Synthesis and biological evaluation of imidazo[2,1-b]thiazole based sulfonyl piperazines as novel carbonic anhydrase ii inhibitors

Article abstract of DOI:10.3390/metabo10040136

A novel series of imidazo[2,1-b]thiazole-sulfonyl piperazine conjugates (9aa-ee) has been synthesized and evaluated for carbonic anhydrase (CA, EC 4.2.1.1) inhibitory potency against four isoforms: The cytosolic isozyme hCA I, II and trans-membrane tumor-

Full text of DOI:10.3390/metabo10040136

H
OH
metabolites
OH
Article
Synthesis and Biological Evaluation of
Imidazo[2,1-b]Thiazole based Sulfonyl Piperazines as
Novel Carbonic Anhydrase II Inhibitors
Kesari Lakshmi Manasa 1, Sravya Pujitha 1, Aaftaab Sethi 1, Mohammed Arifuddin 1,2
,
Mallika Alvala 1,
* *
, Andrea Angeli 3 and Claudiu T. Supuran 3,
1
Department of Medicinal Chemistry, National Institute of Pharmaceutical Education and Research (NIPER),
Hyderabad 500 037, India; manasa.kesari@gmail.com (K.L.M.); sravya.pujitha@gmail.com (S.P.);
sethiaaftaab@gmail.com (A.S.); arifabib@gmail.com (M.A.)
Department of Chemistry, Anwarul Uloom College, 11-3-918, New Malleypally, Hyderabad 500001, T. S.,
India (Present Address)
Neurofarba Dept., Università degli Studi di Firenze, Sezione di Scienze Farmaceutiche e Nutraceutiche,
Via Ugo Schiff 6, 50019 Sesto Fiorentino, Florence, Italy; andrea.angeli@unifi.it
Correspondence: mallikaalvala@yahoo.in (M.A.); claudiu.supuran@unifi.it (C.T.S.);
Tel.: +91-9441117803 (M.A.); +39-0554573729 (C.T.S.)
2
3
*
ꢀꢁꢂꢀꢃꢄꢅꢆꢇ
ꢀꢁꢂꢃꢄꢅꢆ
Received: 12 March 2020; Accepted: 28 March 2020; Published: 31 March 2020
Abstract: A novel series of imidazo[2,1-b]thiazole-sulfonyl piperazine conjugates (9aa-ee) has been
synthesized and evaluated for carbonic anhydrase (CA, EC 4.2.1.1) inhibitory potency against four
isoforms: The cytosolic isozyme hCA I, II and trans-membrane tumor-associated isoform hCA IX
and hCA XII, taking acetazolamide (AAZ) as standard drug, using a stopped flow CO2 hydrase
assay. The results revealed that most of the compounds showed selective activity against hCA II
whereas none of them were active against hCA I, IX, XII (Ki > 100
cytosolic isoform hCA II was inhibited by these molecules with inhibition constants in the range of
57.7–98.2 M. This new derivative, thus, selectively inhibits hCA II over the hCA I, IX, XII isoforms,
µM). The physiologically dominant
µ
which may be used for further understanding the physiological roles of some of these isoforms in
various pathologies.
Keywords: carbonic anhydrase; hCA I; hCA II; hCA IX; hCA XII; imidazo[2,1-b]thiazole;
sulfonyl piperazine
1. Introduction
Carbonic anhydrases (CAs, EC 4.2.1.1) are a group of zinc containing metalloenzymes that
effectively catalyze the reversible hydration of CO2 to bicarbonate and proton, an important reaction
for many physiological processes. The human carbonic anhydrases (hCAs) belong to theα- class of
carbonic anhydrases having sixteen different form of isoforms. CA isoenzymes play an important
role in various cellular processes, such as tumorigenicity, respiration, regulation of pH, electrolytes
secretion and many other processes. hCA I and hCA II act as targets for diseases, such as glaucoma and
epilepsy, while hCA IX and hCA XII are targets for imaging of tumors and are found to over-express in
many cancers. [1–3]. Therefore, it is important to develop an effective approach that can selectively
inhibit these isoforms involved in different diseases. Nowadays, the major concern of the researchers
working in this field is to develop new concept for designing the compounds that are capable of
blocking specifically the process catalyzed by one or two isoform ms of these enzymes.
N and S containing fused heterocyclic systems have gained considerable attraction in the
field of medicinal chemistry due to their broad spectrum of pharmacological activities [4].
Metabolites 2020, 10, 136; doi:10.3390/metabo10040136
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Imidazo[2,1-b]thiazole-guanylhydrazone is a promising lead with potent anticancer activity against a
number of cancer cell lines [ ]. These fused heterocycles exhibit potent anticancer activity through
multiple mechanisms [ ]. However, a number of imidazo[2,1-b][1,3,4]thiadiazole derivatives have
been reported to exhibit antitumor activity [ ]. Sharma and Supuran et al. have reported a series of
benzenesulfonamide bearing imidazothiadiazole and thiazolotriazole hybrids as carbonic anhydrases
IX and XII inhibitors [ ]. The amide derivatives of probenecid have been reported as selective inhibitors
5
6
7
8
of carbonic anhydrase IX and XII by Carradori et al. [9,10] (Figure 1).
Figure 1. Representative examples of imidazothiazole, imidazothiadiazole, sulfonamides as CAIs and
rationale for designed hybrids.
Based on the literature, sulfonamides were the most investigated class of CA inhibitors [11,12].
Acetazolamide (AZA), methazolamide (MZA), ethoxzolamide (EZA), dorzolamide (DZA) (Figure 1)
are few of the many sulfonamide-based carbonic anhydrase inhibitors in clinical use [13 15]. Pazopanib
–
has been clinically used for several years now whereas indisulam and celecoxib are currently under
clinical investigations in various types of tumors (Figure 1) [16]. Supuran et al. have reported various
classes of piperazine derivatives as activators of human carbonic anhydrase I, II, IV and VII [17].
Thus, design of novel heterocyclic/aromatic scaffolds with sulfonamide moiety is crucial in developing
selective CA inhibitors (CAIs) with potent activity.
Propelled by these findings and continuing our interest in the design of diversified classes of
heterocyclic based CAIs, we endeavor to synthesize a new series of imidazo[2,1-b]thiazole-sulfonyl
piperazine conjugates (Figure 1), which have not been reported earlier.
Thus, a novel
imidazo[2,1-b]thiazole-sulfonyl piperazine hybrids (9aa-ee) were synthesized and demonstrated
CA inhibition potential against I, II, IX and XII isoforms of CA using acetazolamide (AAZ) as standard.
2. Results and Discussion
2.1. Chemistry
The designed imidazo[2,1-b]thiazole-sulfonyl piperazine conjugates (9aa-ee) were prepared
according to pathways outlined in Scheme 1. Ethyl-2-aminothiazole-4-carboxylate (3) was synthesized
by the condensation of ethyl bromopyruvate (2) and thiourea (1) in ethanol under reflux for 4 h.
Cyclization of intermediate (3) with various phenacyl bromides (4a-e) in ethanol at reflux temperature
resulted in the formation of intermediates (5a–e), which upon ester hydrolysis in the presence of
lithium hydroxide monohydrate (LiOH
piperazine intermediates (8a-e) were synthesized based on previous reported procedures [19].
·
H2O) produced carboxylic acids (6a–e) [18]. Aryl sulfonyl

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Finally, the key intermediate 6a-e with different substitutions were coupled with 8a-e using
N-(3-dimethylaminopropyl)-N0-ethylcarbodiimide hydrochloride (EDCI) and 1-hydroxybenzotriazole
(HOBt) in dry dimethylformamide (DMF) conditions to afford the corresponding target compounds in
good yields (9aa-ee).
Scheme 1. Synthesis of imidazo[2,1-b]thiazole-sulfonyl piperazine hybrids (9aa-ee).
1
All synthesized compounds (9aa-ee) were characterized by spectral techniques viz. H NMR,
13C NMR and high resolution mass spectrometry (HRMS). The 1H NMR spectrum of 9ab displayed
characteristic protons of piperazine around
was found to be around 2.40 ppm and 3.5–4.0 ppm. All the remaining protons appeared in the range
of δ 6.8–8.20 ppm. 13C NMR spectrum of 9ab showed the characteristic carbonyl and methyl group’s
at 158.61, and 21.02 ppm, respectively and all the remaining carbons appeared in the range of
δ2.8–3.8 ppm. Methyl and Methoxy group of phenyl ring
δ
δ
δ
δ 108.97–158.56 ppm. The similar pattern was observed for the remaining compounds (9aa-ee).
2.2. Carbonic Anhydrase Inhibition
The newly synthesized imidazo[2,1-b]thiazole-sulfonyl piperazines (9aa-ee) were screened for
their CA inhibition activity against cytosolic (hCA I, hCA II) and the tumor associated (hCA IX, hCAXII)
isoforms by a stopped flow CO2 hydrase assay [20]. Acetazolamide (AAZ), a clinically used reference
standard and the obtained results are represented as Ki (µM) are summarized in Table 1. The following
structure-activity relationship (SAR) was figured out from the inhibition data of 9aa-ee as shown in
Table 1:
i.
The cytosolic isoforms hCA I and tumor associated isoform hCA IX, hCAXII were not inhibited
by the compounds 9aa-ee (Ki > 100 µM).
ii. The compounds 9aa-ee showed varied inhibitory profiles against cytosolic isoform hCA II.
Compound 9ae, 9bb, 9ca, 9cc-ce and 9da elicited inhibitory potencies (Ki) of 57.7–67.9 M. Potent
compounds (9ca, 9cc-ce) having chlorine (R) at aromatic ring of imidazo thiazole whereas other
compounds are ineffective. It is assumed that these compounds, i.e., 9ae (Ki = 57.7 M), 9bb
M), 9da
M) were showing inhibition probably due to the presence of 4-OCH3, 4-CH3, 4-Cl and
µ
µ
(
Ki = 76.4 µM), 9ca (Ki =79.9 µM), 9cc (Ki = 57.8 µM), 9cd (Ki = 71.2 µM), 9ce (Ki = 62.1 µ
(Ki = 67.9
µ
4-F as R group and 4-t-butyl, 4-CH3, 4-OCH3, 4-Cl and H as R1 group.
iii. It is evident from the Ki values (Table 1), compound 9ae bearing that R-group (imidazothiazole
part) substituted with 4-methoxy and R1 substituted with 4-t-butyl (sulfonyl piperazine part)
showed promising inhibitory activity.

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iv. Among all the congeners, some of the potent compounds exhibited selective inhibition of hCA II
as compared to hCA IX and hCAXII in micromolar range.
Table 1. Inhibition of hCA isoforms I, II, IX and XII with target compounds (9aa-ee) and acetazolamide
(AAZ) as a standard drug (Ki-µM) a.
Compound
Structure
hCA I
hCA II
hCA IX
hCA XII
9aa
>100
>100
>100
>100
S
N
N
O
O
S
9ab
9ac
9ad
9ae
>100
>100
>100
>100
>100
>100
>100
57.7
>100
>100
>100
>100
>100
>100
>100
>100
N
O
N
O
9ba
9bb
9bc
9bd
>100
>100
>100
nd
>100
76.4
>100
nd
>100
>100
>100
nd
>100
>100
>100
nd
9ca
9cb
9cc
>100
>100
>100
79.9
>100
57.8
>100
>100
>100
>100
>100
>100

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Table 1. Cont.
hCA I
Compound
Structure
hCA II
hCA IX
hCA XII
9cd
>100
>100
71.2
>100
>100
9ce
62.1
>100
>100
S
N
N
F
O
S
9da
9db
>100
>100
67.9
>100
>100
>100
>100
N
N
O
O
O
>100
9dc
>100
>100
98.2
>100
>100
>100
>100
9dd
>100
S
N
F
N
O
9de
9ea
9eb
9ec
9ed
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
N
N
S
O
O
S
N
N
O
N
N
S
O
O
9ee
>100
>100
>100
>100
AAZ
0.25
0.012
0.026
0.006
a Mean from 3 different assays, by a stopped flow technique (errors were in the range of
5–10% of the reported values).
±

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3. Conclusions
In conclusion, we have reported the synthesis of imidazo[2,1-b]thiazole-sulfonyl piperazine
conjugates (9aa-ee), which are designed to target CA isoforms. The synthesized compounds (9aa-ee)
were screened against the cytosolic isoforms hCA I and II, as well as the transmembrane tumor
associated isoforms, hCA IX and XII. Few of the compounds (9ae, 9bb, 9ca, 9cc-ce, 9da and 9dc) exhibited
acceptable inhibitory activity against cytosolic isoform hCA II, Ki value in the range of 57.7–67.9 µM,
while some compounds were found to be weaker inhibitors of tumor associated isoform hCA IX
and hCA XII. Hence, further modifications of these newly designed imidazo[2,1-b]thiazole-sulfonyl
piperazine derivatives (9aa-ee) have the potential to emerge as isoform II selective CAIs. Notably,
as for all secondary/tertiary sulfonamides reported to date as CAIs, the inhibition mechanism with
these derivatives reported here is for the moment unknown [21–23].
4. Experimental Section
4.1. Materials and Methods
All Chemicals and reagents were purchased from the commercial suppliers Alfa Aesar, Sigma
Aldrich and used without further purification. The reaction progress was monitored by Thin layer
chromatography (TLC) was performed using pre-coated silica gel 60 F254 MERCK. TLC plates were
visualized and analyzed by exposure to UV light or iodine vapors and aqueous solution of ninhydrin.
Column chromatography was performed with Merck flash silica gel with 60–120 mesh size. Melting
points were determined on an Electro thermal melting point apparatus and are uncorrected. Nuclear
magnetic resonance spectra for 1H NMR were obtained on Avance 300, 400 and 500 MHz and analyzed
using Mestrenova software and the chemical shifts are reported in ppm from tetramethylsilane (0 ppm)
or the solvent resonance as the internal standard (CDCl3 7.26 ppm, DMSO-d6 2.49 ppm) and for 13
C
NMR the chemical shifts are reported in ppm from the solvent resonance as the internal standard
(CDCl3 77 ppm, DMSO-d6 39.3 ppm). HRMS was performed on a Varian ESI- QTOF instrument
Spectral data for all compounds are available in the Supplementary Materials.
4.1.1. General Synthetic Procedure for the Preparation of Compound 3
Compound 3 was synthesized according to the procedures described in the literature [18].
4.1.2. General Synthetic Procedure for the Preparation of Compound 5a-e
Compound 5a-e was synthesized based on previous synthetic procedures [18].
4.1.3. General Synthetic Procedure for the Preparation of Compound 6a-e
Compound 6a-e was synthesized based on previous synthetic procedures [18].
4.1.4. General Synthetic Procedure for the Preparation of Compound 8a-e
Substituted phenyl sulfonyl piperazines 8a-e was synthesized by adding triethylamine (31.5 mmol)
slowly to a solution of piperazine in CH2Cl2 at 0 ◦C, and then commercially available benzenesulfonyl
chloride (7a-e, 11.4 mmol) was added and stirred for 30 min. After the completion of reaction,
which was confirmed by TLC (petroleum ether and ethyl acetate (2:1)), the reaction was quenched
with water and extracted with CH2Cl2. The organic layer was dried over anhydrous Na2SO4 and
concentrated on reduced pressure to give 8a-e [19].
4.1.5. General Synthetic Procedure for the Preparation of
(5-(aryl)imidazo[2,1-b]thiazol-2-yl)(4-((aryl)sulfonyl)piperazin-1-yl)methanone (9aa-ee)
Above obtained carboxylic acid (6a-e, 1.0 mmol) was dissolved in dry dimethyl formamide (10 mL),
cooled to 0 ◦C (ice bath). EDCI (1.2 mmol), HOBt (1.2 mmol), amine intermediate (8a-e, 1.0 mmol)

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and triethylamine (3 mmol) were added slowly. After 10 min removed the ice bath and the mixture
was stirred at room temperature for 12 h until the starting materials were consumed. Then ice cold
water was added to the reaction mixture and extracted with dichloro methane (DCM). The combined
organic extracts were washed with aq NaHCO3 and dried with Na2SO4 and concentrated in vacuo.
The residue was purified by column chromatography by using ethyl acetate and hexane solvent system
to afford the title compounds (9aa-ee).
(5-(4-Methoxyphenyl)imidazo[2,1-b]thiazol-2-yl)(4-((4-methoxyphenyl)sulfonyl)piperazin-1-
yl)methanone (9aa)
White solid: 191mg; 90% yield; mp: 202–204 ◦C; 1H NMR (300 MHz, DMSO-d6)
7.75 (d, J = 8.6 Hz, 2H), 7.68 (d, J = 8.8 Hz, 2H), 7.65 (s, 1H), 7.17 (d, J = 8.8 Hz, 2H), 6.94 (d, J = 8.7 Hz,
δ: 8.03 (s, 1H),
2H), 3.85 (s, 3H), 3.77 (s, 7H), 3.00 (s, 4H); 13C NMR (126 MHz, DMSO-d6)
δ: 162.9, 158.6, 158.5, 147.5,
146.2, 129.8, 126.6, 126.3, 126.0, 124.0, 116.4, 114.6, 114.0, 108.9, 55.7, 55.0, 45.7; MS (ESI): m/z 513 [M+H]+;
HRMS (ESI): m/z calcd for C24H25N4O5S2: 513.12609; found: 513.12467 [M+H]+.
(5-(4-Methoxyphenyl)imidazo[2,1-b]thiazol-2-yl)(4-tosylpiperazin-1-yl)methanone (9ab)
White solid: 186 mg; 88% yield; mp: 216–218 ◦C; 1H NMR (300 MHz, DMSO-d6)
7.76 (d, J = 8.6 Hz, 2H), 7.65 (s, 2H), 7.62 (s, 1H), 7.47 (d, J = 8.0 Hz, 2H), 6.94 (d, J = 8.6 Hz, 2H), 3.77 (s,
δ: 8.03 (s, 1H),
7H), 3.01 (s, 4H), 2.41 (s, 3H); 13C NMR (101 MHz, DMSO-d6)
δ: 158.6, 158.5, 147.5, 146.2, 143.8, 132.0,
129.9, 127.5, 126.6, 126.0, 124.0, 116.4, 114.0, 108.9, 55.0, 45.6, 21.0; MS (ESI): m/z 497 [M+H]+; HRMS
(ESI): m/z calcd for C24H25N4O4S2: 497.13117; found: 497.12979 [M+H]+.
(1-(4-Methoxyphenyl)-9H-pyrido[3,4-b]indol-3-yl)(4-tosylpiperazin-1-yl)methanone (9ac)
White solid: 185 mg; 85% yield; mp: 243–245 ◦C; 1H NMR (300 MHz, DMSO-d6)
7.77 (s, 1H), 7.74 (s, 2H), 7.70 (s, 2H), 7.67 (s, 1H), 7.61 (s, 1H), 6.91 (d, J = 8.4 Hz, 2H), 3.77 (s, 7H),
δ: 7.98 (s, 1H),
3.07 (s, 4H); 13C NMR (75 MHz, CDCl3 +DMSO-d6)
δ: 158.5, 147.4, 146.2, 138.4, 133.8, 129.4, 129.2,
126.5, 125.9, 123.8, 116.3, 113.8, 108.7, 54.9, 45.4; MS (ESI): m/z 517 [M+H]+; HRMS (ESI): m/z calcd for
C23H22ClN4O4S2: 517.07655; found: 517.07532 [M+H]+.
(5-(4-Methoxyphenyl)imidazo[2,1-b]thiazol-2-yl)(4-(phenylsulfonyl)piperazin-1-yl)methanone (9ad)
White solid: 176 mg; 78% yield; mp: 192–194 ◦C; 1H NMR (300 MHz, DMSO-d6)
7.76 (d, J = 2.1 Hz, 2H), 7.74 (d, J = 2.2 Hz, 3H), 7.68 (d, J = 7.2 Hz, 2H), 7.65 (s, 1H), 6.94 (d, J = 8.8 Hz,
δ: 8.03 (s, 1H),
2H), 3.77 (s, 7H), 3.04 (s, 4H); 13C NMR (101 MHz, DMSO-d6)
δ: 159.2, 159.1, 148.1, 146.8, 135.6, 134.0,
130.1, 128.1, 127.2, 126.7, 124.6, 117.0, 114.6, 109.5, 55.7, 46.3; MS (ESI): m/z 483 [M+H]+; HRMS (ESI):
m/z calcd for C23H23N4O4S2: 483.11552; found: 483.11409 [M+H]+.
(4-((4-(Tert-butyl)phenyl)sulfonyl)piperazin-1-yl)(5-(4-methoxyphenyl)imidazo[2,1-b]thiazol-2-
yl)methanone (9ae)
White solid: 180 mg; 80% yield; mp: 216–218 ◦C; 1H NMR (300 MHz, CDCl3)
(d, J = 8.5 Hz, 2H), 7.67 (d, J = 5.0 Hz, 5H), 6.93 (d, J = 8.6 Hz, 2H), 3.76 (s, 7H), 3.03 (s, 4H), 1.31 (s,
δ: 8.04 (s, 1H), 7.75
9H); 13C NMR (101 MHz, DMSO-d6)
δ: 158.6, 158.5, 156.4, 147.5, 146.2, 132.2, 127.5, 126.6, 126.4, 126.1,
124.0, 116.5, 114.0, 109.0, 55.1, 45.6, 34.9, 30.7; MS (ESI): m/z 539 [M+H]+; HRMS (ESI): m/z calcd for
C27H31N4O4S2: 539.17812; found: 539.17666 [M+H]+.
(4-((4-Methoxyphenyl)sulfonyl)piperazin-1-yl)(5-(p-tolyl)imidazo[2,1-b]thiazol-2-yl)methanone (9ba)
White solid: 185 mg; 84% yield; mp: 209–211 ◦C; 1H NMR (500 MHz, DMSO-d6)
7.72 (d, J = 8.1 Hz, 2H), 7.70–7.67 (m, 2H), 7.66 (s, 1H), 7.18 (d, J = 2.8 Hz, 2H), 7.17 (d, J = 3.7 Hz, 2H),
3.85 (s, 3H), 3.76 (s, 4H), 3.00 (s, 4H), 2.30 (s, 3H); 13C NMR (101 MHz, DMSO-d6)
: 162.9, 158.5, 147.6,
δ: 8.08 (s, 1H),
δ
146.3, 136.3, 131.1, 129.8, 129.2, 126.3, 124.7, 124.0, 116.7, 114.6, 109.6, 55.7, 45.7, 20.8; MS (ESI): m/z 497
[M+H]+; HRMS (ESI): m/z calcd for C24H25N4O4S2: 497.13117; found: 497.13004 [M+H]+.

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(5-(p-Tolyl)imidazo[2,1-b]thiazol-2-yl)(4-tosylpiperazin-1-yl)methanone (9bb)
White solid: 187 mg; 86% yield; mp: 214–216 ◦C; 1H NMR (500 MHz, DMSO-d6)
δ: 8.08 (s, 1H),
7.72 (d, J = 8.1 Hz, 2H), 7.66 (s, 1H), 7.64 (d, J = 8.2 Hz, 2H), 7.46 (d, J = 8.1 Hz, 2H), 7.18 (d, J = 8.0 Hz,
2H), 3.76 (s, 4H), 3.01 (s, 4H), 2.41 (s, 3H), 2.30 (s, 3H); 13C NMR (101 MHz, DMSO-d6)
δ: 158.6, 147.6,
146.3, 143.9, 136.3, 132.0, 131.2, 130.0, 129.2, 127.6, 124.7, 124.0, 116.7, 109.6, 45.6, 21.0, 20.8; MS (ESI):
m/z 481 [M+H]+; HRMS (ESI): m/z calcd for C24H25N4O3S2: 481.13626; found: 481.13497 [M+H]+.
(4-((4-Chlorophenyl)sulfonyl)piperazin-1-yl)(5-(p-tolyl)imidazo[2,1-b]thiazol-2-yl)methanone (9bc)
White solid: 178 mg; 80% yield; mp: 195–197 ◦C; 1H NMR (500 MHz, DMSO-d6)
7.76 (d, J = 4.8 Hz, 3H), 7.72 (d, J = 8.0 Hz, 2H), 7.70 (d, J = 1.7 Hz, 1H), 7.65 (s, 1H), 7.18 (d, J = 7.9 Hz,
δ: 8.09 (s, 1H),
2H), 3.76 (s, 4H), 3.07 (s, 4H), 2.30 (s, 3H); 13C NMR (101 MHz, DMSO-d6)
δ: 158.5, 147.6, 146.3, 138.4,
136.3, 133.8, 131.1, 129.7, 129.4, 129.1, 124.7, 124.0, 116.6, 109.5, 45.5, 20.7; MS (ESI): m/z 501 [M+H]+;
HRMS (ESI): m/z calcd for C23H22ClN4O3S2: 501.08164; found: 501.08059 [M+H]+.
(4-((4-(Tert-butyl)phenyl)sulfonyl)piperazin-1-yl)(5-(p-tolyl)imidazo[2,1-b]thiazol-2-yl)methanone
(9bd)
White solid: 182 mg; 82% yield; mp: 222–224 ◦C; 1H NMR (500 MHz, DMSO-d6)
7.71 (d, J = 8.1 Hz, 2H), 7.68 (s, 4H), 7.67 (s, 1H), 7.17 (d, J = 7.9 Hz, 2H), 3.77 (s, 4H), 3.03 (s, 4H), 2.30 (s,
δ: 8.09 (s, 1H),
3H), 1.31 (s, 9H); 13C NMR (101 MHz, DMSO-d6)
δ: 158.6, 156.4, 147.5, 146.3, 136.3, 132.2, 131.1, 129.1,
127.4, 126.3, 124.7, 124.0, 116.7, 109.6, 45.6, 34.9, 30.7, 20.7; MS (ESI): m/z 523 [M+H]+; HRMS (ESI): m/z
calcd for C27H31N4O3S2: 523.18321; found: 523.18172 [M+H]+.
(5-(4-Chlorophenyl)imidazo[2,1-b]thiazol-2-yl)(4-((4-methoxyphenyl)sulfonyl)piperazin-1-
yl)methanone (9ca)
Off White solid: 184 mg; 85% yield; mp: 216–218 ◦C; 1H NMR (300 MHz, DMSO-d6)
1H), 7.86 (d, J = 8.5 Hz, 2H), 7.69 (s, 2H), 7.67 (s, 1H), 7.42 (d, J = 8.5 Hz, 2H), 7.17 (d, J = 8.8 Hz, 2H),
δ: 8.21 (s,
3.85 (s, 3H), 3.76 (s, 4H), 3.00 (s, 4H); 13C NMR (75 MHz, DMSO-d6)
δ: 162.9, 158.4, 144.9, 132.8, 131.4,
129.7, 128.6, 126.4, 124.0, 117.1, 114.6, 110.5, 55.7, 45.6; MS (ESI): m/z 517 [M+H]+; HRMS (ESI): m/z calcd
for C23H22ClN4O4S2: 517.07655; found: 517.07509 [M+H]+.
(5-(4-Chlorophenyl)imidazo[2,1-b]thiazol-2-yl)(4-tosylpiperazin-1-yl)methanone (9cb)
Brown solid: 182 mg; 84% yield; mp: 228–230 ◦C; 1H NMR (500 MHz, DMSO-d6)
7.86 (d, J = 8.6 Hz, 2H), 7.69 (s, 1H), 7.64 (d, J = 8.2 Hz, 2H), 7.47 (d, J = 8.1 Hz, 2H), 7.42 (d, J = 8.6 Hz,
δ: 8.21 (s, 1H),
2H), 3.76 (s, 4H), 3.01 (s, 4H), 2.41 (s, 3H); 13C NMR (101 MHz, DMSO-d6)
δ: 158.5, 148.0, 145.0, 143.9,
132.8, 132.0, 131.5, 130.0, 128.6, 127.6, 126.5, 124.0, 117.2, 110.6, 45.7, 21.0; MS (ESI): m/z 501 [M+H]+;
HRMS (ESI): m/z calcd for C23H22ClN4O3S2: 501.08164; found: 501.08056 [M+H]+.
(5-(4-Chlorophenyl)imidazo[2,1-b]thiazol-2-yl)(4-((4-chlorophenyl)sulfonyl)piperazin-1-yl)methanone
(9cc)
Brown solid: 190 mg; 90% yield; mp: 226–228 ◦C; 1H NMR (500 MHz, DMSO-d6)
7.86 (d, J = 6.9 Hz, 2H), 7.76 (s, 3H), 7.69 (d, J = 5.6 Hz, 2H), 7.43 (d, J = 7.0 Hz, 2H), 3.76 (s, 4H), 3.06 (s,
δ: 8.22 (s, 1H),
4H); 13C NMR (101 MHz, DMSO-d6)
δ: 158.5, 148.0, 145.0, 138.5, 133.8, 132.8, 131.5, 129.7, 129.5, 128.6,
126.4, 124.0, 117.1, 110.6, 45.6; MS (ESI): m/z 521 [M+H]+; HRMS (ESI): m/z calcd for C22H19Cl2N4O3S2:
521.02701; found: 521.02595 [M+H]+.
(5-(4-Chlorophenyl)imidazo[2,1-b]thiazol-2-yl)(4-(phenylsulfonyl)piperazin-1-yl)methanone (9cd)
Off White solid: 179 mg; 80% yield; mp: 229–231 ◦C; 1H NMR (300 MHz, DMSO-d6)
1H), 7.85 (d, J = 8.1 Hz, 2H), 7.74 (s, 3H), 7.68 (d, J = 6.0 Hz, 3H), 7.42 (d, J = 8.0 Hz, 2H), 3.76 (s, 4H),
3.03 (s, 4H); 13C NMR (126 MHz, DMSO-d6)
: 158.5, 148.0, 145.0, 134.9, 133.5, 132.8, 131.5, 129.6,
δ: 8.20 (s,
δ

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128.6, 127.5, 126.4, 124.0, 117.2, 110.6, 45.7, 45.0; MS (ESI): m/z 487 [M+H]+; HRMS (ESI): m/z calcd for
C22H20ClN4O3S2: 487.06599; found: 487.06481[M+H]+.
(4-((4-(Tert-butyl)phenyl)sulfonyl)piperazin-1-yl)(5-(4-chlorophenyl)imidazo[2,1-b]thiazol-2-
yl)methanone (9ce)
Cream color solid: 178 mg; 76% yield; mp: 272–274 ◦C; 1H NMR (300 MHz, DMSO-d6)
1H), 7.86 (d, J = 8.5 Hz, 2H), 7.70 (s, 1H), 7.68 (s, 4H), 7.42 (d, J = 8.5 Hz, 2H), 3.78 (s, 4H), 3.03 (s, 4H),
δ: 8.21 (s,
1.30 (s, 9H); 13C NMR (101 MHz, DMSO-d6)
δ: 158.5, 156.4, 148.0, 144.9, 132.8, 132.2, 131.5, 128.6, 127.5,
126.4, 126.4, 124.0, 117.2, 110.7, 45.6, 34.9, 30.7; MS (ESI): m/z 543 [M+H]+; HRMS (ESI): m/z calcd for
C26H28ClN4O3S2: 543.12859; found: 543.12754 [M+H]+.
(5-(4-Fluorophenyl)imidazo[2,1-b]thiazol-2-yl)(4-((4-methoxyphenyl)sulfonyl)piperazin-1-
yl)methanone (9da)
Cream color solid: 188 mg; 88% yield; mp: 212–214 ◦C; 1H NMR (300 MHz, DMSO-d6)
1H), 7.92–7.82 (m, 2H), 7.73–7.64 (m, 3H), 7.26–7.12 (m, 5H), 3.85 (s, 3H), 3.76 (s, 4H), 3.00 (s, 4H); 13
δ: 8.15 (s,
C
NMR (101 MHz, DMSO-d6) δ: 162.8, 158.4, 147.6, 145.1, 130.3, 130.4, 129.6, 126.5 (d, J = 8.25 Hz), 126.2,
123.9, 116.8, 115.3 (d, J = 21.45 Hz), 114.5, 109.9, 55.6, 45.5; MS (ESI): m/z 501 [M+H]+; HRMS (ESI): m/z
calcd for C23H22FN4O4S2: 501.10610; found: 501.10522 [M+H]+.
(5-(4-Fluorophenyl)imidazo[2,1-b]thiazol-2-yl)(4-tosylpiperazin-1-yl)methanone (9db)
Cream color solid: 185 mg; 84% yield; mp: 238–240 ◦C; 1H NMR (300 MHz, DMSO-d6)
1H), 7.87 (dd, J = 8.6, 5.6 Hz, 2H), 7.68 (s, 1H), 7.64 (d, J = 8.2 Hz, 2H), 7.47 (d, J = 8.1 Hz, 2H), 7.20 (t,
J = 8.9 Hz, 2H), 3.76 (s, 4H), 3.01 (s, 4H), 2.41 (s, 3H); 13C NMR (101 MHz, DMSO-d6)
: 158.4, 147.6,
δ: 8.15 (s,
δ
145.1, 143.7, 131.9, 130.4(d, J= 2.75 Hz), 129.8, 127.4, 126.6 (d, J = 8.25 Hz), 123.9, 116.8, 115.2, 115.4,
109.9, 45.5, 20.9; MS (ESI): m/z 485 [M+H]+; HRMS (ESI): m/z calcd for C23H22FN4O3S2: 485.11119;
found: 485.11009 [M+H]+.
(4-((4-Chlorophenyl)sulfonyl)piperazin-1-yl)(5-(4-fluorophenyl)imidazo[2,1-b]thiazol-2-yl)methanone
(9dc)
Cream color solid: 180 mg; 82% yield; mp: 219–221 ◦C; 1H NMR (300 MHz, DMSO-d6)
1H), 7.87 (dd, J = 8.6, 5.6 Hz, 2H), 7.76 (s, 3H), 7.69 (d, J = 7.5 Hz, 2H), 7.20 (t, J = 8.9 Hz, 2H), 3.76 (s,
4H), 3.06 (s, 4H); 13C NMR (101 MHz, DMSO-d6)
: 162.6, 160.2, 158.5, 147.8, 145.3, 138.4, 133.8, 130.5,
δ: 8.16 (s,
δ
129.6 (d, J = 24.5 Hz), 126.7 (d, J = 7.9 Hz), 124.0, 116.9, 115.4 (d, J = 21.5 Hz), 110.0, 45.5, 44.9; MS (ESI):
m/z 505 [M+H]+; HRMS (ESI): m/z calcd for C22H19ClFN4O3S2: 505.05656; found: 505.05542 [M+H]+.
(5-(4-Fluorophenyl)imidazo[2,1-b]thiazol-2-yl)(4-(phenylsulfonyl)piperazin-1-yl)methanone (9dd)
Brown color solid: 175 mg; 76% yield; mp: >350 ◦C; 1H NMR (300 MHz, DMSO-d6)
7.92–7.82 (m, 2H), 7.75 (s, 3H), 7.69 (d, J = 4.3 Hz, 3H), 7.20 (t, J = 8.6 Hz, 2H), 3.77 (s, 4H), 3.04 (s, 4H);
13C NMR (101 MHz, DMSO-d6)
: 162.6, 158.5, 147.8, 145.2, 134.9, 133.4, 130.5, 129.5 (d, J = 6.9 Hz),
δ: 8.15 (s, 1H),
δ
127.4 (d, J = 20.0 Hz), 126.6 (d, J = 8.0 Hz), 124.0, 116.9, 115.4 (d, J = 21.5 Hz), 110.0, 45.6, 44.9; MS (ESI):
m/z 471 [M+H]+; HRMS (ESI): m/z calcd for C22H20FN4O3S2: 471.09554; found: 471.09438 [M+H]+.
(4-((4-(Tert-butyl)phenyl)sulfonyl)piperazin-1-yl)(5-(4-fluorophenyl)imidazo[2,1-b]thiazol-2-
yl)methanone (9de)
Cream color solid: 175 mg; 78% yield; mp: 244–246 ◦C; 1H NMR (300 MHz, DMSO-d6)
1H), 7.87 (dd, J = 8.5, 5.6 Hz, 2H), 7.68 (d, J = 4.6 Hz, 5H), 7.19 (t, J = 8.8 Hz, 2H), 3.78 (s, 4H), 3.03 (s,
4H), 1.31 (s, 9H); 13C NMR (101 MHz, DMSO-d6)
: 162.6, 158.5, 156.4, 147.8, 145.2, 132.2, 130.5, 127.5,
δ: 8.16 (s,
δ
126.6 (d, J = 8.0 Hz), 126.3, 124.0, 117.0, 115.4 (d, J = 21.5 Hz), 110.0, 45.6, 34.9, 30.7; MS (ESI): m/z 527
[M+H]+; HRMS (ESI): m/z calcd for C26H28FN4O3S2: 527.15814; found: 527.15693 [M+H]+.

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(4-((4-Methoxyphenyl)sulfonyl)piperazin-1-yl)(5-phenylimidazo[2,1-b]thiazol-2-yl)methanone (9ea)
Brown color solid: 185 mg; 86% yield; mp: 232–234 ◦C; 1H NMR (300 MHz, DMSO-d6)
: 8.15 (s,
1H), 7.83 (d, J = 7.5 Hz, 2H), 7.69 (d, J = 6.3 Hz, 3H), 7.37 (t, J = 7.5 Hz, 2H), 7.26 (d, J = 7.2 Hz, 1H), 7.17
(d, J = 8.7 Hz, 2H), 3.85 (s, 3H), 3.76 (s, 4H), 3.00 (s, 4H); 13C NMR (101 MHz, DMSO-d6)
: 162.9, 158.5,
δ
δ
147.8, 146.2, 133.9, 129.8, 128.6, 127.2, 126.3, 124.8, 124.0, 116.9, 114.7, 110.1, 55.7, 45.7; MS (ESI): m/z 483
[M+H]+; HRMS (ESI): m/z calcd for C23H23N4O4S2: 483.11552; found: 483.11424 [M+H]+.
(5-Phenylimidazo[2,1-b]thiazol-2-yl)(4-tosylpiperazin-1-yl)methanone (9eb)
Cream color solid: 182 mg; 84% yield; mp: 250–252 ◦C; 1H NMR (300 MHz, DMSO-d6)
1H), 7.83 (d, J = 7.3 Hz, 2H), 7.68 (s, 1H), 7.64 (d, J = 8.1 Hz, 2H), 7.47 (d, J = 8.1 Hz, 2H), 7.37 (t, J = 7.5
Hz, 2H), 7.25 (t, J = 7.3 Hz, 1H), 3.76 (s, 4H), 3.01 (s, 4H), 2.40 (s, 3H); 13C NMR (101 MHz, DMSO-d6)
δ: 8.15 (s,
δ
:
158.5, 147.8, 146.2, 143.9, 133.9, 132.0, 130.0, 128.6, 127.6, 127.2, 124.7, 124.0, 116.9, 110.1, 45.7, 21.0; MS
(ESI): m/z 467 [M+H]+; HRMS (ESI): m/z calcd for C23H23N4O3S2: 467.12067; found: 467.11942 [M+H]+.
(4-((4-Chlorophenyl)sulfonyl)piperazin-1-yl)(5-phenylimidazo[2,1-b]thiazol-2-yl)methanone (9ec)
Cream color solid: 180 mg; 80% yield; mp: 245–247 ◦C; 1H NMR (300 MHz, CDCl3+DMSO-d6)
8.16 (s, 1H), 7.83 (d, J = 7.3 Hz, 2H), 7.76 (d, J = 1.3 Hz, 3H), 7.68 (d, J = 7.7 Hz, 2H), 7.38 (t, J = 7.6 Hz,
2H), 7.25 (t, J = 7.3 Hz, 1H), 3.76 (s, 4H), 3.07 (s, 4H); 13C NMR (101 MHz, DMSO-d6)
: 158.5, 147.8,
δ:
δ
146.2, 138.5, 133.9, 133.8, 129.7, 129.5, 128.6, 127.2, 124.7, 124.0, 116.9, 110.1, 45.6, 44.9; MS (ESI): m/z 487
[M+H]+; HRMS (ESI): m/z calcd for C22H20ClN4O3S2: 487.06599; found: 487.06491 [M+H]+.
(5-Phenylimidazo[2,1-b]thiazol-2-yl)(4-(phenylsulfonyl)piperazin-1-yl)methanone (9ed)
Brown color solid: 175 mg; 75% yield; mp: >350 ◦C; 1H NMR (300 MHz, DMSO-d6)
7.83 (d, J = 7.5 Hz, 2H), 7.76 (d, J = 7.4 Hz, 3H), 7.68 (d, J = 4.7 Hz, 3H), 7.37 (t, J = 7.5 Hz, 2H), 7.26 (d,
δ: 8.14 (s, 1H),
J = 7.3 Hz, 1H), 3.77 (s, 4H), 3.04 (s, 4H); 13C NMR (126 MHz, DMSO-d6)
δ: 158.6, 147.8, 146.2, 134.9,
133.9, 133.5, 129.6, 128.6, 127.5, 127.3, 127.1, 124.7, 116.9, 110.1, 45.7, 45.0; MS (ESI): m/z 453 [M+H]+;
HRMS (ESI): m/z calcd for C22H21N4O3S2: 453.10496; found: 453.10394 [M+H]+.
(4-((4-(Tert-butyl)phenyl)sulfonyl)piperazin-1-yl)(5-phenylimidazo[2,1-b]thiazol-2-yl)methanone (9ee)
Cream color solid: 178 mg; 80% yield; mp: 257–259 ◦C; 1H NMR (300 MHz, DMSO-d6)
1H), 7.83 (d, J = 7.3 Hz, 2H), 7.69 (s, 1H), 7.68 (s, 4H), 7.37 (t, J = 7.5 Hz, 2H), 7.24 (t, J = 7.3 Hz, 1H),
δ: 8.15 (s,
3.78 (s, 4H), 3.03 (s, 4H), 1.30 (s, 9H); 13C NMR (101 MHz, DMSO-d6)
δ: 158.6, 156.4, 147.8, 146.1, 133.9,
132.2, 128.6, 127.5, 127.1, 126.4, 124.7, 124.0, 117.0, 110.1, 45.6, 34.9, 30.7; MS (ESI): m/z 509 [M+H]+;
HRMS (ESI): m/z calcd for C26H29N4O3S2: 509.16756; found: 509.16640 [M+H]+.
4.2. CA Inhibition
The inhibition assay of selected CA isozymes was performed using SX.18V-R Applied Photophysics
(Oxford, UK) stopped flow instrument. 10 mM Hepes (pH 7.4) as a buffer, with Phenol Red (at a
concentration of 0.2 mM) as an indicator, 0.1M Na2SO4 or NaClO4 (To maintain the constant ionic
strength; these anions are not inhibitory in the used concentration), following the CA-catalyzed CO2
hydration reaction for a period of 5–10 s. Saturated CO2 solutions in water at 25 ◦C were used as
substrate. Stock solutions 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 7 different
inhibitor concentrations have been used for measuring the inhibition constant. 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 in this paper are the mean of such results. The inhibition
constants were obtained by non-linear least square methods using the Cheng-Prusoff equation,

Metabolites 2020, 10, 136
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as reported earlier, [24
,25] and represent the mean from at least three different determinations. All CA
isozymes used here were recombinant proteins obtained as reported earlier by our group [26–29].
Supplementary Materials: The following are available online at http://www.mdpi.com/2218-1989/10/4/136/s1,
File S1: spectral and chemical data for the new compounds.
Author Contributions: K.L.M. Conceptualization, S.P. and A.S. contributed in the writing-original draft
preparation; M.A. (Mallika Alvala) supervision, review and editing; M.A. (Mohammed Arifuddin) visualization;
C.T.S. and A.A. Investigation and manuscript editing. All authors have read and agreed to the published version
of the manuscript.
Funding: This research receives no external funding.
Acknowledgments: The authors K.L.M., S.P. and A.S. are thankful to National Institute of Pharmaceutical
Education and Research (NIPER), Balanagar, Hyderabad & Department of Pharmaceuticals, Ministry of Chemicals
and Fertilizers, Govt. of India. C.T.S. is grateful to the Italian Ministry for University and Research for the grant
PRIN: rot. 2017XYBP2R.
Conflicts of Interest: The authors declare no conflict of interest.
References
1.
Supuran, C.T. Carbonic anhydrases: Novel therapeutic applications for inhibitors and activators. Nat. Rev.
Drug Discov. 2008, 7, 168–181. [CrossRef] [PubMed]
2.
3.
4.
Supuran, C.T. Structure and function of carbonic anhydrases. Biochem. J. 2016, 473, 2023–2032. [CrossRef]
Supuran, C.T. Carbonic anhydrases and metabolism. Metabolites 2018, 8, 25. [CrossRef] [PubMed]
Karki, S.S.; Panjamurthy, K.; Kumar, S.; Nambiar, M.; Ramareddy, S.A.; Chiruvella, K.K.; Raghavan, S.C.
Synthesis and biological evaluation of novel 2-aralkyl-5-substituted-6-(40-fluorophenyl)-imidazo
[2, 1-b][1, 3, 4] thiadiazole derivatives as potent anticancer agents. Eur. J. Med. Chem. 2011, 46, 2109–2116.
[CrossRef] [PubMed]
5.
Andreani, A.; Granaiola, M.; Leoni, A.; Locatelli, A.; Morigi, R.; Rambaldi, M.; Lenaz, G.;
Fato, R.; Bergamini, C.; Farruggia, G. Potential Antitumor Agents. 37. Synthesis and Antitumor
Activity of Guanylhydrazones from Imidazo[2,1-b]thiazoles and from the New Heterocyclic System
Thiazolo[20,30:2,3]imidazo[4,5-c]quinoline. J. Med. Chem. 2005, 48, 3085–3089. [CrossRef] [PubMed]
Demirayak, S.; Zitouni, G.; Chevallet, P.; Erol, K.; Kilic, F.S. Synthesis and vasodilatory activity of some
thiazolo-triazole derivative. II Farm. 1993, 48, 707–712.
Ibrahim, D.A. Synthesis and biological evaluation of 3,6-disubstituted [1,2,4]triazolo[3,4-b][1,3,4]thiadiazole
derivatives as a novel class of potential anti-tumor agents. Eur. J. Med. Chem. 2009, 44, 2776–2781. [CrossRef]
Kumar, R.; Bua, S.; Ram, S.; Prete, S.D.; Capasso, C.; Supuran, C.T.; Sharma, P.K. Benzenesulfonamide bearing
imidazothiadiazole and thiazolotriazole scaffolds as potent tumor associated human carbonic anhydrase IX
and XII inhibitors. Bioorg. Med. Chem. 2017, 25, 1286–1293. [CrossRef]
6.
7.
8.
9.
Nishimori, I.; Vullo, D.; Innocenti, A.; Scozzafava, A.; Mastrolorenzo, A.; Supuran, C.T. Carbonic Anhydrase
Inhibitors. The Mitochondrial Isozyme VB as a New Target for Sulfonamide and Sulfamate Inhibitors. J. Med.
Chem. 2005, 48, 7860–7866. [CrossRef]
10. Scozzafava, A.; Menabuoni, L.; Mincione, F.; Supuran, C.T. Carbonic Anhydrase Inhibitors. A General
Approach for the Preparation of Water-Soluble Sulfonamides Incorporating Polyamino–Polycarboxylate Tails
and of Their Metal Complexes Possessing Long-Lasting, Topical Intraocular Pressure-Lowering Properties.
J. Med. Chem. 2002, 45, 1466–1476. [CrossRef]
11. Tanpure, R.P.; Ren, B.; Peat, T.S.; Bornaghi, L.F.; Vullo, D.; Supuran, C.T.; Poulsen, S.-A. Carbonic Anhydrase
Inhibitors with Dual-Tail Moieties to Match the Hydrophobic and Hydrophilic Halves of the Carbonic
Anhydrase Active Site. J. Med. Chem. 2015, 58, 1494–1501. [CrossRef] [PubMed]
12. Angapelly, S.; Ramya, P.V.S.; Angeli, A.; Prete, S.D.; Capasso, C.; Arifuddin, M.; Supuran, C.T. Development
of sulfonamides incorporating phenylacrylamido functionalities as carbonic anhydrase isoforms I, II, IX and
XII inhibitors. Bioorg. Med. Chem. 2017, 25, 5726–5732. [CrossRef] [PubMed]
13. Supuran, C.T. Advances in structure-based drug discovery of carbonic anhydrase inhibitors. Expert Opin.
Drug. Discov. 2017, 12, 61–88. [CrossRef] [PubMed]
14. Supuran, C.T.; Vullo, D.; Manole, G.; Casini, A.; Scozzafava, A. Designing of Novel Carbonic Anhydrase
Inhibitors and Activators. Curr. Med. Chem. 2004, 2, 49–68. [CrossRef]

Metabolites 2020, 10, 136
12 of 12
15. Supuran, C.T. Exploring the multiple binding modes of inhibitors to carbonic anhydrases for novel drug
discovery. Expert Opin. Drug Discov. 2020, 25, 1–16, in press. [CrossRef]
16. Supuran, C.T. Carbonic anhydrases: From biomedical applications of the inhibitors and activators to
biotechnological use for CO2 capture. J. Enzym. Inhib. Med. Chem. 2013, 28, 229–230. [CrossRef]
17. Angeli, A.; Chiaramonte, N.; Manetti, D.; Romanelli, M.N.; Supuran, C.T. Investigation of piperazines as
human carbonic anhydrase I, II, IV and VII activators. J. Enzym. Inhib. Med. Chem. 2017, 33, 303–308.
[CrossRef]
18. Shaik, S.P.; Nayak, V.L.; Sultana, F.; Rao, A.V.S.; Shaik, A.B.; Babu, K.S.; Kamal, A. Design and synthesis of
imidazo [2,1-b] thiazole linked triazole conjugates: Microtubule-destabilizing agents. Eur. J. Med. Chem.
2017, 126, 36–51. [CrossRef]
19. Jadala, C.; Sathish, M.; Anchi, P.; Tokala, R.; Lakshmi, U.J.; Reddy, V.G.; Shankaraiah, N.; Godugu, C.; Kamal, A.
Synthesis of Combretastatin-A4 Carboxamidest that Mimic Sulfonyl Piperazines by a Molecular Hybridization
Approach: In vitro Cytotoxicity Evaluation and Inhibition of Tubulin Polymerization. Chemmedchem 2019, 14,
2052–2060. [CrossRef]
20. Khalifah, R.J. The carbon dioxide hydration activity of carbonic anhydrase. I. Stop-flow kinetic studies on
the native human isoenzymes B and C. J. Biol. Chem. 1971, 246, 2561–2573.
21. Maresca, A.; Temperini, C.; Vu, H.; Pham, N.B.; Poulsen, S.A.; Scozzatava, A.; Quinn, P.J.; Supuran, C.T.
Non-zinc mediated inhibition of carbonic anhydrases: Coumarins are a new class of suicide inhibitors. J. Am.
Chem. Soc. 2009, 131, 3057–3062. [CrossRef] [PubMed]
22. Supuran, C.T. Carbonic anhydrase inhibitors and their potential in a range of therapeutic areas. Expert Opin
Ther Pat. 2018, 28, 709–712. [CrossRef]
23. Korkmaz, N.; Obaidi, O.A.; Senturk, M.; Astley, D.; Ekinci, D.; Supuran, C.T. Synthesis and biological activity
of novel thiourea derivatives as carbonic anhydrase inhibitors. J. Enzym. Inhib. Med. Chem. 2015, 30, 75–80.
[CrossRef] [PubMed]
24. Supuran, C.; Nicolae, A.; Popescu, A. Carbonic anhydrase inhibitors. Part 35. Synthesis of Schiff bases
derived from sulfanilamide and aromatic aldehydes: The first inhibitors with equally high affinity towards
cytosolic and membrane-bound isozymes. Eur. J. Med. Chem. 1996, 31, 431–438. [CrossRef]
25. Carta, F.; Aggarwal, M.; Maresca, A.; Scozzafava, A.; McKenna, R.; Masini, E.; Supuran, C.T. Dithiocarbamates
strongly inhibit carbonic anhydrases and show antiglaucoma action in vivo. J. Med. Chem. 2012, 55, 1721–1730.
[CrossRef] [PubMed]
26. Ceruso, M.; Bragagni, M.; AlOthman, Z.; Osman, S.M.; Supuran, C.T. New series of sulfonamides containing
amino acid moiety act as effective and selective inhibitors of tumor-associated carbonic anhydrase XII.
J. Enzym. Inhib. Med. Chem. 2015, 30, 430–434. [CrossRef]
27. Alafeefy, A.M.; Abdel-Aziz, H.A.; Carta, F.; Supuran, C.T.; Pathak, S.K.; Prasad, O.; Sinha, L. Exploring
QSARs of some benzenesulfonamides incorporating cyanoacrylamide moieties as a carbonic anhydrase
inhibitors (specifically against tumorassociated isoforms IX and XII). J. Enzym. Inhib. Med. Chem. 2015, 30,
519–523. [CrossRef]
28. Nocentini, A.; Supuran, C.T. Advances in the structural annotation of human carbonic anhydrases and
impact on future drug discovery. Expert Opin. Drug. Discov. 2019, 14, 1175–1197. [CrossRef]
29. Supuran, C.T. How many carbonic anhydrase inhibition mechanisms exist? J. Enzym. Inhib. Med. Chem.
2016, 31, 345–360. [CrossRef]
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