Microwave-assisted synthesis of some novel azoles and azolopyrimidines as antimicrobial agents

Article abstract of DOI:10.3390/molecules22030346

In this study, new derivatives of pyrazole, isoxazole, pyrazolylthiazole, and azolopyrimidine having a thiophene ring were synthesized under microwave irradiation. Their pharmacological activity toward bacteria and fungi inhibition was screened and compared to the references Chloramphenicol and Trimethoprim/sulphamethoxazole. The antimicrobial results of the investigated compounds revealed promising results and some derivatives have activities similar to the references used.

Full text of DOI:10.3390/molecules22030346

molecules
Article
Microwave-Assisted Synthesis of some Novel Azoles
and Azolopyrimidines as Antimicrobial Agents
1
1,2,
*, Yahia Nasser Mabkhot *, Mohie E. M. Zayed 4
3,
Sobhi M. Gomha , Thoraya A. Farghaly
and Amany M. G. Mohamed 1
1
Department of Chemistry, Faculty of Science, Cairo University, Giza 12613, Egypt;
s.m.gomha@gmail.com (S.M.G.); amaaniq21@yahoo.com (A.M.G.M.)
Department of Chemistry, Faculty of Applied Science, Umm Al-Qura University,
Makkah-Al-mukkarramah 21514, Saudi Arabia
Department of Chemistry, College of Science, King Saud University, P.O. Box 2455, Riyadh-11451,
Saudi Arabia
2
3
4
Chemistry Department, Faculty of Science, King Abdulaziz University, Jeddah B.O. 208203, Saudi Arabia,
mohiem@yahoo.com
*
Correspondence: thoraya-f@hotmail.com (T.A.F.); yahia@ksu.edu.sa (Y.N.M.);
Tel.: +20-1006-745-618 (T.A.F.); +966-11-467-5898 (Y.N.M.); Fax: +966-11-467-5992 (Y.N.M.)
Academic Editors: Panayiotis A. Koutentis and Derek J. McPhee
Received: 1 January 2017; Accepted: 21 February 2017; Published: 23 February 2017
Abstract: In this study, new derivatives of pyrazole, isoxazole, pyrazolylthiazole, and
azolopyrimidine having a thiophene ring were synthesized under microwave irradiation. Their
pharmacological activity toward bacteria and fungi inhibition was screened and compared to the
references Chloramphenicol and Trimethoprim/sulphamethoxazole. The antimicrobial results of the
investigated compounds revealed promising results and some derivatives have activities similar to
the references used.
Keywords: thiophenes; pyrazoles; thiazoles; antimicrobial activity; microwave irradiation
1
. Introduction
Five-membered heterocyclic ring systems are very significant class of compounds, not only
due to their abundance in nature, but also for their chemical and biological value. Thiophene
derivatives have been fully-known for their therapeutic applications. They possess antihypertensive [ ],
antimicrobial [ ], diabetes mellitus [ ], antiviral [ ], analgesic and anti-inflammatory [ ], and antitumor
activities [ ]. Pyrazoles and thiazoles exist in many naturally occurring substances and representing
an interesting array of azole compounds. They have a wide range of biological activities as for example,
anti-inflammatory [ ], antimicrobial [10 13], Akt kinase inhibitive [14], anticonvulsant [15], and
antitumor activities [16]. On the other hand, microwave-assisted organic synthesis is a tool by which
we can achieve goals in a few minutes with high yield as compared to conventional heating [17 21].
Motivated by these findings, and in continuation of our ongoing research program dealing with the
synthesis of bioactive heterocyclic ring systems [22 26], we were encouraged to synthesize heterocyclic
1
2
3
4
5
6,7
8,
9
–
–
–
having thiophene incorporated pyrazole, thiazole, and/or pyrimidine derivatives under microwave
irradiation to investigate their antimicrobial activity.
2
. Results and Discussion
2
.1. Synthesis
1
,3-Di(thiophen-2-yl)prop-2-en-1-one 1 was cyclized with different types of nitrogen nucleophiles,
namely, thiosemicarbazide, hydrazine derivatives 3a
–
c, and hydroxylamine hydrochloride which
Molecules 2017, 22, 346; doi:10.3390/molecules22030346
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Molecules 2017, 22, 346
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afforded pyrazole derivatives
2,
4a–
c
and isoxazole derivative
5, respectively (Scheme 1). The previous
reactions were carried out under conventional heating and under microwave irradiation as shown
in Table 1. The heating under microwave was more efficient than thermal heating as it reduced the
reaction time and increased the product yields in all cases.
It was reported that pyrazolylthiazole derivatives have a wide range of biological activities
such as antimicrobial [27], anti-inflammatory [27], hypotensive [28], and antitumor activities [29].
So we became interested in synthesizing the pyrazolylthiazole derivatives from the reaction of
1
-thiocarbamoyl-3,5-di-(2-thienyl)-2-pyrazoline
heating or microwave irradiation of mixture of carbothioic acid amide derivative
arylpropanehydrazonoyl chloride 6a in dioxane in the existence of a base catalyst yielded in each case
only one isolated product (Scheme 2). The spectroscopic information confirmed the reaction products
2
with hydrazonoyl chlorides. Thus, conventional
2
and 2-oxo-N-
–
e
8
a
–
e
. For example, the mass spectra of the isolated products 8a
–
e
displayed the expected molecular
1
ion. Also, all derivatives 8a
–
e
showed in their H-NMR spectra the characteristic signals for CH , H-5,
3
and CH (see experimental part). The structure of products
8
was further supported by an alternative
with 2-hydrazinyl-4-methyl-5-(phenyldiazenyl)thiazole
under reflux in ethanol led to the formation of product 8a (Scheme 2).
2
synthesis. Thus, reaction of compound
1
9
Scheme 1. Synthesis of pyrazoline derivatives 2, 4a–c, and 5.
Table 1. Comparison between conventional heating and microwave irradiation for synthesis of
compounds 4a–c, 8a–e, 11a,b, 13, and 15.
Reaction Times
Conventional Methods
Reaction Yields (%)
Compound No.
2
Microwave
Conventional Methods
Microwave
2 h [30]
4 h
5 h
5h
6 h
6 h
8 h
10 h
8 h
10 h
10 h
15 h
10 h
13 h
3 min
5 min
8 min
10 min
10 min
8 min
10 min
12 min
9 min
13 min
12 min
15 min
15 min
20 min
66 [30]
70
73
69
67
74
76
68
72
75
70
60
67
84
85
90
88
82
95
90
92
93
90
89
81
88
85
4a
4
4
b
c
5
8a
8
8
b
c
8
8
d
e
1
1
1a
1b
1
3
15
60

Molecules 2017, 22, 346
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Scheme 2. Synthesis of arylazothiazole derivatives 8a–e.
Azolopyrimidines 11a
amines 10a
thermal heating and microwave irradiation for comparison (Scheme 3). Similar to the preparation of
compounds , and 8a , the use of microwave irradiation was more effective in the synthesis of
,
b,
13, and 15 were prepared via the reaction of chalcone
1
with heterocyclic
,b, 12, and 14 in ethanol in the presence of catalytic amount of AcOH using both
2
,
4,
5
–e
azolopyrimidines as illustrated in Table 1. The structure of compounds 11a
by different spectroscopic techniques like IR, H-NMR, mass, and elemental analysis. The IR spectra
,
b
,
13, and 15 was confirmed
1
of 11a
the presence of absorption band for NH group at 3402–3429 cm . The H-NMR spectra of 11a, as
example, showed three characteristic signals for the two CH-pyrimidine, triazole-H, and NH at 5.14
d, J = 4 Hz, 1Ha, CH-pyrimidine), 6.20 (d, J = 4 Hz, 1Hb, CH-pyrimidine), 8.45 (1H, s, triazole-H),
,b, 13, and 15 revealed the absence of any absorption bands for carbonyl group in addition to
−
1
1
δ
(
8
.73 (s, br, 1H, NH).
Scheme 3. Synthesis of azolopyrimidine derivatives 11a,b, 13 and 15.
2
.2. Antimicrobial Activity
In vitro antimicrobial screening of compounds 2, 4a–c, 5, 8a–e, 11a,b, 13,and 15 prepared in
the study was carried out using cultures of two fungal strains Aspergillus niger (ATCC) (ASP) and
Candida albicans (ATCC10231) (CA), as well as three bacteria species, namely, Gram positive bacteria,
Staphylococcus aureus (ATCC 29213) (SA), and Bacillus subtilus (ATCC 6051) (BS) and the Gram negative

Molecules 2017, 22, 346
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bacteria is Escherichia coli (ATCC 25922) (EC). Chloramphenicol and Trimethoprim/sulphamethoxazole
antibacterial agents were used as references to evaluate the potency of the examined compounds
under the same conditions. The activity was investigated by measuring the diameter of inhibition
zone (IZD) in mm
±
standard deviation beyond well diameter (6 mm) generated on a range of
environmental and clinically pathogenic microorganisms (gram-positive and gram-negative bacteria
and fungi) utilizing (0.1 g/mL) concentration of tested samples and the outcomes are portrayed in
Table 2. For the antifungal activity: All tested compounds were inactive against Aspergillus niger
(
1
ATCC) (ASP) while, compounds 4c
0231) (CA) with inhibition zones 23, 24, and 25 respectively. For the antibacterial activity: it was found
that Gram positive bacteria are more sensitive to the tested compounds especially SA rather than BS as
five compounds 4c 8b 8d, and 15 have potent activity against SA while for BS only compounds 4a
and 4c showed good activity. In the case of Gram negative activity with EC, two derivatives and
revealed higher activity. The used solvent DMSO concentration did not exhibit any influence on
bacteria or fungi.
, 8c, and 11b have excellent activity against Candida albicans (ATCC
2
,
,
,
2
8
c
Table 2. Antimicrobial activity of compounds 2, 4a–c, 5, 8a–e, 11a,b, 13, and 15 compared to reference drug.
Gram
Positive Bacteria
Gram Negative
Bacteria
Fungi
Compound Number
ASP
CA
SA
BS
EC
2
NA.
N.A.
N.A.
N.A.
N.A.
N.A
N.A.
N.A.
N.A.
N.A.
N.A.
N.A.
N.A.
N.A.
29
NA.
21
18
17
22
19
12
21
18
22
18
N.A.
19
14
21
30
20
N.A.
19
20
18
20
12
18
18
15
12
14
N.A.
17
11
19
24
23
N.A.
23
15
18
17
17
11
12
23
17
13
10
11
8
4
a
N.A.
20
23
9
10
8
24
N.A.
8
4
4
b
c
5
8
a
8
8
b
c
8
8
d
e
11a
1b
9
1
25
12
11
25
13
N.A.
1
1
3
5
15
29
24
N.A.
Chloramphenicol
Trimethoprim/sulphamethoxazole
DMSO
2.4
N.A.
High activity
Moderate activity
Low activity
N.A. (No activity)
3
. Materials and Methods
3
.1. General Experimental Procedures
Melting points were measured with an IA 9000-series digital melting-point apparatus (Bibby
Sci. Lim. Stone, Staffordshire, UK). Solvents were generally distilled and dried by standard literature
procedures prior to use. IR spectra were recorded in potassium bromide discs on FTIR 8101 PC infrared
spectrophotometers (Shimadzu, Tokyo, Japan). NMR spectra were recorded on a Mercury VX-300
1
NMR spectrometer (Varian, Inc., Karlsruhe, Germany) operating at 300 MHz ( H-NMR) and run in
deuterated dimethylsulfoxide (DMSO-d ). Chemical shifts were related to that of the solvent. Mass
6
spectra were recorded on a Shimadzu GCeMS-QP1000 EX mass spectrometer (Tokyo, Japan) at 70 eV.
Microwave reactions were performed with a Millstone Organic Synthesis Unit with a touch control
terminal (MicroSYNTH, Giza, Egypt) and a continuous focused microwave power delivery system in
a pressure glass vessel (10 mL) sealed with a septum under magnetic stirring. The temperature of the
reaction mixture was monitored using a calibrated infrared temperature control under the reaction

Molecules 2017, 22, 346
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vessel, and control of the pressure was performed with a pressure sensor connected to the septum
of the vessel. Elemental analyses were carried out at the Microanalytical Centre of Cairo University,
Giza, Egypt. Compounds 10a,b, 12, and 14 were purchased from Sigma-Aldrich and utilized as it is
without previous treatments. Compounds
the respective literature [30–32].
1, 2, 6a–e, and 9 were prepared as previously reported in
3
.2. Synthesis of Pyrazoline Derivatives 4a–c
Method A: A mixture of chalcone
1
(0.220 g, 1 mmol) and hydrazine derivative (1 mmol) in
ethanol (20 mL) in the presence of catalytic drops of acetic acid was refluxed for 3–5 h (monitored by
TLC). The reaction mixture was poured into water and the solid product was collected by filtration
followed by washing with ethanol. The crude products were then recrystallized from ethanol to give
pure pyrazolines 4a–c, respectively.
Method B: Repetition of the same reactions of method A with heating in a microwave oven at
◦
5
00 W and 120 C for a period of time. The reaction mixture was treated similar to method A to obtain
compounds 4a–c. Compounds 4a–c with their physical constants and spectral data are depicted as
shown below:
3
-(3,5-Di(thiophen-2-yl)-4,5-dihydro-1H-pyrazol-1-yl)-5,6-diphenyl-1,2,4-triazine (4a). Brown solid, m.p.
◦
−1
1
187–189 C; IR: 3083, 2926 (C-H), 1593 (C=N) cm ; H-NMR (300 MHz, DMSO-d ):
δ
3.05 (dd, 1H,
6
H , J = 17.2, 6.1 Hz), 4.13 (dd, 1H, H , J = 17.2, 12.0 Hz), 6.20 (dd, 1H, H , J = 12.0, 6.1 Hz), 7.18–8.24
A
B
X
+
(
m, 16H, Ar-H); MS, m/z (%) 465 (M , 8), 316 (34), 222 (38), 105 (100), 77 (72), 64 (80). Anal. Calcd. For
C H N S (465.11): C, 67.07; H, 4.11; N, 15.04; found: C, 66.87; H, 4.24; N, 14.90.
26
19
5 2
3
-(3,5-DI(thiophen-2-yl)-4,5-dihydro-1H-pyrazol-1-yl)-3,4-dihydroquinoxalin-2(1H)-one (4b). Brown solid,
◦
−1
1
m.p. 170–172 C; IR: 3435, 3158 (2NH), 3048, 2966 (C-H), 1596 (C=N) cm ; H-NMR (300 MHz,
DMSO-d6): 3.05 (dd, 1H, H , J = 17.2, 6.1 Hz), 4.10 (dd, 1H, H , J = 17.2, 12.0 Hz), 6.18 (dd, 1H, H ,
J = 12.0, 6.1 Hz), 7.04–7.99 (m, 10H, Ar-H), 11.88 (s, br, 1H, NH); MS, m/z (%) 378 (M , 5), 274 (28),
δ
A
B
X
+
1
53 (70), 77 (65), 43 (100). Anal. Calcd. For C H N OS (378.47): C, 60.30; H, 3.73; N, 14.80; found:
19 14 4 2
C, 60.03; H, 3.92; N, 14.52.
2
-(3,5-Di(thiophen-2-yl)-4,5-dihydro-1H-pyrazol-1-yl)-5,7-di(thiophen-2-yl)pyrido[2,3-d]pyrimidin-4(3H)-one
◦
−1
1
(
(
1
4c). Brown solid, m.p. 188–190 C; IR: 3435, 3158 (2NH), 3048, 2966 (C-H), 1596 (C=N) cm ; H-NMR
300 MHz, DMSO-d6): 3.07 (dd, 1H, H , J = 17.2, 6.1 Hz), 4.15 (dd, 1H, H , J = 17.2, 12.0 Hz), 6.16 (dd,
H, H , J = 12.0, 6.1 Hz), 6.92–7.75 (m, 12H, Ar-H), 7.98 (s, 1H, pyridine-H ), 8.63 (s, br, 1H, NH); MS,
δ
A
B
X
4
+
m/z (%) 543 (M , 14), 426 (50), 330 (49), 153 (83), 64 (100), 43 (68). Anal. Calcd. For C H N OS
4
26
17
5
(543.03): C, 57.44; H, 3.15; N, 12.88; found: C, 57.58; H, 3.10; N, 12.63.
3
.3. 3,5-Di(thiophen-2-yl)-4,5-dihydroisoxazole (5)
Method A: A mixture of chalcone (0.220 g, 1 mmol), hydroxylamine. HCl (0.069 g, 1 mmol),
1
and anhydrous sodium acetate (0.3 g) in acetic acid (20 mL) was stirred at room temperature for 6 h.
The formed solid was filtered, washed with water, and crystallized from dioxane to give isoxazoline
derivative 5.
Method B: The above reaction of chalcone
A were heated under microwave irradiation at 500 W and 150 C for 10 min. The reaction mixture was
1
and hydroxylamine with the same quantity in method
◦
◦
treated similarly to method A to obtain compounds
5
as yellow solid; m.p. 212–214 C; IR: 3091, 2922
−
C-H), 1593 (C=N) cm ; H-NMR (300 MHz, DMSO-d ): δ3.09 (dd, 1H, H , J = 17.2, 6.1 Hz), 4.13 (dd,
6 A
1 1
(
1
H, H , J = 17.2, 12.0 Hz), 6.08 (dd, 1H, H , J = 12.0, 6.1 Hz), 7.00–8.23 (m, 6H, Ar-H); MS, m/z (%) 335
B
X
+
(M , 24), 152 (65), 83 (100), 70 (21). Anal. Calcd. for C H NOS (235.01): C, 56.14; H, 3.85; N, 5.95;
11 9 2
found: C, 56.03; H, 3.72; N, 5.74.

Molecules 2017, 22, 346
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3
8
.4. Synthesis of 2-(3,5-Di(thiophen-2-yl)-4,5-dihydro-1H-pyrazol-1-yl)-4-methyl-5-(aryldiazenyl)thiazoles
a–e
Method A: A mixture of 3,5-di(thiophen-2-yl)-4,5-dihydro-1H-pyrazole-1-carbothioamide
2
(
0.293 g, 1 mmol) and the appropriate hydrazonoyl halides 6a (1 mmol) in dioxane (20 mL) containing
–e
TEA (0.5 mL) was refluxed for 6–10 h (monitored by TLC), allowed to cool and the solid formed was
filtered off, washed with ethanol, dried, and recrystallized from dimethylformamide to give 8a–e.
Method B: Repetition of the same reactions of method A with heating in microwave oven at
◦
5
00 W and 150 C for a period of time gave products identical in all respects with those separated from
method A.
2
-(3,5-Di(thiophen-2-yl)-4,5-dihydro-1H-pyrazol-1-yl)-4-methyl-5-(phenyldiazenyl)-thiazole (8a). Red solid,
◦
−1
1
m.p. 164–166 C; IR:2919 (C-H), 1603 (C=N) cm ; H-NMR (300 MHz, DMSO-d ):
δ
2.58 (s, 3H, CH3),
6
3
7
.07 (dd, 1H, H , J = 17.2, 6.1 Hz), 4.17 (dd, 1H, H , J = 17.2, 12.0 Hz), 6.21 (dd, 1H, H , J = 12.0, 6.1 Hz),
.00–7.84 (m, 11H, Ar-H); MS, m/z (%) 435 (M , 5), 339 (14), 205 (50), 75 (42), 50 (100). Anal. Calcd. for
A
B
X
+
C H N S (435.06): C, 57.90; H, 3.93; N, 16.08; found: C, 57.74; H, 3.77; N, 15.82.
21
17
5 3
2
-(3,5-Di(thiophen-2-yl)-4,5-dihydro-1H-pyrazol-1-yl)-4-methyl-5-(o-tolyldiazenyl)-thiazole (8b). Red solid,
◦
−1
1
m.p. 122–124 C; IR: 2921 (C-H), 1600 (C=N) cm ; H-NMR (300 MHz, DMSO-d ):
δ
2.04 (s, 3H, CH3),
6
2
.60 (s, 3H, CH ), 3.09 (dd, 1H, H , J = 17.2, 6.1 Hz), 4.19 (dd, 1H, H , J = 17.2, 12.0 Hz), 6.22 (dd, 1H,
3
A
B
+
H , J = 12.0, 6.1 Hz), 6.93–7.79 (m, 10H, Ar-H); MS, m/z (%) 449 (M , 18), 218 (12), 110 (48), 91 (100), 65
X
(
52). Anal. Calcd. for C H N S (449.08): C, 58.77; H, 4.26; N, 15.58; found: C, 58.52; H, 4.08; N, 15.46.
22 19 5 3
2
-(3,5-Di(thiophen-2-yl)-4,5-dihydro-1H-pyrazol-1-yl)-5-((4-methoxyphenyl)diazenyl)-4-methylthiazole (8c).
◦
−1
1
Red solid, m.p. 143–145 C; IR: 2923 (C-H), 1602 (C=N) cm ; H-NMR (300 MHz, DMSO-d ):
δ
2.56
6
(
6
s, 3H, CH ), 3.04 (dd, 1H, H , J = 17.2, 6.1 Hz), 3.83 (s, 3H, OCH ), 4.12 (dd, 1H, H , J = 17.2, 12.0 Hz),
.13 (dd, 1H, H , J = 12.0, 6.1 Hz), 6.92–7.82 (m, 10H, Ar-H); MS, m/z (%) 465 (M , 3), 368 (9), 218 (13),
X
3
A
3
B
+
1
11 (100), 43 (72). Anal. Calcd. for C H N OS (465.08): C, 56.75; H, 4.11; N, 15.04; found: C, 56.53;
22 19 5 3
H, 4.04; N, 14.86.
5
-((4-Chlorophenyl)diazenyl)-2-(3,5-di(thiophen-2-yl)-4,5-dihydro-1H-pyrazol-1-yl)-4-methylthiazole(8d).
◦
−1
1
Orange solid, m.p. 153–155 C; IR: 3063, 2922 (C-H), 1605 (C=N) cm ; H-NMR (300 MHz, DMSO-d ):
6
δ
2.56 (s, 3H, CH ), 3.08 (dd, 1H, H , J = 17.2, 6.1 Hz), 4.08 (dd, 1H, H , J = 17.2, 12.0 Hz), 6.16 (dd, 1H,
3 A B
+
+
H , J = 12.0, 6.1 Hz), 6.98–7.85 (m, 10H, Ar-H); MS, m/z (%) 471 (M +2, 1), 469 (M , 4), 368 (6), 264 (15),
X
1
11 (59), 77 (57), 43 (100). Anal. Calcd. for C H ClN S (469.03): C, 53.66; H, 3.43; N, 14.90; found:
21 16 5 3
C, 53.49; H, 3.40; N, 14.73.
2
-(3,5-Di(thiophen-2-yl)-4,5-dihydro-1H-pyrazol-1-yl)-4-methyl-5-((4-nitrophenyl)-diazenyl)thiazole (8e).
◦
−1
1
Brown solid, m.p. 162–164 C; IR: 3096, 2920 (C-H), 1590 (C=N) cm ; H-NMR (300 MHz, DMSO-d ):
6
δ
2.61 (s, 3H, CH ), 3.09 (dd, 1H, H , J = 17.2, 6.1 Hz), 4.11 (dd, 1H, H , J = 17.2, 12.0 Hz), 6.21 (dd, 1H,
3 A B
+
H , J = 12.0, 6.1 Hz), 6.58–7.95 (m, 10H, Ar-H); MS, m/z (%) 480 (M , 7), 427 (16), 232 (31), 111 (100),
X
7
7 (59), 43 (86). Anal. Calcd. for C H N O S (480.58): C, 52.48; H, 3.36; N, 17.49; found: C, 52.28; H,
21 16 6 2 3
3
.19; N, 17.33.
3
.5. Alternate Synthesis of 8a
Equimolar amounts of chalcone
1 (0.220 g, l mmol) and 2-hydrazinyl-4-methyl-5-(phenyldiazenyl)
thiazole ( ) (0.233 g, 1 mmol) in 2-propanol (10 mL), was refluxed for 2 h then cooled to room
9
temperature. The solid precipitated was filtered off, washed with water, dried, and recrystallized from
dimethylformamide to give the corresponding product, 8a which were identical in all aspects (m.p.,
mixed m.p. and IR spectra) with those obtained from reaction of 2 with 6a but in 70% yield.

Molecules 2017, 22, 346
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3
.6. General Method for Synthesis of Compounds 11a,b, 13, and 15
Method A: A mixture of chalcone (0.220 g, 1 mmol) and the appropriate heterocyclic amine
10a,b, 12 or 14) (1 mmol) in ethanol (20 mL) in the presence of catalytic drops of acetic acid was
1
(
refluxed for 10–15 h (monitored through TLC). The reaction mixture was poured into water and the
solid product was collected by filtration followed by washing with ethanol. The crude product was
then recrystallized from EtOH or DMF to give pure products 11a,b, 13, and 15, respectively.
Method B: Repetition of the same reactions of method A with heating in microwave oven at
◦
5
00 W and 150 C for a period of time gave products identical in all respects with those separated from
method A. Compounds 11a
,b,
13, and 15 with their physical constants and spectral data are depicted
as shown below:
◦
5
(
,7-Di(thiophen-2-yl)-4,7-dihydro-[1,2,4]triazolo[1,5-a]pyrimidine (11a). Yellow solid m.p. 241–243 C
−
1
1
DMF); IR: 3425 (NH), 3091, 2920 (C-H), 1599 (C=N), cm ; H-NMR: δ 5.14 (d, J = 4 Hz, 1Ha,
CH-pyrimidine), 6.20 (d, J = 4 Hz, 1Hb, CH-pyrimidine), 6.85–8.04 (m, 6H, Ar-H), 8.45 (1H, s,
+
triazole-H), 8.73 (s, br, 1H, NH); MS m/z (%): 286 (M , 31), 284 (100), 111 (52), 69 (44). Anal. Calcd. for
C H N S (286.03): C, 54.52; H, 3.52; N, 19.56; found: C, 54.40; H, 3.64; N, 19.51.
13
10
4 2
◦
,7-Di(thiophen-2-yl)-4,7-dihydrotetrazolo[1,5-a]pyrimidine (11b). Yellow solid, m.p. 266–268 C (DMF);
5
−
1 1
IR: 3402 (NH), 3087, 2924 (C-H), 1636 (C=N), cm ; H-NMR:
.08 (d, J = 4 Hz, 1Hb, CH-pyrimidine), 7.16–8.24 (m, 6H, Ar-H), 8.29 (s,br, 1H, NH); MS m/z (%): 287
δ 5.41 (d, J= 4 Hz, 1Ha, CH-pyrimidine),
6
(
+
M , 20), 259 (73), 220 (99), 111 (100), 65 (48). Anal. Calcd. for C H N S (287.03): C, 50.16; H, 3.16;
12 9 5 2
N, 24.37; found: C, 50.29; H, 3.07; N, 24.39.
◦
2
-Phenyl-5,7-di(thiophen-2-yl)-4,7-dihydropyrazolo[1,5-a]pyrimidine (13). Yellow solid m.p. 218–220 C
−
1 1
(DMF); IR: 3429 (NH), 3095, 3071, 2923 (C-H), 1596 (C=N) cm ; H-NMR:
δ
4.86 (d, J= 4 Hz, 1Ha,
CH-pyrimidine), 6.14 (d, J = 4 Hz, 1Hb, CH-pyrimidine), 6.59 (s, 1H, pyrazole-H), 6.80–8.25 (m, 11H,
+
Ar-H), 8.72 (s,br, 1H, NH); MS m/z (%): 361 (M , 27), 359 (100), 228 (16), 111 (49), 77 (63). Anal. Calcd.
for C H N S (361.07): C, 66.45; H, 4.18; N, 11.62; found: C, 66.61; H, 4.09; N, 11.60.
20
15
3 2
◦
,4-Di(thiophen-2-yl)-1,4-dihydrobenzo[4,5]imidazo[1,2-a]pyrimidine (15). Yellow solid, m.p. 230–232 C
EtOH); IR: 3412 (NH), 3077, 2920 (C-H), 1599 (C=N) cm ; H-NMR: δ 4.79 (d, J = 4 Hz, 1Ha,
2
(
−
1
1
CH-pyrimidine), 6.12 (d, J = 4 Hz, 1Hb, CH-pyrimidine), 6.69–8.27 (m, 10H, Ar-H), 8.49 (s, br, 1H, NH);
+
MS m/z (%): 335 (M , 18), 333 (100), 224 (23), 111 (50), 64 (53). Anal. Calcd. for C H N S (335.06):
18
13
3 2
C, 64.45; H, 3.91; N, 12.53; found: C, 64.68; H, 3.87; N, 12.49.
3
.7. Biological Activity
3
.7.1. Antimicrobial Activity
Antimicrobial activity was determined using the agar disc diffusion assay method as described
previously by Hossain et al. [33]. The tested organisms were sub-cultured on Trypticase soya agar
medium (Oxoid Laboratories, Corporate, UK) for bacteria and Sabouraud dextrose agar (Oxoid
Laboratories, Corporate, UK) for fungi. Chloramphenicol and Trimethoprim/sulphamethoxazole were
used as a positive control and DMSO solvent as a negative control. The plates were done in duplicate
◦
and average zone of inhibition was calculated. Bacterial cultures were incubated at 37 C for 24 h
◦
while the other fungal cultures were incubated at (25–30 C) for 3–5 days. Antimicrobial activity was
determined by measurement zone of inhibition.
3
.7.2. Media Used
Sabouraud dextrose agar: The medium used for isolation of pathogenic yeasts has the following
composition (g/L): glucose, 20; peptone, 10; agar, 25 and distilled water, 1 L, pH was adjusted at 5.4.
◦
The medium was autoclaved at 121 C for 15 min.

Molecules 2017, 22, 346
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Trypticase soya agar (TSA): The medium was used to cultivate tested bacteria. It contains (g/L)
Tryptone (Pancreatic Digest of Casein) 15.0 g, Soytone (Papaic Digest of Soybean Meal) 5.0 g, Sodium
◦
Chloride 5.0 g, Agar 15.0 g, and distilled water 1 L. The medium was autoclaved at 121 C for 15 min.
4
. Conclusions
At the end, we have succeeded in the synthesis of new derivatives of pyrazole, isoxazole,
pyrazolylthiazole, and azolopyrimidine incorporated with a thiophene ring under microwave
irradiation. Different spectroscopic methods and elemental analyses were used to confirm the
structures of the newly synthesized compounds. The antimicrobial results of the examined compounds
revealed promising results and some derivatives have activities similar to the references used.
Acknowledgments: The authors extend their sincere appreciation to the Deanship of Scientific Research at King
Saud University for its funding this Prolific Research group (PRG-1437-29).
Author Contributions: Sobhi M. Gomha, Mohie E.M. Zayed, and Amany M.G. Mohamed conceived and
designed the experiments; Mohie E.M. Zayed, and Amany M.G. Mohamed performed the experiments;
Sobhi M. Gomha, Yahia Nasser Mabkhot and Thoraya A. Farghaly analyzed the data; Sobhi M. Gomha,
Mohie E.M. Zayed, Amany M.G. Mohamed and Yahia Nasser Mabkhot contributed reagents/materials/analysis
tools; Thoraya A. Farghaly and Sobhi M. Gomha wrote the paper. All authors have read and approved the
final manuscript.
Conflicts of Interest: The authors declare no conflict of interest.
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2017 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access
article distributed under the terms and conditions of the Creative Commons Attribution
CC BY) license (http://creativecommons.org/licenses/by/4.0/).
(