Multi-component reaction to access a library of polyfunctionally substituted 4,7-dihydropyrazolo[3,4-b]pyridines

Article abstract of DOI:10.1080/00397911.2019.1582064

A practical approach to polyfunctionally substituted 4,7-dihydropyrazolo[3,4-b]pyridine derivatives from heteroaryl hydrazine, 3-aryl-3-oxopropanenitriles and aldehydes have been described in the report. The present catalyst-free protocol involves the intermediacy of 5-aminopyrazole and α-cyanochalcone, which undergoes in situ Michael addition to afford title compounds in moderate to good yields. All the steps were conducted concomitantly to render the procedure as practical and straightforward as possible. The expeditious synthetic protocol experiment takes less than one hour and shows broad substrate scope.

Full text of DOI:10.1080/00397911.2019.1582064

Synthetic Communications
An International Journal for Rapid Communication of Synthetic Organic
Chemistry
ISSN: 0039-7911 (Print) 1532-2432 (Online) Journal homepage: https://www.tandfonline.com/loi/lsyc20
Multi-component reaction to access a
library of polyfunctionally substituted 4,7-
dihydropyrazolo[3,4-b]pyridines
Ranjana Aggarwal, Suresh Kumar & Gulshan Singh
To cite this article: Ranjana Aggarwal, Suresh Kumar & Gulshan Singh (2019): Multi-component
reaction to access a library of polyfunctionally substituted 4,7-dihydropyrazolo[3,4-b]pyridines,
Synthetic Communications, DOI: 10.1080/00397911.2019.1582064
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https://doi.org/10.1080/00397911.2019.1582064
Multi-component reaction to access a library of
polyfunctionally substituted
4,7-dihydropyrazolo[3,4-b]pyridines
Ranjana Aggarwal, Suresh Kumar , and Gulshan Singh
Department of Chemistry, Kurukshetra University, Kurukshetra, Haryana, India
ABSTRACT
ARTICLE HISTORY
Received 15 November 2018
A practical approach to polyfunctionally substituted 4,7-dihydropyra-
zolo[3,4-b]pyridine derivatives from heteroaryl hydrazine, 3-aryl-3-
oxopropanenitriles and aldehydes have been described in the report.
The present catalyst-free protocol involves the intermediacy of
5-aminopyrazole and a-cyanochalcone, which undergoes in situ
Michael addition to afford title compounds in moderate to good
yields. All the steps were conducted concomitantly to render the
procedure as practical and straightforward as possible. The exped-
itious synthetic protocol experiment takes less than one hour and
shows broad substrate scope.
KEYWORDS
Aldehydes; 4,7-
dihydropyrazolo[3,4-b]pyri-
dines; heteroarylhydrazines;
multi-component reaction;
3-oxo-3-arylpropanenitriles
GRAPHICAL ABSTRACT
R
NH2
N
N
R
H
EtOH,
Conc. HCl
N
Ar
R'
O
O
CN
CN
HN
Ar'
Ar'
Reflux,
45-50 min
Ar
O
CN
R'
H
Metal free
Broad substrate scope
Simple efficient pracꢀcal experimental procedure
Green mulꢀ-component strategy
Introduction
Azaheterocycles are ubiquitous scaffolds in pharmaceuticals, natural products, and bio-
logically active compounds. Pyrazolo[3,4-b]pyridine system, in particular, constitutes a
privileged substructure and has gained special attention of the researchers in the last
few decades. These compounds have been reported to exhibit antimicrobial,[1,2] anti-
inflammatory,[3,4] A1 adenosine receptor inhibitor,[5] anticancer,[6,7] glycogen synthase
CONTACT Ranjana Aggarwal
ranjanaaggarwal67@gmail.com
Department of Chemistry, Kurukshetra University,
Kurukshetra, Haryana 136119, India.
Supplemental data for this article is available online at on the publisher’s website.
Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/lsyc.
ß 2019 Taylor & Francis Group, LLC

2
R. AGGARWAL ET AL.
Figure 1. Representatives drugs and bioactive pyrazolo[3,4-b]pyridines.
kinase-3[8,9] (1, Figure 1), inhibitors of cyclin-dependent protein kinase-2 (cdk-2)
(2, Figure 1),[10] antiplatelet,[11] and human nicotinamide phosphoribosyltransferase
(NAMPT) inhibitor[12] activities. These compounds have also been demonstrated as
promising pharmaceuticals in the treatment of anxiety,[13] depression,[14] schizophrenia
and Alzheimer’s disease.[3,15] Cartazolate and Etazolate (3 and 4, respectively, Figure 1)
are two of the marketed drugs having pyrazolo[3,4-b]pyridine nucleus, being used for
their anxiolytic activity.
Moreover, its 4,7-dihydro derivative is also emerging as a privileged heterocyclic scaf-
fold known for its biological and pharmaceutical potency[6,16] and is reported to exhibit
anti-cancer[17] and vasodilating activities.[18] The saturated carbon in the nuclear frame
of 4,7-dihydropyrazolo[3,4-b]pyridine derivative brings an additional non-linear dimen-
sional feature to the scaffold thus making it a better pharmacophore than its planar aro-
matic counterpart.
Although a variety of methods are used to prepare pyrazolo[3,4-b]pyridines[19–24], the
synthetic access to polysubstituted-polyfunctionalized derivatives remains a serious chal-
lenge. Among the reported methods, the reaction between 5-aminopyrazoles and bielec-
trophiles seems to be the most prevalent method.[25] Moreover, isolation of its dihydro
derivative, 4,7-dihydropyrazolo[3,4-b]pyridine is reported only in few cases.[26,27]
Kolosov et al.[28] utilized a two step synthetic procedure which involved the synthesis of
intermediate a-cyanochalcones and their subsequent condensation with phenylhydra-
zine. Recently, M. D. Hill[29] reported a three-component synthesis involving the reac-
tion of 5-aminopyrazoles, 3-oxopropanenitriles and aldehydes in DMF for 16 hours.
However, all these synthetic protocols employ lengthy procedures, harsh reaction condi-
tions, e.g. additives and catalysts moreover, setting up of polyfunctional groups on the
nucleus is particularly difficult.
Meanwhile, multi-component reactions are one such synthetic strategy which can be
employed for diversity-oriented target synthesis in fewer synthetic steps and short
reaction time.[30–32] Such reactions provide improved yields and structural diversity in
economical reaction conditions.[33] Multi-component reactions (MCRs) are becoming
more prevalent over conventional linear-type syntheses due to associated significant

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Scheme 1. Recently reported reaction of aryl/heteroarylhydrazines with 3-oxo-3-arylpropanenitriles.
advantages in organic and medicinal chemistry particularly for the generation of diverse
chemical libraries having drug-like features.[34,35] In recent years, we have developed
several fused pyrazole derivatives including pyrazolo[3,4-b]pyridines using MCRs.[36,37]
Recently, we have reported that the reaction of aryl/heteroaryl hydrazine (5) with
3-oxo-3-arylpropanenitrile (6) in the presence of conc. HNO3 which resulted in an
unexpected formation of 4,7-dihydropyrazolo[3,4-b]pyridine (7) (Scheme 1).[38] The
structure was confirmed by using several spectroscopic techniques like mass spectrom-
etry, IR, NMR (1H and 13C), HMBC and x-ray crystallographic studies. The mechanistic
study of the reaction revealed that there is in situ oxidation of ethanol to acetaldehyde
by conc. HNO3 which turns the reaction into a multi-component assembly where acet-
aldehyde serves as one of the reactants (Scheme 1). The fascinating results[38] of the
reaction inspired us to expand the scope of the reaction using different heteroaryl
hydrazine, two moles of same or one mole of each different b-ketonitriles with ali-
phatic/aromatic aldehydes (added externally) for the formation of densely substituted
novel 4,7-dihydropyrazolo[3,4-b]pyridines bearing heteroaryl, aryl, alkyl at 1,3,4 and 6
positions. Moreover, the nitrile groups at position-5 can be explored further for conver-
sion into amide, acid, carbonyl groups to generate more functionalized
dihydropyrazolopyridines.
Results and discussion
In our initial attempts, a reaction of (benzo[d]thiazol-2-yl)hydrazine (5a) with equimo-
lar amount of 3-oxo-3-(4-bromophenyl)propanenitrile (6a) and propionaldehyde (8a)
was carried out in ethanol in the presence of two drops of conc. HCl at reflux tempera-
ture (Scheme 2).
Regular monitoring of the reaction by TLC indicated the consumption of reactants
and development of a new spot. Completion of the reaction was observed in 45 minutes
with the separation of a solid product in the reaction mixture. Filtration of the solid
product from reaction mixture provided 7a in 43% yield. The solid product 7a, thus
1
obtained was characterized by IR, H, 13C and HMBC-HSQC spectroscopic data. The
IR spectrum of the compound 7a exhibited two characteristic absorption bands at 2208
and 3340 cmꢀ1 corresponding to –CN and –NH groups respectively. Formation of dihy-
dro derivative 7a was confirmed by the appearance of a distinct triplet at d 4.45 ppm
corresponding to 4-H and characteristic splitting pattern for ethyl group with signal of
CH3 protons appearing as triplet at d 0.88 ppm and CH2 protons as multiplet at d
1.80 ppm, along with the signals corresponding to benzothiazolyl group and two aryl

4
R. AGGARWAL ET AL.
Scheme 2. Synthesis of 1-(benzo[d]thiazol-2-yl)-3,6-bis(4-fluorophenyl)-4-methyl-4,7-dihydro-1H-pyra-
zolo[3,4-b]pyridine-5-carbonitrile 7a in ethanol by four component reaction.
substituents in aromatic region. A total of 21 signals appeared in 13C spectrum of a
solid product which included the signal for 1ꢁ carbon CH3 at dC 8.8 ppm, 2ꢁ carbon
CH2 at dC 28.2 ppm and 3ꢁ carbon 4-C at dC 36.6 ppm. The structure was further con-
firmed using HMBC NMR (2D) spectroscopy where the correlation between CH3 (dH
0.87–0.90 ppm) protons with 2ꢁ carbon CH2 (dC 28.2 ppm) and 3ꢁ carbon 4-C (dC
36.6 ppm) were established. Correlations of CH2 protons (dC 1.71-1.89 ppm) of ethyl
group with four carbon atoms with 1ꢁ methyl carbon (dC 8.8 ppm), one 3ꢁ carbon 4-C
(dC 36.6 ppm), two quaternary carbons 5-C (dC 84.6 ppm) and 9-C (dC 99.3 ppm) were
also observed. In addition, the correlation of 4-H (dC 4.44–4.46 ppm) with seven car-
bons viz. CH3, CH2, CN (dC 121.7 ppm), 5-C, 6-C (dC 132 ppm), 9-C and 8-C (dC
148 ppm) and correlations of 7-H (dC 9.1 ppm) with five carbon atoms viz. 5-C, 6-C, 8-
C, 9-C and 10-C (4-bromophenyl) (dC 121.9 ppm) were also seen in the spectrum. All
observed correlations established the structure of the solid product as 1-(benzo[d]thiazol-
2-yl)-3,6-di(4-bromophenyl)-4-ethyl-4,7-dihydro-1H-pyrazolo[3,4-b]pyridine-5-carbonitrile
(7a) (Figure 2).
To improve the low yield of the 4,7-dihydropyrazolo[3,4-b]pyridine 7a, we attempted
the reaction of two moles of 3-oxo-3-(4-bromophenyl)propanenitrile 6a with one mole
each of benzothiazolyl hydrazine 5a and propionaldehyde 8a, which resulted in consid-
erable increase in yield from 43 to 62%. On getting successful results, we next planned
to study the effect of solvent on the reaction yield in various polar and protic solvents.
The results of the solvent screening are summarized in Table 1. Though the reaction
has been reported in high boiling polar solvents e.g. DMSO,[39] DMF,[27] acetic acid[21]
etc. in some of the literature reports, but we avoided their use due to difficulty in their
vacuum elimination. From the Table 1, it may be concluded that ethanol is optimal
solvent for this four component condensation which afforded significant yields (62%) of
1-(benzo[d]thiazol-2-yl)-3,6-di(4-bromophenyl)-4-methyl-4,7-dihydro-1H-pyrazolo[3,4-
b]pyridine-5-carbonitrile 7a at reflux temperature in short time (Table 1, entry 2). It is
worth mentioning that reaction also worked well in other homologous alcohols like
methanol, propanol, and isopropanol with slightly lower yields (53, 48, and 44%,
respectively) (Table 1, entries 1,3,4). However, 5-aminopyrazole was the major product
when reactions were carried in polar aprotic solvents or under solvent-free conditions
(Table 1, entries 5–9).
To examine the efficiency of this new multi-component reaction to synthesize various
1-(hetroaryl)-4,7-dihydro-3,6-diaryl-4-aryl/alkyl-1H-pyrazolo[3,4-b]pyridine-5-nitriles, 7a–i,

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Figure 2. Significant correlations observed in HMBC data of compound 7a.
Table 1. Reaction profile of Solvent screening for synthesis of compound 7a.
Entry
Solvent
Temperature
Product
Time (min)
Isolated Yield (%)
1
2
3
4
5
6
7
8
9
Methanol
Ethanol
65 ꢁC
78 ꢁC
97 ꢁC
83 ꢁC
62 ꢁC
82 ꢁC
101 ꢁC
66 ꢁC
rt
4,7-dihydropyrazolo[3,4-b]pyridine
4,7-dihydropyrazolo[3,4-b]pyridine
4,7-dihydropyrazolo[3,4-b]pyridine
4,7-dihydropyrazolo[3,4-b]pyridine
5-aminopyrazole
5-aminopyrazole
5-aminopyrazole
45–50
45–50
60–65
60–65
180
180
180
53
62
48
44
35
65
45
52
82
Propanol
Isopropanol
Chloroform
Acetonitrile
Dioxane
THF
Solvent free
5-aminopyrazole
5-aminopyrazole
180
20
Scheme 3. General route for the synthesis of novel 4,7-dihydropyrazolo[3,4-b]pyridines 7a-i.
a series of different aldehydes were employed (Scheme 3). As seen in Table 2, this
protocol can be employed to aliphatic (CH3, CH3CH2) and aromatic aldehydes
bearing electron donating groups as well as electron withdrawing groups. Furthermore,
the substrate scope was explored by employing various heteroaryl hydrazine (5a–c) and
3-aryl-3-oxopropanenitriles (6a–d). Improved yield was obtained when 6-methylben-
zo[d]thiazolylhydrazine, 5 b, was used with 3-(4-tolyl)-3-oxopropanenitrile 8d, and pro-
pionaldehyde 8a, for the synthesis of 4,7-dihydro-1H-pyrazolo[3,4-b]pyridine, 7c, (74%
yield). The reaction of 4-chlorobenzaldehyde (8e) and 4-methylbenzaldehyde (8d) with
4,6-dimethylpyrimidin-2-ylhydrazine (5c) and 3-(4-chlorophenyl)-3-oxopropanenitrile
(6c) afforded corresponding 4,7-dihydropyrazalo[3,4-b]pyridines in 62% (7h) and 60%
(7i) yields, respectively.
Encouraged by the success of our protocol, the scope of the methodology was further
investigated in the reactions with heteroaryl hydrazine (5a–c), two different 3-oxopropa-
nenitriles (6a–e) and various aldehydes (8a–f) so as to achieve 4,7-dihydropyrazo-
lo[3,4-b]pyridines (7j–r) with non-identical aryl groups at 3 and 6 positions. The model

6
R. AGGARWAL ET AL.
Table 2. Scope of heteroarylhydrazines 5a-c, 3-aryl-3-oxopropanenitriles 6a-e, aldehyde 8a-g and
4,7-dihydropyrazolo[3,4-b]pyridine derivatives 7a-ia.
aIsolated yield.
reaction was carried out with sequential addition of reactants by refluxing the mixture
of benzo[d]thiazolylhydrazine (5a) and 3-phenyl-3-oxopropanenitrile (6e) for 20 minutes
(Scheme 4). On completion of the reaction, 3-(4-bromophenyl)-3-oxopropanenitrile
(6a) and acetaldehyde (8b) were added subsequently to the refluxing reaction mixture
and heated for another 20 minutes. 1-(Benzo[d]thiazol-2-yl)-6-(4-bromophenyl)-4-
methyl-3-phenyl-4,7-dihydropyrazolo[3,4-b]pyridine-5-carbonitrile (7j) was isolated in a

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Table 3. Substrate scope for the preparation of 4,7-dihydropyrazolo[3,4-b]pyridine derivativesa 7j-r.
aIsolated yield.
Scheme 4. Synthesis of unsymmetrically substituted 4,7-dihydropyrazolo[3,4-b]pyridines 7j-r.
modest 54% yield. Further, the same reaction was extended to incorporate ethyl group
on 4,7-dihydropyrazolo[3,4-b]pyridine nucleus by replacing the acetaldehyde with pro-
pionaldehyde 8a. The reaction substrate scope was further extended to various aromatic
aldehydes (8c–f), 3-oxopropanenitriles (6a–e) and heteroaryl hydrazines (5a–c) as
shown in Table 3. The reaction yields depend on the substrate diversity but still, it can
be generalized that in all the cases yields in sequential addition reaction were slightly
lower (45–50%) than the former multi-component reactions (60–70%).
1
The structural characterization of products was carried out by IR, H & 13C NMR
spectroscopy and mass spectrometry.

8
R. AGGARWAL ET AL.
Scheme 5. Plausible mechanism for the formation of 4,7-dihydropyrazolo[3,4-b]pyridine-6-nitriles 7.
The plausible mechanism depicted in Scheme 5 may involve the following tandem
reaction steps:
i. Formation of 5-aminopyrazole 10, by reaction between heteroaryl hydrazine 5
and one mole of 3-oxo-3-arylpropanenitrile 6.
ii. Knoevenagel condensation between aldehyde 8 and another mole of 3-oxo-3-
arylpropanenitrile 6 afford a-cyanochalcone 11.
iii. In situ Michael addition of 5-aminopyrazole 10 and a-cyanochalcone 11 fol-
lowed by cyclization and dehydration to give 4,7-dihydropyrazolo[3,4-b]pyridine
7 (Scheme 5).
Conclusions
In conclusion, one step multi-component reaction of structurally diverse aldehydes,
hydrazines, and 3-oxopropanenitriles resulted in the formation of polyfunctionalized
4,7-dihydropyrazolo[3,4-b]pyridines. The protocol has the merits of being environmen-
tally friendly, economical, simple in operation having the easy work-up procedure, with
good to moderate yields. To the best of our knowledge, this is the first report on
the synthesis of 4,7-dihydropyrazolo[3,4-b]pyridines in one step by the four-component
reaction. The dehydrogenative oxidation of corresponding 4,7-dihydropyrazolo
[3,4-b]pyridine derivatives to corresponding pyrazolo[3,4-b]pyridines will be presented
in due course.

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9
Experimental section
General
Commercial solvents and other reagents were used as purchased without any purifica-
tion. Melting points were determined in open capillaries on digital Melting Point
Apparatus (MEPA), Lab India and were uncorrected. IR spectra were recorded on Buck
1
Scientific IR M-500 spectrophotometer using KBr pellets (ꢀmax in cmꢀ1), H and 13C
NMR spectra on a Bruker instrument at 400 and 100 MHz, respectively, using deuterio-
chloroform as a solvent. (1H-13C) gs-HMQC, (1H-13C) and gs-HMBC, of compound 7a,
1
were acquired on a Bruker DRX 400 (9.4 Tesla, 400 MHz for H and 100 MHz for 13C)
spectrometer with a 5 mm inverse-detection H-X probe equipped with a z-gradient coil,
at 300 K and processed using standard Bruker NMR software and in non-phase-sensitive
mode. Gradient selection was achieved through a 5% sine truncated shaped pulse gradi-
ent of 1 ms. Elemental analyses were performed at Sophisticated Analytical Instrument
Facility, Panjab University, Chandigarh. All the compounds gave C, H, and N analysis
within 0.5 of the theoretical values.
Synthesis
Heteroarylhydrazines 5 and 3-aryl-3-oxopropanenitriles 6 were prepared according to
literature procedures.[40–43]
Synthesis of 1-(Benzo[d]thiazol-2-yl)-4,7-dihydro-4-ethyl-3,6-di(4-bromophenyl)-
1H-pyrazolo[3,4-b]pyridine-5-nitrile (7a). To a solution of 0.45 g of 3-(4-bromo-
phenyl)-3-oxopropanenitrile (6a, 2.0 mmol) in 25 mL of ethanol, 0.165 g of
benzothiazolylhydrazine (5a, 1.0 mmol) and 0.058 g of propionaldehyde (8a, 1.0 mmol)
were added along with 2 drops of conc. HCl. The reaction mixture was heated to reflux
for 45 minutes until the formation of a solid product in the reaction mixture. The hot
reaction mixture was filtered at the vacuum pump and washed with hot ethanol to
afford the pure compound 7a.
All other compounds (7b–i) were synthesized according to the procedure mentioned
for 7a using heteroarylhydrazines (5a–c), different 3-aryl-3-oxopropanenitriles (6a–d)
and aldehydes (8a–d).
1-(Benzo[d]thiazol-2-yl)-4,7-dihydro-4-ethyl-3,6-di(4-bromophenyl)-1H-pyra-
zolo[3,4-b]pyridine-5-nitrile (7a). Yield 62%; M.p. 240–245 ꢁC; IR (KBr, cmꢀ1): 2208
1
(CꢂN), 3340 (N–H); H NMR (400 MHz, CDCl3): d 0.87–0.90 (t, 3 H, CH3, J 6.8 Hz),
1.71–1.89 (m, 2 H, CH2), 4.44–4.46 (t, 1 H, 4-H, J 4 Hz), 7.38–7.42 (m, 1 H, 6’-H),
7.48–7.51 (m, 1 H, 50-H), 7.62–7.69 (m, 6 H, Ph-H), 7.72–7.74 (m, 2 H, 2’’-H), 7.78–7.80
(d, 1 H, 70-H, J 8.0 Hz), 7.86–7.88 (d, 1 H, 40-H, J 8.0 Hz), 9.1 (s, 1 H, exchangeable with
D2O, 7-H); 13C NMR (75 MHz, CDCl3): d 8.8, 28.2, 36.6, 84.7, 99.5, 121.7, 121.9, 123.4,
125.1, 125.4, 126.8, 128.7, 129.3, 130.9, 131.5, 132.0, 132.6, 139.9, 148.4, 150.3, 160.7;
MS: m/z 615.97 [M þ 1]þ, 617.97 [M þ 1 þ 2]þ, 619.97 [M þ 1 þ 4]þ, (1:2:1); Elemental
analysis: Calcd. for C28H19Br2N5S: C, 54.47; H, 3.10; N, 11.34; Found: C, 53.35; H, 2.63;
N, 11.12.
Synthesis of 1-(benzo[d]thiazol-2-yl)-6-(4-bromophenyl)-4-methyl-3-phenyl-4,7-
dihydro-1H-pyrazolo[3,4-b]pyridine-5-carbonitrile (7j). The solution of 0.145 g 3-

10
R. AGGARWAL ET AL.
phenyl-3-oxopropanenitrile (6e 1.0 mmol) in 25 mL of ethanol and 0.165 g benzothiazo-
lylhydrazine (5a, 1 mmol) was refluxed for 20 minutes in the presence of conc. HCl.
The progress of the reaction was monitored by TLC (ethyl acetate/n-hexane: 1/4). After
complete consumption of reactants, the reaction mixture was added with 0.225 g 3-(4-
bromophenyl)-3-oxopropanenitrile (6a, 1 mmol) and 0.044 g acetaldehyde (8 b, 1 mmol).
The reaction mixture was heated again to reflux for another 20 minutes till solid prod-
uct separates out in the reaction mixture. The reaction mixture was filtered at the vac-
uum pump and washed well with hot ethanol to afford the pure 7j.
Compounds (7k–r) were synthesized using the same procedure with sequential add-
ition of appropriate reactants.
1-(benzo[d]thiazol-2-yl)-6-(4-bromophenyl)-4-methyl-3-phenyl-4,7-dihydro-1H-pyr-
azolo[3,4-b]pyridine-5-carbonitrile (7j). Yield 54%; M.p. 250–255 ꢁC; IR (KBr, cmꢀ1):
1
3321 (N–H), 2212 (–CꢂN); H-NMR (300 MHz, CDCl3): d 1.43–1.45 (d, 3 H, CH3, J
6.8 Hz), 4.30–4.39 (q, 1 H, J 6.0 Hz), 7.21 (m, 1 H, 60-H), 7.29–7.33 (m, 1 H, 5’-H),
7.35–7.38 (t, 1 H, 7’-H, J 6.6 Hz), 7.42–7.50 (m, 3 H, 2000-H, 40-H), 7.61–7.63 (d, 2 H, 3000-
H, J 8.4 Hz), 7.68–7.72 (m, 2 H, 3’’-H), 7.74–7.79 (m, 2 H, 2’’-H), 7.82-7.85 (m, 1 H, 4’-
H), 9.04 (s, 1 H, –7-NH); 13C NMR (CDCl3, 100 MHz): d 23.7, 31.2, 87.1, 102.0, 121.7,
121.9, 124.9, 126.7, 127.1, 128.4, 128.8, 129.1, 129.3, 132.5, 150.4. MS: m/z 538.12
[M þ 1]þ, 540.18 [M þ 1 þ 2]þ, (1:1); Elemental analysis: Calcd. for C28H20BrN5S: C,
62.46; H, 3.74; N, 13.01; Found: C, 62.19; H, 3.53; N, 12.87.
1
Full experimental details, H and 13C NMR spectra can be found in supplementary
content section of this article’s webpage.
Acknowledgments
Thanks are also due to Central Instrumentation Laboratory, Guru Jambheshwar University of
Science and Technology, Hisar, for spectral studies.
Funding
We are thankful to University Grant Commission, New Delhi for providing financial assistance
in the form of Rajiv Gandhi National, Senior Research Fellowship to Suresh Kumar. We are also
thankful to Council of Scientific and Industrial Research, New Delhi for providing financial sup-
port in the form of Senior Research Fellowship to Gulshan Singh.
ORCID
Suresh Kumar
http://orcid.org/0000-0002-5569-5001
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