Three new aromatic sulfonamide inhibitors of carbonic anhydrases I, II, IV and XII

Article abstract of DOI:10.3109/14756366.2011.649269

4-Sulfamoyl-N-(3-morpholinopropyl)benzamide (I-1), N-(3-morpholinopropyl)benzene-1,4-disulfonamide (I-2) and N-(4-diethylaminoethoxybenzyl)benzene-1,4-bis(sulfonamide (I-3), were prepared and assayed as inhibitors of four carbonic anhydrase (CA) isoenzyme

Full text of DOI:10.3109/14756366.2011.649269

Journal of Enzyme Inhibition and Medicinal Chemistry, 2012, 1–5, Early Online
© 2012 Informa UK, Ltd.
ISSN 1475-6366 print/ISSN 1475-6374 online
DOI: 10.3109/14756366.2011.649269
orIgInal arTIClE
ree new aromatic sulfonamide inhibitors of carbonic
anhydrases I, II, IV and XII
C.T. Supuran1, A. Maresca1, F. Gregáň2, and M. Remko3
1Dipartimento di Chimica, Università di Firenze, Via della Lastruccia, Sesto Fiorentino (Firenze), Italy, 2Department
of Chemistry, Faculty of Natural Sciences, Matej Bell University, Banská Bystrica, Slovakia, and 3Department of
Pharmaceutical Chemistry, Faculty of Pharmacy, Comenius University, Bratislava, Slovakia
abstract
4-Sulfamoyl-N-(3-morpholinopropyl)benzamide (I-1), N-(3-morpholinopropyl)benzene-1,4-disulfonamide (I-2) and
N-(4-diethylaminoethoxybenzyl)benzene-1,4-bis(sulfonamide (I-3), were prepared and assayed as inhibitors of four
carbonic anhydrase (CA) isoenzymes hCA I, hCA II, hCA IV and hCA XII. These compounds exhibited nanomolar half
maximal inhibitory concentration (IC ) ranging from 58 to 740 nmol/L. All three aromatic sulfonamides show different
activities for the isoenzymes studied5w0 ith lowest affinity against isoenzyme hCA XII.
Keywords: Aromatic sulfonamides, carbonic anhydrase inhibitors, glaucoma
Introduction
and
N-(4-diethylaminoethoxybenzyl)benzene-1,
4-bis(sulfonamide (I-3), with favorable structural,
physicochemical and some pharmacokinetic properties
comparable to those obtained for clinically useful aceta-
zolamide, dorzolamide and brinzolamide13–16. e new
compounds reported here were in vitro tested on the
enzymatic hCA I, hCA II, hCA IV and hCA XII activities.
Affinities in the nanomolar range were found for those
compounds against all four isoenzymes studied.
Compounds bearing sulfonamide groups have long been
known to be potent inhibitors of the carbonic anhydrases
(CA1–3). Various substituted aromatic and heterocyclic sul-
fonamides have been synthesized and evaluated for possi-
ble therapeutic use as antiglaucoma agents1,2,4–6. ey bind
as anions to the Zn2+ ion within the enzyme active site1–3
(with abnormally high affinities of around 10−6–10−9 M−1
for isozyme CA II, refs 7–9). Clinically used sulfonamide
antiglaucoma drugs include orally administered aceta-
zolamide, ophthalmic suspension of brinzolamide and
ophthalmic solution of dorzolamide5,6. In the case of these
human carbonic acid inhibitors for optimal in vivo activ-
ity the balanced hydro- and liposolubility is necessary. It is
well established10,11 that a water-soluble sulfonamide, also
possessing relatively balanced lipid solubility, would be an
effective antiglaucoma drug via the topical route. One of the
conditions needed for a sulfonamide to act, as an effective
intraocular pressure-lowering agent, is to possess modest
Experimental section
Chemistry
General
1H NMR spectra at 300MHz were measured on Varian
Gemini spectrometer (chemical shifts are expressed as
δ values relative to TMS as standard). Melting points
were determined on Kofler block and are uncorrected.
Elemental analysis: Carlo Erba Model 1106 Instrument
Elemental Analyser. e obtained results showed a
maximum deviation of 0.3% compared to the theoreti-
cal values. All reactions were monitored by thin-layer
chromatography (TLC) using silica gel plates (E. Merck)
in system acetone–methanol (3:1).
lipid solubility attributable to its unionized form8,10–12
In this work, we report the synthesis of a novel
drug-like aromatic sulfonamides 4-sulfamoyl-
N-(3-morpholinopropyl) benzamide (I-1), N-(3-
morpholinopropyl)benzene-1,4-disulfonamide (I-2)
.
Address for Correspondence: Prof. Milan Remko, Department of Pharmaceutical Chemistry, Faculty of Pharmacy, Comenius University,
Bratislava, Slovakia. E-mail: remko@fpharm.uniba.sk
(Received 20 November 2011; revised 07 December 2011; accepted 09 December 2011)
1

2
C.T. Supuran et al.
Procedure for the preparation of compounds I-1, I-2 and I-3
4-Sulfamoyl-N-(3-morpholinopropyl)benzamide (I-1)
and
N-(3-morpholinopropyl)benzene-1,4-disulfon-
amide (I-2) were prepared according to the procedure
described in ref. 16 and depicted in Scheme 1 and 2. N-(4-
diethylaminoethoxybenzyl)benzene-1,4-bis(sulfonamide)
(I-3) was prepared as depicted in Scheme 3.
Synthesis of 4-diethylaminoethoxybenzaldehyde III
To the solution of 4-hydroxybenzaldehyde 18.30 g
(0.15 mol) in anhydrous acetone (100 ml) N, N-diethyl-
2-chloroethylamine II, 21.70 g (0.16 mol) and anhydrous
potassium carbonate 22.10 g (0.16 mol) were added. e
stirred mixture was refluxed for 12 h, than cooled to 0°C
and the precipitated potassium chloride was filtered
off and washed with acetone (20ml). From filtrate the
acetone was distilled off and the residual oil was frac-
tionated in vacuum. Colorless liquid, yield 20.02 g (57%),
b.p. 150–151°C/2 torr, n20D = 1.5360. Elemental analysis
for C13H19N2 (M.r. 221.30), calculated (found, %): C 70.56
(70.80), H 8.65 (8.38), N 6.33 (6.22). 1H NMR (CDCl3) 1.07
(t, 6H, CH3), 2.64 (q, 4H, CH2-N), 4.12 (t, 2H, CH2-O), 7.01
(d, 2H, Har.), 7.83 (d, 2H, Har.) 9.88 (s, 1H, CHO).
Scheme 3 Synthesis of N-(4-diethylaminoethoxybenzyl)benzene-
1,4-bis(sulfonamide (I-3).
solution of ammonia in ethanol (80ml). e mixture was
hydrogenated at 80°C and pressure of 1.000 psi for 6h in
argon atmosphere. e catalyst was filtered off, washed with
ethanol (10ml). Ethanol was distilled off and liquid residual
oil was fractionated in vacuum. Yield 13.10g (72.8%), yellow
liquid b.p. 145–146°C/2 torr, n20D =1.5471. Elemental analy-
sis for for C13H22N2O (M.r. 222.33), calculated/found, %): C
70.23 (70.39), H 9.98 (9.72), N 12.66 (12.81). 1H NMR (CDCl3)
1.07 (t, 6H, CH3), 1.84 (s, 2H, NH2), 2.64 (q, 4h, CH2-N), 2.87
(t, 2H, CH2-N), 3.79 (s, 2H, CH2-Phenyl), 4.04 (t, 2H, CH2-O),
6.87 (d, 2H, Har.), 7.21 (d, 2H, Har.).
Synthesis of 4-diehylaminoethoxy benzylamine IV
Raney nickel (4.00g) was added to a solution of 4-dieth-
ylaminoethoxybenzaldehyde 17.93g (0.080mol) in 10%
Synthesis of N-[4-(diethylaminoethoxybenzyl)]benzene-1,4-
disulfonamide I-3
To the could solution 4-diethylaminoethoxy benzylam-
ine IV in acetone (12 ml) solution of sodium carbonate
2.34 g (0.022 mol) in water (10 ml) in a small portion dur-
ing 5 min was added. To this stirred mixture 4-sulfamoyl-
benzenesulfonylchloride 5.12 g (0.02 mol) during 30 min.
at 10°C was added. After then the reaction mixture was
stirred 12 h at room temperature. e solid inorganic
salt was filtered, washed with acetone (5 ml). e solvent
from filtrate was evaporated using a vacuum rotatory
evaporator. e residue was mixed three times with cold
water (3 × 10 ml). e crude solid was filtered and puri-
fied by crystallization from 2-propanol. Colorless solid,
yield 6.10 g (69.3%), m.p. 72−74°C.
Scheme 1 Synthesis of 4-sulfamoyl-N-(3-morpholinopropyl)
benzamide (I-1).
Elemental analysis for C19H27N3O5S2 (M.r. 441.57), cal-
culated (found): C 51.68 (51.86) H 6.16 (6.02), N (9.52)
(9.38), S 14.52 (14.23). 1H NMR (DMSO) 1.07 (t, 6H,
CH3), 2.64 (q, 4H, CH2-N), 2.87 (t, 2H, CH2-N), 4.04 (t, 2H,
CH2-O), 6.89 (d, 2H, Har.), 7.12 (d, 2H, Har.-O), 7.63 (s, 2H,
SO2-NH2), 8.00 (dd, 4H, Har.-SO2), 8.39 (t, 1H, NH-SO2).
4-Sulfamoylbenzenesulfamoylchloride (V) was pre-
pared by multistep synthesis from 4-aminobenzenesul-
fonamide as starting compound, treated with sodium
Scheme 2 Synthesis of N-(3-morpholinopropyl)benzene-1,
4-disulfonamide (I-2).
Journal of Enzyme Inhibition and Medicinal Chemistry

Three new aromatic sulfonamide inhibitors
3
nitrite, sulfur dioxide, copper dioxide and hydrogen
chloride in acetic acid as solvent17. e crude product
was crystallized from 1,2-dichloroethane as colorless
compound, yield 58%, m.p. 154–156°C. e measured
physicochemical characteristic of this product corre-
sponds to the similar data found in ref. 17.
dorzolamide) given topically. Both topical drugs can
cause a bitter taste. Dorzolamide can cause ocular
burning. Systemic reactions are very rare but have been
documented2,23
.
In our work we applied methods of manual design
within the so-called “tail” approach2,24 for identification
of a single lead compound. Within this approach a series
of new aromatic sulfonamides was modeled. In the early
stages of the design it was becoming more important to
determine the pKa, water solubility, Lipinsky parameters
and other physicochemical properties associated with a
sulfonamides,beforesyntheticworkisundertaken,withthe
aim of avoiding the synthesis of compounds that are pre-
Carbonic anhydrase I, II, IV and XII assay-IC50
determination
An Applied Photophysics stopped-flow instrument has
been used for assaying the CA catalysed CO2 hydration
activity18. Phenol red (at a concentration of 0.2mM) has
been used as indicator, working at the absorbance maxi-
mum of 557nm, with 10–20mM Hepes (pH 7.5) as buffer,
and 20mM Na2SO4 (for maintaining constant the ionic
strength), following the initial rates of the CA-catalyzed
CO2 hydration reaction for a period of 10–100 s. e CO2
concentrations ranged from 1.7 to 17mM for the determi-
nation of the kinetic parameters and inhibition constants.
For each inhibitor at least six traces of the initial 5–10%
of the reaction have been used for determining the initial
velocity. e uncatalyzed rates were determined in the
samemannerandsubtractedfromthetotalobservedrates.
Stock solutions of inhibitor (10mM) were prepared in dis-
tilled–deionised water and dilutions up to 0.01nM were
done thereafter with distilled–deionised water. Inhibitor
and enzyme solutions were preincubated together for
15min at room temperature prior to assay, in order to
allow for the formation of the E-I complex. e inhibi-
tion constants were obtained by non-linear least-squares
methods using PRISM 3, whereas the kinetic parameters
for the uninhibited enzymes from Lineweaver–Burk plots,
as reported earlier19–21, and represent the mean from at
least three different determinations.
dicted to have poor biopharmaceutical characteristics14,15
.
is approach led us to the discovery of two new aromatic
sulfonamides containing morpholinopropyl “tail” (I-1 and
I-2), which exhibit drug-like properties comparable with
dorzolamide and/or brinzolamide15. e morpholine oxy-
gen can form a new productive hydrogen bond interaction
with complementary CA active site domain. For develop-
ment of third inhibitor (I-3) previously designed scaffold
of the benzene-1,4-disulfonamide type was applied.
Extended tail of this derivative contains diethylamino-
ethoxybenzyl moiety and exploit the strategy of enhanced
hydrophobic interactions between hydrophobic moieties
of both active site of enzyme and inhibitor. is strategy
was successfully applied by Whiteshides’ group2,12. is
strategy led, however, to the increase of lipophilicity for
I-3 (1.65) by comparison with I-1 (−0.30) and I-2 (−0.86),
XLOGP2 method15. Tail extension strategy produced also
very effective hCA I and hCA II inhibitor I-3 without any
appreciable increase of its IC50 values compared to those
data for I-2 (Table 1). However, it is probable that dieth-
ylaminoethoxybenzyl moiety of I-3 is not sufficiently long
to interact effectively with hydrophobic regions at the
entrance of the enzyme active site and contribute appre-
ciably to the specificity and strength of interaction with the
active site of the hCA isozymes studied.
Second main goal of design was improvement
of solubility of new compounds. Insoluble com-
pounds can plague discovery. Good drug solubility
is especially needed for topical eye drop formulation.
Solubility of designed compounds was evaluated
using AB/logS method implemented in the ACD/Labs
software25. Our strategy to improve solubility was to
introduce polarity on the “tail” part of molecule by
polar morpholine substituent. In comparison with
the parent brinzolamide and dorzolamide three basic
results and discussion
In despite of fact that several thousand different aro-
matic sulfonamide CA inhibitors were prepared and
tested during the last 50 years in the search of diverse
antiglaucoma agents22 the clinically useful aromatic sul-
fonamide is not yet available. Orally active heterocyclic
acetazolamide can cause several side effects, (including
paresthesia of the fingertips and toes, fatigue, depression,
kidney stones, nausea and diarrhea, metabolic acidosis,
agranulocytosis, aplastic anemia, and Stevens–Johnsons
syndrome) and its use rapidly decreased after approval
of two heterocyclic sulfonamides (brinzolamide and
Table 1. Biochemical activity IC50 (nmol/L) and solubility of the CA inhibitors investigated.
Inhibitor
Acetazolamide
Dorzolamide
Brinzolamide
I-1
hCA I
250a
hCA II
12a
3.74b
hCA IV
70 (bCA IV)a
43c
hCA XII
Solubility
4.14g/L
0.50g/L
0.25g/L
7.50g/L
5.76g/L
1.63g/L
277.15b
231.4
57.7
59.8
215.8
65.8
81.1
611.1
645.2
517.2
736.7
I-2
498.8
I-3
507.9
aReference 27, bReference 28, cReference 29.
© 2012 Informa UK, Ltd.

4
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compounds (I-1, I-2, I-3) exhibit improved solubility
(Table 1) and can be easily prepared in the form of
corresponding salts16.
All three new compounds were each assayed for
hCA I, hCA II, hCA IV and hCA XII isozymes binding
by stopped flow technique and results of which are
presented in Table 1. According to in vitro assays these
compounds can be characterized as isozyme-specific
inhibitors. ey were a relatively weak inhibitors of hCA
XII with IC50 of about 520–740 nmol/L, derivative I-2
containing benzene-1,4-disulfonamide moiety being
most active. e activity of benzene-1,4-disulfonamide
derivatives I-2 and I-3 towards isoenzyme hCA I is very
high and comparable with their analogous activity for
hCA II (Table 1). However, while the pharmacological
function of hCA I is still not clear, for effective lowering
of intraocular pressure, 99.99% inhibition of CA II and
98% inhibition of CA IV is required26. e activity of
compounds I-1, I-2 and I-3 towards hCA II and hCA IV
is different, but this difference is not regular. I-1 being
2.8 times, I-2 7.5 times and I-3 6.2 times more active for
hCA II. e small preference of aromatic sulfonamides
towards CA II in comparison with CA IV was observed
for the largest majority of these derivatives2. Compounds
I-2 and I-3 containing two sulfonamide moieties interact
with pharmacologically important hCA II and hCA IV
much stronger (Table 1).
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Conclusions
ree novel potent inhibitors of hCA I, hCA II, hCA IV
and hCA XII has been discovered using operator directed
drug design techniques and synthesis of limited num-
ber of new aromatic sulfonamides. is strategy led to
synthesis of new derivatives with improved solubility
while maintaining CA activity. Derivatives containing
benzene-1,4-disulfonamide group being more active
than structure with the 4-sulfamoylbenzamide moiety.
e inhibitors studied have been shown a net preference
for hCA II in comparison with hCA IV.
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19. Pacchiano F, Carta F, Vullo D, Scozzafava A, Supuran CT.
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20. Kolayli S, Karahalil F, Sahin H, Dincer B, Supuran CT.
Characterizationandinhibitionstudiesofanα-carbonicanhydrase
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Declaration of interest
e authors report no conflicts of interest.
21. Innocenti A, Scozzafava A, Supuran CT. Carbonic anhydrase
inhibitors. Inhibition of cytosolic isoforms I, II, III, VII and XIII
with less investigated inorganic anions. Bioorg Med Chem Lett
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© 2012 Informa UK, Ltd.