Synthesis and biological evaluation of novel 8-substituted quinoline-2-carboxamides as carbonic anhydrase inhibitors

Article abstract of DOI:10.1080/14756366.2019.1626376

A series of novel 8-substituted-N-(4-sulfamoylphenyl)quinoline-2-carboxamides was synthesised by the reaction of 8-hydroxy-N-(4-sulfamoylphenyl) quinoline-2-carboxamide with alkyl and benzyl halides. The compounds were assayed for carbonic anhydrase (CA)

Full text of DOI:10.1080/14756366.2019.1626376

Journal of Enzyme Inhibition and Medicinal Chemistry
ISSN: 1475-6366 (Print) 1475-6374 (Online) Journal homepage: https://www.tandfonline.com/loi/ienz20
Synthesis and biological evaluation of novel 8-
substituted quinoline-2-carboxamides as carbonic
anhydrase inhibitors
Pavitra S. Thacker, Pirpasha Shaikh, Andrea Angeli, Mohammed Arifuddin &
Claudiu T. Supuran
To cite this article: Pavitra S. Thacker, Pirpasha Shaikh, Andrea Angeli, Mohammed Arifuddin &
Claudiu T. Supuran (2019) Synthesis and biological evaluation of novel 8-substituted quinoline-2-
carboxamides as carbonic anhydrase inhibitors, Journal of Enzyme Inhibition and Medicinal
Chemistry, 34:1, 1172-1177, DOI: 10.1080/14756366.2019.1626376
To link to this article: https://doi.org/10.1080/14756366.2019.1626376
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JOURNAL OF ENZYME INHIBITION AND MEDICINAL CHEMISTRY
2019, VOL. 34, NO. 1, 1172–1177
https://doi.org/10.1080/14756366.2019.1626376
RESEARCH PAPER
Synthesis and biological evaluation of novel 8-substituted
quinoline-2-carboxamides as carbonic anhydrase inhibitors
Pavitra S. Thackera, Pirpasha Shaikha, Andrea Angelib , Mohammed Arifuddina and Claudiu T. Supuranb
b
aDepartment of Medicinal Chemistry, National Institute of Pharmaceutical Education and Research (NIPER), Hyderabad, India; Neurofarba
Department, Section of Pharmaceutical Chemistry, University of Florence, Florence, Italy
ABSTRACT
ARTICLE HISTORY
Received 2 May 2019
Revised 26 May 2019
Accepted 28 May 2019
A series of novel 8-substituted-N-(4-sulfamoylphenyl)quinoline-2-carboxamides was synthesised by the
reaction of 8-hydroxy-N-(4-sulfamoylphenyl) quinoline-2-carboxamide with alkyl and benzyl halides. The
compounds were assayed for carbonic anhydrase (CA) inhibitory activity against four hCA isoforms, hCA I,
hCA II, hCA IV, and hCA IX. Barring hCA IX, all the isoforms were inhibited from low to high nanomolar
range. hCA I was inhibited in the range of 61.9–8126 nM, with compound 5h having an inhibition con-
stant of KI ¼ 61.9 nM. hCA II was inhibited in the range of 33.0–8759 nM, with compound 5h having an
inhibition constant of 33.0 nM and compounds 5a and 5b having inhibition constants of 88.4 and
85.7 nM, respectively. hCA IV was inhibited in the range of 657.2–6757 nM. Hence, compound 5h, possess-
ing low nanomolar hCA I and II inhibition, can be selected as a lead for the design of novel CA I and II
inhibitors.
KEYWORDS
Carbonic anhydrases;
metalloenzyme;
sulfonamides; quinoline; tail
approach
H
N
H
N
H
N
N
N
N
O
O
O
O
O
O
SO2NH2
SO2NH2
SO2NH2
5h
5b
Br
5a
hCA I Ki - 61.9 nM
hCA II Ki - 33 nM
hCA IV Ki - 1749 nM
hCA IX Ki - >10000 nM
hCA I Ki - 444.4 nM
hCA II Ki - 85.7 nM
hCA IV Ki - 3927 nM
hCA I Ki - 640.7 nM
hCA II Ki - 88.4 nM
hCA IV Ki - 691.5 nM
NO2
hCA IX Ki - >10000 nM
hCA IX Ki - >10000 nM
1. Introduction
protozoa, algae, bacteria, and the cytoplasm of green plants. The
b-CAs are bacteria, algae, fungi, some archaea, and the chloro-
plasts of monocots and dicots. The c-CAs are found in archaea
and bacteria. The d-, f-, -, h-, and i-CAs are present in marine dia-
toms. The g-CAs are present in various Plasmodium species5.
a-CAs are widely distributed in many organisms and their num-
ber of isoforms is rather high, with 15 such CAs being present in
humans and other primates and 16 in other mammals. In humans,
the sub-cellular localisation of the isoforms is as follows: CA I, CA
II, CA III, CA VII, CA VIII, CA X, CA XI, and CA XIII are cytosolic, CA
IV, CA IX, CA XII, CAX IV, and CA XV are membrane-bound, CA VA
and VB are mitochondrial, whereas CA VI is secreted in milk and
saliva1–4. Different isoforms are implicated in different diseases;
hence, selective inhibition of a particular isoform may lead to the
rectification of that particular disease in which it plays a major
Carbonic anhydrases (CAs, EC 4.2.1.1) are a group of convergently
evolved, ubiquitous metalloenzymes, which play a pivotal role in
the maintenance of pH homoeostasis across all living phyla1–4
.
They catalyse the reversible interconversion of carbon dioxide to
bicarbonate and protons under physiological conditions via a ping
pong mechanism, which is normally very slow under non-catalytic
conditions (reaction 1):
HCO3- + H+
(1)
CO2 + H2O
By efficiently catalysing the above reaction, CAs play an
important role in many metabolic processes like facilitating the
transport of CO2 between the metabolising tissues and lungs, lipo-
genesis, gluconeogenesis, and ureagenesis1–4
.
role1–4
.
Up until now, eight genetically distinct families of CAs are
known to be present across all phyla. These seven families are a-,
b-, c-, d-, f-, g-, h-, and the recently reported i-class5. The metal
ion at the active site, which plays a highly important role in the
catalytic activity of the enzyme, is variable among the different
families, and can be Zn(II), Cd(II), Fe(II), and even Mn(II) in the
Sulfonamides and their isosteres (sulfamates and sulfamides)
have been known for many years for their effective inhibition of
many CA isoforms5–8. Their mode of inhibition is by binding to
the metal ion present in the active site, in a deprotonated form,
as sulfonamidate anion. About 20 compounds incorporating the
i-CAs1–5. The a-CAs are predominantly found in vertebrates, sulfonamide moiety are in clinical use for many years, with one of
CONTACT Mohammed Arifuddin
arif.niperhyd@gov.in
Department of Medicinal Chemistry, National Institute of Pharmaceutical Education and Research
claudiu.supuran@unifi.it Neurofarba Deparment, Sezione di Scienze Farmaceutiche e
(NIPER), Balanagar, Hyderabad 500037, India; Claudiu T. Supuran
ꢀ
Nutraceutiche, Universita degli Studi di Firenze, Via Ugo Schiff 6, Sesto Fiorentino, Florence 50019, Italy
Supplemental data for this article can be accessed here.
ß 2019 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group.
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use,
distribution, and reproduction in any medium, provided the original work is properly cited.

JOURNAL OF ENZYME INHIBITION AND MEDICINAL CHEMISTRY
1173
H3C
N
N
N
N
N
SO2NH2
H3COCHN
SO2NH2
H3COCN
SO2NH2
S
S
S
EtO
Acetazolamide
Methazolamide
Ethoxzolamide
SO2NH2
NHEt
NHEt
N
SO2NH2
SO2NH2
S
Me
S
O O
S
MeO(H2C)3
S
N
N
O O
CH3
Dorzolamide
Brinzolamide
F
F
F
Celecoxib
O
H
N
H
N
NH
S
O
O
O
H2NO2S
F
SLC-0111
Saccharin
Figure 1. Structures of some clinically used sulfonamides.
melting point apparatus (SMP 30) was used in determining the
melting points of the compounds, which are uncorrected. 1H and
13C NMR spectra were recorded using Bruker Avance 500 MHz and
125 MHz respectively using DMSO-d6 as the solvent. Chemical shift
values are recorded in ppm using TMS as the internal standard.
HRMS were determined by Agilent QTOF mass spectrometer 6540
series instrument and were performed using ESI techniques
at 70 eV.
H
N
N
O
O
R
SO2NH2
Head Part
Tail Part
Figure 2. The “Tail approach” method for the design of novel CA inhibitors in
this work.
the compounds, SLC-0111, developed by one of our groups, being
in phase II clinical trials. Some of the sulfonamide molecules in
2.1.1. General procedure for the preparation of 8-hydroxy-N-(4-
sulfamoylphenyl)quinoline-2-carboxamide
clinical use since many years are shown in Figure 16–11
.
To a stirred solution of intermediate 3 (1 g, 5 mmol 1 eq.) in dry
DMF (10 ml) HATU was added (3 g, 7.9 mmol, 1.5 eq.) at 0 ꢀC. The
resultant solution was stirred for one hour at 0 ꢀC. Thereafter, sulf-
anilamide (1 g, 5.5 mmol, 1.1 eq.) and DIPEA (2 g, 15 mmol, 3 eq.)
were added to the reaction mixture and the resultant solution
was allowed to stir for overnight at room temperature. The com-
pletion of the reaction was monitored by TLC. On completion of
the reaction mixture as evidenced by the TLC, it was dumped into
crushed ice. The precipitated solid was collected by filtration and
it was subjected to column chromatography using silica gel
60–120 mesh as the stationary phase and EtOAc:hexane 6:4 as
Quinoline is an aromatic, heterocyclic, nitrogen containing
compound which is having a benzene ring fused with a pyridine
ring at two adjacent carbon atoms12. The quinoline nucleus
exhibit diverse biological activities such as anticancer, antimalarial,
antitubercular, antibacterial, antiprotozoal, antiproliferative, anti-
inflammatory, antihypertensive, and anti-HIV activity13. One of the
potent quinoline derivatives is 8-hydroxy quinoline. It is obtained
from plants as well as by synthesis. It is basically a small, planar
and lipophilic molecule having an array of biological activities and
also good metal chelating properties14. Supuran and coworkers
have previously investigated the quinoline scaffold, wherein they
mobile phase to afford intermediate
Yield (60%).
4 as a beige solid.
found it to exhibit potent activities on various CA isoforms15–17
.
Hence, in order to further probe the efficacy of the quinoline scaf-
fold for CA inhibition, the “tail approach” (Figure 2) was adopted
and novel 8-substituted-N-(4-sulfamoylphenyl) quinoline-2-carbox-
amides were synthesised and assayed for their CA inhibitory activ-
ity against four CA isoforms, namely, CA I, II, IV, and IX. The drug
acetazolamide (AAZ) was used as a drug standard.
2.1.2. General procedure for the preparation of 8-substituted-N-(4-
sulfamoylphenyl)quinoline-2-carboxamidederivatives (5a–h)
To a stirred solution of intermediate 4 (80 mg, 0.2 mmol, 1 eq.) in
acetone (5 ml) K2CO3 was added (22 mg, 0.4 mmol, 2 eq.) and the
resultant solution was allowed to stir for 15 min. Thereafter, alkyl
or benzyl halide (1.5 eq.) was added to the reaction mixture and
it was allowed to stir for overnight at room temperature. The
completion of the reaction was monitored by TLC. The reaction
solvent was distilled off under vacuum and the crude residue
was subjected to column chromatography using silica gel
60–120 mesh as the stationary phase and EtOAc:hexane 4:6 as
2. Materials and methods; chemistry part
2.1. General
All the chemicals and solvents were procured and utilised as such
from the suppliers. Wherever necessary, anhydrous solvents were
used. Thin layer chromatography (TLC) analysis was done by utilis-
ing Merck silica gel 60 F254 aluminium plates. Stuart digital mobile phase to afford the final compounds 5a–h.

1174
P. S. THACKER ET AL.
2.1.3. 8-((4-Nitrobenzyl)oxy)-N-(4-sulfamoylphenyl)quinoline-2-car- 2.1.8. 8-((2,5-Difluorobenzyl)oxy)-N-(4-sulfamoylphenyl)quinoline-
2-carboxamide (5f)
Yellow solid, yield: 55%; mp: 257–259 ꢀC; 1H NMR (500 MHz, Yellow solid, yield: %;65 mp: 260–262 ꢀC H NMR (500 MHz, DMSO)
boxamide (5a)
1
d 10.84 (s, 1H), 8.63 (d, J ¼ 8.5 Hz, 1H), 8.25 (d, J ¼ 8.5 Hz, 1H), 8.02
(d, J ¼ 8.7 Hz, 2H), 7.87 (d, J ¼ 8.6 Hz, 4H), 7.71 (d, J ¼ 6.7 Hz, 2H),
7.51 (dd, J ¼ 6.5, 2.2 Hz, 1H), 7.35–7.31 (m, 3H), 5.49 (s, 2H). 13C
NMR (125 MHz, DMSO) d 163.38, 159.82, 157.91, 157.19, 155.27,
154.19, 148.75, 141.38, 139.66, 138.81, 138.49, 130.77, 129.57,
127.29, 120.98, 119.59, 117.45, 117.19, 116.62, 116.16, 112.48,
64.56. HRMS (ESI): m/z calculated for C23H17F2N3O4S 470.0986,
found 470.0994 [M þ H]þ.
DMSO) d 10.78 (s, 1H), 8.62 (d, J ¼ 8.5 Hz, 1H), 8.31 (d, J ¼ 8.5 Hz,
2H), 8.26 (d, J ¼ 8.5 Hz, 1H), 8.01 (d, J ¼ 8.6 Hz, 2H), 7.97 (d,
J ¼ 8.4 Hz, 2H), 7.90 (d, J ¼ 8.6 Hz, 2H), 7.68 (d, J ¼ 7.0 Hz, 2H), 7.42
(d, J ¼ 6.0 Hz, 1H), 7.35 (s, 2H), 5.62 (s, 2H). 13C NMR (125 MHz,
DMSO) d 163.46, 154.24, 148.83, 147.53, 145.62, 141.35, 139.69,
138.78, 138.45, 130.82, 129.49, 128.39, 127.34, 124.04, 120.81,
119.86, 119.69, 112.24, 69.58. HRMS (ESI): m/z calculated for
C23H18N4O6S 479.1025, found 479.1030 [M þ H]þ.
2.1.9. 8-(Prop-2-yn-1-yloxy)-N-(4-sulfamoylphenyl)quinoline-2-car-
boxamide (5g)
2.1.4. 8-((2-Bromobenzyl)oxy)-N-(4-sulfamoylphenyl)quinoline-2-
carboxamide (5b)
1
Yellow solid, yield: 30%; mp: 240–242 ꢀC H NMR (500 MHz, DMSO)
1
Yellow solid, yield: 40%; mp: 270–272 ꢀC H NMR (500 MHz, DMSO)
d 10.76 (s, 1H), 8.62 (d, J ¼ 8.5 Hz, 1H), 8.24 (d, J ¼ 8.5 Hz, 1H), 8.07
(d, J ¼ 8.7 Hz, 2H), 7.89 (t, J ¼ 8.7 Hz, 2H), 7.74–7.70 (m, 2H),
7.49–7.43 (m, 1H), 7.33 (s, 2H), 5.17 (d, J ¼ 2.1 Hz, 2H), 3.67 (t,
J ¼ 2.1 Hz, 1H). 13C NMR (125 MHz, DMSO) d 163.79, 153.50, 149.21,
141.47, 139.69, 138.72, 138.51, 130.78, 129.25, 127.22, 121.08,
120.26, 119.81, 112.64, 79.58, 79.34, 57.15. HRMS (ESI): m/z calcu-
lated for C19H15N3O4S 382.0862, found 404.0684 [M þ Na]þ.
d 10.76 (s, 1H), 8.62 (d, J ¼ 8.5 Hz, 1H), 8.25 (d, J ¼ 8.5 Hz, 1H), 7.98
(d, J ¼ 8.7 Hz, 2H), 7.92–7.85 (m, 2H), 7.68 (d, J ¼ 6.4 Hz, 2H), 7.65
(s, 3H), 7.41 (dd, J ¼ 6.2, 2.6 Hz, 1H), 7.33 (s, 2H), 5.45 (s, 2H). 13C
NMR (125 MHz, DMSO) d 162.43, 153.40, 147.68, 140.27, 138.61,
137.71, 137.46, 136.14, 130.76, 129.73, 128.78, 128.47, 126.30,
120.25, 119.52, 118.71, 118.53, 111.26, 68.88. HRMS (ESI): m/z cal-
culated for C23H18BrN3O4S 512.0280, found 514.0265 [M þ 2]þ.
2.1.10. 8-Methoxy-N-(4-sulfamoylphenyl)quinoline-2-carboxa-
mide (5h)
2.1.5. 8-(Benzyloxy)-N-(4-sulfamoylphenyl)quinoline-2-carboxa-
mide (5c)
Yellow solid, yield: 50%; mp: 261–263 ꢀC; 1H NMR (500 MHz,
DMSO) d 10.77 (s, 1H), 8.59 (d, J ¼ 8.5 Hz, 1H), 8.23 (d, J ¼ 8.4 Hz,
1H), 8.10 (dd, J ¼ 18.5, 8.6 Hz, 2H), 7.85 (dd, J ¼ 24.8, 8.6 Hz, 2H),
7.72–7.63 (m, 2H), 7.40–7.31 (m, 3H), 4.08 (s, 3H). 13C NMR
(125 MHz, DMSO) d 163.82, 155.77, 148.91, 141.50, 139.65, 138.55,
138.25, 130.67, 129.59, 128.29, 127.20, 120.49, 120.27, 119.92,
119.76, 109.97, 56.44. HRMS (ESI): m/z calculated for C17H15N3O4S
358.0862, found 358.0865 [M þ H]þ. Spectral data are provided in
the Supplemental data, available online on the journal website.
Yellow solid, yield: 60%; mp: 247–249 ꢀC1H NMR (500 MHz, DMSO)
d 10.79 (s, 1H), 8.60 (t, J ¼ 8.4 Hz, 1H), 8.24 (d, J ¼ 8.4 Hz, 1H), 7.97
(d, J ¼ 8.6 Hz, 2H), 7.91 (d, J ¼ 8.6 Hz, 2H), 7.70 (d, J ¼ 7.4 Hz, 2H),
7.67 (d, J ¼ 4.2 Hz, 2H), 7.47 (t, J ¼ 7.4 Hz, 2H), 7.44–7.41 (m, 1H),
7.40 (d, J ¼ 7.4 Hz, 1H), 7.35 (s, 2H), 5.46 (s, 2H). 13C NMR (125 MHz,
DMSO) d 163.40, 154.65, 148.55, 141.33, 139.67, 138.75, 138.53,
137.72, 129.58, 128.91, 128.27, 127.64, 127.41, 120.70, 120.39,
119.61, 119.48, 112.14, 70.64, 48.96. HRMS (ESI): m/z calculated for
C23H19N3O4S434.1175, found 434.1175 [M þ H]þ.
2.2. CA inhibition assay
An SX.18V-R Applied Photophysics (Oxford, UK) stopped flow
instrument has been used to assay the catalytic/inhibition of vari-
ous CA isozymes18. Phenol Red (at a concentration of 0.2 mM) has
been used as an indicator, working at an absorbance maximum of
557 nm, with 10 mM Hepes (pH 7.4) as a buffer, 0.1 M Na2SO4 or
NaClO4 (for maintaining constant the ionic strength; these anions
are not inhibitory in the used concentration), following the CA-cat-
alysed CO2 hydration reaction for a period of 5–10 s. Saturated
CO2 solutions in water at 25 ꢀC were used as substrate. Stock solu-
tions of inhibitors were prepared at a concentration of 10 mM (in
DMSO–water 1:1, v/v) and dilutions up to 0.01 nM done with the
assay buffer mentioned above. At least seven different inhibitor
concentrations have been used for measuring the inhibition con-
stant. Inhibitor and enzyme solutions were pre-incubated together
for 10 min at room temperature prior to assay, in order to allow
for the formation of the E–I complex. Triplicate experiments were
done for each inhibitor concentration, and the values reported
throughout the paper is the mean of such results. The inhibition
constants were obtained by non-linear least squares methods
using the Cheng–Prusoff equation, as reported earlier, and repre-
sent the mean from at least three different determinations. All CA
isozymes used here were recombinant proteins obtained as
2.1.6. 8-((3,5-Dimethylbenzyl)oxy)-N-(4-sulfamoylphenyl)quinoline-
2-carboxamide (5d)
1
Yellow solid, yield: 50%; mp: 290–292 ꢀC H NMR (500 MHz, DMSO)
d 10.79 (s, 1H), 8.61 (d, J ¼ 8.5 Hz, 1H), 8.24 (d, J ¼ 8.4 Hz, 1H), 7.97
(d, J ¼ 8.6 Hz, 2H), 7.87 (d, J ¼ 8.7 Hz, 2H), 7.69–7.66 (m, 2H), 7.42
(dd, J ¼ 5.7, 2.7 Hz, 1H), 7.35 (s, 2H), 7.30 (s, 2H), 7.01 (s, 1H), 5.35
(s, 2H), 2.32 (s, 6H), 2.09 (s, 3H).13C NMR (125 MHz, DMSO) d
163.45, 154.72, 148.58, 141.36, 139.66, 138.77, 138.47, 137.96,
137.48, 130.79, 129.65, 127.27, 125.24, 120.36, 119.67, 119.54,
112.01, 70.75, 21.43. HRMS (ESI): m/z calculated for
C25H23N3O4S462.1488, found 462.1492 [M þ H]þ.
2.1.7. 8-((3-Chlorobenzyl)oxy)-N-(4-sulfamoylphenyl)quinoline-2-
carboxamide (5e)
1
Yellow solid, yield: 60%; mp: 279–281 ꢀC H NMR (500 MHz, DMSO)
d 10.85 (s, 1H), 8.66 (d, J ¼ 8.2 Hz, 1H), 8.29 (d, J ¼ 8.2 Hz, 1H), 8.06
(d, J ¼ 8.0 Hz, 2H), 7.93 (d, J ¼ 8.9 Hz, 3H), 7.73 (s, 2H), 7.66 (d,
J ¼ 6.7 Hz, 1H), 7.58–7.45 (m, 3H), 7.39 (s, 2H), 5.50 (s, 2H). 13C
NMR (125 MHz, DMSO) d 163.36, 154.41, 148.62, 141.31, 140.30,
139.66, 138.77, 138.42, 133.76, 130.79, 129.56, 128.18, 127.31,
127.21, 126.09, 120.59, 119.68, 119.55, 112.01, 69.69.
reported earlier by our group19,20
.

JOURNAL OF ENZYME INHIBITION AND MEDICINAL CHEMISTRY
1175
more than four times compared to the standard AAZ, with a
KI of 61.9 nM.
3. Results and discussion
3.1. Chemistry
ii. The cytosolic isoform, hCA II, which is also one of the physio-
logically relevant isoforms, was inhibited in a diverse manner
by the compounds 5a–h, with the inhibition constants rang-
ing from 33.0 to 8759 nM. The most potent inhibitor was
again found to be compound 5h, with an inhibition constant
of 33.0 nM. Compounds 5a and 5b, possessing a 4-nitro ben-
zyl and 2-bromo benzyl substitution at 8-OH position, also
showed low nanomolar inhibitory potencies with KI values of
88.4 and 85.7 nM, respectively.
iii. The membrane-bound isoform, hCA IV, was inhibited with a
moderate to weak inhibition profile by the compounds 5a–h.
The inhibition constants ranged from 657.2 to 6757 nM, as
compared to the standard, AAZ, which showed a much
stronger inhibition at 74 nM.
A series of structurally diverse 8-substituted quinoline-2-carboxa-
mides were synthesised according to general synthetic route as
illustrated in Scheme 1. In brief, 8-hydroxy quinaldine (1) was
treated with selenium dioxide to yield 8-hydroxyquinoline-2-car-
baldehyde (2) which was further treated with H2O2 in the pres-
ence of formic acid to yield 8-hydroxyquinoline-2-carboxylic acid21
(3). This intermediate was further subjected to acid-amine cou-
pling with sulfanilamide to give the amide product (4). This
was further subjected to O-alkylation using various aliphatic and
benzylic halides to afford the final products (5a–h). All the final
products were confirmed using various analytical and spectral
techniques.
iv. The tumour-associated isoform, hCA IX, was not at all inhib-
ited by the compounds 5a–h (KI > 10,000 nM).
3.2. CA inhibition studies
The newly synthesised 8-substituted quinoline-linked sulfonamide
derivatives were evaluated for their inhibitory activity against the
cytosolic isoforms hCA I and II, the membrane-bound isoform hCA
IV and the transmembrane isoform hCA IX. Acetazolamide was
used as a standard drug. The following structure–activity relation-
ship (SAR) may be inferred from the inhibition data shown in
Table 1:
4. Conclusions
A series of novel 8-substituted quinoline-linked sulfonamide deriv-
atives (5a–h) were synthesised and assayed for inhibitory activity
against a series of CA isoforms, namely, hCA I and II which are
cytosolic, hCA IV which is membrane-bound and hCA IX which is
tumour-associated isoform. Except for hCA IX, the synthesised
compounds exhibited a variable degree of inhibition profiles for
the other isoforms, ranging from low nanomolar to high nanomo-
lar. Among all the compounds, compound 5h exhibited low nano-
molar inhibitory profiles for hCA I, with KI 61.9 nM (wherein it
proved to be four times more potent than the standard AAZ) and
i. The ubiquitous cytosolic isoform, hCA I, which is localised in
the erythrocytes, gastrointestinal tract and eye, was inhibited
from low to high nanomolar range, with the inhibition con-
stants ranging from 61.9 to 8126 nM. The best inhibition con-
stant was shown by compound 5h, possessing a methyl hCA II, with KI of 33.0 nM. Compounds 5a and 5b showed inhib-
substitution on the 8-OH group. It elicited an inhibition of ition constants of 88.4 and 85.7 nM respectively for hCA II.
(i)
(ii)
(iii)
O
O
N
N
N
OH
OH
OH
N
OH
1
2
3
H
N
H
(iv)
N
N
OH
O
O
O
5
SO2NH2
R
SO2NH2
4
Scheme 1. General synthetic route for the synthesis of 8-substituted quinoline-linked sulfonamide derivatives (5a–h). Reagents and conditions: (i) SeO2, 1,4-dioxane,
110 ꢀC, 12 h, (ii) H2O2, Formic acid, 0 ꢀC, 12 h, (iii) Sulfanilamide, HATU, DIPEA, DMF, 0 ꢀC-rt, 12–15 h, and (iv) R-X, K2CO3, Acetone, r.t., 12–15 h.
Table 1. CA inhibition data with the synthesised compounds 5a–5h and acetazolamide as standard drug, by a stopped flow CO2 hydrase assay.
KI (nM)a
Compound
R
hCA I
hCA II
hCA IV
hCA IX
5a
5b
5c
5d
5e
5f
5g
5h
AAZ
4-Nitrobenzyl
2-Bromobenzyl
Benzyl
3,5-Dimethylbenzyl
3-Chlorobenzyl
2,5-Difluorobenzyl
Prop-2-yn-1-yl
Methyl
640.7
444.4
5290
8126
6470
6561
6914
61.9
88.4
85.7
691.5
3927
6410
6757
806.7
786.9
657.2
1749
74
>10,000
>10,000
>10,000
>10,000
>10,000
>10,000
>10,000
>10,000
25.8
8342
8759
5175
956.7
5111
33.0
–
250
12.1
aMean from three different assays, by a stopped flow technique (errors were in the range of 5–10% of the reported values).

1176
P. S. THACKER ET AL.
Apart from that, all the compounds showed moderate to high
nanomolar inhibition for hCA I, II, and IV. Hence, compound 5h
can be developed further as a lead compound to design more
effective hCA I and hCA II inhibitors.
Pat 2018;28:709–12. (b) Supuran CT. Applications of carbonic
anhydrases inhibitors in renal and central nervous system
diseases. Expert Opin Ther Pat 2018;28:713–21. (c) Winum
JY, Temperini C, El Cheikh K, et al. Carbonic anhydrase inhib-
itors: clash with Ala65 as a means for designing inhibitors
with low affinity for the ubiquitous isozyme II, exemplified
by the crystal structure of the topiramate sulfamide ana-
Disclosure statement
logue.
J Med Chem 2006;49:7024–31. (d) Supuran CT.
No potential conflict of interest was reported by the authors.
Carbonic anhydrase inhibitors in the treatment and prophy-
laxis of obesity. Expert Opin Ther Pat 2003;13:1545–50.
5. Jensen EL, Clement R, Kosta A, et al. A new widespread sub-
class of carbonic anhydrase in marine phytoplankton. ISME J
2019. DOI:10.1038/s41396-019-0426-8
Funding
PST will like to thank the Department of Pharmaceuticals, Ministry
of Chemicals and Fertilizers, Govt. of India, New Delhi for provid-
ing NIPER Ph.D. fellowship.
6. (a) Supuran CT. Carbon-versus sulphur-based zinc binding
groups for carbonic anhydrase inhibitors? J Enzyme Inhib
Med Chem 2018;33:485–95. (b) Pastorekova S, Casini A,
Scozzafava A, et al. Carbonic anhydrase inhibitors: the first
selective, membrane-impermeant inhibitors targeting the
tumor-associated isozyme IX. Bioorg Med Chem Lett 2004;
14:869–73. (c) Melis C, Meleddu R, Angeli A, et al. Isatin: a
privileged scaffold for the design of carbonic anhydrase
inhibitors. J Enzyme Inhib Med Chem 2017;32:68–73. (d) Gul
HI, Mete E, Eren SE, et al. Designing, synthesis and bioactiv-
ities of 4-[3-(4-hydroxyphenyl)-5-aryl-4,5-dihydro-pyrazol-1-
yl]benzenesulfonamides. J Enzyme Inhib Med Chem 2017;32:
169–75. (e) Gul HI, Mete E, Taslimi P, et al. Synthesis, car-
bonic anhydrase I and II inhibition studies of the 1,3,5-tri-
substituted-pyrazolines. J Enzyme Inhib Med Chem 2017;32:
189–92.
7. (a) Supuran CT. How many carbonic anhydrase inhibition
mechanisms exist? J Enzyme Inhib Med Chem 2016;31:
345–60. (b) da Silva Cardoso V, Vermelho AB, Ricci Junior E,
et al. Antileishmanial activity of sulphonamide nanoemul-
sions targeting the b-carbonic anhydrase from Leishmania
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Akocak S, Lolak N, Vullo D, et al. Synthesis and biological
evaluation of histamine Schiff bases as carbonic anhydrase I,
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ment of idiopathic intracranial hypertension. Expert Rev
Neurother 2015;15:851–6.
ORCID
Andrea Angeli
Claudiu T. Supuran
http://orcid.org/0000-0002-1470-7192
http://orcid.org/0000-0003-4262-0323
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