Synthesis of diaryl ethers with acetylcholinesterase, butyrylcholinesterase and carbonic anhydrase inhibitory actions

Article abstract of DOI:10.1080/14756366.2016.1189422

A series of diaryl ethers were synthesized and their human (h) carbonic anhydrase (CA) isoenzymes hCA I and II, acetylcholinesterase (AChE), and butyrylcholinesterase (BuChE) inhibitory actions were investigated. The new compounds were synthesized from th

Full text of DOI:10.1080/14756366.2016.1189422

Journal of Enzyme Inhibition and Medicinal Chemistry
ISSN: 1475-6366 (Print) 1475-6374 (Online) Journal homepage: http://www.tandfonline.com/loi/ienz20
Synthesis of diaryl ethers with
acetylcholinesterase, butyrylcholinesterase and
carbonic anhydrase inhibitory actions
Fadime Özbey, Parham Taslimi, İlhami Gülçin, Ahmet Maraş, Süleyman
Göksu & Claudiu T. Supuran
To cite this article: Fadime Özbey, Parham Taslimi, İlhami Gülçin, Ahmet Maraş, Süleyman
Göksu & Claudiu T. Supuran (2016): Synthesis of diaryl ethers with acetylcholinesterase,
butyrylcholinesterase and carbonic anhydrase inhibitory actions, Journal of Enzyme Inhibition
and Medicinal Chemistry, DOI: 10.1080/14756366.2016.1189422
To link to this article: http://dx.doi.org/10.1080/14756366.2016.1189422
Published online: 31 May 2016.
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2016 Informa UK Limited, trading as Taylor & Francis Group. DOI: 10.1080/14756366.2016.1189422
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RESEARCH ARTICLE
Synthesis of diaryl ethers with acetylcholinesterase,
butyrylcholinesterase and carbonic anhydrase inhibitory actions
1
1
Fadime Ozbey , Parham Taslimi , Ilhami Gu¨lc¸in1,2, Ahmet Maras¸1, Su¨leyman Go¨ksu1, and Claudiu T. Supuran3,4
_
¨
2
1Department of Chemistry, Faculty of Science, Atatu¨rk University, Erzurum, Turkey, Department of Zoology, College of Science, King Saud
3
University, Riyadh, Saudi Arabia, Dipartimento di Chimica Ugo Schiff, Universita degli Studi di Firenze, Sesto Fiorentino, Firenz, Italy, and
4Neurofarba Department, Section of Pharmaceutical and Nutriceutical Sciences, Universita degli Studi di Firenze, Sesto Fiorentino, Florence, Italy
Abstract
Keywords
A series of diaryl ethers were synthesized and their human (h) carbonic anhydrase (CA)
isoenzymes hCA I and II, acetylcholinesterase (AChE), and butyrylcholinesterase (BuChE)
inhibitory actions were investigated. The new compounds were synthesized from the
corresponding phenols and bromobenzenes via the Ullmann reaction, by using dipicolinic
acid as a copper (I) complexing ligand. hCA I and II were inhibited with Kis in the low nanomolar
range of 102.01–127.13 nM against hCA I, and of 73.71–113.40 nM against hCA II, whereas the
inhibition constants against AChE were of 15.35–18.34 nM and against BChE in the range of
9.07–22.90 nM. The CA inhibition mechanism with these ethers is unknown, but may be similar
to that of aryl methyl ethers investigated earlier by computational approaches.
Acetylcholinesterase, butyrylcholinesterase,
carbonic anhydrase, diaryl ethers, enzyme
inhibition
History
Received 26 March 2016
Revised 10 May 2016
Accepted 10 May 2016
Published online 30 May 2016
Introduction
mechanism. They are ubiquitous metalloenzymes and present in
almost all living organism18,20–23. In humans, CAs are present
in a large variety of tissues such as the gastrointestinal tract,
the nervous system, the reproductive tract, lungs, kidneys, skin
and eyes24–26. This regulatory reaction supports many biochem-
ical and physiological processes associated with pH control, fluid
Diaryl ethers are important compounds in synthetic organic
chemistry and pharmaceutical chemistry. These compounds are
found in the substructures of some natural products. Hormones
such as triiodothyronine (1) and thyroxine (2)1, a trace amine
thyronamine (3) which is active at trace amine associated
receptors2, incorporate diaryl ether scaffolds in their structures.
The diaryl ether 4 is a natural product and is isolated from the arid
plant Prosopis cineraria (Fabaceae)3. Lactoperoxidase (LPO),
cyclooxygenase-1 and 2 (COX1 and COX2) enzymes inhibition of
4 has been reported by Liu et al.3 Another natural product,
obavatol (5), isolated from Magnolia obovata, has anti-inflam-
matory4 and anti-tumor activities5 (Figure 1). In addition, g/d
PPAR agonistic6, Candida albicans isocitrate lyase inhibitory7,
antimicrobial7, nitric oxide synthase inhibitory8 and some other
important inhibitory properties of diaryl ethers have been
reported9. Furthermore, CA inhibitory properties of dia-
rylthioethers10, coumarines and thiocoumarines were also stu-
died11,12. In our early studies, we explained the synthesis,
carbonic anhydrase (CA)13–16 and acetylcholinesterase
(AChE)17–19 inhibition of some aryl methyl ether derivatives.
The carbonic anhydrases (CAs, EC 4.2.1.1) are a superfamily
of metalloenzymes, which catalyze the interconversion between
secretion and ion transport27–29
.
CA
CO2 þ H2O , H2CO3 , HCOꢀ3 þ Hþ
Six distinct genetic CA families, the a-, b-, g-, d-, z- and
Z-CAs, are known to date, constituting an interesting example of
convergent evolution at the molecular level30–32. Also, to date, 16
different CA isoenzymes are described in various organisms33,34
.
These enzymes differ in their subcellular localization, catalytic
activity and susceptibility to different classes of inhibitors. Some
of them are cytosolic (CA I, CA II, CA III, CA VII and CA XIII),
others are membrane bound (CA IV, CA IX, CA XII and CA
XIV), two are mitochondrial (CA VA and CA VB), and one is
secreted in saliva (CA VI)35–37. It has been recently reported that
CA XV isoform is not expressed in humans or in living primates.
It is abundant in rodents and other higher vertebrates. Three
catalytic forms, namely CARP VIII, X and XI are the only known
CA-related proteins (CARP)38–40
.
ꢀ
CO2 and HCO3 by using a metal hydroxide nucleophilic
Inhibitors of carbonic anhydrase enzymes (CAIs) have a large
number of applications in therapy, including anticancer, anti-
glaucoma, and anti-osteoporosis agents. They used as diuretics,
anti-obesity, and anti-infective drugs. Also, these CAIs have been
used for the management of Alzheimer’s disease and a variety of
neurological disorders, among others. Many types of CAIs such
new derivatives have been reported recently, together with their
potential applications34,41. These chemical groups are used for the
¨
Address for correspondence: Prof. Dr. Su¨leyman Goksu, Faculty of
Science, Department of Chemistry, Atatu¨rk University, Erzurum, Turkey.
Tel: +90 442 2314389. Fax: +90 442 234109. E-mail: sgoksu@atau-
ni.edu.tr
Assoc. Prof. Dr. Ahmet Maras¸, Faculty of Science, Department of
Chemistry, Atatu¨rk University, Erzurum, Turkey. Tel: +90 442 2314375.
Fax: +90 442 234109. E-mail: amaras@atauni.edu.tr
clinical treatment of some conditions for decades42,43
.

¨
F. Ozbey et al.
2
J Enzyme Inhib Med Chem, Early Online: 1–7
CO H
CO H
I
I
I
I
I
2
2
NH
NH
2
2
HO
O
HO
O
I
I
1
Triiodothyronine
2 Thyroxine
HO
HO
OH
NH
2
O
HO
O
O
HO
OH
OH
3 Thyronamine
4
5
Obavatol
Figure 1. Some selected natural diaryl ethers 1–5.
Acetylcholinesterase (AChE) is an important component of procedures. Silica gel (SiO2, 60 mesh; Merck, Darmstadt,
central and peripheral cholinergic vertebrate synapses, where Germany) was used for column chromatography (CC). 1 mm of
it hydrolyzes acetylcholine (ACh) to choline (Ch) and acetate SiO2 60 PF (Merck) on glass plates was used for preparative thick-
(CH3COO-)44–46. ACh is one of the most important neurotrans- layer chromatography. Melting point of all compounds was
mitters found in the human central and peripheral nervous determined with capillary melting-point apparatus (BUCHI 530;
systems. An abnormally low concentration of ACh can cause Meierseggstrasse 40, 9230 Flawil, Switzerland) and recorded
various neuropsychological and neuropsychiatric disorders such uncorrected. IR spectra were recorded as solutions in 0.1 mm cells
as Alzheimer’s diseases (AD) and Parkinson’s diseases (PD)47,48
.
with a Mattson 1000 FT-IR spectrophotometer (Unicam. Ltd.,
AD is a progressive neurodegenerative disorder of the brain, York Street, Cambridge, UK). H- and 13C-NMR spectra were
which most commonly leads to dementia among the elderly. The recorded on 400 (100)-MHz Varian spectrometer (Danbury, CT)
main reason behind the AD is the decreased levels of ACh and the in deuterated solvents (CDCl3 and D2O) with tetramethylsilane
enzymes responsible for its synthesis and degradation in the (TMS, SiMe4) as an internal standard for protons and solvent
brain49,50. Also, butyrylcholinesterase (BChE, E.C. 3.1.1.8) is signals, as internal standard for carbon spectra. Chemical shift
involved in hydrolysis and regulation of butyrylcholine. AChE values were mentioned in ppm. Elemental analyses were recorded
and BChE sequences are similar up to 84% and hence, their on Leco CHNS-932 apparatus (Saint Joseph, MI). CA, AChE and
1
responses to a definite therapy almost yield in similar results51,52
.
BChE inhibitory properties of samples were determined as
However, during the progression of AD, brain AChE levels spectrophotometericaly (UV-1208, Shimadzu Co., Kyoto, Japan).
decline while BChE activity increases, suggesting that ACH
hydrolysis may occur to a greater extent via BChE catalysis53.
To date, most of the drugs and chemicals approved for treating
AD are AChE inhibitors (AChEIs), such as tacrine, rivastigmine,
galantamine and donepezil. However, some undesirable side
General procedure for the synthesis of diaryl ethers via
Ullmann Coupling
Dipicolinic acid (DPA, 0.4 mmol) and Cs2CO3 (2.8 mmol) was
dissolved in dry DMSO (10 mL) and it was stirred for neutral-
effects including vomiting, nausea and weight loss were observed
with these AChEIs while tacrine was found to be hepatotoxic54.
ization for 10 minutes under N2 atmosphere in a pressure tube. To
the solution CuI (0.2 mmol), phenol (1.2 mmol) and aryl halide
So, the design of novel agents such as AChEIs is still urgently
(1 mmol) was added under N2 atmosphere and nitrogen gas was
needed for AD treatment.
passed through the tube until it was closed. After the sealed tube
was stirred for 18 h at 120 ꢁC, the reaction mixture was cooled to
diaryl ethers have not been investigated properly. As the title
Tothebestofourknowledge,hCA,AChEandBChEinhibitionof
RT and diluted with CH2Cl2 (40 mL). Organic layer was washed
with 1 N NaOH (2 ꢂ 20 ml) and dried over MgSO4. Column
compounds show a wide biological activity spectrum, synthesis of
these compounds and their derivatives attract scientific attentions
for synthetic and biological properties. In this context, in the present
study, weaimedtoextend our studies onthesynthesis and biological
investigation of some novel diaryl ethers. For this purpose, the
chromatography of the residue with (Silica gel, 20 g;
EtOAc:Hexane 1:20) gave light yellow oily diaryl ethers 11–14.
synthesis of novel diaryl ethers was achieved via Ullmann nucleo-
philic coupling. All synthesized compounds were investigated for
their inhibition against AChE, BChE and hCA I, II isoenzymes.
In this context many efforts have been made for the develop-
ment of specific CAIs, and some remarkable results have been
achieved in the past 15 years55–59. In this study, we synthesized
some novel diaryl ethers 11–14. We determined their inhibition
properties against hCA I, hCA II, AChE and BChE and compared
their inhibition properties to acetazolamide (AZA) as a clinical
used carbonic anhydrase inhibitor. On the other hand, tacrine
(TAC) was used as standard AChE and BChE inhibitor.
3,3’-Oxybis(methoxybenzene) (11)
1H NMR (400 MHz, CDCl3) ꢀ 7.12 (1H, dd, J ¼ 15.2 Hz,
J ¼ 6.2 Hz, Ar-H), 6.68–6.59 (2H, dm, J ¼ 6.2 Hz, Ar-H), 6.58–
6.57(1H, m, Ar-H), 3.77 (9H, s, OCH3). 13C NMR (100 MHz,
CDCl3) ꢀ 161.1 (2OC), 158.45 (2OC), 130.3 (2CH), 111.3 (2CH),
109.2 (2CH), 105.2 (2CH), 55.6 (2OCH3). IR (CH2Cl2, cm ꢀ 1):
3052, 2924, 1587, 1455, 1264, 1149, 862, 686. Anal. Calcd for
(C14H14O3): C, 73.03; H, 6.13. Found: C, 73.30; H, 6.25
1,2-Dimethoxy-4-(3-methoxyphenoxy)benzene (12)
1H NMR (400 MHz, CDCl3) ꢀ 7.18 (1H, t, J ¼ 8.4 Hz, Ar-H), 6.81
(1H, d, J ¼ 8.4 Hz, Ar-H), 6.65–6.52 (4H, m, Ar-H), 3.86 (3H, s,
OCH3), 3.82 (3H, s, OCH3), 3.75 (3H, s, OCH3). 13C NMR
(100 MHz, CDCl3) ꢀ 161.1 (OC), 159.8 (OC), 150.3 (OC), 150.1
(OC), 145.8 (OC), 130.3 (CH), 128.6 (CH), 111.9 (CH), 111.3
(CH), 108.3 (CH), 104.8 (CH), 103.9 (CH), 56.5 (OCH3), 56.1
Experimental section
General information
All chemicals and solvents are commercially available. All
solvents were distilled and dried according to standard

DOI: 10.1080/14756366.2016.1189422
Metabolic enzymes inhibitory effects of diaryl ethers
3
(OCH3), 55.7 (OCH3). IR (CH2Cl2, cm ꢀ 1): 3065, 2929, 1663, (DTNB, D8130-1G, Sigma-Aldrich, Steinheim, Germany) was
1487, 1260, 1196, 841, 729. Anal. Calcd for (C15H16O4): C, used for the measurement of the AChE/BChE activities. Briefly,
69.22; H, 6.20. Found: C, 69.40; H, 6.32.
100 mL of Tris/HCl buffer (1 M, pH 8.0), 10 mL of sample
solution dissolved in deionized water at different concentrations
and 50 mL AChE/BChE (5.32 ꢂ 10ꢀ3 U) solution were mixed
and incubated for 10 min at 25 ꢁC. Then 50 mL of DTNB
(0.5 mM) was added. The reaction was then initiated by the
addition of 50 mL of AChI/BChI. The hydrolysis of these sub-
strates of AChI/BChI was monitored spectrophotometrically by
the formation of the yellow 5-thio-2-nitrobenzoate anion as the
result of the reaction of DTNB with thiocholine, released by
enzymatic hydrolysis of AChI/BChI, with absorption maximum
at a wavelength of 412 nm.
1,3-Dimethoxy-5-(4-methoxyphenoxy)benzene (13)
1H NMR (400 MHz, CDCl3) ꢀ 6.95 (2H, d, J ¼ 9.2 Hz, Ar-H),
6.87 (2H, d, J ¼ 9.2 Hz, Ar-H), 6.17–6.15 (2H, m, Ar-H), 6.12–
6.09 (1H, m, Ar-H), 3.80 (3H, s, OCH3), 3.73 (6H, s, OCH3). 13
C
NMR (100 MHz, CDCl3) ꢀ 161.7(2OC), 160.8 (OC), 156.3 (OC),
149.8 (OC), 121.3 (2CH), 115.0 (2CH), 96.3 (2CH), 94.8 (CH),
55.8 (OCH3), 55.7 (OCH3), 55.5 (OCH3). IR (CH2Cl2, cmꢀ1):
3024, 2925, 1595, 1463, 1212, 1131, 825, 720. Anal. Calcd for
(C15H16O4): C, 69.22; H, 6.20. Found: C, 69.40; H, 6.53.
Results and discussion
5,5’-Oxybis(1,3-dimethoxybenzene) (14)
Synthesis
1H NMR (400 MHz, CDCl3) ꢀ 6.16 (2H, bs, Ar-H), 6.13 (4H, bs,
Ar-H), 3.68 (6H, s, OCH3), 3.67 (6H, s, OCH3). 13C NMR
(100 MHz, CDCl3) ꢀ 161.7 (2OC), 160.8 (2OC), 158.8 (2OC),
97.7 (CH), 95.8 (CH), 55.5 (4 OCH3). IR (CH2Cl2, cmꢀ1): 3094,
2924, 1600, 1428, 1205, 1129, 823, 737. Anal. Calcd for
(C16H18O5): C, 66.20; H, 6.25. Found: C, 66.45; H, 6.35.
C(aryl)-O bond formation is one of the most important synthetic
methods for the synthesis of diaryl ethers. Copper (I)-mediated
Ullmann coupling reactions of aryl halides with phenols in the
presence of bases, ligands and in different solvents have widely
been used for the synthesis of diaryl ethers78. The main problem
on the Ullmann reaction is the harsh reaction conditions used for
the preparation of the ethers and the relatively moderate yields.
Different catalysts such as phenanthroline, 2,20-bipyridine,
tiophen carboxylic acid, picolinic acid, N-methylmorpholine and
some other compounds (i.e., acting as ligands for the copper ions)
have been investigated to improve the yields79. In addition,
different solvents (dioxane, DMF, DMSO and acetonitrile) and
different bases (pyridine, Cs2CO3 and K2CO3) have also been
used in the Cu (I)-catalyzed Ullmann reactions. In the present
study, Copper (I)-catalyzed Ullmann reactions of methoxy-
substituted bromobenzenes with methoxy-substituted phenols
were carried out in the presence of several ligands (nicotinic
acid, picolinic acid, dipicolinic acid, tiophene carboxylic acid),
bases (Na2CO3, K2CO3, Cs2CO3) and solvents (acetonitrile, DMF,
dioxane, DMSO) at different temperatures (25–120 ꢁC) to pene-
trate the most efficient reaction conditions. From these experi-
mental results, we found out that the most convenient method
for the synthesis of diaryl ethers was CuI catalyzed the reactions
of aryl bromides with phenols in the presence of dipicolinic
acid (DPA), Cs2CO3, DMSO in pressure tube at 120 ꢁC.
Therefore, the Ullmann reaction of aryl bromides 6 and 7 with
phenols 8–10 gave novel diaryl ethers 11–14 in high yields
(Scheme 1 and Table 1).
Biochemical studies
Carbonic anhydrase I and II isoenzyme purification and
inhibition studies
Recently, a specific interest has been oriented toward the slow
cytosolic isoform hCA I, and dominant physiologic isoform
hCA II60. Two physiologically relevant CA isoforms, hCA I, and
II, were included61,62. In this study, both hCA I, and II isoenzymes
were purified by Sepharose-4B-L-tyrosine-sulfanilamide affinity
chromatography63–65
. The affinity chromatography consists
Sepharose-4B-L-tyrosine-sulfanilamide that acts as affinity
matrix for selective retention of CA isoenzymes66–68. The
column material was prepared according to
a previous
method69. Thus, homogenate solution acidity was adjusted and
supernatant was transferred to the previously prepared column70.
The proteins flow in the column eluates was spectrophotometric-
ally determined at 280 nm. Sodium dodecyl sulphate–polyacryl-
amide gel electrophoresis (SDS–PAGE) was applied for detection
for of both isoenzymes purity71. After the visualizing by SDS–
PAGE process, a single band was observed for each isoenzyme.
This protein-imaging method was previously described72. In this
application, the imaging method was performed out in 10 and 3%
acrylamide for the running and the stacking gel, respectively, with
0.1% SDS61.
Biological activity
Both CA isoenzymes activities were determined according to
the method of Verpoorte et al.73 and described previously74. The
protein quantity was spectrophotometrically measured at 595 nm
during the purification steps according to the Bradford method75.
Bovine serum albumin was used as the standard protein61. For
determining the inhibition effect of each isoenzyme, some novel
diaryl ether (11–14) derivatives and an Activity (%) ꢀ [Diaryl
ethers] graph was drawn. To determine Ki values, three different
novel diaryl ether 11–14 concentrations were tested. In these
experiments, different substrat concentration was used and
Lineweaver–Burk curves were drawn76, as previously described70.
Both physiologically relevant hCA I, and II isoforms and AChE
and BChE were studied in the enzyme inhibition part of this
study. A detailed in below, some novel diaryl ethers 11–14 were
evaluated for their inhibition properties against hCA I, and II
isoenzymes, showing generally an efficient inhibition. The
chemical structures of some novel diaryl ethers 11–14 are given
in Table 1. Also, CA I, and II inhibiting effects of some novel
diaryl ethers 11–14 are shown in Table 2. It was well known that
developing isoenzyme-specific CAIs should be highly beneficial
in obtaining novel classes of drugs devoid of various undesired
side-effects80. We declare here the first study on the inhibitory
effects of novel diaryl ethers 11–14 against hCA I, and II using
esterase activity.
AChE/BChE activity determination
The inhibitory effect of some novel diaryl ethers 11–14 on
Low cytosolic isoenzyme hCA I is found in many tissues,
AChE/BChE activities were measured according to spectro- however, it was demonstrated that this isoenzyme is involved in
photometric method of Ellman et al.77 Acetylthiocholine iodide retinal and cerebral edema, and its inhibition may be a valuable
or butyrylthiocholine iodide (AChI/BChI) were used as sub- tool for fighting these conditions. The hCA I is ubiquitously
strates for both reactions. 5,50-Dithio-bis(2-nitro-benzoic)acid expressed in the body and can be found in high concentrations

¨
F. Ozbey et al.
4
J Enzyme Inhib Med Chem, Early Online: 1–7
in the blood and gastrointestinal tract. The results obtained from inhibitor and is approved for the treatment of a range of conditions
this study clearly indicate that these some novel diaryl ethers 11– including glaucoma, epilepsy, and altitude sickness81.
14 had effective inhibition profile against slow cytosolic isoform
Cytosolic hCA II isoenzyme is involved in different diseases
hCA I, and cytosolic dominant rapid isozymes hCA II with low including edema, epilepsy, altitude sickness and glaucoma. For
nanomolar range. Ki values are in the range of 102.01 2.81– the physiologically dominant isoform hCA II, all novel diaryl
108.35 5.02 nM for hCA I isoenzyme. On the other hand, ethers 11–14 showed Kis of 73.71 1.50–113.40 2.55 nM
acetazolamide (AZA) was considered for broad-specificity CA (Table 2). However, novel diaryl ether 14, possessing two
inhibitor owing to its widespread inhibition of CAs, dwhich methoxy groups (ꢀOCH3) at the meta-position at the each
showed Ki value of 190.56 1.31 nM against hCA I. However, phenyl ring, was the best hCA II inhibitor (Ki: 73.71 1.50 nM).
diaryl ethers (12), possessing methoxy (–OCH3) group at However, all novel diaryl ethers 11–14 have greater inhibition
the ortho-position at the phenyl ring was the best hCA I inhibitor profiles against hCA II and these inhibition values were lower
(Ki: 102.01 2.81 nM). The inhibition effects of all novel diaryl than that of AZA (Ki: 40.81 1.35 nM).
ethers (11–14) are higher than that of acetazolamide (AZA;
The chemical possessing AChE inhibitory effects are used for
Ki: 190.56 1.31 nM) (Table 2). AZA is considered the good CA the treatment of AD. However, these drugs have many undesired
side effects including vomiting, nausea and weight loss. For
example, tacrine as AChEIs was found to be hepatotoxic54. So, the
design of novel agents as AChEIs is still urgently needed for AD
HO
Br
+
O
treatment. Thus, the development and utilization of new effective
AChEIs is highly desired. Currently, the most prescribed cholin-
esterase inhibitors (ChEIs) are donepezil, galantamine, and
rivastigmine. These drugs are used to treat patients with
mild-to-moderate AD. BChE has a specific role in cholinergic
CuI, DPA
R
R
R
R
Cs2CO3, DMSO
120°C, 18h
Scheme 1. The synthesis of diaryl ethers 11–14.
Table 1. Reagents, products and yields.
Aryl halide
Phenol
Diaryl ether
Yield (%)
O
OH
OH
OH
Br
Br
Br
O
O
O
O
O
O
O
O
H C
3
CH
CH
CH
3
3
3
H C
3
CH
3
85
6
6
11
8
O
O
O
O
O
H C
3
H C
3
CH
3
82
86
9
12
H C
3
H C
3
O
CH
3
H C
3
H C
3
O
O
O
O
13
7
8
O
O
CH
CH
3
3
OH
O
O
Br
O
H C
3
H C
3
CH
CH
3
3
83
14
7
10
O
O
O
O
CH
H C
3
CH
H C
3
3
3
Table 2. Human carbonic anhydrase I and II isoenzymes (hCA I and II), acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) enzymes
inhibition effects of some novel diaryl ethers 11–14.
IC50 (nM)
r2
AChE
Ki (nM)
Compounds hCA I
r2
hCA II
r2
BChE
r2
hCA I
hCA II
AChE
BChE
11
12
161.16 0.9661 111.77
111.77 0.9768 103.43
0.9780 18.93 0.9671 45.89 0.9850 104.01 5.05 103.84 3.11 17.64 0.34 14.39 0.24
0.9436 11.91 0.9823 37.87 0.9868 102.01 2.81 113.40 2.55 15.35 0.22 22.90 0.42
13
14
AZA*
TAC**
144.37 0.9530
133.27 0.9577
130.74 0.9923
97.605 0.9731 16.78 0.9867 40.06 0.9765 127.13 4.92
88.846 0.9907 15.29 0.9837 19.63 0.9906 108.35 5.02
93.85 2.85 16.86 0.23 12.58 0.13
73.71 1.50 18.34 0.43
9.07 0.22
–
23.49 0.74 46.80 0.22
64.166 0.9949
–
–
–
–
–
39.15 0.9951 15.07 0.9895
190.56 1.31
–
40.81 1.35
–
–
–
–
–
*Acetazolamide (AZA) was used as a standard inhibitor for both hCA I and II isoenzymes.
**Tacrine (TAC) was used as a standard inhibitor for AChE and BChE enzymes.

DOI: 10.1080/14756366.2016.1189422
Metabolic enzymes inhibitory effects of diaryl ethers
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neurotransmission and it has been associated with AD. Individual
ChEIs differ from each other with respect to their pharmacologic
properties. Galantamine and donepezil are short-acting reversible
competitive inhibitors, whereas rivastigmine is actively metabo-
lized by ChE. Also, primary target of donepezil and galantamine
is AChE; however, rivastigmine shows equal affinity for both
AChE and BChE enzymes. BChE levels in the body exceed those
of AChE in all tissues except muscle and brain. The human body
contains 10 times more BChE than AChE. It was reported that in
AD, AChE is lost up to 85% in specific brain regions, whereas
BChE levels rise with disease progression. It was also shown that
the main AChE inhibitory effect was primarily associated with
aromatic compounds and, to a lesser degree, with aliphatic
compounds50,75. Novel diaryl ethers 11–14, effectively inhibited
AChE and BChE with Ki values ranging 15.35 0.22–
18.34 0.43 and 9.07 0.22–22.90 0.42 nM, respectively
(Table 2), which were calculated from Lineweaver–Burk
plots77. On the other hand, donepezil, which is used for the
treatment of mild-to-moderate AD and various other memory
impairments, had been shown to lower AChE inhibition activity
(IC50: 55 nM)82. In our study, we found that tacrine, which
clinically acts as AChE/BChE inhibitors showed Ki values of
23.49 0.74 nM for AChE and 46.80 0.22 nM for BChE. These
results clearly showed that novel diaryl ethers 11–14 had more
inhibition profile against BChE compared to both standard AChE/
BChE inhibitors (Tacrine and donepezil).
Conclusion
¨
15. Goksu S, Naderi A, Akbaba Y, et al. Carbonic anhydrase inhibitory
properties of novel benzylsulfamides using molecular modeling and
experimental studies. Bioorg Chem 2014;56:75–82.
In conclusion, the Cu(I)-catalyzed Ullmann reaction of aryl
bromides 6 and 7 with phenols 8–10 in DMSO in the presence of
DPA as a ligand and Cs2CO3 base gave novel diaryl ethers 11–14
in good yields. Compound 14 is a methoxylated derivative of the
natural product 4. Therefore, the synthetic methodology described
here is also an alternative method for the synthesis of 4. All novel
diaryl ethers 11–14 were evaluated against cytosolic hCA I, and II
isoenzymes, AChE and BChE. These novel diaryl ethers 11–14
have shown effective nanomolar inhibition against hCA I, and II
isoenzymes, AChE and BChE. Novel diaryl ethers 11–14 potently
inhibited these metabolic enzymes. The CA inhibition mechanism
with these ethers is unknown, and may be similar to that of the
reported aryl methyl ether derivatives, investigated earlier by
computational methods13.
˘
16. Balaydın HT, Durdagı S, Ekinci D, et al. Inhibition of human
carbonic anhydrase isozymes I, II and VI with a series of bisphenol,
methoxy and bromophenol compounds. J Enzyme Inhib Med Chem
2012;27:467–75.
_
17. Aksu K, Topal F, Gulcin I, et al. Acetylcholinesterase inhibitory and
antioxidant activities of novel symmetric sulfamides derived from
phenethylamines. Arch Pharm 2015;348:446–55.
_
¨
¨
18. Akincioglu A, Goc¸er A, Gulc¸in I, et al. Discovery of potent carbonic
anhydrase and acetylcholine esterase inhibitors: Novel sulfamoyl-
carbamates and sulfamides derived from acetophenones. Bioorg
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¨
19. Oztas¸kın N, C¸ etinkaya Y, Taslimi P, et al. Antioxidant and
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derivatives. Bioorg Chem 2015;60:49–57.
20. Supuran CT. Carbonic anhydrase inhibitors: an editorial. Expert
Opin Ther Pat 2013;23:677–9.
21. Scozzafava A, Kalın P, Supuran CT, et al. The impact of
hydroquinone on acetylcholine esterase and certain human carbonic
anhydrase isoenzymes (hCA I, II, IX, and XII). J Enzyme Inhib Med
Chem 2015;30:941–6.
Declaration of interest
There is no declaration of interest for this work. The authors are
indebted to the Scientific and Technological Research Council of
22. Yıldırım A, Atmaca U, Keskin A, et al. N-Acylsulfonamides
strongly inhibit human carbonic anhydrase isoenzymes I and II.
Bioorg Med Chem 2015;23:2598–605.
¨
_
Turkey (TUBITAK, Grant No. 115Z422) for financial support of
this work.
23. Supuran CT. Carbonic anhydrases: novel therapeutic applications for
inhibitors and activators. Nat Rev Drug Discov 2008;7:168–81.
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