed by elements
other than carbon, and are able to impact strongly the
physicochemical properties of the substances (Martins
et al. 2015). Also, the incorporation of heterocyclic like
fragments is a commonly strategy used in medicinal
chemistry to design prototypes with enhanced potency and
selectivity, and bioisosteric replacements are often tried
goaling to affect the lipophilicity, polarity, and aqueous
solubility of the substances, as a way to obtain
2007; Verma et al. 2014; Rodrigues et al. 2014; De Souza
et al. 2018; Cardoso et al. 2017; Amim et al. 2016; Candéa
et al. 2009.
Supplementary information The online version of this article (https://
doi.org/10.1007/s00044-020-02592-7) contains supplementary
material, which is available to authorized users.
As a part of a study goaling to investigate the impor-
tance of the nitrogen to the biological activity presented
by six membered heterocycle derivatives, this manuscript
present the antimicobacterial activity of componds con-
taining the nitrogen at position 2 and 4 of the heterocycle
moiety (identified as 2-pyridinylhydrazone and 4-
pyridinylhydrazone derivatives), and also nitrogen dis-
substituted heterocycles, defined as pyrazinylhydrazone
derivatives.
*
Marcus V. N. de Souza
marcos_souza@far.fiocruz.br
1
2
Fundação Oswaldo Cruz, Instituto de Tecnologia em Fármacos-
Farmanguinhos, Rio de Janeiro, RJ 21041-250, Brazil
Fundação Oswaldo Cruz, Instituto Nacional de Infectologia
Evandro Chagas, Departamento de Bacteriologia, Manguinhos,
Rio de Janeiro 21045-900, Brazil

Medicinal Chemistry Research
substituted hydrazones. The most active compound of all
series, the 4-pyridinylhydrazone, 5-nitrothien-2-yl 3h, pre-
sent a remarkable activity, being more active than the first
line tuberculostatic drug ethambutol.
The 2-hydroxylphenyl derivatives, a-f compounds, are
much more active than heteroarylic compounds in 2 and 4
series. In previous studies a role considered for the sali-
cyldehyde hydrazones that of a chelator, and this capacity
seems to be optimized when there is a nitrogen at position 2
of the main ring. Salicyldehyde derivatives are known to be
able to act as tridentate O,N,N-ligands, and thereby form
strong complexes with metals. It is considered that the
removal of a metal vital for cell reproduction on complexation
by the drug can take a major role in these drug interactions.
For compounds 3 the opposite is observed. Heteroaryl
derivatives 3g-h showed an improved activity if compared
with hidroxylated compounds 3a–f. The activity of the 5-
nitrothienyl and 5-nitrofuranyl derivatives has been attrib-
uted to the redox potentials of such compounds (Mahmud
et al. 1998; Rakesh et al. 2014; Squella et al. 2005).
The lipophilicities of 2, 3, and 4, expressed as logP
values, were determined using the Data Warrior program
and are listed in Table 1. Pharmacocinetic studies indicate
that a good balance between permeability and aqueous
solubility for a drug is indicated by a logP value between 0
and 3. The value found for the most active compound of this
study, 3h, falls within this range, being 2.80.
Other compounds with remarkable activities are the 2-
hydroxylphenyl derivatives 2b, 2e, 4d, and 4f, being only
the pyrazinyl derivatives 4d and 4f, with logP values of
2.4991 and 1.9232, included in the ideal range. The
obtained values suggest that these substances will be more
soluble in water than 3h.
The toxicity of the compounds 2, 3, and 4 was also
determinated using the Data Warrior program, see Table 2.
The most promising compound of this study, compound 3h,
as well as 2e, 4d, and 4f, were found to be nonmutagenic or
tumorigenic.
Scheme 1 Synthesis of 2-pyridinylhydrazone derivatives 2a–i, 4-
pyridinylhydrazone derivatives 3a–i and 2-pyrazinylhydrazone deri-
vatives 4a-i
Results and discussion
The leishmanicidal activities of series 2 and 4 were pre-
viously reported by our research group (De Souza et al.
2
018). Concerning to 4-pyridinyl derivatives, compounds
3
b, 3d, 3e, 3g, and 3h are novel, and compounds 3c and 3f
were reported previously, but their spectral data have not
been described in the literature.
Synthesis and characterization
The synthesis of planned 2-pyridinylhydrazone, 2, 4-pyr-
idinylhydrazone, 3, and 2-pyrazinylhydrazone, 4, derivatives
1
1
were accomplished according to the reported procedure as
shown in Scheme 1. It was employed, respectively, com-
mercial 2-hydrazinylpyridine, 4-hydrazinylpyridine, or 2-
hydrazinylpyrazine as starting material, and appropriated
aromatic or heteroaromatic aldehydes in ethanol at room
temperature for 5 min-78 h (Table 1). The compounds were
obtained in 35–97% yields. It is important to mention that
aromatic aldehydes containing hydroxyl, metoxyl and nitro
substituents, and heteroaromatic aldehydes were selected due
to their activity in different series previously study from our
group being the most actives (Rodrigues et al. 2014; Coimbra
et al. 2013; Nogueira et al. 2019; Cardoso et al. 2014).
All these new compounds were identified by detailed
1
13
spectral data, including H NMR, C NMR, high-
resolution mass spectrometry and infrared spectrometry.
1
In general, the H NMR spectrum showed the pyridine
Based on the results obtained for compound 3h, we can
conclude that this compound has a remarkable profile and
could be considered as a reasonable starting point to find
new compounds with improved antitubercular activity.
protons of compounds 2a-i at 6.72–8.17 and ranging from
7
.19 to 13.20 for compounds 3a–i. In addition, the pyrazine
protons of compounds 4a–i were observed at 7.94–8.70
ppm and the N=CH protons of all series are presented
ranging from 7.27 to 8.37 ppm. The N=CH functional
group is also observed in infrared spectra, exhibiting an IR
Conclusion
−
1
band at 1557–1645 cm .
In this study, we reported the antimycobacterial activity of 27
pyrimidinyl and pyrazinyl derivatives, which have been
evaluated against M. tuberculosis ATTC 27294 using the
MTT assay. Compounds 3h, 2e, 4d, and 4f displayed the best
tuberculostatic profiles in all experiments. The most active
compound, a 2-hydroxyl-5-nitrophenyl, 4-pyridinylhydrazone
derivative 3h, showed good biodisponibility and
Anti-mycobacterial activity
The antimycobacterial activity of compounds 2, 3, and 4 are
shown in Table 2. This work is a continuation of previous
studies of our group, when it was observed the highlighted
activities presented by 2-hydroxylphenyl and heteroaryl

Medicinal Chemistry Research
Table 1 2-pyridinylhydrazone
clog Pa
Compound
X
Y
Z
R
Melting point (°C)
Yield (%)
2
a–i, 4-pyridinylhydrazone 3a–i
and 2-pyrazinylhydrazone 4a–i
derivatives
215b
195c
221d
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
a
b
c
d
e
f
N
N
N
N
N
N
N
N
N
C
C
C
C
C
C
C
C
C
N
N
N
N
N
N
N
N
N
C
C
C
C
C
C
C
C
C
N
N
N
N
N
N
N
N
N
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
N
N
N
N
N
N
N
N
N
2-OH
65
65
81
42
64
81
37
78
52
81
96
97
94
95
95
70
81
37
60
80
87
75
86
78
35
52
72
3.84
2,3-diOH
2,4-diOH
2,5-diOH
2-OH, 4-CH3
2- OH, 5-NO2
5-NO2-Fur
5-NO2-Thio
2-Py
3.50
3.50
230
3.50
220
4.19
250
201e
260f
178g
2.75
g
h
i
2.64
3.16
3.24
a
b
c
d
e
f
2-OH
261–263h
257–259
200–203
243–245
290–292
294–296
280–282
288–290
250–252i
220
3.49
2,3-diOH
2,4-diOH
2,5-diOH
2-OH, 4-CH3
2-OH, 5-NO2
5-NO2-Fur
5-NO2-Thio
2-Py
3.15
3.15
3.15
3.84
2.40
g
h
i
2.29
2.80
2.89
a
b
c
d
e
f
2-OH
2.8448
2.4991
2.4991
2.4991
3.1887
1.9232
1.809
2.3251
2.2436
2,3-diOH
2,4-diOH
2,5-diOH
2-OH, 4-CH3
2- OH, 5-NO2
5-NO2-Furj
5-NO2-Thiol
2-Pym
242
296–298
280–283
222
250
282k
g
h
i
280
206n
aCalculated using Data Warrior program (http://www.openmolecules.org/datawarrior)
bSyeda and Srinivasan (1965)
cSandbhor et al. (2002)
d2-py: aryl group = pyrindin-2-yl
eBerge (1983)
fSondhi et al. (2008)
gLions and Martin (1958)
hAlptüzün et al. (2009)
iHegarty et al. (1973)
j5-NO2-Fur: aryl group = 5-nitrofuran-2-yl
kKakemi et al. (1961)
l5-NO2-Thio: aryl group = 5-nitrothien-2-yl
mCushman et al. (1991)
nCase (1976)
nonmutagenic or tumorigenic profiles in preliminaries in
silico studies, and exceptional in vitro activity, being com-
pared with the reference drug ethambutol. These results
suggest that this compound could be a useful starting point for
further studies for new tuberculostatic drugs and confirm the
potential of 4-pyridinylhydrazone derivatives as lead com-
pounds in antituberculosis drug discovery.
Material and methods
Experimental
Melting points were determined using an MQAPF-302
(MicroQuímica Ltd, Santa Catarina, Brazil) apparatus.
Infrared spectra were recorded on a Thermo Nicolet Nexus

Medicinal Chemistry Research
Table 2 The in vitro activity of compounds 2, 3, and 4 against
Mycobacterium tuberculosis H37Rv strain (ATCC 27294, susceptible
to ethambutol)
thickness of 0.25 mm, using ultraviolet light irradiation. For
column chromatography, Merck silica gel (70–230 or
230–400 mesh) was used.
Compound
Substituents in the
phenyl ring
MIC
(µM)
Mutagenic/
Tumorigenic
a
General procedure for the synthesis of 2-
pyridinylhydrazone derivatives 2a-i (GP1)
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
a
b
c
d
e
f
2-OH
117,4
54,6
none/none
high/none
none/none
none/none
none/none
none/none
high/high
none/none
low/none
none/none
high/none
none/none
none/none
none/none
none/none
high/high
none/none
low/none
none/none
high/none
none/none
none/none
none/none
none/none
high/high
none/none
low/none
–
2,3-diOH
2,4-diOH
2,5-diOH
2-OH, 4-CH3
2- OH, 5-NO2
218,3
109,2
55,1
To a stirred solution of 2-hydrazinylpyridine (1.0 mmol) in
ethanol (10 mL) was added the appropriate benzaldehyde
(0.9 mmol), and the reaction mixture was stirred for 5 min –
78 h at room temperature. The reaction mixture was con-
96,9
centrated under reduced pressure, and the residue was
purified by washing with cold water (3 × 10 mL), affording
the 2-pyridinylhydrazone derivatives 2a–i as solid in
g
h
i
5-NO -Fur
>500
>500
252,5
469,5
>500
>500
>500
110,1
387,6
107,8
12,6
2
5-NO2-Thio
2-Py
37–81% yields.
a
b
c
d
e
f
2-OH
2,3-diOH
2,4-diOH
2,5-diOH
2-OH, 4-CH3
2-OH, 5-NO2
General procedure for the synthesis of 4-
pyridinylhydrazone derivatives 3a–i (GP2)
To a stirred solution of 4-hydrazinylpyridine (1.0 mmol)
in ethanol (10 mL) was added the appropriate benzalde-
hyde (1.0 mmol), and the reaction mixture was stirred for
g
h
i
5-NO -Fur
2
5-NO2-Thio
2-Py
2
0 min –24 h at room temperature. The reaction mixture
>500
233,6
434,8
108,7
54,3
was concentrated under reduced pressure, and the residue
was purified by washing with cold diethyl ether (3 × 10 mL),
leading to the 4-pyridinylhydrazone derivatives 3a–i as
solid in 37–97% yields.
a
b
c
d
e
f
2-OH
2,3-diOH
2,4-diOH
2,5-diOH
2-OH, 4-CH3
2- OH, 5-NO2
5-NO2-Furb
5-NO2-Thioc
2-Pyd
109,6
48,3
General procedure for the synthesis of 2-
pyrazinylhydrazone derivatives 4a–i (GP3)
g
h
i
214,6
>500
>500
15.3
To a stirred solution of 2-hydrazinylpyrazine (1.0 mmol) in
ethanol (10 mL) was added the appropriate benzaldehyde
(1.05 mmol), and the reaction mixture was stirred for 2–48 h
at room temperature. The reaction mixture was concentrated
under reduced pressure, and the residue was purified by
washing with cold water (3 × 10 mL), cold ether (3 ×
10 mL), or by column chromatography purification using
hexane/ethyl acetate (50 → 100%) as eluent, thus affording
the 2-pyrazinylhydrazone derivatives 4a–i in 35–87%
yields.
Ethambutol
Isoniazide
–
–
0.46
–
aCalculated using Data Warrior program (http://www.openmolecules.
org/datawarrior)
b5-NO2-Fur: aryl group = 5-nitrofuran-2-yl
c5-NO2-Thio: aryl group = 5-nitrothien-2-yl
d2-py: aryl group = pyrindin-2-yl
The series 2 and 4 compounds were previously synthe-
sized by our research group, and the antileishmanial activ-
ities published (De Souza et al. 2018). The compounds of
series 3 are described below.
6
700 spectrometer as potassium bromide pellets and fre-
−1
quencies are expressed in cm . NMR spectra were were
analysed using a Bruker Avance 400 operating at
4
1
13
00.00 MHz ( H) and 100.0 MHz ( C) in DMSO-d .
6
Chemical shifts are reported in ppm (δ) relative to tetra-
methylsilane and J-coupling in Hertz (Hz). Proton and
carbon spectra were typically obtained at room temperature.
High-resolution mass spectra were acquired on a Bruker
compact-TOF. The progress of the reactions was monitored
by thin-layer chromatography (TLC) on 2.0 cm × 6.0 cm
aluminum sheets (silica gel 60, HF-254, Merck) with a
(E)-2-((2-(pyridin-4-yl)hydrazono)methyl)phenol (3a) GP2
was followed using 4-hydrazinylpyridine (109 mg,
1.0 mmol), ethanol (10 mL), and was added 2-
hydroxybenzaldehyde (122 mg, 1.0 mmol). The desired
compound was obtained as amorphous colorless solid
(172 mg, 81%); m.p. 261–263 °C; IR (KBr) ν 3085,
−
1 1
1633 cm ; H NMR (400 MHz, DMSO-d ): δ = 13.92 (s,
6

Medicinal Chemistry Research
1
8
H, NH), 12.76 (s, 1H, H-2’ or H-4’), 10.30 (s, 1H, OH),
.64 (s, 1H, H-2’ or H-4’), 8.32 (s, 1H, H-1’ or H-5’), 8.31
(s, 1H, H-2’ or H-4’), 9.59 (s, 1H, OH), 9.02 (s, 1H, OH),
8.56 (s, 1H, H-2’ or H-4’), 8.32 (s, 2H, H-1’ and H-5’), 7.44
(s, 1H, N=CH), 7.22 (d, J = 2.8 Hz, 1H, H-5), 6.79 (d, J =
8.7 Hz, 1H, H-2), 6.74 (dd, J = 8.7, 2.8 Hz, 1H, H-3) ppm;
(
s, 1H, H-1’ or H-5’), 7.84 (dd, J = 7.7, 1.6 Hz, 1H, H-5),
7
3
0
1
1
.51 (s, 1H, N=CH), 7.28 (ddd, J = 8.3, 7.7, 1.6 Hz, 1H, H-
1
3
), 6.98 (dd, 1H, J = 8.3, 0.8 Hz, H-2), 6.89 (dt, J = 7.7,
C-NMR (100 MHz, DMSO-d ): δ = 154.4 (C-1); 149.9
6
13
.8 Hz, 1H, H-4) ppm; C-NMR (100 MHz, DMSO-d ): δ =
(C-2’); 149.8 (C-4’); 144.6 (C-4); 140.8 (C=NNH); 139.7
(C-6’); 119.8 (C-6); 119.6 (C-3); 117.1 (C-2); 110.7 (C-5);
107.9 (C-5’); 105.8 (C-1’) ppm; HRESIMS m/z: 230.0927
C H N O (calcd. 230.0925).
6
56.7 (C-1), 154.5 (C-2’), 144.4 (C-4’), 140.8 (CH=NNH),
39.8 (C-3), 131.8 (C-5), 126.0 (C-6’), 119.6 (C-4), 119.3
(
C-6), 116.2 (C-2), 107.8 (C-5’), 106.0 (C-1’) ppm; HRE-
1
2
12
3
2
SIMS m/z: 214.0983 C H N O (calcd. 214.0975).
12
12
3
(
E)-5-methyl-2-((2-(pyridin-4-yl)hydrazono)methyl)phenol
(
(
(
E)-3-((2-(pyridin-4-yl)hydrazono)methyl)benzene-1,2-diol
3b): GP2 was followed using 4-hydrazinylpyridine
109 mg, 1.0 mmol), ethanol (10 mL), and was added 2,3-
(3e): GP2 was followed using 4-hydrazinylpyridine
(109 mg, 1.0 mmol), ethanol (10 mL), and was added 2-
dihydroxy-4-methylbenzaldehyde (136 mg, 1.0 mmol). The
desired compound was obtained as amorphous white solid
(216 mg, 95%); m.p. 290–292 °C; IR (KBr) ν 3191,
dihydroxybenzaldehyde (138 mg, 1.0 mmol). The desired
compound was obtained as amorphous white solid (220 mg,
9
−
1
1
−1 1
6%); m.p. 257–259 °C; IR (KBr) ν 2930, 1634 cm ; H
1635 cm ; H NMR (400 MHz, DMSO-d ): δ = 13.98 (s,
6
NMR (400 MHz, DMSO-d ): δ = 12.69 (s, 1H, H-2’ or H-
1H, NH), 12.81 (s, 1H, H-2’ or H-4’), 10.24 (s, 1H, OH),
8.61 (s, 1H, H-2’ or H-4’), 8.30 (s, 2H, H1’ and H-5’), 7.71
(d, J = 8.0 Hz, 1H, H-5), 7.48 (s, 1H, N=CH), 6.81 (s, 1H,
6
4
’), 9.72 (s, 1H, OH), 9.32 (s, 1H, OH), 8.62 (s, 1H, H-2’ or
H-4’), 8.32 (s, 1H, H-1’ or H-5’), 8.30 (s, 1H, H-1’ or H-5’),
7
6
.28 (dd, J = 7.9, 1.5 Hz, 1H, H-5), 7.27 (s, 1H, N=CH),
.89 (dd, J = 7.9, 1.5 Hz, 1H, H-3), 6.71 (t, J = 7.9 Hz, 1H,
H-2), 6.71 (d, J = 8.0 Hz, 1H, H-4), 2.27 (s, 3H, CH ) ppm;
3
1
3
C-NMR (100 MHz, DMSO-d ): δ = 156.8 (C-1); 154.4
6
1
3
H-4) ppm; C-NMR (100 MHz, DMSO-d ): δ = 154.3 (C-
(C-3); 144.8 (C-2’); 142.1 (C-4’); 140.8 (C=NNH); 139.7
(C-5); 126.1 (C-6’); 120.5 (C-4); 117.1 (C-6); 116.6 (C-2);
6
1
), 145.7 (C-2), 145.5 (C-2’), 144.8 (C-4’), 140.6
(
(
C=NNH), 120.3 (C-6’), 120.3 (C-5), 119.2 (C-4), 119.2
C-6), 117.1 (C-3), 116.3 (C-5’), 106.9 (C-1’) ppm; HRE-
107.9 (C-5’); 105.9 (C-1’); 21.2 (CH ) ppm; HRESIMS m/z:
3
228.1138 C H N O (calcd. 228.1137).
1
3
14
3
SIMS m/z: 230.0932 C H N O (calcd. 230.0925).
12
12
3
2
(
E)-4-nitro-2-((2-(pyridin-4-yl)hydrazono)methyl)phenol
(
(
(
E)-4-((2-(pyridin-4-yl)hydrazono)methyl)benzene-1,3-diol
3c): GP2 was followed using 4-hydrazinylpyridine
109 mg, 1.0 mmol), ethanol (10 mL), and was added 2,4-
(3f): GP2 was followed using 4-hydrazinylpyridine
(109 mg, 1.0 mmol), ethanol (10 mL), and was added 2-
hydroxy-5-nitrobenzaldehyde (167 mg, 1.0 mmol). The
desired compound was obtained as amorphous white solid
(245 mg, 95%); m.p. 294–296 °C; IR (KBr) ν 1635, 1519,
dihydroxybenzaldehyde (138 mg, 1.0 mmol). The desired
compound was obtained as amorphous pale yellow solid
(
1
1
1
H-1’ and H-5’), 7.63 (d, J = 8.6 Hz, 1H, H-5), 7.41 (s, 1H,
N=CH), 6.42 (d, J = 2.2 Hz, 1H, H-2), 6.35 (dd, J =
8
d6): δ = 161.2 (C-1); 158.4 (C-3); 154.0 (C-2’); 145.3 (C-
4
−
1 1
222 mg, 97%); m.p. 200–203 °C; IR (KBr) ν 3164,
1336 cm ; H NMR (400 MHz, DMSO-d ): δ = 12.93 (s,
6
−
1 1
624 cm ; H NMR (400 MHz, DMSO-d ): δ = 13.71 (s,
1H, H-2’ or H-4’), 8.65 (d, J = 2.9 Hz, 1H, H-5), 8.61 (s,
1H, H-2’ or H-4’), 8.38 (s, 1H, H-1’ or H-5’), 8.36 (s, 1H,
H-1’ or H-5’), 8.18 (dd, J = 9.1, 2.9 Hz, 1H, H-3), 7.58 (s,
6
H, NH), 12.51 (s, 1H, H-2’ or H-4’), 10.21 (s, 1H, OH),
0.03 (s, 1H, OH), 8.50 (s, 1H, H-2’ or H-4’), 8.25 (s, 2H,
1
3
1H, N=CH), 7.21 (d, J = 9.1 Hz, 1H, H-2) ppm; C-NMR
(100 MHz, DMSO-d ): δ = 162.1 (C-1); 154.7 (C-4); 141.6
6
.6 Hz, 2.2, 1H, H-4) ppm; 13C-NMR (100 MHz, DMSO-
(C=NNH); 139.9 (C-2’); 139.9 (C-4’); 126.8 (C-5); 121.3
(C-3); 120.5 (C-6’); 120.5 (C-6); 116.8 (C-2); 108.1 (C-5’);
106.5 (C-1’) ppm; HRESIMS m/z: 259.0822 C H N O
3
’); 140.7 (C=NNH); 139.3 (C-5); 127.7 (C-6’); 111.1 (C-
); 108.1 (C-5’); 107.5 (C-1’); 105.5 (C-4); 102.3 (C-2)
1
2
11
4
6
(calcd. 259.0826).
ppm HRESIMS m/z: 230.0935 C H N O (calcd.
12
12
3
2
2
30.0925).
(E)-4-(2-((5-nitrofuran-2-yl)methylene)hydrazinyl)pyridine
3g): GP2 was followed using 4-hydrazinylpyridine
(
(
(
(
E)-2-((2-(pyridin-4-yl)hydrazono)methyl)benzene-1,4-diol
3d): GP2 was followed using 4-hydrazinylpyridine
109 mg, 1.0 mmol), ethanol (10 mL), and was added 2,5-
(109 mg, 1.0 mmol), ethanol (10 mL), and was added 5-
nitrofuran-2-carbaldehyde (141 mg, 1.0 mmol). The desired
compound was obtained as amorphous yellow solid
(162 mg, 70%); m.p. 280–282 °C; IR (KBr) ν 1643, 1534,
dihydroxybenzaldehyde (138 mg, 1.0 mmol). The desired
compound was obtained as amorphous white solid (215 mg,
9
−
1 1
1346 cm ; H NMR (400 MHz, DMSO-d ): δ = 14.20 (s,
6
−
1 1
4%); m.p. 243–245 °C; IR (KBr) ν 3236, 1635 cm ; H
1H, NH), 13.20 (s, 1H, H-2’ or H-4’), 8.45 (s, 1H, H-1’ or
NMR (400 MHz, DMSO-d ): δ = 13.92 (s, 1H, NH), 12.69
H-5’), 8.43 (s, 1H, H-1’ or H-5’), 8.30 (s, 1H, H-2’ or H-4’),
6

Medicinal Chemistry Research
7
.83 (d, J = 4.0 Hz, 1H, H-3), 7.41 (s, 1H, N=CH), 7.38 (d,
controls, respectively), or different concentrations of com-
pounds (1.0, 10.0, and 100 μg/mL) in a triplicate assay. After
48 h, stock MTT solution (5 mg/mL of saline; 20 mL/well)
was added to the culture and 4 h later, the plate was cen-
trifuged for 2 min at 2800 rpm, supernatant was discharged,
and dimethyl sulfoxide (DMSO) (100 μL/well) was added to
formazan crystals solubilization, and the absorbance was
ready at 540 nm in a plate reader (Biorad – 450).
13
J = 4.0 Hz, 1H, H-4) ppm; C-NMR (100 MHz, DMSO-
d6): δ = 154.8 (C-2); 152.0 (C-5); 151.0 (C-2’); 151.0 (C-
4
4
2
’); 141.2 (C=NNH); 134.9 (C-6’); 116.1 (C-3); 116.1 (C-
); 114.7 (C-5’); 108.2 (C-1’) ppm; HRESIMS m/z:
33.0677 C H N O (calcd. 233.0670).
1
0
9
4
3
(
E)-4-(2-((5-nitrothiophen-2-yl)methylene)hydrazinyl)pyri-
dine (3h): GP2 was followed using 4-hydrazinylpyridine
109 mg, 1.0 mmol), ethanol (10 mL), and was added 5-
(
Acknowledgements We are grateful to the Brazilian agency CNPq
(Conselho Nacional de Desenvolvimento Cientifico e Tecnológico) for
nitrothiophene-2-carbaldehyde (157 mg, 1.0 mmol). The
desired compound was obtained as amorphous white solid
fellowships and financial support.
(
1
201 mg, 81%); m.p. 288–290 °C; IR (KBr) ν 1639, 1522,
Compliance with ethical standards
−
1 1
329 cm ; H NMR (500 MHz, DMSO-d ): δ = 14.11 (s,
6
1
H, NH), 13.11 (s, 1H, H-2’ or H-4’), 8.52 (s, 1H, H-2’ or
Conflict of interest The authors declare that they have no conflict of
interest.
H-4’), 8.42 (s, 1H, H-1’ or H-5’), 8.41 (s, 1H, H-1’ or H-5’),
8
7
.16 (d, J = 4.3 Hz, 1H, H-3), 7.65 (d, J = 4.3 Hz, 1H, H-4),
.41 (s, 1H, N=CH) ppm; C-NMR (125 MHz, DMSO-
13
Publisher’s note Springer Nature remains neutral with regard to
jurisdictional claims in published maps and institutional affiliations.
d6): δ = 154.6 (C-5); 151.1 (C-2); 145.7 (C-2’); 145.7 (C-
4
4
2
’); 141.2 (C=NNH); 140.4 (C-6’); 130.6 (C-3); 130.6 (C-
); 130.1 (C-5’); 130.1 (C-1’) ppm; HRESIMS m/z:
49.0450 C H N O S (calcd. 249.0441).
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