Preparation and Biological Activities of Novel Cuminaldehyde Derivatives

Full text of DOI:10.1080/00304948.2020.1871574

Organic Preparations and Procedures International
The New Journal for Organic Synthesis
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Preparation and Biological Activities of Novel
Cuminaldehyde Derivatives
Pardeep Kaur, Sunita Sharma & Jyoti Gaba
To cite this article: Pardeep Kaur, Sunita Sharma & Jyoti Gaba (2021): Preparation and Biological
Activities of Novel Cuminaldehyde Derivatives, Organic Preparations and Procedures International,
DOI: 10.1080/00304948.2020.1871574
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ORGANIC PREPARATIONS AND PROCEDURES INTERNATIONAL
https://doi.org/10.1080/00304948.2020.1871574
EXPERIMENTAL PAPER
Preparation and Biological Activities of Novel
Cuminaldehyde Derivatives
Pardeep Kaura, Sunita Sharmab, and Jyoti Gabaa
b
aDepartment of Chemistry, Punjab Agricultural University, Ludhiana, India; Department of Plant
Breeding and Genetics, Punjab Agricultural University, Ludhiana, India
ARTICLE HISTORY Received 30 May 2020; Accepted 3 September 2020
Currently the development of non-hazardous high-value chemicals from natural resour-
ces is one of the biggest challenges for organic chemists.1 In this connection, derivatiza-
tion of bioactive compounds isolated from natural resources such as spices has become
a field of great interest.2 Plants of the Apiaceae family possess a wide range of com-
pounds with numerous biological activities.3–17 Cumin (Cuminum cyminum) is an
annual herbaceous plant belonging to this family.18 Cuminaldehyde is derived from the
essential oil of the plant’s seeds, and the aldehyde is known for its biological activ-
ities,19–31 but only somewhat limited work has been done on its carbonyl deriva-
tives.32–36 We now report on the preparation of novel cuminaldehyde Schiff bases,
thiosemicarbazones and hydrazones. We provide information on the biological activities
which we observed.
The synthetic routes to prepare the compounds are outlined in Scheme 1.
Condensation reactions of cuminaldehyde with different primary amines, thiosemicarba-
zides and hydrazines in the presence of catalytic amounts of glacial acetic acid yielded
the respective Schiff bases, thiosemicarbazones and hydrazones, respectively (see
Experimental section).
The new compounds were fully characterized and were screened for their antioxidant
potential via the 2,2-diphenyl-1-picryl-hydrazyl-hydrate (DPPH) assay (Table 1,
Figure 1) and for their antimicrobial activity (Table 2, Figure 2) against three gram-
negative bacteria (Pseudomonas sp., Klebsiella sp. and Enterobacter sp.).
The new Schiff bases demonstrated higher antioxidant potentials as compared to their
thiosemicarbazone and hydrazone counterparts. Out of all Schiff bases, compounds 2b
and 2g exhibited the highest antioxidant potentials. Azomethine groups increase the anti-
oxidant potential of the synthesized products. The effectiveness of compound 2b may be
due to the presence of the phenolic OH group. Gaikwad and his workers reported a simi-
lar result.37 This is consistent with the bonding characteristics needed for an efficient anti-
oxidant38,39 and with the ability of phenols to act as free radical terminators.40
Antimicrobial results include values of zones of inhibition (disc diffusion assays) and
minimum inhibitory concentrations (MICs). All the cuminaldehyde derivatives that we
CONTACT Sunita Sharma
sunita_sharma@pau.edu
Department of Chemistry, Punjab Agricultural University,
Ludhiana-141004, India
Supplemental data for this article can be accessed here.
ß 2021 Taylor & Francis Group, LLC

2
P. KAUR ET AL.
CHO
S
NH2
NH2
H
N
R'
H2N
H2N
R''
CH3COOH
H
CH3COOH
CH3COOH
R
NH2
CH3COOH
H
N
H
N
H
S
H
C
N
N
R''
H
C
H
H
C
N
R
N
N
C
N R'
N
N
(4a-4c)
(2a-2j)
(3a-3b)
(2k)
2a
2b
2c
OCH3
2d
H2
2e
N
R
OH
C
2f
2g
2h
2i
CH3
2j
N
N
R
N
N
N
N
CH3
N
N
N
H3C
O
4a
4b
4c
3a
3b
R'
H
R''
NO2
NO2
O2N
Scheme 1. Synthetic route for synthesis of novel derivatives of cuminaldehyde.
prepared exhibited moderate to good antimicrobial potential. Inhibition zone data were
analyzed statistically by single factor analysis of variance to determine the significant
differences among the activities of the new compounds against the three microbes
studied. The data in Table 3 suggest that the bioactivity of the cuminaldehyde deriva-
tives varied significantly at the 1% and 5% levels.
In conclusion, we prepared novel cuminaldehyde Schiff bases, thiosemicarbazones
and hydrazones and fully characterized them. We determined antioxidant and anti-
microbial activities. Compounds 2b and 2g showed promising antioxidant activities at
higher concentrations. Compounds 2h, 3b, and 4c showed significant activities against
Pseudomonas sp., Klebsiella sp., and Enterobacter sp., respectively. It is our hope that
our synthetic procedures and demonstration of desirable biological activities will spur
further investigation into these useful derivatives of the natural product cuminaldehyde.
Experimental section
Cuminaldehyde was purchased from Hi-media Laboratories Private Limited (Mumbai,
India) and used without further purification. All other chemicals and solvents were

ORGANIC PREPARATIONS AND PROCEDURES INTERNATIONAL
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4
P. KAUR ET AL.
2989
3000
2500
2000
1500
1000
500
2676
2185
2137
1826
1583
1271
1109
4b
1049
2j
839
2k
703
4a
59
2b
61
2g
0
2c
2d
2e
2f
2h
2i
4c
Compounds
Figure 1. IC50 of different substituted Schiff bases (2b-2k) and hydrazones (4a-4c).
purchased from Loba Chemie Private Limited (Mumbai, India), S.D. Fine Chemicals
Limited (Mumbai, India) and Sisco Research Laboratories Private Limited (Mumbai,
India). Nutrient broth and agar agar used for evaluating the antimicrobial potential was
also purchased from Hi-media Laboratories Private Limited (Mumbai, India). Melting
points of the solid samples were determined in open capillaries using melting point
apparatus (Relitech, Haryana, India) and were uncorrected. The purity of compounds
was checked by thin layer chromatography (TLC), and the visualization was done in an
iodine chamber. Electronic spectra (kmax in nm) were recorded on a Techcomp UV
1
2600 spectrophotometer. Fourier transform infrared (FT-IR), H and 13C NMR spectra
were scanned courtesy of the Central Instrument Laboratory, Sophisticated Analytical
Instrumentation Facility, Punjab University, Chandigarh, India. FT-IR spectra were
recorded on a Perkin-Elmer FT-IR Spectrum 400 spectrophotometer in the range of
1
4000-400 cmꢀ1. The H and 13C NMR spectra were recorded on a Bruker Avance II
400 MHz spectrophotometer and a Bruker Avance Neo 500 MHz spectrophotometer
using tetramethylsilane as internal standard. The chemical shifts were expressed in d
1
(ppm) values. Common aliphatic and aromatic H coupling constants were in the range
of 4-8 Hz and were not specifically enumerated. CHN analysis was performed on a
Vario El III Elementor analyzer.
N-(4-Isopropylbenzylidene)benzenamine (2a)
Equimolar amounts of cuminaldehyde (0.0100 mole, 1.51 mL) and aniline (0.0100 mole,
0.91 mL) were mixed in a 250 mL round bottom flask with ethanol (15 mL) as a solvent.
A catalytic amount of glacial acetic acid (5 drops) was added to the reaction mixture.
The reaction mixture was refluxed for 4 hours. Progress of the reaction was monitored
by thin layer chromatography (silica gel, ethanol). The product appeared as a solid. The
product was filtered off to give 2a, 1.70 g, 70%, brown powder, mp 133-135 ꢁC, Rf 0.60
1
(silica gel, ethanol). UV-vis (kmax): 302 nm. IR: (cmꢀ1) 1622 (C ¼ N). H NMR (CDCl3):
d 8.39 (s, 1H), 7.77-7.83 (m, 2H), 7.13-7.38 (m, 7H), 2.90-2.97 (m, 1H), 1.25-1.26 (d,
6H). 13C NMR (CDCl3) ppm: d 166.64, 149.99, 147.63, 134.33, 131.31, 128.60, 127.70,
126.73, 123.34, 39.09, 28.90.

ORGANIC PREPARATIONS AND PROCEDURES INTERNATIONAL
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6
P. KAUR ET AL.
500
450
400
Pseudomonas sp.
Klebsiella sp.
Enterobacter sp.
430
425
410
410
400
390
310
350
350
350
310
300
325
320
315
315
300
270
295
290
280
250
220
195
175
145
210
210
200
170
195
165
190
155
200 180
180
170
160
120
125
155
140
85
150
100
50
130
90
95
95
40
90
80
75
12
6
5
0
Compounds
Figure 2. MIC values of synthesized compounds against different bacteria.
Anal. Calcd for C16H17N: C, 86.05; H, 7.67; N, 6.27. Found: C, 86.09; H, 7.69;
N, 6.22.
4-(4-Isopropylbenzylideneamino)phenol (2b)
The Schiff base was prepared by condensation of cuminaldehyde (0.0100 mole, 1.51 mL)
with p-aminophenol (0.0100 mole, 1.09 g) in the presence of a catalytic amount of glacial
acetic acid (5 drops) using ethanol (15 mL) as a solvent and the mixture was refluxed
for 4 hours. The progress of reaction was monitored by TLC (silica gel, ethanol). On
completion of the reaction, the mixture was filtered, dried, and recrystallized from
chloroform to give solid compound 2b, 2.81g, 84%, light brown powder, mp 93-95 ꢁC,
1
Rf 0.71 (silica gel, ethanol). UV-vis (kmax): 310 nm. IR: (cmꢀ1) 1609 (C ¼ N). H NMR
(CDCl3): d 9.32 (s, 1H), 8.50 (s, 1H), 6.78-8.18 (m, 8H), 2.52-2.53 (m, 1H), 1.25-1.26 (d,
6H). 13C NMR (CDCl3): d 160.16, 157.11, 153.24, 145.11, 130.05, 128.77, 127.17, 122.33,
116.13, 34.22, 23.80.
Anal. Calcd for C16H17NO: C, 80.30; H, 7.16; N, 5.85. Found: C, 80.27; H, 7.19;
N, 5.90.
N-(4-Isopropylbenzylidene)-3-methoxybenzenamine (2c)
A mixture of cuminaldehyde (0.0100 mole, 1.51 mL) and m-anisidine (0.0100 mole,
1.12 mL) was dissolved in ethanol (15 mL). The contents were subjected to refluxing for
4 hours after adding a catalytic amount of glacial acetic acid (5 drops). Thin layer chro-
matography was used to check the progress of reaction (silica gel, ethanol). After the
completion of the reaction, the light brown solid product was obtained after pouring
the hot reaction mixture into ice cold water. The solid product was then filtered and
recrystallized from chloroform to give compound 2c, 2.02 g, 77%, light brown powder,
mp 207-209 ꢁC, Rf 0.65 (silica gel, ethanol). UV-vis (kmax): 312 nm. IR: (cmꢀ1) 1614
1
(C ¼ N). H NMR (CDCl3) ppm: d 9.31 (s, 1H), 6.95-7.47 (m, 8H), 3.68 (s, 3H), 2.81-

ORGANIC PREPARATIONS AND PROCEDURES INTERNATIONAL
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Table 3. Statistical analysis of synthesized products against three gram negative bacteria.
Pseudomonas sp.
Tabulated F
5% 1%
1.28
Source of variation
Degree of Freedom
Sum of Squares
Mean Square
Computed Fb
ꢂꢂ
Treatment
Experimental error
Total
127
255
382
1565.86
62.00
1627.86
12.33
0.24
50.71
1.42
acv ¼ 6.44
b
ꢂꢂ
¼ significant at 1% level
Klebsiella sp.
Tabulated F
Source of variation
Degree of Freedom
Sum of Squares
Mean Square
Computed Fb
5%
1%
ꢂꢂ
Treatment
Experimental error
Total
127
255
382
4112.69
58.75
4171.44
32.38
0.23
140.57
1.28
1.42
acv ¼ 5.62
b
ꢂꢂ
¼ significant at 1% level
Enterobacter sp.
Tabulated F
Source of variation
Degree of Freedom
Sum of Squares
Mean Square
Computed Fb
5%
1%
ꢂꢂ
Treatment
Experimental error
Total
127
255
382
1524.57
43.43
1568.00
12.00
0.17
70.76
1.28
1.42
acv ¼ 5.50
b
ꢂꢂ
¼ significant at 1% level.
2.90 (m, 1H), 1.32-1.33 (d, 6H). 13C NMR (CDCl3): d 165.92, 161.51, 149.64, 147.85,
135.74, 133.65, 127.25, 125.57, 121.27, 112.20, 105.79, 49.17, 39.55, 22.65.
Anal. Calcd for C17H19NO: C, 80.60; H, 7.56; N, 5.53. Found: C, 80.65; H, 7.60;
N, 5.48.
N-(4-Isopropylbenzylidene)(phenyl)methanamine (2d)
Equimolar amounts of cuminaldehyde (0.0100 mole, 1.51 mL) and benzylamine
(0.0100 mole, 1.09 mL) were dissolved in ethanol (15 mL). Then were added 5 drops of
glacial acetic acid to the reaction mixture and it was refluxed for 8 hours. Thin layer
chromatography (silica gel, ethanol) was used to check the reaction progress of solid
compound 2d, 1.84 g, 71%, brown powder, mp 121-123 ꢁC, Rf 0.52 (silica gel, ethanol).
1
UV-vis (kmax): 306 nm. IR: (cmꢀ1) 1607 (C ¼ N). H NMR (CDCl3): d 8.38 (s, 1H),
7.16-7.65 (m, 9H), 4.47 (s, 2H), 2.80-2.86 (m, 1H), 1.34-1.36 (d, 6H). 13C NMR
(CDCl3): d 166.16, 151.11, 149.14, 145.81, 138.30, 136.66, 131.28, 123.65, 122.61, 58.96,
36.17, 23.49.
Anal. Calcd for C17H19N: C, 86.03; H, 8.07; N, 5.90. Found: C, 86.07; H, 8.13;
N, 5.80.
N-(4-Isopropylbenzylidene)pyridin-2-amine (2e)
2-Aminopyridine (0.0100 mole, 0.94 g) was dissolved in ethanol (15 mL) in the presence
of glacial acetic acid (5 drops). A solution of cuminaldehyde (0.0100 mole, 1.51 mL) was

8
P. KAUR ET AL.
added dropwise and refluxed for 4 hours. Monitoring of reaction progress was done by
TLC (silica gel, ethanol). The white solid was isolated, then recrystallized from chloro-
form to give compound 2e, 1.76 g, 72%, white crystals, mp 110-112 ꢁC, Rf 0.66 (silica
1
gel, ethanol). UV-vis (kmax): 315 nm. IR (cmꢀ1) 1592 (C ¼ N). H NMR (CDCl3): d 8.31
(s, 1H), 7.27-7.47 (m, 5H), 6.95-7.02 (m, 3H), 2.78-2.86 (m, 1H), 1.30-1.31 (d, 6H). 13C
NMR (CDCl3): d 193.40, 163.83, 162.22, 158.88, 156.55, 137.24, 129.67, 127.00, 125.54,
120.00, 35.92, 23.32.
Anal. Calcd for C15H16N2: C, 80.32; H, 7.19; N, 12.49. Found: C, 80.40; H, 7.17;
N, 12.43.
N-(4-Isopropylbenzylidene)pyridin-4-amine (2f)
An equimolar ethanolic solution (15 mL) of 4-aminopyridine (0.0100 mole, 0.94 g) and
cuminaldehyde (0.0100 mole, 1.51 mL) was mixed completely in the presence of a cata-
lytic amount of glacial acetic acid (5 drops) and refluxed for 4 hours. The white crystal-
line product was filtered and recrystallized from chloroform. A single spot on a
chromatographic plate (silica gel, ethanol) confirmed the purity of compound 2f, 1.84 g,
75%, white crystals, mp 105-107 ꢁC, Rf 0.69 (silica gel, ethanol). UV-vis (kmax): 308 nm.
1
IR (cmꢀ1) 1596 (C ¼ N). H NMR (CDCl3) ppm: d 8.38 (s, 1H), 7.20-7.45 (m, 8H),
2.71-2.74 (m, 1H), 1.54-1.56 (d, 6H). 13C NMR (CDCl3): d 161.06, 157.00, 152.79,
148.87, 144.02, 136.64, 129.16, 123.34, 38.72, 28.74.
Anal. Calcd for C15H16N2: C, 80.32; H, 7.19; N, 12.49. Found: C, 80.38; H, 7.23;
N, 12.39.
N-(4-Isopropylbenzylidene)-3-methylpyridin-2-amine (2g)
N-(4-Isopropylbenzylidene)-3-methylpyridin-2-amine was synthesized by refluxing for
4 hours an equimolar amount of cuminaldehyde (0.0100 mole, 1.51 mL) and 2-amino-3-
methylpyridine (0.0100 mole, 1.08 g) in the presence of glacial acetic acid (5 drops)
using ethanol (15 mL) as a solvent. TLC (silica gel, ethanol) was used to check the pur-
ity of compound 2g, 2.12 g, 82%, white crystals, mp 97-99 ꢁC, Rf 0.58 (silica gel, etha-
1
nol). UV-vis (kmax): 314 nm. IR: (cmꢀ1) 1590 (C ¼ N). H NMR (CDCl3) ppm: d 9.02
(s, 1H), 7.09-7.35 (m, 7H), 2.31 (s, 3H), 2.12-2.13 (m, 1H), 1.35-1.36 (d, 6H). 13C NMR
(CDCl3): d 192.28, 163.47, 161.10, 157.83, 155.57, 134.30, 129.65, 127.00, 126.24, 110.94,
33.71, 22.82, 15.93.
Anal. Calcd for C16H18N2: C, 80.63; H, 7.61; N, 11.75. Found: C, 80.60; H, 7.67;
N, 11.73.
N-(4-Isopropylbenzylidene)pyrimidin-2-amine (2h)
A
mixture of cuminaldehyde (0.0100 mole, 1.51 mL) and 2-aminopyrimidine
(0.0100 mole, 0.95 g) and a catalytic amount of glacial acetic acid (5 drops) in ethanol
(15 mL) was refluxed for 4 hours with continuous monitoring by TLC (silica gel, etha-
nol). Then the reaction mixture was filtered to get solid compound 2h, 1.96 g, 80%,
white crystals, mp 144-146 ꢁC, Rf 0.61 (silica gel, ethanol). UV-vis (kmax): 324 nm. IR:

ORGANIC PREPARATIONS AND PROCEDURES INTERNATIONAL
9
1
(cmꢀ1) 1587 (C ¼ N). H NMR (CDCl3) ppm: d 1.29-1.28 (d, 6H), 2.88-2.99 (m, 1H),
6.99-7.48 (m, 7H), 9.22 (s, 1H). 13C NMR (CDCl3) ppm: d 177.72, 156.40, 139.56,
137.46, 129.70, 126.09, 118.99, 112.70, 34.11, 23.78.
Anal. Calcd for C14H15N3: C, 74.64; H, 6.71; N, 18.65. Found: C, 74.58; H, 6.75;
N, 18.67.
4-(4-Isopropylbenzylideneamino)-2,3-dimethyl-1-phenyl-1,2-dihydropyrazol-5-one (2i)34
Condensation of cuminaldehyde (0.0100 mole, 1.51 mL) with 4-aminophenazone
(0.0100 mole, 2.03 g) in refluxing ethanol (15 mL) occurred in the presence of glacial
acetic acid (5 drops) over 4 hours. Thin layer chromatography was used to confirm the
reaction completion (silica gel, ethanol) and purity of compound 2i, 3.04 g, 86%, pale-
yellow powder, mp 138-140 ꢁC, Rf 0.73 (silica gel, ethanol). UV-vis (kmax): 316 nm. IR:
1
(cmꢀ1) 1567 (C ¼ N), lit IR: (cmꢀ1) 1605 (C ¼ N)34. H NMR (CDCl3): d 9.72 (s, 1H),
7.77-7.80 (m, 2H), 7.28-7.50 (m, 7H), 3.14 (s, 3H, N-CH3), 2.85-2.94 (m, 1H), 2.48 (s,
1
3H), 1.26-1.29 (m, 6H), lit H NMR (CDCl3): d 9.56 (s, 1H), 7.31-7.88 (m, 9H), 3.34 (s,
3H), 2.88-2.97 (m, 1H), 2.50 (s, 3H), 1.21-1.23 (m, 6H).34 13C NMR (CDCl3) ppm: d
160.96, 157.41, 151.88, 151.37, 129.16, 127.87, 126.83, 126.64, 126.50, 124.34, 118.90,
35.92, 34.16, 23.71, 10.13.
Anal. Calcd for C21H23N3O: C, 75.65; H, 6.95; N, 12.60. Found: C, 75.62; H, 6.93;
N, 12.63.
N-(4-Isopropylbenzylidene)-4H-1,2,4-triazol-4-amine (2j)
Cuminaldehyde (0.0100 mole, 1.51 mL) and 4-amino-1,2,4-triazole (0.0100 mole, 0.84)
were dissolved in ethanol (15 ml), to which was added 5 drops of glacial acetic acid.
The mixture was refluxed for 4 hours, cooled and poured into crushed ice. The precipi-
tate obtained was recrystallized using ethanol to obtain compound 2j, 1.93 g, 82%, off-
white crystals, mp 154-156 ꢁC, Rf 0.63 (silica gel, ethanol). UV-vis (kmax): 292 nm. IR:
1
(cmꢀ1) 1608 (C ¼ N). H NMR (CDCl3): d 1.23-1.25 (m, 6H), 2.89-2.94 (m, 1H), 7.32-
7.34 (d, 2H), 7.67-7.69 (m, 2H), 8.37-8.39 (d, 2H), 11.95 (s, 1H). 13C NMR (CDCl3): d
157.67, 154.28, 138.69, 129.33, 128.27, 127.16, 34.27, 23.67.
Anal. Calcd for C12H14N4: C, 67.27; H, 6.59; N, 26.15. Found: C, 67.24; H, 6.63;
N, 26.13.
(N1E,N2E)-N1,N2-bis(4-Isopropylbenzylidene)benzene-1,2-diamine (2k)
Cuminaldehyde (0.0200 mole (3.02 mL)) was mixed with o-phenylenediamine
(0.0100 mole, 1.08 g) in ethanol (15 mL) in the presence of a catalytic amount of glacial
acetic acid (5 drops). The mixture was refluxed for four hours to obtain solid
compound 2k, 3.56 g, 87%, brown crystals, mp 192-194 ꢁC, Rf 0.68 (silica gel, ethanol).
1
UV-vis (kmax): 375 nm. IR: (cmꢀ1) 1586 (C ¼ N). H NMR (CDCl3): d 12.71 (s, 2H),
8.10-8.15 (m, 2H), 7.14-7.72 (m, 10H), 2.53-2.99 (m, 2H), 1.17-1.29 (m, 12H). 13C NMR
(CDCl3) ppm: d 167.61, 159.27, 134.33, 131.83, 127.97, 124.25, 114.49, 110.22,
38.52, 23.27.

10
P. KAUR ET AL.
Anal. Calcd for C26H28N2: C, 84.74; H, 7.66; N, 7.60. Found: C, 84.70; H, 7.64;
N, 7.66.
1-(4-Isopropylbenzylidene)thiosemicarbazide (3a)32
Cuminaldehyde (0.0100 mole, 1.51 mL) and thiosemicarbazide (0.0100 mole, 0.75 g) were
taken in a round bottom flask with ethanol (15 mL) as a solvent. Then were added 5
drops of glacial acetic acid and the mixture was refluxed for 3 hours. On cooling, a
white product was obtained which was filtered and dried. TLC (silica gel, ethanol) was
used to confirm the formation of compound 3a, 2.01 g, 89%, white crystals, mp 146-
148 ꢁC, lit mp 144-147 ꢁC32, Rf 0.65 (silica gel, ethanol). UV-vis (kmax): 305 nm. IR:
(cmꢀ1) 1590 (C ¼ N), lit IR: (cmꢀ1) 1590.32 1H NMR (CDCl3): d 9.57 (s, 1H), 7.84 (s,
1H), 7.56-7.59 (m, 2H), 7.23-7.28 (m, 2H), 6.38 (bs, 2H), 2.90-2.95 (m, 1H), 1.25-1.27
(d, 6H). 13C NMR (CDCl3): d 178.21, 152.19, 144.29, 130.59, 127.63, 127.02,
34.16, 23.75.
Anal. Calcd for C11H15N3S: C, 59.69; H, 6.83; N, 18.99; S, 14.49. Found: C, 59.65; H,
6.80; N, 19.05; S, 14.50. lit Anal. Calcd for C11H15N3S: C, 59.5; H, 6.2; N, 18.9; S, 14.4.
Found: C, 59.7; H, 6.8; N, 18.9; S, 14.5.32
1-(4-Isopropylbenzylidene)-4-phenylthiosemicarbazone (3b)32
1-(4-Isopropylbenzylidene)-4-phenylthiosemicarbazide was synthesized by reacting phe-
nylthiosemicarbazide with cuminaldehyde. Phenylthiosemicarbazide was synthesized by
reacting equimolar amounts of phenylisothiocyanate (0.0100 mole, 1.20 mL) and hydra-
zine hydrate (0.0100 mole, 0.48 mL). The reaction was completed in 5 minutes and a
white solid product was obtained. The product was washed with water in order to
remove excess hydrazine hydrate. The product was filtered and dried and used directly
for the synthesis of thiosemicarbazone.
In a 250 mL round bottomed flask, an equimolar amount of cuminaldehyde
(0.0100 mole, 1.51 mL) and phenylthiosemicarbazide (0.0100 mole, 1.67 g) was mixed
with ethanol (15 mL) and 5 drops of glacial acetic acid. The mixture was refluxed for
3 hours. TLC (silica gel, ethanol) was used to monitor the formation of compound 3b,
2.86 g, 90%, white crystals, mp 140-142 ꢁC, lit mp 140-142 ꢁC32, Rf 0.67 (silica gel, etha-
1
nol). UV-vis (kmax): 323 nm. IR: (cmꢀ1) 1591 (C ¼ N), lit IR: (cmꢀ1) 1596 (C ¼ N). H
NMR (CDCl3): d, 9.88 (s, 1H), 9.21 (s, 1H), 7.60-7.90 (m, 5H), 7.40-7.44 (m, 2H), 7.25-
7.29 (m, 2H), 2.92-2.97 (m, 1H), 1.26-1.28 (d, 6H). 13C NMR (CDCl3): d 176.63, 164.53,
152.82, 139.49, 135.08, 130.82, 123.88, 118.99, 116.33, 113.69, 39.17, 23.88.
Anal. Calcd for C17H19N3S: C, 68.65; H, 6.44; N, 14.13; S, 10.78. Found: C, 68.68; H,
6.46; N, 14.17; S, 10.69. lit Anal. Calcd for C17H19N3S: C, 68.5; H, 6.2; N, 13.9; S, 10.7.
Found: C, 68.6; H, 6.4; N, 14.1; S, 10.8.32
1-(4-Isopropylbenzylidene)-2-phenylhydrazine (4a)
In a 250 ml round bottomed flask, cuminaldehyde (0.0100 mole, 1.51 mL) was dissolved
in ethanol (15 mL) and an equimolar amount of phenylhydrazine (0.0100 mole, 0.98 mL)

ORGANIC PREPARATIONS AND PROCEDURES INTERNATIONAL
11
and glacial acetic acid (5 drops) were added. The reaction mixture was refluxed for
1 hour. The progress of the reaction was monitored by TLC (silica gel, ethanol). The
hot reaction mixture was poured onto crushed ice. A brown precipitate was formed, fil-
tered and dried to yield 4a, 1.74 g, 70%, brown crystals, mp 110-112 ꢁC, Rf 0.55 (silica
1
gel, ethanol). UV-vis (kmax): 369 nm. IR: (cmꢀ1) 1617 (C ¼ N). H NMR (CDCl3): d
7.67 (s, 1H), 6.86-7.59 (m, 9H), 4.01 (s, 1H), 2.88-2.94 (m, 1H), 1.25-1.29 (m, 6H). 13C
NMR (CDCl3): d 149.49, 144.86, 137.54, 132.98, 129.24, 126.71, 126.25, 119.93, 112.72,
34.02, 23.89.
Anal. Calcd for C16H18N2: C, 80.63; H, 7.61; N, 11.75. Found: C, 80.58; H, 7.63;
N, 11.78.
1-(4-Isopropylbenzylidene)-2-(4-nitrophenyl)hydrazine (4b)
Cuminaldehyde (0.0100 mole, 1.51 mL) and p-nitrophenylhdrazine (0.0100 mole, 1.53 g)
were dissolved in ethanol (15 mL). After adding a catalytic amount of glacial acetic acid
(5 drops), the mixture was refluxed. TLC (silica gel, ethanol) was used to check the
preparation of compound 4b, 2.64 g, 87%, orange crystals, mp 135-137 ꢁC, Rf 0.57 (silica
1
gel, ethanol). UV-vis (kmax): 373 nm. IR: (cmꢀ1) 1612 (C ¼ N). H NMR (CDCl3) ppm:
d 8.40 (s, 1H), 7.51-7.53 (m, 2H), 7.39-7.41 (m, 2H), 7.25-7.26 (m, 4H), 4.12 (s, 1H),
2.91-2.94 (m, 1H), 1.24-1.26 (d, 6H). 13C NMR (CDCl3): d 160.60, 157.87, 150.50,
146.88, 144.29, 139.97, 129.77, 124.66, 118.87, 37.73, 23.22.
Anal. Calcd for C16H17N3O2: C, 67.83; H, 6.05; N, 14.83. Found: C, 67.79; H, 6.10;
N, 14.86.
1-(4-Isopropylbenzylidene)-2-(2,4-dinitrophenyl)hydrazine (4c)
In a 100 mL beaker, 0.74 g of cuminaldehyde was dissolved in some ethanol and a solu-
tion of 2,4-dinitrophenylhydrazine was added. (The latter had been prepared by dissolv-
ing 1.00 g of 2,4-dinitrophenylhydrazine (0.00500 mole) in 5 mL of concentrated H2SO4
and then slowly adding this solution to 7.0 mL water in 25 mL 95% ethanol.) A dark
orange precipitate was obtained. This was washed lavishly with water, then filtered and
dried. A single spot on the chromatographic plate (silica gel, ethanol) was consistent
with the formation of compound 4c, 1.62 g, 92%, red crystals, mp 140-142 ꢁC, Rf 0.63
1
(silica gel, ethanol). UV-vis (kmax): 390 nm. IR: (cmꢀ1) 1651 (C ¼ N). H NMR (CDCl3)
ppm: d 1.28-1.30 (d, 6H), 2.96-2.99 (m, 1H), 7.32-7.34 (m, 2H), 7.69-7.71 (m, 2H),
8.08-8.11 (m, 2H), 8.34-8.37 (m, 1H), 9.15 (s, 1H), 11.30 (s, 1H,). 13C NMR (CDCl3): d
152.53, 148.09, 144.87, 138.13, 130.77, 130.01, 129.29, 127.78, 127.18, 123.54, 116.77,
34.23, 23.76.
Anal. Calcd for C16H16N4O4: C, 58.53; H, 4.91; N, 17.06. Found: C, 58.57; H, 4.93;
N, 17.08.
Biological assessments
The free radical scavenging activity of the compounds was estimated by their capacity
to bleach the stable radical 2,2-diphenyl-1-picrylhydrazyl (DPPH).41 DPPH gives a

12
P. KAUR ET AL.
strong absorption band at 517 nm in the visible region. Different concentrations (3000,
2000, 1000, 500, 250, 100, 50 and 25 mg mLꢀ1) of test compounds (40 mL) and ascorbic
acid (40 mL), dissolved in methanol, were added to 3.96 mL of the DPPH solution. After
30 min, the absorbance was read at 517 nm at room temperature, and the scavenging
activity was calculated as a percentage of the radical reduction. Each experiment was
executed thrice. Methanol was used as a control and ascorbic acid was used as standard.
The radical scavenging activity was obtained as follows:
Â
Ã
Radical Scavenging Activity ð%Þ ¼
A
control ꢀ Asample =A
ꢃ 100
ð
Þ
control
Where Acontrol and Asample were the absorbances of the blank (methanol) and test
compounds, respectively at 517 nm.
Authentic pure cultures of bacteria (Pseudomonas sp., Klebsiella sp., and Enterobacter
sp.) were procured from the Department of Plant Breeding and Genetics, Punjab
Agricultural University, Ludhiana, India. The new compounds (against the standard
Ampicilin) were screened for their antimicrobial potential at different concentrations
(3000, 2000, 1000, 500, 250, 100, 50 and 25 mg mLꢀ1) against the three above-men-
tioned gram negative bacteria, by using the filter paper disc diffusion method on nutri-
ent agar medium.42 The nutrient broth medium (Himedia, 24 g, Mumbai, India) was
suspended in distilled water (1000 mL) and heated until it dissolved completely. The
medium was autoclaved at a pressure of 15 Pa for 20 min and poured into petri plates.
After the setting of the nutrient agar medium, nutrient broth containing the test bac-
teria was inoculated onto the petri plates. Sterile discs having diameter 6 mm were
treated with the compounds of interest at different concentrations and then placed on
the inoculated plates. The plates were incubated for 24 hours in an incubator at 37 ꢁC
and the inhibition zone around the disc was measured in mm. Each treatment was
replicated thrice. MIC values of synthesized products were determined using a
known method.43
Acknowledgment
The authors are thankful to the Pulses Microbiology Laboratory, Department of Plant Breeding
and Genetics, Punjab Agricultural University, Ludhiana, for providing the pure cultures
of bacteria.
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