Separation and identification of the mixture of 2-(3,4-dimethoxyphenyl)-1-n-propyl or (4-chlorobenzyl)-5 and (6)-1H-benzimidazolecarbonitriles

Full text of DOI:10.1002/mrc.4463

Letter - spectral assignment
Received: 11 April 2016
Revised: 13 May 2016
Accepted: 19 May 2016
Published online in Wiley Online Library
(wileyonlinelibrary.com) DOI 10.1002/mrc.4463
Separation and identification of the mixture of
2-(3,4-dimethoxyphenyl)-1-n-propyl or
(4-chlorobenzyl)-5 and (6)-
1H-benzimidazolecarbonitriles
Fatima Doganc, Mehmet Alp and Hakan Goker*
apparatus. All NMR experiments were carried out by using
VARIAN (AGILENT) MERCURY 400 MHz (Varian, Palo Alto, CA)
Introduction
Benzimidazoles are very useful intermediates/subunits for the de-
velopment of molecules of pharmaceutical or biological interest.
Appropriately substituted benzimidazole derivatives have found di-
verse therapeutic applications such as antimicrobial, antiprotozoal,
antibacterial, antiallergic, HIV inhibitors, antiviral, antiparasitic, anti-
tumoral, antihypertensive, cardiotonic, antiulcer, anti-inflammatory,
analgesic, antioxidant, antidiabetic, diuretic, androgen receptor an-
tagonist, anticonvulsant and anticoagulant.[1–3] Optimization of
benzimidazole-based structures has resulted in various drugs such
as Mebendazole as antihelmentic, Clemizole and Astemizole as an-
tihistaminic, Droperidol as antipsychotic, Omeprazole and
Lansoprazole as antiulcer, Bendamustin as anti-tumoral and
Candesartan as antihypertensive medications.
Benzimidazole with unsubstituted NH groups exhibit fast
prototropic tautomerism which leads to equilibrium mixtures of
asymmetrically substituted compounds. The 1,3-tautomerism asso-
ciated with benzimidazoles is a very popular topic, and the exis-
tence of this tautomerism has been proved by several
approaches, including NMR spectroscopy.[4] This 1,3-migration is
not found when the imidazole hydrogen is replaced by other sub-
stituents such as an alkyl group or under special circumstances
where the hydrogen migration is affected by inter- and/or intramo-
lecular hydrogen bonding.[5]
at
a
proton resonance frequency of 400.1779 and
100.6243 MHz for carbon, equipped with a 5-mm broadband-
observed probe head. The NMR spectrum optimization was
conducted by using Agilent VnmrJ version 3.2 revision A soft-
ware and all parameters were set in it. The samples (6–20 mg)
were prepared in 0.7 ml of DMSO-d6, CDCl3 and CD2Cl2. The
1H NMR experiments were traditionally carried out with TMS
as an internal standart and its chemical shift set at δ = 0
ppm, at room temperature (Only for compound 4a, 40 °C).
Pulse programme for 1H spectra was relax. delay 1 s; pulse
45.0°; 8 or 16 repetitions; acquisition time 2.559 s; width
6402.0 Hz. Pulse programme for 13C spectra was relax. delay
1 s; pulse 45.0°; 2000 repetitions; acquisition time 1.304 s;
width 21 141.6 Hz. The DEPT pulse programme for carbon
was relax. delay 1 s; pulse 90.0°; acquisition time 1.304 s; width
21 141.6 Hz; 64 repetitions. The HMBC pulse programme for
proton-carbon was relax. delay 1 s; acquisition time 0.15 s;
width 6402.0 Hz; 2D width 21 633.3 Hz; 8 repetitions; 2 × 256
increments. The HSQC pulse programme for proton-carbon
was relax. delay 1 s; acquisition time 0.15 s; width 6402.0 Hz;
2D width 17 105.0 Hz; 8 repetitions; 2 × 256 increments. The
NOESY pulse programme for proton was relax. delay 1 s; ac-
quisition time 0.15 s; width 4046.9 Hz; 2D width 4046.9 Hz; 8
repetitions; 2 × 200 increments. The COSY pulse programme
for proton was relax. delay 1 s; acquisition time 0.15 s; width
4046.9 Hz; 2D width 4046.9 Hz; 4 repetitions; 128 increments.
The LC/MS spectra were taken on a Waters Micromass ZQ
connected with Waters Alliance HPLC (Waters Corporation,
Milford, MA), using ESI(+) method, with C-18 column (XTerra®,
4.6 × 250 mm, 5 μm). The analytical condition of mass spec-
trometry was as follows: capillary voltage: 3.11 kV, cone volt-
age: 29 V, source temperature: 100 °C: desolvation
temperature: 300 °C. For compounds 4a, 4b and 5a, 5b, the
In our previous studies,[6,7] we have also reported synthesis of
some regioisomers of benzimidazoles. At that old time, their struc-
tural elucidation has been achieved by obtaining only one
regiosomer with selective synthesis. Similarly, Willis and co-
workers[8] reported a regio-controlled synthesis for 1-benzyl-2-phe-
nyl-1H-benzimidazole-6-carbonitrile. As a further contribution to
this field, now we report the synthesis of a series of 2-phenyl-5(6)-
cyanosubstituted-1H-benzimidazoles containing a propyl and 4-
chlorobenzyl groups on the N1-position and their tautomeric be-
haviours. After separating the regiosomers from each others, for
their structural elucidation, Nuclear Overhauser Effect Spectroscopy
(NOESY) 2D experiments were used.
*
Correspondence to: Hakan Goke, Department of Pharmaceutical Chemistry,
Faculty of Pharmacy, Ankara University, 06100 Tandogan, Ankara, Turkey. E-
mail: goker@ankara.edu.tr
Experimental
Uncorrected melting points were measured on an Büchi B-540
(Buchi, Labortechnik, Flawil, Switzerland) capillary melting point
Department of Pharmaceutical Chemistry, Faculty of Pharmacy, Ankara
University, Tandogan, Ankara 06100, Turkey
Magn. Reson. Chem. (2016)
Copyright © 2016 John Wiley & Sons, Ltd.

F. Doganc, M. Alp and H. Goker
mixtures of H2O: CH3CN: MeOH : 0.1% HCOOH in CH3CN (55 :
25 : 10 : 10) and H2O: CH3CN: MeOH : 0.1% HCOOH in CH3CN
(45 : 35 : 10 : 10) were selected as mobile phases, with 0.4
and 0.7 ml/min flow rate, respectively. The eluate was moni-
tored by a photo-diode array detector at 254 nm.
was added in portions. The reaction mixture was stirred vigorously
and more EtOH was added. The mixture was kept in a refrigerator
for a several hours. The white precipitate was filtered and dried,
and used for the further steps without purification and
characterization.
3,4-Diaminobenzonitrile 1
2-(3,4-Dimethoxyphenyl)-1H-benzimidazole-5(6)-carbonitrile 3
4-Amino-3-nitrobenzonitrile (1.0 g, 6.1 mmol) was dissolved in
50-ml ethanol and was subjected to hydrogenation using
35 psi of H2 and 10% Pd.C until uptake of H2 ceased. The cat-
alyst was filtered on a bed of Celite, washed with ethanol and
concentrated in vacuo. Powder residue was used for the sub-
sequent steps without crystallization. The obtained compound
was used without crystallization in further steps. Yield 88%
(0.72 g). Mp: 144–146 °C.[9]
The mixture of 1 (0.133 g, 1 mmol) and 2 (0.270 g, 1 mmol)
and in DMF (2 ml) was heated at 120 °C, for 3.5 h. The reaction
mixture was cooled, poured into water and made alkaline
with dilute K2CO3 solution. The resulting precipitate was col-
lected by filtration dried and crystallized from EtOH, mp
205–207 °C, yield 70.4%, 0.19 g. MS (ESI+) m/z : 280 (M + H,
%100), C16H13N3O2; 1H-NMR (400 MHz, DMSO) δ ppm (J, Hz)
: 3.83(s,3H,5′-OCH3), 3.87(s,3H,4′-OCH3), 7.14(d,1H,Jo = 8.4 Hz,H-
3′), 7.54(d,1H,Jo = 8.4,H-6); 1H-NMR (400 MHz, DMSO-d6 + NaH
+ D2O) δ ppm (J, Hz) : 3.76(s,3H,5′-OCH3), 3.82(s,3H,4′-OCH3),
6.94(s,1H, Jo = 8.4 Hz,H-3′), 7.07(dd,1H,Jo = 8.4 and Jm = 1.6 Hz,
H-6), 7.43(d,1H,Jo = 8.4 Hz,H-7), 7.72(d, 1H,Jm = 1.6 Hz,H-4), 7.81
(dd,1H,Jo = 8.4 and Jm = 1.6 Hz,H-2′), 7.90(d,1H, Jm = 1.6 Hz,H-6′),
Sodium metabisulfite adduct of 3,4-dimethoxybenzaldehyde 2
3,4-Dimethoxybenzaldehyde (1.245 g, 7.5 mmol) was dissolved in
EtOH (25 ml), and sodium metabisulfite (0.8 g) (in 5 ml of water)
Table 1. 1H,13C, COSY, NOESY, DEPT, HSQC and HMBC data of 4a and 4b
Compound 4a
Compound 4b
No
1H δ, 13C δ, HSQC
DEPT* COSY NOESY
HMBC
No
1H δ, 13C δ, HSQC
DEPT*
COSY
NOESY
HMBC
2
156.16
H-9,13,16
H-7
2
156.88
H-9,13,16
H-5,7
3a
4
142.47
124.6
3a
4
145.8
8.01 (d,1H,
m = 1.6)
1
H-6
7.83 (d,1H,
Jo = 8.4)
120.53
1
1
H-5
H-4
J
5
105.6
125.9
H-7
H-4
5
7.53 (dd,1H,
Jo = 8.4,
125.94
H-7
Jm = 1,6)
6
7
7.53 (dd,1H,
1
1
H-7
H-6
6
7
105.25
114.85
H-4
H-5
Jo = 8.4, Jm = 1,6)
7.44 (d,1H,Jo = 8.4) 110.97
H-16
H-16
7.72 (d,1H,
1
H-16
H-16
Jo = 1.2)
7a
8
138.46
121.95
H-4,6,16
**
7a
8
135.36
121.82
121.85
H-4,16
**
9
7.23 (dd,1H,
Jo = 8.4, Jm = 2)
7.00 (d,1H,
Jo = 8.4)
121.86
1
1
H-10
H-9
H-10,13
9
7.23 (dd,1H,
Jo = 8.4, Jm = 2)
7.00 (d,1H,
Jo = 8.4)
1
1
H-10
H-9
H-10,13
10
111.2
10
111.02
11
12
13
151.05
149.5
H-9,10,13,15 11
H-10,13,14 12
150.96
149.38
112.49
H-9,10,13,15
H-10,13,14
H-9
7.29 (d,1H,
Jo = 2)
112.74
1
H-9
13
7.29 (d,1H,
Jo = 2)
1
14
15
16
3.95 (s,3H)
3.96 (s,3H)
4.23 (t,2H,
J = 7.6)
56.02
56.14
46.71
3
3
2
14
15
16
3.95 (s,3H)
3.96 (s,3H)
4.23 (t,2H,
J = 7.6)
56.03
56.11
46.81
3
3
2
H-17 H-7,H-9
H-16,18
H-17,18
H-16,18
H-16,17
H-4,6
H-17
H-16,H-18
H-17
H-7,H-9
H-17,18
H-16,18
H-16,17
H-5,7
17
18
19
1.84 (m,2H,
J = 7.6)
23.16
11.13
2
3
17 1.86 (m,2H,J = 7.6) 23.24
18 0.916 (t,3H,J = 7.6) 11.12
2
3
0.89 (t,3H,
J = 7.6)
H-17
119.81
19
119.97
δ ppm in CDCl3, J in Hz.
* Number in DEPT is the number of attached protons.
** Not observable since overlapped with C-9.
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Magn. Reson. Chem. (2016)

Structural elucidation with NOESY experiment
COSY : [H-6 : H-7] and [H-2′ : H-3′], 13C-NMR (100 MHz,
DMSO-d6 + NaH + D2O), HSQC and HMBC δ ppm : 164.3(C-2),
151.3(C-7a), 149.1(C-4′), 148.7(C-5′), 147.11(C-3a), 129.7(C-1′),
123.06(CN), 121.00(C-6H), 120.15(C-4H), 119.90(C-2′H), 116.63
(C-7H), 111.84(C-3′H), 110.97(C-6′H), 97.69(C-5), 55.89(C4′-
OMe), 55.76(C5′-OMe).
2-(3,4-Dimethoxyphenyl)-1-propyl-1H-benzimidazole-6-
carbonitrile 4b
After separation of 4a the supernatant liquid was evaporated, and
purification of this residue by column chromatography (EtOAc 15
: n-hexane 85) gave the pure compound 4b (from the second frac-
tion), mp 142–144 °C, yield 18.8%, 0.013 g, MS (ESI+) m/z : 322 (M
+ H, %100), C19H19N3O2, (NMR data in Table 1).
Synthesis of the mixture of 4a and 4b
Synthesis of the mixture of 5a and 5b
A mixture of 3 (0.060 g, 0.215 mmol), n-propylbromide (0.037 g,
0.3 mmol) and sodium hydride (95%) (0.01 g, 0.4 mmol) in N,N-
dimethylformamide (0.5 ml) was stirred at 60°C for 5 h. The reaction
mixture was cooled, poured into water and made alkaline with di-
lute K2CO3 solution. The resulting precipitate was collected by filtra-
tion and dried.
A mixture of 3 (0.060 g, 0.215 mmol), 4-chlorobenzyl chloride
(0.048 g, 0.3mmol) and sodium hydride (95%), (0.01 g, 0.4 mmol)
in N,N-dimethylformamide (0.5 ml) was stirred at 60 °C for 5 h. The
reaction mixture was cooled, poured into water and made alkaline
with dilute K2CO3 solution. The resulting precipitate was collected
by filtration and dried.
2-(3,4-Dimethoxyphenyl)-1-propyl-1H-benzimidazole-5-
carbonitrile 4a
1-(4-Chlorobenzyl)-2-(3,4-dimethoxyphenyl)-1H-benzimid-
azole-5-carbonitrile 5a
Two times crystallization of this precipitate from EtOH afforded
pure 4a. Mp 148–150 °C, yield 30.3%, 0.021 g, MS (ESI+) m/z : 322
(M+ H, %100), C19H19N3O2, (NMR data in Table 1).
Purification of the above residue by column chromatography
(EtOAc 35 : n-hexane 65) gave the pure compound 5a from the first
Table 2. 1H,13C, COSY, NOESY, DEPT, HSQC and HMBC data of 5a and 5b
Compound 5a
Compound 5b
No
1H δ, 13C δ, HSQC
DEPT* COSY
NOESY
HMBC No
1H δ, 13C δ, HSQC
DEPT* COSY
NOESY
HMBC
2
156.57
H-9,13,16
H-7
2
157.67
H-9,13,16
H-5,7
3a
4
142.47
124.45
3a
4
146.37
120.83
8.13 (d,1H,
m = 1.6)
1
H-6
7.86 (dd,1H,
1
1
H-5
H-4
J
Jo = 8.4, Jp = 0.8)
7.56 (dd,1H,
5
6
7
105.82
126.16
111.22
H-7
H-4,7
H-6
5
6
7
115.49
106.05
126.73
H-7
H-4
H-5
Jo = 8.4, Jm = 1,6)
7.53 (dd,1H,
Jo = 8.4, Jm = 1,6)
7.30 (d,1H,
1
1
H-7
H-6
H-16
7.55 (d,1H,
1
H-16
Jo = 8.4)
Jo = 1.2)
7a
8
138.46
121.95
121.88
H-4,6,16 7a
136.20
121.5
H-4,16
H-10
H-10
H-13
8
9
9
7.19 (dd,1H,
Jo = 8.4, Jm = 2)
6.94 (d,1H,
Jo = 8.4)
1
1
H-10
H-9
H-16
H-15
7.22 (dd,1H,
Jo = 8.4, Jm = 2)
6.95 (d,1H,
Jo = 8.4)
122.43
1
1
H-10
H-9
H-16
H-15
H-13
10
111.25
10
111.74
11
12
13
151.05
149.5
H-9,13,15 11
H-10,13,14 12
151.88
149.91
112.87
H-9,10,13,15
H-10,13,14
H-9
7.21 (d,1H,
Jo = 2)
112.36
1
H-14,16
H-9
13
7.23 (d,1H,
Jo = 2)
1
H-14,16
14
15
16
3.75 (s,3H)
3.89 (s,3H)
5.48 (s,2H)
55.71
55.85
48.07
3
3
2
14
15
16
3.75 (s,3H)
3.89 (s,3H)
5.47 (s,2H)
56.20
56.32
48.65
3
3
2
**H-7,9,13
***H-7,9, 13
H-18(weak)
H-18
H-18(weak)
17
18
134.49
127.38
H-16,19 17
134.74
127.80
H-16,19
H-16
7.05 (d,2H,
Jo = 8.4)
1
1
H-19 H-16(weak)
H-18
H-16
18
7.05 (d,2H,
Jo = 8.4)
1
1
H-19 H-16(weak)
H-18
19
7.35 (d,2H,
Jo = 8.4)
129.28
19
7.35 (d,2H,
Jo = 8.4)
129.81
20
21
133.78
119.81
H-18
20
21
134.34
120.10
H-18
H-4,6
H-5,7
δ ppm in CD2Cl2, J in Hz.
* Number in DEPT is the number of attached protons.
** When the spectrum is run in CD3CN, H-16 interaction with H-9 and H-13 are observed separately.
*** When the spectrum is run in CDCl3, H-16 interaction with H-9 and H-13 are observed separately.
Magn. Reson. Chem. (2016)
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F. Doganc, M. Alp and H. Goker
coming out fraction, which is crystallized from EtOH, mp 196–
199 °C, yield 24%, 0.021g, MS (ESI+) m/z : 404(M + H, %100), 406
(M+ H + 2, %34), C23H18ClN3O2, (NMR data in Table 2).
Hydrogen atom attached to nitrogen in the 1-position readily
tautomerise.[10] This may be depicted as in compound 3 in
(Fig. 1). Thus, 1H-benzimidazole-5-carbonitrile is a tautomer
of 1H-benzimidazole-6-carbonitrile, and both structures repre-
sent the same compound as 5(6). The NMR spectra of benz-
imidazoles show the presence of two tautomeric forms,
which are rapidly equilibrating on the NMR timescale, and
the relations between the tautomer and nontautomer type
were reported in different deuterated solvents.[11–13] Figure 2
1-(4-Chlorobenzyl)-2-(3,4-dimethoxyphenyl)-1H-benzimid-
azole-6-carbonitrile 5b
The crystallization of second fraction from EtOH: n-hexane gave the
pure compound 5b. Mp 200–202 °C, Yield 11.5%, 0.010 g, MS (ESI+)
m/z : 404(M + H, %100), 406(M + H + 2, % 32), C23H18ClN3O2. 1H-
NMR (400 MHz, CDCl3) δ ppm (J, Hz) : 3.82(s,3H,14-OCH3), 3.93
(s,3H,15-OCH3), 5.48(s,2H,H-16), 6.93(d,1H,Jo = 8 Hz,H-10), 7.04(d,2H,
Jo = 8.8Hz,H-18), 7.19(dd,1H,Jm = 2 Hz and Jo = 8 Hz,H-9), 7.27(d,1H,
Jm = 1.6Hz,H-13), 7.36(d,2H,Jo = 8.8Hz,H-19), 7.51(s,1H,H-7), 7.58
(dd,1H, Jm = 1.2 Hz and Jo = 8.4 Hz,H-5), 7.92(d,1H,Jo =8.4 Hz,H-4).
13C-NMR (100 MHz, CDCl3) δ ppm (J, Hz) : 157.06, 151.48, 149.48,
145.22, 135.48, 134.38, 133.72, 129.67, 127.10, 126.73, 121.97,
120.56, 119.54, 114.93, 112.32, 111.15, 106.08, 56.05, 55.96, 48.32
(One carbon atom is missing, that is why, the NMR spectra of this
compound was run in CD2Cl2 in Table 2). COSY : [H-10 : H-9], [H-
18 : H-19], [H-5 : H-4], NOESY : [H-16 : H-7, H-9, H-13, H-18], [H-10 :
H-15], [H-13 : H-14] (Fig. 5).
1
shows the H and 13C NMR spectra of compound 3 under nor-
mal conditions. Because of the mixture of tautomers in com-
pound 3, its 1H-NMR spectra were not clear enough under
standard conditions as expected. Similar situation was also
observed with the 13C spectra of same compound; some car-
bon peaks are missing. After elimination of the tautomeric ef-
fects by addition of a tiny amount of dry NaH, and two to
three drops of D2O, all the protons with expected splitting
patterns and carbon atoms including C3a/C7a, C4/C7 and
C5/C6 have been observed as sharp peaks, in its NMR spectra
(Fig. 2). Hence, very fine NMR assignments without tautomer-
ism were made by combination of 1D and 2D NMR
techniques.
Furthermore, elimination of NH proton then substitution of this
nitrogen atom would prevent rapid tautomerism and lead to a sep-
arable equimolar mixture of 1,5- and 1,6-substituted products.[14]
When we have attempted alkylation of compound 3, with n-propyl
bromide and 4-chlorobenzyl chloride under strong basic conditions
(NaH 95%, DMF), because of the tautomerism of the imidazole moi-
ety, alkylation occurred at both N1 and N3 positions and two
regioisomers: 4a, 4b and 5a, 5b were formed as a solid mixture
as expected, respectively.
Alkylations of benzimidazoles give frequently similiar yields
of both regioisomers;[15–17] sometimes they give a different
ratio.[6,18–20] It has been reported that, when 5(6)- or 4(7)-
substituted benzimidazoles are alkylated, the product ratios
depend on the resonance electronic effects as well as position
of the substituent.[21] In our experiments, propylation and
benzylation of compound 3 (Fig. 1) gave the compounds 4a,
5a (1,5-isomers) and 4b, 5b (1,6-isomers) with the ratio of
70 : 30 and 72 : 28, according to their LC chromatograms, re-
spectively (Fig. 3). We were able to separate regioisomers
from each other by crystallization or column chromatography
as reported in the experimental part. Because the ratio of 4a
is much higher than 4b, it was possible to obtain 4a only
Results and Discussion
Compounds 4a, 4b and 5a, 5b (Tables 1 and 2) were pre-
pared using the methods outlined in Fig. 1. Reduction of 4-
amino-3-nitrobenzonitrile with H2/Pd-C afforded 3,4-
diaminobenzonitrile 1. Cyclization of
1
with sodium
metabisulfite adduct of 3,4-dimethoxybenzaldehyde gave
benzimidazolecarbonitrile 3. In benzimidazole ring, the nitro-
gen bears a hydrogen atom (N1) that seems like a pyrrole-like
N-atom; the other (N3) resembles a pyridine-like N-atom.
Figure 2. (A) Aromatic region of 1H and 13C-NMR spectra of compound 3
1
under normal conditions. (B) Aromatic region of H and 13C-NMR spectra
Figure 1. Synthesis of targeted 1H-benzimidazoles 4a, 4b and 5a, 5b.
of compound 3 after elimination tautomerism.
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Structural elucidation with NOESY experiment
Figure 3. HPLC chromatogram of compounds 4a–4b and 5a–5b.
by crystallization. Characterization of the individual isomeric
products was determined by observation of 1H-NMR NOESY
enhancements between methylene protons H-16 and H-7,
allowing the H-7 proton to be characterized and identified
for each particular nitrile substituted isomers on the basis of
its 1H-NMR splitting pattern. Actually, in NOESY spectrum
(Fig. 4) of compound 4a, very strong correlation has been ob-
served between the H-16 and aromatic proton H-7. Because
this best correlated benzene proton (H-7) having orto
coupling constant (J = 8.4 Hz), it means that this structure of
the regioisomer must be the 1,5-isomer without any doubt.
Weaker NOE occurs between the methylene protons and 2-
phenyl aromatic H-9 and H-13 protons. In contrast, in NOESY
spectrum of compound 4b, this time best correlated benzene
proton with H-16 give the meta-coupling constant (J = 1.2 Hz),
so the CN group must be substituted at C-6 position. Similar
observation was received in the NOESY spectra of the com-
pound 5a and 5b. Because some of the aromatic protons of
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F. Doganc, M. Alp and H. Goker
Figure 4. NOESY spectrum of compound 4a in CDCl3.
Figure 5. NOESY spectrum of compound 5b in CDCl3.
compound 5b in CD2Cl2 are observed as overlapped, the
spectrum was run in CDCl3 for NOESY experiment (Fig. 5). This
time NOESY interaction particularly between H-16 and H-7 has
been observed very clearly. However, in the CDCl3 one carbon
atom was missing (overlapped), that is why, total NMR charac-
terization was made in CD2Cl2 in Table 2. The complete as-
signments of 4a, 4b (Table 1) and 5a, 5b (Table 2) were
made using 1D and 2D NMR including full DEPT, COSY,
NOESY, HSQC and HMBC techniques in CDCl3 and CD2Cl2.
Conclusion
It is well known since 19th century,[22] there is a rapid exchange be-
tween the ―NH― and ¼NH― nitrogen atoms in benzimidazole
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Magn. Reson. Chem. (2016)

Structural elucidation with NOESY experiment
[8] J. R. Sadig, R. Foster, F. Wakenhut, M. C. Willis. J. Org. Chem. 2012, 77,
9473–9486.
[9] T. A. Fairley, R. R. Tidwell, I. Donkor, N. A. Naiman, K. A. Ohemeng,
R. J. Lombardy, J. A. Bentley, M. Cory. J. Med. Chem. 1993, 36,
1746–1753.
[10] J. B. Wright. Chem. Rev. 1951, 397–541.
[11] S. Ozden, F. Usta, N. Altanlar, H. Göker. J. Heteocycl. Chem. 2011, 48,
1317–1322.
ring, and two tautomers may be drawn for the compound 3 (Fig. 1).
The 5 and 6 positions (as well as 4 and 7 positions) and any group
present at that position in the ring system is chemically equivalent.
However, tautomerism is no longer possible in N-substituted benz-
imidazoles and two distinct non-equivalent molecules or
regioisomers may be isolated and characterized. NOESY experi-
ments is the best available methods for the structural elucidation
of these regioisomers.
[12] M. A. Garcia, R. M. Claramunt, T. Solcan, V. Milata, I. Alkorta, J. Elguero.
Magn. Reson. Chem. 2009, 47, 100–104.
[13] C. Nieto, P. Cabildo, M. A. Garcia, R. M. Claramunt, I. Alkorta, J. Elguero.
Beilstein J. Org. Chem. 2014, 10, 1620–1629.
[14] H. Kadri, C. S. Matthews, T. D. Bradshaw, M. F. G. Stevens, A. D. Westwell.
J. Enzyme Inhib. Med. Chem. 2008, 23(5), 641–647.
[15] H. Green, A. R. Day. J. Am. Chem. Soc. 1942, 64(5), 1167–1173.
[16] J. H. Wikel, C. J. Paget. 1977 USA 4,008,243.
[17] T. Fuente, M. Martin-Fontecha, J. Sallander, B. Benhamu, M. Campillo,
R. A. Medina, L. P. Pellissier, S. Claeysen, A. Dumuis, L. Pardo,
M. L. Lopez-Rodriguez. J. Med. Chem. 2010, 53, 1357–1369.
[18] A. Al-Azmi, P. George, O. M. E. El-Dusouqui. J. Hetercycl. Chem. 2007, 44,
515–520.
Acknowledgement
Central Laboratory of Pharmacy Faculty of Ankara University pro-
vided support for the acquisition of the NMR and mass spectrome-
ter used in this work.
[19] S. Prinka, L. Vijay, P. Kamaldeep. Bioorg. Med. Chem. 2015, 23,
1691–1700.
[20] R. M. Claramunt, C. Lopez, I. Alkorta, J. Elguero, R. Yang, S. Schulman.
Magn. Reson. Chem. 2004, 42, 712–714.
References
[1] G. Yadav, S. Ganguly. Eur. J. Med. Chem. 2015, 97, 419–443.
[2] Y. Bansal, O. Silakari. Bioorg. Med. Chem. 2012, 20, 6208–6236.
[3] T. M. Kalyankar, S. S. Pekamwar, S. J. Wadher, P. S. Tiprale, G. H. Shinde.
Int. J. Chem. Pharm. Sci. 2012, 3(4), 01–10.
[21] M. R. Grimmett, in Imidazole and Benzimidazole Synthesis (Ed: O. Meth-
Cohn), Academic, London, 1997, pp. 202.
[4] C. Zucco, E. L. Dall’Oglio, G. V. Salmoria, H. Gallardo, A. Neves,
M. C. Rezende. J. Phys. Org. Chem. 1998, 11, 411–418.
[5] V. Sridharan, S. Saravanan, S. Muthusubramanian, S. Sivasubramanian.
Magn. Reson. Chem. 2005, 43, 551–556.
[6] H. Goker, S. Olgen, R. Ertan, H. Akgun, S. Ozbey, E. Kendi, G. Topcu.
J. Heterocycl. Chem. 1995, 32, 1767–1773.
[22] A. Kaiser. Ber. Chem. 1885, 18, 2942.
Supporting information
Additional supporting information may be found in the online ver-
sion of this article at the publisher’s web site.
[7] H. Göker, C. Kuş, D. W. Boykin, S. Yildiz, N. Altanlar. Bioorg. Med. Chem.
2002, 10, 2589–2596.
Magn. Reson. Chem. (2016)
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