Regioselective reaction: Synthesis, characterization and pharmacological studies of some new Mannich bases derived from 1,2,4-triazoles

Article abstract of DOI:10.1016/j.ejmech.2009.04.038

In the present investigation, a series of new 4[(3-substituted-1H-pyrazol-4-yl)methyleneamino]-5-substituted-2-[(4-methylpiperzine-1-yl)methyl]-2H-1,2,4-triazole-3(4H)-thiones (4) were synthesized by the aminomethylation of 4-(3-substituted-1H-pyrazol-3-y

Full text of DOI:10.1016/j.ejmech.2009.04.038

European Journal of Medicinal Chemistry 44 (2009) 3784–3787
Contents lists available at ScienceDirect
European Journal of Medicinal Chemistry
journal homepage: http://www.elsevier.com/locate/ejmech
Short communication
Regioselective reaction: Synthesis, characterization and pharmacological
studies of some new Mannich bases derived from 1,2,4-triazoles
,
b
c
Arun M. Isloor a , Balakrishna Kalluraya , Prashanth Shetty
*
a Department of Chemistry, National Institute of Technology-Karnataka, Surathkal, Mangalore 575 025, India
b Department of P.G Studies and Research in Chemistry, Mangalore University, Mangalagangothri 574 199, India
c Department of Pharmacology, NGSM Institute of Pharmaceutical Sciences, Paneer, Deralakatte, Mangalore 574160, India
a r t i c l e i n f o
a b s t r a c t
Article history:
In the present investigation, a series of new 4[(3-substituted-1H-pyrazol-4-yl)methyleneamino]-5-
substituted-2-[(4-methylpiperzine-1-yl)methyl]-2H-1,2,4-triazole-3(4H)-thiones (4) were synthesized
by the aminomethylation of 4-(3-substituted-1H-pyrazol-3-yl)methyleneamino-5-substituted-4H-1,2,4-
triazole-3-thiols (3) with formaldehyde and N-methylpiperzine. These newly synthesized Schiff and
Mannich bases were characterized by IR, 1H NMR, mass spectral data and elemental analyses. These
compounds were screened for their antibacterial and antifungal activity. Some of the compounds were
found to exhibit significant antimicrobial activity.
Received 15 August 2008
Received in revised form
10 April 2009
Accepted 23 April 2009
Available online 5 May 2009
Keywords:
1,2,4-Triazoles
Schiff bases
Ó 2009 Elsevier Masson SAS. All rights reserved.
Mannich bases
Antibacterial activity
Antifungal activity
1. Introduction
2. Chemistry
The 1,2,4-triazole and its derivatives were reported to exhibit
various pharmacological activities such as antimicrobial, analgesic,
anti-inflammatory, anticancer and antioxidant properties [1–4].
Some of the present day drugs such as Ribavirin (antiviral agent),
Rizatriptan (antimigraine agent), Alprazolam (anxiolytic agent),
Fluconazole and Itraconazole (antifungal agents) are the best
examples for potent molecules possessing triazole nucleus. Further
1,2-pyrazole derivatives were also found to possess various bio-
logical activities [5–7]. Many literatures have shown that Mannich
bases possess potent biological activities such as antibacterial,
antifungal, anti-inflammatory, antimalarial and pesticide proper-
ties [8–11]. Few Mannich bases derived from 1,2,4-triazoles
carrying N-methylpiperzine substituent were biologically active
[12,13]. In view of these facts and as continuation of our research on
pharmaceutically important heterocycles [14–16], hereby we
report the synthesis of a new series of Mannich bases containing
both 1,2,4-triazoles and pyrazole skeletons.
3-Substituted-4-amino-5-mercapto-1,2,4-triazoles (1) were
synthesized as reported in the literature [17,18] and 3-substituted-
1H-pyrazole-4-carbaldehyde (2) were synthesized by the Wils-
mayer Haack reaction of semicarbazones [19]. Condensation of
amino mercapto triazoles (1) with various 3-substituted-1H-pyr-
azole-4-carbaldehyde (2) in the presence of concentrated sulphuric
acid in ethanol–dioxane mixture yielded Schiff bases (3). Mannich
bases (4) were synthesized by reacting Schiff bases (3) with N-
methylpiperzine in the presence of formaldehyde and ethanol–
dioxane medium. Newly synthesized compounds (3 and 4) were
characterized by IR, NMR, mass spectral and C, H, N analyses
(Scheme 1; Tables 1 and 2).
3. Results and discussion
The antibacterial and antifungal screening revealed that some of
the tested compounds showed good inhibition at 3
mg/ml concen-
tration. The antibacterial screening indicated that among the tested
compounds, 4h showed excellent activity against all the tested
bacterial strains, namely Staphylococcus aureus, Bacillus subtilis,
Escherichia coli and Pseudomonas aeruginosa. The remaining
compounds found to be active at higher concentrations, e.g., 6 and
* Corresponding author. Fax: þ91 824 2474033.
E-mail address: isloor@yahoo.com (A.M. Isloor).
12.5 mg/ml.
0223-5234/$ – see front matter Ó 2009 Elsevier Masson SAS. All rights reserved.
doi:10.1016/j.ejmech.2009.04.038

A.M. Isloor et al. / European Journal of Medicinal Chemistry 44 (2009) 3784–3787
3785
1
4. Conclusions
R
CHO
N
N
A series of novel Mannich bases, namely 4[(3-substituted-1H-
pyrazol-4-yl)methyleneamino]-5-substituted-2-[(4-methylpiper
zine-1-yl)methyl]-2H-1,2,4-triazole-3(4H)-thiones were synthe-
sized and characterized by NMR, mass spectrometry and IR studies.
All the newly synthesized compounds were screened for their
antibacterial and antifungal activities by the method of minimum
inhibitory concentration (MIC). Antimicrobial study reveals that
compound 4h having p-chloro substitution exhibited maximum
inhibition against all the tested microorganisms. Similarly,
compounds 4k and 4l also showed significant activity against
microorganism P. aeruginosa, which have p-methoxy and p-methyl
substituent on the phenyl ring, respectively. All remaining
compounds showed moderate inhibition. 1,2,4-Triazole nucleus is
one of the active components present in all molecules. Also the
presence of N-methylpiperazine moiety is contributing to the net
biological activity of the system (Table 3).
R
+
SH
N
N
N
H
(1)
(2)
NH
2
+
EtOH/H
H
N
N
S
R
N
N
1
R
CH
(3)
N
N
H
R
1
HN
HCHO, Dioxan
5. Experimental
R
2
5.1. Chemistry
R
1
N
N
N
CH
2
Melting points were determined by open capillary method and
were uncorrected. The IR spectra (in KBr pellets) were recorded on
a Shimadzu FT-IR 157 spectrophotometer. 1H NMR spectra were
recorded on a Perkin–Elmer EM 300 MHz spectrometer using TMS
as internal standard. The mass spectra were recorded on a JEOL
JMS-D 300 spectrometer operating at 70 eV. Purity of the
compounds was checked by TLC silica coated plates obtained from
Merck.
R
2
S
R
N
1
R
N
CH
(4)
N
N
H
Where R = CH , C H , C H
6 5
3
3
7
1
R
= CH , C H , p-Cl.C H , p-OCH .C H , p-CH .C H
3 6 5 6 4 3 6 4 3 6 4
NR R =N methyl piperzine
5.2. 4-[(3-Substituted-1H-pyrazol-3-yl)methyleneamino]-5-
substituted-4H-1,2,4-triazole-3-thiols (3)
1
2
Scheme 1.
To a suspension of various 3-substituted-1H-pyrazole-4-car-
baldehyde (2; 10 mmol) in ethanol–dioxane mixture (2:1), an
equimolar amount of the corresponding 3-substituted-4-amino-5-
mercapto-1,2,4-triazole (4) was added. The suspension was heated
till a clear solution was obtained. Then 2–3 drops of concentrated
sulphuric acid was added and solution was refluxed on water bath
The antifungal screening revealed that among the tested
compounds, 4h and 4l showed excellent activity against fungal
strain Candida albicans at
3 mg/ml concentration. However,
remaining compounds were active at 6 mg/ml concentration.
Table 1
Characterization data of 4-[(3-substituted-1H-pyrazol-3-yl)methyleneamino]-5-substituted-4H-1,2,4-triazole-3-thiols.
Compound
R
R1
Melting point
(ꢀC)
Yield (%)
Molecular formula
(mol. wt.)
Analyses (%) found (calculated)
C
H
N
3a
3b
3c
3d
3e
3f
3g
3h
3i
CH3
CH3
CH3
CH3
C3H7
C3H7
C3H7
C3H7
C6H5
C6H5
C6H5
C6H5
CH3
C6H5
207–208
218–220
259–260
236–238
191–192
154–155
219–220
213–214
228–229
212–213
229–230
208–209
74
65
55
58
55
62
60
70
53
83
56
80
C8H10N6S (222)
C13H12N6S (284)
C14H14N6OS (314)
C14H14N6S (298)
C15H16N6S (312)
C16H18N6OS (342)
C16H18N6S (326)
C15H15ClN6S (346)
C13H12N6S (284)
C18H14N6S (346)
C19H16N6OS (376)
C19H16N6S (360)
43.21 (43.24)
54.90 (54.92)
53.52 (53.50)
56.36 (56.37)
57.71 (57.69)
56.18 (56.14)
58.90 (58.89)
51.95 (51.95)
54.93 (54.92)
62.40 (62.42)
60.63 (60.63)
63.32 (63.33)
4.53 (4.50)
4.25 (4.22)
4.46 (4.45)
4.65 (4.69)
5.13 (5.12)
5.25 (5.26)
5.53 (5.52)
4.30 (4.32)
4.23 (4.22)
4.03 (4.04)
4.27 (4.25)
4.46 (4.44)
37.82 (37.83)
29.56 (29.57)
26.78 (26.75)
28.15 (28.18)
26.90 (26.92)
24.54 (24.56)
25.77 (25.76)
24.23 (24.24)
29.59 (29.57)
24.30 (24.27)
2.34 (2.34)
4-OCH3 C6H4
4-CH3 C6H4
C6H5
4-OCH3 C6H4
4-CH3 C6H4
4-Cl C6H4
CH3
C6H5
4-OCH3 C6H4
4-CH3 C6H4
3j
3k
3l
23.35 (23.33)
IR (KBr, cmꢁ1): 3a, 3120 and 3050 (NH/SH str),1615 (C]N), 2835 (C–H str),1282 (C]S),1030 (C–S str); 3j, 3115 and 3018 (NH/SH str), 2932 (C–H str),1232 (C]S),1035 (C–S str).
1H NMR (CDCl3, 300 MHz): 3a,
11.58 (s,1H, NH of pyrazole), 7.9 (s, 1H of pyrazole, 5H), 2.45 (s, 3H methyl of pyrazole), 8.07 (s, 1H, N]C–H),1.95 (s, 3H triazole); 3b, 13.63 (br,
1H, SH), 2.24 (S, 3H, CH3), 7.3–7.9 (m, 6H, Ar–H and pyrazole 5H), 9.50 (s,1H, N]CH),12.9 (s,1H, NH); 3c, 11.58 (s,1H, NH of pyrazole), 7.904 (s,1H, 5H of pyrazole), 3.7 (s, 3H of
O–CH3), 8.07 (s, 1H, N]C–H), 1.95 (s, 3H of triazole); 3g, 11.58 (s, 1H, NH of pyrazole), 7.904 (s, 1H of pyrazole, 5H), 7.014–8.014 (m, 7H of p-methyl phenyl), 8.07 (s, 1H, N]C–
H); 3h, 11.58 (s, 1H, NH of pyrazole), 8.07 (s, 1H of pyrazole, 5H), 7.014–8.014 (m, 4H of p-chlorophenyl), 8.07 (s, 1H, N]C–H); 3k, 3.84 (s, 3H, OCH3), 7.0 (d, 2H, ortho protons
3.10
d
d
d
d
d
d
of p-anisyl, J ¼ 9 Hz), 7.66 (d, 2H, meta protons of p-anisyl, J ¼ 9 Hz), 7.4–8.0 (m, 6H, Ar–H and pyrazole 5H), 9.58 (s, 1H, N]CH), 12.9 (br s, 1H, NH), 13.97 (br s, 1H, SH); 3i,
d
(s, 3H, CH3), 13.85 (br s, 1H, SH), 7.35–8.0 (m, 6H, Ar–H and pyrazole 5H), 9.65 (s, 1H, N]CH), 12.8 (br s, 1H, NH). Mass: 3j, m/z 346 (Mþ), 176 (3-mercapto-4(H)-1,2,4-triazole),
169 (phenylpyrazolenitrile), 77 (phenyl nucleus); 3a, m/z 222 (Mþ), 115 (3-mercapto-4-(H)-1,2,4-triazole), 106 (methylpyrazolenitrile), 80 (loss of CNꢁ from 3-mercapto-4(H)-
1,2,4-triazole).

3786
A.M. Isloor et al. / European Journal of Medicinal Chemistry 44 (2009) 3784–3787
Table 2
Characterization data of 4[(3-substituted-1H-pyrazol-4-yl)methyleneamino]-5-substituted-2-[(4-methylpiperzine-1-yl)methyl]-2H-1,2,4-triazole-3(4H)-thiones.
Compound
R
R1
Melting point
(ꢀC)
Yield (%)
Molecular formula
(mol. wt.)
Analyses (%) found (calculated)
C
H
N
4a
4b
4c
4d
4e
4f
4g
4h
4i
CH3
CH3
CH3
CH3
C3H7
C3H7
C3H7
C3H7
C6H5
C6H5
C6H5
C6H5
CH3
C6H5
155–157
175–176
202–204
185–187
134–136
111–112
182–184
174–175
179–181
167–169
159–161
136–138
74
65
55
58
55
62
60
70
53
83
56
80
C14H22N8S (334)
C19H24N8S (396)
C20H26N8OS (426)
C20H26N8S (410)
C21H28N8S (424)
C22H30N8OS (454)
C22H30N8S (438)
C21H27ClN8S (458)
C19H24N8S (396)
C24H26N8S (458)
C25H28N8OS (488)
C25H28N8S (472)
50.34 (50.29)
57.54 (57.57)
56.39 (56.33)
58.56 (58.53)
59.40 (59.43)
58.18 (58.14)
60.30 (60.27)
55.02 (55.02)
53.08 (53.03)
62.93 (62.88)
61.38 (61.47)
63.48 (63.55)
6.34 (6.58)
6.08 (6.06)
6.14 (6.10)
6.30 (6.34)
6.35 (6.60)
6.58 (6.60)
6.90 (6.84)
5.75 (5.89)
7.20 (7.18)
5.50 (5.67)
5.68 (5.73)
5.97 (5.93)
33.45 (33.53)
28.30 (28.28)
26.32 (26.29)
27.30 (27.31)
26.42 (26.41)
24.56 (24.66)
25.56 (25.57)
24.45 (24.45)
30.98 (30.93)
24.48 (24.45)
22.90 (22.95)
23.67 (23.72)
4-OCH3 C6H4
4-CH3 C6H4
C6H5
4-OCH3 C6H4
4-CH3 C6H4
4-Cl C6H4
CH3
C6H5
4-OCH3 C6H4
4-CH3 C6H4
4j
4k
4l
IR (KBr, cmꢁ1): 4a, 3400 (NH str), 1612 (C]N), 2800 (CH str), 1280 (C]S), 1033 (C–S str), 800 (Ar–H str); 4e, 3390 (NH str), 1610 (C]N), 2792 (CH str), 1280 (C]S), 1030 (C–S
str), 810 (Ar–H str). 1H NMR (CDCl3, 300 MHz): 4a,
5.17 (s, 2H, N–CH2),1.58 (s, 3H, N–CH3), 2.2 (s, 3H, CH3), 2.8 (t, 4H, CH2–N–CH2), 3.6 (t, 4H, CH2–N–CH2), 7.12–8.2 (m, 6H, Ar–
H and pyrazole 5H), 10.18 (s, 1H, N]CH), 12.63 (br s, 1H, NH); 4b, 11.58 (s, 1H, NH of pyrazole), 7.904 (s, 1H of pyrazole, 5H), 7.35–7.96 (m, 5H of phenyl), 7.48 (s, 1H, N]C–H),
1.94 (s, 3H of methyl), 5.40 (s, 2H N–CH2–N), 2.23 (s, 3H CH3 of piperzine), 2.38–2.87 (m, 8H of piperzine); 4g, 11.58 (s,1H, NH of pyrazole), 7.904 (s,1H, pyrazole 5H), 7.35–7.96
(m, 7H of p-methyl phenyl), 2.3 (s, 3H, CH3 of p-phenyl), 7.48 (s, 1H, N]C–H), 5.40 (s, 2H, N–CH2–N), 2.23 (s, 3H, CH3 of piperzine), 2.38–2.87 (m 8H piperzine); 4j, 1.8 (s, 3H,
N–CH3), 2.7 (t, 4H, CH2–N–CH2), 3.5 (t, 4H, CH2–N–CH2), 5.08 (s, 2H, N–CH2–N), 7.0–8.8 (m, 10H, Ar–H and pyrazole 5H), 9.95 (s, 1H, N]CH), 12.85 (br s, 1H, pyrazole NH); 4k,
d
d
d
d
d
11.58 (s, 1H, NH of pyrazole), 7.904 (s, 1H, pyrazole 5H), 7.35–7.96 (m, 7H, p-methoxy phenyl), 3.7 (s 3H, O–CH3 of p-methoxy phenyl), 7.48 (s, 1H, N]C–H), 8.2–7.3 (m, 5H of
phenyl), 5.40 (s, 2H N–CH2–N), 2.23 (s, 3H, CH3 of piperzine), 2.38–2.87 (m, 8H of piperzine). Mass: 4c m/z 426 (Mþ), 113 (N-methylpiperzinomethyl cation), 77 (phenyl
nucleus), 103 (3-mercapto-4(H)-1,2,4 triazole), 200 (p-methoxyphenylpyrazolenitrile); 4g m/z 438 (Mþ), 113 (N-methylpiperzinomethyl cation), 77 (phenyl nucleus), 143 (3-
mercapto-4-(H)-1,2,4-triazole), 183 (p-methylphenylpyrazolenitrile).
for 7–8 h. Completion of reaction was monitored by TLC. After
cooling it for overnight, the precipitated solid was filtered off and
recrystallized from a mixture of hot ethanol–dioxane (2:1) to afford
the title compounds.
5.4. Pharmacology
5.4.1. Antimicrobial studies
All the newly synthesized Mannich bases were screened for
their antibacterial and antifungal activity. For antibacterial studies
microorganisms employed were S. aureus, B. subtilis, E. coli and
P. aeruginosa. For antifungal, C. albicans was used as organism. Both
microbial studies were assessed by minimum inhibitory concen-
tration (MIC) by serial dilution method [20]. For this the compound
whose MIC has to be determined is dissolved in serially diluted
DMF. Then a standard drop of the culture prepared for the assay is
added to each of the dilutions, and incubated for 16–18 h at 37 ꢀC.
MIC is the highest dilution of the compound, which shows clear
fluid with no development of turbidity.
5.3. 4[(3-Substituted-1H-pyrazol-4-yl)methyleneamino]-5-substi
tuted-2-[(4-methylpiperzine-1-yl)methyl]-2H-1,2,4-triazole-
3(4H)-thiones (4)
The Schiff base (3; 10 mmol) was dissolved in a mixture of
absolute ethanol–dioxane (2:1) mixture. Then formaldehyde (40%,
1.5 ml) and N-methylpiperzine (10 mmol) in absolute ethanol were
introduced to this solution. The mixture was stirred for 5–6 h and
kept overnight at room temperature. The solid separated was
collected by filtration and recrystallized from a mixture of ethanol–
dioxane (2:1) to afford title compounds (4).
Acknowledgements
The authors are thankful to the RSIC, CDRI Lucknow and
Director, RSIC, Punjab University, Chandigarh for providing micro-
analysis, NMR and mass spectral data. Also we sincerely thank Prof.
A.V. Adhikari and Prof. S. Sanchethi for providing research facilities.
Table 3
Antibacterial and antifungal activity data of 4[(3-substituted-1H-pyrazol-4-yl)me-
thyleneamino]-5-substituted-2-[(4-methylpiperzine-1-yl)methyl]-2H-1,2,4 triazole
-3(4H)-thiones.
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