S. Bua et al.
Bioorganic Chemistry 86 (2019) 183–186
Table 1
Inhibition data of α-CAs VchCAα, hCA I, hCA II and β-CAs VchCAβ and mtCA3, with sulfonamides 3–10, 13–17 reported here and the standard inhibitor acet-
azolamide (AAZ) by a Stopped Flow CO hydrase assay [30].
Cmpd
2
K
I
*(nM)
X
R
VchCAα
VchCAβ
mtCA3
hCAI
hCAII
3
4
5
6
7
8
9
1
1
1
1
1
1
O
O
O
O
O
S
H
6.0
393.4
472.7
531.0
489.7
367.6
409.3
283.6
4916.1
54.8
278.2
648.2
691.1
260.2
228.5
344.9
340.0
9479.5
71.7
349.9
406.8
351.1
512.6
123.0
195.7
7.9
1.0
m-CH
3
18.5
22.6
13.7
4.8
1.5
m-OCH
3
3
1.5
p-OCH
4.3
pyridyl-3-yl
1.4
H
H
–
8.0
1.5
NH
–
0.72
> 10,000
63.9
121.7
50.3
57.2
77.8
6.8
0.83
> 10,000
1.2
0
3
4
5
6
7
> 10,000
565.6
278.1
949.8
> 10000
92.8
–
H
–
m-OCH
p-F
3
90.9
192.5
34.1
12.4
2.6
–
85.0
–
p-CF
3
102.4
60.9
28.2
15.7
1.0
–
p-OH
81.1
AAZ
–
–
451
104
250
12
*
Mean from 3 different assays, by a stopped flow technique (errors were in the range of ± 5–10% of the reported values).
those of the first set (K
I
s ranging between 283.6 and 4916.1 nM).
sulfonamides with K s significantly lower than those observed
I
The active site of β-CAs is known to be narrower than that of α-
CAs, resulting in better efficacy of derivatives endowed with
greater flexibility after the portion that binds the zinc [4]. Also
against this isoform, the introduction of the methoxy group in meta
or para position to the outer phenyl ring slightly reduced the in-
against the pathogens CAs. Of note, the most active inhibitor
against the target CAs, that is 9 against VchCAα, solely showed a
competitive K
I
(0.72 nM) with that measured against hCA II (K of
I
0.83 nM).
hibitory potency of compounds 5, 6 and 14 (K
I
= 531.0, 489.7 and
4. Conclusions
9
0.9 nM, respectively) compared to the unsubstituted analogs.
Within the second series of derivatives, the incorporation of a
fluorine atom or trifluoromethyl group in para position to the
aromatic ring led to a decrease of the inhibitory activity of com-
A series of 1,2,3-triazole-bearing benzenesulfonamides was assessed
for the inhibition of CAs from bacteria Vibrio cholerae (VchCAα and
VchCAβ) and Mycobacterium tuberculosis (β-mtCA3). There is a urgent
need of new antimicrobial agents exploiting alternative mechanisms of
action because of the globally spreading resistance phenomena against
existing antimicrobial drugs. The discovery of new potential anti-mi-
crobial targets and drugs is in line with two global strategies: the first,
launched in 2017 by Global Task Force on Cholera Control aims to
reduce cholera deaths by 90% [14] and the second one schedules the
eradication of the TB epidemy by 2030 (Sustainable Development
Goals) [15]. The first subset of derivatives potently inhibits VchCAα in
pounds 15 (K
I
= 85.0 nM) and 16 (K = 102.4 nM), respectively,
I
with respect to the best compound of second set, the unsubstituted
1
3 that showed a K of 54.8 nM. The structural variations on the
I
linker or substitutions on the aromatic ring did not lead to sig-
nificant improvements in the inhibitory trend of the first series
derivatives with respect to the lead 3 (K = 393.4 nM).
I
(
iii) The general tendencies described above are also applicable for
isoform mtCA3, β-CA from M. tuberculosis. In fact, compounds of
the second set (13–17) reported better inhibitory activity than
compounds of the first set (3–9). For instance, a significant in-
hibition difference can be noted, regardless of the nature of the
a low nanomolar range (K s between 0.72 and 22.6 nM). The com-
I
pounds of a second subset that possess a different kind of connection
between the molecular portions, preferentially inhibit VchCAβ (K s in
I
XCH
2
linker, within two couples of derivatives: 3 and 13
the range 54.8–102.4 nM) and β-mtCA3 (K s in the range
I
(
K
I
s = 278.2 and 71.7 nM, respectively) and 5 and 14 (K
I
s = 691.1
28.2–192.5 nM) even more than the clinically used AAZ, used as the
and 192.5 nM, respectively), bearing an unsubstituted and m-CH
3
standard. All these derivatives represent interesting leads towards the
optimization of new antibiotic agents showing excellent inhibitory ef-
ficiency and selectivity for the target CAs over the human (h) off-target
isoform hCA I.
substituted phenyl ring, respectively. An interesting inhibition
profile was observed for compounds 15 and 16. The combination
of a more flexible linker and a para-substitution with a fluorine
atom or trifluoromethyl group had a positive effect on the deri-
vatives inhibitory activity, such to make compounds 15 and 16 the
5
. Experimental sections
best inhibitors among those studied with K s of 34.1 and 28.2 nM,
I
respectively. Whereas the substitution of the outer phenyl ring
with a pyridyl one (7) seems to be effective in inducing strong α-
CA inhibitory effects, in contrast, it reduced the activity against β-
5
.1. Chemistry
The synthesis and characterization of sulfonamides 3–10, 13–17
CAs with K
I
in high nanomolar range (K = 367.6 for VchCAβ and
I
was reported earlier by our group [28].
K = 228.5 for mtCA3). Compound 10 reported a weak inhibitory
I
activity against VchCAβ and mtCA3 with K
I
s ranging between 4.9
6
. Carbonic anhydrase inhibition
and 9.5 μM.
An Applied Photophysics stopped-flow instrument has been used for
(
iv) All compounds (except 10) showed an improved efficacy in in-
hibiting VchCAα in comparison to hCA I, whereas only compounds
of the second set inhibited VchCAβ and mtCA3 significantly more
efficiently than the same ubiquitous isoform that is responsible for
most side effects related to the use of non-selective hCAIs. Isoform
hCA II is conversely potently inhibited by the reported triazole
assaying the CA-catalysed CO hydration activity [30]. Phenol red (at a
2
concentration of 0.2 mM) has been used as indicator, working at the
absorbance maximum of 557 nm, with 20 mM Hepes (pH 7.5) as buffer,
and 20 mM Na
2
SO (for maintaining constant the ionic strength), fol-
4
lowing the initial rates of the CA-catalysed CO
2
hydration reaction for a
period of 10–100 s. The CO concentrations ranged from 1.7 to 17 mM
2
185