Synthesis of a novel barbiturate from 1-chloro-2,4-dinitrobenzene as an anticonvulsant agent

Article abstract of DOI:10.1007/s00044-007-9072-1

A new barbiturate has been synthesized from the ethanolic solution of 1-chloro-2,4-dinitrobenzene, barbituric acid, and triethylamine. The structure of the isolated molecule has been confirmed by ultraviolet (UV)-visible (VIS), infrared (IR), proton magnetic resonance (PMR), ¹³ C nuclear magnetic resonance (NMR), correlation spectroscopy (COSY) and mass spectrometry (MS) spectral studies. Elemental analysis and other qualitative tests have also been carried out to elucidate the proposed structure. The anticonvulsant activity of the synthesized molecule was tested by the maximal electro shock method. Albino rats of either sex weighing 150-200 g were used for the study. The drug was given 1h before the induction of maximal electro shock test. The different stages of convulsions such as tonic flexor, tonic extensor, clonus convulsion, stupor, and recovery/death were examined. Reduction in the extensor phase of convulsion was noted for the synthesized barbiturate.

Full text of DOI:10.1007/s00044-007-9072-1

MEDICINAL
CHEMISTRY
RESEARCH
Med Chem Res (2008) 17:369–373
DOI 10.1007/s00044-007-9072-1
ORIGINAL RESEARCH
Synthesis of a novel barbiturate from 1-chloro-2,4-
dinitrobenzene as an anticonvulsant agent
D. Kalaivani Æ R. Malarvizhi Æ R. Subbalakshmi
Received: 16 November 2007 / Accepted: 19 November 2007 / Published online: 8 January 2008
¨
Ó Birkhauser Boston 2008
Abstract A new barbiturate has been synthesized from the ethanolic solution of 1-
chloro-2,4-dinitrobenzene, barbituric acid, and triethylamine. The structure of the
isolated molecule has been confirmed by ultraviolet (UV)-visible (VIS), infrared (IR),
proton magnetic resonance (PMR), 13 C nuclear magnetic resonance (NMR), corre-
lation spectroscopy (COSY) and mass spectrometry (MS) spectral studies. Elemental
analysis and other qualitative tests have also been carried out to elucidate the proposed
structure. The anticonvulsant activity of the synthesized molecule was tested by the
maximal electro shock method. Albino rats of either sex weighing 150–200 g were
used for the study. The drug was given 1h before the induction of maximal electro
shock test. The different stages of convulsions such as tonic flexor, tonic extensor,
clonus convulsion, stupor, and recovery/death were examined. Reduction in the
extensor phase of convulsion was noted for the synthesized barbiturate.
Keywords Barbiturate ꢀ Carbanionic sigma complex ꢀ Anticonvulsant ꢀ
1-Chloro-2,4-dinitrobenzene
Introduction
Barbiturates are drugs that act as sedative–hypnotic agents. The short-acting
barbiturates such as thiopental are used as intravenous anesthetics. The long-acting
barbiturates such as phenobarbital are anticonvulsant agents, and are used for the
suppression of anxiety, the induction of sleep, and the control of seizures (Nogrady,
1988; Ashutoshkar 1993; Hardman and Limbird, 2001; Yadav 2004; Nadkarni
et al., 2005; Jain et al., 2006). Epilepsy affects approximately 1% of the world’s
D. Kalaivani (&) ꢀ R. Malarvizhi ꢀ R. Subbalakshmi
Post Graduate and Research Department of Chemistry, Seethalakshmi Ramaswami College,
Tiruchirappalli 620 002, Tamil Nadu, India
e-mail: kalaivbalaj@yahoo.co.in

370
Med Chem Res (2008) 17:369–373
population and many of the marketed anticonvulsant drugs have profound side
effects (Huseyin et al., 1998; Srivastava et al., 2000; Dipiro et al., 2002; Gitto et al.,
2006; Rana et al., 2007). Hence it is necessary to search for safer and more effective
new antiepileptic drugs. A number of stable crystalline adducts have been reported
from the electron-deficient nitroaromatics and b-diketones (Terrier 1982; Gnana-
doss and Kalaivani 1985; Gnanadoss and Kalaivani 1985). As barbituric acid
contains an active methylene group like the b-diketones, an attempt has now been
made to prepare a crystalline carbanionic sigma adduct from it.
Experimental section
Analytic-grade 1-chloro-2,4-dinitrobenzene (DNCB) and barbituric acid (BBA)
were used as supplied. Triethylamine (NEt3) was refluxed over small quantities of
phenyl isocyanate and distilled (Saur, 1963). DNCB (0.01 mol) in absolute ethanol
was mixed with 0.01 mol barbituric acid in absolute ethanol. Triethylamine (0.02
mol) was then added and the mixture was shaken well for 5–6 h. The solution was
filtered and kept for 48 hours. On standing, maroon red crystals come out of the
solution. The crystals were powdered well and washed with copious amount of
ethanol and dry ether and recrystallized from absolute alcohol (yield of pure crystals
60%, m.p. 535–537 K, solubility in H2O 4 g/dm3 at 298K).
The visible data were obtained on a Perkin–Elmer Lambda 15 UV/VIS
spectrometer. The IR spectra were recorded using a Perkin–Elmer spectrum RXI
infrared spectrophotometer as KBr pellets. The NMR spectra were obtained from a
Bruker DRX–300 spectrometer with deuterated dimethyl-sulphoxide (DMSO) d6 as
the solvent and tetramethyl silane (TMS) as an internal reference. The fast atom
bombardment (FAB) mass spectra were recorded on a JEOL SX 102/DA–6000 mass
spectrometer. kmax of barbiturate in ethanol -420 nm. IR (DNCB) -1545 cm-1 (-
NO2 asym.str.), 1351 cm-1 (-NO2 sym.str.), 732 cm-1 (C-Cl str.), IR (BBA) -1716
cm-1 (C=O str.), 3479 cm-1, 3529 cm-1 (N-H str.). IR (barbiturate) -1516 cm-1 (-
NO2 asym.str.) 1343 cm-1 (-NO2 sym. str.), 1712 cm-1 (C=O str.), *1600 cm-1
1
(C=C str.), 2700–3400 cm-1 (N-H str.) H1 NMR (DNCB) -d 8.76 (s, 1H, ring
proton of nitro moiety), d8.46 (d, J = 4Hz , 1H, adjacent ring proton of nitro moiety), d
1
7.92 (d, J = 4Hz , 1H, adjacent ring proton of nitro moiety). H1 NMR (BBA) -d
11.09 (s, 2H, N–H protons), d 3.39 (s, 2H, -CH2 protons). 1H1 NMR (barbiturate) -d
9.66 (s, 2H, N–H protons), d 8.36 (s, 1H, ring proton of nitro moiety), d 8.20 (m, 2H,
adþjacent ring protons of nitro moiety), d 1.50 [t, J = 8Hz , 9H, -CH3 of
þ
HN(CH2CH3)3], d 3.08 [q, J = 4Hz, 5Hz, 6H, -CH2 of HN(CH2CH3)3]. CHN analysis
of barbiturate – found (calculated) C48.83 (48.60), H4.87 (5.31), N 18.08 (17.72).
Results and discussion
Although a number of trinitro aromatics gave a pasty mass with barbituric acid, the
ethanolic solution of 1-chloro-2,4-dinitrobenzene and barbituric acid in the presence
of excess triethylamine yielded a crystalline product. The isolated barbiturate is
colored because of charge delocalization. Qualitative tests (Vogel, 1978) on the

Med Chem Res (2008) 17:369–373
371
Scheme 1 Synthetic route for the formation of the barbiturate

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Table 1 Anticonvulsant activity of barbiturate against maximal electro-shock-induced convulsion in
albino rats
S. no. Treatment
Time (s) in various phases of convulsion
Flexor Extensor Clonus Stupor
Recovery/
death
1.
2.
3.
4.
Control (saline)
3.24 0.09 13.3 0.25 9.24 0.21 137 8.24 Recovered
Barbiturate (25 mg/kg) 4.20 0.23 13.2 0.51 7.20 0.31 105.5 6.8 Recovered
Barbiturate (50 mg/kg) 3.10 0.05 6.5 0.65 5.10 0.61 82.2 6.1 Recovered
Barbiturate (100 mg/
kg)
2.90 0.05 2.0 0.0 5.60 0.46 85.7 6.9 Recovered
5.
Phenytoin (25 mg/kg) 2.66 0.55 0.0 0.12 4.60 0.38 62.1 3.3 Recovered
synthesized barbiturate revealed the presence of the nitrogen atom, nitro groups, and
the absence of chlorine. In DNCB, a strong sharp absorption band characteristic of
C–Cl stretching mode was observed at 732 cm-1, which is absent in the isolated
barbiturate, clearly shows that chlorine is removed from DNCB during the
formation of barbiturate. Since, upon the formation of the barbiturate, the aromatic
nitro group is converted to one bearing partial negative charge, the asymmetric and
symmetric absorption frequencies are expected to decrease (Terrier, 1982;
Gnanadoss and Kalaivani, 1985; Kalaivani et al., 2005). This was observed in the
present study also. The broad band observed at 2700–3400 cm-1 in barbiturate is
characteristic of the triethyl ammonium cation (Silverstein and Webster, 2004). In
the synthesized barbiturate a C=C stretching band appears at *1600 cm-1 as a
strong sharp band instead of at *1640 cm-1. This may be due to stretching of the
C=C bond during delocalization. In barbituric acid the N–H proton signal appears at
d 11.09. During the formation of the barbiturate, the negative charge is delocalized
over a large area up to the keto functions nearer the N–H groups. Hence the N–H
protons are shielded to some extent and show a shift towards high field. The
adjacent ring protons of the nitro moiety appear as double doublet in DNCB.
whereas in barbiturate it became a multiplet centered at d 2.33, supporting the
delocalization of the negative charge. The quartet at d 3.08 and triplet at d 1.50
correspond to the –CH2 and -CH3 of the cation moiety, respectively. In COSY,
1H-1H coupling was noticed between the ring protons of the nitro moiety and ethyl
group protons in the cation moiety. The 13C spectrum of barbituric acid exhibits two
signals at d 151.7 and d 167.8 due to the keto group carbon atoms. Six signals were
observed in the 13C spectrum of DNCB. The carbon atom bearing the Cl appears at
d 133.6. The synthesized barbiturate exhibits 11 signals in the 13C spectrum. The
absorption peaks at d 8.6 and d 45.8 are due to the carbon environments of the -
CH3 and -CH2 groups, respectively, of the triethylammonium ion. The absorption
peak at d 86.6 is not observed in DNCB and barbituric acid but only in the
barbiturate, possibly due to the newly formed carbon environment (C=C) (Kemp,
1991). In the FABMS spectrum, the base peak corresponds to triethylammonium
cation (m/z = 102). Based on the spectral observations, the barbiturate may have
structure 1 shown in Scheme 1.

Med Chem Res (2008) 17:369–373
373
The synthesized barbiturate was screened for anticonvulsant activity (Kulkarini,
1999). The barbiturate was given 1 h before the induction of the maximal electro shock
test (150 mA, 0.2 s). The current was applied to the animals using corneal electrodes.
The substance showed activity even at a low concentration of 50 mg/kg (Table 1).
The LD50 value of the synthesized barbiturate was calculated as per OECD
guidelines (revised draft 423). The barbiturate falls under class 3 (LD50 [1000 mg/
kg). The animals did not show any signs of acute toxicity or behavioral changes.
The synthesized barbiturate may be a potent drug in future due to its extraordinary
stability, low toxicity, high solubility in water, and easy method of preparation.
Acknowledgement The authors are very grateful to the Central Drug Research Institute, Lucknow for
the spectral data.
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