Synthesis, pharmacological screening, quantum chemical and in vitro permeability studies of N-Mannich bases of benzimidazoles through bovine cornea

Article abstract of DOI:10.1016/j.ejmech.2008.03.043

A novel series of N-Mannich bases of benzimidazole derivatives were synthesized and characterized by ¹H NMR, IR spectral studies and elemental analysis. The compounds were screened for analgesic and anti-inflammatory activity. 1-((Diethylamino)-methyl)-2-styryl benzimidazole 4 at 40 mg/kg was found to be equipotent to paracetamol. 1-((Piperidin-1-yl) methyl)-2-styryl-benzimidazole 6 at 40 mg/kg was found to be more potent than Diclofenac. Corneal permeability and quantum chemical calculations were performed to correlate the hydrogen bonding ability with permeability and activity. The energies of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) were correlated with pharmacological activity. The semi-empirical PM3 calculations (quantum chemical calculations) revealed that E_LUMO and energy gap ΔE were capable of accounting for the high in vitro bovine corneal permeability and activity of the compounds.

Full text of DOI:10.1016/j.ejmech.2008.03.043

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European Journal of Medicinal Chemistry 44 (2009) 2307e2312
http://www.elsevier.com/locate/ejmech
Laboratory note
Synthesis, pharmacological screening, quantum chemical
and in vitro permeability studies of N-Mannich bases of
benzimidazoles through bovine cornea
E. Philip Jesudason a,d,1,2, S.K. Sridhar b,d, E.J. Padma Malar c, P. Shanmugapandiyan d,1
,
Mohammed Inayathullah a,3, V. Arul a,4, D. Selvaraj a, R. Jayakumar a,
*
a Bio-Organic and Neurochemistry Laboratory, Central Leather Research Institute, Sardar Patel Road, Adyar, Chennai 600020, Tamil Nadu, India
b Pharmacy Department, Higher College of Technology, P.O. Box 74, Code: 133, Al-Khuwair, Muscat, Sultanate of Oman
c Department of Physical Chemistry, University of Madras, Guindy Campus, Chennai 600 025, Tamil Nadu, India
d Department of Pharmaceutical Chemistry, Vel’s College of Pharmacy, Pallavaram, Chennai 117, Tamil Nadu, India
Received 24 January 2008; received in revised form 21 March 2008; accepted 27 March 2008
Available online 11 April 2008
Abstract
1
A novel series of N-Mannich bases of benzimidazole derivatives were synthesized and characterized by H NMR, IR spectral studies and
elemental analysis. The compounds were screened for analgesic and anti-inflammatory activity. 1-((Diethylamino)-methyl)-2-styryl benzimid-
azole 4 at 40 mg/kg was found to be equipotent to paracetamol. 1-((Piperidin-1-yl) methyl)-2-styryl-benzimidazole 6 at 40 mg/kg was found to
be more potent than Diclofenac. Corneal permeability and quantum chemical calculations were performed to correlate the hydrogen bonding
ability with permeability and activity. The energies of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular
orbital (LUMO) were correlated with pharmacological activity. The semi-empirical PM3 calculations (quantum chemical calculations) revealed
that ELUMO and energy gap DE were capable of accounting for the high in vitro bovine corneal permeability and activity of the compounds.
Ó 2008 Elsevier Masson SAS. All rights reserved.
Keywords: Mannich base; Benzimidazole; Analgesic; Anti-inflammatory; Corneal permeability; Quantum chemical calculations
1. Introduction
in medicinal chemistry. Among the various compounds
developed as anti-inflammatory [1] and analgesic agents [2],
the 2-substituted benzimidazoles [3,4] and N-Mannich bases
of various heterocyclic compounds [5e8] were reported to
exhibit anti-inflammatory [9] and analgesic properties. The
aim of the present work is to incorporate both modules to the
same molecule, with an anticipation of enhanced drug activity.
As clinical efficacy of these kinds of molecules depends
upon tissue penetrations and retention, in vitro corneal perme-
ability studies were performed by measurement of transcor-
neal flux in the isolated bovine cornea. Isolated tissues
containing different endothelial and epithelial cell lines were
subjected to drug permeation studies [10e12]. The cornea is
one of the most widely used tissues for biological tissue
permeability studies [13]. The permeation of non-polar com-
pounds through cornea depends on their oil/water partition
The search for novel analgesic and anti-inflammatory agents
devoid of side effects, such as irritant reactions on gastric mu-
cosa, profound respiratory depression, nausea, constipation and
physical dependence, continues to be an active area of research
* Corresponding author. Present address: School of Medicine, Stanford Uni-
versity, Stanford, CA, USA. Tel.: þ91 44 24911386x324; fax: þ91 44
24911589.
E-mail address: karkuvi77@yahoo.co.uk (R. Jayakumar).
These authors equally contributed to this work.
1
2
Department of Comparative Biomedical Sciences, School of Veterinary
Medicine, Louisiana State University, Baton Rouge, LA 70803, USA.
3
Department of Neurology, David Geffen School of Medicine, University of
California, Los Angeles, USA.
4
Department of Pediatrics, University of Alberta, Edmonton, AB, Canada.
0223-5234/$ - see front matter Ó 2008 Elsevier Masson SAS. All rights reserved.
doi:10.1016/j.ejmech.2008.03.043

2308
E.P. Jesudason et al. / European Journal of Medicinal Chemistry 44 (2009) 2307e2312
coefficients [14]. For instance, the influence of the substituent
in a series of p-amino phenyl derivatives was correlated to
their transport through rabbit cornea [15].
IR spectra were recorded by dispersing the compounds in KBr
pellets on a Bomem FT-IR spectrophotometer M.B Serial II.
1H NMR spectra were recorded on a 300 MHz Bruker DPX
200. The H chemical shifts are reported as parts per million
downfield from tetramethyl silane (Me4Si). The purities of
1
Electronic and steric effects have also been shown to
control the pharmacological activities of drugs [16]. Quantum
chemical parameters in quantitative structureeactivity rela-
tionships (QSAR) are reported to yield promising results for
correlation of biological activity [17,18]. At the molecular
level, the reactivity of a molecule is dominated by the frontier
molecular orbitals (FMO), namely the highest occupied
molecular orbital (HOMO) and the lowest unoccupied molec-
ular orbital (LUMO). The effects of electron withdrawing or
donating substituents will be manifested in the HOMO and
LUMO energies and in the molecular orbital coefficients.
Consequently, these quantum chemical parameters can act as
good indicators in QSAR studies. The energy of the lowest
unoccupied molecular orbital (LUMO) was established as
a good parameter [19] for hydrogen bond donor capacity. It
is observed that the energy of LUMO, ELUMO, correlates
well with the experimental hydrogen bond acidity parameter
Sa2H [20,21]. It should be also noted that when a2H is
high, ELUMO is small.
In our present investigation, the benzimidazole derivatives
of N-Mannich bases were synthesized (Fig. 1) and their anal-
gesic and anti-inflammatory activities were studied. Corneal
permeability of the synthesized compounds was assessed by
measuring the transcorneal flux of the compounds through
isolated bovine cornea. The resulting permeability data are
compared with quantum chemical parameters, such as the en-
ergies of HOMO and LUMO [22]. Our study is important,
since it provides information on the physical, chemical, and
biological activities of N-Mannich bases of benzimidazoles.
the compounds were checked by TLC on SiO2 gel (HF254
,
200 mesh) coated glass plates using benzene:methanol
(9:1 v/v for 2 and 3) and chloroform:methanol (8:2 v/v for 1,
4, 5 and 6) and visualized by iodine vapors. Microanalyses
for C, H, and N were performed in a Heraeus CHN Rapid
Analyzer, Division of Catalysis and Kinetics, Department of
Chemistry, Indian Institute of Technology, Madras, India.
UV measurements were made in a Shimadzu 1601 UVeVis
Spectrophotometer. 1H NMR, IR and MS data were consistent
with the assigned structures.
3. Biological investigation
The synthesized compounds were evaluated for analgesic
and anti-inflammatory activities. Statistical analysis (student’s
t-test) was performed for the activities to ascertain their signif-
icance. The dose was fixed between the minimal effective dose
and maximal non-lethal dose. The test compounds were
administered in the form of a suspension (1% carboxy methyl
cellulose as vehicle).
3.1. Acute toxicity studies
Acute toxicity tests [23] were performed on the compounds
to determine LD50 values by Karber’s arithmetical method.
Each group consisted of six Wistar albino mice of either
sex. The synthesized compounds were administered at doses
of 100, 200, 400, 800 or 1000 mg/kg orally by gavage. The
animals were observed for 24 h for mortality. The data are pre-
sented in Table 1.
2. Chemistry
Melting points were determined in open capillary tubes on
a Thomas-Hoover melting point apparatus and are uncorrected.
3.2. Analgesic activity
Analgesic activity [23] was determined by the acetic acid-
induced writhing method using Wistar albino mice of either
NH2
NH2
N
R1 - COOH, NH3
R2H
R1
N
H
Table 1
Analgesic activity and LD50 of the synthesized compounds
HCHO
Compound
Dose (mg/kg)
% Protection
LD50 (mg/kg)
1
100
200
100
200
100
200
20
25.87**
31.4**
11.35*
43.8**
8.5*
>1000
N
2
>1000
>1000
175
R1
N
3
16.1*
CH2
R1 = H, CH3, -CH=CH-C6H5
R2
4
32.2**
47.49**
20.58**
27.45**
29.56**
43.80**
47.76
40
20
5
200
40
20
6
180
,
O
N
R2 = -N(CH3)2, -N(C2H5)2, -N(C6H5)2,
N
40
100
Paracetamol
e
Fig. 1. Protocol for the synthetic compounds.
* p < 0.05 and ** p < 0.001 compared to control.

E.P. Jesudason et al. / European Journal of Medicinal Chemistry 44 (2009) 2307e2312
2309
DQ
sex selected by random sampling techniques. A dose level of
100 mg/kg paracetamol (oral) served as the standard drug
for comparison. The test compounds were administered orally
at two doses by gavage 30 min prior to administration of the
writhing agent (0.6% v/v aqueous acetic acid e 1 mL/100 g).
The writhings produced in the animal were observed for
30 min and percentage protection was calculated for analgesic
activity. Results are presented in Table 1.
Papp
¼
DtAC0
where Q is the total amount permeated at time t; DQ/Dt (the
slope of the linear portion of the graph) is the steady flux of
the compound (1e8) to the receiver’s side (mg/min); A is the
corneal surface area (1 cm2) and C0 is the initial donor side
drug concentration C (mg/mL). The lag time of permeation
(tL) is obtained from the above plot of concentration versus
time (Figs. 2 and 3). This is the time required to establish
a steady concentration gradient within the membrane separat-
ing the donor from the receptor compartment [13]. The data
obtained are presented in Table 4.
3.3. Anti-inflammatory activity
Anti-inflammatory activity [24] was determined by the
formalin-induced paw edema method in Wistar albino rats
by using plethysmography. Diclofenac sodium at an oral
dose of 50 mg/kg served as the standard drug for comparison.
The test compounds were administered orally 30 min prior to
administration of formalin (0.1 mL of 1% w/v) in the plantar
region of the paw. The paw volumes were measured at 30,
60, 90 and 120 min after formalin administration. The results
are presented in Table 2.
4. Results and discussion
4.1. Pharmacological screening
The synthesized compounds were evaluated for analgesic
and anti-inflammatory effects against chemically induced
nociception [26] and formalin-induced acute paw edema
methods. The results of the evaluations for analgesic and anti-
inflammatory effects are shown in Tables 1 and 2, respectively.
The data indicate that the compounds exhibited dose dependent
analgesic properties. One of the compounds, 1-((diethylamino)-
methyl)-2-styryl-benzimidazole 4, was found to be equipotent
to paracetamol, at a dose of 40 mg/kg.
The decreases in paw volume noted after administration of
the compounds (1e9) indicate that these compounds possess
highly significant anti-inflammatory properties. Among the
compounds 1-((piperidino-1-yl)-methyl)-2-styryl-benzimid-
azole 6 was found to be more potent than Diclofenac, at
a dose of 40 mg/kg. According to previous reports, the anti-in-
flammatory activity of substituted benzimidazoles may be due
to 5-lipoxygenase [4] and/or due to inhibition of immigration
of leukocytes and the exudation of proteins into the site of in-
jury [27].
3.4. In vitro permeability studies
Bovine corneas were obtained within 1 h of sacrifice. In-
tegrity of the corneal tissue was checked by microscopic
observation. The eye was proptosed, a small transverse inci-
sion was made about 5 mm from the limbus, and the cornea
with the scleral ring was carefully excised. Forceps were
used to delicately remove first the lens and then the iris,
with the cornea being left as a transparent film. The fresh
cornea [13,25] was placed between the donor and receptor
cell of a side-by-side perfusion apparatus, which maintained
the corneal curvature. The donor contained 7 mL of a prede-
termined concentration of drug solution buffered by 0.01 M
methanolic phosphate buffer solution (pH 7). Samples of
1 mL were taken from the receptor side at 15 min intervals
for 3 h. The sample volume was immediately replaced with
an equal amount of 0.01 M methanolic phosphate buffer
solution, pre-equilibrated at 37 ꢀC. The amount of the drug
diffused was determined by measurement of its absorption
in a UVevis spectrophotometer.
The molecular orbital calculations revealed that ELUMO and
the energy gap DE are capable of accounting for the high
80
1
2
3
4
5
6
7
8
9
The apparent corneal permeability coefficient (Pappp cm/s)
was determined according to the following formula:
70
60
50
40
30
20
10
0
Table 2
Anti-inflammatory activity (formalin-induced paw edema method)
Compound
Dose (mg/kg)
% Reduction of edema
30 min
60 min
90 min
120 min
1
200
200
200
40
48
28
32
20
52
48
48
51
59
54
50
59
56
65
64
63
60
51
74
59
64
53
61
56
56
70
62
65
2
3
4
0
50
100
150
200
5
40
40
Time (min)
6
Diclofenac
50
Fig. 2. Cumulative release of the synthesized compounds across bovine
cornea.
Significance level ¼ p < 0.001 compared to control.

2310
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E.P. Jesudason et al. / European Journal of Medicinal Chemistry 44 (2009) 2307e2312
observed that the HOMO energy is higher in the styryl deriv-
atives. Similar results were observed using the semi-empirical
AM1 method.
90
80
70
60
50
40
30
20
10
0
According to the FMO concept [22], the HOMO and
LUMO of a molecule play important roles in intermolecular
interactions. Extending the concept to binding in druge
receptor systems, the major contribution to binding involves
the interaction between the HOMO of the drug with the
LUMO of the receptor and that between LUMO of the drug
with the HOMO of the receptor. The extents of these stabiliz-
ing interactions are inversely related to the energy gap be-
tween the interacting orbitals. Higher HOMO energy and
lower LUMO energy in the drug molecule result in larger
stabilizing interactions and, hence, binding with the receptor.
It is remarkable that compound 6, having the lowest energy
gap of DE of 7.776 eV, exhibits the highest anti-inflammatory
activity.
Paracetamol
Diclofenac
0
50
100
Time (min)
150
200
Fig. 3. Cumulative amount of standard drugs permeated through isolated bo-
vine cornea.
Our investigation revealed that the analgesic and anti-
inflammatory activities of benzimidazole derivatives are related
to different substituent effects. Electron withdrawing substitu-
ents increase the activity. According to the observed influence
of HOMO orbitals on the analgesic and anti-inflammatory
activities, it can be concluded that the receptor sites seem to
have an electron accepting property.
permeability and pharmacological activity of the N-Mannich
bases of 2-styryl-benzimidazole derivatives.
4.2. Quantum chemical analyses
The quantum chemical parameters of the synthesized
compounds (1e9) were determined using semi-empirical
PM3 calculations. Results are summarized in Table 3. ELUMO
is significantly low (ꢁ0.71 to ꢁ0.83 eV) in the 2-styryl-benz-
imidazole derivatives (4, 5, 6 and 9), while in the remaining
derivatives ELUMO is high in the range ꢁ0.15 to ꢁ0.05 eV.
The theoretical results predict that the hydrogen bond donor
ability is highest in 1-morpholino-methyl-2-styryl-benzimid-
azole 5, which has the lowest ELUMO of ꢁ0.83 eV. The 2-
styryl-benzimidazoles (4, 5, and 6), having low ELUMO values,
show high permeability. On the other hand, the derivatives of
N-Mannich bases of benzimidazole, which have high ELUMO
values, show low permeability.
The relative permeability within the 2-styryl derivatives and
non-styryl derivatives could not be predicted with precision
due to the different factors operating in the experimental
systems. However, the present study clearly indicates that it
is able to explain the high permeability observed in the com-
pounds (4, 5 and 6). The presence of a hydrophobic phenyl
nucleus in these derivatives lowers ELUMO due to the elec-
tronic effects originating from the p-conjugation. We also
4.3. In vitro permeability studies using isolated
bovine corneas
The efficacies of the compounds (1e9) for corneal penetra-
tion were assessed by measuring the transcorneal flux (Fig. 1)
of the drug through isolated bovine cornea. Results indicate
that among the compounds, 4 exhibits maximum permeability
with a permeability coefficient of 17.44 ꢂ 10ꢁ2 cm/s and 2
exhibits the least permeability, with a permeability coefficient
of 1.92 ꢂ 10ꢁ2 cm/s. Benzimidazole 7, when compared with
styryl benzimidazole 9, shows high permeability (permeability
coefficients of 9.21 ꢂ 10ꢁ2 and 3.03 ꢂ 10ꢁ2 cm/s, respec-
tively). No significant differences were observed between the
permeability coefficient of 2-methyl benzimidazole
8
(6.56 ꢂ 10ꢁ2 cm/s) and that of 1-diphenyl amino-methyl-2-
methyl benzimidazole 3 (6.83 ꢂ 10ꢁ2 cm/s). From the perme-
ability data, it can be concluded that when an N-Mannich base
was incorporated with styryl benzimidazole, there was a rapid
increase in the permeability coefficient (Table 4). The lag
Table 3
Quantum chemical parameters of the synthesized compounds
Compound
EHOMO (eV)
ELUMO (eV)
DE
Molecular weight
Molar volume (A0)3
1-((Dimethylamino)-methyl)-benzimidazole 1
1-((Diethylamino)-methyl)-benzimidazole 2
1-((Diphenylamino)-methyl)-2-methyl-benzimidazole 3
1-((Diethylamino)-methyl)-2-styryl-benzimidazole 4
1-((Morpholino)-methyl)-2-styryl-benzimidazole 5
1-((Piperidin-1yl)-methyl)-2-styryl-benzimidazole 6
Benzimidazole 7
ꢁ8.897
ꢁ8.869
ꢁ8.680
ꢁ8.626
ꢁ8.656
ꢁ8.482
ꢁ8.889
ꢁ8.822
ꢁ8.593
ꢁ0.11
þ8.787
þ8.780
þ8.534
þ7.828
þ7.827
þ7.776
þ8.819
þ8.768
þ7.817
175.2
203.3
313.4
305.4
333.4
317.4
118.1
132.2
220.3
196.1
236.0
342.0
344.5
361.4
355.8
112.0
144.5
212.6
ꢁ0.089
ꢁ0.146
ꢁ0.798
ꢁ0.829
ꢁ0.706
ꢁ0.070
ꢁ0.054
ꢁ0.776
2-(Methyl)-benzimidazole 8
2-(Styryl)-benzimidazole 9

E.P. Jesudason et al. / European Journal of Medicinal Chemistry 44 (2009) 2307e2312
2311
Table 4
Permeability coefficients and lag times (tL) of N-Mannich bases of benzimid-
azole and standard drugs Diclofenac and paracetamol
5.1.3. 1-((Diphenylamino) methyl)-2-methyl-
benzimidazole 3
Yield ¼ 72%, m.p 165e167 ꢀC, Rf ¼ 0.47. 1H NMR
(CDCl3) d: 6.84e7.45 (m, 4H; 4,5,6,7H), 6.55e6.84 (m,
10H; AreH), 3.16e3.74 (s, 2H; eCH2e), 2.48e2.81 (s, 3H;
2-CH3). IR (KBr) cmꢁ1: 3041 (Ar CeH), 1457, 1450 (Aliph
CeH), 1395 (Ar CeN), 1319 (Aliph CeN). Anal. Calcd for
C21H19N3: C, 80.50; H, 6.07; N, 13.43. Found: C, 80.56; H,
6.16; N, 13.21. Mþ 313, 252, 129, 117, 105, 91, 77.
Compound
Papp ꢂ 10ꢁ2 tL
(cm/s)
(min)
1-((Dimethylamino)-methyl)-benzimidazole 1
1-((Diethylamino)-methyl)-benzimidazole 2
5.29
1.92
15.31
16.79
23.49
4.90
1-((Diphenylamino)-methyl)-2-methyl-benzimidazole 3 6.83
1-((Diethylamino)-methyl)-2-styryl-benzimidazole 4
1-((Morpholino)-methyl) 2-styryl-benzimidazole 5
1-((Piperidin-1yl)-methyl)-2-styryl-benzimidazole 6
Benzimidazole 7
17.44
8.88
16.08
9.21
6.56
3.03
23.1
21.3
7.33
4.51
18.81
11.68
9.57
2-(Methyl)-benzimidazole 8
2-(Styryl)-benzimidazole 9
5.1.4. 1-((Diethylamino) methyl)-2-styryl-benzimidazole 4
Yield ¼ 81%, m.p 181e183 ꢀC, Rf ¼ 0.65. 1H NMR
(CDCl3) d: 7.07e8.10 (m, 9H; AreH), 6.38e6.69 (d, 2H;
vinyl-H), 3.59e3.86 (s, 2H; eCH2e), 2.84e3.11 (q, 4H;
e[CH2]2), 0.91e1.57 (t, 6H; e[CH3]2). IR (KBr) cmꢁ1: 3102
(Ar CeH), 3022 (Vinyl CeH str), 1682 (C]C), 1448 (Aliph
CeH), 1395 (Ar CeN), 1203, 1159 (Aliph CeN), 979 (Al-
kene CeH). Anal. Calcd for C20H23N3: C, 78.68; H, 7.54;
N, 13.77. Found: C, 78.07; H, 7.65; N, 13.62. Mþ 305, 240,
129, 117, 105, 91, 77.
Paracetamol 10
Diclofenac 11
1.55
3.36
Papp ¼ permeability coefficient, tL ¼ lag time.
times of the compounds (1e11) are inversely related to the
permeability coefficients. The permeability coefficients of
the standard drugs paracetmol and Diclofenac are shown in
Fig. 3. The present permeability data on the compounds stud-
ied do not correlate with the molecular size given by molecular
weight and molar volume (Table 3).
5.1.5. 1-((Morpholino) methyl)-2-styryl-benzimidazole 5
Yield ¼ 82%, m.p 131e133 ꢀC, Rf ¼ 0.46. 1H NMR
(CDCl3), d: 7.04e6.75 (m, 9H; AreH), 4.45e4.83 (s, 2H; e
CH2e), 3.60e4.02 (t, 4H; 200,600H), 2.85e3.56 (t, 4H;
300,500H). IR (KBr) cmꢁ1: 3080 (Ar CeH), 3027 (Vinyl Ce
H), 1642 (C]C), 1496, 1448 (Aliph CeH), 1389, 1374 (Ar
CeN), 1102, 1075 (Aliph CeN), 976, 963 (Alkene CeH),
776, 732, 718 (Ar CeH). Anal. Calcd for C20H21N3O: C,
75.22; H, 6.58; N, 13.17. Found: C, 78.98; H, 7.74; N,
12.88. Mþ 319, 240, 129, 117, 105, 91, 77.
5. Experimental protocols
5.1. General procedure for the synthesis of N-Mannich
bases of benzimidazole
Formaldehyde (0.05 mol) was added slowly to 0.05 mol of
benzimidazole/2-substituted benzimidazole and 0.05 mol of
secondary amine (dimethyl amine, diethyl amine, diphenyl-
amine, piperidine and morpholine) in 15 mL of ethanol, with
continuous stirring for 45 min, and refrigerated overnight.
The product was filtered, recrystallized using absolute alcohol,
and vacuum dried.
5.1.6. 1-((Piperidin-1-yl) methyl)-2-styryl-benzimidazole 6
Yield ¼ 78%, m.p 142e144 ꢀC, Rf ¼ 0.71. 1H NMR
(CDCl3) d: 7.01e8.12 (m, 9H; AreH), 6.35e6.60 (d, 2H;
vinyl-H), 4.50e4.91 (s, 2H; eCH2e), 2.81e3.30 (t, 4H; 200,
600H), 1.37e1.93 (m, 6H; 300,400,500H). IR (KBr) cmꢁ1: 3402
(Ar CeH), 2948 (Vinyl CeH), 1687 (C]C), 1448 (Aliph
CeH), 1390 (Ar CeN), 1238, 1027 (Aliph CeN), 980, 971
(Alkene CeH). Anal. Calcd for C21H23N3: C, 79.48; H,
7.25; N, 13.26. Found: C, 75.16; H, 7.08; N, 12.92. Mþ 317,
252, 129, 117, 105, 91, 77.
Microanalytical CHN results were within ꢃ0.4% of theo-
retical values.
5.1.1. 1-((Dimethylamino)-methyl)-benzimidazole 1
Yield ¼ 78%, m.p 156e158 ꢀC, Rf ¼ 0.78. 1H NMR
(CDCl3) d: 7.26e8.06 (m, 4H; 4,5,6,7H), 5.17e5.27 (s, 1H;
2H), 4.86e5.03 (s, 2H; eCH2e), 2.24e2.42 (s, 6H; e
[CH3]2). IR (KBr) cmꢁ1: 3115 (Ar CeH), 1587, 1496 (Aliph
CeH), 1364, 1346 (Ar CeN), 1244, 1202 (Aliph CeN). Anal.
Calcd for C10H13N3: C, 68.57; H, 7.43; N, 24.01. Found: C,
68.04; H, 7.84; N, 24.20. Mþ 175, 129, 117, 105, 91.
5.2. Quantum chemical analyses
5.1.2. 1-((Diethylamino)-methyl)-benzimidazole 2
Quantum chemical computations were performed for com-
pounds 1e9 by all valence electron semi-empirical molecular
orbital method PM3 [28,29], using MOPAC 2000 software.
The molecules were subjected to complete structural optimiza-
tion using the PRECISE option and the energy minimization
was carried out until the gradient norm dropped to 0.05 or
lower. Molar volume was computed at the PM3 optimized
geometry using MOLDRAW software (release 1.0, version
E). The data are presented in Table 3.
Yield ¼ 77%, m.p 122e124 ꢀC, Rf ¼ 0.53. 1H NMR
(CDCl3) d: 7.24e8.23 (m, 4H; 4,5,6,7H), 5.88e6.64 (s, 1H;
2H), 4.87e5.04 (s, 2H; eCH2e), 2.49e2.77 (q, 4H;
e[CH2]2), 0.80e1.45 (t, 6H; e[CH3]2). IR (KBr) cmꢁ1: 3100
(Ar CeH), 1459 (Aliph CeH), 1362, 1326 (Ar CeN), 1028
(Aliph CeN). Anal. Calcd for C12H17N3: C, 69.42; H, 8.81;
N, 21.77. Found: C, 70.31; H, 8.51; N, 20.27. Mþ 193, 129,
117, 105, 91.

2312
E.P. Jesudason et al. / European Journal of Medicinal Chemistry 44 (2009) 2307e2312
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