Synthesis and antibacterial evaluation of hydrazone derivatives bearing 6-chlorothieno[3,2-c]pyridine Moiety

Article abstract of DOI:10.14233/ajchem.2019.21461

The present investigation describes the overall preparation of 6-chlorothieno[3,2-c]pyridine-2-carbohydrazide-hydrazone subsidiaries (7a-r) from industrially accessible ethyl-4,6-dichloronicotinate as starting material. The synthesis of these derivatives

Full text of DOI:10.14233/ajchem.2019.21461

Asian Journal of Chemistry; Vol. 31, No. 3 (2019), 627-632
A
SIAN
J
OURNAL OF HEMISTRY
C
https://doi.org/10.14233/ajchem.2019.21461
Synthesis and Antibacterial Evaluation of Hydrazone
Derivatives Bearing 6-Chlorothieno[3,2-c]pyridine Moiety
1
1
N. SREE LAKSHMANA RAO , MANDAVA V. BASAVESWARA RAO2,* and K.R.S. PRASAD
1Department of Chemistry, Koneru Lakshmiah Education Foundation, Green Fields, Vaddeswaram-522502, India
2Department of Chemistry, Krishna University, Machilipatnam-521001, India
*Corresponding author: E-mail: mandavabasaveswararaov@gmail.com
Received: 19 May 2018;
Accepted: 21 November 2018;
Published online: 31 January 2019;
AJC-19258
The present investigation describes the overall preparation of 6-chlorothieno[3,2-c]pyridine-2-carbohydrazide-hydrazone subsidiaries (7a-r)
from industrially accessible ethyl-4,6-dichloronicotinate as starting material. The synthesis of these derivatives involve some prominent
reactions such as (i) NaBH4 reduction of ethyl ester group (ii) MnO2 oxidation of 1º alcohol (iii) cyclization of aldehyde with ethylmercapto
acetate leading to thieno[3,2-c]pyridine ring (iv) hydrazinolysis of the ethyl group (v) condensation of selected aldehydes with 6-
chlorothieno[3,2-c]pyridine-2-carbohydrazide leading to the desired 6-chlorothieno[3,2-c]pyridine-2-carbohydrazide-hydrazone derivatives
(7a-r). The structure of the derivatives was characterized by elemental analysis, NMR, infrared and mass spectroscopic analysis. These
compounds were screened for their antibacterial property towards Gram positive and Gram negative bacterial strains using agar diffusion
method with reference to norfloxacin as reference antibiotic.
Keywords: Ethyl-4,6-dichloronicotinate, Carbohydrazide-hydrazone, Antibacterial activity, Thieno[3,2-c]pyridine.
ounds.Thiophenes with fused six membered hetrocyclic ring
are currently attracting special interest. In numerous therapeutic
areas, thieno[3,2-c]pyridine derivatives was found to exhibit
various medicinal properties viz., antithrombin activity [4],
antipsychotic activity [5] and as a protease kinase inhibitor
[6]. Furthermore, in recent years, some of thieno[3,2-c] deriv-
atives exhibited fluorescence properties [7,8].
Hydrazone derivatives have created a lot of widespread
research in their utility and have been utilized as important
precursors in the construction of various heterocyclic ring reac-
tions [9]. Hydrazones constitute a class of organic compounds,
which attracts the attention of medicinal chemists due to the
fact that they contain azomethine group (-NH-N=CH-) connected
with carbonyl group, which is responsible for their various
biological activities [9], viz., anticancer [10], anti-inflammatory
[11], antiviral [12]. In recent years, compounds with hydrazide-
hydrazone structure have been found to exhibit antibacterial
activity to a significant level [13]. Certain complexes of hydrazones
catalyze physiological processes so as to get transformed to
go about as sterilants for houseflies, nematocides, herbicides,
bug sprays, rodenticides and plant development controllers
INTRODUCTION
The drugs especially antibiotics related to microorganism
infections presently characterize a considerable therapeutic
task throughout the world.Although these antibiotics are utilized
for many infectious, the influx of newest infectious diseases as
well as additive levels of resistance in some pathogens-impend
to weaken the success of the few remaining medication offered
for the treatment of those infections [1,2]. The scarcity of inno-
vation within the development of latest antibiotics has consi-
derably inflated the challenge of treating and eliminating bound
infecting pathogens, that cause a hour fall within the numbers
of latest approvals and few novel molecules [2]. Whereas this
trend is dynamic, there's an pressing demand for the event of
latest medicinal drug agents with divergent and distinctive
structural options that operate via a distinct mechanisms of
action to those of existing antimicrobial agents [2,3].
In recent years, interest in one of the important hetrocyclic
ring nuclei such as thieno[3,2-c]pyridines has emerged due to
their similarity to benzofuran, quinoline and isoquinoline, which
are important nuclei present in many biologically active comp-
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628 Rao et al.
Asian J. Chem.
[14-16]. Furthermore, hydrazones discover applications in
colorimetric or fluorimetric determinations, specifically, an
expanding number of N-N bond-containing heterocycles and
peptidomimetics have advanced into commercial applications
as pharmaceutical and horticultural agents [17-19].
Inspired with the above biological activities of hydrazide-
hydrazones and in continuation to previous research on thiophene-
[3,2-c]pyridine and furo[3,2-c]pyridine hydrazide-hydrazone
derivative [20,21], we report here in the preparation, structural
determination and screening results of antibacterial activity of
a new series of 6-chlorothieno[3,2-c]pyridine-2-carbohydrazide-
hydrazone derivatives (7a-r).
Elemental analysis of C10H8NO2SCl calcd. (found) %: C 49.69
(49.71), H 3.34 (3.32), N 5.80 (5.77)
6-Chlorothieno[3,2-c]pyridine-2-carbohydrazide (5):
Hydrazine hydrate monohydrate (4.88 mL, 99.58 mmol) was
added to a pre-mixed solution of compound 4 (3.0 g, 12.44
mmol) in ethanol (240 mL). The reaction content was stirred
at room temperature for 1 h and later heated to 80 ºC for 18 h.
The reaction mixture was evaporated under reduced pressure
and the residue was triturated with n-pentane followed by
methanol to result in compound 5. Off white solid;Yield: 2.5
g, 88 %); m.p.: 282-286 ºC; IR (KBr, νmax, cm-1): 3316 (-NH2-),
1647 (-C=O), 1574 (-C=N str.), 1367 (C-N str.). 1H NMR (500
MHz, DMSO-d6): δ 10.30 (brs, 1H), 9.10 (s, 1H), 8.30 (s, 1H),
8.18 (s, 1H), 4.75 (brs, 2H). 13C NMR (100 MHz, DMSO-d6):
δ 160.40, 149.58, 147.02, 145.29, 141.19, 135.32, 121.89,
117.48; ESI MS: m/z, 28.08 (M+H)+. Elemental analysis of
C8H6N3OSCl calcd. (found) %: C 42.20 (42.18); H 2.66 (2.68);
N 18.46 (18.44).
EXPERIMENTAL
Reagents and solvents obtained from commercial suppliers
were used without purification or drying unless otherwise
noted. 1H NMR were recorded using Bruker & Agilent instru-
ment at 400 MHz and TMS was used as an internal standard.
LCMS analysis was performed on Waters UPLC with SQD-2
mass detector (single quadrupole). δ parts per million (ppm) a
unit of measurement for chemical shifts are reported downfield
from tetramethylsilane (TMS) with reference to internal solvent
and coupling constants in Hz. The mass spectra were recorded
on Agilent ion trap MS. Infrared spectra were recorded on a
Perkin Elmer FT-IR spectrometer. TLC analysis was monitored
used silica gel 60 F254 pre-coated plates prior to the use with
appropriated eluents necessary for the experiments. Silica gel
60-120/100-200 mesh was used for column chromatography.
Mel-temp apparatus was used for the determination of melting
point and are uncorrected.
Synthesis of 6-chlorothieno[3,2-c]pyridine-2-carbohy-
drazide-hydrazone derivatives (7a-r): Respective aromatic/
hetro aromatic aldehydes (6a-r) (0.43 mmol) was added to a
pre-mixed solution of compound 5 (0.43 mmol) in ethanol.
The reaction content was refluxed for 0.5 h. The solids was
filtered and rinsed with ethanol and dried to afford the respective
hydrazone derivatives (7a-r) in 82-93 % yield (Scheme-I).
(E)-N′-Benzylidene-6-chlorothieno[3,2-c]pyridine-2-
carbohydrazide (7a): White solid; Yield: 120 mg, 86.5%;
m.p.: 275-279 ºC; IR (KBr, νmax, cm-1): 3228 (-CO-NH str.),
1638 (-C=O str.), 1558 (-C=N str.), 1364 (-C=C str.), 1263 (-C-N
1
str.), 636 (C-Cl). H NMR (500 MHz, DMSO-d6): δ 12.32
(4,6-Dichloropyridin-3-yl)methanol (2): In a mixture of
tetrahydrofuran:methanol (8:2) (200 mL) was added ethyl-4,
6-dichloronicotinate (1) (10.0 g, 45.45 mmol) followed by
NaBH4 (3.45 g, 90.90 mmol) at 0 ºC. After 4 h of stirring at
room temperature, the reaction mixture was quenched with
water at 0 ºC and extracted with ethyl acetate.After usual work
up procedure, compound 2 was isolated.Yellow solid; Yield:
7.2 g, 82 %.Elemental analysis of C6H5NOCl2 calcd. (found)
%: C 40.48 (40.50); H 2.83 (2.80); N 7.87 (7.86).
4,6-Dichloronicotinaldehyde (3): MnO2 (21.23 g, 244
mmol) was added to a pre-mixed solution of compound 2 (7.2 g,
40.67 mmol) in methanol (140 mL). The reaction content was
stirred and heated to 60 ºC for 18 h and filtered while hot and
the inorganic discharge was washed with methanol. The combined
filtrate was concentrated to obtain compound 3.Yellow solid;
Yield: 5 g, 70 %. Elemental analysis of C6H3NOCl2 calcd.
(found) %: C 40.95 (40.97); H 1.72 (1.70); N 7.96 (7.94).
Ethyl 6-chlorothieno[3,2-c]pyridine-2-carboxylate (4):
A pre-mixed stirred solution of compound 3 (7.4 g, 42.28
mmol) in dichloromethane (40 mL) containing triethyl amine
(11.37 mL, 84.56 mmol) was added ethylmercapto acetate
(5.59 mL, 50.74 mmol) at 0 ºC. The reaction mixture was stirred
at room temperature for 1 h and then to 50 ºC for 18 h. The
reaction mixture was quenched with water and extracted with
ethyl acetate.After usual standard work up procedure and puri-
fication by column chromatography (silica gel: 100-200 mesh,
eluent: 5% ethyl acetate in pet ether) isolated compound 4;
Light Yellow solid; Yield: 5.7 g, 56 %; m.p.: 108-112 ºC.
(*12.23, s, 1H), 9.16 (d, J = 9.5 Hz, 1H), 8.55 (*8.48, s, 1H),
8.36 (d, J = 8.0 Hz, 2H), 8.19 (s, 1H), 7.87 (d, J = 7.0 Hz, 1H),
7.77 (d, J = 5.5 Hz, 1H), 7.54-7.48 (m, 3H); ESI MS: m/z
313.8 (M-H)+. Elemental analysis of C15H10N3OSCl calcd.
(found) %: C 57.05 (57.07); H 3.19 (3.21); N 13.31 (13.33).
(E)-6-Chloro-N′-((pyridin-2-yl)methylene)thieno[3,2-c]-
pyridine-2-carbohydrazide (7b): Off white solid;Yield: 120
mg, 86.2 %; m.p. 295-298 ºC; IR (KBr, νmax, cm-1): 3081
(-CO-NH str.), 1667 (-C=O), 1554 (-C=N str.), 1376 (C=C str.),
1260 (-C-N str.), 638 (C-Cl).1H NMR (500 MHz, DMSO-d6):
δ 12.47 (*12.40, s, 1H), 9.17 (s, 1H), 8.65 (d, J = 4.5 Hz, 1H),
8.57 (*8.49, s, 1H), 8.35 (s, 1H), 8.23 (s, 1H), 7.98-7.94 (m, 2H),
7.47 (brs, 1H); ESI MS: m/z, 314.3 (M-H)+. Elemental analysis
of C14H9N4OSCl calcd. (found) %: C 53.08 (53.05); H 2.86
(2.85); N 17.69 (17.66).
(E)-6-Chloro-N′-((pyridin-3-yl)methylene)thieno[3,2-c]-
pyridine-2-carbohydrazide (7c): Light yellow solid; Yield:
115 mg, 82.6%; m.p.: 310-313 ºC; IR (KBr, νmax, cm-1): 3078
(-CO-NH str.),1665 (-C=O), 1552 (-C=N str.), 1374 (C=C str.),
1260 (-C-N str.), 636 (C-Cl). 1H NMR (500 MHz, DMSO-d6):
δ 12.46 (* 12.37, s, 1H), 9.17 (s, 1H), 9.01 (*8.90, s, 1H), 8.66
(s, 1H), 8.54 (d, J = 10.0 Hz, 1H), 8.37 (d, J = 6.0 Hz, 1H), 8.38-
8.17 (m, 2H), 7.53 (brs, 1H); ESI MS: m/z, 316.7 (M+H)+.
Elemental analysis of C14H9N4OSCl calcd. (found)%: C 53.08
(53.04); H 2.86 (2.88); N 17.69 (17.66).
(E)-6-Chloro-N′-((pyridin-4-yl)methylene)thieno[3,2-c]-
pyridine-2-carbohydrazide (7d): Off white solid;Yield: 119
mg, 85.5 %; m.p. 357-359 ºC; IR (KBr, νmax, cm-1): 3081

Vol. 31, No. 3 (2019)
Synthesis of Hydrazone Derivatives Bearing 6-Chlorothieno[3,2-c]pyridine Moiety 629
O
Cl
Cl
O
Cl
O
b
CO2Et
c
a
S
OH
H
Cl
N
Cl
N
Cl
N
Cl
N
2
1
3
4
O
NH2
Aryl / Hetero
Aldehydes
6a-r
N
O
H
d
S
S
Aryl / Hetero Aryl
rings
Cl
N N
e
H
R
N
Cl
N
7a-r
5
List of R = Aryl / Hetero Aryl aldehydes
N
N
N
OH
OH
6b
6c
6d
6a
6g
6l
6e
6f
OH
Cl
F
OH
CF3
Cl
6h
F
OH
6j
6i
6k
CF3
N
CF3
O
6m
6n
6o
O
N
N
N
O
6p
6q
6r
Reaction conditions: a) NaBH4, THF: MeOH, 0 °C to room temperature, 4 h; b) MnO2, methanol, 60 °C, 18 h; c) ethylmercapto acetate, triethylamine,
dichloromethane, 50 °C for 8 h; d) hydrazine-hydrate, ethanol, 80 °C, 18 h; e) aromatic/hetro aromatic aldehydes 6a-r, ethyl alcohol, 80 °C, 30 min
Scheme-I: 6-Chlorothieno[3,2-c]pyridine-2-carbohydrazide derivatives (7a-r)
(-CO-NH str.),1667 (-C=O), 1588 (-CH=CH-CO, α,β-unsatu-
rated str.), 1376 (C=C str.). 1H NMR (500 MHz, DMSO-d6): δ
10.23 (*10.09, s, 1H), 9.18 (*9.03, s, 1H), 8.89 (d, J = 4.5 Hz,
1H), 8.76-8.66 (m, 1H), 8.37 (*8.29, s, 1H), 8.12 (s, 1H), 7.8
1 (d, J = 4.5 Hz, 2H); ESI MS: m/z 317.08 (M+H)+. Elemental
analysis of C14H9N4OSCl, calcd. (found)%: C 53.08 (53.10);
H 2.86 (2.89); N 17.69 (17.70).
(E)-N′-(2-Hydroxybenzylidene)-6-chlorothieno[3,2-c]-
pyridine-2-carbohydrazide (7e):White solid;Yield: 120 mg,
82.3 %; m.p. 289-282 ºC; IR (KBr, νmax, cm-1): 3330 (-OH str.),
3218 (-CO-NH str.), 1666 (-C=O str.), 1588 ( -C=N str.), 1433
(-C=C str.), 1378 (-C-N str.), 615 (C-Cl). 1H NMR (500 MHz,
DMSO-d6): δ 12.52 (*12.11, s, 1H), 9.70 (*9.65, s, 1H), 9.16
(s, 1H), 8.53 (s, 1H), 8.39-8.34 (m, 1H), 8.09 (s, 1H), 7.33-
7.22 (m, 3H), 6.88 (t, J = 10.0 Hz, 1H); ESI MS: m/z, 317.08
(M+H)+. Elemental analysis of C15H10N3O2SCl calcd. (found)
%: C 54.32 (54.30); H 3.04 (3.01); N 12.67 (12.66).
(E)-N′-(3-Hydroxybenzylidene)-6-chlorothieno[3,2-c]-
pyridine-2-carbohydrazide (7f): Off white solid;Yield: 124
mg, 85.1 %; m.p. 290-293 ºC; IR (KBr, νmax, cm-1): 3322 (-OH
str.), 3220 (-CO-NH str.), 1668 (-C=O str.), 1581 (-C=N str.),
1436 (-C=C str.), 1374 (-C-N str.), 621 (C-Cl) . 1H NMR (500
MHz, DMSO-d6): δ 12.26 (*12.17, s, 1H), 9.71 (*9.69, s, 1H),
9.15 (d, J = 8.5 Hz,1H), 8.53 (*8.09,s, 1H), 8.38-8.31 (m,
2H), 7.31-7.13 (m, 3H), 6.87 (t, J = 10.0 Hz, 1H); ESI MS:
m/z, 317.08 (M+H)+. Elemental analysis of C15H10N3O2SCl
calcd. (found) %: C 54.28 (54.30); H 3.02 (3.01); N 12.64
(12.62).

630 Rao et al.
Asian J. Chem.
(E)-N′-(4-Hydroxybenzylidene)-6-chlorothieno[3,2-c]-
ental analysis of C16H9N3OSClF3 calcd. (found) %: C 51.06
(51.08); H 2.28 (2.31); N 11.88 (11.91).
pyridine-2-carbohydrazide (7g): White solid;Yield: 119 mg,
81.6 %; m.p. 319-321 ºC; IR (KBr, νmax, cm-1): 3314 (-OH str.),
3234(-CO-NH str.), 1666 (-C=O str.), 1576 (-C=N str.), 1428
(-C=C str.), 1370 (-C-N str.), 628 (C-Cl). 1H NMR (500 MHz,
DMSO-d6): δ 12.28 (*12.10, s, 1H), 9.76 (*9.66, s, 1H), 9.18
(d, J = 8.5 Hz,1H), 8.50 (*8.10, s, 1H), 8.38-8.31 (m, 3H),
7.31-7.13 (m, 4H), 6.86 (t, J = 10.0 Hz, 1H); ESI MS: m/z,
317.08 (M+H)+. Elemental analysis of C15H10N3O2SCl calcd.
(found) %: C 54.34 (54.29); H 3.06 (3.03); N 12.62 (12.60).
(E)-N′-(2,3-Dihydroxybenzylidene)-6-chlorothieno[3,2-
c]pyridine-2-carbohydrazide (7h): Off white solid; Yield:
130 mg, 85.1 %; m.p. 318-321 ºC; IR (KBr, νmax, cm-1): 3343
(-OH str.), 3222(-CO-NH str.), 1668 (-C=O str.), 1572 (-C=N
str.), 1417 (-C=C str.), 1366 (-C-N str.), 632 (C-Cl). 1H NMR
(500 MHz, DMSO-d6): δ 12.52 (*12.11, s, 1H), 10.67 (*9.71,
s, 1H), 9.33 (*9.11, s, 1H), 9.16 (s, 1H), 8.65 (*8.54, s, 1H),
8.36 (d, J = 4.0 Hz, 2H), 7.44 (*7.05, d, J = 6.0 Hz, 1H), 6.89-
6.74 (m, 2H); ESI MS: m/z, 345.7 (M+H)+. Elemental analysis
of C15H10N3O3SCl calcd. (found) %: C 51.80 (51.83); H 2.90
(2.89); N 12.08 (12.10).
(E)-N′-(2,6-Dichlorobenzylidene)-6-chlorothieno[3,2-
c]pyridine-2-carbohydrazide (7i): Off white solid;Yield: 140
mg, 82.8 %; m.p. 289-292 ºC; IR (KBr, νmax, cm-1): 3162 (-CO-
NH str.), 1657 (-C=O str.), 1575 (-C=N str.), 1409 (-C=C str.),
1360 (-C-N str.), 717 (C-Cl). 1H NMR (500 MHz, DMSO-d6):
δ 12.56 (*12.42, s, 1H), 9.12 (br.s, 1H), 8.68 (*8.56, s, 1H),
8.38 (t, J = 10.5 Hz, 1H), 8.29 (s, 1H), 7.60 (s, 2H), 7.48 (s, 1H);
ESI MS: m/z, 385.96 (M+H)+. Elemental analysis of C15H8N3OSCl3
calcd. (found) %: C 46.84 (46.80), H 2.10 (2.12), N 10.92 (10.95).
(E)-N′-(2,6-Difluorobenzylidene)-6-chlorothieno[3,2-
c]pyridine-2-carbohydrazide (7j): Light yellow solid;Yield:
137 mg, 88.6 %; m.p.: 253-256 ºC; IR (KBr, νmax, cm-1): 3222
(-CO-NH str.), 1668 (-C=O str.), 1572 ( -C=N str.), 1422 (-C=C
str.), 1368 (-C-N str.), 628 (C-Cl). 1H NMR (500 MHz, DMSO-
d6): δ 12.45 (*12.31, s, 1H), 9.15 (*9.10, s, 1H), 8.64 (*8.60,
s, 1H), 8.37-8.24 (m, 2H), 7.56 (d, J = 6.4 Hz, 1H), 7.26 (t, J =
9.2 Hz, 2H); ESI MS: m/z, 352.05 (M+H)+. Elemental analysis
of C15H8N3OSClF2 calcd. (found) %: C 51.22 (51.20); H 2.29
(2.27); N 11.95 (11.97).
(E)-N′-(2-(Trifluoromethyl)benzylidene)-6-chloro-
thieno[3,2-c]pyridine-2-carbohydrazide (7k): Off white solid;
Yield: 139 mg, 82.4 %; m.p.: 292-294 ºC; IR (KBr, νmax, cm-1):
3218 (-CO-NH str.), 1667 (-C=O str.), 1575 ( -C=N str.), 1428
(-C=C str.), 1366 (-C-N str.), 626 (C-Cl). 1H NMR (500 MHz,
DMSO-d6): δ 12.58 (*12.46, s, 1H), 9.16 (d, J = 10.5 Hz, 1H),
8.84 (s, 1H), 8.56 (d, J = 8.0 Hz, 1H), 8.38-8.35 (m, 3H), 8.24
(d, J = 7.5 Hz, 2H); ESI MS: m/z, 383.60 (M+H)+. Elemental
analysis of C16H9N3OSClF3 calcd. (found) %: C 50.07 (50.11);
H 2.36 (2.38); N 10.95 (10.97).
(E)-N′-(3-(Trifluoromethyl)benzylidene)-6-chlorothieno
[3,2-c]pyridine-2-carbohydrazide (7l): Off white solid;Yield:
142 mg, 84.24 %; m.p.: 267-269 ºC; IR (KBr, νmax, cm-1): 3165
(-CO-NH str.), 1663 (-C=O str.), 1573 (-C=N str.), 1435 (-C=C
str.), 1392 (-C-N str.), 1119 (C-F), 666 (C-Cl). 1H NMR (500
MHz, DMSO-d6): δ 12.53 (*12.43, s, 1H), 9.16 (s, 1H), 8.55
(s, 1H), 8.40-8.25 (m, 3H), 8.12-8.07 (m, 2H), 7.84 (d, J = 6.4 Hz,
1H), 7.76-7.71 (m, 1H); ESI MS: m/z, 384.11 (M+H)+. Elem-
(E)-N′-(4-(Trifluoromethyl)benzylidene)-6-chlorothieno-
[3,2-c]pyridine-2-carbohydrazide (7m): Off white solid;
Yield: 150 mg, 88.98 %; m.p.: 309-312 ºC; IR (KBr, νmax, cm-1):
3160 (-CO-NH str.), 1664 (-C=O str.), 1571 ( -C=N str.), 1432
(-C=C str.), 1392 (-C-N str.), 1119 (C-F), 666 (C-Cl). 1H NMR
(500 MHz, DMSO-d6): δ 12.51 (*12.40, s, 1H), 9.18 (s, 1H),
8.53 (s, 1H), 8.38-8.23 (m, 3H), 8.10-8.05 (m, 2H), 7.85 (d, J
= 6.4 Hz, 1H), 7.74-7.70 (m, 1H); ESI MS: m/z, 384.11 (M+H)+.
Elemental analysis of C16H9N3OSClF3 calcd. (found) %: C
50.27 (50.24); H 2.34 (2.30); N 10.97 (10.88).
(E)-N′-([1,1′-Biphenyl]-4-ylmethylene)-6-chlorothieno-
[3,2-c]pyridine-2-carbohydrazide (7n): Light yellow solid;
Yield: 142 mg, 82.7%; m.p.: 294-296 ºC; IR (KBr, νmax, cm-1):
3155 (-CO-NHstr.), 1654 (-C=O str.), 1573 ( -C=N str.), 1400
(-C=C str.), 1340 (-C-N str.), 572 (C-Cl). 1H NMR (500 MHz,
DMSO-d6): δ 12.36 (*12.28, s, 1H), 9.18 (*9.15, s, 1H), 8.56
(*8.52, s, 1H), 8.38 (*8.23, s, 1H), 8.36 (s, 1H), 7.96 (d, J =
10.5 Hz, 1H), 7.87-7.79 (m, 3H), 7.75 (d, J = 9.5 Hz, 2H), 7.51
(t, J = 9.0 Hz, 2H), 7.43 (d, J = 8.5 Hz, 1H); ESI MS: m/z,
392.10 (M+H)+. Elemental analysis of C21H14N3OSCl calcd.
(found) %: C 64.36 (64.33); H 3.60 (3.59); N 10.72 (10.74).
(E)-N′-(4-(Pyridin-4-yl)benzylidene)-6-chlorothieno-
[3,2-c]pyridine-2-carbohydrazide (7o): Off white solid;
Yield: 160 mg, 93 %; m.p.: 325-328 ºC; IR (KBr, νmax, cm-1):
3155 (-CO-NH str.), 1661 (-C=O str.), 1585 ( -C=N str.), 1506
(-C=C str.), 1398 (-C-N str.), 671 (C-Cl). 1H NMR (500 MHz,
DMSO-d6): δ 12.42 (*12.33, s, 1H), 9.17 (d, J = 7.4 Hz, 1H),
8.68 (s, 2H), 8.57 (*8.25, s, 2H), 8.54 (*8.39, s, 2H), 8.03-
7.91 (m, 3H), 7.78 (d, J = 6.0 Hz, 2H); ESI MS: m/z, 392.17
(M+H)+. Elemental analysis of C20H13N4OSCl calcd. (found) %:
C 61.14 (61.11); H 3.34 (3.37); N 14.26 (14.28).
(E)-N′-(4-(Benzyloxy)benzylidene)-6-chlorothieno[3,2-
c]pyridine-2-carbohydrazide (7p): Light yellow solid;Yield:
171 mg, 92.4 %; m.p.: 262-266 ºC; IR (KBr, νmax, cm-1): 3162
(-CO-NH str.), 1664 (-C=O), 1575 (-C=N str.), 1506 (-C=C str.),
1389 (C-NC str.), 676 (C-Cl). 1H NMR (500 MHz, DMSO-d6):
δ 12.20 (*12.11, s, 1H), 9.15 (d, J = 8.0 Hz, 1H), 8.53 (*8.41,
s, 1H), 8.34 (s, 1H), 8.12 (s, 1H), 7.81 (d, J = 8.8 Hz, 1H), 7.71
(d, J = 8.8 Hz, 1H), 7.48-7.35 (m, 5H), 7.14 (t, J = 6.4 Hz, 2H);
ESI MS: m/z, 412.7(M+H)+. Elementalanalysisof C22H16N3O2SCl,
calcd. (found)%: C 62.63 (62.65); H 3.82 (3.85); N 9.96 (9.97).
(E)-N′-(4-(Benzyloxy)-3-methoxybenzylidene)-6-chloro-
thieno[3,2-c]pyridine-2-carbohydrazide (7q): Off white solid;
Yield: 169 mg, 85.3 %; m.p.: 212-216 ºC; IR (KBr, νmax, cm-1):
3154 (-CO-NH str.), 1652 (-C=O str.), 1577 (-C=N str.), 1508
(-C=C str.), 1391 (-C-N str.), 1271 (C-O-C-l), 615 (C-Cl). 1H
NMR (500 MHz, DMSO-d6): δ 12.21 (*12.18, s, 1H), 9.14 (s,
1H), 8.54 (*8.40, s, 1H), 8.34 (d, J = 9.0 Hz, 1H), 8.09 (s, 1H),
7.52 (d, J = 1.5 Hz, 1H), 7.48 (d, J = 2.0 Hz, 2H), 7.46-7.35
(m, 5H), 7.14 (d, J = 10.5 Hz, 1H), 5.17 (*5.16, s, 2H), 3.92
(*3.84, s, 3H); ESI MS: m/z, 452.15 (M+H)+. Elemental analysis
of C23H18N3O3SCl calcd. (found)%: C 61.13 (61.10); H 4.01
(3.99); N 9.30 (9.28).
(E)-N′-(4-(4H-1,2,4-Triazol-4-yl)benzylidene)-6-chloro-
thieno[3,2-c]pyridine-2-carbohydrazide (7r): Off white solid;
Yield: 152 mg, 90.58 %; m.p.: 350-353 °C; IR (KBr, νmax, cm-1):

Vol. 31, No. 3 (2019)
Synthesis of Hydrazone Derivatives Bearing 6-Chlorothieno[3,2-c]pyridine Moiety 631
3155 (-CO-NH str.), 1661 (-C=O str.), 1585 (-C=N str.), 1506
(-C=C str.), 1398 (-C-N str.), 671 (C-Cl). 1H NMR (500 MHz,
DMSO-d6): δ 12.42 (*12.34, s, 1H), 9.48 (s, 1H), 9.42 (s, 1H),
8.57-8.52 (m, 1H), 8.39-8.30 (m, 3H), 8.07-7.95 (m, 4H); ESI
MS: m/z, 383.12 (M+H)+. Elemental analysis of C17H11N6OSCl
calcd. (found) %: C 53.34 (53.37); H 2.90 (2.87); N 21.95 (21.92).
Biological assay: The antibacterial activity experiments
were carried out following our previously reported procedure
[20,21]. The 6-chlorothieno[3,2-c]pyridine-2-carbohydrazide-
hydrazone derivatives (7a-r) (50 µg/mL concentration) were
tested in contradiction to Staphylococcus aureus (MTCC 96),
Streptococcus pyogenes (MTCC 442) belonging to Gram negative
strain and Escherichia coli (MTCC 443), Pseudomonas aerugi-
nosa (MTCC 424) belonging to Gram positive strain, utilizing
a standard methodology viz., agar diffusion method where in
norfloxacin was used as the reference antibiotic.
the remaining compounds 7a-r have been fully characterized
as per the above description.
Antibacterial activity: The zone of inhibition values of
6-chlorothieno[3,2-c]pyridine-2-carbohydrazide-hydrazone
derivatives (7a-r) obtained from the antibacterial experimen-
tation is given in Table-1. It is evident that compound 7b (R =
2-substituted pyridine), 7c (R = 3-substituted pyridine), 7d (R
= 4-substituted pyridine), 7o (R = 4-phenyl pyridine), 7r (R =
4-phenyl-4H-1,2,4-triazole) exhibited good antibacterial activity.
Compounds 7e (R = o-hydroxyphenyl), 7f (R = m-hydroxy-
phenyl), 7g (R = p-hydroxyphenyl), 7h (R = o, m-hydroxy-
phenyl), 7k (R = o-CF3 Phenyl), 7l (R = m-CF3 phenyl) and
7m (R = p-CF3 phenyl) moderate antibacterial activity, while
compounds 7a (R = phenyl), 7i (R = 2,6-dichloro phenyl), 7j
(R = 2,6-difluorophenyl) showed weak antibacterial activity.
Finally, compounds 7n (R = biphenyl), 7p (R= (phenoxy-methyl)-
benzene) and 7q (R = (2-methoxyphenoxy)methyl) benzene)
did not show any antibacterial activity as they exhibited zero
zone of inhibition.
RESULTS AND DISCUSSION
Sodium borohydride reduction of ethyl-4,6-dichloronico-
tinate (1) in THF:methanol at 0 ºC to room temperature for 4 h
gave (4,6-dichloropyridin-3-yl)methanol (2). MnO2 oxidation
of alcohol 2 in methanol at 60 ºC for 18 h produced 4,6-dichloro-
nicotinaldehyde (3). Condensation of aldehyde 3 with ethyl
mercapto acetate in presence of dichloromethane at 50 ºC for
8 h gave cyclized ethyl ester intermediate 4. Hydrazinolysis
of ethyl ester 4in ethanol at 80 ºC for 18 h gave the desired product
carbohydrazide [5]. Condensation of carbohydrazide 5 with
various aromatic/hetro aromatic aldehydes 6a-r at reflux in
ethanol for 30 min produced 6-chlorothieno[3,2-c]pyridine-
2-carbohydrazide-hydrazone derivatives (7a-r).
The synthesized hydrazone derivatives of (E)-N′-(2,6-
dichlorobenzylidene)-6-chlorothieno[3,2-c]pyridine-2-
carbohydrazide (7a-r) were sufficiently characterized using
1H NMR, mass and IR spectroscopic techniques.These hydrazone
derivatives were found to exist as a mixture of two rotameric
forms in solution [22,23] as indicated by their 1H NMR spectrum.
The basis of the 'E' geometry of C=N bond by 1H NMR was
established based on the reported literature data [24,25].
As a representative example, structural interpretation of
(E)-N′-(2,6-dichlorobenzylidene)-6-chlorothieno[3,2-c]-
pyridine-2-carbohydrazide (7i), is described here, the protons
resonating at 9.12 ppm appeared as singlet (1H integration)
and the proton resonating at 8.29 ppm as singlet (1H integ-
ration) corresponds to the pyridine ring and proton signal at
7.48 ppm as singlet with (1H integration) is assigned to the
fused thiophene ring while the protons signals resonating at
12.56 (*12.42, singlet, 1H) ppm and 8.68 (*8.56, singlet, 1H)
ppm corresponds to -CO-NH- and -N=CH- groups in the scaffold,
respectively. Finally, the proton signals resonating at 8.38 ppm
(triplet, 1H) and 7.60 ppm (singlet, 2H) corresponds to 2,6-
chlorophenyl ring system. The mass spectrum of compound
7i showed a molecular ion peak at m/z 385.96 and is in agree-
ment with the desired molecular formula. The distinguished
absorption peaks in the region 3162, 1657, 1575, 1360 cm-1
confirms the presence of the desired functional group -CONH-,
-C=O, -C=N and -C-N, respectively as indicated from the IR
spectra of compound 7i. Based on the above analytical descrip-
tion, the structure of compound 7i was determined. Similarly,
TABLE-1
ZONE OF INHIBITION VALUES OF COMPOUNDS 7a-r
(50 µg/mL) FOR THE DETERMINATION OF
ANTIBACTERIAL ACTIVITY
Gram-negative
Gram-positive
Compd. No.
E.
P.
S.
S.
coli
aeruginosa
aureus
pyogenes
7a
8
7
7
6
7b
7c
7d
7e
7f
7g
7h
7i
7j
7k
7l
7m
24
22
21
15
16
16
15
11
10
16
15
16
–
19
17
18
11
14
13
14
10
7
15
14
13
–
22
21
20
14
16
16
15
11
6
12
14
15
–
18
17
17
10
13
12
13
8
5
14
12
11
–
7n
7o
7p
22
–
18
–
20
–
18
–
7q
7r
–
25
26
–
19
21
–
23
25
–
18
20
*Standard drug
Conclusion
The synthesis, characterization and antibacterial activity
of some new hydrazone derivatives (7a-r) obtained from conden-
sation of 6-chlorothieno[3,2-c]pyridine-2-carbohydrazide and
corresponding aromatic and hetroaromatic aldehydes. The anti-
bacterial results of the study demonstrated that compound 7b
(R = 2-substituted pyridine), 7c (R = 3-substituted pyridine),
7d (R = 4-substituted pyridine), 7o (R = 4-phenyl pyridine),
7r (R = 4-phenyl-4H-1,2,4-triazole) exhibited good antibacterial
activity. Compounds 7e (R = o-hydroxyphenyl), 7f (R = m-
hydroxyphenyl), 7g (R = p-hydroxyphenyl), 7h (R = o, m-
hydroxyphenyl), 7k (R = -o-CF3 Phenyl), 7l (R = m-CF3 phenyl)
and 7m (R = p-CF3 phenyl) moderate antibacterial activity,
while the compounds 7a (R = phenyl), 7i (R = 2,6-dichloro-

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activity. Finally, compounds 7n (R = biphenyl), 7p (R = (phe-
noxymethyl)benzene) and 7q (R = (2-methoxyphenoxy)-
methyl)benzene) did not show any antibacterial activity.
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CONFLICT OF INTEREST
The authors declare that there is no conflict of interests
regarding the publication of this article.
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