Synthesis and antimicrobial activity of 1-aryl-2-amino-3-(4-arylthiazol- 2-yl)/(benzothiazol-2-yl)guanidines

Article abstract of DOI:10.1016/S0014-827X(00)00032-X

The synthesis of fifteen new 1-aryl-2-amino-3-(4-arylthiazol-2- yl)/(benzothiazol-2-yl)guanidines is described. They were screened for their antimicrobial susceptibility by the standard disc diffusion method of the World Health Organization (WHO) and the activities compared with that of standard strain of Escherichia coli NCTC 10418. The sensitive aminoguanidines were further subjected to the minimum inhibitory concentration (MIC) test. (C) 2000 Elsevier Science S.A.

Full text of DOI:10.1016/S0014-827X(00)00032-X

www.elsevier.nl/locate/farmac
Il Farmaco 55 (2000) 331–337
Synthesis and antimicrobial activity of
1-aryl-2-amino-3-(4-arylthiazol-2-yl)/(benzothiazol-2-yl)guanidines
Ram Lakhan a,*, Bimal Prasad Sharma a, Bishwa Nath Shukla b
a Department of Chemistry, Banaras Hindu Uni6ersity, Varanasi 221 005, India
b Department of Microbiology, Institute of Medical Sciences, Banaras Hindu Uni6ersity, Varanasi 221 005, India
Received 10 January 1999; accepted 16 February 2000
Abstract
The synthesis of fifteen new 1-aryl-2-amino-3-(4-arylthiazol-2-yl)/(benzothiazol-2-yl)guanidines is described. They were screened
for their antimicrobial susceptibility by the standard disc diffusion method of the World Health Organization (WHO) and the
activities compared with that of standard strain of Escherichia coli NCTC 10418. The sensitive aminoguanidines were further
subjected to the minimum inhibitory concentration (MIC) test. © 2000 Elsevier Science S.A. All rights reserved.
Keywords: Antimicrobial activity; Minimum inhibitory concentration; Guanidines
1. Introduction
2. Experimental
A number of thiazolyl and benzothiazolyl guanidines
have been reported to exhibit antitubercular, antimalar-
ial, CNS depressant, analgesic [1–8] and antimicrobial
activity against both Gram-positive and Gram-negative
bacteria [9]. The related N-aminoguanidines are very
scarcely reported in the literature; an exception being
their report as tuberculostatic agents [10]. Therefore, we
considered it interesting to synthesize and evaluate the
antibacterial activity of some new 1-aryl-2-amino-3-(4-
arylthiazol-2-yl)/(benzothiazol-2-yl)guanidines.
All melting points (m.p.) were determined in open
capillaries on a Gallenkamp apparatus and are uncor-
rected. The purity of the compounds was routinely
checked by thin layer chromatography (TLC) using
The synthetic approach to these compounds [2,4] is
outlined in Schemes 1 and 2. The starting materials,
2-amino-4-arylthiazoles and 2-aminobenzothiazole were
refluxed with substituted phenyl isothiocyanates in dry
benzene. Subsequent desulfurization of the resulting
thioureas 1 and 3 with yellow lead oxide in ethanol in
the presence of hydrazine hydrate gave 2 and 4, respec-
tively, in 45–75% yields. The structure of the com-
pounds 1–4 were confirmed by elemental analyses, IR
1
and H NMR spectral data.
* Corresponding author. Tel.: +91-542-21 1979; fax: +91-542-31
7074.
Scheme 1.
0014-827X/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.
PII: S0014-827X(00)00032-X

332
R. Lakhan et al. / Il Farmaco 55 (2000) 331–337
(broad, 1H, NH, D2O exchangeable), 6.90–8.00 (m,
10H, ar), 11.25–11.50 (broad, 1H, NH, D2O
exchangeable).
2.2. 1-p-Bromophenyl-3-(4-p-totylthiazol-2-yl)-
2-thiourea (1g)
The compound was prepared by condensing 2-
amino-4-p-tolylthiazole with p-bromophenyl isothio-
cyanate in dry benzene as above; yield 58%, m.p.
225°C. Analysis: C17H14BrN3S2 (C, H, N, S). IR (KBr,
cm−1): 3450 m, 3350 m (NꢀH str), 1660 m, 1600 m,
1540 s (aromatic ring), 1230 s (CꢁS str). NMR (DMSO-
d6): l 2.20 (s, 3H, CH3), 7.13–7.90 (m, 10H, 9 ar and
one NH, D2O exchange), 9.04 (s, 1H, NH, D2O ex-
change). Other thioureas 1 were prepared similarly in
46–73% yields. Their m.p. and characteristic IR data
(Nujol) are reported in Table 1.
Scheme 2.
silica gel G (E. Merck). A Jeol FX-90Q Fourier trans-
form spectrometer was used for recording 1H NMR
spectra at 27°C with TMS as an internal standard. A
Jasco FT-IR 5300 spectrophotometer was used for IR
spectra and a Perkin–Elmer CHN Analyzer 240C for
elemental analyses. The analytical values for all the new
compounds were within 90.3% of the theoretical
values.
2.3. 1-p-Bromophenyl-3-(benzothiazol-2-yl)-2-thiourea
(3a)
The compound was prepared by refluxing 2-
aminobenzothiazole with p-bromophenyl isothio-
cyanate in dry benzene as above; yield 95%, m.p.
231°C. Analysis: C14H10BrN3S2 (C, H, N, S). IR (KBr,
cm−1): 3480 m, 3340 w (NꢀH str), 1660 w, 1640 s, 1550
s (aromatic ring), 1240 (CꢁS str). NMR (DMSO-d6): l
6.50–8.45 (m, 8H, ar), 9.20 (broad, 1H, NH, D2O
exchange), 11.92 (broad, 1H, NH, D2O exchange). By
following this procedure, thioureas 3b–d were also
prepared. Their yields, m.p. and characteristic IR data
(Nujol) are given in Table 2.
2.1. 1-p-Bromophenyl-3-(4-phenylthiazol-2-yl)-
2-thiourea (1a)
An equimolecular mixture of 2-amino-4-phenylthia-
zole (4.0 g, 23 mmol) and p-bromophenyl isothio-
cyanate (5.3 g, 25 mmol) in 30 ml of dry benzene was
refluxed in a water-bath for 10 h. After cooling, the
solid product was filtered and washed with ether fol-
lowed by dilute HCl. The product was finally washed
with water and crystallized from ethanol to give color-
less crystals; yield 73%, m.p. 255°C. Analysis:
C16H12BrN3S2 (C, H, N, S). IR (Nujol, cm−1): 3400 m,
3345 s (NꢀH str), 1640 s, 1590 m, 1460 m (aromatic
ring), 1200 s (CꢁS str). NMR (DMSO-d6): l 3.50–3.89
2.4. 1-p-Bromophenyl-2-amino-3-(4-phenylthiazol-
2-yl)guanidine (2a)
A mixture of 1-p-bromophenyl-3-(4-phenylthiazol-2-
yl)-2-thiourea (4.0 g, 0.01 mol), yellow lead oxide (2.2 g,
Table 1
Characterization data of 1-aryl-3-(4-arylthiazol-2-yl)-2-thioureas (1)
Comp.
Ar
X
m.p. (°C)
Molecular formula
Characteristic IR bands (cm−1
)
wNH
wCꢁS
1a
1b
1c
1d
1e
1f
1g
1h
1i
4-BrC6H4
C6H5CH2
2-ClC6H4
H
H
H
H
H
H
CH3
CH3
CH3
CH3
CH3
255
178
148
210
222
120
225
237
194
228
205
C16H12BrN3S2
C17H15N3S2
3400 m, 3345 s
3350–3250 br
3250 s, 3240 s
3400 m, 3330 m
3460–3200 br
3420 m, 3280 m
3450 m, 3350 m
3440–3350 br
3480 s, 3320 m
3400 m, 3200 m
3400–3250 br
1200 s
1210 m
1205 s
1205 s
1200 s
1205 m
1230 s
1220 m
1205 s
1210 s
1210 s
C16H12ClN3S2
C16H12ClN3S2
C17H17N3OS2
C16H12N4O2S2
C17H14BrN3S2
C18H17N3S2
C17H14ClN3S2
C17H14ClN3S2
C19H19NOS2
3-ClC6H4
4-C2H5OC6H4
2-NO2C6H4
4-BrC6H4
C6H5CH2
2-ClC6H4
1j
1k
3-ClC6H4
4-C2H5OC6H4

R. Lakhan et al. / Il Farmaco 55 (2000) 331–337
333
Table 2
Characterization data of 1-aryl-3-(benzothiazol-2-yl)-2-thioureas (3)
Comp.
Ar
Yield (%)
m.p. (°C)
Molecular formula
Characteristic IR bands (cm−1
)
wNH
wCꢁS
3a
3b
3c
3d
4-BrC6H4
C6H5CH2
2-ClC6H4
4-C2H5OC6H4
95
55
51
49
221
181
155
198
C14H10BrN3S2
C15H13N3S2
C14H10ClN3S2
C16H15N3OS2
3480 m, 3340 w
3300 s, 3280 m
3240 s, 3180 m
3440 s, 3280 m
1240 m
1200 m
1210 m
1230 s
0.01 mol) and hydrazine hydrate (1.5 ml, 0.03 mol) in
30 ml of ethanol was heated in a sealed glass tube on a
water-bath for 8 h. Lead sulfide was filtered while hot
and the residue extracted with hot ethanol. The filtrates
were concentrated to get the required guanidine, which
was crystallized from ethanol to form light yellow
crystals; yield 45%, m.p. 240°C. Analysis: C16H14BrN5S
(C, H, N, S). IR (KBr, cm−1): 3420 m, 3350 w (NH2
and NH str), 1640 s, 1600 s, 1540 s, 760 m. NMR
(DMSO-d6): l 5.27 (s, 2H, NH2, D2O exchange),
6.90–8.00 (m, 10H, ar), 8.85 (s, 1H, NH, D2O
exchange), 10.79–11.66 (broad, 1H, NH, D2O ex-
change). By the above procedure, a series of 1-aryl-2-
amino-3-(4-phenylthiazol-2-yl)guanidines (2b–f) were
prepared and crystallized from ethanol. Their yields,
m.p., characteristic IR and NMR data are recorded in
Table 3.
(m, 10H, 8 ar and NH2, D2O exchange), 9.35 (s, 1H,
NH, D2O exchange), 11.35–11.88 (broad, 1H, NH,
D2O exchange).
Similarly, a series of 1-aryl-2-amino-3-(benzothiazol-
2-yl)guanidines (4b–d) were prepared. Their yields,
m.p. and characteristic IR and NMR data are recorded
in Table 4.
3. Antimicrobial screening results
The 1-aryl-2-amino-3-(4-arylthiazol-2-yl)guanidines
(2) and 1-aryl-2-amino-3-(benzothiazol-2-yl)guanidines
(4) were screened for their antimicrobial activity against
seventeen different pathogenic strains of microorgan-
isms such as Staphylococcus aureus, Staphylococcus epi-
dermidis, Escherichia coli, Klebsiella pneumoniae,
Pseudomonas aeruginosa, Citrobacter freundii, Proteus
6ulgaris, Pro6idencia rettgeri, Edwardsiela tarda,
Salmonella typhi, Salmonella typhimurium, Strigella
dysenteriae, Vibrio cholerae 01 classical, Vibrio cholerae
non 01, Vibrio parahaemolyticus, Aeromonas hydrophila
and Plesimonas shigelloides. The antimicrobial suscepti-
bility was determined by the Stokes disc diffusion tech-
nique [11] whereas minimum inhibitory concentration
(MIC) was determined by the Stokes and Ridgeway
plate dilution method [11]. Zones of inhibition of the
test microorganisms were compared with that of the
control NCTC strain of E. coli 10418.
The antimicrobial susceptibility was measured at a
concentration of 40 mg/disc. The analysis of various
patterns of susceptibility is shown in Table 5. The
results reveal that there are a wide variety of combina-
tions of the synthesized compounds to which strains
were sensitive. The synthesized N-aminoguanidines are
most active against S. epidermidis, K. pneumoniae, S.
dysenteriae, V. cholerae 01 classical, V. cholerae non 01
and A. hydrophila. In general, those aminoguanidines
which have para or meta halogen substituent in the
phenyl ring show remarkable antibacterial activity.
The sensitive aminoguanidines from antimicrobial
susceptibility test were further subjected to the MIC test
as follows. Freshly prepared solutions of synthesized
compounds diluted to different concentrations were
2.5. 1-p-Bromophenyl-2-amino-3-(4-p-tolylthiazol-
2-yl)guanidine (2g)
The guanidine was prepared from 1-p-bromophenyl-
3-(4-p-tolylthiazol-2-yl)-2-thiourea by heating for 7 h;
yield 48%, m.p. 114°C. Analysis: C17H16BrN5S (C, H,
N, S). IR (KBr, cm−1): 3450 m, 3350 m (NH2 and
NH str), 1640 m, 1600 m, 1540 s (aromatic ring),
760 s. NMR (DMSO-d6): l 2.35 (s, 3H, CH3), 6.00
(s, 2H, NH2, D2O exchange), 7.12–7.90 (m, 10H, 9 ar
and one NH, D2O exchange), 9.00 (s, 1H, NH,
D2O exchange). Similarly, a series of 1-aryl-2-amino-3-
(4-p-tolylthiazol-2-yl)guanidines (2h–k) were prepared
and crystallized from ethanol. Their yields, m.p., char-
acteristic IR and NMR (DMSO-d6) data are given in
Table 3.
2.6. 1-p-Bromophenyl-2-amino-3-(benzothiazol-
2-yl)guanidine (4a)
The compound was prepared from 1-p-bromophenyl-
3-(benzothiazol-2-yl)-2-thiourea as above. The heating
period was 6 h; yield 75%, m.p. 190°C. Analysis:
C14H12BrN5S (C, H, N, S). IR (KBr, cm−1): 3600–
3200 broad (NH2 and NH str), 1620 m, 1600 m, 1560 s
(aromatic ring), 740 m. NMR (DMSO-d6): l 6.83–8.39

334
R. Lakhan et al. / Il Farmaco 55 (2000) 331–337

R. Lakhan et al. / Il Farmaco 55 (2000) 331–337
335

336
R. Lakhan et al. / Il Farmaco 55 (2000) 331–337
added to Mueller–Hinton agar (Hi-Media), at 45–
50°C. It was mixed well and poured into 100-mm
petridishes; 20 ml gave a depth of about 4 mm. Plates
were dried prior to experiment and each plate was
divided into equal sections. Overnight broth cultures of
the test strains and control of E. coli NCTC 10418 were
diluted to 1:1000 in phosphate buffer solution PBS (pH
7.4) to a concentration of about 104–105 viable cells/ml.
Aliquots of 0.01 ml of the diluted cultures were
spotted on the different sectors on the agar plates
containing the serial dilutions 2.0, 1.0, 0.5, 0.25 and
0.125 mg/ml of the synthesized compounds. Inocula
were allowed to dry and the plates were incubated at
30°C overnight. All the test strains were also inoculated
on a control plate containing no synthesized com-
pound. The MIC of the synthesized compound was the
lowest concentration of the compound per milliliter of
medium that completely inhibited visible growth of the
corresponding test strain.
The MIC of the various antimicrobial agents for
species tested is shown in Table 6. The MIC values for
the compounds showed a range from 0.125 to 2 mg/ml.
Table 5
Antimicrobial screening results of 1-aryl-2-amino-3-(4-arylthiazol-2-yl)guanidines (2) and 1-aryl-2-amino-3-(benzothiazol-2-yl)guanidines (4)a
Microorganisms
Comp. no.
2a
2b
2c
2d
2e
2f
2g
2h
2i
2j
2k
4a
4b
4c
4d
S. aureus
S. epidermidis
E. coli
K. pneumoniae
P. aeruginosa
C. freundii
P. 6ulgaris
P. rettgeri
E. tarda
S. typhi
S. typhimurium
S. dysenteriae
V. cholerae 01 classical
V. cholerae non 01
V. parahaemolyticus
A. hydrophila
P. shigelloides
S
S
S
S
R
R
S
S
S
S
R
S
S
S
S
S
S
R
R
R
R
R
R
R
R
R
S
R
R
R
R
R
R
R
R
R
R
R
R
R
S
S
S
S
S
S
S
S
S
R
S
S
S
S
S
S
S
S
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
S
S
S
S
R
S
S
S
S
S
S
S
S
S
R
S
S
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
S
S
R
S
R
R
R
R
R
R
R
R
S
R
R
R
S
S
R
S
S
R
S
S
S
R
R
S
R
S
R
S
R
R
R
S
S
R
S
S
R
S
R
S
S
R
S
S
S
S
R
R
S
R
R
R
S
S
S
R
S
R
R
S
S
R
R
S
S
S
R
R
S
S
S
R
R
R
R
S
S
S
S
R
R
R
S
R
R
S
S
S
R
S
S
S
S
R
S
R
S
R
R
S
R
R
S
S
R
R
R
R
R
R
S
S
S
S
S
S
S
R
R
R
R
S
S
R
S
a S=sensitive; R=resistant.
.
Table 6
MIC of 1-aryl-2-amino-3-(4-arylthiazol-2-yl)guanidines (2) and 1-aryl-2-amino-3-(benzothiazol-2-yl)guanidines (4)a
Microorganisms
Comp. no.
2a
2b 2c
2d
2e
2f
2g
2h 2i
2j
2k 4a
4b 4c
4d
S. aureus
S. epidermidis
E. coli
K. pneumoniae
P. aeruginosa
C. freundii
2
2
1
1
1
1
1
0.125
2
1
0.125
2
0.125
2
1
0.125
1
1
1
2
0.125
2
1
0.5
2
2
1
2
2
2
P. 6ulgaris
P. rettgeri
1
2
E. tarda
S. typhi
2
2
1
S. typhimurium
S. dysenteriae
V. cholerae 01 classical
V. cholerae non 01
V. parahaemolyticus
A. hydrophila
P. shigelloides
0.5
2
1
2
0.5
2
1
1
1
1
2
0.5
1
0.5
1
1
2
2
2
2
2
2
2
1
2
2
2
2
2
1
1
2
2
1
a MIC=minimum inhibitory concentration. The figures are in mg/ml.

R. Lakhan et al. / Il Farmaco 55 (2000) 331–337
337
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The authors wish to thank Professor R. Balaji Rao,
Head of the Department of Chemistry and to the Head
of the Department of Microbiology, IMS, Banaras
Hindu University for providing the necessary facilities.
The financial assistance by the Tribhuvan University,
Kathmandu, Nepal, for the award of a Teacher Re-
search Fellowship under the Faculty Development pro-
gram to B.P.S. is also gratefully acknowledged.
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