Synthesis and antimicrobial evaluation of guanylsulfonamides

Article abstract of DOI:10.1016/j.bmcl.2007.09.060

A series of guanylsulfonamides, 2-amino-9-[2-substituted-4-(4-substituted piperidin-1-sulfonyl)phenyl]-1,9-dihydropurin-6-ones, was synthesized by adopting reductive aminoformylation of 2-amino-5-nitro-6-[4-(piperidin-1-sulfonyl)phenylamino]-3H-pyrimidin- 4-one and subsequent intramolecular ring condensation as key steps. All the guanylsulfonamides were assayed for their in vitro antibacterial activities against Klebsiella pneumoniae, Escherichia coli, Pseudomonas aeruginosa, Bacillus subtilis, Staphylococcus aureus, and Streptococcus faecalis, and their antifungal activities against Aspergillus flavus, Aspergillus niger, and Candida albicans. Of the guanylsulfonamides, 13e and 13f displayed better antibacterial activities than that of Norfloxacin against the bacterial strains S. aureus and S. faecalis except 13f against S. faecalis, which exhibited the activity similar to that of Norfloxacin. Against the fungal strains A. flavus and A. niger, 13g and 13h showed similar activities to that of Griseoflavin-16 except 13h against A. niger, which displayed a profound drop in the activity compared to that of Griseoflavin-16. The remarkable inhibition of the growth of the bacterial and fungal strains makes these substances promising microbial agents.

Full text of DOI:10.1016/j.bmcl.2007.09.060

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Bioorganic & Medicinal Chemistry Letters 17 (2007) 6610–6614
Synthesis and antimicrobial evaluation of guanylsulfonamides
Pratik R. Patel, Chennan Ramalingan and Yong-Tae Park*
Department of Chemistry, Kyungpook National University, Taegu 702-701, Republic of Korea
Received 1 July 2007; revised 3 September 2007; accepted 17 September 2007
Available online 20 September 2007
Abstract—A series of guanylsulfonamides, 2-amino-9-[2-substituted-4-(4-substituted piperidin-1-sulfonyl)phenyl]-1,9-dihydropurin-
6-ones, was synthesized by adopting reductive aminoformylation of 2-amino-5-nitro-6-[4-(piperidin-1-sulfonyl)phenylamino]-3H-
pyrimidin- 4-one and subsequent intramolecular ring condensation as key steps. All the guanylsulfonamides were assayed for their
in vitro antibacterial activities against Klebsiella pneumoniae, Escherichia coli, Pseudomonas aeruginosa, Bacillus subtilis, Staphylo-
coccus aureus, and Streptococcus faecalis, and their antifungal activities against Aspergillus flavus, Aspergillus niger, and Candida
albicans. Of the guanylsulfonamides, 13e and 13f displayed better antibacterial activities than that of Norfloxacin against the bac-
terial strains S. aureus and S. faecalis except 13f against S. faecalis, which exhibited the activity similar to that of Norfloxacin.
Against the fungal strains A. flavus and A. niger, 13g and 13h showed similar activities to that of Griseoflavin-16 except 13h against
A. niger, which displayed a profound drop in the activity compared to that of Griseoflavin-16. The remarkable inhibition of the
growth of the bacterial and fungal strains makes these substances promising microbial agents.
Ó 2007 Elsevier Ltd. All rights reserved.
In recent decades, microbial diseases are more prevalent
than they were during the first half of the last century
and are still difficult to be diagnosed clinically. To com-
bat them, various synthetic and semi-synthetic antimi-
crobial drugs have been used in clinical practice.1,2 In
spite of many significant developments in the antimicro-
bial therapy, many problems remain to be solved for
most of the antimicrobial drugs available. Hence, dis-
covery of novel antimicrobial agents with better phar-
macological profile is still highly desirable.
On the other hand, 9-substituted purine derivatives pos-
sess broad pharmacological activity. For example, acy-
clovir,5 and ganciclovir,6 are active against viral
diseases caused by HSV-1, HSV-2, VZV, and the human
CMV7 while 9-benzylpurine derivative, 2-chloro-6-(2-
furyl)-9-(4-methoxyphenylmethyl)-9H-purine, and 9-
sulfonylated/sulfenylated-6-mercaptopurine derivatives
are active against bacterial diseases caused by Mycobac-
terium tuberculosis.8 Also, 9-aryl-2,6-diaminopurines
and 2-amino-9-methyl-6-purinethiol show antitumor
activity.9 Furthermore, several 9-phenylguanine deriva-
tives are found to be good irreversible inhibitors of Gua-
nosine deaminase10 and Xanthine oxidase.11 Having
these observations in mind, we designed and synthesized
a series of novel heterocyclic chemical entities, guanyl-
sulfonamides, possessing bioactive guanine and sulfon-
amide scaffolds and evaluated their antimicrobial
activities against various bacterial and fungal strains.
Sulfonamides are among the most widely used antibac-
terial agents in the world, chiefly because of their low
cost, low toxicity, and good activity against common
bacterial diseases. The synergetic action of sulfonamides
with Trimethoprim has brought about enormous resur-
gence of sulfonamide usage everywhere over the last
decade. However, the most common side effects of this
class of drugs are nausea, vomiting, diarrhea, anorexia,
and hypersensitivity reaction.3 Piperazine sulfonamides
exhibit diverse pharmacological activity such as MMP-
3 inhibition, antibacterial activity, and Carbonic anhy-
drase inhibition.4
For the construction of the target guanylsulfonamides, a
retrosynthetic approach was designed based on intramo-
lecular ring closure of arylamino pyrimidines (see Chart
1) and is furnished in Chart 2. The intramolecular ring
closure precursor 12 was envisioned to derive from 11
since a disconnection of the bond between C-8 and
N-9 on the target molecule, guanylsulfonamide gives a
synthon, A of the intramolecular ring closure precursor
12 and a disconnection of the imine bond of the synthon
A provides a synthetic equivalent for the pre precursor
11. The compound 11 could be derived from 6 and 10
Keywords: Guanylsulfonamides; Reductive aminoformylation; Intra-
molecular ring condensation; Antibacterial activity; Antifungal
activity.
*
Corresponding author. Tel.: +82 53 950 5334; fax: +82 53 950
6330; e-mail: ytpark@knu.ac.kr
0960-894X/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2007.09.060

P. R. Patel et al. / Bioorg. Med. Chem. Lett. 17 (2007) 6610–6614
6611
Y
N
Y
Hydrolysis of 4 using strong NaOH followed by
nitration provided 2-amino-6-chloro-3H-pyrimidin-4-
one (5) and 6, respectively.
Y
N
NH2
NH2
Cl
N
N
b
a
N
N
N
X
NHAr
X
N
X
On the other hand, an equivalent synthon C, 2-substi-
tuted-4-(4-substituted piperidin-1-sulfonyl)phenylamine
derivatives (10a–10h), was synthesized by adopting a
four-stage synthetic strategy as shown in Scheme 2.
Compound 8a, synthesized from aniline using acetyla-
tion15 followed by chlorosulfonylation methods,16 was
subjected to substitution followed by hydrolysis reac-
tions to afford 9a and 10a, respectively. In a similar
manner, 10b–10h were synthesized.
Ar
Chart 1. (a) Ar–NH2; (b) CH(OEt)3, H+.
O
N
O
N
N
H
X
N
HN
HN
H2N
N
H2N
N
X
Eventually, guanylsulfonamide analogues (13a–13h)
were synthesized by adopting a three-step strategy as de-
picted in Scheme 3. When 11a, obtained by the substitu-
tion of 6 with 10a, was submitted to reductive
aminoformylation and subsequent intramolecular ring
closure reactions, guanylsulfonamide 13a resulted as a
sole product. Analogues 13b–13h were synthesized akin
to the method used for 13a.
O2S
O2S
N
N
Synthon A
13
Y
Y
O
NO2
HN
All the guanylsulfonamides 13a–13h were assayed for
their in vitro antibacterial activity against a panel of
pathogenic bacterial strains such as Klebsiella pneumo-
niae (ATCC-13883), Escherichia coli (ATCC-25922),
Pseudomonas aeruginosa (ATCC-27853), Bacillus subtilis
(ATCC-6033), Staphylococcus aureus (ATCC-25923),
and Streptococcus faecalis (ATCC-29212). The assays
were carried out using twofold serial dilution technique.
O
H2N
N
NO2
Synthon B
HN
+
H2N
N
NH
X
NH
X
O2S
N
NH2
NHCOCH3
X
NHCOCH3
X
O2S
N
Y
X
a
b
Y
11
Synthon C
SO2Cl
Chart 2.
X = H
F
7a; X = H
7b; X = F
8a-d
Cl
OCH3
7c; X = Cl
7d; X = OCH3
as its retrosynthetic analysis produces synthon B and
synthon C.
Y
c
N
H
The compound 6, 2-amino-6-chloro-5-nitro-3H-pyrimi-
din-4-one, was synthesized by adopting the methods
given in the literature (Scheme 1).12–14
NH2
NHCOCH3
X
X
When pyrimidinone, 2-amino-6-hydroxy-3H-pyrimidin-
4-one (3), obtained by the condensation of guanidine
with malonic acid diethylester was treated with
POCl3, 4,6-dichloropyrimidin-2-ylamine (4) was formed.
d
O2S
O2S
N
N
Y
Y
10a; X = H, Y = H
10b; X = H, Y = CH3
10c; X = F, Y = H
10d; X = F, Y = CH3
10e; X = Cl, Y = H
10f; X = Cl, Y = CH3
10g; X = OCH3, Y = H
9a; X = H, Y = H
9b; X = H, Y = CH3
9c; X = F, Y = H
9d; X = F, Y = CH3
9e; X = Cl, Y = H
O
O
O
C2H5
O
O
HN
NO2
Cl
a, b, c, d
HN
NH2
+
H2N
H2N
N
9f; X = Cl, Y = CH3
9g; X = OCH3, Y = H
HCl
C2H5
10h; X = OCH3, Y = CH3
9h; X = OCH3, Y = CH3
6
1
2
Scheme 1. Reagents: (a) MeOH, NaOMe; (b) POCl3, Et3N; (c) 1 N
NaOH, H2O; (d) HNO3, H2 SO4.
Scheme 2. Reagents: (a) (CH3CO)2O, H2O; (b) ClSO3H; (c) MeOH;
(d) HCl, MeOH.

6612
P. R. Patel et al. / Bioorg. Med. Chem. Lett. 17 (2007) 6610–6614
O
NH2
NO2
X
11a; X = H, Y = H
HN
O
N
11b; X = H, Y = CH3
11c; X = F, Y = H
11d; X = F, Y = CH3
11e; X = Cl, Y = H
11f; X = Cl, Y = CH3
11g; X = OCH3, Y = H
11h; X = OCH3, Y = CH3
NO2
Cl
H2N
N
NH
HN
a
+
X
O2S
H2N
N
Y
O2S
N
6
10
Y
b
O
N
O
N
H
N
H
X
N
N
HN
HN
12a; X = H, Y = H
12b; X = H, Y = CH3
12c; X = F, Y = H
12d; X = F, Y = CH3
12e; X = Cl, Y = H
12f; X = Cl, Y = CH3
12g; X = OCH3, Y = H
12h; X = OCH3, Y = CH3
13a; X = H, Y = H
13b; X = H, Y = CH3
13c; X = F, Y = H
13d; X = F, Y = CH3
13e; X = Cl, Y = H
13f; X = Cl, Y = CH3
13g; X = OCH3, Y = H
13h; X = OCH3, Y = CH3
O
N
H2N
NH
H2N
c
X
O2S
O2S
N
Y
Y
Scheme 3. Reagents: (a) MeOH, Et3N; (b) Zn, HCOOH; (c) H+, HOCH2 CH2OH.
Dimethyl sulfoxide and one of the potent antibacterial
drugs Norfloxacin, an oral broad-spectrum fluoroquino-
lone antibacterial agent used for the treatment of
urinary tract infections, were used as solvent control
and standard, respectively. The results are furnished in
Table 1.
Against all the organisms except P. aeruginosa, 13c witha –
F on the 2-position of the –Ph exhibited enhanced activity
compared to its unsubstituted analogue 13a. Introduction
of a –CH3 on the 4-position of the piperidine ring of 13c,
thereby producing analogue 13d, did not alter the activity
against K. pneumoniae, P. aeruginosa, and S. aureus. How-
ever, due to the –CH3 introduction, an increase in the
activity, about twofold, against E. coli as well as a decrease
in the activity, about twofold, against B. subtilis and S. fae-
calis were observed.
Among the guanylsulfonamide analogues, 13a and 13b
having no substituents on the 2-position of the –Ph and
the 4-position of the piperidine ring were inactive at the
maximum concentration (64 lg mLÀ1
)
against K.
pneumoniae, E. coli, and B. subtilis except 13b against B.
subtilis. However, these compounds (13a and 13b)
showed activity against P. aeruginosa, S. aureus, and S.
faecalis at the maximum concentration. When a
–CH3 was introduced at the 4-position of the piperidine
ring, there were no profound loss or gain in the activities
observed against P. aeruginosa, S. aureus, and
S. faecalis.
When the –F was substituted by a –Cl in 13c, thereby pro-
ducing analogue 13e, a remarkable enhancement in the
activity was observed against S. aureus and S. faecalis.
Due to the –Cl, the growths of S. aureus and S. faecalis
were inhibited at a minimum concentration of 4 lg mLÀ1
.
An appreciable enhancement in the activities of 13e was
noticed against rest of the organisms as well. The guanyl-
sulfonamide 13f with a –CH3 at the 4-position of the
Table 1. Antibacterial activities of 2-amino-9-[2-substituted-4-(4-substituted piperidin-1-sulfonyl)phenyl]-1,9-dihydropurin-6-ones (13a–13h)
Compound
X
Y
MIC, lg mLÀ1
K. pneumoniae
E. coli
P. aeruginosa
B. subtilis
S. aureus
S. faecalis
13a
13b
H
H
—
—
32
32
16
16
32
32
16
—
—
64
32
16
16
32
16
16
64
64
64
64
8
—
64
32
64
32
32
16
16
32
64
64
32
32
4
64
64
16
32
4
H
CH3
H
13c
13d
F
F
Cl
CH3
H
13e
13f
Cl
OCH3
OCH3
CH3
H
16
64
64
8
4
8
13g
13h
64
32
8
64
32
8
CH3
Norfloxacin

P. R. Patel et al. / Bioorg. Med. Chem. Lett. 17 (2007) 6610–6614
6613
piperidine ring and a –Cl on –Ph has similar activity as
13e against all the organisms except P. aeruginosa and
S. faecalis. Against these two organisms, the –CH3
replacement caused a profound drop in the activity to lev-
els lower than that of 13e.
On the other hand, replacement of the –Cl by a –OCH3
(13g) remarkably enhanced the activity against all the
fungal strains. Against A. flavus and A. niger, 13g dis-
played activity at a minimum inhibitory concentration
of 16 lg mLÀ1. In 13g, substitution of a –CH3 on the
4-position of the piperidine ring (13h) showed no differ-
ence in the activity compared to 13g against A. flavus
and C. albicans, whereas the –CH3 substitution caused
a profound drop in the activity to the level lower than
that of 13g.
On the other hand, substitution of a –OCH3 in place of
the –Cl in 13e remarkably decreased the activity against
all the organisms except B. subtilis. Against B. subtilis,
the –OCH3 substitution noticeably enhanced the activity
displayed by the –Cl substituted analogue 13e. When a
–CH3 was introduced at the 4-position of the piperidine
moiety in 13g, an increase in the activity was observed
against E. coli, S. aureus, and S. faecalis whereas there
was no appreciable difference in the activity noticed
against K. pneumoniae, P. aeruginosa, and B. subtilis.
In summary, syntheses of guanylsulfonamides, 2-amino-
9-[4-(piperidin-1-sulfonyl)phenyl]-1,9-dihydropurin-6-ones,
were accomplished by the combination of three synthon
components. Firstly, the equivalent of synthon B, the
compound 6, was synthesized by the condensation of
guanidine and diethyl malonate, followed by chlorina-
tion, hydrolysis, and nitration reactions. Secondly, the
equivalent of synthon C, the compounds 10a–10h, was
synthesized by acetylation of anilines, followed by chlo-
rosulfonylation, condensation, and hydrolysis reactions.
Eventually, substitution reaction between 6 and 10a–10h
followed by reductive aminoformylation and intramolec-
ular cyclization reactions afforded the guanylsulfona-
mide 13a–13h, respectively. Most of the target chemical
entities 13a–13h exhibit modest antibacterial and anti-
fungal activities against a wide spectrum of pathogenic
bacterial and fungal strains. Particularly, the guanylsulf-
onamides 13e and 13f with –Cl displayed better antibac-
terial efficacy than that of the standard drug Norfloxacin
against S. aureus and S. faecalis, while 13e showed
antibacterial efficacy akin to that of Norfloxacin against
P. aeruginosa. Against the fungal strains A. flavus and A.
niger, the guanylsulfonamides 13g and 13h carrying
–OCH3 exhibited antifungal potency akin to that of the
standard drug Griseoflavin-16 except 13h against A. ni-
ger. The appreciable antibacterial and antifungal effica-
cies of the new guanylsulfonamides deserve further
investigation in order to establish the mode of action.
The antifungal activity of the guanylsulfonamides 13a–
13h on a panel of pathogenic fungal strains such
as Aspergillus flavus (NCIM-539), Aspergillus niger
(NCIM-590), and Candida albicans (NCIM-C27) was
evaluated using twofold serial dilution method. Dimethyl
sulfoxide and Griseoflavin-16, an antifungal drug
commonly used to cure fungal infection affecting the
skin, hair, and nail known as ringworm, were used as sol-
vent control and standard, respectively. The results are
presented in Table 2.
Of the guanylsulfonamides 13a–13h, 13a did not show
activity against all the fungal strains at the maximum
concentration (64 lg mLÀ1). In 13a, a –CH3 substitution
at the 4-position of the piperidine ring (13b) or a –F sub-
stitution at the 2-position of the –Ph (13c) also did not
exhibit activity at the maximum concentration against
all the fungal strains. However, 13d having –CH3 on
the 4-position of the piperidine ring and –F on the 2-po-
sition of the –Ph displayed activity at 64 lg mLÀ1
against A. flavus and C. albicans and at 32 lg mLÀ1
against A. niger.
Introduction of a –Cl instead of the –F on the 2-position
of the –Ph in 13c (resulting in analogue 13d) exhibited
activity at the maximum concentration against all the
fungal strains. In 13e, when the –H at 4-position of
the piperidine ring was replaced by a –CH3 resulting
in analogue 13f, the activity was enhanced to twofold
against A. flavus and A. niger, whereas, the activity
remained unchanged against C. albicans.
Acknowledgment
This work was supported by Korea Research Founda-
tion Grant (KRF-2006-005-J02401).
Supplementary data
Experimental details and characterization data for com-
pounds 8a–8d, 9a–9h, 10a–10h, 11a–11h, 12a–12h, and
13a–13h. Supplementary data associated with this article
can be found, in the online version, at doi:10.1016/
j.bmcl.2007.09.060.
Table 2. Antifungal activities of 2-amino-9-[2-substituted-4-(4-substi-
tuted piperidin-1-sulfonyl) phenyl]-1,9-dihydropurin-6-ones (13a–13h)
Compound
X
Y
MIC, lg mLÀ1
A. flavus A. niger C. albicans
13a
13b
H
H
—
—
—
—
—
—
32
64
32
16
32
16
—
—
—
64
64
64
32
32
8
H
CH3
H
13c
13d
F
References and notes
F
Cl
CH3 64
64
CH3 32
16
13e
13f
H
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