Synthesis and antibacterial activity of some new hydrazones

Article abstract of DOI:10.1007/s00044-012-0278-5

New hydrazone derivatives were synthesized by the condensation of some selected heteroaromatic hydrazines with appropriate aromatic ketones at high temperature (100 °C). The structures of the synthesized compounds were established by elemental (CHN) and spectral (IR, ¹HNMR, and Mass) analysis. The synthesized compounds were screened for their antibacterial (Bacillus subtilis, Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, Salmonella typhi, Proteus mirabilis) activities, which reveal that all the compounds possess activity against all the tested organisms.

Full text of DOI:10.1007/s00044-012-0278-5

MEDICINAL
CHEMISTRY
RESEARCH
Med Chem Res (2013) 22:2840–2846
DOI 10.1007/s00044-012-0278-5
ORIGINAL RESEARCH
Synthesis and antibacterial activity of some new hydrazones
•
M. Rudrapal R. Siva Satyanandam
•
•
T. Sri Swaroopini T. Naga Lakshmi
•
•
S. Kamar Jaha S. Zaheera
Received: 4 July 2012 / Accepted: 9 October 2012 / Published online: 30 October 2012
Ó Springer Science+Business Media New York 2012
Abstract New hydrazone derivatives were synthesized
by the condensation of some selected heteroaromatic
hydrazines with appropriate aromatic ketones at high
temperature (100 °C). The structures of the synthesized
compounds were established by elemental (CHN) and
spectral (IR, 1HNMR, and Mass) analysis. The synthesized
compounds were screened for their antibacterial (Bacillus
subtilis, Staphylococcus aureus, Escherichia coli, Pseudo-
monas aeruginosa, Salmonella typhi, Proteus mirabilis)
activities, which reveal that all the compounds possess
activity against all the tested organisms.
and Peoples, 1954). In recent days, many newer hydrazone
derivatives have also been known to possess antimicrobial
(Vicini et al., 2002), anticonvulsant (Dimmock et al., 2000),
analgesic, antiinflammatory, antiplatelet (Todeschini et al.,
1998), antimalarial (Walcourt et al., 2004), and antitumor
´
activities (Abadi et al., 2003; Imramovsky et al., 2007).
It is believed that the azomethine (–NHN=CH–) moiety
is essential for the bioactivity of hydrazones and/or
hydrazone derivatives as reported in various literatures
(Rollas and Ku¨c¸u¨kgu¨zel, 2007). A large number of het-
eroaromatic scaffolds possessing a wide range of biologic
including antimicrobial activities have also been investi-
gated (Mariappan et al., 2011; Pattan et al., 2006; Singh
et al., 2010). In view of the above-mentioned facts, an
assumption has been made to design some newer hydra-
zone derivatives using such bioactive heteroaromatic
scaffolds as the basic structural unit. Some important
pharmacophoric scaffolds which include 4-benzylidene-2-
Keywords Hydrazone Á Azomethine Á
Heteroaromatic scaffold Á Antibacterial
Introduction
Hydrazones containing an azomethine –NHN=CH– group
represent an important class of compounds which possess a
wide range of biologic activities (Corey and Enders, 1976).
For this reason, hydrazones derived from a diverse group of
heteroaromatic scaffolds (Rollas and Ku¨c¸u¨kgu¨zel, 2007)
have successfully been incorporated into a number of
therapeutically useful drug candidates. For example, iso-
niazid (isonicotinoyl hydrazone) is a well known and
potent antitubercular drug with very high in vivo inhibitory
activity against Mycobacterium tuberculosis H37Rv (Sah
methyloxazol-5-one,
2-(4-aminophenyl)benzimidazole,
2-amino-4-phenylthiazole, and isonicotinoyl hydrazide
were selected for the present study. We reported herein the
synthesis and evaluation of the antibacterial activity of
some new hydrazone derivatives.
Experimental
Chemicals and analysis
All chemicals and solvents of synthetic grade were pro-
cured from Sd Fine Chemicals Ltd., Mumbai, and used
without further purification unless otherwise stated. Melt-
ing points (m.p.) were measured in open capillaries using
an electric melting point apparatus and are uncorrected.
The progress of reactions was constantly monitored by the
M. Rudrapal (&) Á R. S. Satyanandam Á
T. S. Swaroopini Á T. N. Lakshmi Á S. K. Jaha Á S. Zaheera
Aditya Institute of Pharmaceutical Sciences and Research,
Surampalem, E. G. Dist. 533 437, Andhra Pradesh, India
e-mail: rs_rudrapal@yahoo.co.in
123

Med Chem Res (2013) 22:2840–2846
2841
silica gel-G TLC and spots were detected by exposure to
iodine vapors. The kmax (nm) was recorded on an Elico SL
164 UV–Vis spectrophotometer. IR spectra (t, cm-1) were
obtained on the FT-IR Perkin Elmer Spectrum RX-I
spectrometer using a KBR disk. 1HNMR spectra were
recorded on a Bruker AC-F 400 FT-NMR spectrometer
using acetone-d6 as the solvent and TMS as the internal
reference standard (chemical shift d, ppm). Mass spectra
were obtained with the LC–MS Water 4000 ZQ instrument
using electrospray ionization. Elemental analysis was per-
formed on a Perkin Elmer 2400 Series II CHNS/O
analyzer.
mixture was refluxed for 1.5 h, cooled to room temperature,
and then in refrigerator for at least 1 h. The separated solid
was poured into 50 mL of ice-cold water and the precipitated
product was filtered under suction, washed thoroughly with
cold water, and dried. The crude solid was recrystallized
from the alcohol-water (1:1) mixture and left to dry over-
night (Cocco et al., 1999).
Analytical and spectral data
(7a) Yield 76 %, Rf 0.35, m.p. 158–162 °C. UV–Vis
(acetone), kmax (nm): 412. IR (KBr), t (cm-1): 3345 (N–H
str., [NH); 3065 (Ar. C–H str.); 2960, 2854 (C–H str., tas
& ts –CH3); 1678 ([C=N– str.); 1352, 1260 (C–N str.);
1046 (C–O–C str.). 1HNMR (acetone-d6), d (ppm): 1.85 (s,
3H, CH3); 5.63 (bs, 1H, NH); 5.98 (s, 1H,[C=CH–C6H5);
6.46–6.62 (m, 5H, –C6H5), 7.21–7.30 (m, 5H, –C6H5). MS
(ESI), m/z (%): 278.72 (100), (M?H)?. CHN anal.
(C17H15N3O); calc. (%): C, 73.63; H, 5.45; N, 15.15; found
(%): C, 73.55; H, 5.53; N, 15.00.
Two strains of Gram-positive bacteria, viz. Bacillus
subtilis, Staphylococcus aureus; and four strains of Gram-
negative bacteria, viz. Eschericia coli, Pseudomonas
aeruginosa, Salmonella typhi, Proteus mirabilis, were used
for the study. The cultures of bacteria were maintained in
their appropriate agar slants at 4 °C throughout the study
and used as stock cultures.
General procedure for the synthesis of 1-(4-
phenylthiazol-2-yl)hydrazine, 9/1-(4-(benzimidazol-2-
yl)phenyl)hydrazine, 15
(7b) Yield 76 %, Rf 0.37, m.p. 175–178 °C. UV–Vis
(acetone), kmax (nm): 576. IR (KBr), t (cm-1): 3348 (N–H
str., [NH); 3068 (Ar. C–H str.); 2965, 2855 (C–H str., tas
& ts –CH3); 1672 ([C=N– str.); 1528, 1378 ((N=O)2 str.,
tas & ts Ar. NO2); 1352, 1266 (C–N str.); 1032 (C–O–C
5 g (0.0011 mol) of 2-amino-4-phenylthiazole (Pattan et al.,
2006), 8/6 g (0.055 mol) of 2-(4-aminophenyl)benzimidazole
(Mariappan et al., 2011), 14 were dissolved in 3.0 mL of conc.
HCl and 5.0 mL of water in a 250-mL conical flask. The
mixture was cooled to 0–5 °C in an ice bath with vigorous
shaking. The hydrochloride salt of amine was separated as a
fine crystalline precipitate. A solution of 3.3 g (0.048 mol) of
NaNO2 in 10 mL of water was prepared in a 100-mL beaker,
cooled to 0–5 °C,andaddedslowlyintotheflaskforaperiodof
15 min. The reaction mixture was then stirred well for a period
of at least 1 h. The hydrochloride salt of amine was dissolved
as the very soluble diazonium chloride salt was formed. The
completion of the reaction was checked by KI-starch paper as
indicated by the formation of blue color due to presence of
slight excess of free nitrous acid in the solution. The cold
diazonium chloride solution was added slowly into cold tin
(2 g)-conc. HCl (15 mL) mixture with frequent stirring of the
mixture. The mixture was refluxed in a water bath for an
additional 2 h with occasional shaking and then cooled in an
ice bath. The separated solid was collected by filtration, dried
in air, and recrystallized from ethanol (Furniss et al., 2007).
1
str.). HNMR (acetone-d6), d (ppm): 1.89 (s, 3H, CH3);
5.87 (bs, 1H, NH); 6.13 (s, 1H, [C=CH– C6H5));
6.52–6.67 (m, 5H, –C6H5), 7.21–7.30 (m, 3H, –C6H3
(NO2)2). MS (ESI), m/z (%): 368.13 (100), (M?H)?. CHN
anal. (C17H13N5O5); calc. (%): C, 55.59; H, 3.57; N, 19.07;
found (%): C, 56.01; H, 3.56; N, 19.09.
(10a) Yield 68 %, Rf 0.32, m.p. 137–140 °C. UV–Vis
(acetone), kmax (nm): 427. IR (KBr), t (cm-1): 3369 (N–H
str., [NH); 3044 (Ar. C–H str.); 2958, 2854 (C–H str., tas
& ts –CH3); 1668 ([C=N– str.); 1635, 1610 (C=C str.,
–C=C–Ar.); 1354, 1260 (C–N str.). 1HNMR (acetone-d6), d
(ppm): 1.87 (s, 3H, CH3); 5.50 (bs, 1H, NH); 5.86 (d, 1H,
J = 8.2 Hz, =C(alkyl)–CH =); 6.12 (d, 1H, J = 8.6 Hz),
=CH–C6H5); 6.22 (s, 1H, thiazolyl-H5); 7.12–7.29 (m, 5H,
–C6H5); 7.32–7.42 (m, 5H, –C6H5). MS (ESI), m/z (%):
320.45 (100), (M?H)?. CHN anal. (C19H17N3S); calc. (%):
C, 71.44; H, 5.36; N, 13.15; found (%): C, 70.98; H, 5.55;
N, 13.47.
(10b) Yield 77 %, Rf 0.36, m.p. 165–168 °C. UV–Vis
(acetone), kmax (nm): 476. IR (KBr), t (cm-1): 3336 (N–H
str.,[NH); 3048 (Ar. C–H str.); 1662 ([C=N– str.); 1639,
1602 (C=C str., –C=C–Ar.); 1354, 1260 (C–N str.).
1HNMR (acetone-d6), d (ppm): 5.55 (bs, 1H, NH); 5.88 (d,
1H, J = 8.0 Hz, =C(aryl)–CH=); 6.17 (d, 1H, J = 8.3 Hz),
=CH–C6H5); 6.25 (s, 1H, thiazolyl-H5); 7.08–7.12 (m, 5H,
–C6H5); 7.26–7.32 (m, 5H, –C6H5); 7.56–7.62 (m, 5H,
–C6H5). MS (ESI), m/z (%): 382.59 (100), (M?H)?. CHN
General procedure for the synthesis of hydrazones
A solution of appropriate hydrazine (0.02 mol in 24 mL of
alcohol-water mixture) was added into the solution of
appropriate aromatic ketone (0.02 mol in 15 mL of ethanol)
contained in a 250-mL RBF (round bottom flask). The
123

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Med Chem Res (2013) 22:2840–2846
anal. (C24H19N3S); calc. (%): C, 75.56; H, 5.02; N, 11.01;
found (%): C, 75.83; H, 5.75; N, 10.99.
str., –C=C–Ar.); 1682 ([C=N– str.). 1HNMR (acetone-d6),
d (ppm): 1.90 (s, 3H, CH3); 5.68 (bs, 1H, NH); 1.86 (s, 3H,
CH3); 5.40 (bs, 1H, NH); 5.88 (d, 1H, J = 7.4 Hz,
=C(alkyl)–CH=); 6.34 (d, 1H, J = 7.9 Hz), =CH-C6H5);
7.35–7.41 (m, 5H, –C6H5), 7.52–7.59 (m, 4H, –C6H4). MS
(ESI), m/z (%): 266.32 (100), (M?H)?. CHN anal.
(C21H18N2); calc. (%): C, 72.43; H, 5.70; N, 15.84; found
(%): C, 72.62; H, 5.81; N, 15.17.
(16a) Yield 68 %, Rf 0.35, m.p. 158–162 °C. UV–Vis
(acetone), kmax (nm): 488. IR (KBr), t (cm-1): 3358 (N–H
str.,[NH); 3069 (Ar. C–H str.); 2978, 2858(C–H str., tas &
ts –CH3); 1668 ([C=N– str.); 1630, 1600 (C=C str.,
–C=C–Ar.); 1345, 1276 (C–N str.). 1HNMR (acetone-d6), d
(ppm): 1.97 (s, 3H, CH3); 5.00 (bs, 1H, –NH, benzimi-
dazolyl-H1); 5.67 (bs, 1H, –NH–C6H5); 5.68 (d, 1H,
J = 7.9 Hz, =C(alkyl)–CH=); 6.27 (d, 1H, J = 7.8 Hz),
=CH–C6H5); 7.26–7.31 (m, 5H, –C6H5), 7.38–7.46 (m, 4H,
–C6H4); 7.64–7.87 (m, 4H, benzimidazolyl-H4, H5, H6 &
H7). MS (ESI), m/z (%): 353.03 (100), (M?H)?. CHN
anal. (C23H20N4); calc. (%): C, 78.38; H, 5.72; N, 15.90;
found (%): C, 78.73; H, 5.90; N, 15.01.
(19b) Yield 78 %, Rf 0.46, m.p. 178–180 °C. UV–Vis
(acetone), kmax (nm): 476. IR (KBr), t (cm-1): 3347 (N–H
str., [NH); 3065 (Ar. C–H str.); 1725 ([C=O str.,
–CONH–); 1687 ([C=N– str.); 1626, 1492, 1476, 1448
1
(C=C str., Ar. ring). HNMR (acetone-d6), d (ppm): 5.73
(bs, 1H, NH); 5.83 (d, 1H, J = 7.3 Hz, =C(aryl)–CH=);
6.38 (d, 1H, J = 7.1 Hz), =CH–C6H5); 7.33–7.438 (m, 5H,
–C6H5), 7.44–7.49 (m, 4H, –C6H4). MS (ESI), m/z (%):
328.13 (100), (M?H)?. CHN anal. (C21H17N3O); calc.
(%): C, 77.04; H, 5.23; N, 12.84; found (%): C, 77.79; H,
5.51; N, 11.68.
(16b) Yield 74 %, Rf 0.37, m.p. 175–178 °C. UV–Vis
(acetone), kmax (nm): 496. IR (KBr), t (cm-1): 3366 (N–H
str.,[NH); 3073 (Ar. C–H str.); 1677 ([C=N– str.); 1632,
1598 (C=C str., –C=C–Ar.); 1343, 1286 (C–N str.).
1HNMR (acetone-d6), d (ppm): 5.16 (bs, 1H, –NH, benz-
imidazolyl-H1); 5.66 (bs, 1H, –NH–C6H5); 5.98 (d, 1H,
J = 8.3 Hz, =C(aryl)–CH=); 6.34 (d, 1H, J = 8.4 Hz),
=CH–C6H5); 7.29–7.36 (m, 5H, –C6H5), 7.43–7.48 (m, 4H,
–C6H4); 7.56–7.62 (m, 4H, benzimidazolyl-H4, H5, H6 &
H7). MS (ESI), m/z (%): 415.21 (100), (M?H)?. CHN
anal. (C28H22N4); calc. (%): C, 81.13; H, 5.35; N, 13.52;
found (%): C, 82.03; H, 5.40; N, 13.74.
Antibacterial screening
The antibacterial activity of the synthesized compounds
was evaluated against six different strains of Gram-positive
and Gram-negative bacteria by the agar diffusion method
(Collee et al., 1989; Hewitt, 2004). The test solutions of
each compound were prepared in two different concentra-
tions, viz. 100 and 50 lg/mL using DMF as solvent. A
freshly prepared and cooled (45–50 °C) medium of about
25 mL was inoculated aseptically with each standardized
inoculum (0.5–1.0 mL) in a laminar air flow unit. The
medium was then poured into a previously sterilized petri
plate to occupy a depth of 4 mm. The plates were left at
room temperature to allow solidification. A sterilized disk
(6-mm diameter) of Whatman filter paper No.2 impreg-
nated with DMF was used as the negative control. Under
aseptic condition, empty sterilized disks were impregnated
with the test drug solutions of two different doses (50 and
100 lg/mL) and with vehicle control DMF. After solvent
evaporation, the dried disks were placed on the surface of
the agar medium and the plates were left undisturbed for an
hour at room temperature for pre-incubation diffusion to
minimize the effects of variation in time between the
applications of different solution.
(17a) Yield 69 %, Rf 0.38, m.p. 132–136 °C. UV–Vis
(acetone), kmax (nm): 457. IR (KBr), t (cm-1): 3376 (N–H
str., [NH); 3089 (Ar. C–H str.); 2974, 2866 (C–H str., tas
& ts –CH3); 1665 ([C=N– str.); 1626, 1590 (C=C str.,
–C=C–Ar.); 1358, 1278 (C–N str.). 1HNMR (acetone-d6), d
(ppm): 1.86 (s, 3H, CH3); 5.40 (bs, 1H, NH); 5.74 (d, 1H,
J = 8.0 Hz, =C(alkyl)–CH=); 6.26 (d, 1H, J = 8.2 Hz,
=CH–C6H5); 7.26–7.32 (m, 5H, –C6H5), 7.44–7.49 (m, 4H,
–C6H4). MS (ESI), m/z (%): 237.15 (100), (M?H)?. CHN
anal. (C16H16N2); calc. (%): C, 81.32; H, 6.82; N, 11.85;
found (%): C, 81.79; H, 6.00; N, 11.69.
(17b) Yield 74 %, Rf 0.42, m.p. 165–168 °C. UV–Vis
(acetone), kmax (nm): 588. IR (KBr), t (cm-1): 3378 (N–H
str.,[NH); 3075 (Ar. C–H str.); 1658 ([C=N– str.); 1604,
1568, 1498, 1425 (C=C str., Ar. ring); 1545, 1389 ((N=O)2
1
str., tas & ts Ar. NO2); 1366, 1274 (C–N str.). HNMR
(acetone-d6), d (ppm): 5.46 (bs, 1H, NH); 5.77 (d, 1H,
J = 8.6 Hz, =C(aryl)–CH=); 6.46 (d, 1H, J = 7.9 Hz),
=CH–C6H5); 7.35–7.42 (m, 5H, –C6H5), 7.57–7.64 (m, 4H,
–C6H4). MS (ESI), m/z (%): 266.73 (100), (M?H)?. CHN
anal. (C21H18N2); calc. (%): C, 84.53; H, 6.08; N, 9.39;
found (%): C, 85.06; H, 6.38; N, 9.72.
Ciprofloxacin injection I.P. (200 mg/100 mL) was dilu-
ted to 50 lg/mL with normal saline and used as the positive
control. After incubation of the plates at 37 1 °C for 24 h,
the diameters of the zones of complete inhibition surround-
ing each of the disk were measured including the diameter of
the disk with a centimeter scale. The average zone of inhi-
bition was obtained from three replicates of the test/standard
compounds.
(19a) Yield 75 %, Rf 0.43, m.p. 158–160 °C. UV–Vis
(acetone), kmax (nm): 488. IR (KBr), t (cm-1): 3342 (N–H
str., [NH); 3057 (Ar. C–H str.); 2965, 2853 (C–H str., tas
& ts –CH3); 1720 ([C=O str., –CONH–); 1625, 1600 (C=C
123

Med Chem Res (2013) 22:2840–2846
2843
Results and discussion
yields of all the compounds were found to be satisfactory.
Hydrazones were obtained as pale yellow-, orange-, or red-
colored products. The purity of the compounds was
ascertained by melting point determinations and TLC (Rf
value). Furthermore, the results of elemental analyses were
within the acceptable limits of the calculated values as
presented in the analytical and spectral data subsection.
The UV–Vis spectra of the synthesized compounds
The present study reports the in vitro antibacterial activity
of some newly synthesized hydrazone derivatives. New
hydrazone derivatives were synthesized by condensation of
various aromatic/heteroaromatic hydrazines with the
appropriate ketone at high temperature, preferably 100 °C.
Hydrazones were formed by the replacement of the oxygen
of carbonyl compounds (Scheme 1) with the –NHNH2
(hydrazinoyl) group of hydrazines. The synthesis of these
hydrazones is depicted in Schemes 2, 3, 4, 5 and 6. The
showed characteristic absorption maxima (kmax) of
longer wavelength, indicating the presence of strong
chromophoric groups such as oxazolyl, –NO2 (7a, 7b);
C CHCOCH3
H
CH3COCH3
(2a)
NaOH
-H2O
(3a)
+
C O
H
HC=HCOC
(3b)
H3COC
(2b)
(1)
Scheme 1 Synthesis of benzal acetone/chalcone; (1)-benzaldehyde, (2a)-acetone, (2b)-acetophenone, (3a)-benzal acetone, (3b)-chalcone
O
N
OH
CH3COONa/ (CH3CO)2O
Reflux, 2 h
H3C
N
H
CH3
+
(1)
O
O
+
O
(5)
(4)
N
O
CH3
NHNH2 HCl
(6a)
N
7a: R=
EtOH/H2SO4
Reflux, 1.5 h
NH
(7)
R
NO2
(5)
NO2
O2N
NHNH2
(6b)
7b: R=
NO2
Scheme 2 Synthesis of (4-benzylidene-2-methyloxazol-5(4H)-yli-
dene)-2-substituted hydrazone; (4)-N-acetyl glycine, (5)-4-benzyli-
dene-2-methyloxazol-5-one, yield-85 %, m.p.-148–150 °C; (6a)-phenyl
hydrazine hydrochloride, (6b)-2,4-DNPH, (7a)-(4-benzylidene-2-
methyloxazol-5(4H)-ylidene)-2-phenylhydrazone, (7b)-(4-benzylidene-
2-methyloxazol-5(4H)-ylidene)-2-(2,4-dinitrophenyl)phenylhydrazone
S
Sn/HCl
Br2
NaNO2/HCl
0-5OC, 1 h
NH2
N
(2b)
+
NH2CNH2
Reflux, 2 h
N
Reflux, 8 h
N
S
NHNH2
N2Cl
S
S
(8)
(9)
(3a)
EtOH
10a: R=CH3
+
(9)
R
Reflux, 1.5 h
N
S
10b: R=C6H5
(3b)
NHN=C CH=CH
(10)
Scheme 3 Synthesis of 1-Substituted-(4-phenylthiazol-2-yl)hydra-
zone; NH2CSNH2- thiourea, (8)-2-amino-4-phenylthiazole, yield-
85 %, m.p.-122–124 °C, (9)-1-(4-phenylthiazol-2-yl)hydrazine, yield-
75 %, m.p.-128–130 °C, (10a)-1-(4-phenylbut-3-en-2-ylidene)-(4-
phenylthiazol-2-yl)hydrazone, (10b)-1-(1,3-diphenylallylidene)-(4-
phenylthiazol-2-yl) hydrazone
123

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Med Chem Res (2013) 22:2840–2846
COOH
NH2
NaNO2/HCl
(0-5OC, 1 h)
N
N
HCl
NH2
NHNH2
+
Reflux, 3 h
Sn/HCl
NH
NH
(15)
NH2
Reflux, 2 h
NH2
(13)
(14)
(12)
R
(3a)
(3b)
N
EtOH
NHN=C CH
C
H
(15)
+
16a: R=CH3
16b: R=C6H5
Reflux, 1.5 h
N
H
(16)
Scheme 4 Synthesis of 1-Substituted-(4-(1H-benzimidazol-2-yl)phe-
nyl)hydrazone; (12)-o-phenylenediamine, (13)-PABA, (14)-2-(4-ami-
nophenyl)benzimidazole, yield- 78 %, m.p.-140–142 °C, (15)-1-(4-
(1H-benzimidazol-2-yl)phenyl)hydrazine, yield- 65 %, m.p.-155–158 °C,
(16a)-1-(4-phenylbut-3-en-2-ylidene)-(4-(1H-benzimidazol-2-yl)phe-
nyl)hydrazone, (16b)-1-(1,3-diphenylallylidene)-(4-(1H-benzimidaz-
ol-2-yl)phenyl)hydrazone
R3
Scheme 5 Synthesis of
1-Substituted-2-phenyl/
(2,4-dintrophenyl)hydrazone;
(17a)- 1-(4-phenylbut-3-en-2-
ylidene)-2-phenylhydrazone,
(17b)- 1-(1,3-
NHN=C
R1
CH=CH
R3
(6a)
(3a) +
R1
H
R2
H
EtOH
Reflux, 1.5 h
17a:
17b:
CH3
C6H5
+
(3b) (6b)
R2
diphenylallylidene)-2-
(2,4-dinitrophenyl)hydrazone
(17)
NO2
NO2
R
anticipated structure of the synthesized compounds
(Silverstein and Webster, 2005). The prominent molecular
ion peaks, [M?H]?, are in accordance with the anticipated
mass of the synthesized compound (Silverstein and
Webster, 2005).
CONHNH2
(3a)
CONHN=C
CH=CH
HCl, EtOH
+
Reflux, 1h
(3b)
N
N
19a: R=CH3
19b: R=C6H5
(18)
All the synthesized compounds were found to be active
against all the tested strains of Gram-positive and Gram-
negative bacteria at two different tested doses, viz. 50 and
100 lg/mL. There was no inhibition of growth of vehicle
control (DMF). The results depicted in Table 1 clearly
indicate that all the compounds were equally active with
some degree of variations, but were less potent when
compared with the standard drug, ciprofloxacin. No sig-
nificant difference was found in activities between the
higher and lower dose of compounds.
Scheme 6 Synthesis of 1-Substituted-2-isonicotinohydrazone; (19a)-
1-(4-phenylbut-3-en-2-ylidene)-2-isonicotinohydrazone, (19b)-1-(1,3-
Diphenylallylidene)-2-isonicotinohydrazone
thiazolyl (10a, 10b); benzimidazolyl (16a, 16b); conju-
gated alkene with aryl (17a and 17b); and pyridyl (19a and
19b) moieties in the structure of the synthesized com-
pounds. The structure of the compounds was supported by
the infrared spectral data which showed characteristic
absorption bands for specific functional groups like [NH,
(3345 cm-1, 7a); aryl-CONH (1720 cm-1, 19a); [C=N–
(1662 cm-1, 10b); conjugated –C=C– with aryl ring (1630,
Among the synthesized compounds, 7a showed the
highest activity (14.0 mm and 16.0 mm at 50 and 100
lg/mL, respectively) which, however, was considerably
less than that of the standard drug, ciprofloxacin (18 mm at
50 lg/mL), particularly against S. aureus. In contrast, the
activity of the other compounds listed in Table 1 was less
than that of compound 7a. The activity of 10a, for instance,
was found to be 6.5 mm and 9.5 mm at 50 and 100 lg/mL,
respectively, against S. aureus. Results clearly reveal that all
the new hydrazones containing various heteroaromatic
scaffolds possess antibacterial activity against all the tested
strains. From the results, it could be assumed that hetero-
aromatic scaffolds are linked with the hydrazinoyl functional
moiety; =N–NH– is an important structural prerequisite for
1600 cm-1, 16a); aromatic (N=O)2 (1545, 1389 cm-1
17b); C–N (1343, 1286 cm-1, 16b)., C–O–C (1032 cm-1
,
,
7b), etc. (Silverstein and Webster, 2005). The assignment
of protons is fully supported by their characteristic chem-
ical shift values for –CH3 (sharp singlet at d 1.85, 7a); –NH
of benzimidazolyl-H1 (broad singlet at d 5.16, 16a);
=C(Me)–CH= (doublet at d 5.74, J = 7.9 Hz, 17a); [NH
of =N–NH–Ar. (broad sharp singlet at d 5.87, 7b); –NH of
–CONH (broad sharp singlet at d 5.73, 19b); =CH–C6H5
(doublet at d 6.12, J = 8.6 Hz, 10a); and thiazole-H5
(sharp singlet at d 6.12, 10b) groups present in the
123

Med Chem Res (2013) 22:2840–2846
2845
Table 1 Antibacterial activity of the synthesized compounds
Compounds
Conc. (lg/mL) in DMF
Zone of inhibition in mm*
B. s
S. a
E. c
P. a
S. t
6.0
P. m
7a
50
100
50
6.0
9.5
6.0
9.0
6.0
8.5
6.5
8.5
6.0
8.5
6.0
8.5
6.5
8.5
6.5
9.0
6.0
8.5
6.0
8.5
18.0
–
14.0
16.0
6.5
9.0
6.5
9.5
6.5
8.5
6.5
8.0
6.5
9.0
6.0
8.5
6.0
8.5
6.0
8.5
6.0
8.0
18.0
–
6.5
9.0
6.0
8.5
6.0
9.0
7.0
8.5
6.5
9.0
6.0
8.5
6.0
8.5
6.5
8.0
6.0
8.0
6.0
8.0
18.5
–
6.0
8.0
6.0
8.5
6.0
8.0
6.0
8.0
6.0
8.0
6.0
8.5
6.0
8.5
6.0
8.5
6.0
8.0
6.0
8.5
19.0
–
6.5
8.5
6.0
9.5
6.5
8.0
6.5
8.5
6.5
8.5
6.0
8.5
6.0
9.0
6.5
9.5
6.0
8.5
6.5
8.0
19.5
–
8.0
6.5
8.0
6.0
8.0
6.0
8.0
6.0
8.0
6.5
8.0
6.5
8.5
6.5
8.5
6.0
8.5
6.0
8.0
18.0
–
7b
100
50
10a
10b
16a
16b
17a
17b
19a
19b
100
50
100
50
100
50
100
50
100
50
100
50
100
50
100
50
Ciprofloxacin#
Control (DMF)
–
B. s, Bacillus subtilis; S. a, Staphylococcus aureus; E. c, Escherichia coli; P. a, Pseudomonas aeruginosa; S. t, Salmonella typhi; P. m, Proteus
mirabilis
* Values are mean inhibition zone (mm) of three replicates
#
Reference standard
the bioactivity of the prepared hydrazones. Furthermore, it
has been observed that 7a possess more enhanced activity
than the rest of the compounds, which indicates that
4-benzylidene-2-methyloxazol-5-one scaffold linked with
unsubstituted phenyl hydrazinoyl substituent has a better
contributing effect toward the activity of the compound
than the substituted one (2,4-dinitrophenyl-, 7b) or any
other substituents present in the rest of the compounds.
considerably less than that of the standard drug, ciproflox-
acin. From our present investigation, it can be concluded
that the selected heteroaromatic scaffolds when linked with
the =N–NH– fragment become an important structural
prerequisite for the bioactivity of the prepared hydrazones.
Acknowledgments The authors express their sincere thanks to the
Principal, the Aditya Institute of Pharmaceutical Sciences and
Research, Surampalem, E. G. Dist., Andhra Pradesh, India, for his
help and cooperation toward completion of this research work. The
authors also wish to thank Mr. N. Satish Reddy, Vice-Chairman, the
Aditya Educational Institutions, Surampalem, E. G. Dist., Andhra
Pradesh, India, for providing laboratory facilities and financial sup-
port to carry out the work.
Conclusion
The present study involves the synthesis of some new
hydrazone derivatives and the evaluation of their antibac-
terial activity against both Gram-positive and Gram-negative
bacteria. The structural assignments of all the compounds
were made on the basis of UV–Vis, IR, NMR, Mass spec-
troscopic data, and elemental analysis. All the synthesized
compounds exhibited some degree of in vitro antibacterial
activity at the tested doses which, however, was
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