Synthesis and antimicrobial activity of some new thiazole, thiophene and pyrazole derivatives containing benzothiazole moiety

Article abstract of DOI:10.1016/j.ejmech.2010.05.018

In an attempt to find a new class of antimicrobial agents, a series of thiazole, thiophene, pyrazole and other related products containing benzothiazole moiety were prepared via the reaction of N-(benzothiazol-2-yl)-2- cyanoacetamide (1) with appropriate chemical reagents. These compounds were screened for their antibacterial activity against Gram-positive bacteria (Staphylococcus aureus and Streptococcus pyogenes), Gram-negative bacteria (Pseudomonas phaseolicola and Pseudomonas fluorescens) and antifungal activity against Fusarium oxysporum and Aspergillus fumigatus. Among the synthesized compounds, thiophene 13 showed equal activity with chloroamphenicol against S. aureus (MIC 3.125 μg/mL), while its activity was 50% lower than of chloroamphenicol against S. pyogenes. Thiazole 3 and pyrazolo[1,5-a]pyrimidine 21b were found to exhibit the most potent in vitro antifungal activity with MICs (6.25 μg/mL) against A. fumigatus and F. oxysporum. Structures of the newly synthesized compounds were established by elemental analysis and spectral data.

Full text of DOI:10.1016/j.ejmech.2010.05.018

European Journal of Medicinal Chemistry 45 (2010) 3692e3701
Contents lists available at ScienceDirect
European Journal of Medicinal Chemistry
journal homepage: http://www.elsevier.com/locate/ejmech
Original article
Synthesis and antimicrobial activity of some new thiazole, thiophene and
pyrazole derivatives containing benzothiazole moiety
*
Samir Bondock , Walid Fadaly, Mohamed A. Metwally
Department of Chemistry, Faculty of Science, Mansoura University, ET-35516 Mansoura, Egypt
a r t i c l e i n f o
a b s t r a c t
Article history:
In an attempt to find a new class of antimicrobial agents, a series of thiazole, thiophene, pyrazole and
other related products containing benzothiazole moiety were prepared via the reaction of N-(benzo-
thiazol-2-yl)-2-cyanoacetamide (1) with appropriate chemical reagents. These compounds were
screened for their antibacterial activity against Gram-positive bacteria (Staphylococcus aureus and
Streptococcus pyogenes), Gram-negative bacteria (Pseudomonas phaseolicola and Pseudomonas fluorescens)
and antifungal activity against Fusarium oxysporum and Aspergillus fumigatus. Among the synthesized
Received 22 April 2010
Received in revised form
9 May 2010
Accepted 10 May 2010
Available online 15 May 2010
compounds, thiophene 13 showed equal activity with chloroamphenicol against S. aureus (MIC 3.125 mg/
mL), while its activity was 50% lower than of chloroamphenicol against S. pyogenes. Thiazole 3 and
pyrazolo[1,5-a]pyrimidine 21b were found to exhibit the most potent in vitro antifungal activity with
Keywords:
Benzothiazole
Thiazole
Thiophene
Pyrazole
MICs (6.25
were established by elemental analysis and spectral data.
Ó 2010 Elsevier Masson SAS. All rights reserved.
mg/mL) against A. fumigatus and F. oxysporum. Structures of the newly synthesized compounds
Pyrazolo[1,5-a]pyrimidine
Antimicrobial activity
1. Introduction
[36,37], antiparasitic [38], antivirial [39], and antineoplastic agents
[40,41].
The benzothiazole ring is present in various marine or terrestrial
natural compounds which have useful biological activities [1e5].
Benzothiazole derivatives have attracted a great deal of interest due
to their anticancer [6], antitumor [7], anticonvulsant [8], antiviral
[9], antibacterial [10], antimicrobial [11] and fungicidal activities
[12]. Theyare also useful as anti-allergic [13], anti-inflammatory [14]
and anthelmintic [15] agents and as appetite depressants [16],
intermediates for dyes [17], plant protectants [18], histamine H2
antagonists [19] and photographic sensitizers [20]. On the other
hand, careful literature survey revealed that thiazole, thiophene and
pyrazole ring systems have occupied a unique position in the design
and synthesis of novel biological active agents with remarkable
analgesic and anti-inflammatory activities [21e24], in addition to
their well documented potential antimicrobial activities [25e28].
Morever, thiazoles have found application in drug development for
the treatment of hypertension [29], schizophrenia [30], HIV infec-
tions [31], and as new inhibitors of bacterial DNA gyrase B [32]. Also,
a large number of thiophene derivatives have found to exhibit
pharmacological activity [33e35]. Furthermore, diverse chemo-
therapeutic activities have ascribed to pyrazoles as antimicrobial
In view of the above-mentioned facts and in continuation of our
interest in the synthesis of heterocycles containing benzothiazole
moiety [42e44], to identify new candidates that may be value in
designing new, potent, selective and less toxic antimicrobial agents,
we report herein the synthesis and antimicrobial evaluation of some
novel structure hybridsincorporatingboth thebenzothiazole moiety
with either the thiazole, thiophene or pyrazole ring systems through
different linkages. This combination was suggested in an attempt to
investigate the influence of such hybridization and structure varia-
tion on the anticipated biological activities, hoping to add some
synergistic biological significance to the target molecules. The target
compounds were rationalized so as to comprise some pharmaco-
phoresthatarebelievedtoberesponsibleforthebiologicalactivityof
some relevant chemotherapeutic agents such as the carboxamido
and thiocarbamyl functionalities [45,46]. The substitution pattern of
thiazole, thiophene and pyrazole rings was carefully selected so as to
confer different electronic environment to the molecules.
2. Results and discussion
2.1. Chemistry
The synthetic strategies adopted for the synthesis of the inter-
mediates and target compounds are depicted in schemes 1e3. In
* Corresponding author. Tel.: þ20 502369267; fax: þ20 502246781.
E-mail address: Bondock@mans.edu.eg (S. Bondock).
0223-5234/$ e see front matter Ó 2010 Elsevier Masson SAS. All rights reserved.
doi:10.1016/j.ejmech.2010.05.018

S. Bondock et al. / European Journal of Medicinal Chemistry 45 (2010) 3692e3701
3693
N
O
S
N
O
N
O
PhCOCH2Br
CN
N
CN
_
PhNCS
S
N
S
N
H
CN
H
S
N
KOH / DMF
+
H
Ph
PhHN
S K
1
O
3
2
Ph
HS
PhNCS
S, TEA
OH
N
O
pyridine
ClCH2CO2Et
CN
S
S
N
H
4
Ph
N
N
O
O
N
O
O
N
S
N
S
H
O
N
O
S
NH
H2N
S
Cl
N
S
CN
9
Me
NH
8
S
N
H
Ph
Ph
N
S
(EtO)3CH
Ac2O
Me
NH
dil. HCl
O
N
5
N
N
S
S
O
N
S
O
N
S
CN
CN
S
N
Ph
Br2
N
N
S
H
H
10
PhHN
S
HN
6
7
Scheme 1. Synthetic route to thiazoles.
Scheme 1, the starting compound N-(benzothiazol-2-yl)-2-cya-
noacetamide (1) was prepared by the cyanoacetylation of 2-ami-
(benzothiazol-2-yl)-2-cyano-2-(3,4-diphenylthiazol-2-ylidene)
acetamide (3). Elemental analysis and spectral data were in favor of
these proposed thiazole structure. The IR spectrum of 3 showed
absorption bands at 3384, 2178 and 1625 cmꢀ1 due to NH, CN and
carboxamide groups, respectively. The 1H NMR spectrum showed
nobenzothiazole
with
1-cyanoacetyl-3,5-dimethylpyrazole
according to a literature procedure [47]. The active methylene
moiety of N-(benzothiazol-2-yl)-2-cyanoacetamide (1) was
allowed to react with phenyl isothiocyanate in dimethylformamide
in the presence of an equimolar amount of potassium hydroxide
yielded the non-isolable intermediate potassium sulphide salt 2,
which reacted in situ with phenacyl bromide to afford N-
a multiplet signals in the region at
to the aromatic protons together with the thiazole-H5 and a singlet
signal at 10.59 ppm exchangeable with D2O for NH proton. The
d 7.18e7.86 ppm corresponding
d
mass spectrum revealed a molecular ion peak at m/z ¼ 452
O
N
O
N
O
NH2
PhCOCH2Br
DMF / TEA
S
S
N
S
N
H
H
S / morpholine
H
PhHN
S
COPh
H2N
11
S
1 - PhNCS
12
N
N
N
Me
6
DMF/KOH
2- dil. HCl
_
+
N
O
HCl
N
N
NH2
ClCH2COOEt
DMF / TEA
Me
N
O
H
N
N
H
N
Me
CN
pyridine / 0-5 C
N
S
N
H
PhHN
13
S
COOEt
N
N
H
1
CHO
Ph
Me
16
N
O
N
CN
N
Ph
AcOH
NH
N
H
S
Ph
EtOH / 10%NaOH
N
O
H
N
N
N
Me
N
1- PhNCS
KOH/DMF
2- MeI
N
S
N
H
Ph
14
N
N
N2H4 .H2O
EtOH
Me
17
N
N
O
N
O
NH2
NH
N
O
CN
S
Ph
N
H
N
H
S
NH2
NH
NH2NH2.H2O
N
S
H
N
PhHN
S Me
PhHN
N
N
18
19
Ph
15
Scheme 2. Synthetic route to thiophenes and pyrazoles.

3694
S. Bondock et al. / European Journal of Medicinal Chemistry 45 (2010) 3692e3701
N
O
N
Me
X = Me
- H2O
S
N
H
N
O
O
PhHN
N
Me
N
Me
X
20a
N
O
AcOH
N
O
X = Me, NHPh
N
Ph
S
N
Me
Ar
- PhNH2
H
S
S
N
H
N
N
Ph
N
N
PhHN
N
N
CN
X = NHPh
PhHN
N
NH2
22a
OH
N
CN
NC
20b
EtONa
N
O
N
O
N
N
NH2
CN
H
S
S
N
H
NMe2
O
- HNMe2
- HNMe2
PhHN
N
PhHN
Ar
21a
Ph
19
22b
AcOH
N
O
N
O
N
Ar =
OHC
N
S
N
S
H
NH
N
NMe2
NH
N
DMF-DMA
Dioxane
PhHN
N
Ar
21b
N
PhHN
23
O
Ph
NH
EtOH / pip.
EtOH / pip.
N
O
AcOH
-NHMe2
N
Ph
O
N
N
O
N
NH
Ph
S
NH
N
S
N
N
S
NH
N
N
Ph
O
O
NH
NH
N
NH
N
N
PhHN
PhHN
PhHN
25
24
26
Scheme 3. Reactions of aminopyrazole with some electrophilic reagents.
corresponding to a molecular formula C25H16N4OS2. In contrast to
the behavior of the intermediate 2 towards phenacyl bromide, it
has been found that, the in situ reaction of 2 with 2-chloro-N-p-
elemental analysis and spectral data. The IR spectrum of thiazoline
9 revealed the absence of C^N absorption band and the presence of
new absorption bands at 3430, 3345 cmꢀ1 assignable to the amino
group and a band at 1231 cmꢀ1 due to C]S group. The 1H NMR
spectrum of compound 10 was characterized by the existence of
tolylacetamide afforded thiazolidin-4-one
4 rather than the
expected thiazoline 5. The formation of thiazolidin-4-one 4 may be
rationalized through the first S-alkylation followed by nucleophilic
addition of NH group to the amidic carbonyl followed by elimina-
tion of p-toluidine. The structure of the isolated product 4 was
elucidated on the basis of their spectral data (IR, MS and 1H NMR)
and also, by independent synthesis via treatment of the interme-
diate 2 with ethyl chloroacetate.
Treatment of the non-isolable potassium salt 2 with dilute
hydrochloric acid furnished the corresponding thiocarbamoyl
derivative 6. Oxidative cyclization of thiocarbamoyl derivative 6
with bromine in ethyl acetate furnished 2-(benzothiazol-2-yli-
dene)-N-(benzothiazol-2-yl)-2-cyanoacetamide (7). The formation
of benzothiazole 7 is in the line with previous reports [48,49].
On the other hand, thiazolidin-4-one 8 could be achieved via the
reaction of amide 1 with thioglycolic acid in boiling pyridine. The
Gewald reaction of amide 1 with elemental sulfur and phenyl iso-
thiocyanate in a mixture of EtOH/DMF containing triethylamine as
a basic catalyst led to functionalized thiazoline 9. Cyclization of
thiazoline 9 with triethyl orthoformate in acetic anhydride afforded
thiazolo[4,5-d]pyrimidine 10 as deazapurine analogue. The struc-
ture of the prepared compounds was elucidated on the basis of
thiazolopyrimidine H-5 at
d 9.39 ppm. Its mass spectrum showed
a molecular ion peak at m/z ¼ 394 corresponding to a molecular
formula C18H10N4OS3.
Shifting to Scheme 2, 2-amino-N-(benzothiazol-2-yl)-4,5,6,7-
tetrahydrobenzothiophene-3-carboxamide (11) could be achieved
according to the method described by Gewald, by reacting amide 1
with sulfur and cyclohexanone in the presence of morpholine as
a basic catalyst. The assignment of the structure of compound 11
was based on analytical and spectroscopic data. Thus, its IR spec-
trum displayed absorption bands at 3440, 3333 and 3210 cmꢀ1
assignable to NH2 and NH groups. The mass spectrum showed
a molecular ion peak at m/z ¼ 329 corresponding to a molecular
formula C16H15N3OS2.
To investigate the structureeactivity relationship with respect
to antimicrobial properties we cyclized the thiocarbamoyl func-
tionality of compound 6 to thiophene. Thus, refluxing of thio-
carbamoyl derivative 6 with phenacyl bromide and/or ethyl
chloroacetate in dimethylformamide containing a catalytic amount
of triethylamine afforded 4-amino-2-anilino-3-[(benzothiazol-2-
ylamino)carbonyl]-5-benzoylthiophene (12) and ethyl 3-amino-5-

S. Bondock et al. / European Journal of Medicinal Chemistry 45 (2010) 3692e3701
3695
anilino-4-[(benzothiazol-2-ylamino)carbonyl]thiophene-2-
carboxylate (13), respectively. The IR spectra of the isolated prod-
ucts showed the absence of C^N group and the presence of NH2
group at 3425e3370 cmꢀ1. The 1H NMR spectrum of compound 12
Furthermore, the reaction of aminopyrazole 19 with 3-(N,N-
dimethylamino)-1-(thiophen-2-yl)prop-2-en-1-one [60] in glacial
acetic acid at reflux afforded pyrazolo[1,5-a]pyrimidine derivative
21b rather than 21a. The reaction product 21b was confirmed on
the basis of its elemental analysis and spectral data. The formation
of compound 21b is assumed to take place via an initial Michael
addition of the exocyclic amino group in 19 to the activated double
bond in enaminone followed by cyclization and aromatization via
loss of both dimethylamine and water molecules.
showed three singlet signals at
d 13.35, 11.83 and 8.78 ppm due to
amidic NH, NH and NH2 protons, respectively. Moreover, the mass
spectrum showed a molecular ion peak at m/z ¼ 470 corresponding
to a molecular formula C25H18N4O2S2.
To further explore the synthetic potentially of amide 1, the
Knoevenagel condensation of amide 1 with 1,3-diphenylpyrazole-
4-carboxaldehyde [50] was investigated. Heating amide 1 with 1,3-
The reactivity of aminopyrazole 19 towards benzylidene malo-
nonitrile was also investigated as an alterative route to obtain pyr-
diphenylpyrazole-4-carboxaldehyde
in
ethanolic
sodium
azolo[1,5-a]pyrimidine derivative. Thus, reaction of 19 with a-
hydroxide (10%) afforded N-(benzothiazol-2-yl)-2-cyano-3-(1,3-
diphenyl-1H-pyrazol-4-yl)acrylamide (14). The addition of hydra-
zine hydrate to the activated double bond of compound 14 in
boiling ethanol afforded 5-amino-N-(benzothiazol-2-yl)-10,30-
diphenyl-1H,10H-3,40-bipyrazole-4-carboxamide (15).
Coupling of amide 1 with diazotized 3-amino-4,6-dimethyl-2H-
pyrazolo[3,4-b]pyridine [51] in pyridine at 0e5 ꢁC gave the
hydrazono derivative 16. Formation of the triazine derivative 17
was achieved in an excellent yield by heating compound 16 in
glacial acetic acid. Elemental analysis, IR, NMR and MS are in
agreement with the proposed structure.
cyanocinnamonitrile in ethanolic sodium ethoxide solution yielded
product for which structure 22a or 22b seemed possible. Structure
22aappearsmorelikelythan22bonthebasisthatringnitrogenisthe
most steric hindrance center in the molecule [61]. The structure of
22awas assigned on thebasis of elemental analysis andspectral data.
Moreover, heating 19 with dimethylformamideedimethylacetal
(DMFeDMA) in dioxane furnished azaenaminopyrazole 23 in
a reasonable yield. Elemental analysis and spectral data were in
agreement with the formation of the azaenamine product 23. Its 1H
NMR spectrum showed a new singlet signals at
d 3.19, 3.23 and
8.33 ppm corresponding to the protons of the two methyl groups
and the methine proton. The mass spectrum showed a molecular
ion peak at m/z ¼ 405 corresponding to a molecular formula
C20H19N7OS. Compound 23 was converted to pyrazolo[3,4-d]
pyrimidine derivative 24 upon heating in glacial acetic acid.
In addition, the condensation of 19 with 1,3-diphenylpyrazole-4-
carboxaldehyde and isatin in boiling ethanol in the presence of
catalytic amount of piperidine furnished the corresponding Schiff’s
base 25 and 26 in excellent yield. The chemical structure of 25 and 26
were supported on the basis of elemental analysis and spectral data.
On the other hand, the 3-amino-5-anilinopyrazole 19 was
served as key intermediate in Scheme 3. It was prepared in two
consequence steps by reacting 1 with phenyl isothiocyanate and
methyl iodide in basic dimethylformamide to give the ketene N,S-
acetal 18 that reacted with hydrazine hydrate in boiling ethanol to
give the target compound 19. The structure of the aminopyrazole
19 was identified as the reaction product on the basis of its
elemental analysis and spectroscopic data. Its IR spectrum dis-
played the lacks of absorption band assignable to the C^N group
and the presence of a new absorption band at 3412, 3355 cmꢀ1
1
assignable to NH2 group. The H NMR spectrum displayed a broad
singlet signal at
a multiplet signals at
protons, and another three singlet signals at
d
6.43 ppm corresponding to the NH2 protons,
6.86e7.84 ppm related to the aromatic
9.32, 11.09 and
3. Pharmacology
d
d
3.1. Antimicrobial evaluation
12.99 ppm assignable to three NH protons. The 13C NMR spectrum
was characterized by signals at 116e140 ppm assignable to
aromatic carbons and a signal at 166 ppm corresponding to
carbonyl carbon atom. Moreover, the mass spectrum showed
a molecular ion peak at (Mþ) m/z ¼ 350 corresponding to
a molecular formula C17H14N6OS.
3(5)-Aminopyrazoles are versatile reagents and have been
extensively used as synthetic starting materials for the synthesis
of several polysubstituted fused pyrazoles of potential biological
activity [52e55]. It was thus of interest to study the reactivity of
5-aminopyrazole 19 towards a variety of chemical reagents. The
general literature procedure [56e59] for the synthesis of pyrazolo
[1,5-a]pyrimidines involves cyclocondensation of aminopyrazoles
Fourteen of the newly synthesized target compounds were
evaluated for their in vitro antibacterial activity against Staphylo-
coccus aureus (ATCC 25923) and Streptococcus pyogenes (ATCC
19615) as examples of Gram-positive bacteria and Pseudomonas
phaseolicola (GSPB 2828) and Pseudomonas fluorescens (S 97) as
examples of Gram-negative bacteria. They were also evaluated for
their in vitro antifungal potential against Fusarium oxysporum and
Aspergillus fumigatus fungal strains.
Agar-diffusion method was used for the determination of the
preliminary antibacterial and antifungal activity. Chlor-
oamphenicol, cephalothin and cycloheximide were used as refer-
ence drugs. The results were recorded for each tested compound as
the average diameter of inhibition zones (IZ) of bacterial or fungal
growth around the disks in mm. The minimum inhibitory
concentration (MIC) measurement was determined for compounds
showed significant growth inhibition zones (>12 mm) using
with reagents having 1,3-electrophilic centers such as b-diketones
or enaminones. Cyclocondensation of compound 19 with either
acetyl acetone or acetoacetanilide in boiling acetic acid produced
in each case a single product, as evidenced by TLC. The reaction
products can be formulated as pyrazolo[1,5-a]pyrimidine deriva-
tives 20a and 20b, evidence for assigned structures being
provided by analytical and spectroscopic data. For example, The IR
spectrum of compound 20a showed the appearance of absorption
band at 1661 cmꢀ1 corresponding to the amidic carbonyl group.
The 1H NMR spectrum exhibited two additional singlet signals at
twofold serial dilution method [62]. The MIC (
mg/mL) and inhibition
zone diameters values are recorded in Table 1.
The results depicted in Table 1 revealed that most of tested
compounds displayed variable inhibitory effects on the growth of
the tested Gram-positive and Gram-negative bacterial strains, and
also against antifungal strains.
d
2.46 and 2.54 ppm assignable to the protons of two methyl
In general, most of the tested compounds revealed better activity
against the Gram-positive rather than the Gram-negative bacteria. It
would be also noticed that compounds belonging to the thiophene
and pyrazole series (Schemes 2 and 3) exhibited better antibacterial
potentials than members of the thiazole one (Scheme 1).
groups in pyrimidine ring and a singlet signal at 6.82 ppm for
d
proton in the pyrimidine ring. The mass spectrum showed
a molecular ion peak at m/z ¼ 414 corresponding to a molecular
formula C22H18N6OS.

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S. Bondock et al. / European Journal of Medicinal Chemistry 45 (2010) 3692e3701
Table 1
Minimal inhibitory concentrations (MIC,
m
g/mL) and inhibition zone (mm) of some new synthesized compounds.
Compound no.
MICa in
Bacteria
mg/mL, and zone of inhibition (mm)
Fungi
Gram-positive bacteria
Gram-negative bacteria
S. aureus
S. pyogenes
P. phaseolicola
P. fluorescens
F. oxysporum
A. fumigatus
3
4
7a
8
9
11
12
13
15
17
20b
21b
24
25
50 (19)
100 (15)
25 (25)
100 (15)
100 (14)
25 (25)
100 (14)
100 (15)
50 (19)
100 (14)
50 (20)
100 (14)
50 (19)
50 (19)
100 (14)
100 (15)
25 (26)
100 (15)
6.25 (38)
100 (15)
50 (19)
100 (17)
100 (14)
6.25 (37)
100 (16)
100 (16)
50 (20)
e
100 (15)
100 (14)
100 (15)
100 (16)
12.5 (31)
100 (15)
100 (14)
100 (14)
50 (19)
6.25 (38)
50 (19)
eb
25 (26)
25 (25)
50 (20)
100 (16)
50 (19)
e
12.5 (32)
6.25 (38)
6.25 (38)
3.125 (43)
12.5 (32)
100 (14)
25 (25)
100 (14)
100 (15)
3.125 (44)
100 (14)
6.25 (38)
6.25 (37)
6.25 (38)
6.25 (38)
100 (15)
6.25 (37)
100 (15)
100 (15)
6.25 (37)
12.5 (31)
e
50 (20)
12.5 (32)
50 (19)
50 (18)
100 (15)
50 (19)
25 (26)
50 (19)
100 (14)
25 (26)
100 (15)
100 (14)
100 (15)
6.25 (37)
50 (19)
25 (26)
Reference drugs
Chloramphenicol
Cephalothin
Cycloheximide
3.125 (42)
6.25 (36)
NT
3.125 (44)
6.25 (37)
NT
6.25 (37)
6.25 (38)
NT
6.25 (38)
6.25 (37)
NT
NTc
NT
3.125 (43)
NT
NT
3.125 (42)
a
MIC: Minimal inhibitory concentration values with SEM ¼ 0.02.
(e): totally inactive (no inhibition zone).
NT: Not tested.
b
c
Regarding the structureeactivity relationship of the thiophenes
also the antimicrobial activity. On the other hand, incorporation of
benzothiazole nucleus to thiazole derivatives at position 2 in
compounds 3, 4, and 8 unfortunately produced weak antimicrobial
activity. High biological activity can be correlated with low electron
density of ring systems.
In conclusion, the objective of the present study was to
synthesize and investigate the antimicrobial activities of some new
thiazoles, thiophenes and pyrazoles incorporating benzothiazole
moiety with the hope of discovering new structure leads serving as
potent antimicrobial agents. Our aim has been verified by the
synthesis of three different groups of structure hybrids comprising
basically the benzothiazole moiety attached to either poly-
substituted thiazole, thiophene or pyrazole counter parts through
various linkages of synthergistic purpose. The obtained results
clearly revealed that compounds derived from thiophenes and
pyrazoles exhibited better antimicrobial activity than their thiazole
structure variants.
against Gram-positive bacteria, the results revealed that
compounds 11, 12, and 13 exhibited broad spectrum antibacterial
profile against the tested organisms. Thiophenes with electron
withdrawing groups such as CO2Et or PhCO recorded higher
activity. In this view, compound 13 was equipotent to chlor-
oamphenicol in inhibiting the growth of S. aureus (MIC 3.125 mg/
mL), while its activity was 50% lower than of chloroamphenicol
against S. pyogenes. Compounds 11 and 12 showed 50% of the
activity of chloroamphenicol (MIC 6.25
equipotent to cephalothin in inhibiting the growth of S. aureus and
S. pyogenes (MIC 6.25 g/mL).
mg/mL) but they were
m
On the other hand, compounds 3, 7a, 8, 9, 15, 20b and 24
exhibited weak to moderate growth inhibitory activity against
Gram-positive bacteria as revealed from their MIC values
(25e100
tively good growth inhibitory profiles against S. aureus (MIC
12.5 g/mL) which were about 25% of the activity of chlor-
mg/mL). Among these compounds 9 and 15 showed rela-
m
oamphenicol and 50% of cephalothin against the same organism.
Moreover, distinctive anti-Gram-positive profile was displayed by
compound 25 where it proved to be equipotent as chlor-
4. Experimental
All melting points were measured on a Gallenkamp electro-
thermal melting point apparatus. IR spectra were recorded for KBr
disc on a Mattson 5000 FTIR spectrophotometer. 1H NMR spectra
were measured on a Bruker AC 300 (300 MHz) in CDCl3 or DMSO-d6
as solvent, using TMS as an internal standard, and chemical shifts
are expressed as dppm. Mass spectra were determined on Finnigan
Incos 500 (70 ev). Elemental analyses were carried out in the
Microanalytical Unit of the Faculty of Science, Cairo University. N-
(Benzothiazol-2-yl)-2-cyanoacetamide (1) [47], 1,3-diphenyl-pyr-
azole-4-carboxaldehyde [50], 4,6-dimethyl-1H-pyrazolo[3,4-b]
pyridin-3-amine [51], and 3-(N,N-dimethylamino)-1-(thiophen-2-
yl)prop-2-en-1-one [60] were prepared following literature
procedure.
oamphenicol against S. aureus (MIC 3.125
mg/mL) together with
a significant activity against S. pyogenes (MIC 6.25
mg/mL).
Concerning the antibacterial activity of the compounds 3, 12, 15,
and 20b revealed weak growth inhibitory against the tested Gram-
negative bacteria (MIC 50
mg/mL). On the other hand, compounds 8
and 24 showed equipotent activity as chloroamphenicol and
cephalothin (MIC 6.25
mg/mL) against P. fluorescens and P.
phaseolicola.
Regarding the activity of thiazoles, thiophenes and pyrazoles
incorporating benzothiazole moiety, against antifungal strains, the
results revealed that compounds 3 and 21 were 50% lower than
cycloheximide in inhibitory the growth of A. fumigatus and F. oxy-
sporum(MIC6.25
mg/mL),whilethereactivityofcompound9was 25%
lower than cycloheximide against F. oxysporum (MIC 12. 5
m
g/mL).
4.1. General procedure for the synthesis of thiazoline (3) and
thiazolidin-4-one (4)
The substitution pattern was also crucial. It is worth mentioning
that incorporation of benzothiazole to thiophene nucleus at posi-
tion 3 via a carboxamide linker produced a high antimicrobial
activity. Conversion of aminopyrazole 19 to Schiff base 25 enhanced
To a cold suspension of powdered divided KOH (0.56 g,
0.01 mol) in DMF (20 mL) was added amide 1 (2.17 g, 0.01 mol) and

S. Bondock et al. / European Journal of Medicinal Chemistry 45 (2010) 3692e3701
3697
phenyl isothiocyanate (1.2 mL, 0.01 mol). The reaction mixture was
4.4. Synthesis of N-(benzothiazol-2-yl)-2-(4-oxo-4,5-
dihydrothiazol-2-yl) acetamide (8)
stirred at room temperature for 24 h, and then treated with phe-
nacyl bromide and/or 2-chloro-N-p-tolylacetamide (0.01 mol) and
the stirring was continued at room temperature for further 5 h. The
reaction mixture was poured into 50 mL of cold water. The resultant
solid products were collected by filtration and recrystallized from
a mixture of EtOH/DMF (1:1) to give compounds 3 and 4.
A mixture of compound 1 (2.17 g, 0.01 mol) and thioglycolic acid
(0.69 mL, 0.01 mol) in dry pyridine (20 mL) was heated under reflux
for 3 h, allowed to cool, and poured into cold water (50 mL). The
solid product obtained was collected by filtration, dried and
recrystallized from ethanol to give compound 8.
4.1.1. N-(Benzothiazol-2-yl)-2-cyano-2-(3,4-diphenylthiazol-2-
White crystals; Yield 62%; mp 350e352 ꢁC; IR (KBr): ymax
/
ylidene)acetamide (3)
cmꢀ1 ¼ 3165 (NH), 1699, 1664 (2C]O). 1H NMR (DMSO-d6):
dppm ¼ 2.77 (s, 2H, CH2), 3.34 (s, 2H, CH2eS), 7.23e7.86 (m, 4H, Ar-
H), 11.21 (s, 1H, NH). MS m/z (%): 291 (Mþ, 5.2), 178 (0.9), 150 (100),
114 (21.7), 105 (10.8), 98 (1.4), 77 (2.6), 68 (71.8). Anal. For
C12H9N3O2S2 (291.35) Calcd.: C 49.47; H 3.11; N 14.42%, Found: C
49.37; H 2.99; N 14.21%.
White powder; Yield 74%; mp 302e304 ꢁC; IR (KBr) ymax
/
cmꢀ1 ¼ 3384 (NH), 2178 (C^N), 1625 (C]O). 1H NMR (DMSO-d6):
dppm ¼ 7.18e7.86 (m, 15H, Ar-H, thiazoline H-5), 10.59 (s, 1H, NH).
MS m/z (%): 452 (Mþ, 16.3), 304 (17.6), 303 (100), 150 (2.4), 134
(12.7), 77 (14.2). Anal. For C25H16N4OS2 (452.55) Calcd.: C 66.35; H
3.56; N 12.38%, Found: C 66.32; H 3.49; N 12.19%.
4.5. Synthesis of 4-amino-N-(benzothiazol-2-yl)-2,3-dihydro-3-
phenyl-2-thioxo-thiazole -5-carboxamide (9)
4.1.2. N-(Benzothiazol-2-yl)-2-cyano-2-(4-oxo-3-
phenylthiazolidin-2-ylidene)acetamide (4)
Pale yellow sheets; Yield 66%; mp 214e216 ꢁC; IR (KBr) ymax
/
To a solution of amide 1 (2.17 g, 0.01 mol) in ethanol (15 mL)
containing triethylamine (0.5 mL), elemental sulfur (0.32 g,
0.01 mol) and phenyl isothiocyanate (1.35 mL, 0.01 mol) were
added. The reaction mixture was heated at 60 ꢁC for 2 h with
continuous stirring and then poured into a beaker containing an
ice-water mixture with few drops of HCl. The formed solid product
was collected by filtration, dried and recrystallized from EtOH to
give compound 9.
cmꢀ1 ¼ 3488 (NH), 2208 (C^N), 1736 (C]O), 1643 (C]O). 1H NMR
(CDCl3): dppm ¼ 3.95 (s, 2H, CH2), 7.26e7.83 (m, 9H, Ar-H), 11.35 (s,
1H, NH). MS m/z (%): 392 (Mþ, 30.5), 244 (11.4), 243 (70.6), 217 (6.8),
215 (100), 169 (21.5), 150 (8.2), 132 (34.3), 77 (62.3). Anal. For
C19H12N4O2S2 (392.45) Calcd.: C 58.15; H 3.08; N 14.28%, Found: C
57.97; H 2.98; N 14.31%.
Yellow sheets; Yield 72%; mp 242e244 ꢁC, IR (KBr) ymax
/
cmꢀ1 ¼ 3430, 3345 (NH2), 3253 (NH), 1690 (C]O), 1231 (C]S). 1H
NMR (DMSO-d6): dppm ¼ 7.14 (s, 2H, NH2), 7.31e7.91 (m, 9H, Ar-H),
10.62 (s, 1H, NH). MS m/z (%): 384 (Mþ, 100), 235 (87.8), 208 (29),
178 (10), 176 (34.7), 150 (71.1), 136 (40.8), 77 (80.6). Anal. For
C17H12N4OS3 (384.50) Calcd.: C 53.10; H 3.15; N 14.57%, Found: C
52.84; H 2.99; N 14.23%.
4.2. Synthesis of 3-anilino-N-(benzothiazol-2-yl)-2-cyano-3-
thioxopropanamide (6)
To a stirred solution of powdered KOH (0.56 g, 0.01 mol) in DMF
(20 mL) was added compound 1 (2.17 g, 0.01 mol). After the
mixture was stirred for 0.5 h, phenyl isothiocyanate (1.2 mL,
0.01 mol) was added and the stirring was continued at room
temperature for 24 h. The reaction mixture was poured onto
(100 mL) ice-cold water containing few drops of HCl (0.1 N). The
solid product that separated was filtered, washed with water and
recrystallized from EtOH to give compound 6.
4.6. Synthesis of 6-(benzothiazol-2-yl)-2,3-dihydro-3-phenyl-2-
thioxothiazolo[4,5-d] pyrimidin-7(6H)-one (10)
A solution of compound 9 (3.8 g, 0.01 mol) in a mixture of
triethyl orthoformate (2.5 mL) and acetic anhydride (2.5 mL) was
heated under reflux for 8 h and then allowed to cool. The precipi-
tate that formed was collected by filtration, dried and recrystallized
from acetic acid to give compound 10.
Yellow crystals; Yield 82%; mp 202e204 ꢁC; IR (KBr) ymax
/
cmꢀ1 ¼ 3440, 3227 (2NH), 2183 (C^N), 1636 (C]O), 1288 (C]S).
1H NMR (DMSO-d6): dppm ¼ 4.28 (s, 1H, CH), 7.10e7.80 (m, 9H, Ar-
H), 9.85 (s, 1H, NH), 13.52 (s, 1H, CONH). Anal. For C17H12N4OS2
(352.43) Calcd.: C 57.93; H 3.43; N 18.90%, Found: C 57.82; H 3.37; N
18.75%.
Yellow brightness crystals; Yield 43%; mp 316e318 ꢁC, IR (KBr)
ymax/cmꢀ1 ¼ 1686 (C]O), 1249 (C]S). 1H NMR (DMSO-d6):
dppm ¼ 7.24e7.74 (m, 9H, Ar-H), 9.39 (s, 1H, thiazolopyrimidine H-
5). MS m/z (%): 394 (Mþ, 46.3), 351 (9.8), 320 (17.1), 225 (51.2), 134
(34.1), 96 (68.3), 77 (100), 69 (24.4). Anal. For C18H10N4OS3 (394.49)
Calcd.: C 54.80; H 2.56; N 14.20%, Found: C 54.59; H 2.38; N 14.08%.
4.3. Synthesis of 2-(benzothiazol-2-ylidene)-N-(benzothiazol-2-yl)-
2-cyanoacetamide (7)
To a cold suspension of compound 6 (0.352 g, 0.001 mol) in ethyl
acetate (20 mL), pyridine (1.6 mL) was added dropwise during
10 min, with stirring. The solution of bromine (0.16 g, 0.002 mol) in
ethyl acetate (10 mL) was added dropwise during 10 min and the
stirring was continued for further 3 h. The yellow precipitate
formed was filtered and washed with ethyl acetate followed by
ether. The product was dried and recrystallized from a mixture of
EtOH/DMF (1:1) to give compound 7.
4.7. Synthesis of 2-amino-N-(benzothiazol-2-yl)-4,5,6,7-
tetrahydrobenzothiophene-3-carboxamide (11)
A mixture of compound 1 (2.17 g, 0.01 mol), cyclohexanone
(0.98 g, 0.01 mol), and elemental sulfur (0.35 g, 0.015 mol) in
ethanol (20 mL) containing morpholine (0.87 g, 0.01 mol) was
heated at 60 ꢁC for 2 h with stirring. After the reaction mixture was
allowed to cool, the precipitate that formed was collected by
filtration, dried and recrystallized from chloroform to give 11.
Pale yellow crystals; Yield 55%; mp 238e240 ꢁC; IR (KBr) ymax
/
cmꢀ1 ¼ 3436, 3190 (2NH), 2223 (C^N), 1685 (C]O). 1H NMR
(DMSO-d6): dppm ¼ 7.06e8.33 (m, 8H, Ar-H), 8.72 (s, 1H, NH), 10.01
(s, 1H, NH). MS m/z (%): 350 (Mþ, 42.8), 202 (2.6), 178 (2.8), 174 (24),
150 (100),149 (8.4),135 (3.2),123 (9.8),110 (6.4), 77 (29.3). Anal. For
C17H10N4OS2 (350.42) Calcd.: C 58.27; H 2.88; N 15.99%, Found: C
58.12; H 2.71; N 15.76%.
Pale yellow crystals; Yield 86%; mp 250e252 ꢁC; IR (KBr) ymax
/
cmꢀ1 ¼ 3440, 3333 (NH2), 3210 (NH), 1635 (C]O). 1H NMR (DMSO-
d6): dppm ¼ 1.10e1.16 (m, 8H, ring 4CH2), 5.98 (s, 2H, NH2),
7.25e7.92 (m, 4H, Ar-H), 11.97 (s, 1H, NH). MS m/z (%): 329 (Mþ,
30.5), 181 (11.7), 179 (100), 153 (5.5), 150 (24.3), 118 (21.2), 77 (13.2).

3698
S. Bondock et al. / European Journal of Medicinal Chemistry 45 (2010) 3692e3701
Anal. For C16H15N3OS2 (329.44) Calcd.: C 58.33; H 4.59; N 12.76%,
Found: C 58.24; H 4.41; N 12.63%.
(DMSO-d6): dppm ¼ 7.39e8.04 (m, 14H, Ar-H), 8.36 (s, 1H, pyrazole
H-5), 8.68 (s, 2H, NH2), 9.15 (s, 1H, NH), 10.82 (s, 1H, CONH). MS m/z
(%): 477 (Mþ, 14.2), 259 (1), 244 (5.3), 220 (1.6), 178 (3), 150 (0.8),
144 (3.2), 77 (100), 68 (0.4). Anal. For C26H19N7OS (477.54) Calcd.: C
65.39; H 4.01; N 20.53%, Found: C 65.21; H 3.95: N 20.42%.
4.8. General procedure for synthesis of thiophene derivatives (12)
and (13)
To a solution of compound 6 (3.52 g, 0.01 mol) in 20 mL ethanol,
the appropriate
a-halocarbonyl compounds such as phenacyl
4.11. Synthesis of N-(benzothiazol-2-yl)-2-cyano-2-[(4,6-dimethyl-
bromide and ethyl chloroacetate (0.01 mol) and few drops of trie-
thylamine was added. The reaction mixture was refluxed for 5 h,
and then allowed to cool. The formed solid product was collected
by filtration, washed with ethanol and recrystallized from
a mixture of EtOH/DMF (2:1) to afford the corresponding thiophene
derivatives 12 and 13.
1H-pyrazolo[3,4-b]pyridine-3-yl)hydrazono]acetamide (16)
To a cold solution of compound 1 (2.17 g, 0.01 mol) in pyridine
(15 mL), was added the diazonium salt of 4,6-dimethyl-2H-pyr-
azolo[3,4-b]pyridine-3-yl [prepared by dissolving sodium nitrite
(0.07 g, 0.01 mol) in water (2 mL) and adding to a cold solution of 3-
amino-4,6-dimethyl-2H-pyrazolo[3,4-b]pyridine (1.62 g, 0.01 mol)
containing the appropriate amount of hydrochloric acid with
continuous stirring] portion wise over a period of 30 min. The
reaction mixture was kept in an ice bath for 24 h and then diluted
with water, filtered off, dried, and recrystallized from a mixture of
DMF/EtOH (2:1) to afford compound 16.
4.8.1. 4-Amino-2-anilino-3-[(benzothiazol-2-ylamino)carbonyl]-5-
benzoylthiophene (12)
Pale yellow crystals; Yield 72%; mp 292e294 ꢁC; IR (KBr) ymax
/
cmꢀ1 ¼ 3425, 3370 (NH2), 3233 (NH), 3190 (NH), 1723 (C]O), 1620
(C]O), 1562 (C]N). 1H NMR (DMSO-d6): dppm ¼ 7.21e7.89 (m, 14H,
Ar-H), 8.78 (br.s, 2H, NH2), 11.83 (s, 1H, NH), 13.35 (s, 1H, CONH). MS
m/z (%): 470 (Mþ, 41), 454 (6.2), 350 (1.2), 322 (3.7), 320 (31.6), 319
(90), 294 (12.6), 217 (7), 202 (7.6), 178 (5.8), 177 (11.6), 176 (11.2),
150 (15.7), 135 (2.7), 106 (7.6), 98 (1.7), 92 (4.5), 84 (10.7), 77 (100).
Anal. For C25H18N4O2S2 (470.57) Calcd.: C 63.81; H 3.86; N 11.91%,
Found: C 63.74; H 3.79; N 11.68%.
Orange crystals; Yield 91%; mp 290e292 ꢁC; IR (KBr) ymax
/
cmꢀ1 ¼ 3367, 3287, 3190 (3NH), 2202 (C^N), 1650 (C]O). 1H NMR
(DMSO-d6): dppm ¼ 2.52 (s, 3H, CH3), 2.70 (s, 3H, CH3), 7.13 (s, 1H,
pyridine H-5), 7.24e7.86 (m, 4H, Ar-H), 8.12 (s, 1H, NH), 8.65 (s, 1H,
NH), 9.61 (s, 1H, CONH). MS m/z (%): 390 (Mþ, 100), 358 (7.1), 346
(21), 241 (28.3), 174 (20.2), 162 (20.3), 150 (39), 147 (10), 77 (15.8).
Anal. For C18H14N8OS (390.42) Calcd.: C 55.37; H 3.61; N 28.70%,
Found: C 55.24; H 3.58; N 28.59%.
4.8.2. Ethyl 3-amino-5-anilino-4-[(benzothiazol-2-ylamino)
carbonyl]thiophene-2-carboxylate (13)
Yellow powder; Yield 76%; mp 262e264 ꢁC; IR (KBr) ymax
/
cmꢀ1 ¼ 3425, 3365 (NH2), 3340, 3270 (2NH), 1660, 1645 (2C]O),
1560 (C]N). 1H NMR (DMSO-d6): dppm ¼ 1.21 (t, J ¼ 7.2 Hz, 3H,
CH3), 4.11 (q, J ¼ 7.2 Hz, 2H, OeCH2), 7.23e7.84 (m, 9H, Ar-H), 8.21
(s, 2H, NH2), 11.74 (s, 1H, NH), 13.53 (s, 1H, CONH). MS m/z (%): 438
(Mþ, 44), 366 (1.6), 290 (2.4), 262 (4.2), 242 (100), 178 (1.2), 151
(21.8), 84 (7.7), 77 (50.7). Anal. For C21H18N4O3S2 (438.52) Calcd.: C
57.52; H 4.14; N 12.78%, Found: C 57.42; H 4.03; N 12.59%.
4.12. Synthesis of N-(benzothiazol-2-yl)-4-imino-8,10-dimethyl-
4,6-dihydropyrido [20,30:3,4]pyrazolo[5,1-c][1,2,4]triazine-3-
carboxamide (17)
A solution of compound 16 (3.9 g, 0.01 mol) in glacial acetic acid
(15 mL) was refluxed for 2 h, and then allowed to cool. The
precipitate that formed was collected by filtration, washed with
ethanol and recrystallized from a mixture of DMF/EtOH (1:1) to
give compound 17.
4.9. Synthesis of N-(benzothiazol-2-yl)-2-cyano-3-(1,3-diphenyl-
1H-pyrazol-4-yl) acrylamide (14)
Yellow crystals; Yield 86%; mp 362e364 ꢁC; IR (KBr) ymax
/
cmꢀ1 ¼3437, 3394, 3158, 3201 (4NH),1675 (C]O). 1H NMR (DMSO-
d6): dppm ¼ 2.72 (s, 3H, CH3), 3.01 (s, 3H, CH3), 7.25 (s, 1H, pyridine
H-5), 7.41e8.12 (m, 4H, Ar-H), 9.18 (s,1H, NH), 9.62 (s,1H, NH),12.51
(s, 1H, CONH). Anal. For C18H14N8OS (390.42) Calcd.: C 55.37; H
3.61; N 28.70%, Found: C 55.29; H 3.56; N 28.62%.
To a solution of compound 1 (2.17 g, 0.01 mol) in absolute
ethanol (15 mL) containing 3 drops of sodium hydroxide (10%), 1,3-
diphenyl-pyrazole-4-carboxaldehyde (2.48 g, 0.01 mol) was added.
The reaction mixture was heated under reflux for 1 h, and then
allowed to cool. The precipitate that formed was collected by
filtration, washed with ethanol, dried and recrystallized from
a mixture of EtOH/DMF (1:1) to give compound 14.
Yellow powders; Yield 87%; mp 296e298 ꢁC; IR (KBr) ymax
/
4.13. Synthesis of 3-anilino-N-(benzothiazol-2-yl)-2-cyano-3-
(methylthio)acrylamide (18)
cmꢀ1 ¼ 3430 (NH), 2214 (C^N), 1628 (C]O). MS m/z (%): 447 (Mþ,
12.8), 298 (100), 231 (48), 149 (12.8), 113 (38.3), 108 (25.5), 77
(13.8). Anal. For C26H17N5OS (447.51) Calcd.: C 69.78; H 3.83; N
15.65%, Found: C 69.76; H 3.68; N 15.64%.
To a stirred solution of potassium hydroxide (0.56 g, 0.01 mol) in
dimethylformamide (20 mL) was added compound 1 (2.17 g,
0.01 mol). After the mixture was stirred for 30 min, phenyl iso-
thiocyanate (1.2 mL, 0.01 mol) was added to the resulting mixture.
Stirring was continued for 6 h, and then methyl iodide (0.62 mL,
0.01 mol) was added and stirring was continued for additional 6 h.
The reaction mixture was poured onto ice-cold water. The solid
product that formed was collected by filtration, dried and recrys-
tallized from ethanol to give compound 18.
4.10. Synthesis of 5-amino-N-(benzothiazol-2-yl)-10,30-diphenyl-
1H,10H-3,40-bipyrazole-4-carboxamide (15)
To a boiling solution of compound 14 (4.47 g, 0.01 mol) in
ethanol (20 mL), hydrazine hydrate (1.5 mL, 0.01 mol) was added.
The reaction mixture was refluxed for 7 h and then cooled. The solid
product so formed was collected by filtration, washed with ethanol
and recrystallized from a mixture of DMF/EtOH (1:1) to give
compound 15.
Orange crystals; Yield 86%; mp 163e165 ꢁC; IR (KBr) ymax
/
cmꢀ1 ¼3447, 3395 (2NH), 2192 (C^N),1627 (C]O),1600 (C]C). 1H
NMR (CDCl3): dppm ¼ 2.25 (s, 3H, SCH3), 7.26e7.81 (m, 9H, Ar-H),
9.82 (s, 1H, NH), 12.19 (s, 1H, CONH). Anal. For C18H14N4OS2 (366.46)
Calcd.: C 58.99; H 3.85; N 15.29%, Found: C 58.76; H 3.59; N 15.06%.
Yellow crystals; Yield 43%; mp 228e230 ꢁC; IR (KBr) ymax
/
cmꢀ1 ¼ 3432, 3418 (NH2), 3317, 3245 (2NH), 1659(C]O). 1H NMR

S. Bondock et al. / European Journal of Medicinal Chemistry 45 (2010) 3692e3701
3699
4.14. Synthesis of 5-amino-3-anilino-N-(benzothiazol-2-yl)-1H-
pyrazole-4-carboxamide (19)
5), 8.71 (d, J ¼ 4.6 Hz, 1H, pyrimidine H-4), 9.12 (s, 1H, Ph-NH), 11.40
(s, 1H, CONH). MS m/z (%): 468 (Mþ, 51), 319 (100), 292 (11.5), 189
(8.2), 162 (3.4), 149 (2.5), 84 (4.6), 77 (5.9), 65 (10). Anal. For
C24H16N6OS2 (468.55) Calcd.: C 61.52; H 3.44; N 17.94%, Found: C
61.41; H 3.32; N 17.83%.
A mixture of compound 18 (3.66 g, 0.01 mol) and hydrazine
hydrate 98% (0.01 mol) were heated on a steam bath for 1 h, then
left to cool. The reaction mixture was triturated with ethanol and
the resulting solid was filtered off and recrystallized from ethanol
to give compound 19.
4.17. Synthesis of 7-amino-2-anilino-N-(benzothiazol-2-yl)-6-
cyano-5-phenyl-pyrazolo[1,5-a]pyrimidine-3-carboxamide (22a)
White crystals; Yield 73%; mp 216e218 ꢁC; IR (KBr) ymax
/
cmꢀ1 ¼ 3412, 3355 (NH2), 3302, 3240, 3179 (3NH), 1620 (C]O). 1H
NMR (DMSO-d6): dppm ¼ 6.43 (br.s, 2H, NH2), 6.86e7.84 (m, 9H, Ar-
H), 9.32 (s, 1H, NH), 11.09 (s, 1H, NH), 12.99 (s, 1H, CONH). 13C NMR
(DMSO-d6): dppm ¼ 89.9, 115.9 (2C), 116.3, 118.9, 121.8, 126.0, 129.1
(2C), 130.6, 133.2, 140.0, 142.8, 144.4, 150.5, 151.2, 166.2. MS m/z (%):
350 (Mþ, 80), 201 (80.2), 200 (100), 174 (15.6), 159 (2.1), 151 (24.2),
150 (26.2), 145 (19.1), 117 (13.7), 77 (44.5). Anal. For C17H14N6OS
(350.40) Calcd.: C 58.27; H 4.03; N 23.98%, Found: C 58.12; H 3.97; N
23.69%.
2-Benzylidene malononitrile (1.54 g, 0.01 mol) was added to
a mixture of aminopyrazole 19 (3.5 g, 0.01 mol) in sodium ethoxide
(prepared from 0.23 g of sodium metal and 20 mL of absolute
ethanol). The reaction mixture was heated under reflux for 8 h, left
to cool and poured onto ice-cold water containing few drops of 1 N
HCl. The precipitate that formed was collected by filtration, washed
with ethanol and recrystallized from ethanol to afford compound
22a.
Yellow crystals; Yield 44%; mp 340e342 ꢁC; IR (KBr) ymax
/
cmꢀ1 ¼ 3430, 3313 (NH2), 3231, 3165 (2NH), 2216 (C^N), 1650 (C]
O). 1H NMR (DMSO-d6): dppm ¼ 7.02e7.98 (m, 14H, Ar-H), 8.35 (s,
2H, NH2), 9.16 (s, 1H, NH), 11.43 (s, 1H, CONH). MS m/z (%): 502 (Mþ,
27.5), 383 (60), 354 (23.8), 326 (100), 217 (12.5), 217 (13), 77 (60).
Anal. For C27H18N8OS (502.55) Calcd.: C 64.53; H 3.61; N 22.30%,
Found: C 64.26; H 3.57; N 22.23%.
4.15. General procedure for the reaction of 3(5)-aminopyrazole 19
with 1,3-dicarbonyl compounds
To a mixture of compound 19 (3.5 g, 0.01 mol) in glacial acetic
acid (25 mL), an appropriate 1,3-dicarbonyl compounds (acetyla-
cetone or acetoacetanilide) (0.01) was added. The reaction mixture
was refluxed for 12 h, and then poured into crushed ice. The solid
product was collected by filtration, dried and recrystallized from
a suitable solvent to give compounds 20a and 20b.
4.18. Synthesis of 3-anilino-N-(benzothiazol-2-yl)-5-
((dimethylamino)methyleneamino)-1H-pyrazole-4-carboxamide
(23)
4.15.1. N-(Benzothiazol-2-yl)-5,7-dimethyl-2-(phenylamino)
pyrazolo[1,5-a]pyrimidine-3-carboxamide (20a)
To a solution of compound 19 (3.5 g, 0.01 mol) in dry dioxane
(20 mL), N,N-dimethylformamideedimethylacetal (DMFeDMA)
(1.32 mL, 0.01 mol) was added. The reaction mixture was refluxed
for 2 h. After cooling, the precipitated product that formed was
collected by filtration, washed with petroleum ether (40e60 ꢁC),
dried and recrystallized from a mixture of EtOH/DMF (1:1) to give
compound 23.
Deep brown crystals (DMF); Yield 46%; mp 242e244 ꢁC; IR (KBr)
ymax/cmꢀ1 ¼ 3428, 3336 (2NH), 1661 (C]O), 1601 (C]C), 1535 (Ar).
1H NMR (DMSO-d6): dppm ¼ 2.46 (s, 3H, CH3), 2.54 (s, 3H, CH3), 6.82
(s, 1H, pyrimidine-H), 6.96e7.92 (m, 9H, Ar-H), 8.80 (s, 1H, NH),
11.08 (s, 1H, CONH). MS m/z (%): 414 (Mþ, 15.1), 266 (17), 265 (100),
238 (5.4), 150 (1.1), 107 (3.6), 77 (5.6), 65 (10.5), 67 (4.1). Anal. For
C22H18N6OS (414.48) Calcd.: C 63.75; H 4.38; N 20.28%, Found: C
63.42; H 4.19; N 20.08%.
White crystals; Yield 62%; mp 304e306 ꢁC; IR (KBr) ymax
/
cmꢀ1 ¼ 3420, 3352, 3174 (3NH), 1649 (C]O), 1610 (C]N). 1H NMR
(DMSO-d6): dppm ¼ 3.19 (s, 3H, NCH3), 3.23 (s, 3H, CH3), 6.86e7.98
(m, 9H, Ar-H), 8.33 (s, 1H, CH]N), 8.47 (s, 1H, NH),10.68 (s, 1H, NH),
12.07 (s, 1H, CONH). MS m/z (%): 405 (Mþ, 20.4), 360 (40), 312
(10.6), 255 (20.8), 211 (15), 177 (6.7), 161 (9.8), 77 (100), 68 (8.2).
Anal. For C20H19N7OS (405.48) Calcd.: C 59.24; H 4.72; N 24.18%,
Found: C 59.13; H 4.72; N 24.23%.
4.15.2. 2-Anilino-N-(benzothiazol-2-yl)-7-hydroxy-5-methyl-
pyrazolo[1,5-a]pyrimidine-3-carboxamide (20b)
Buff powder (DMF/CHCl3); Yield 86%; mp 308e310 ꢁC; IR (KBr)
ymax/cmꢀ1 ¼ 3430 (OH), 3285, 3186 (2NH), 1665 (C]O). 1H NMR
(DMSO-d6): dppm ¼ 2.46 (s, 3H, CH3), 6.83 (s, 1H, pyrimidine-H),
6.96e7.96 (m, 9H, Ar-H), 9.57 (s, 1H, NH), 11.49 (s, 1H, CONH), 13.35
(s, 1H, OH). MS m/z (%): 416 (Mþ, 93.2), 268 (34.1), 237 (34.1), 267
(100), 240 (84.1), 225 (39.4), 176 (69.7), 150 (95.5), 123 (45.5), 97
(11.4), 82 (23.5), 77 (84.1). Anal. For C21H16N6O2S (416.46) Calcd.: C
60.56; H 3.87; N 20.18%, Found: C 60.42; H 3.69; N 20.20%.
4.19. Synthesis of 3-anilino-5-(benzothiazol-2-yl)-1,5-dihydro-4H-
pyrazolo[3,4-d]pyrimidin-4-one (24)
A solution of compound 23 (4 g, 0.01 mol) in glacial acetic acid
(20 mL), was refluxed for 1 h, and then allowed to cool. The
precipitate that formed was collected by filtration, washed with
ethanol, dried and recrystallized from a mixture of DMF/EtOH (1:1)
to give compound 24.
4.16. Synthesis of 2-anilino-N-(benzothiazol-2-yl)-7-(thiophen-2-
yl)pyrazolo[1,5-a]pyrimidine-3-carboxamide (21b)
Gray sheets; Yield 47%; mp 322e324 ꢁC; IR (KBr) ymax
/
A solution of compound 19 (3.5 g, 0.01 mol) in glacial acetic acid
(15 mL) and 3-(dimethylamino)-1-(thiophen-2-yl)prop-2-en-1-
one (2.39 g, 0.01 mol) was heated under reflux for 3 h. The solvent
was evaporated under vacuum and the residue was triturated with
ethanol. The solid deposited was collected by filtration and
recrystallized from ethanol to give compound 21b.
cmꢀ1 ¼ 3293 (NH), 1664 (C]O),1600 (CH]N). 1H NMR (DMSO-d6):
dppm ¼ 6.83e7.68 (m, 9H, Ar-H), 8.03 (s, 1H, NH), 8.67 (s, 1H, CH]
N). MS m/z (%): 360 (Mþ, 45.9), 226 (2.3), 200 (11), 187 (2.3), 157
(8.7), 150 (26.1), 135 (21.6), 77 (100). Anal. for C18H12N6OS (360.39)
Calcd.: C 59.99; H 3.36; N 23.32%, Found: C 59.73; H 3.26; N 23.19%.
Yellow crystals; Yield 90%; mp 320e322 ꢁC; IR (KBr) ymax
/
4.20. General procedure for the reaction of 3(5)-aminopyrazole 19
with 1,3-diphenylpyrazole-4-carboxaldehyde and isatin
cmꢀ1 ¼ 3435, 3264 (2NH), 1661 (C]O), 1601 (C]N). 1H NMR
(DMSO-d6): dppm ¼ 7.06 (t, J ¼ 7.8 Hz, 1H, thiophene H-4), 7.30e7.68
(m, 9H, Ar-H), 7.74 (d, J ¼ 8 Hz, 1H, thiophene H-3), 8.26 (d,
J ¼ 7.5 Hz, 1H, thiophene H-5), 8.53 (d, J ¼ 4.8 Hz, 1H, pyrimidine H-
A mixture of compound 19 (3.5 g, 0.01 mol) and 1,3-diphe-
nylpyrazole-4-carboxaldehyde or isatin (0.02 mol) in ethanol

3700
S. Bondock et al. / European Journal of Medicinal Chemistry 45 (2010) 3692e3701
(30 mL) containing a few drops of piperidine (3 drops) was refluxed
for 5 h. The reaction mixture was cooled and the solid obtained was
collected by filtration, washed with ethanol, dried, and recrystal-
lized from an appropriate solvent to give compounds 25 and 26.
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Acknowledgments
The authors are very grateful to Dr. Ibrahim Hassan, Department
of Botany diseases, Faculty of Agriculture, Al-Azahr University,
Cairo, Egypt for performing the antimicrobial evaluation.

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