Synthesis, spectroscopic and cytotoxic studies of biologically active new Schiff bases derived from p-nitrobenzaldehyde

Article abstract of DOI:10.1248/cpb.55.1070

Thirteen new Schiff bases derived from p-nitrobenzaldehyde were synthesized by condensation with the appropriate amines. An unusual reduction of the p-nitrobenzaldehyde to the corresponding alcohol was also observed in one of the reactions. The structures of the compounds were identified using spectroscopic techniques. Cytotoxicity for the titled compounds was studied against Brine Shrimp, used as the test animal.

Full text of DOI:10.1248/cpb.55.1070

1070
Notes
Chem. Pharm. Bull. 55(7) 1070—1072 (2007)
Vol. 55, No. 7
Synthesis, Spectroscopic and Cytotoxic Studies of Biologically Active New
Schiff Bases Derived from p-Nitrobenzaldehyde
Amjid IQBAL,a Hamid Latif SIDDIQUI,*,a Chaudhary Muhammad ASHRAF,b
a
Mujahid Hussain BUKHARI,a and Chaudhary Muhammad AKRAM
a Institute of Chemistry, University of the Punjab; Lahore–54590, Pakistan: and b Department of Chemistry, Forman
Christian College (A Chartered University); Lahore–54600, Pakistan.
Received January 7, 2007; accepted April 3, 2007; published online May 1, 2007
Thirteen new Schiff bases derived from p-nitrobenzaldehyde were synthesized by condensation with the ap-
propriate amines. An unusual reduction of the p-nitrobenzaldehyde to the corresponding alcohol was also ob-
served in one of the reactions. The structures of the compounds were identified using spectroscopic techniques.
Cytotoxicity for the titled compounds was studied against Brine Shrimp, used as the test animal.
Key words p-nitrobenzadehyde; primary amine; unusual aldehyde reduction; biological activity
Schiff bases are potentially biologically active compounds agent. It is known that condensation of amines with alde-
and have been reported to possess antifungal,1,3) anti- hydes is favoured by a polar medium.15) The Schiff bases
cancer,4—7) anticonvulsant8) and diuretic9) activities. Schiff 2a—m were identified by IR, 1H-NMR and mass spec-
bases derived from various heterocycles were reported to troscopy. Compounds 2a—m showed in the IR spectra an ab-
possess cytotoxic activity.10) It is believed that the presence sorption band at 1618—1690 cmꢀ1, typical of the stretching
of a nitro group in the p-position appears to be an important vibrations of the double CꢁN bond. The absence of absorp-
condition for the development of bacteriostatic activity.11) Ni- tion in the regions of 1720 and 3400 cmꢀ1 indicates complete
troaromatic compounds are widely used in medicine, indus- transformation of the CꢁO and NH2 groups respectively.
try and agriculture.12) The anti-malarial activity of nitroaro- However, compound 2b showed absorption at 3404 cmꢀ1 due
matic compounds was attributed to the formation of reactive to NH/OH group (different tautomeric forms possible) in the
oxygen species during flavoenzyme catalyzed redox cycling pyrimidine nucleus of the Schiff base. While compounds 2e
reactions and/or oxyhemoglobin oxidation.13,14) With this en- and 2h show absorption at 3438 and 3443 indicating NH
vision in mind, we synthesized several new Schiff bases group and OH group respectively. Compound 2k indicates
derived from p-nitrobenzaldehyde by condensation with the absorption at 3466 showing one amino group unreacted. The
appropriate amines. An unusual reduction of the p-nitrobenz- 1H-NMR spectra of 2a—m contained multiplet signals due
aldehyde to the corresponding alcohol was also observed in to aromatic protons in the region d 7.17—8.31 ppm, and sin-
one of the reactions. The structures of the compounds were glets at d 8.15—8.91 ppm from the C–H protons of the
identified using spectroscopic techniques. Cytotoxicity for CHꢁN groups.
the titled compounds was studied against the brine shrimp,
While condensing 4-nitrobenzaldehyde with 2-amino-4,6-
used as the test animal. The mortality rate was observed to dimethylpyrimidine, an unusual reduction reaction occurred,
increase with increasing conc. of the sample.
in addition to the formation of a Schiff base (2c), p-nitroben-
zyl alcohol 3 was isolated from the product mixture in 30%
yield. It was identified by IR, NMR and FAB-MS spec-
Results and Discussion
The Schiff bases 2a—m were synthesized by the conden- troscopy. It is not clear how this compound was formed in
sation of p-nitrobenzaldehyde with various amines by reac- the absence of any reducing reagents in the reaction mixture,
tion in hot ethanol using molecular sieves as dehydrating but possibly a Cannizzaro-type reaction may have occurred.
However, no p-nitrobenzoic acid, the expected co-product for
a Cannizzaro reaction was detected. Possibly hydride transfer
from the hemi-aminal intermediate 4 to another molecule of
the aldehyde could have occurred as shown in Chart 1, but
none of the amide 5 expected as a by-product of this process
was detected. The proposed mechanistic aspects have not
been fully explored. However, further investigations on the
Chart 1. Probable Mechanism for the Formation of p-Nitrobenzyl Alcohol
∗ To whom correspondence should be addressed. e-mail: drhamidlatif@yahoo.com
© 2007 Pharmaceutical Society of Japan

July 2007
1071
tion from EtOH, the yield of the title Schiff base was calculated.
Table 1. Correlation between Concentration and LC50 Value
4ꢀ-Nitrobenzylidene-(2-chlorobenzyl)amine 2a The yield of the title
Schiff base was found to be 80%, mp 76—77 °C, HR-MS (FAB, MHꢂ):
Calcd for C14H11N2O2Cl 275.0587, Found 275.0592; IR (nmax, KBr, cmꢀ1):
1647, 1601, 1518, 1345; Anal. Calcd for C14H11N2O2Cl: C, 61.21; H, 4.04;
N, 10.19. Found: C, 61.16; H, 4.16; N, 9.93; 1H-NMR (400 MHz, CDCl3): d
8.48 (1H, s, CHꢁN), 8.27—7.17 (8H, m, ArH), 4.95 (2H, s, CH2N).
4ꢀ-Nitrobenzylidene-(6-hydroxy-2-methyl-5-nitrosopyrimidin-4-yl)-
amine (2b) Compound 2b was synthesized following the method
described above. The yield of the compound was found to be 60% and mp
115 °C; HR-MS (FAB, MHꢂ): Calcd for C12H9N5O4 288.0732, Found
288.0726; IR (nmax, DCM, cmꢀ1) 3404 (br), 1689, 1598, 1461, 1409, 1273,
1101; 1H-NMR (400 MHz, CDCl3): d 8.32 (1H, s, CHꢁN), 8.31—8.08 (4H,
m, ArH), 3.38 (3H, s, CH3).
LC50 of title compounds at various concentrations
Compounds
50 mg/ml
100 mg/ml
150 mg/ml
2a
2b
2c
2d
2e
2f
2g
2h
2i
1.30
1.20
2.45
1.80
2.35
2.15
2.50
2.50
2.45
2.30
1.30
2.35
2.10
1.25
1.10
2.40
1.65
2.35
2.05
2.45
2.50
2.45
2.25
1.20
2.30
2.00
1.20
1.05
2.30
1.50
2.30
2.00
2.35
2.45
2.40
2.10
1.10
2.20
2.00
4ꢀ-Nitrobenzylidene-(4,6-dimethylpyrimidin-2-yl)amine 2c Compound
(2c) was synthesized by the method described above. However, in the reac-
tion mixture, two spots were observed on TLC with Rf values 0.68 and 0.29
(after 3 elutions of the plate), unlike and otherwise different, from those of
the reactants, using the solvent system pet. ether/EtOAc 7 : 3. The two com-
ponents as Fr. 1 and Fr. 2 were separated by column chromatography in the
solvent system pet. ether/EtOAc 4 : 1. Fraction 1 was determined as the title
compound 2c with an Rf value 0.69 and Fr. 2 as 4-nitrobenzyl alcohol on the
basis of spectroscopic data. The title compound was oil and was obtained in
40% yield; HR-MS (FAB, MHꢂ): Calcd for C13H12N4O2 257.1038, Found
2j
2k
2l
2m
mechanism of this reaction are in progress.
Cytotoxic Activity. Test Animal Brine shrimp (Artemia
salina) was used as the test animal for the investigation of
cytotoxicity.
1
257.1035; IR (nmax, DCM, cmꢀ1): 1682, 1590, 1566, 1450, 1347; H-NMR
(400 MHz, CDCl3): d 8.15 (1H, s, CHꢁN), 8.12—7.62 (4H, m, ArH), 6.38
(1H, s, ArH), 2.25 (6H, s, 2ꢃCH3).
The yield of nitrobenzyl alcohol in Fr. 2 was 30% with mp 90 °C (lit.16)
Brine shrimp was kept at ambient temperature and salinity
of 30—35 ppm, a pH of 8.0—9.0 and strong aeration under a 91—92 °C) the molecular ion peak in the FAB-MS of Fr. 2 showed the MHꢂ
at m/z 153.0426 in agreement with the molecular formula C7H7NO3 (Calcd
continuous light regime. Subsequently, about one teaspoon of
brine shrimp eggs were added into the systems and approxi-
mately after 12 h hatching the phototropic nauplii were col-
153.0425); IR (nmax, DCM, cmꢀ1): 3519 (br), 1685, 1602, 1509, 1458, 1402,
1
1342; H-NMR (400 MHz, CDCl3): 8.16—7.59 (4H, m, ArH), 4.77 (2H, s,
CH2).
lected with a pipette from the lighted side and concentrated
in a small beaker and applied for testing.
4-Iodo-N-(4-nitrobenzylidene)aniline (2d) Yield of title compound
was found to be 83%, mp 204 °C. MS (Mꢂ): Calcd for C13H9IN2O2
351.9709, Found 352.0. IR (nmax, KBr, cmꢀ1); 1624, 1594, 1508, 1470,
1350. Elemental analysis Calcd: C, 44.34; H, 2.58; N, 7.96. Found C, 44.15;
H, 2.61; N, 7.90. 1H-NMR (400 MHz): 7.16 (2H, d, Jꢁ8.6 Hz), 7.79 (2H, d,
Jꢁ8.6 Hz), 8.18 (2H, d, Jꢁ8.7 Hz), 8.36 (2H, d, Jꢁ8.8 Hz), and 8.81 (1H, s).
N-(4-(4-Nitrobenzylideneamino)phenyl)acetamide (2e) Yield was
found to be 92%, mp 156 °C. MS (Mꢂ): Calcd for C15H13N3O3 283.282,
Found 283.1. IR (nmax, KBr, cmꢀ1): 3438, 1681, 1597, 1407, 1346. Elemen-
tal analysis Calcd: C, 63.60; H, 4.63; N, 14.83. Found C, 63.30; H, 4.69; N,
14.70. 1H-NMR (400 MHz): 3.31 (3H, s), 7.36 (2H, d, Jꢁ8.7 Hz), 7.70 (2H, d,
Jꢁ8.7 Hz), 8.16 (2H, d, Jꢁ8.7 Hz), 8.34 (2H, d, Jꢁ8.6 Hz), and 8.83 (1H, s).
4-Chloro-N-(4-nitrobenzylidene)aniline (2f) Yield was found to be
87%, mp 128 °C. MS (Mꢂ): Calcd for C13H9ClN2O2 260.0353, Found 260.1.
IR (nmax, KBr, cmꢀ1): 1628, 1598, 1516, 1483, 1343. Elemental analysis
Preparation of Test Sample For cytotoxicity study,
dimethyl sulfoxide (DMSO) was used as a solvent and mor-
tality was observed almost zero. Different concentrations
(150, 100, 50 mg/ml) of the test samples were prepared and
taken into the separated test tubes, so that each test tube con-
tained not more than 50 ml of DMSO. Now three brine shrimps
were transferred to each test tube using micro pipettes.
Counting of Nauplii The test tubes containing different
concentrations of test samples were observed and the number
of survived nauplii in each test tube was counted. From this
the percentage of lethality of brine shrimp nauplii was counted
at each concentration for each sample. An approximate linear
correlation was observed between the logarithm of concen-
tration and percentage of mortality while the values of LC50
were calculated using a simple PC program. Although there
was no mortality in the control group, the test samples shown
different mortality rate at different concentrations, which was
found to increase with increasing concentration of the sample.
Table 1 indicates that compounds 2a, 2b, 2d and 2k were
found to be more effective as compared to others.
1
Calcd: C, 59.90; H, 3.48; N, 10.75. Found C, 59.60; H, 3.69; N, 10.70. H-
NMR (400 MHz): 7.37 (2H, d, Jꢁ8.4 Hz), 7.51 (2H, d, Jꢁ8.4 Hz), 8.18 (2H,
d, Jꢁ8.8 Hz), 8.36 (2H, d, Jꢁ8.4 Hz), 8.82 (1H, s).
4-(4-Nitrobenzylideneamino)benzonitirle (2g) Yield was found to be
60%, mp 169 °C. MS (Mꢂ): Calcd for C14H9N3O2 251.0695, Found 251.1.
IR (nmax, KBr, cmꢀ1): 1629, 1595, 1489, 1412, 1340; Elemental analysis
1
Calcd: C, 66.93; H, 3.61; N, 16.73. Found C, 66.60; H, 3.69; N, 16.70; H-
NMR (400 MHz): 7.46 (2H, d, Jꢁ8.4 Hz), 7.92 (2H, d, Jꢁ8.4 Hz), 8.20 (2H,
d, Jꢁ8.4 Hz), 8.38 (2H, d, Jꢁ8.4 Hz), 8.81 (1H, s).
4-(4-Nitrobenzylideneamino)phenol (2h) Yield was found to be 65%,
mp 176 °C. MS (Mꢂ): Calcd for C13H10N2O3 242.0691, Found 242.1. IR
(nmax, KBr, cmꢀ1): 3443, 1624, 1596, 1509, 1440; Elemental analysis Calcd:
1
Experimental
C, 64.46; H, 4.16; N, 11.56. Found C, 64.60; H, 4.30; N, 11.70; H-NMR
General All the chemicals were obtained commercially from Lancaster (400 MHz): 6.83 (2H, d, Jꢁ1.6 Hz), 7.30 (2H, d, Jꢁ8.8 Hz), 8.13 (2H, d, Jꢁ
Research Chemicals. 1H-NMR spectra were recorded on a Bruker DPX-400 8.8 Hz), 8.33 (2H, d, Jꢁ8.3 Hz), and 8.80 (1H, s).
instrument at 400 MHz. Chemical shifts are reported in ppm referenced to
1-(4-Methoxyphenyl)-N-(4-nitrobenzylidene)methanamine (2i) Yield
the residual solvent signal. Mass spectra were recorded on a Jeol SX-102 was found to be 71%, mp 161 °C. MS (Mꢂ): Calcd for C15H14N2O3
instrument and IR spectra were recorded on a Perkin Elmer Paragon 1000 270.1004, Found 270.0. IR (nmax, KBr, cmꢀ1): 1639, 1608, 1411, 1343; Ele-
spectrometer. Elemental analysis was carried out using a Perkin-Elmer mental analysis Calcd: C, 66.66; H, 5.22; N, 10.36. Found C, 66.60; H, 5.30;
1
2400-CHN analyzer. Melting points were recorded on a Stuart Scientific- N, 10.70; H-NMR (400 MHz): 3.72 (3H, s), 4.76 (2H, s), 6.87 (2H, d, Jꢁ
SMP3 apparatus and are uncorrected.
8.5 Hz), 7.25 (2H, d, Jꢁ8.5 Hz), 8.01 (2H, d, Jꢁ8.8 Hz), 8.29 (2H, d, Jꢁ
General Procedure for the Synthesis of 2a—k p-Nitrobenzaldehyde 8.7 Hz), 8.62 (1H, s).
(1.0 mmol, 0.15 g) was added to respective primary amine (1.0 mmol) in
2,5-Dichloro-N-(4-nitrobenzylidene)aniline (2j) Yield was found to be
EtOH (absolute, 10 ml) in addition to molecular sieves and refluxed (oil bath 70%, mp 132 °C. MS (Mꢂ): Calcd for C13H8Cl2N2O2 293.9963, Found
at 90 °C) for 4 h under N2 (g). After filtration, evaporation and recrystalliza- 294.0. IR (nmax, KBr, cmꢀ1): 1627, 1599, 1520, 1468, 1380; Elemental

1072
Vol. 55, No. 7
analysis Calcd: C, 52.91; H, 2.73; N, 9.49. Found C, 52.60; H, 2.90; N, 9.70. hore and Loughborough University for financial support. We thank Mr. John
1H-NMR (400 MHz): 7.35 (1H, dd, Jꢁ2.3, 8.5 Hz), 7.51 (1H, d, Jꢁ2.3 Hz),
7.58 (1H, d, Jꢁ6.5 Hz), 8.20 (2H, d, Jꢁ8.7 Hz), 8.39 (2H, d, Jꢁ8.7 Hz),
8.80 (1H, s).
C. Kershaw for running mass spectra and Mr. J. Alastair Daley for elemental
analysis.
N3-(4-Nitrobenzylidene)pyridine-2,3-diamine (2k) Yield was found to References
be 80%, mp 220 °C. MS (Mꢂ): Calcd for C12H10N4O2 242.0804, Found
242.1. IR (nmax, KBr, cmꢀ1): 3466, 1618, 1593, 1508, 1472; Elemental
analysis: Calcd: C, 59.50; H, 4.16; N, 23.13. Found C, 59.40; H, 4.60; N,
23.70. 1H-NMR (400 MHz): 6.59 (1H, dd, Jꢁ4.9, 7.6 Hz), 7.89 (1H, dd,
Jꢁ1.4, 4.8 Hz), 8.32 (4H, q, Jꢁ8.8 Hz), 8.87 (1H, s).
1) Safwat H. M., Ragab F. A., Eid N. M., Abdel Gawad. M., Egyptian J.
Pharm. Sci., 29, 99—110 (1988).
2) Metri R., Yadawe M., Patil S. A., Orient. J. Chem., 12, 101—102
(1996).
3) Hossain M. E., Allam M. N., Begum J., Akbar M. A., Uddin M. N.,
Smith F. E., Hynes R. C., Inorg. Chim. Acta, 249, 207—213 (1996).
4) Kuz’min V. E., Artemenko A. G., Lozytska R. N., Fedtchouk A. S.,
Lozitsky V. P., Muratov E. N., Mescheriakov A. K., SAR and QSAR in
Environmental Research, 16, 219—230 (2005).
5) Hodnett E. M., Dunn W. J., J. Med. Chem., 13, 768—770 (1970).
6) Shingare M. S., Ingle D. B., J. Indian Chem. Soc., 53, 1036 (1976).
7) Jo Y. S., Hwahak Kwa Kongop Ui Chinbo, 12, 432—436 (1972).
8) Tewari S. S., Husain M. I., Srivastava G. C., J. Indian Chem. Soc., 58,
214—216 (1981).
1,2-Bis(4-nitrobenzylidene)hydrazine (2l) p-Nitrobenzaldehyde (2.0
mmol, 0.30 g) was added to hydrazine hydrate (1.0 mmol, 0.049 ml) in EtOH
(absolute, 10 ml) in addition to molecular sieves and stirred at room temper-
ature for 5 min under N2 (g). After filtration and recrystallization from EtOH,
the yield of title compound was found to be 89%, mp 178 °C. MS (Mꢂ):
Calcd for C14H10N4O4 298.2536, Found 298.0. IR (nmax, KBr, cmꢀ1): 1630,
1596, 1522, 1382. Elemental analysis Calcd: C, 56.38; H, 3.38; N, 18.78.
1
Found C, 56.15; H, 3.61; N, 18.90. H-NMR (400 MHz): 8.15 (2H, d, Jꢁ
8.7 Hz), 8.38 (2H, d, Jꢁ8.7 Hz), 8.86 (1H, s).
N4,N4ꢀ-Bis(4-nitrobenzylidene)biphenyl-4,4ꢀ-diamine (2m) p-Nitrobenz-
aldehyde (2.0 mmol, 0.30 g) was added to benzidine (1.0 mmol, 0.184 g) in
9) Mishra P., Gupta P. N., Shakya A. K., Shukla R., Srimal R. C., Indian
J. Physiol. Pharmacol., 39, 169—171 (1995).
EtOH (absolute, 10 ml) in addition to molecular sieves and stirred at room 10) Tarafder M. T., Kasbollah A., Saravan N., Crouse K. A., Ali A. M., Tin
temperature for 10 min under N2 (g). After filtration and recrystallization
from EtOH, the yield of title compound was found to be 90%, mp 250 °C;
MS (Mꢂ): Calcd for C26H18N4O4 450.1328, Found 450.1. IR (nmax, KBr,
cmꢀ1): 1628, 1597, 1515, 1341. Elemental analysis Calcd: C, 69.33; H,
O. K., J. Biochem., Mol. Biol. Biophys., 6, 85—91 (2002).
11) Ma Y., Fan Y., Wang D., Chen Y., Jinan J. D. X., Ziran Kexueban, 17,
292—294 (2003).
12) Purohit V., Basu A. K., Chem. Res. Toxicol., 13, 673—692 (2000).
4.03; N, 12.44. Found C, 69.15; H, 4.21; N, 12.90. 1H-NMR (400 MHz): 13) Vennerstrom L. J., Eaton J. W., J. Med. Chem. 31, 1269—1277 (1988).
7.48 (2H, d, Jꢁ8.1 Hz), 7.83 (2H, d, Jꢁ8.2 Hz), 8.21 (2H, d, Jꢁ8.4 Hz), 14) Docampo R., Chem. Biol. Interact. 73, 1—27 (1990).
8.38 (2H, d, Jꢁ8.3 Hz), 8.91 (1H, s).
15) Reichardt C., “Solvents and Solvent Effects in Organic Chemistry,”
2nd ed., Weinheim VCH, 1988.
Acknowledgements We greatly acknowledge the Higher Education 16) Kotsuki H., Ushio Y., Yoshimura N., Ochi M., Bull. Chem. Soc. Jpn.,
Commission of Pakistan, Islamabad, as well as University of the Punjab, La- 61, 2684—2686 (1988).