Synthesis and antioxidant properties of benzimidazole derivatives with isobornylphenol fragments

Article abstract of DOI:10.1007/s11172-019-2510-7

A series of new 2-substituted-1H-benzimidazoles was synthesized on the basis of 4-hydroxybenzaldehydes. Their antioxidant properties were evaluated in the in vitro models and compared with those of known analogs. The structural specifi c features of the m

Full text of DOI:10.1007/s11172-019-2510-7

Russian Chemical Bulletin, International Edition, Vol. 68, No. 5, pp. 1000—1005, May, 2019
1000
Synthesis and antioxidant properties of benzimidazole derivatives
with isobornylphenol fragments
I. A. Dvornikova,a E. V. Buravlev,a I. V. Fedorova,a O. G. Shevchenko,b I. Yu. Chukicheva,a and A. V. Kutchina
аInstitute of Chemistry of the Komi Science Centre of the Ural Branch of the Russian Academy of Sciences,
48 ul. Pervomaiskaya, 167000 Syktyvkar, Russian Federation.
Fax: +7 (821 2) 21 9916. E-mail: dvornikova-ia@chemi.komisc.ru
bInstitute of Biology of the Komi Science Centre of the Ural Branch of the Russian Academy of Sciences,
28 ul. Kommunisticheskaya, 167982 Syktyvkar, Russian Federation.
Fax: +7 (821 2)24 0163
A series of new 2-substituted-1H-benzimidazoles was synthesized on the basis of 4-hydroxy-
benzaldehydes. Their antioxidant properties were evaluated in the in vitro models and compared
with those of known analogs. The structural specific features of the molecules responsible for
the high antioxidant activity were revealed. Among tested derivatives, 2-substituted 1H-benz-
imidazole containing a phenol fragment with isobornyl and tert-butyl groups was found to have
the greatest ability to protect biomolecules and cells under conditions of acute oxidative stress.
Key words: 1H-benzimidazoles, sterically hindered phenols, isobornylphenols, antioxidant
activity, membrane-protective activity, red blood cells, oxidative hemolysis.
A promising approach to the development of drugs with
Results and Discussion
a wide range of action is the synthesis of biologically active
compounds containing several different pharmacophore
groups in their structure. One of these groups of interest
for medicinal chemistry is a benzimidazole core. Com-
pounds containing a benzimidazole fragment exhibit
a variety of pharmacological properties.1—7 2-Phenyl-
substituted 1H-benzimidazoles are known to manifest
antimicrobial,8 antiviral,9 antiparasitic,10 antibacterial,11
anticancer,12 antiinflammatory,13 hypotensive,14 antidia-
betic,15 immunomodulatory,13 antioxidant (AO),8 and
other activities. At the same time, sterically hindered
phenols are biologically active compounds with a wide
range of activities. A special place among them is taken by
isobornylphenols, which exhibit hemorheological, anti-
platelet, and cardioprotective properties, have low toxicity
and are efficient inhibitors of free-radical processes.16—20
A combination of two biologically active structures in one
molecule can increase the efficiency of pharmacological
action of the constituents or give new properties to the
resulting hybrid drug.
The present work reports the synthesis of a number of
new hybrid structures containing fragments of benzimid-
azole and sterically hindered phenol with terpene sub-
stituents. The effect of the benzimidazole fragment on the
toxicity of the synthesized compounds was studied, and
the AO activity (AOA) was evaluated using in vitro models.
Compounds promising for further modification and phar-
macological studies were identified.
2-Phenyl-1H-benzimidazoles were synthesized by the
reaction of ortho-phenylenediamine with the correspond-
ing aldehyde according to the procedure described in the
literature21 (Scheme 1).* To evaluate the effect of sub-
stituents in the phenol fragment on the AO properties of
substituted benzimidazoles, we synthesized compounds 7
and 8 with two isobornyl substituents (meso-stereoisomer
and racemate, respectively) and compounds 9 and 10 with
isobornyl and tert-butyl or methyl substituents. The
known22,23 benzimidazoles 11 (with two tert-butyl groups)
and 12 (without substituents in the phenol ring) were
synthesized for a comparative evaluation of biologi-
cal activity.
The structure of benzimidazoles synthesized for the
1
first was established based on the spectral data. The H
and 13С NMR spectra of compounds 7—10 contain signals
for isobornylphenol and benzimidazole fragments. In the
1H NMR spectra, the signal for the NH proton appeared
as a singlet in the region of H 12.62—12.71; in the 13С
NMR spectra, the signal for the C(2) atom is observed in
the region of C 155.92—157.13. The ratio of the integral
intensities of the protons of aromatic rings and terpene
* The numbering system of C atoms is introduced for the con-
venience of reading the NMR spectra. Compounds 1 and 7 are
meso-stereoisomers, 2—4, 8—10 are racemates.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1000—1005, May, 2019.
1066-5285/19/6805-1000 © 2019 Springer Science+Business Media, Inc.

Benzimidazole derivatives
Russ. Chem. Bull., Int. Ed., Vol. 68, No. 5, May, 2019
1001
Scheme 1
Table 1. Comparative evaluation of antioxidant* and radical
scavenging** activities of compounds 7—13
–1
Com-
pound
TBA-RS/nmol mL
RSА
(% of inhi-
bition)
–1
–1
100 μmol L
10 μmol L
7
8
9
10
11
12
13
23.4 0.2
4.5 0.3
4.6 0.3
4.5 1.5
49.9 0.2
22.8 0.4
4.7 0.2
37.6 0.1
20.6 0.6
5.2 0.2
5.8 0.1
59.4 0.8
70.3 0.2
7.1 0.2
16.4 1.5
25.4 1.1
15.6 0.2
17.1 1.1
22.6 0.4
0.3 0.1
75.3 1.2
* The antioxidant activity (test on the substrate from the brain
of laboratory mice) of compounds under study at concentra-
tions of 100 and 10 μmol L–1 was evaluated by the ability to in-
hibit the accumulation of secondary lipid peroxidation (LPO)
products reacting with 2-thiobarbituric acid (TBA-RS) in
the substrate obtained from the brain of laboratory mice (1 h
after the Fe2+/ascorbate initiation of LPO). The concentration
of TBA-RS in the control (without compounds) and in the intact
(without initiation of oxidation) samples was 88.01.3 and
42.90.8 nmol mL–1, respectively.
** The radical scavenging activity of compounds at a concentra-
tion of 100 μmol L–1 was determined in a test with DPPH.
suggests an insignificant influence of the structure of ortho-
substituents of the phenol ring on the ability of compounds
to reduce the stable DPPH radical (see Table 1). An excep-
tion is compound 12, which does not contain any sub-
stituents at ortho-position with respect to the phenol
hydroxy group and shows almost no RSA even at a con-
centration of 100 μmol L–1. Using non-cellular model
systems, it was shown that of diastereomers 7 and 8, race-
mate 8 is more active in all respects (see Table 1).
All the synthesized benzimidazoles showed extremely
low hemolytic activity in red blood cells as a model object.
The death of erythrocytes during 5 h of incubation with
compounds 7—12 at a concentration of 10 μmol L–1 did
not exceed 5%.
The highest MP activity (MPA) among the synthesized
compounds was observed for benzimidazole 9, compound
10 was found to be a little less active in the indicated tests
(Table 2). The same derivatives most actively inhibited the
oxidation of native hemoglobin and the accumulation of
secondary lipid peroxidation (LPO) products in erythro-
cytes. According to the regression analysis, the MPA of
the test compounds in the cellular model system closely
correlates with the results of the study of AOA on brain
lipids (Rs = 0.90, p = 0.002, n = 8).
fragments in the 1H NMR spectra indicates the formation
of 2-substituted benzimidazoles.
For derivatives 7—12, the radical scavenging activity
(RSA) was evaluated in the diphenylpycrylhydrazyl (DPPH)
test, AOA was studied on a substrate obtained from the
brain of laboratory mice; the hemolytic activity, AOA, and
membrane-protective (MP) properties were studied using
red blood cells of laboratory mice. 2,6-Diisobornyl-4-
methylphenol (13) possessing a high AOA24 was used as
a reference compound. The listed test systems were previ-
ously used by us for the comparative evaluation of AOA
of different phenolic compounds.19,25—27
Using a substrate obtained from the brain tissue of
animals, it was shown that the presence of substituents
and their structure are essential for the AOA of benzimid-
azoles (Table 1). The highest AOA at concentrations of
100 and 10 μmol L–1 (at the level of compound 13 and
above) was observed in compounds 9 and 10, each con-
taining one isobornyl and one alkyl substituent at ortho-
position to the phenol hydroxy group. Derivatives 7 and
8 with two isobornyl fragments showed somewhat lower
activity. 2-Phenyl-1H-benzimidazoles 11 and 12 without
terpene substituents possess the lowest AOA. The enhance-
ment of AOA after the introduction of an isobornyl sub-
stituent was observed by us earlier for 2,2-dimethyl-
chroman-6-ol.28 The radical scavenging activity of benz-
imidazoles 7—12 varied within a narrower range, which
To clarify the differences in the MPA between com-
pounds 9, 13 and the well-known antioxidant 2,6-di-tert-
butyl-4-methylphenol (BHT), a similar experiment was
conducted, in which the concentration of compounds was
reduced to 0.1 μmol L–1 (Table. 3). It was found that at

1002
Russ. Chem. Bull., Int. Ed., Vol. 68, No. 5, May, 2019
Dvornikova et al.
Table 2. Comparative evaluation of membrane-protective and antioxidant activities of compounds 7—13 at a con-
centration of 0.1 μmol L–1, using red blood cells of laboratory mice
Compound
MPA (% of hemolysis)
3 h
TBA-RS/
metHb*
oxyHb
ferrylHb**
oxyHb
nmol mL–1
1 h
5 h
Control
31.0 1.5
22.0 1.3
17.3 2.3
2.1 0.2
3.1 0.1
14.1 1.0
23.8 1.0
1.6 0.0
43.7 0.9
37.2 3.0
35.4 0.8
4.5 0.1
12.8 0.9
33.4 1.1
38.1 2.3
4.0 0.3
49.8 0.7
41.2 2.1
38.7 1.1
5.8 0.3
16.1 0.7
39.1 1.5
42.4 2.1
5.3 0.1
1.87 0.01
1.83 0.08
1.39 0.01
1.17 0.06
1.23 0.07
2.11 0.09
1.50 0.06
1.41 0.01
2.003 0.055
1.860 0.231
1.873 0.095
0.878 0.102
1.001 0.041
1.785 0.123
1.395 0.111
1.145 0.063
0.945 0.012
0.844 0.050
0.753 0.021
0.537 0.023
0.598 0.026
0.808 0.059
0.649 0.008
0.563 0.014
7
8
9
10
11
12
13
* metHb is methemoglobin, oxyHb is oxyhemoglobin.
** ferrylHb is ferrylhemoglobin.
solutions of compounds in CDCl3 and DMSO-d6. The signals
were assigned using 13C NMR spectra recorded in the J-modul-
ation mode; the HSQC procedure was used in some cases.
IR diffuse reflectance spectra were recorded on a Shimadzu IR
Prestige 21 Fourier-transform IR spectrometer in KBr pellets.
Melting points were determined on a Sanyo Gallenkamp MPD 350
apparatus and were not corrected. Elemental analysis was performed
on a vario Micro cube automatic analyzer in the CHNS mode.
The reaction progress and the purity of the synthesized
compounds were monitored by TLC on the Sorbfil plates (IMID
Ltd.). Column chromatography was carried out on 0.06—0.2 mm
silica gel (Alfa Aesar). All solvents were dried and purified by
standard procedures.
this concentration, benzimidazole 9 containing isobornyl
and tert-butyl groups is slightly more active than BHT in
certain indices, but inferior to compound 13.
In conclusion, new hybrid compounds 7—10 contain-
ing a benzimidazole ring and an isobornylphenol fragment
were synthesized, and it was found that the introduction
of a benzimidazole fragment does not lead to the appear-
ance of toxicity. It was shown that the presence and struc-
ture of substituents in the phenol fragment of the com-
pounds obtained significantly affect their AO properties
in various model systems. It was noted that the fact of the
presence of an alkyl and/or a terpene substituent is im-
portant for RSA in the test with DPPH, while the AOA
on a substrate containing natural lipids significantly de-
pends on their structure. A close positive relationship was
found between the MPA of the studied compounds in the
cell model system and their AOA on a substrate containing
brain lipids. All the derivatives with isobornyl substituents
are promising for further research. 2-(3-tert-Butyl-5-
isobornyl-4-hydroxyphenyl) benzimidazole (9) was found
to have the highest ability to protect biomolecules and cells
under conditions of acute oxidative stress.
The starting aldehydes 1,29 2,30 4,31 and 532 were prepared
according to procedures described previously; 4-hydroxybenzal-
dehyde (6) (Alfa Aesar) was used without additional purification.
The analysis of the synthesized compounds is partially per-
formed using the equipment of the "Chemistry" Center for
Collective Use at the Institute of Chemistry, Komi Scientific
Centre (SC), Ural Branch of the Russian Academy of Sciences
(UB RAS). The activity of compounds was studied using the
equipment of the Molecular Biology Center for Collective Use
of the Institute of Biology, Komi SC UB RAS. The animals used
in the work were from a scientific collection of experimental
animals of the Institute of Biology, Komi SC UB RAS (http://
www.ckp-rf.ru/usu/471933/).
Experimental
3-(tert-Butyl)-4-hydroxy-5-{1,7,7-trimethylbicyclo[2.2.1]-
hept-exo-2-yl}benzaldehyde (3) was obtained according to the
procedure described earlier32 with some modifications. 2-tert-
Butyl-6-isobornyl-4-methylphenol33 (1.43 g, 4.76 mmol) was
1Н and 13С NMR spectra were recorded on a Bruker Avance
II 300 spectrometer (300.17 and 75.48 MHz, respectively) for
Table 3. Comparative evaluation of membrane-protective and antioxidant activity of derivative 9 at a concentration
of 0.1 μmol L–1, using red blood cells of laboratory mice
Compound
MPA (% of hemolysis)
3 h
TBA-RS/
metHb/
oxyHb
Ifl
nmol mL–1
/arb. units*
1 h
5 h
Control
ВНТ
9
22.3 0.4
10.7 0.2
8.9 0.8
5.3 0.7
33.7 0.6
29.2 0.7
25.5 1.3
10.5 0.7
43.2 0.7
36.0 0.6
35.3 1.4
17.3 0.6
1.36 0.04
1.41 0.05
1.34 0.05
1.30 0.10
1.591 0.079
1.129 0.137
1.311 0.049
0.964 0.088
7.38 0.08
7.30 0.09
6.56 0.14
6.27 0.08
13
* The fluorescence intensity (Ifl) in the intact sample was 2.49 0.01 arb. units.

Benzimidazole derivatives
Russ. Chem. Bull., Int. Ed., Vol. 68, No. 5, May, 2019
1003
dissolved in ButOH (50 mL) with heating. The solution was
cooled to ~40 C, followed by the addition of Br2 (0.56 mL,
9.52 mmol) in small portions. The reaction mixture was stirred
for 3 h at 20 C and left for 16 h. The volatile components were
removed under reduced pressure, the residue was dissolved in
CHCl3 (25 mL), washed with saturated solution of Na2S2O3
(3×10 mL) and water (2×10 mL), dried with Na2SO4. The solvent
was removed under reduced pressure, the reaction product was
precipitated from PhH. A colorless powder, m.p. 210—212 C
(decomp.). The yield was 0.71 g (47%). Found (%): C, 80.11; H,
: 0.71 (s, 6 H, C(10´)H3, C(10´´)H3); 0.80 (s, 6 H, C(8´)H3,
C(8´´)H3); 0.88 (s, 6 H, C(9´)H3, C(9´´)H3); 1.25—1.42 (m, 2 H,
C(5´)H, C(5´´)H); 1.52—1.66 (m, 6 H, C(3´)H, C(3´´)H,
C(6´)H2, C(6´´)H2); 1.78—1.86 (m, 4 H, C(5´)H, C(5´´)H,
H(4´), H(4´´)); 2.23—2.41 (m, 2 Н, C(3´)H, C(3´´)H); 3.27—2.42
(m, 2 Н, H(2´), H(2´´), overlapped by the signal of HOD);
7.06—7.20 (m, 2 Н, Н(5), Н(6)); 7.47, 7.61 (both d, 1 H each,
Н(4), Н(7), J = 6.8 Hz, J = 6.8 Hz); 7.98 (s, 2 Н, Н(11), Н(15));
8.22 (s, 1 Н, OH); 12.67 (s, 1 Н, NH). 13C NMR (DMSO-d6),
: 12.24 (C(10´), C(10´´)); 20.16, 21.27 (C(8´), C(8´´), C(9´),
C(9´´)); 27.07 (C(5´), C(5´´)); 33.65 (C(3´), C(3´´)); 38.61
(С(6´), C(6´´)); 44.59, 44.96 (C(2´), C(2´´), C(4´), C(4´´));
47.72 (C(1´), C(1´´)); 49.28 (C(7´), C(7´´)); 110.69, 118.17 (С(4),
С(7)); 120.14 (С(10)); 121.13, 121.62 (С(5), С(6)); 123.74 (С(11),
С(15)); 130.74 (С(12), С(14)); 134.90, 143.81 (С(8), С(9)); 152.41
(C(13)); 156.77 (C(2)).
9.46. C21H30O2. Calculated (%): C, 80.21; H, 9.62. IR, /cm–1
:
3414 (ОH); 2955, 2878, 1435, 1385 (CH3, CH2); 1668 (С=O).
1H NMR (CDCl3), : 0.79 (s, 3 Н, C(10´)H3); 0.86, 0.87 (both
s, 3 H each, C(8´)H3, C(9´)H3); 1.45 (s, 9 Н, С(СН3)3);
1.31—1.49, 1.61—1.81, 1.85—2.05 (all m, 2 H each, H(3´), Н(4´),
С(5´)H2, С(6´)H2); 2.31—2.43 (m, 1 Н, H(3´)); 2.88 (t, 1 H,
H(2´), J = 8.4 Hz); 5.60 (s, 1 H, OH); 7.69, 7.74 (both s, 1 H each,
Н(11), Н(15)); 9.85 (1 H, CHO). 13C NMR (CDCl3), : 12.27
(С(10´)); 20.18 (С(9´)); 21.29 (C(8´)); 27.53 (C(5´)); 29.57
(C(CH3)3); 34.30 (C(3´)); 34.58 (C(CH3)3); 40.37 (C(6´)); 45.27
(C(4´)); 46.19 (C(2´)); 48.55 (C(7´)); 49.63 (C(1´)); 127.30,
128.12 (C(11), С(15)); 128.64, 129.48, 136.31 (C(10), С(12),
С(14)); 159.28 (C(13)); 191.71 (CHO).
Synthesis of 2-phenylbenzimidazoles 7—12 (general proce-
dure). A procedure similar to that described in the work21 was
used. A mixture of o-phenylenediamine (0.053 g, 0.49 mmol),
aldehyde 1—6 (0.51 mmol), and NH4OAc (0.038 g, 0.49 mmol)
in anhydrous EtOH (15 mL) was stirred for 10 h at 75 C. The
reaction mixture was cooled to room temperature, the precipitate
was collected by filtration, washed with EtOAc, and dried. An
additional amount of the product was obtained after evaporation and
precipitation from the mother liquor. Compounds 9, 10, and 12
were isolated by column chromatography (eluent PhH—MeOH
(9), petroleum ether—EtOAc (10, 12)).
4-(1H-Benzо[d]imidazol-2-yl)-2-tert-butyl-6-{1,7,7-trimeth-
ylbicyclo[2.2.1]hept-exo-2-yl}phenol (9). A light beige powder,
m.p. 278—280 C (with decomp.). The yield was 50%. Found (%):
С, 80.23; Н, 8.37; N, 6.70. C27H34N2O. Calculated (%): С, 80.55;
Н, 8.51; N, 6.96. IR, /cm–1: 3631, 3597, 2953, 1620, 1535, 1456,
1425, 1394, 1361, 1323, 1271, 1190, 742. 1H NMR (DMSO-d6),
: 0.73 (s, 3 H, C(10´)H3); 0.79 (s, 3 H, C(8´)H3); 0.83 (s, 3 H,
C(9´)H3); 1.31—1.87 (m, 6 Н, C(3´)H, H(4´), C(5´)H2, C(6´)H2);
1.44 (s, 9 Н, С(СН3)3); 2.33—2.46 (m, 1 Н, C(3´)H);
3.30—3.41 (m, 1 Н, H(2´), overlapped by the signal of HOD);
7.10—7,18 (m, 2 Н, Н(5), Н(6)); 7.48 (d, 1 Н, Н(4), Н(7),
J = 7.4 Hz, J = 7.4 Hz); 7.92, 7.99 (both s, 1 H each, Н(11), Н(15));
8.11 (s, 1 Н, OH); 12.71 (s, 1 Н, NH). 13C NMR (DMSO-d6),
: 11.87 (C(10´); 20.01, 21.26 (C(8´), C(9´)); 27.17 (C(5´)); 29.71
(С(CH3)3); 33.23 (C(3´)); 34.63 (С(CH3)3); 38.16 (С(6´)); 44.10
(C(2´)); 44.96 (C(4´)); 47.91 (C(1´)); 49.33 (C(7´)); 110.75,
118.20 (С(4), С(7)); 120.69 (С(10)); 121.16, 121.67 (С(5), С(6));
122.55, 123.91 (С(11), С(15)); 131.60, 134.93, 138.05, 143.83
(С(8), С(9), С(12), С(14)); 152.42 (C(13)); 156.45 (C(2)).
4-(1H-Benzо[d]imidazol-2-yl)-2-methyl-6-{1,7,7-trimethyl-
bicyclo[2.2.1]hept-exo-2-yl}phenol (10). A light beige powder,
m.p. 256—258 C (with decomp.). The yield was 86%. Found (%):
С. 79.38; Н, 7.86; N, 7.41. C24H28N2O. Calculated (%): С, 79.96;
Н, 7.83; N, 7.77. IR, /cm–1: 3599, 3572, 2949, 1602, 1539, 1452,
1433, 1392, 1327, 1271, 1192, 744. 1H NMR (DMSO-d6), : 0.75
(s, 3 H, C(10´)H3); 0.81 (s, 3 H, C(8´)H3); 0.90 (s, 3 H, C(9´));
1.30—1,39 (m, 1 H, C(5´)H); 1.48—1.60 (m, 3 H, C(3´)H,
C(6´)H2); 1.76—1.90 (m, 2 H, C(5´)H, H(4´)); 2.24—2.38 (m, 1 Н,
C(3´)H); 2.28 (s, 3 Н, C(14)CH3); 3.26—3.41 (m, 1 Н, H(2´),
overlapped by the signal of HOD); 7.06—7.20 (m, 2 Н, Н(5),
Н(6)); 7.46—7.57 (m, 2 Н, Н(4), Н(7)); 7.77, 7.96 (both s,
1 H each, Н(11), Н(15)); 8.62 (s, 1 Н, OH); 12.62 (s, 1 Н, NH).
13C NMR (DMSO-d6), : 12.08 (C(10´)); 17.03 (C(14)CH3);
20.06, 21.22 (C(8´), C(9´)); 27.04 (C(5´)); 33.29 (C(3´)); 38.94
(С(6´)); 44.68, 44.95 (C(2´), C(4´)); 47.57 (C(1´)); 49.35
(C(7´)); 110.70, 118.07 (С(4), С(7)); 120.50 C(10); 121.23, 121.59
(С(5), С(6)); 123.82, 126.41 (С(11), С(15)); 130.66, 136.22,
143.80 (С(8), С(9), С(12), С(14)); 152.09 (C(13)); 155.92 (C(2)).
4-(1H-Benzо[d]imidazol-2-yl)-2,6-di-tert-butylphenol (11).22
The yield was 70%. 1H NMR (DMSO-d6), : 1.46 (s, 18 Н);
7.08—7.21 (m, 2 Н); 7.39—7.70 (m, 2 Н); 7.96 (s, 2 Н); 12.70 (s, 1 Н).
4-(1H-Benzо[d]imidazol-2-yl)phenol (12).23 The yield was
54%. 1H NMR (DMSO-d6), : 6.92 (d, 2 Н, J = 8.4 Hz);
7.05—7.24 (m, 2 Н); 7.39—7.70 (m, 2 Н); 8.01 (d, 2 Н, J = 8.4 Hz);
9.99 (s, 1 Н); 12.66 (s, 1 Н).
4-(1H-Benzо[d]imidazol-2-yl)-2,6-di-{1,7,7-trimethylbi-
cyclo[2.2.1]hept-exo-2-yl}phenol (7) (meso-stereoisomer). A white
powder, m.p. >300 C. The yield was 63%. Found (%): С, 81.79;
Н, 8.78; N, 5.78. C33H42N2O. Calculated (%): С, 82.11; Н, 8.77;
N, 5.80. IR, /cm–1: 3597, 2949, 2875, 1620, 1537, 1458, 1431,
1361, 1321, 1273, 1186, 742. 1H NMR (DMSO-d6), : 0.78 (s, 6 H,
C(10´)H3, C(10´´)H3); 0.81 (s, 6 H, C(8´)H3, C(8´´)H3); 0.90
(s, 6 H, C(9´)H3,C(9´´)H3); 1.26—1.41 (m, 2 H, C(5´)H, C(5´´)H);
1.51—1.68 (m, 6 H, C(3´)H, C(3´´)H, C(6´)H2, C(6´´)H2);
1.81—1.88 (m, 4 H, C(5´)H, C(5´´)H, H(4´), H(4´´)); 2.34—2.47
(m, 2 Н, C(3´)H, C(3´´)H); 3.25—3.40 (m, 2 Н, H(2´), H(2´´),
overlapped by the signal of HOD); 7.07—7.20 (m, 2 Н, Н(5),
Н(6)); 7.47, 7.61 (both d, 1 H each, Н(4), Н(7), J = 7.4 Hz,
J = 7.1 Hz); 8.00 (s, 2 Н, Н(11), Н(15)); 8.03 (s, 1 Н, OH); 12.70
(s, 1 Н, NH). 13C NMR (DMSO-d6), : 12.28 (C(10´), C(10´´));
20.00, 21.21 (C(8´), C(8´´), C(9´), C(9´´)); 27.09 (C(5´), C(5´´));
33.21 (C(3´), C(3´´)); 38.45 (С(6´), C(6´´)); 44.63, 44.92 (C(2´),
C(2´´), C(4´), C(4´´)); 47.72 (C(1´), C(1´´)); 49.77 (C(7´),
C(7´´)); 110.66, 118.16 (С(4), С(7)); 120.49 (С(10)); 121.12,
121.63 (С(5), С(6)); 123.55 (С(11), С(15)); 131.08 (С(12), С(14));
134.90, 143.79 (С(8), С(9)); 152.28 (C(13)); 157.13 (C(2)).
4-(1H-Benzо[d]imidazol-2-yl)-2,6-di-{1,7,7-trimethylbicy-
clo[2.2.1]hept-exo-2-yl}phenol (8) (racemate). A light brown
powder, m.p. 238—242 C. The yield was 64%. Found (%):
С, 82.00; Н, 8.56; N, 5.73. C33H42N2O. Calculated (%): С, 82.11;
Н, 8.77; N, 5.80. IR, /cm–1: 3601, 2949, 2875, 1620, 1535, 1458,
1
1431, 1399, 1365, 1321, 1271, 1184, 742. H NMR (DMSO-d6),

1004 Russ. Chem. Bull., Int. Ed., Vol. 68, No. 5, May, 2019
Dvornikova et al.
Antioxidant activity of compounds was evaluated by their
ability to inhibit the LPO processes in the substrate obtained
from the brain of laboratory mice.34,35 The brain was homo-
genized (10%) in physiological solution (0.9% aqueous NaCl,
pH 7.4) and centrifuged for 10 min. Then the supernatant (S1)
was collected, which contained water, proteins, DNA, RNA,
and lipids. The test compounds were added to the super-
natant as solutions in acetone (a final concentrations of 10 and
100 μmol L–1). After 30 min, LPO was initiated by the addition
of freshly prepared FeCl2 and ascorbic acid,36 the test samples
were incubated for 1 h at 37 C with slow stirring. The TBA-RS
content was determined on a Thermo Spectronic Genesys 20
spectrophotometer at  = 532 nm; the extinction coefficient 
used for calculations was equal to 1.56•105 L mol–1 cm–1 (see
Refs 35, 37, and 38).
Radical scavenging activity of the compounds was evaluated
by their ability to react with DPPH.39 The test compounds were
added to a solution of DPPH in MeOH (a final concentration
100 μmol L–1) with stirring, 30 min later the optical density of
the solution was measured at  = 517 nm on a Thermo Spectronic
Genesys 20 spectrophotometer.
Russian Federation (State Assignment Nos АААА-
А18-118012490385-8 and АААА-А18-118011120004-5).
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Received November 15, 2018;
in revised form March 21, 2019;
acceptedMarch 22, 2019