Inhibitory effects of benzimidazole containing new phenolic Mannich bases on human carbonic anhydrase isoforms hCA I and II

Article abstract of DOI:10.3109/14756366.2016.1156675

New phenolic mono and bis Mannich bases incorporating benzimidazole, such as 2-(aminomethyl)-4-(1H-benzimidazol-2-yl)phenol and 2,6-bis(aminomethyl)-4-(1H-benzimidazol-2-yl)phenol were synthesized starting from 4-(1H-benzimidazol-2-yl)phenol. Amines used

Full text of DOI:10.3109/14756366.2016.1156675

Journal of Enzyme Inhibition and Medicinal Chemistry
ISSN: 1475-6366 (Print) 1475-6374 (Online) Journal homepage: http://www.tandfonline.com/loi/ienz20
Inhibitory effects of benzimidazole containing
new phenolic Mannich bases on human carbonic
anhydrase isoforms hCA I and II
Halise Inci Gul, Zehra Yazici, Muhammet Tanc & Claudiu T. Supuran
To cite this article: Halise Inci Gul, Zehra Yazici, Muhammet Tanc & Claudiu T. Supuran
(2016): Inhibitory effects of benzimidazole containing new phenolic Mannich bases on
human carbonic anhydrase isoforms hCA I and II, Journal of Enzyme Inhibition and Medicinal
Chemistry, DOI: 10.3109/14756366.2016.1156675
To link to this article: http://dx.doi.org/10.3109/14756366.2016.1156675
Published online: 17 Mar 2016.
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ISSN: 1475-6366 (print), 1475-6374 (electronic)
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2016 Taylor & Francis. DOI: 10.3109/14756366.2016.1156675
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RESEARCH ARTICLE
Inhibitory effects of benzimidazole containing new phenolic Mannich
bases on human carbonic anhydrase isoforms hCA I and II
Halise Inci Gul1, Zehra Yazici1, Muhammet Tanc2, and Claudiu T. Supuran2
1Department of Pharmaceutical Chemistry, Faculty of Pharmacy, Ataturk University, Erzurum, Turkey and 2Neurofarba Department e Laboratorio di
Chimica Bioinorganica, Universita Degli Studi di Firenze, SestoFiorentino (Florence), Italy
Abstract
Keywords
New phenolic mono and bis Mannich bases incorporating benzimidazole, such as
2-(aminomethyl)-4-(1H-benzimidazol-2-yl)phenol and 2,6-bis(aminomethyl)-4-(1H-benzimida-
zol-2-yl)phenol were synthesized starting from 4-(1H-benzimidazol-2-yl)phenol. Amines used
for the synthesis included dimethylamine, pyrrolidine, piperidine, N-methylpiperazine and
morpholine. The CA inhibitory properties of these compounds were tested on the human
carbonic anhydrase (CA, EC 4.2.1.1) isoforms hCA I and hCA II. These new compounds, as many
phenols show moderate CA inhibitory properties.
Benzimidazole, carbonic anhydrase, enzyme
inhibition, Mannich bases, phenol
History
Received 26 January 2016
Revised 16 February 2016
Accepted 17 February 2016
Published online 17 March 2016
Introduction
glaucoma, neurological disorders including epilepsy and
Alzheimer’s disease27–29. Phenols also constitute an interesting
Mannich bases are an important group of compounds in medicinal
chemistry and they are synthesized by the Mannich reaction1,2
class of CA inhibitors (CAIs)30–34
.
.
Based on these informations, in this study, it was aim to
synthesize 2-(aminomethyl)-4-(1H-benzimidazol-2-yl)phenol and
2,6-bis(aminomethyl)-4-(1H-benzimidazol-2-yl)phenols incorpor-
ating benzimidazole moieties (Scheme 1) and to investigate their
CA inhibitory properties on hCA I and II.
Mannich bases have a wide range of biological activities, such as
cytotoxic3–6, anti-inflammatory7 and anticonvulsant8 activities.
Several types of phenolic Mannich bases were also reported with
cytotoxic6,9 and carbonic anhydrase (CA) inhibitory10 activities.
The reported biological mechanisms of action of Mannich bases
include thiol alkylation11–13; inhibition of mitochondrial respir-
Experimental
ation14,15
polymerization17.
;
topoisomerase
inhibition16
and
tubulin
Materials
One of the ring systems that is present in many pharmaco-
logical agents is the benzimidazole. The importance of this ring
system has been the subject of many reviews18,19. One of these
reviews summarized the anticancer, protein kinase, tyrosine
kinase, antihelmintic, antidiabetic, anticoagulant, analgesic, anti-
inflammatory, antiallergic and antihormonal activities of benzi-
midazole derivatives19.
Carbonic anhydrase (CA, EC 4.2.1.1) enzymes play important
roles in physiological and pathological processes20–26. Sixteen CA
isoforms have been identified in mammals. CA isoforms take part
in several vital biological processes, such as electrolyte secretion,
1H NMR (400 MHz) spectra was taken using a Bruker DPX-
500FT-NMR (Billerica, MA) and 13C NMR (100 MHz) spectra
was taken using a Varian spectrometer (Palo Alto, CA) Chemical
shifts (ꢀ) were reported in ppm. Melting points were determined
using an Electrothermal 9100 (IA9100, Bibby Scientific Limited,
Staffordshire, UK) instrument and are uncorrected. Mass specta
was taken using a Thermo Electron Coop. Finnigor LTQ (IT-MS/
ESI-MS).
Methods
acid-base balance, ion transport and lipogenesis, ureagenesis and Synthesis of 4-(1H-benzimidazol-2-yl)phenol (1)
bone resorption. Inhibitors or activators of these enzymes have
medical applications, such as diuretics, in the treatment of
The mixture of 4-hydroxybenzaldehyde (24.6 mmol) and sodium
hydrogen sulphide (24.6 mmol, 40%) in ethanol-water (3:1,
60 mL) was stirred at room temperature for 120 min. The white
solid precipitated, sodiumhydroxy(4-hydroxyphenyl)methanesul-
fonate, was filtered, and dried35. The mixture of sodiumhy-
droxy(4-hydroxyphenyl)methanesulfonate (4.4 mmol) and o-
phenylendiamine (4.4 mmol) in acetonitrile (15 mL) was heated
in a microwave oven (13.8 barr, 145 ꢀC, 200 W) for 10 min.
Reaction was monitored by TLC. Reaction was stopped when
sodiumhydroxy(4-hydroxyphenyl)methanesulfonate in reaction
Address for correspondence: Prof. Halise Inci Gul, Department of
Pharmaceutical Chemistry, Faculty of Pharmacy, Ataturk University,
Erzurum, Turkey. E-mail: incigul1967@yahoo.com
Prof. Claudiu T. Supuran, Neurofarba Department
e Laboratorio
di Chimica Bioinorganica, Universita Degli Studi di Firenze, via U.
Schiff 6, SestoFiorentino (Florence), 50019, Italy. E-mail:
claudiu.supuran@unifi.it

2
H. I. Gul et al.
J Enzyme Inhib Med Chem, Early Online: 1–5
medium finished. The solid precipitated was seperated, dried and heated in a microwave oven (13.8 barr, 110 ꢀC, 100 W) for 5 min.
crystallized from the mixture of methanol water (3:1). The dark- The reaction was followed by TLC. Reaction was stopped
1
brown colored compound (1) was obtained (74%)36,37. H NMR when compound 1 was consumed. The solvent was removed
(400 MHz, ppm, ꢀ) 6.92 (dd, J ¼ 6.8, 2.0 Hz, 2H), 7.16–7.19 (m, under vacuum. The viscous residue was triturated with diethyl
2H), 7.51–7.55 (m, 2H), 7.92 (dd, J ¼ 6.8, 2.0 Hz, 2H). 13C NMR ether and it was solidified. The crude compound was purified by
(100 MHz, ppm, ꢀ) 114.3, 115.7, 120.9, 122.3, 128.3, 152.7, crystallization from methanol:diethylether. The brown colored
159.8. M++1 Calculated: 211.2; M++1 Found: 211.2.
solid compound 5 was obtained (44%), m.p.: 189–191 ꢀC.
1H NMR (400 MHz, ppm, ꢀ) 1.71 (s, 8H), 2.52 (s, 8H), 3.68 (s,
4H), 7.18 (dd, J ¼ 5.9, 3.3 Hz, 2H), 7.56 (bs, 2H), 7.83 (s, 2H).
13C NMR (100 MHz, ppm, ꢀ) 23.7, 53.9, 56.4, 120.3, 122.4,
124.5, 127.1, 152.9, 158.9. M++1 Calculated: 377.4; M++1
Found: 377.3.
Synthesis of 4-(1H-benzimidazol-2-yl)-2-[(dimethylamino)-
methyl]phenol (2)
The mixture of the compound 1 (2.4 mmol), paraformaldehyde
(9.5 mmol) and water solution of dimethylamine (40%, 2.4 mmol)
in acetonitrile (10 mL) was refluxed for 90 min. The reaction was
monitored by TLC (chloroform:methanol (80:20)). When the
compound 1 finished, reaction was stopped. The reaction solvent
Synthesis of 4-(1H-benzimidazol-2-yl)-2-[(piperidin-1-yl)
methyl]phenol (6)
was removed under vacuum. The residue was purified by column The mixture of the compound 1 (2.9 mmol), formaldehyde
chromatography [silicagel 60 (70–230 mesh) and choloroform: solution (37%, 11.4 mmol) and piperidine (2.9 mmol) in aceto-
methanol (80:20)]. The white solid compound 2 was obtained nitrile (15 mL) was heated in a microwave oven (13.8 barr,
1
(37%); m.p.: 187–189 ꢀC. H NMR (400 MHz, ppm, ꢀ) 2.13 (s, 120 ꢀC, 100 W) for 5 min. The reaction was followed by TLC.
6H), 3.33 (s, 2H), 6.77 (d, J ¼ 8.4 Hz, 1H), 7.20 (dd, J ¼ 5.9, 3.1 Reaction was stopped when compound 1 was consumed. The
Hz, 2H), 7.60 (dd, J ¼ 5.9, 3.1 Hz, 2H), 7.96 (s, 1H), 8.07 (dd, solvent was removed under vacuum. The residue was purified by
J ¼ 8.5, 1.5 Hz, 1H). 13C NMR (100 MHz, ppm, ꢀ) 44.4, 62.4, column chromatography [silicagel 60 (70–230 mesh) and
115.1, 116.8, 120.9, 122.7, 122.7, 127.9, 139.5, 153.4, 160.6. chloroform:methanol (70:30)]. The suitable fraction was crystal-
M++1 Calculated: 268.3; M++1 Found: 268.2.
lized from methanol three times. The white solid compound 6 was
1
obtained (39%); m.p.: 254–256 ꢀC. H NMR (400 MHz, ppm, ꢀ)
Synthesis of 4-(1H-benzimidazol-2-yl)-2,6-bis[(dimethylamino)-
methyl]phenol (3)
1.59 (bs, 10H), 3.56 (s, 2H), 6.83 (d, J ¼ 8.4 Hz, 1H), 7.22 (dd,
J ¼ 5.9, 3.3 Hz, 2H), 7.58 (bs, 2H), 7.78 (dd, J ¼ 8.4, 1.8 Hz, 1H),
7.84 (s, 1H). 13C NMR (100 MHz, ppm, ꢀ) 25.9, 53.9, 61.9, 76.9,
116.7, 120.8, 122.6, 122.8, 126.9, 127.9, 152.5, 127.9. M++1
Calculated: 308.3; M++1 Found: 308.3.
The mixture of the compound 1 (14.3 mmol), paraformaldehyde
(57.1 mmol) and water solution of dimethylamine (40%,
57.1 mmol) in acetonitrile (40 mL) was heated in a microwave
oven (13.8 barr, 110 ꢀC, 150 W) for 5 min. The reaction was
monitored by TLC. Reaction was stopped when compound 1 was
consumed. The solvent was removed under vacuum and the
Synthesis of 4-(1H-benzimidazol-2-yl)-2,6-bis[(piperidin-1-yl)
methyl]phenol (7)
residue was purified by column chromatography [silicagel 60 The mixture of the compound 1 (4.8 mmol), paraformaldehyde
(70–230 mesh) and chloroform:methanol:ammonium hydroxyde (19 mmol) and piperidine (14.3 mmol) in acetonitrile (15 mL) was
(80:20:2)]. The light yellow colored solid compound 3 was heated in a microwave oven (13.8 barr, 120 ꢀC, 100 W) for 5 min.
1
obtained (26%); m.p.: 170–172 ꢀC. H NMR (400 MHz, ppm, ꢀ) The reaction was monitored by TLC. Reaction was stopped when
2.05 (s, 12H), 3.30 (s, 4H), 7.10 (dd, J ¼ 6.0, 3.1 Hz, 2H), 7.52 the compound 1 was consumed. The solvent was removed under
(dd, J ¼ 6.0, 3.1 Hz, 2H), 7.92 (s, 2H). 13C NMR (100 MHz, ppm, vacuum. The viscous residue obtained was trituated with
ꢀ) 44.7, 60.0, 115.0, 120.5, 122.4, 123.7, 128.2, 139.6, 153.3, diethylether and solidified. It was filtered and washed with
159.3 M++1 Calculated: 325.2; M++1 Found: 325.2.
acetone (2 ꢁ 10 mL) and dried. The crude compound was
crystallized from ethylacetate:methanol. The white colored com-
pound 7 was obtained (16%); m.p.: 238–240 ꢀC. 1H NMR
(400 MHz, ppm, ꢀ) 1.52 (bs, 4H), 1.58–1.62 (m, 6H), 2.49 (bs,
6H), 3.63 (s, 4H), 7.23 (dd, J ¼ 5.9, 2.9 Hz, 2H), 7.50 (bs, 2H),
7.82 (s, 2H). 13C NMR (100 MHz, ppm, ꢀ) 24.2, 25.9, 54.4, 59.4,
94.6, 120.3, 122.6, 123.5, 127.5, 159.3. M++1 Calculated: 405.5;
M++1 Found: 405.3.
Synthesis of 4-(1H-benzimidazol-2-yl)-2-[(pyrrolidin-1-yl)
methyl]phenol (4)
The mixture of the compound 1 (2.4 mmol), paraformaldehyde
(9.5 mmol) and pyrrolidine (2.4 mmol) in acetonitrile (7 mL) was
heated in a microwave oven (13.8 barr, 120 ꢀC, 100 W) for 5 min.
The reaction was monitored by TLC. Reaction was stopped when
compound 1 was consumed. The solvent was removed under
vacuum and the residue was purified by column chromatography Synthesis of 4-(1H-benzimidazol-2-yl)-2-[(4-methylpiperazin-1-
[silicagel 60 (70–230 mesh) and chloroform:methanol: ammo- yl)methyl]phenol (8)
nium hydroxyde (70:30:1)]. The orange coloured solid 4 was
The mixture of the compound 1 (1.4 mmol), formaldehyde
1
obtained (26%); m.p.: 200–203 ꢀC. H NMR (400 MHz, ppm, ꢀ)
solution (37%, 5.7 mmol) and N-methlypiperazine (1.4 mmol) in
1.73 (s, 4H), 2.42 (s, 4H), 3.53 (s, 2H), 6.76 (d, J ¼ 8.4 Hz, 1H),
acetonitrile (7 mL) was heated in a microwave oven (13.8 barr,
7.19 (dd, J ¼ 5.9, 3.1 Hz, 2H), 7.58 (dd, J ¼ 5.9, 3.1 Hz, 2H), 7.92
(d, J ¼ 1.5 Hz, 1H), 8.01 (dd, J ¼ 8.4, 1.5 Hz, 1H). 13C NMR
(100 MHz, ppm, ꢀ) 23.8, 53.4, 58.4, 115.0, 116.6, 120.8, 122.6,
123.2, 127.5, 127.6, 139.5, 153.3, 160.6. M++1 Calculated:
294.3; M++1 Found: 294.2.
120 ꢀC, 100 W) for 5 min. The reaction was monitored by TLC.
Reaction was stopped when compound 1 was consumed. The
solvent was removed under vacuum. The crude compound was
purified by column chromatography [silicagel 60 (70–230 mesh)
and choloroform:methanol:ammonium hydroxyde (70:30:1)]. The
yellow solid compound 8 was obtained (21%); m.p.:116–118 ꢀC.
1H NMR (400 MHz, ppm, ꢀ) 2.15 (s, 3H), 2.39–2.16 (m, 8H), 3.38
(s, 2H), 6.73 (d, J ¼ 8.6 Hz, 1H), 7.16 (dd, J ¼ 5.9, 3.2 Hz, 2H),
Synthesis of 4-(1H-benzimidazol-2-yl)-2,6-bis[(pyrrolidin-1-yl)
methyl]phenol (5)
The mixture of the compound 1 (9.5 mmol), paraformaldehyde 7.55 (dd, J ¼ 5.9, 3.2 Hz, 2H), 7.82 (d, J ¼ 1.8 Hz, 1H), 7.95 (dd,
(38 mmol) and pyrrolidine (38 mmol) in acetonitrile (30 mL) was J ¼ 8.6, 1.8 Hz, 1H). 13C NMR (100 MHz, ppm, ꢀ) 45.9, 52.2,

DOI: 10.3109/14756366.2016.1156675
Benzimidazole containing new phenolic Mannich bases
3
O
Scheme 1. Synthesis method of mono and bis
Mannich bases.
HO
SO Na
3
i
H
H
NaHSO3
+
HO
HO
ii
N
OH
N
H
1
iii
A
A
N
N
OH
A
OH
N
H
N
H
3, 5, 7, 9, 11
2, 4, 6, 8, 10
CH3
N
O
N
N
N
N
N
A:
4, 5
6, 7
8, 9
10, 11
2, 3
Amine : Corresponding amine of A
54.8, 60.8, 115.0, 116.8, 121.2, 121.9, 122.7, 127.8, 128.1, 139.4, 2H), 3.70 (bs, 4H), 6.83 (d, J ¼ 9.1 Hz, 1H), 7.23 (dd, J ¼ 6.0, 3.0
152.9, 160.0. M++1 Calculated: 323.4; M++1 Found: 323.3.
Hz, 2H), 7.60 (dd, J ¼ 6.0, 3.0 Hz, 2H), 7.89–7.91 (m, 2H). 13C
NMR (100 MHz, ppm, ꢀ) 52.9, 61.5, 66.8, 115.1, 116.8, 121.2,
121.7, 122.9, 127.5, 128.3, 152.5, 160.0. M++1 Calculated:
310.3; M++1 Found: 310.2.
Synthesis of 4-(1H-benzimidazol-2-yl)-2,6-bis[(4-methylpipera-
zin-1-yl)methyl]phenol (9)
The mixture of the compound 1 (4.8 mmol), paraformaldehyde
(19 mmol) and N-methlypiperazine (19 mmol) in acetonitrile
(20 mL) was heated in a microwave oven (13.8 barr, 120 ꢀC,
Synthesis of 4-(1H-benzimidazol-2-yl)-2,6-bis[(morpholin-4-
yl)methyl]phenol (11)
100 W) for 5 min. The reaction was monitored by TLC. Reaction The mixture of compound 1 (2.4 mmol), paraformaldehyde
was stopped when compound 1 was consumed. The solvent was (9.5 mmol) and morpholine (9.5 mmol) in acetonitrile (10 mL)
removed under vacuum. The viscous residue was triturated with was heated in a microwave oven (13.8 barr, 80 ꢀC, 200 W) for
diethylether to solidify. The solid obtained was crystallized from 20 min. Heating was continued for additional 90 min (at 1 atm,
methanol:diethylether. The white solid compound 9 was obtained 80 ꢀC, 300 W). The reaction was monitored by TLC. Although
1
(47%); m.p.: 231–233 ꢀC. H NMR (400 MHz, ppm, ꢀ) 2.19 (s, 110 min heating period was over and since reaction did not go
6H), 2.22–2.42 (m, 16H), 3.54 (s, 4H), 7.20 (d, J ¼ 4.8 Hz, 2H), further, reaction was stopped. The solvent was removed under
7.41 (bs, 2H), 7.75 (dd, J ¼ 7.0 Hz, 2H). 13C NMR (100 MHz, vacuum and the residue was purified by column chromatography
ppm, ꢀ) 46.0, 52.9, 54.9, 58.9, 111.0, 119.2, 120.7, 122.5, 122.8, [silicagel 60 (70–230 mesh) and diisopropylether:methanol
123.3, 127.9,152.5, 158.7. M++1 Calculated: 435.5; M++1 (80:20)]. The white colored solid 11 was obtained (26%);
Found: 435.3.
m.p.:209–210 ꢀC. 1H NMR (400 MHz, ppm, ꢀ) 2.28 (s, 8H),
3.39 (s, 4H), 3.51 (s, 8H), 7.14 (dd, J ¼ 5.7, 3.1 Hz, 2H), 7.51 (bs,
2H), 7.97 (s, 2H). 13C NMR (100 MHz, ppm, ꢀ) 53.2, 59.2, 66.8,
120.8, 122.7, 123.1, 128.3, 153.0, 158.5. M++1 Calculated:
409.4; M++1 Found: 409.3.
Synthesis of 4-(1H-benzimidazol-2-yl)-2-[(morpholin-4-yl)
methyl]phenol (10)
The mixture of the compound 1 (2.4 mmol), paraformaldehyde
(9.5 mmol) and morpholine (2.4 mmol) in acetonitrile (7 mL) was
heated in a microwave oven (13.8 barr, 120 ꢀC, 100 W) for 5 min.
Carbonic anhydrase inhibition assay
The reaction was monitored by TLC. Reaction was stopped when An Applied Photophysics stopped-flow instrument has been used
compound 1 was consumed. The solvent was removed under for assaying the CA catalyzed CO2 hydration activity by using
vacuum. The residue was purified by column chromatography method given by Khalifah38. Phenol red (at a concentration of
[silicagel 60 (70–230 mesh) and diisopropylether:methanol 0.2 mM) has been used as an indicator, working at the absorbance
(80:20)]. The white colored solid 10 was obtained (64%); m.p.: maximum of 557 nm, with 20 mM Hepes (pH 7.5) as buffer, and
1
120–123 ꢀC. H NMR (400 MHz, ppm, ꢀ) 2.42 (bs, 4H), 3.54 (s, 20 mM Na2SO4 (for maintaining constant the ionic strength),

4
H. I. Gul et al.
Table 1. Percent inhibition of hCA I and hCA II by
J Enzyme Inhib Med Chem, Early Online: 1–5
compared with hCA II. As seen from the data given in Table 1,
as many phenols the Mannich bases reported here are poor hCA
I/II inhibitors.
the synthesized compounds at 1 mM concentration of
inhibitor in the assay system.
Compound
hCA I (%)
hCA II (%)
Conclusion
1
2
3
4
5
6
7
8
20
26
20
20
18
23
21
22
19
18
18
84
10
21
7
In this study, new phenolic mono and bis Mannich bases were
prepared, and their CA inhibiting properties against hCA I and
hCA II were investigated. In our previous study, mono and bis
Mannich bases of [2–(4-hydroxybenzylidene)-2,3-dihydro-1H-
inden-1-one] were synthesized and their CA inhibitory properties
had been investigated10. In that study, preparation of Mannich
bases had decreased the CA inhibiting properties of the
compounds comparing to the ones they are derived from 2–
(4-hydroxybenzylidene)-2,3-dihydro-1H-inden-1-one. This situ-
ation had been attributed to bulky functionalities available at the
ortho position of phenol, which may affect the interaction of OH
group with the active site of the enzymes hCA I and hCA II10. The
increases in CA inhibition profile of the series reported here may
result from the benzimidazole moiety, which may interact with
the active site of CA enzyme in a hydroxybenzylidene manner.
11
12
20
13
20
14
24
25
92
9
10
11
Acetazolamide
following the initial rates of the CA-catalyzed CO2 hydration
reaction for a period of 10–100 s. The CO2 concentrations ranged
from 1.7 to 17 mM for the determination of the kinetic parameters
and inhibition constants. For each inhibitor at least six traces of
the initial 5–10% of the reaction have been used for determining
the initial velocity. The uncatalyzed rates were determined in the
same manner and subtracted from the total observed rates. Stock
solutions of inhibitor (0.1 mM) were prepared in distilled-
deionized water and dilutions up to 0.01 nM were done thereafter
with the assay buffer. Inhibitor and enzyme solutions were
preincubated together for 15 min at room temperature prior to
assay, in order to allow for the formation of the E-I complex. The
inhibition constants were obtained by non-linear least-squares
methods using PRISM (www.graphpad.com), and non-linear least
squares methods, values representing the mean of at least three
different determinations, as described earlier by us39. All CA
isoforms were recombinant ones obtained in-house as reported
earlier21. The cell pellets were lysed, and hCA II and hCA I were
purified through affinity chromatography using pAMBS resin.
Declaration of interest
The authors report no conflicts of interest. They are responsible
for the contents and writing of the paper.
Prof. H. Inci Gul thanks Ataturk University, BAP Department,
Turkey for the financial supports to this study.
References
1. Dimmock JR, Shyam K, Logan BM, et al. Syntheses and evaluation
of some Mannich bases derived from acetophenones against P388
lymphocytic leukemia and toxicological assessment of 3-dimethyl-
amino-2-dimethylaminomethyl-1-(4-methoxyphenyl)-1-propanone
dihydrochloride in rats. J Pharm Sci 1984;73:471–7.
2. Roman G. Mannich bases in medicinal chemistry and drug design.
Eur J Med Chem 2015;89:743–816.
3. Gul HI, Gul M, Erciyas E. Toxicity of some bis Mannich bases and
corresponding piperidinols in the brine shrimp (Artemia salina)
bioassay. J Appl Toxicol 2003;23:53–7.
4. Gul HI, Yerdelen KO, Gul M, et al. Synthesis of 40-hydroxy-30-
piperidinomethylchalcone derivatives and their cytotoxicity against
PC-3 cell lines. Arch Pharm (Weinheim) 2007;340:195–201.
5. Gul HI, Yerdelen KO, Das U, et al. Synthesis and cytotoxicity of
novel 3-aryl-1-(30-dibenzylaminomethyl-40-hydroxyphenyl)-prope-
nones and related compounds. Chem Pharm Bull (Tokyo) 2008;
56:1675–81.
6. Tugrak M, Yamali C, Sakagami H, Gul HI. Synthesis of mono
Mannich bases of 2-(4-hydroxybenzylidene)-2,3-dihydroinden-1-
one and evaluation of their cytotoxicities. J Enzyme Inhib Med
Chem 2016. [Epub ahead of print]. DOI: 10.3109/
14756366.2015.1070263.
7. Gul HI, Suleyman H, Gul M. Evaluation of the anti-inflammatory
activity of N,N0-bis(3-dimethylamino-1-phenyl-propylidene)hydra-
zinedihydrochloride. Pharm Biol 2009;47:968–72.
8. Gul HI, Calis U, Ozturk Z, et al. Evaluation of anticonvulsant
activities of bis(3-aryl-3-oxo-propyl) ethylamine hydrochlorides
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Arzneimittelforschung 2007;57:133–6.
Results and discussion
Synthesis of the starting compound 1 (4–(1H-benzimidazol-2-yl)-
phenol), was initially achieved according to literature proced-
ure36,37. In this study, compounds 2–11 (Scheme 1) were
successfully synthesized by the reaction of different and suitable
ratios of compound 1, paraformaldehyde/formaldehyde solution,
and amine in acetonitrile by the conventional method (2) or
microwave irradiation method (the other compounds except 2)
with yields of 16–63%. Their chemical structures were confirmed
by 1H NMR, 13C NMR and MS spectra. Experimental and
spectral details were presented in the ‘‘Experimental’’ section.
Amines used were dimethylamine (2, 3), pyrrolidine (4, 5),
piperidine (6, 7), N-methylpiperazine (8, 9), morpholine (10, 11).
Different amines having different pKa values were considered
since it may govern the deamination ratio of the Mannich bases,
thiol alkilating potential of them, and their bioactivities. Carbonic
anhydrase inhibiting properties of the compounds on hCA I and
hCA II isoenzymes were investigated at 10ꢂ6 M concentration
and the results are reported as percent inhibition in Table 1.
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compounds were higher values than the ones on hCA II, except
10 and 11, which are morpholine containing Mannich bases.
Especially, in the case of the compounds 1 (starting compound, 2
times), 3 (bis Mannich base with dimethylamine, 2.9 times), 4
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