One pot synthesis and SAR of some novel 3-substituted 5,6-diphenyl-1,2,4-triazines as antifungal agents

Article abstract of DOI:10.1016/j.bmcl.2009.11.048

An improved protocol for the synthesis of a novel series of 1,2,4-triazines possessing 1,2,3-triazole and piperidine ring using 1-(1-substituted piperidin-4-yl)-1H-1,2,3-triazole-4-carbohydrazide, benzil, ammonium acetate and ZrOCl₂·8H₂O as a catalyst in ethanol-water has been presented. The yields obtained are in the range of 87-94%. All the synthesized compounds (4a-4l) are novel and were evaluated for their in vitro antifungal activity. SAR for the series has been developed by comparing their MIC values with miconazole and fluconazole. Based on activity data SAR for the series has been developed. Compound 4c from the series was equipotent to miconazole against Candida albicans (MIC-25), Aspergillus niger (MIC-12.5) and Cryptococcus neoformans (MIC-25). Compound 4d was equipotent with miconazole against all tested organisms except Cryptococcus neoformans. Also compound 4i was equipotent with miconazole against C. albicans, A. niger and Fusarium oxysporum.

Full text of DOI:10.1016/j.bmcl.2009.11.048

Bioorganic & Medicinal Chemistry Letters 20 (2010) 742–745
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
One pot synthesis and SAR of some novel 3-substituted 5,6-diphenyl-1,2,4-
triazines as antifungal agents
*
Jaiprakash N. Sangshetti, Devanand B. Shinde
Department of Chemical Technology, Dr. Babasaheb Ambedkar Marathwada University, Aurangabad 431 004 (MS), India
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 15 May 2009
Revised 30 September 2009
Accepted 12 November 2009
Available online 15 November 2009
An improved protocol for the synthesis of a novel series of 1,2,4-triazines possessing 1,2,3-triazole and
piperidine ring using 1-(1-substituted piperidin-4-yl)-1H-1,2,3-triazole-4-carbohydrazide, benzil,
ammonium acetate and ZrOCl2Á8H2O as a catalyst in ethanol–water has been presented. The yields
obtained are in the range of 87–94%. All the synthesized compounds (4a–4l) are novel and were evalu-
ated for their in vitro antifungal activity. SAR for the series has been developed by comparing their MIC
values with miconazole and fluconazole. Based on activity data SAR for the series has been developed.
Compound 4c from the series was equipotent to miconazole against Candida albicans (MIC-25), Asper-
gillus niger (MIC-12.5) and Cryptococcus neoformans (MIC-25). Compound 4d was equipotent with mico-
nazole against all tested organisms except Cryptococcus neoformans. Also compound 4i was equipotent
with miconazole against C. albicans, A. niger and Fusarium oxysporum.
Keywords:
One pot synthesis
1,2,4-Triazines
Hydrazides
1,2,3-Triazole
Piperidine
Ó 2009 Elsevier Ltd. All rights reserved.
MIC values
SAR
1,2,4-Triazines and their analogues have gained considerable
attention because of their synthetic, as well as biological utility.
1,2,4-Triazine is an important core found in numerous natural
and synthetic biologically active compounds. Well-known antiviral
drug azaribine is structurally based on the 1,2,4-triazine scaffold.1
Also, certain azanucleosides, for example, 6-azacytosine and 6-aza-
uracil, with 1,2,4-triazine heterocycle, have reported in literature
as antiviral,2,3 antitumour4,5 and antifungal6 activities. Further-
more, 6-azaisocytosine (3-amino-1,2,4-triazin-5(2H)-one), an isos-
teric isomer of 6-azacytosine and 6-azauracil, is of great biological
interest due to its resistance to deaminase. Some condensed deriv-
atives like pyrrolo-1,2,4-triazines are reported as anticancer agent-
s.7a In the literature there is a report of 3-heterocycle substituted
1,2,4-triazines which have been prepared from hydrazides.7b
1,2,3-Triazole and its derivatives are important heterocycles with
different activities like potent antineoplastic,8 antimicrobial,9–
11analgesic,12 anti-inflammatory, local anesthetic,13 anticonvul-
sant,14 antimalarial,15 anti HIVagents.16 Some 1,2,3-triazole deriv-
atives were used as DNA cleaving agents17 and potassium
channel activators,18 cannabinoid CB1 receptor antagonists19 and
antitubercular agents.20
continuation of our work on synthesis of pharmacologically signif-
icant heterocycles,21 a novel series of 1,2,4-triazines has been syn-
thesized by one pot reaction of benzil, hydrazide and ammonium
acetate in ethanol–water using ZrOCl2Á8H2O as a catalyst.
The ester compound 1 was prepared from commercially avail-
able N-Boc piperidone as described in our previously reported
method.21d Starting hydrazide compound has been prepared from
ester compound 1 using hydrazine hydrate in methanol and fur-
ther deprotection using trifluoroacetic acid. Deprotected hydrazide
compound on alkylation or acylation in presence of triethylamine
in tetrahydrofuran gave compounds 2a–2l as shown in Scheme 1.
Corresponding hydrazide compounds, benzil, ammonium acetate
were heated at 100 °C in ethanol–water (1:2; v/v) using 10 mol %
ZrOCl2Á8H2O (Scheme 2). The reaction has also been tried using
other acid catalysts the detail of the reactions with different cata-
lyst is summarized in Table 1. From the table it is found that use of
ZrOCl2Á8H2O was more effective.
Catalytic property of ZrOCl2Á8H2O has been studied considering
synthesis of (3a). Effect of various solvents like THF, acetonitrile,
ethanol, have also been studied. Among the results obtained, use
of 10-mol % ZrOCl2Á8H2O in ethanol–water gave the better yield
(94%) for the synthesis of 4a (Table 2). The use of environmental
benign solvent such as water has got very much importance in
‘Green Chemistry’. To study this aspect, the reaction was carried
out for synthesis of 4a using 10 mol % ZrOCl2Á8H2O, and
corresponding substrates in water. The reaction was found to be
sluggish and it may be due to the less solubility of substrates. To
Literature reveals that there are no reports of a molecular scaf-
fold containing these two important cores. With this view consid-
ering the biological significance of triazine and 1,2,3-triazole and in
* Corresponding author.
E-mail address: dbshinde.2007@rediffmail.com (D.B. Shinde).
0960-894X/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2009.11.048

J. N. Sangshetti, D. B. Shinde / Bioorg. Med. Chem. Lett. 20 (2010) 742–745
743
Table 1
O
O
Comparison of the reaction using different catalyst for the synthesis of tert-butyl 4-(4-
(5,6-diphenyl-1,2,4-triazin-3-yl)-1H-1,2,3-triazol-1-yl)piperidine-1-carboxylate (4a)
using 10 mmol of hydrazide (2a), 10 mmol of benzil and 40 mmol of ammonium
acetate in ethanol
NHNH2
O
N
N
N
Catalyst
Mol %
Reaction time
Yielda (%)
N
N
N
N
No catalyst
—
48 h
5 h 40 min
4 h
3 h 30 min
4 h 30 min
1 h 40 min
No product
Bismuth trichloride
Sulfamic acid
Oxalic acid
Zinc chloride
Zirconyl chloride
20
20
20
20
20
77
80
85
75
94
1) a
2)
3)
b
c
N
R
a
Yields refer to the isolated pure products.
Boc
1
2a-2l
Table 2
Optimization of reaction conditions and the quantity of ZrOCl2 for the synthesis of
tert-butyl 4-(4-(5,6-diphenyl-1,2,4-triazin-3-yl)-1H-1,2,3-triazol-1-yl)piperidine-1-
carboxylate (4a) at 100 °C
Scheme 1. Reagents and conditions: (a) Hydrazine hydrate, methanol, reflux, 8 h;
(b) TFA, dichloromethane, rt, 16 h; (c) triethylamine, R–X or RCOX, tetrahydrofuran,
0–5 °C to rt, 2.5 h.
Solvent
Mol % of ZrOCl2
Reaction time
Yielda (%)
THF
Acetonitrile
20
20
20
20
20
10
5
3 h
3 h 30 min
4 h
1 h 40 min
1 h 40 min
1 h 40 min
2 h 20 min
75
85
70
94
94
94
82
avoid this problem, the ethanol–water (1:2; v/v) solvent was used
and found to be effective for synthesis of 4a (94% in 100 min). The
synthetic procedure was extended for synthesis of all the com-
pounds 4a–4l using different hydrazides, benzil, and ammonium
acetate. Results are summarized in Table 3. The yields were ob-
tained in the range of 87–94%. All synthesized derivatives were
characterized using mass and 1H NMR.
Acetonitrile–water (1:1)
Ethanol
Ethanol–water (1:2)
Ethanol–water (1:2)
Ethanol–water (1:2)
a
Yields refer to the isolated pure products.
All the synthesized compounds were screened for in vitro anti-
fungal activity. The antifungal activity was evaluated against dif-
ferent fungal strains such as Candida albicans (NCIM3471),
Fusarium oxysporum (NCIM1332) Aspergillus flavus (NCIM539)
Aspergillus niger (NCIM1196), Cryptococcus neoformans (NCIM576).
Minimum inhibitory concentration (MIC) values were determined
using standard agar plate method.22 Miconazole and Fluconazole
were used as a standard for the comparison of antifungal activity.
1
N
6
O
2 N
5
NHNH2
N
N
3
4
N
N
N
N
N
O
a
+
O
N
N
R
R
4a-4l
3
2a-2l
4a R = -Boc
4c R = -CH3
4b R = -H
4d R = -CH2CH3
4e R = -COCH3
4f R = -COC2H5
4h R =-COC6H5
4g R = -COC3H7
4i R = -COC6H5, 4 Cl
4k R = - SO2C6H5 CH3
4j R = - SO2CH3
4l R = -CH2C2H5
Scheme 2. Reagents and conditions: (a) ZrOCl2Á8H2O (10 mol %), ammonium acetate, ethanol–water (1:2), 100 °C, 100–120 min.

744
J. N. Sangshetti, D. B. Shinde / Bioorg. Med. Chem. Lett. 20 (2010) 742–745
Table 3
Experimental data of the synthesized compounds 4a–41
Entry
Time in minutes
Yield* (%)
Molecular formula/molecular weight
Elemental analysis%
Found (calcd)
C
H
N
4a
4b
4c
4d
4e
4f
100
100
110
110
100
120
120
100
100
100
110
110
94
94
90
88
90
88
87
90
90
92
88
88
C27H29N7O2
483
C22H21N7
383
C23H23N7
397
C24H25N7
412
C24H23N7O
425
C25H25N7O
439
C26H27N7O
453
C29H25N7O
487
67.14
(67.06)
68.87
(68.91)
69.50
(69.53)
70.05
(70.00)
67.77
(67.75)
68.30
(68.32)
68.82
(68.85)
71.43
(71.44)
66.75
(66.73)
59.50
(59.51)
64.77
(64.79)
73.57
6.10
(6.04)
5.50
(5.52)
5.83
(5.83)
6.15
(6.12)
5.46
(5.45)
5.73
(5.70)
6.00
(6.02)
5.19
(5.17)
4.62
(4.63)
5.00
(5.02)
5.08
(5.06)
5.74
20.28
(20.27)
25.57
(25.59)
24.67
(24.67)
23.82
(23.80)
23.04
(23.04)
21.30
(21.31)
21.60
(21.62)
20.10
(20.11)
18.90
(18.88)
21.25
(21.24)
18.24
(18.24)
20.75
4g
4h
4i
C
29H24 Cl N7O
522
C23H23N7O2S
461
C29H27N7O2S
537
C29H27N7
473
4j
4k
4l
(73.55)
(5.75)
(20.70)
*
Yields refer to the isolated pure products.
Dimethyl sulfoxide was used as solvent control. MIC values of the
tested compounds are presented in Table 4.
nitrogen further enhance activity against F. oxysporum (MIC-25)
and A. flavus (MIC-12.5) whereas there is no effect on activity
against C. albicans, A. niger as evidenced by same MIC. Compound
4d was equipotent with miconazole against all tested organisms
except C. neoformans (MIC-35) whereas 2–5 times less active com-
pared to fluconazole. Introduction of acetyl group on nitrogen (4e)
reduces the antifungal activity compared with unsubstituted
piperidine against all tested organisms. There was further decrease
in antifungal activity if acetyl group replaced by propionyl (4f) and
butyryl group (4g). Introduction of benzoyl group on nitrogen (4h)
shows significant enhancement of activity compared with acetyl or
propionyl substituent. Compound (4h) is marginally less active
compared with miconazole. Introduction of Cl group on 4 position
of Phenyl (4i) further increases the antifungal activity compared
with unsubstituted phenyl. Compound (4i) was equipotent with
miconazole against C. albicans, A. niger and F. oxysporum. Introduc-
tion of mesyl group on piperidine nitrogen (3j) shows increase in
activity against C. albicans, A. flavus and F. oxysporum compared
with unsubstituted nitrogen. Replacement of mesyl group by tosyl
group (4k) reduces the antifungal activity.
Many of the newly synthesized compounds were found to show
good antifungal activity. From the antifungal activity data (Table
4), it is observed that compounds 4c, 4d and 4i are the most active
among all tested compounds against most of the tested organisms.
N-Protected compound 4a shows very less antifungal activity com-
parable to miconazole and fluconazole. Deprotected compound 4b
shows significant rise in activity compared to 4a (activity increases
by double as reflected in reduced MIC). Substitution of methyl
group (4c) on piperidine nitrogen increases the antifungal activity
compared with unsubstituted nitrogen (4b). Compound 4c was
equipotent to miconazole (activity comparable to fluconazole)
against C. albicans (MIC-25), A. niger (MIC-12.5) and C. neoformans
(MIC-25) where as slightly less active against F. oxysporum (MIC-
30) and A. flavus (MIC-17.5). Substitution of ethyl group (4d) on
Table 4
Antifungal activity of the synthesized compounds
In conclusion, we have developed a new, convenient, simple
and efficient method for the synthesis of novel series of 3-(1-(1-
substitutedpiperidin-4-yl)-1H-1,2,3-triazol-4-yl)-5,6-diphenyl-1,2,
4-triazines using ZrOCl2Á8H2O as a catalyst in good yields. The
synthesized compounds were tested for in vitro antifungal activity.
Based on the activity data SAR for the series has been developed.
From the series it is found that compounds 4c, 4d and 4i are the
most active compounds from series suggesting that compounds
from present series of 1,2,4-triazine with piperidino-1,2,3-triazole
on 3rd position bearing substitutions like methyl, ethyl or benzoyl
on piperidine nitrogen can serve as a important scaffold for the de-
sign and development of new lead as antifungal agent.
Compound
MIC values in
C. albicans F. oxysporum A. flavus A. niger C. neoformans
l
g/mLa
*
*
4a
4b
4c
4d
4e
4f
4g
4h
4i
70
30
25
25
35
50
62.5
30
25
50
90
40
55
100
45
25
40
30
25
40
50
65
30
25
60
100
60
25
5
37.5
17.5
12.5
20
20
35
17.5
15
30
42.5
12.5
12.5
20
20
40
35
*
—
—
*
75
55
15
12.5
30
*
*
4j
4k
4l
35
47.5
95
150
*
—
*
Miconazole 25
Fluconazole
12.5
5
12.5
10
25
5
Acknowledgements
5
*
The authors are thankful to Council for Scientific and Industrial
Research (CSIR), New Delhi for financial assistance. The authors are
No activity was observed up to 200
Values are the average of three readings.
l
g/mL.
a

J. N. Sangshetti, D. B. Shinde / Bioorg. Med. Chem. Lett. 20 (2010) 742–745
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Supplementary data associated with this article can be found, in
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