Benzenesulfonamides incorporating nitrogenous bases show effective inhibition of β-carbonic anhydrases from the pathogenic fungi Cryptococcus neoformans, Candida glabrata and Malassezia globosa

Article abstract of DOI:10.1016/j.bioorg.2019.01.030

There is an urgent need for new chemotherapic agents to treat human fungal infections due to emerging and spreading globally resistance mechanisms. Among the new targets that have been recently investigated for the development of antifungal drugs there are the metallo-enzymes Carbonic Anhydrases (CAs, EC 4.2.1.1). The inhibition of the β-CAs identified in many pathogenic fungi leads to an impairment of parasite growth and virulence, which in turn leads to a significant anti-infective effect. Based on antifungal nucleoside antibiotics, the inhibition of the β-CAs from the resistance-showing fungi Candida glabrata (CgNce103), Cryptococcus neoformans (Can2) and Malasszia globosa (MgCA) with a series of benzenesulfonamides bearing nitrogenous bases, such as uracil and adenine, is here reported. Many such compounds display low nanomolar (<100 nM) inhibitory potency against Can2 and CgNce103, whereas the activity of MgCA is considerably less affected (inhibition constants in the range 138.8–5601.5 nM). The β-CAs inhibitory data were compared with those against α-class human ubiquitous isoforms. Interesting selective inhibitory activities for the target fungal CAs over hCA I and II were reported, which make nitrogenous base benzenesulfonamides interesting tools and leads for further investigations in search of new antifungal with innovative mechanisms of action.

Full text of DOI:10.1016/j.bioorg.2019.01.030

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Accepted Manuscript
Benzenesulfonamides incorporating nitrogenous bases show effective inhibi-
tion of β-carbonic anhydrases from the pathogenic fungi Cryptococcus neofor-
mans, Candida glabrata and Malassezia globosa
Silvia Bua, Sameh M. Osman, Zeid AlOthman, Claudiu T. Supuran, Alessio
Nocentini
PII:
S0045-2068(18)31115-5
DOI:
https://doi.org/10.1016/j.bioorg.2019.01.030
YBIOO 2734
Reference:
Bioorganic Chemistry
To appear in:
Received Date:
Revised Date:
Accepted Date:
1 October 2018
12 December 2018
17 January 2019
Please cite this article as: S. Bua, S.M. Osman, Z. AlOthman, C.T. Supuran, A. Nocentini, Benzenesulfonamides
incorporating nitrogenous bases show effective inhibition of β-carbonic anhydrases from the pathogenic fungi
Cryptococcus neoformans, Candida glabrata and Malassezia globosa, Bioorganic Chemistry (2019), doi: https://
doi.org/10.1016/j.bioorg.2019.01.030
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Benzenesulfonamides incorporating nitrogenous bases show effective inhibition of β-carbonic
anhydrases from the pathogenic fungi Cryptococcus neoformans, Candida glabrata and
Malassezia globosa
Silvia Buaa, Sameh M. Osmanb, Zeid AlOthmanb, Claudiu T. Supurana,b*, Alessio Nocentinia,*
a
University of Florence, Department of Neuroscience, Psychology, Drug Research and Child's Health,
Section of Pharmaceutical and Nutraceutical Sciences, via Ugo Schiff 6, 50019, Sesto Fiorentino, Italy
b Department of Chemistry, College of Science, King Saud University, Riyadh, Saudi Arabia
Abstract
There is an urgent need for new chemotherapic agents to treat human fungal infections due to
emerging and spreading globally resistance mechanisms. Among the new targets that have been
recently investigated for the development of antifungal drugs there are the metallo-enzymes
Carbonic Anhydrases (CAs, EC 4.2.1.1). The inhibition of the β-CAs identified in many pathogenic
fungi leads to an impairment of parasite growth and virulence, which in turn leads to a significant
anti-infective effect. Based on antifungal nucleoside antibiotics, the inhibition of the β-CAs from
the resistance-showing fungi Candida glabrata (CgNce103), Cryptococcus neoformans (Can2) and
Malasszia globosa (MgCA) with a series of benzenesulfonamides bearing nitrogenous bases, such
as uracil and adenine, is here reported. Many such compounds display low nanomolar (< 100 nM)
inhibitory potency against Can2 and CgNce103, whereas the activity of MgCA is considerably less
affected (inhibition constants in the range 138.8-5601.5 nM). The β-CAs inhibitory data were
compared with those against α-class human ubiquitous isoforms. Interesting selective inhibitory
activities for the target fungal CAs over hCA I and II were reported, which make nitrogenous base
benzenesulfonamides interesting tools and leads for further investigations in search of new
antifungal with innovative mechanisms of action.
Keywords: Carbonic anhydrase, inhibitor, metalloenzymes, adenine, uracil, antifungal.
____
* Corresponding authors: (C.T.S.) Phone: +39-055-4573729; email: claudiu.supuran@unifi.it
(A.N.) Phone: +39-055-4573685; email:alessio.nocentini@unifi.it

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Introduction
Anti-microbial resistance is one of the biggest threats to global health and a major concern
in clinical practice because it impairs the efficacy of common therapies for infectious diseases,
among which fungal infections.[1-4] Invasive fungal infections can cause disability and death.
Some species of fungi are naturally resistant to treatment with some antifungal medications. Other
species can develop resistance due to improper antifungal use, such as too low dosages or treatment
courses that are not long enough.[5] Antifungal resistance is a noteworthy problem with Candida
infections. Some types of Candida are increasingly resistant to the first-line and second-line
antifungal medications, such as fluconazole and the echinocandins [6]. Treatment failures against
Cryptococcus neoformans also continue to occur for a variety of reasons including direct antifungal
drug resistance. Cryptococcosis has become a relatively common infection worldwide mainly
affecting the lungs, but also responsible for meningitis and encephalitis [7]. Malassezia globosa is
considered as the most probable causative agent for the onset of dandruff. Many drug-resistant
fungal strains of M. globosa to azole antifungals have been reported and impair the efficacy of
common anti-dandruff cosmetic treatments.[8].
A main strategy to overtake the spread of antimicrobial resistance consists in the
identification of novel therapeutic targets and thus anti-infectives with alternative mechanisms of
action. The metalloenzymes carbonic anhydrases (CAs, EC 4.2.1.1) are essential in the life cycle
(pH homeostasis and biosynthetic reactions) as well as in the virulence of many bacterial, fungal
and protozoan pathogens.[9] Many data exist in the literature, which show that interference with CA
activity in various parasites leads to an impairment of parasite growth and virulence.[9] CA
enzymes are classified into seven structurally unrelated groups, α-, β-, γ-, δ-, ζ- η- and θ-CAs.[10-
13] In particular, β-CAs isoforms were identified in many pathogenic fungi, among which C.
glabrata (CgNce103), C. neoformans (Can2) and M. globosa (MgCA).[9-11]. Several works
demonstrated that these CAs play an important role in the CO2 sensing of the pathogens and in the
regulation of sexual development [9,14-16]. For instance, physiological concentrations of
-
CO2/HCO3 induce prominent virulence attributes in C. glabrata or C. neoformans through direct
activation of the fungal adenylyl cyclase [14,15].
The inhibitory profile against β-CAs of most important classes of CA inhibitors, such as
sulfonamides and bioisosteres, inorganic anions, and carboxylate, have been investigated in
detail.[16-18] Recently, new chemotypes, such as phenols, dithiocarbamates, and benzoxaboroles
were also reported as efficient fungal β-CA inhibitors.[19-25] MgCA inhibition by sulfonamides led
to growth defects of the fungus in vivo, exhibiting antidandruff effects equivalent to those of the
standard azole drug ketoconazole.[16]

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Nucleoside antibiotics represent a unique class of antimicrobial products derived from
nucleosides and nucleotides.[26] They display diverse biological activities including antibacterial,
antifungal, antiviral, insecticidal, immunostimulative, immunosuppressive, and antitumor activities.
For all these reasons, we investigate here nitrogenous bases-bearing benzenesulfonamides as
inhibitors of CgNce103, Can2 and MgCA. The compounds were designed according to the
molecular hybridization approach to strengthen the anti-fungal effect of the pathogen CA inhibition
with the anti-microbial activity of nitrogenous bases, such as uracil and adenine, derivatives.
Chemistry
A benzenesulfonamide scaffold was variably appended with uracil and adenine moieties by means
of different length spacer of the ether, amide and its bioisoster triazole types, as previously reported
by us.[27] The bioisosteric amide/triazole substitution was pursued due to the anti-fungal activity
that triazoles and their derivatives were shown to possess.[28] Uracil and adenine were linked to the
main scaffold through the N1 and N9 moieties, respectively, to keep the connection by which
nitrogenous bases are incorporated in nucleotides and nucleic acids.
The triazole derivatives (11-12, 15-16) were prepared by copper-catalyzed azide−alkyne
cycloadditions (CuAAC), using N1-propargyluracil (8) or the N9-propargyladenine (14) (Schemes
1 and 2).[27]
Scheme 1. General synthetic procedure for uracil derivatives 2-12.
The amide derivatives (3-7, 22-29) were prepared according to two diverse synthetic pathways
depending on the considered nitrogenous base (Schemes 1 and 2).[27]