Bioorganic & Medicinal Chemistry Letters
Synthesis and antimycobacterial evaluation of N-substituted
5-chloropyrazine-2-carboxamides
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b
a
a
a
Barbora Servusová a, , Jana Vobicková , Pavla Paterová , Vladimír Kubícek , Jirí Kuneš , Martin Dolezal ,
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Jan Zitko a
a Faculty of Pharmacy in Hradec Králové, Charles University in Prague, Heyrovského 1203, Hradec Králové 500 05, Czech Republic
b Department of Clinical Microbiology, University Hospital Hradec Králové, Sokolská 581, Hradec Králové 500 05, Czech Republic
a r t i c l e i n f o
a b s t r a c t
Article history:
To develop new potential antimycobacterial drugs, a series of pyrazinamide derivatives was designed,
synthesized and tested for their ability to inhibit the growth of selected mycobacterial strains (Mycobac-
terium tuberculosis H37Rv, Mycobacterium kansasii and two strains of Mycobacterium avium). This Letter is
focused on binuclear pyrazinamide analogues containing the –CONH–CH2– bridge, namely on N-benzyl-
5-chloropyrazine-2-carboxamides with various substituents on the phenyl ring and their comparison
with some analogously substituted 5-chloro-N-phenylpyrazine-2-carboxamides. Compounds from
the N-benzyl series exerted lower antimycobacterial activity against M. tuberculosis H37Rv then
Received 13 March 2013
Revised 4 April 2013
Accepted 6 April 2013
Available online 21 April 2013
Keywords:
Pyrazinamide derivatives
Benzylamines
Anilines
Antimycobacterial activity
Lipophilicity
corresponding anilides, however comparable with pyrazinamide (12.5–25
5-chloro-N-(4-methylbenzyl)pyrazine-2-carboxamide (8, MIC = 3.13 g/mL) and 5-chloro-N-(2-chloro-
benzyl)pyrazine-2-carboxamide (1, MIC = 6.25 g/mL) were active against M. kansasii, which is naturally
unsusceptible to PZA. Basic structure–activity relationships are presented.
lg/mL). Remarkably,
l
l
Ó 2013 Published by Elsevier Ltd.
Tuberculosis (TB) is considered to be one of the most frequent
infectious diseases especially in developing countries. In 2011,
there were about 8.7 million new cases of TB and 1.4 million
deaths.1 Multidrug-resistant TB (MDR-TB, characterized as resis-
tance to, at least, isoniazid and rifampicin), extensively drug-resis-
tant TB (XDR-TB), totally drug-resistant TB (TDR-TB) and also
co-infection with HIV2 remain a serious public health problem
primarily in underdeveloped countries and underline the need to
develop novel anti-tubercular agents.1
Pyrazinamide (PZA), a nicotinamide analogue, plays an impor-
tant role in TB-therapy.3 PZA has multiple mechanisms of action
and as a prodrug, it is metabolized via mycobacterial enzyme
pyrazinamidase (EC 3.5.1.19) to form pyrazinoic acid (POA).4 POA
accumulates intracellularly and lowers pH in mycobacterial cell,
which leads to inhibition of membrane transport and depletion
of energy.5 Along with rifampicin, PZA has also a sterilizing activ-
ity, which is a crucial factor in shortening the duration of therapy.6
During the last years, the specific targets of PZA and/or POA were
recognized. As previous studies suggested,7–10 both PZA and POA
were confirmed as inhibitors of fatty acid synthase I (FAS I), which
participates in the synthesis of cell wall components. The studies
of Sayahi et al. showed that PZA11 and 5-Cl-PZA12 are able to compet-
itively displace the NADPH cofactor from FAS I. Finally, another spe-
cific target for POA (but not for PZA), ribosomal protein S1 (RpsA)
involvedin proteintranslation, was identified. POA preventsbinding
of tmRNA to RpsA and thus blocks trans-translation (the process
involving the release of ribosomes stalled during translation).13
5-Cl-PZA proved to be active in vitro against both PZA susceptible
Mycobacterium tuberculosis strains (MIC = 16 lg/mL) and PZA resis-
tant mycobacterial strains (Mycobacterium bovis, Mycobacterium
kansasii, Mycobacterium fortuitum and Mycobacterium avium;
MIC = 8–64 l
g/mL).14 Therefore it became a pattern for target
compounds mentioned in this paper. The series of substituted
N-benzyl-5-chloropyrazine-2-carboxamides (1–10) and 5-chloro-
N-phenylpyrazine-2-carboxamide (1a–6a) were synthesized and
compared to study the influence of incorporated methylene moiety
in the connecting bridge and also to continue to study of the
substituent variability influence on the biological activity.
Final structures were prepared by convenient two-step
synthesis15
using
5-hydroxypyrazine-2-carboxylic
acid
(5-hydroxy-POA) as a starting material (see Scheme 1). During
the first step 5-hydroxy-POA was treated with thionyl chloride to
form 5-chloropyrazine-2-carbonyl chloride.16 Dimethylformamide
(DMF) was added to the reaction mixture as a catalyst.17 Final
structures were prepared by aminolysis of the corresponding
acyl chloride by various anilines and benzylamines. Reaction
proceeded under mild conditions (at RT in acetone), triethylamine
(TEA) was used to neutralize the originating HCl. All prepared
compounds (white solid or crystalline) were characterized by
analytical data (1H NMR, 13C NMR, IR spectroscopy, melting
point and elementary analysis). The analytical data were fully
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0960-894X/$ - see front matter Ó 2013 Published by Elsevier Ltd.