Design and synthesis of novel antifungal triazole derivatives with good activity and water solubility

Article abstract of DOI:10.1016/j.cclet.2013.01.047

In order to find novel antifungal agents with good activity and aqueous solubility, a series of SYN-2869 analogues containing a pyridine ring were synthesized and evaluated for their in vitro antifungal activity and water solubility. The results indicated that some compounds showed potent activity against six pathogenic fungi. In particular, the analogue 17a having an isobutyl substitution on the triazolone exhibited significant broad spectrum antifungal activity. In addition, the water solubility of compound 17a was sufficiently improved over SYN-2869.

Full text of DOI:10.1016/j.cclet.2013.01.047

Chinese Chemical Letters 24 (2013) 303–306
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Chinese Chemical Letters
journal homepage: www.elsevier.com/locate/cclet
Original article
Design and synthesis of novel antifungal triazole derivatives with good activity
and water solubility
Xu-Feng Cao a, Wen-Jing Chu a, Yong-Bing Cao b, Yu-She Yang a,
*
a State Key Laboratory of Drug Research, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai 20103, China
b School of Pharmacy, Second Military Medical University, Shanghai 200433, China
A R T I C L E I N F O
A B S T R A C T
Article history:
In order to find novel antifungal agents with good activity and aqueous solubility, a series of SYN-2869
analogues containing a pyridine ring were synthesized and evaluated for their in vitro antifungal activity
and water solubility. The results indicated that some compounds showed potent activity against six
pathogenic fungi. In particular, the analogue 17a having an isobutyl substitution on the triazolone
exhibited significant broad spectrum antifungal activity. In addition, the water solubility of compound
17a was sufficiently improved over SYN-2869.
Received 6 November 2012
Received in revised form 14 January 2013
Accepted 16 January 2013
Available online 7 March 2013
Keywords:
ß 2013 Yu-She Yang. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights
reserved.
Synthesis
Antifungal
SYN-2869 analogues
Triazole
Water solubility
1. Introduction
In our previous research [9], we replaced one of the phenyl rings
in Itraconazole with a pyridine ring to obtain a series of novel
During the past two decades, the incidence of invasive fungal
infections has rapidly been increasing in immuno-compromised
patients emerging from organ transplants, cancer chemotherapy
and the HIV epidemic [1], which has caused significant
morbidity and mortality in patients [2]. For the treatment of
these infections, orally active triazoles, such as Fluconazole and
Itraconazole (Fig. 1) have been widely used in clinic use [3].
However, several factors have limited their practical applica-
tions. For example, aspergillous have become so common in
recent years that many experts even believed that aspergilus
rather than Candida is the major problem [4]. But unfortunately,
this organism is intrinsically resistant to Fluconazole [5]. In
addition, with the increased use of Fluconazole, the number of
strains resistant to Fluconazole has increased significantly [6].
The use of another triazole antifungal compound, Itraconazole,
which demonstrated stronger activity against aspergilus than
Fluconazole does, is also hampered by their poor aqueous
solubility and absorption [7]. Therefore, the need for novel
antifungal agents that exhibit broad spectrum and good water
solubility has become more pressing [8].
Itraconazole analogues. Most of the compounds showed excellent
in vitro antifungal activity. And, more importantly, several of these
compounds had higher water solubility and bioavailability than
those of Itraconazole. Here we attempt to use this strategy, which
has been widely applied in drug design, to obtain more novel
potential antifungal agents.
SYN-2869 (Fig. 1) is a novel orally active antifungal agent,
which has potent antifungal activity against Candida species [10].
However, its efficacy to treat other fungal infections, particularly
Aspergillus fumigatus and its water solubility are still far from
satisfactory [11]. To overcome these drawbacks, we focused our
efforts on a similar approach described above that replaces a
benzene ring on the SYN-2869 side chain with a pyridine ring to
develop a series of novel SYN-2869 analogues.
2. Experimental
The synthetic route of triazolone intermediates 8a–g with
various side chains was outlined in Scheme 1. Compound 2 was
obtained by the reaction of compound 1 and mono-N-Boc-
piperazine in DMF. Compound 2 was reduced with 10% Pd/C
under H2 atmosphere to afford compound 3. The reaction of
compound 3 with phenyl chloroformate and pyridine afforded
compound 4, which was converted to semicarbazide 5 in high
* Corresponding author.
E-mail address: ysyang@mail.shcnc.ac.cn (Y.-S. Yang).
1001-8417/$ – see front matter ß 2013 Yu-She Yang. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
http://dx.doi.org/10.1016/j.cclet.2013.01.047

[
X.-F. Cao et al. / Chinese Chemical Letters 24 (2013) 303–306
O
OH
O
N
N
N
F
N
N
N
N
O
N
N
N
OH
F
O
N
N
N
N
F
N
N
N
N
N
O
N
N
N
F
OCF3
F
F
SYN-2869
Itraconazole
Fluconazole
Fig. 1. The structure of Fluconazole, Itraconazole, SYN-2869.
[(Scheme_1)TD$FIG]
O
OPh
c
a
b
Boc
N
N
NH
Cl
NO2
Boc
N
N
N
NH2
Boc
N
N
N
NO2
N
N
N
N
4
1
3
2
O
O
O
R
NHNH2
f
N
N
e
NH
N
d
Boc
N
N
NH
Boc
N
g
N
N
Boc
N
N
N
N
R
7a-g
5
6
a
(CH3)2CHCH2-
(CH3)2CH-
b
c
d
e
f
4-CF3OC6H4CH2-
4-CF3C6H4CH2-
3,5-(CF3)2C6H3CH2-
3-CF3C6H4CH2-
2,3,5-F3C6H2CH2-
O
R
N
N
HN
N
N
N
g
8a-g
Scheme 1. Conditions and reagents: (a) K2CO3, N,N-dimethyl formamide, tert-butylpiperazine-1-carboxylate, 110 8C, 90.0%; (b) H2, 10% Pd/C, THF, rt, 96.5%; (c) phenyl
carbonchloridate, pyridine, CH2Cl2, 0 8C, 90.7%; (d) hydrazine hydrate, 1,4-dioxane, reflux, 90.5%; (e) formamidine acetate, DMF, 120 8C, 50.0%; (f) RBr, Cs2CO3, DMF, reflux,
50.0–85.0%; (g) trifluoroacetic acid, rt, 80.0–95.0%.
yield. The cyclization of compound 5 afforded the triazolone
intermediate 6. Then, compound 6 was treated with RBr in DMF,
giving the substituted triazolone 7a–g. Finally, triazolone 7a–g was
reacted with trifluoroacetic acid to yield 8a–g.
3. Results and discussion
All the titled compounds containing pyridine were new
compounds and their structures were confirmed by 1H NMR, 13C
NMR, MS-ESI.
The synthetic route of triazolone 15a–f was outlined in Scheme
2. The intermediates 13a–f were obtained via similar procedures
described in Scheme 1. The coupling reaction between compound
13a–f and N-Boc-piperazine afforded compound 14a–f, which
were mixed and stirred in TFA to yield the key intermediates 15a–f.
The titled compounds 17a–g and 18a–f [12] were synthesized
via ring-opening reactions between 17a–g or 18a–f and (2R, 3S)-2-
(2,4-difluorophenyl)-3-methyl-2-(1H-1,2,4-triazole-1-yl)methyl
oxirane 16 in the presence of LiClO4 in refluxing acetonitrile
(Scheme 3) [13]. The oxirane intermediate 16 was prepared by
using a known method [14].
Minimum inhibitory concentrations (MICs) of the titled
compounds were determined by the method recommended by
the National Committee for Clinical Laboratory Standards using the
serial dilution method in 96-well microtest plates [15]. Test fungal
strains were obtained from ATCC or clinical isolates. The MIC
values of all titled compounds were listed in Table 1. All the titled
compounds were active against six fungi to some extent.
Compared to Fluconazole and Voriconazole, some compounds
exhibited stronger or comparable activity against Candida albicans
and Cryptococcus neoformans. The activity of compounds 17a, 17b,
[(Scheme_2)TD$FIG]
O
OPh
NHNH2
c
a
b
Br
Br
NH
Br
NH2
Br
NH
N
N
N
10
9
11
O
O
O
N
R
R
N
NH
N
N
N
e
d
Br
N
Boc
N
f
N
N
N
N
N
N
12
14a-f
13a-f
R
a
b
c
d
e
f
(CH3)2CH-
4-CF3C6H4CH2-
O
R
4-CF3OC6H4CH2-
3,5-(CF3)2C6H3CH2-
3-CF3C6H4CH2-
N
N
HN
N
N
N
2,3,5-F3C6H2CH2-
15a-f
Scheme 2. Conditions and reagents: (a) phenyl carbonchloridate, pyridine, CH2Cl2, 0 8C, 91.5%; (b) hydrazine hydrate, reflux, 1,4-dioxane, 86.5%; (c) formamidine acetate,
DMF, 120 8C, 45.5%; (d) RBr, Cs2CO3, DMF, reflux, 55.0–83.6%; (e) tert-butylpiperazine-1-carboxylate, Pd2(dba)3, t-BuONa, rac-BINAP, toluene, 60 8C, 35.0–65.5%; (f) TFA, rt,
80.0%–95.0%.

[
X.-F. Cao et al. / Chinese Chemical Letters 24 (2013) 303–306
305
Scheme 3. Conditions and reagents: (a) LiClO4, CH3CN, 80 8C, 41.0–65.0%.
18a, which contained short alkyl side chains, are more potent than
control drugs against Candida parapsilosis, whereas the compounds
with long benzyl side chains showed weaker activity. In addition,
compounds 17a and 18a also demonstrated much stronger activity
against A. fumigatus than Fluconazole and SYN-2869. In general,
the compounds 17a–g exhibited higher activity than compounds
18a–f, which suggested that the position of the N atom in the
pyridine ring influenced the antifungal activity of these SYN-2869
analogues.
in Table 2, all of the tested compounds are more soluble than SYN-
2869, especially under acidic conditions, which indicated that the
incorporation of a pyridine ring may have been the reason for this
improved water solubility. In particular, the short alkyl-substitut-
ed compounds 17a, 17b and 18a are more soluble than compounds
17c and 18c, which contained a longer benzyl side chain. The
combined results indicated that their absorption might be
improved.
Meanwhile, we evaluated the water solubility of compounds
17a, 17b, 17c, 18a, 18c at pH 1.2 and pH 7.4, respectively. As shown
4. Conclusion
In conclusion, a series of SYN-2869 derivatives containing a
pyridine ring were synthesized and evaluated. The results
indicated that some titled compounds retained the good activity
of SYN-2869. In particular, compound 17a exhibited the most
potent antifungal activity, broadest antifungal spectrum and
highest water solubility and is worth further investigations.
Table 1
Structures and in vitro antifungal activity of title compounds.
Compound MIC80
(mg/mL)
C. alb Y0109 C. alb SC5314 C. par C. neo C. gla
A. fum
17a
0.03
0.06
0.125
0.25
0.06
0.06
8
0.25
1
0.25
0.5
0.25
0.25
8
4
16
8
4
16
16
16
32
32
16
4
17b
17c
8
Acknowledgments
17d
17e
8
8
8
16
16
8
16
16
8
17f
4
4
8
8
4
We are grateful to the National Science and Technology Major
Project for the support of this research. The project described was
supported by Key New Drug Creation and Manufacturing Program,
China (No. 2009ZX09301-001).
17g
18a
8
8
16
0.25
4
8
0.5
8
0.5
2
1
18b
18c
8
8
16
32
32
16
16
32
>64
4
8
8
4
8
8
18d
18e
8
16
4
16
8
16
8
Appendix A. Supplementary data
4
4
4
18f
8
16
16
16
8
SYN-2869
FLU
VCZ
0.06
0.5
0.25
0.06
0.5
0.25 16
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.cclet.2013.01.047.
1
1
2
16
0.125
0.5
0.5
0.25
Abbreviations: C. alb Y0109, Candida albicans Y0109; C. alb SC5314, Candida albicans
SC5314; C. par, Candida parapsilosis; C. neo, Cryptococcus neoformans; C. gla, Candida
glabrata; A. fum, Aspergillus fumigatus; FLU, Fluconazole; VCZ, Voriconazole.
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