Identification of N-phenyl-2-(phenylsulfonyl)acetamides/propanamides as new SLC-0111 analogues: Synthesis and evaluation of the carbonic anhydrase inhibitory activities

Article abstract of DOI:10.1016/j.ejmech.2021.113360

As a front-runner selective CA IX inhibitor currently in Phase Ib/II clinical trials, SLC-0111 has been herein exploited as a lead molecule for development of new different sets of N-phenyl-2-(phenylsulfonyl)acetamides/propanamides incorporating different functionalities; primary sulfonamide (5a-f), free carboxylic (8a, 8d), ethyl ester (8b, 8e), acetyl (8c, 8f) and nitro (10a, 10b), as potential carbonic anhydrase (CA, EC 4.2.1.1) inhibitors. All the prepared analogues have been examined for their CA inhibitory activities towards four human (h) isoenzymes, hCA I, II, IX and XII. Interestingly, replacement of SLC-0111 ureido linker with the flexible sulfonyl acetamide linker, as well as linker branching and elongation strategies successfully enhanced the inhibitory action toward hCA IX isoform, such as in sulfones 5a-d and 5f which displayed better activity than SLC-0111. Furthermore, sulfonamide-based sulfone (5f) and carboxylic acid-based sulfones (8a and 8d) demonstrated interesting selectivity toward the tumor-related hCA IX isoform over both hCA I and hCA II, which suggests them as promising candidates for further development as potential anticancer candidates. Thereafter, the anti-proliferative action for sulfones 5f, 8a and 8d was examined against breast (MCF-7) and colon (HCT-116) cancer cell lines. Also, sulfone 5f was further assessed for its impact on the cell cycle progression and apoptosis in HCT-116 cells.

Full text of DOI:10.1016/j.ejmech.2021.113360

European Journal of Medicinal Chemistry 218 (2021) 113360
Contents lists available at ScienceDirect
European Journal of Medicinal Chemistry
journal homepage: http://www.elsevier.com/locate/ejmech
Identification of N-phenyl-2-(phenylsulfonyl)acetamides/
propanamides as new SLC-0111 analogues: Synthesis and evaluation
of the carbonic anhydrase inhibitory activities
,
,
, d
Mostafa M. Elbadawi a b, Wagdy M. Eldehna a *, Alessio Nocentini c
,
Mahmoud F. Abo-Ashour e, Eslam B. Elkaeed f g, Mohamed A. Abdelgawad h,
,
Khalid S. Alharbi i, Hatem A. Abdel-Aziz j, Claudiu T. Supuran c **, Paola Gratteri d,
,
Mohammad M. Al-Sanea h
a Department of Pharmaceutical Chemistry, Faculty of Pharmacy, Kafrelsheikh University, Kafrelsheikh 33516, Egypt
b Department of Chemistry, Graduate School of Science, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8526, Japan
c Department of NEUROFARBA, Section of Pharmaceutical and Nutraceutical Sciences, University of Florence, Polo Scientifico, Via U. Schiff 6, 50019, Sesto
Fiorentino, Firenze, Italy
d Department of NEUROFARBA, Section of Pharmaceutical and Nutraceutical Sciences, Laboratory of Molecular Modeling Cheminformatics & QSAR,
University of Florence, Polo Scientifico, Via U. Schiff 6, 50019, Sesto Fiorentino, Firenze, Italy
e Department of Pharmaceutical Chemistry, Faculty of Pharmacy, Egyptian Russian University, Badr City, Cairo 11829, Egypt
f Department of Pharmaceutical Sciences, College of Pharmacy, AlMaarefa University, Ad Diriyah 13713, Riyadh, Saudi Arabia
g Department of Pharmaceutical Organic Chemistry, Faculty of Pharmacy (Boys), Al-Azhar University, Nasr City 11884, Cairo, Egypt
h Department of Pharmaceutical Chemistry, College of Pharmacy, Jouf University, Sakaka, Aljouf 72341, Saudi Arabia
i Department of Pharmacology, College of Pharmacy, Jouf University, Sakakah, 72341, Saudi Arabia
j Department of Applied Organic Chemistry, National Research Center, Dokki, Cairo 12622, Egypt
a r t i c l e i n f o
a b s t r a c t
Article history:
As a front-runner selective CA IX inhibitor currently in Phase Ib/II clinical trials, SLC-0111 has been herein
exploited as a lead molecule for development of new different sets of N-phenyl-2-(phenylsulfonyl)
acetamides/propanamides incorporating different functionalities; primary sulfonamide (5a-f), free car-
boxylic (8a, 8d), ethyl ester (8b, 8e), acetyl (8c, 8f) and nitro (10a, 10b), as potential carbonic anhydrase
(CA, EC 4.2.1.1) inhibitors. All the prepared analogues have been examined for their CA inhibitory ac-
tivities towards four human (h) isoenzymes, hCA I, II, IX and XII. Interestingly, replacement of SLC-0111
ureido linker with the flexible sulfonyl acetamide linker, as well as linker branching and elongation
strategies successfully enhanced the inhibitory action toward hCA IX isoform, such as in sulfones 5a-
d and 5f which displayed better activity than SLC-0111. Furthermore, sulfonamide-based sulfone (5f) and
carboxylic acid-based sulfones (8a and 8d) demonstrated interesting selectivity toward the tumor-
related hCA IX isoform over both hCA I and hCA II, which suggests them as promising candidates for
further development as potential anticancer candidates. Thereafter, the anti-proliferative action for
sulfones 5f, 8a and 8d was examined against breast (MCF-7) and colon (HCT-116) cancer cell lines. Also,
sulfone 5f was further assessed for its impact on the cell cycle progression and apoptosis in HCT-116 cells.
© 2021 Elsevier Masson SAS. All rights reserved.
Received 18 December 2020
Received in revised form
3 March 2021
Accepted 3 March 2021
Available online 13 March 2021
Keywords:
Carbonic anhydrase inhibitors
Sulfones
Benzenesulfonamide
SLC-0111 analogues
Carboxylic acids
Tail approach
1. Introduction
Carbonic anhydrases (CAs, EC 4.2.1.1) are prevalent and ubiqui-
tous metalloenzymes in all life kingdoms and catalyze a simple but
crucial physiological reaction, the conversion of CO2 and water into
bicarbonate and proton [1]. This CA-catalyzed reaction is crucial in
various physiological and pathological processes, such as several
* Corresponding author.
** Corresponding author.
E-mail addresses: wagdy2000@gmail.com (W.M. Eldehna), claudiu.supuran@
unifi.it (C.T. Supuran).
metabolic
reactions
(like
lipogenesis,
ureagenesis
and
https://doi.org/10.1016/j.ejmech.2021.113360
0223-5234/© 2021 Elsevier Masson SAS. All rights reserved.

M.M. Elbadawi, W.M. Eldehna, A. Nocentini et al.
European Journal of Medicinal Chemistry 218 (2021) 113360
gluconeogenesis), pH and CO2 homeostasis, electrolyte secretion,
bone resorption, tumorigenicity and respiration, to name a few [2].
So far, eight evolutionarily unrelated gene CA families have been
characterized: a-, b-, g-, d-, z-, h-, q- and i-CAs. The a-CAs are present
in vertebrates, bacteria, algae, protozoa, corals, and the cytoplasm of
green plants [3].
and rigid piperazinyl-ureido linkers (Compound V, Fig. 1) [14].
Though most these reported SLC-0111 analogues elicited an
enhanced hCA IX inhibitory activity, their inhibition profiles
exhibited loss of selectivity toward hCA IX over the cytosolic hCA II
isozyme, which should be attributable to the concurrent consid-
erable improvement of hCA II inhibitory activity.
Regarding the human
a
-CAs (hCAs), fifteen assorted isoforms
Herein we report the design and synthesis of new SLC-0111
analogues based on N-phenyl-2-(phenylsulfonyl)acetamide/prop-
anamide scaffold that incorporates different functionalities; pri-
mary sulfonamide (5a-f), free carboxylic acid (8a and 8d), ethyl
ester (8b and 8e), acetyl (8c and 8f) and nitro (10a-b), as (Fig. 2).
The utilized design strategy is based on replacement of the SLC-
0111 ureido linker with the flexible sulfonyl acetamide linker.
Thereafter, the sulfonyl acetamide linker was either branched or
elongated. Moreover, a bioisosteric replacement for the sulfamoyl
zinc-binding group with carboxylic acid functionality as well as
ethyl ester, acetyl and nitro groups, was carried out. All the newly
prepared N-phenyl-2-(phenylsulfonyl)acetamides/propanamides
5a-f, 8a-f and 10a-b will be characterized and biologically evalu-
ated towards a panel of hCA I, II, IX and XII isoforms.
have been identified to date, all of them are catalytically active
except CA VIII, X, and XI that are completely lacking the catalytic
activity which is attributable to the absence of the essential histi-
dine residues that involved in the catalytic mechanism via coordi-
nating the zinc ion [3]. The twelve catalytically active hCAs
possessed various tissue distribution and location: IV, IX, XII, and
XIV are membrane-associated; I, II, III, VII, and XIII are cytosolic; VA
and VB are mitochondrial; and VI is secreted in saliva and milk.
Inhibition of many of these hCA isoforms was demonstrated to
provide substantial druggable therapeutic effects for different dis-
orders such as edema (hCA II, IV, XIV), glaucoma (hCA II, IV and XII),
CNS-associated pathologies (hCA VII and XIV), and cancers (hCA IX
and hCA XII) [4].
Due to its overexpression in a range of human malignancies, hCA
IX has been validated as a promising new target in anticancer drug
discovery and development for the management of hypoxic tumors
[5]. One of the important issues to be considered in the design of
hCA IX inhibitors is their selectivity over the physiologically rele-
vant cytosolic hCA I and II isoforms. In spite of identifying several
approaches that develop selective hCA IX inhibitors, the “tail
approach” emerged as the most exploited and successful one [6]. In
this approach, ‘‘tails’’ with a varied chemical nature, are appended
to an aromatic/heterocyclic ring featuring a zinc binding group
(ZBG), such as primary sulfamoyl and carboxylic acid functional-
ities, through a flexible linker.
SLC-0111, a front-runner small molecule CAI, is currently in
Phase I/II clinical trials for the treatment of metastatic solid hypoxic
tumors. As it entails the “tail approach” design, SLC-0111 has high
selectivity toward hCA IX isoform over the physiologically relevant
hCA I and II isoforms [7,8]. Furthermore, a recent study [9] has
revealed that utilization of SLC-0111 in a combination therapy with
3-O-acetylbetulin has efficiently improved the cytotoxicity,
enhanced DNA damage, inhibited the cell motility, and enhanced
the radiosensitivity. Thence, this study [9] has suggested SLC-0111-
based combination therapy as a promising therapeutic approach
for targeting different hypoxic tumors.
2. Results and discussion
2.1. Chemistry
The synthetic routes followed to synthesize the differently
substituted
N-phenyl-2-(phenylsulfonyl)acetamides/prop-
anamides (5a-f, 8a-f and 10a-b) are depicted in Schemes 1 and 2.
In Scheme 1, synthesis of the target benzenesulfonamide-
containing derivatives (5a-f) was started by acylation of the basic
amino function of sulfanilamide 1 with bromoacetyl bromide 2a, 2-
bromopropionyl bromide 2b, or 3-chloropropionyl chloride 2c in
dry dioxane in the presence of potassium carbonate to afford the
key intermediates 3a-c, respectively. Then, intermediates 3a-c
were reacted with sodium sulfinates 4a,b in absolute ethanol to
afford the target benzenesulfonamide-based sulfones 5a-f (Scheme
1).
With the aim of introducing different isosteres for the sulfon-
amide functionality, four different aniline derivatives 6a-d (4-
aminobenzoic
acid,
ethyl
4-aminobenzoate,
4-
aminoacetophenone and 4-nitroaniline) were acylated by bro-
moacetyl bromide 2a as described above to afford intermediates
7a-c and 9, respectively. Thereafter, intermediates 7a-c and 9 were
reacted with sodium sulfinates 4a,b in absolute ethanol to furnish
the target sulfones 8a-f and 10a-b, respectively (Scheme 2).
All herein prepared target sulfones 5a-f, 8a-f and 10a-b were
obtained in good yields and thoroughly characterized by 1H NMR,
13C NMR and HRMS.
With the prime aim of identifying new different SLC-0111 ana-
logues, the bioisosteric replacement approach was ultimately
fostered by many research groups: the SLC-0111 ureido linker has
been replaced with a thioureido and selenoureido (Compound I,
Fig. 1) [10], 1,3-triazene (Compound II, Fig. 1) [11], cyanoguanidine
(Compound III, Fig. 1) [12], enaminone (Compound IV, Fig. 1) [13],
Fig. 1. Structure of SLC-0111 and its analogues IeV.
2

M.M. Elbadawi, W.M. Eldehna, A. Nocentini et al.
European Journal of Medicinal Chemistry 218 (2021) 113360
Fig. 2. The design for the target N-phenyl-2-(phenylsulfonyl)acetamides/propanamides 5a-f, 8a-f and 10a, b.
Scheme 1. Synthesis of target sulfonamides 5a-f; Reagents and conditions: (i) Dioxane, K2CO3, stirring 3 h, (ii) Ethanol/reflux 14 h.
2.2. Carbonic anhydrase inhibition
Tables 1 and 2.
Regarding the CA inhibitory activities of sulfonamide-based N-
phenyl-2-(phenylsulfonyl)acetamides/propanamides (5a-f), all de-
rivatives displayed potent to moderate inhibitory action towards
the ubiquitous cytosolic hCA I isoform with KI values ranging from
72.1 to 320.4 nM, Table 1. In particular, sulfonamide-based sulfones
5b, 5c and 5d exhibited the best hCA I inhibitory activity with two-
The CA inhibitory impact for all herein prepared target sulfones
5a-f, 8a-f and 10a-b, as well as the standard CAI acetazolamide
(AAZ) was estimated against the ubiquitous cytosolic CA I and II,
and cancer-related CA IX and XII isoforms, by the use of a stopped-
flow CO2 hydrase assay [15]. Certain structureeactivity relationship
(SAR) could be collected from the reported inhibition data in
digit nanomolar activities (KIs
¼
72.1, 92.6 and 83.8 nM,
3

M.M. Elbadawi, W.M. Eldehna, A. Nocentini et al.
European Journal of Medicinal Chemistry 218 (2021) 113360
Scheme 2. Synthesis of target sulfones 8a-f and 10a, b; Reagents and conditions: (i) Dioxane, K2CO3, stirring 3 h, (ii) Ethanol/reflux 10 h.
respectively), whereas sulfones 5a, 5e and 5f exerted moderate
activity with KIs equal 320.4, 114.2 and 129.7 nM, respectively. It is
worth stressing that grafting a p-methyl group (compound 5b;
KI ¼ 72.1 nM) within the phenyl tail of sulfone 5a (KI ¼ 320.4 nM)
resulted in a more than 4-fold inhibition increase for the cytosolic
hCA I isoform. Also, it is noted that branching and elongation of the
sulfonyl acetamide linker in the phenyl tail-bearing sulfone 5a
(KI ¼ 320.4 nM) resulted in a slight enhancement of isoform hCA I
inhibitory activity (compounds 5c and 5e; KIs ¼ 92.6 and 114.2 nM,
respectively). On the other hand, branching and elongation of the
sulfonyl acetamide linker in the p-tolyl tail-bearing sulfone 5b
(KI ¼ 72.1 nM) led to sulfones 5d and 5f with slight decreased ac-
tivity against hCA I isoform (KIs ¼ 83.8 and 129.7 nM, respectively).
Furthermore, exploring the inhibitory activity of herein reported
sulfonamide-based sulfones (5a-f) against the physiologically
dominant hCA II isoform revealed that it was effectively inhibited
by sulfones (5a-f) with KI spanning in the range 5.9e43.6 nM,
Table 1. Superiorly, sulfones 5c and 5d exerted single-digit nano-
molar inhibitory activities against hCA II isoform (KIs ¼ 7.4 and
5.9 nM, respectively), in addition sulfones 5a, 5b, 5e and 5f dis-
played inhibition constants equal 43.6, 14.7, 31.8 and 20.3 nM,
respectively. It is worthy to mention that replacement of the phenyl
tail of sulfone 5a (KI ¼ 43.6 nM) with a p-tolyl one, as in compound
5b, resulted in about 3-fold enhanced inhibitory potency toward
hCA II isoform (KI ¼ 14.7 nM). Moreover, branching of the sulfonyl
acetamide linker as well as its elongation improved the hCA II
inhibitory action for the phenyl tail-bearing sulfone 5a; (com-
pounds 5c and 5e; KIs ¼ 7.4 and 31.8 nM, respectively).
The obtained inhibition constants for the tumor-related isoform
hCA IX (Table 1), showed that all sulfonamide-based sulfones (5a-f)
were capable of inhibiting this isoform in the low nanomolar range
(KIs: 4.3e46.1 nM). Sulfones 5c and 5f emerged as the most potent
herein reported hCA IX inhibitors endowed with single-digit
nanomolar KI values equal 6.5 and 4.3 nM, respectively, Table 1.
Similar to the SAR for inhibition of hCA I and II; grafting a p-methyl
group (compound 5b; KI ¼ 15.9 nM) within the phenyl tail of sul-
fone 5a (KI ¼ 22.7 nM) was advantageous for inhibitory activity
against hCA IX. Also, branching of the sulfonyl acetamide linker
incorporated in the phenyl tail-bearing sulfone 5a was more
beneficial for hCA IX inhibition (compound 5c; KI ¼ 6.5 nM),
whereas, elongation of such linker resulted in about 2-fold
decreased activity towards hCA IX isoform (compound 5e;
KI ¼ 46.1 nM). On the contrary, elongation of the sulfonyl acetamide
linker in the p-tolyl tail-bearing sulfone 5b (KI ¼ 15.9 nM) to a
sulfonyl propanamide linker led to the most efficient hCA IX in-
hibitor (5f) with KI ¼ 4.3 nM, whereas linker branching for sulfone
5b decreased the activity approximately by half (KI ¼ 29.8 nM),
Table 1.
Finally, the displayed in vitro inhibition data (Table 1) high-
lighted that the cancer-related hCA XII isoform has been effectively
inhibited by all the sulfonamide-bearing sulfones (5a-f) herein
reported. The hCA XII inhibition profiles were almost flat, with
measured KI values ranged from 5.1 to 42.4 nM. The SAR outcomes
pointed out that incorporation of a branched sulfonyl propanamide
linker led to sulfones 5c and 5d which stood out as most efficient
hCA XII inhibitors in this work with single-digit nanomolar
4

M.M. Elbadawi, W.M. Eldehna, A. Nocentini et al.
European Journal of Medicinal Chemistry 218 (2021) 113360
Table 1
Table 2
Inhibition data for hCA I, II, IX and XII isoforms with sulfonamide-based N-phenyl-2-
(phenylsulfonyl)acetamides/propanamides (5a-f), SLC-0111, and the standard AAZ.
Inhibition data for hCA isoforms I, II, IX and XII with non-sulfonamide-based N-
phenyl-2-(phenylsulfonyl)acetamides 8a-f and 10a-b.
Code Structure
KI (nM)a
Code
Structure
KI (
mM)
CA I
CA II CA IX CA XII
CA I
CA II
31.7
CA IX
0.93
CA XII
0.85
5a
320.4 43.6
22.7
11.2
8a
>100
>100
>100
8b
8c
>100
>100
17.2
1.4
5b
5c
5d
72.1
92.6
83.8
14.7
7.4
15.9
42.4
>100
>100
6.5
5.1
7.9
8d
8e
8f
55.7
15.8
91.4
>100
0.72
29.5
>100
0.53
5.9
29.8
>100
>100
>100
>100
5e
5f
114.2 31.8
129.7 20.3
46.1
4.3
32.6
35.8
10a
10b
>100
>100
>100
>100
>100
>100
>100
>100
SLC-0111
AAZ
5080 960.0 45.0
250.0 12.0 25.0
4.5
5.7
a; Mean from three different assays, via a stopped flow technique.
inhibitory potencies (KIs ¼ 5.1 and 7.9 nM, respectively), Table 1.
With regard to the newly synthesized non-sulfonamide-based
N-phenyl-2-(phenylsulfonyl)acetamides (8a-f and 10a-b), their
hCA inhibitory activities were assessed and the obtained inhibition
data were listed in Table 2.
Bioisosteric replacement of the sulfamoyl zinc-binding group in
sulfones 5a and 5b with the carboxylic acid functionality (sulfones
8a and 8d) dramatically affected the inhibitory activities. Both
carboxylic acid-based sulfones 8a and 8d displayed diminished or
sulfonamide-based sulfone (5f) and carboxylic acid-based sulfones
(8a and 8d) demonstrated interesting selectivity toward the tumor-
related hCA IX isoform over both hCA I (S.I. ¼ 30.2, >107 and 77.4,
respectively) and hCA II (S.I. ¼ 4.7, 34.1 and 21.9, respectively),
Table 3. This selectivity manner for sulfones 5f, 8a and 8d suggests
them as interesting and promising candidates for further devel-
opment as potential anticancer agents.
Lastly, the herein utilized bioisosteric replacement approach via
replacing the SLC-0111 ureido linker with the flexible sulfonyl
acetamide linker, as well as linker branching and elongation stra-
tegies successfully enhanced the inhibitory action toward hCA IX
isoform, such as sulfones 5a-d and 5f (KIs ¼ 22.7, 11.2, 6.5, 5.1 and
32.6 nM, respectively, vs KI ¼ 45.0 for SLC-0111). Regrettably, the
enhanced activity toward hCA IX was accompanied with an
improved activity against hCA II isoform, as well, which led to a
decreased hCA IX/II selectivity index for target sulfones. Thus,
further structural modifications are required to optimize the hCA
IX/II selectivity.
weak inhibition against hCA I (KIs ¼ >100 and 55.7
tively) and hCA II (KIs ¼ 31.7 and 15.8 M, respectively) isoforms,
whereas they displayed moderate sub-micromolar inhibitory po-
tencies against hCA IX (KIs ¼ 0.93 and 0.72 M, respectively) and
M, respectively) isoforms, Table 2.
mM, respec-
m
m
hCA XII (KIs ¼ 0.85 and 0.53
m
Furthermore, ester analogues (8b and 8e) of carboxylic acid-
based sulfones 8a and 8d displayed much lower inhibitory activ-
ities towards the examined hCA I (KIs ¼ >100
and 91.4
M, respectively), IX (KIs ¼ 17.2 and 29.5
and XII (KIs ¼ 1.4 and > 100 M, respectively) isoforms, Table 2.
m
M), II (KIs ¼ >100
m
m
M, respectively),
m
On the other hand, replacement of the primary sulfonamide
functionality in sulfones 5a and 5b with acetyl (sulfones 8c and 8f)
or nitro (sulfones 10a and 10b) functionalities diminished the
inhibitory activities toward all the examined hCA isoforms I, II, IX
and XII (KIs > 100
It is worth highlighting that carbonic anhydrase inhibitory
profiles presented in Tables and hinted out that only
mM), Table 2.
1
2
5

M.M. Elbadawi, W.M. Eldehna, A. Nocentini et al.
European Journal of Medicinal Chemistry 218 (2021) 113360
Table 3
Calculated selectivity indexes (S.I.s) for inhibition of hCA IX over hCA I and II
isoforms for sulfonamide-bearing sulfone (5f), carboxylic acid-based sulfones (8a
and 8d), and acetazolamide.
Compound
I/IX
II/IX
5f
8a
8d
AAZ
30.2
>107
77.4
10.0
4.7
34.1
21.9
0.5
2.3. Anticancer study
2.3.1. Anti-proliferative activity against HCT-116 and breast MCF-
7 cell lines
Fig. 3. Effect of sulfonamide-based sulfone 5f on the cell cycle phases in HCT-116 cells.
On account of their favorable selectivity profile towards hCA IX,
sulfones 5f, 8a and 8d were selected to be assessed for their po-
tential anti-proliferative action against human colorectal (HCT-116)
and breast (MCF-7) cancer cell lines, under hypoxic conditions
utilizing the protocol of the MTT assay. The assay results have been
expressed as IC50 values and listed in Table 4.
between ligand structure and inhibition potency against hCAs II, IX
and XII. Sulfonamide-based sulfones 5a and 5e were chosen as
representative of the sulfonamide subset, and 8a as exemplary
carboxylate.
All docking solutions found the benzenesulfonamide moiety of
sulfones 5a and 5e coordinated to the zinc ion by the negatively
charged nitrogen atom according to a tetracoordinated geometry.
Furthermore, the poses were stabilized by two H-bonds established
by the sulfonamide S]O and NHꢀ groups with the NH backbone
and OH side chain of residues T199, respectively. The phenyl ring
formed hydrophobic contacts with nonpolar residues V121, V143
and L198 (Fig. 5).
The phenylsulfonyl tail of the two ligands, which only differ in
length for a eCH2- group, accommodated over the hydrophobic
area of the active site of hCAs II, IX and XII. This area, lined by the
residue 91, 121, 131, 135, 141, 143, 198, 201, 202, 204, shows in hCA II
the most lipophilic properties and the smallest volume among this
hCA subset due to the presence of the F131 residue that is replaced
by valine/XX in the CA IX/XII isoforms. This enables an efficient fit of
Investigating the MTT assay results highlighted that the tested
sulfones 5f, 8a and 8d possessed excellent to moderate growth
inhibitory activity against both HCT-116 and MCF-7 cell lines.
Interestingly sulfonamide-based sulfone 5f, which displayed potent
hCA IX inhibitory activity, showed excellent sub-micromolar anti-
proliferative activity against HCT-116 (IC50 ¼ 0.57 0.02) and MCF-
7 cells (IC50 ¼ 0.67
0.03). Moreover, non-sulfonamide-based
sulfones 8a and 8d exhibited moderate activity against HCT-116
0.44 and 2.23 0.08, respectively) and MCF-7
(IC50 ¼ 11.58
(IC50 ¼ 5.29 0.2 and 3.41 0.13, respectively) cells, Table 4.
2.3.2. Cell cycle analysis
The impact of sulfonamide-based sulfone 5f on the cell cycle
progression in colorectal HCT-116 cells was explored via a flow
cytometric analysis.
Analyzing the obtained results hinted out that exposure of HCT-
116 cells to sulfone 5f for 24 h affected the cell cycle progression.
Sulfone 5f was found to increase the percentage of apoptotic cells
within Sub-G1 phase, in addition to the cell populations in the S-
phase. Moreover, 5f decreased the G2-M phase populations by 3-
fold compared to the control, Fig. 3.
the ligand tails within this area, further stabilized by
p and hy-
drophobic interactions (Fig. 5A). These ligand orientations appear
to tolerate a p-methylation on the outer phenyl ring, as in 5b, 5d or
5f that increased the inhibition potency.
Equally lipophilic, in hCA IX the same area displays a greater
volume because of the F131V mutation with respect to hCA II. Thus,
the phenylsulfonyl tail is able to stretch inside the cleft forming a
wide set of
p-alkyl and hydrophobic interactions (Fig. 5B). These
2.3.3. Annexin V-FITC/Propidium Iodide (AV/PI) apoptosis assay
The potential apoptotic effect of sulfone 5f in colorectal HCT-
116 cells was examined, utilizing (AV/PI) dual staining assay. The
assay outputs highlighted the ability of sulfone 5f to persuade
apoptosis in HCT-116 cells as suggested by the significant increase
in the percent of AV-positive apoptotic cells in the late apoptosis
phase from 0.22% to 21.45% (Fig. 4).
orientations also appear to tolerate the p-methylation, as in 5b, or
5f, that in fact increased the compound inhibition potency. The
lipophilic features of the same area in hCA XII is significantly
reduced because of the L204 N, V135 and G132S mutations with
respect to hCA II. The phenylsulfonyl group of the ligand is involved
in a wide network of VdW interactions with S132, S136, N136, P202
and N204 which together efficiently stabilize the binding orienta-
tions (Fig. 5C). However, the nature of the pocket did not tolerate
the ligand p-methylation and induced, in the case of hCA XII a slight
decrease of inhibition potency for the toluyl derivatives 5b and 5f.
Carboxylates are generally much less efficient than primary
sulfonamides as zinc-binders for CA inhibition [2]. Likewise, car-
boxylates 8a, 8b, 8d, and 8e acted as significantly worse CAIs than
sulfonamides 5a-f (Table 2). The docking solutions for the carbox-
ylic acid 8a showed the COOꢀ group coordinating the zinc ion by a
tetrahedral geometry in the active site of hCA II, IX and XII. The
orientation of 8a zinc-binding function was significantly stabilized
by a H-bond with T199 backbone NH in the active site of hCAs IX
and XII (Fig. 6). The presence of F131 was shown to narrow hCA II
active site enough to hinder the aforesaid positioning and stabili-
zation for the benzoate portion, that overall decreased the
2.4. Docking study
A docking study was implemented to estimate the correlation
Table 4
Anti-proliferative impact of sulfones 5f, 8a and 8d against human colorectal (HCT-
116) and breast (MCF-7) cancer cell lines, under hypoxic conditions.
Comp.
IC50 (m
M)a
HCT-116
MCF-7
5f
8a
8d
0.57 0.02
11.58 0.44
2.23 0.08
0.67 0.03
5.29 0.2
3.41 0.13
a
IC50 values are the mean S.D. of three experiments.
6

M.M. Elbadawi, W.M. Eldehna, A. Nocentini et al.
European Journal of Medicinal Chemistry 218 (2021) 113360
Fig. 4. Effect of sulfonamide-based sulfone 5f on the percentage of AV-positive staining in in colorectal HCT-116 cells.
Fig. 5. Predicted binding orientations of sulfonamide-based sulfones 5a (cyan) and 5e (green) within the active site of A) hCA II, B) hCA IX and C) hCA XII. H-bonds are represented
as black dashed lines.
Fig. 6. Predicted binding orientations of carboxylic acid 8a within the active site of A) hCA II, B) hCA IX and C) hCA XII. H-bonds are represented as black dashed lines.
inhibition potency against hCA II with respect to hCAs IX and XII
(Table 2). As a result of the different positioning of the benzoate
core, the ligand tail protruded towards the pocket lined by residues
91, 92, and 131 in the active site of the tumor-associated CAs, ac-
commodating over the area formed by Q92, E69, N67 and L60 in
hCA II binding cleft. In all the three active site ligand amidic
carbonyl group received a H-bond by Q92 side chain NH2 (Fig. 6).
3. Conclusion
In this work, novel N-phenyl-2-(phenylsulfonyl)acetamides/
propanamides incorporating primary sulfonamide (5a-f), free car-
boxylic (8a, 8d), ethyl ester (8b, 8e), acetyl (8c, 8f) and nitro (10a,
10b) functionalities have been designed and prepared as novel SLC-
0111 analogues. Sulfonamide-based sulfones 5 displayed much
7

M.M. Elbadawi, W.M. Eldehna, A. Nocentini et al.
European Journal of Medicinal Chemistry 218 (2021) 113360
better activity than their carboxylic acids and esters analogues,
whereas acetyl and nitro counterparts showed diminished CA
inhibitory activities. Sulfonamide-based sulfones 5 displayed KIs in
the nanomolar range; 72.1e320.4 nM for CA I, 5.9e43.6 nM for CA
II, 4.3e46.1 nM for CA XI, and 5.1e42.4 nM for CA XII. The SAR
analysis pointed out that replacement of the phenyl tail with a p-
tolyl one, as well as branching of the sulfonyl acetamide linker are
more advantageous for the inhibitory activities towards hCA I, II
and IX isoforms. Superiorly, sulfones 5c and 5f emerged as the most
potent herein reported hCA IX inhibitors with single-digit nano-
molar potency (KI ¼ 6.5 and 4.3 nM, respectively), whereas sulfones
5c and 5d stood out as most efficient single-digit nanomolar hCA
XII inhibitors in this study with KIs ¼ 5.1 and 7.9 nM, respectively.
Furthermore, sulfonamide-based sulfone (5f) and carboxylic acid-
based sulfones (8a and 8d) demonstrated interesting selectivity
(100 MHz)
d
ppm: 21.57, 62.76, 119.08,125.98, 126.48, 128.55, 130.17,
130.95, 136.90, 142.67, 145.13, 160.56, 167.28; HRMS (ESI) for
C
15H17O5N2S2, calcd 369.05734, found 369.05809 [MþH]þ.
4.1.2.3. 2-(Phenylsulfonyl)-N-(4-sulfamoylphenyl)propanamide 5c.
White crystals, m.p. 196e197 ꢁC, yield 79%, 1H NMR (400 MHz)
d
ppm: 1.40 (d, 3H, -CH3-CH-CO, J ¼ 6.8 Hz), 4.36 (q, 1H, eCH3-CH-
CO, J ¼ 6.8 Hz), 7.29 (s, 2H, NH2), 7.65e7.68 (m, 4H, AreH),
7.76e7.80 (m, 3H, AreH), 7.83e7.86 (m, 2H, AreH), 10.62 (s, 1H,
NH); 13C NMR (100 MHz)
d ppm: 12.41, 65.96, 119.57, 127.26, 129.57,
129.71, 134.87, 136.81, 139.73, 141.64, 164.11; HRMS (ESI) for
C
15H17O5N2S2, calcd 369.05734, found 369.05727 [MþH]þ.
4.1.2.4. N-(4-Sulfamoylphenyl)-2-tosylpropanamide 5d. White crys-
tals, m.p. 205e206 ꢁC, yield 71%, 1H NMR (400 MHz)
ppm: 1.37 (d,
d
toward the tumor-related hCA IX isoform over both hCA
I
3H, -CH3-CH-CO, J ¼ 7.2 Hz), 2.41 (s, 3H, eC6H4eCH3), 4.33 (q, 1H,
eCH3-CH-CO, J ¼ 6.8 Hz), 7.29 (s, 2H, NH2), 7.46 (d, 2H, AreH,
J ¼ 8.0 Hz), 7.67 (d, 2H, AreH, J ¼ 8.8 Hz), 7.71 (d, 2H, AreH,
J ¼ 8.0 Hz), 7.78 (d, 2H, AreH, J ¼ 8.8 Hz), 10.63 (s, 1H, NH); 13C
(S.I. ¼ 30.2, >107 and 77.4, respectively) and hCA II (S.I. ¼ 4.7, 34.1
and 21.9, respectively), which suggested them for further biological
evaluation as potential anticancer agents. The anti-proliferative
action for sulfones 5f, 8a and 8d was then examined against
breast (MCF-7) and colon (HCT-116) cancer cell lines. Moreover,
sulfone 5f was further assessed for its action on the cell cycle dis-
tribution and apoptosis in HCT-116 cells. Finally, the molecular
docking study has justified the obtained CA inhibitory activities,
and has explored the binding mode for the target sulfones within
hCA II, IX and XII active sites.
NMR (100 MHz)
d ppm: 12.52, 21.58, 65.98, 119.54, 127.26, 129.61,
130.16, 133.98, 139.63, 141.56, 145.51, 164.12; HRMS (ESI) for
C
16H19O5N2S2, calcd 383.07299, found 383.07305 [MþH]þ.
4.1.2.5. 3-(Phenylsulfonyl)-N-(4-sulfamoylphenyl)propanamide 5e.
White crystals, m.p. 185e186 ꢁC, yield 75%, 1H NMR (400 MHz)
d
ppm: 2.71 (t, 2H, eCH2-CH2-CO, J ¼ 7.6 Hz), 3.62 (t, 2H, -CH2-CH2-
CO, J ¼ 7.6 Hz), 7.23e7.29 (m, 3H, AreH), 7.64e7.75 (m, 4H, AreH),
7.80 (s, 2H, NH2), 7.92e7.99 (m, 2H, AreH), 10.77 (s, 1H, NH);13
NMR (100 MHz) ppm: 29.96, 51.02, 119.07, 119.79, 127.14, 127.32,
4. Experimental
C
d
4.1. Chemistry
128.25, 129.98, 130.31, 134.45, 135.44,139.10, 140.54, 142.24, 168.37;
HRMS (ESI) for C15H17O5N2S2, calcd 369.05734, found 369.05820
[MþH]þ.
4.1.1. General
The NMR spectra have been recorded on Bruker spectropho-
tometer at 400 MHz. 13C spectra were run at 100 MHz in deuterated
dimethyl sulfoxide (DMSO‑d6). Chemical shifts (dH) are reported
relative to TMS as internal standard. High-resolution mass spectra
have been recorded on Bruker MicroTOF spectrometer. Compounds
3a-c [16e19], 7a-c [20e22] and 9 [23] were previously synthesized.
4.1.2.6. N-(4-Sulfamoylphenyl)-3-tosylpropanamide 5f. White crys-
tals, m.p. 219e221 ꢁC, yield 73%, 1H NMR (400 MHz)
d ppm: 2.38 (s,
3H, eC6H4eCH3), 2.69 (t, 2H, eCH2-CH2-CO, J ¼ 7.2 Hz), 3.57 (t, 2H,
-CH2-CH2-CO, J ¼ 7.2 Hz), 7.24 (s, 2H, NH2), 7.44 (d, 2H, AreH,
J ¼ 7.6 Hz), 7.62 (d, 2H, AreH, J ¼ 8.8 Hz), 7.73 (d, 2H, AreH,
J ¼ 8.8 Hz), 7.78 (d, 2H, AreH, J ¼ 8.0 Hz), 10.33 (s, 1H, NH); 13C
4.1.2. General procedure for preparation of target N-phenyl-2-
(phenylsulfonyl) acetamides/propanamides 5a-f, 8a-f and 10a-b
To a hot stirred solution of 2-bromo-N-phenylacetamides (3a-b,
7a-c and 9) and 3-chloro-N-(4-sulfamoylphenyl)propanamide (3c)
intermediates (0.5 mmol) in absolute ethanol (15 mL), sodium
sulfinates 4a,b (0.65 mmol) were added. The reaction mixture was
then heated under reflux for 14 h (for sulfonamides 5a-f) or 10 h
(for sulfones 8a-f and 10a-b). After the completion of the reaction,
the reaction mixture was evaporated under reduced pressure, and
then cold water (20 mL) was added to the residue. The remaining
solid was filtered-off, dried, and crystalized from acetonitrile to
produce the target sulfones (5a-f, 8a-f and 10a-b) in 68e85% yield.
NMR (100 MHz) d ppm: 21.51, 30.24, 51.10, 119.06, 119.67, 127.11,
128.33, 130.39, 134.87, 136.13, 138.87, 142.18, 144.97, 168.47; HRMS
(ESI) for C16H19O5N2S2, calcd 383.07299, found 383.07307 [MþH]þ.
4.1.2.7. 4-(2-(Phenylsulfonyl)acetamido)benzoic acid 8a. White
crystals, m.p. 247e249 ꢁC, yield 80%, 1H NMR (400 MHz)
d ppm:
4.53 (s, 2H, -CH2-CO), 7.65e7.77 (m, 5H, AreH), 7.86 (d, 2H, AreH,
J ¼ 8.8 Hz), 7.91e7.93 (m, 2H, AreH), 10.77 (s, 1H, NH), 12.01 (s,
1H, COOH); 13C NMR (100 MHz)
d ppm: 62.63, 119.36, 128.52,
129.50, 129.76, 134.37, 134.60, 139.59, 143.10, 160.78, 169.17; HRMS
(ESI) for
C15H13O5NNaS, calcd 342.04066, found 342.04087
[MþNa]þ.
4.1.2.1. 2-(Phenylsulfonyl)-N-(4-sulfamoylphenyl)acetamide
5a.
4.1.2.8. Ethyl
4-(2-(phenylsulfonyl)acetamido)benzoate
8b.
White crystals, m.p. 213e215 ꢁC, yield 72%, 1H NMR (400 MHz)
White crystals, m.p. 171e173 ꢁC, yield 83%, 1H NMR (400 MHz)
d
ppm: 4.52 (s, 2H, -CH2-CO), 7.31 (s, 2H, NH2), 7.59 (d, 2H, AreH,
d
ppm: 1.28 (t, 3H, CH3eCH2-, J ¼ 7.2 Hz), 4.25 (q, 2H, CH3eCH2-,
J
¼
8.8 Hz), 7.65e7.77 (m, 3H, AreH), 7.89 (d, 2H, AreH,
J ¼ 7.2 Hz), 4.54 (s, 2H, -CH2-CONH-), 7.62 (d, 2H, AreH, J ¼ 8.8 Hz),
7.67 (d, 2H, AreH, J ¼ 8.0 Hz), 7.74 (t, 1H, AreH, J ¼ 8.0 Hz), 7.91 (d,
J ¼ 8.4 Hz), 7.91 (d, 2H, AreH, J ¼ 8.8 Hz), 10.60 (s, 1H, NH); 13C
NMR (100 MHz)
d
ppm: 62.84, 119.10, 126.47, 128.49, 129.75, 130.96,
4H, AreH, J ¼ 8.8 Hz), 10.64 (s, 1H, NH); 13C NMR (100 MHz)
d ppm:
134.57, 139.81, 142.45, 160.41, 167.07.
14.66, 61.00, 62.61, 119.18, 125.54, 128.48, 129.75, 130.79, 134.57,
139.66, 142.93, 160.54, 165.67; HRMS (ESI) for C17H18O5NS, calcd
348.09002, found 348.09024 [MþH]þ.
4.1.2.2. N-(4-Sulfamoylphenyl)-2-tosylacetamide 5b. White crystals,
m.p. 227e228 ꢁC, yield 68%, 1H NMR (400 MHz)
d ppm: 2.42 (s, 3H,
eC6H4eCH3), 4.47 (s, 2H, -CH2-CO), 7.27 (s, 2H, NH2), 7.45 (d, 2H,
AreH, J ¼ 8.0 Hz), 7.60 (d, 2H, AreH, J ¼ 8.8 Hz), 7.78 (d, 2H, AreH,
J ¼ 8.4 Hz), 7.90 (d, 2H, AreH, J ¼ 8.4 Hz), 10.59 (s, 1H, NH); 13C NMR
4.1.2.9. N-(4-Acetylphenyl)-2-(phenylsulfonyl)acetamide
White crystals, m.p. 209e210 ꢁC, yield 74%, 1H NMR (400 MHz)
ppm: 2.51 (s, 3H, -COCH3), 4.53 (s, 2H, -CH2-CONH-), 7.61 (d, 2H,
8c.
d
8

M.M. Elbadawi, W.M. Eldehna, A. Nocentini et al.
European Journal of Medicinal Chemistry 218 (2021) 113360
AreH, J ¼ 8.8 Hz), 7.67 (d, 2H, AreH, J ¼ 8.0 Hz), 7.74 (t, 1H, AreH,
J ¼ 7.6 Hz), 7.91e7.95 (m, 4H, AreH), 10.64 (s, 1H, NH); 13C NMR
PI apoptosis [31,32] assays were performed as reported previously,
and the detailed procedures were provided in the Supporting
Materials.
(100 MHz)
d ppm: 26.92, 62.66, 119.08, 128.50, 129.75, 130.02,
132.90, 134.58, 139.63, 142.89, 160.54, 197.03; HRMS (ESI) for
C
16H16O4NS, calcd 318.07946, found 318.07966 [MþH]þ.
4.4. Docking
4.1.2.10. 4-(2-Tosylacetamido)benzoic acid 8d. White crystals, m.p.
255e256 ꢁC, yield 80%, 1H NMR (400 MHz)
ppm: 2.41 (s, 3H,
The crystal structures of hCA II (PDB 3K34) [33], hCA IX (PDB
5FL4) [34] hCA XII (PDB 1JD0) [35] were prepared using the Protein
d
€
eC6H4eCH3), 4.48 (s, 2H, -CH2-CO), 7.45 (d, 2H, AreH, J ¼ 8.0 Hz),
7.69 (d, 2H, AreH, J ¼ 8.8 Hz), 7.78 (d, 2H, AreH, J ¼ 8.0 Hz), 7.86 (d,
2H, AreH, J ¼ 8.8 Hz), 10.75 (s, 1H, NH D2O exchangeable), 12.01 (s,
Preparation Wizard tool implemented in the Schrodinger suite [36].
The energy minimization protocol with a root mean square devi-
ation (RMSD) value of 0.30 Å was applied using force field OPLS3e.
The ligand structures were prepared by Maestro [36b] and evalu-
ated for their ionization states at pH 7.4 0.5 with Epik [36c]. The
conjugate gradient method in Macromodel [36e] was used for en-
ergy minimization (maximum iteration number: 2500; conver-
gence criterion: 0.05 kcal molꢀ1Åꢀ1). The software Glide was used
for docking [36f]. Grids were centered on the centroids of the zinc-
coordinating residues and ligands were docked using standard
precision mode (SP). The best pose for each compound, evaluated in
terms of coordination, hydrogen bond interactions and hydropho-
bic contacts, was refined by MM-GBSA computations with Prime
[36a] using a VSGB solvation model considering the target flexible
within 3 Å around the ligand, with this latter distance being
considered the best compromise to achieve most reliable binding
free energies [37e39].
1H, COOH D2O exchangeable); 13C NMR (100 MHz)
d ppm: 21.57,
62.78, 119.33, 128.56, 129.49, 130.19, 134.27, 137.02, 143.14, 145.26,
160.84, 169.25; HRMS (ESI) for C16H16O5NS, calcd 334.07437, found
334.07463 [MþH]þ.
4.1.2.11. Ethyl 4-(2-tosylacetamido)benzoate 8e. White crystals, m.p.
187e189 ꢁC, yield 72%, 1H NMR (400 MHz)
d ppm: 1.28 (t, 3H,
CH3eCH2-, J ¼ 7.2 Hz), 2.41 (s, 3H, eC6H4eCH3), 4.26 (q, 2H,
CH3eCH2-, J ¼ 7.2 Hz), 4.48 (s, 2H, -CH2-CONH-), 7.45 (d, 2H, AreH,
J ¼ 8.0 Hz), 7.63 (d, 2H, AreH, J ¼ 6.8 Hz), 7.78 (d, 2H, AreH,
J ¼ 6.8 Hz), 7.92 (d, 4H, AreH, J ¼ 6.8 Hz), 10.64 (s, 1H, NH); 13C
NMR (100 MHz)
d ppm: 21.56, 60.99, 62.76, 119.17, 125.52, 128.53,
130.17, 130.79, 136.86, 142.98, 145.14, 160.61, 165.68; HRMS (ESI) for
C
18H19O5NNaS, calcd 384.08761, found 384.08751 [MþNa]þ.
4.1.2.12. N-(4-Acetylphenyl)-2-tosylacetamide 8f. White crystals,
m.p. 216e218 ꢁC, yield 76%, 1H NMR (400 MHz)
ppm: 2.42 (s, 3H,
Funding
d
eC6H4eCH3), 2.53 (s, 3H, -COCH3), 4.47 (s, 2H, -CH2-CONH-), 7.45
(d, 2H, AreH, J ¼ 8.0 Hz), 7.62 (d, 2H, AreH, J ¼ 8.8 Hz), 7.78 (d, 2H,
AreH, J ¼ 8.4 Hz), 7.93 (d, 2H, AreH, J ¼ 8.8 Hz),10.64 (s,1H, NH D2O
The authors extend their appreciation to the Deputyship for
Research & Innovation, Ministry of Education in Saudi Arabia for
funding this work through the project number "375213500".
exchangeable); 13C NMR (100 MHz)
d ppm: 21.56, 26.91, 62.79,
119.07, 128.54, 130.01, 130.18, 132.88, 136.83, 142.94, 145.16, 160.61,
Declaration of competing interest
197.02; HRMS (ESI) for
C17H18O4NS, calcd 332.09565, found
332.09521 [MþH]þ.
Conflicts of Interest: The authors have declared no conflict of
interest.
4.1.2.13. N-(4-Nitrophenyl)-2-(phenylsulfonyl)acetamide
Yellow crystals, m.p. 228e230 ꢁC, yield 85%, 1H NMR (400 MHz)
ppm: 4.55 (s, 2H, -CH2-CONH-), 7.65e7.77 (m, 5H, AreH), 7.91 (d,
2H, AreH, J ¼ 8.8 Hz), 8.22 (d, 2H, AreH, J ¼ 7.6 Hz), 10.92 (s, 1H, NH
D2O exchangeable); 13C NMR (100 MHz)
ppm: 62.69, 119.60,
125.54, 128.52, 129.78, 134.65, 139.52, 143.32, 144.66, 160.97; HRMS
10a.
Acknowledgments
d
The authors would like to extend their sincere appreciation to
the central laboratory at Jouf University for supporting this study.
M.M. Al-Sanea also extends his appreciation to the Korea Institute
of Science and Technology (KIST) for funding this work through the
Grant name “2021 KIST School Partnership Project”.
d
(ESI) for
C14H12O5N2NaS, calcd 343.03591, found 343.03600
[MþNa]þ.
4.1.2.14. N-(4-Nitrophenyl)-2-tosylacetamide 10b. Yellow crystals,
m.p. 235e236 ꢁC, yield 82%, 1H NMR (400 MHz)
ppm: 2.42 (s, 3H,
Appendix A. Supplementary data
d
eC6H4eCH3), 4.51 (s, 2H, -CH2-CONH-), 7.46 (d, 2H, AreH,
J ¼ 8.0 Hz), 7.74 (d, 2H, AreH, J ¼ 9.2 Hz), 7.79 (d, 2H, AreH,
J ¼ 8.0 Hz), 8.22 (d, 2H, AreH, J ¼ 9.2 Hz), 10.91 (s, 1H, NH D2O
Supplementary data to this article can be found online at
https://doi.org/10.1016/j.ejmech.2021.113360.
exchangeable); 13C NMR (100 MHz)
d ppm: 21.57, 62.82, 119.58,
References
125.54, 125.88, 128.57, 130.21, 136.78, 143.41, 144.67, 145.24, 161.05;
HRMS (ESI) for C15H14O5N2NaS, calcd 357.05156, found 357.05161
[MþNa]þ.
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