Synthesis and antibiotic activity of a small molecules library of 1,2,3-triazole derivatives

Article abstract of DOI:10.1016/j.bmcl.2007.11.111

A small library of simple 1,4-disubstituted 1,2,3-triazoles was prepared using a known one-pot procedure starting from organic halides and terminal alkynes. The compounds were then tested for their antibacterial activity against normal and resistant speci

Full text of DOI:10.1016/j.bmcl.2007.11.111

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Bioorganic & Medicinal Chemistry Letters 18 (2008) 1195–1198
Synthesis and antibiotic activity of a small molecules library
of 1,2,3-triazole derivatives
Marie Aufort, Jean Herscovici, Pascale Bouhours, Nicole Moreau and Christian Girard*
Unite´ de Pharmacologie Chimique et Ge´ne´tique UMR8151 CNRS / U640 INSERM, and
`
Equipe de Biochimie, Laboratoire de Synthese Organique Selective et Produits Naturels UMR7573 CNRS, IFR 2769
Chimie Mole´culaire de Paris Centre, Ecole Nationale Supe´rieure de Chimie de Paris, 75005 Paris, France
´
Received 26 November 2007; revised 28 November 2007; accepted 29 November 2007
Available online 4 December 2007
Abstract—A small library of simple 1,4-disubstituted 1,2,3-triazoles was prepared using a known one-pot procedure starting from
organic halides and terminal alkynes. The compounds were then tested for their antibacterial activity against normal and resistant
species of Staphylococcus aureus.
Ó 2007 Elsevier Ltd. All rights reserved.
Drug resistance to antibiotics, especially the multiple
one (MDR), is nowadays an alarming and major public
health concern worldwide.1 Many strains of bacteria
have developed resistances through the years following
the clinical use of the first antibiotics and there is contin-
uous emergence and spreading of antibiotic-resistant
bacteria. Several strains causing infectious diseases that
seemed to be in control are once again causing deaths
each year due to the absence of an appropriate antibi-
otic.2 There is thus still a need for seeking new molecules
that can be added to the pharmacopeia in order to treat
these infections.3
treatment of several infections.5 For the 1,2,3 isomer,
this new life is mainly due to the discovery of copper
(I)-catalyzed versions of the usual thermal conditions
for the [3+2] Huisgen’s cycloaddition reaction between
azides and terminal alkynes.6
In this communication, we wish to report the synthesis
of a series of 1,2,3-triazoles and the results for their bio-
logical activity evaluation on some normal and resistant
bacterial strains.
The triazole synthesis was conducted accordingly to
previously published one-pot procedures.6b,7 Advanta-
ges of these methods are the in situ generation of cop-
per (I) salts needed for the catalysis from the stable
copper (II) sulfate/sodium ascorbate redox system,
in situ synthesis of the organic azide from an organic
halide and sodium azide, and the isolation of the sole
1,4-disubstituted isomer. Several attempts were made
in order to optimize the reaction conditions for our
needs: equivalents of NaN3, number of mol% of
CuSO4 and sodium ascorbate, with or without added
base (Na2CO3) and catalyst (proline) and this in differ-
ent solvent systems (DMF, dioxane, DMSO, with or
without water, degassed or not) at room temperature
and higher, for short and long reaction times. The best
general conditions were found to be 1.2 equiv NaN3,
5 mol% CuSO4, 0.1 equiv Na ascorbate, 0.2 equiv
Na2CO3, 0.2 equiv DL-proline in DMSO/H2O 9/1 at
65 °C until the reaction was complete (Fig. 1).7a All
compounds were obtained by simple aqueous work-
up followed by a purification.
Staphylococcus aureus is a bacterium found on the skin
and mucosa of one-third of the population. S. aureus
is very reactive towards the antibiotic pressure and
was the first species in which a penicillin resistance was
found right after the beginning of its industrial produc-
tion. S. aureus is furthermore the causal agent in 40% of
septicemia cases and half infections caused by this bac-
terium are presenting MDR (penicillin, methicillin, tet-
racyclin, erythromycin, etc.).4
Triazole ring is a potential pharmacophore that has
gained in interest over the past few years. Several deriv-
atives have already shown interesting biological activi-
ties and a few were found to be efficient in the
Keywords: Click-chemistry; Huisgen’s cycloaddition; Triazole; Antibi-
otic; MDR; S. aureus.
*
Corresponding author. Tel.: +33 1 44 27 67 22; fax: +33 1 43 25 79
75; e-mail: Christian-Girard@enscp.fr
0960-894X/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2007.11.111

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M. Aufort et al. / Bioorg. Med. Chem. Lett. 18 (2008) 1195–1198
NaN 1.2 eq
3,
CuSO 5%
4
2
Na ascorbate 0.1 eq
R
1
2
+
R X
R
N
N
1
N
Na CO 0.2 eq
R
2
3
DL-proline 0.2 eq
DMSO/H O, 65˚C
2
Figure 1. One-pot copper (I)-catalyzed 1,4-disubstituted 1,2,3-triazole
synthesis.
The results for the synthesis of thirty derivatives are pre-
sented in Table 1. The compounds were isolated in var-
iable yields ranging from poor to good (5–96% yield,
40% average). The reactions were conducted using alkyl,
allyl and benzyl bromides as well as with iodoaromatics
giving the opportunity to introduce different substitu-
tions on the N1 of the triazole. Reactions of propa-
rgylphthalimide (triazoles 1–9) gave highly crystalline
compounds with the phthalimidomethyl group on the
C4 of the ring, the yields being lower with iodoaryl part-
ners. When using phenyl propargyl ether (10–15), good
yields of the corresponding C4-phenoxymethyl substi-
tuted triazoles were obtained in most cases. The same
was observed for propiolaldehyde diethyl acetal (16–
20). The yields for the reaction of propiolic acid (21–
25) were fair after, of course, acidification during the
work-up procedure. However, reactions of propiolic
acid methyl ester (26–28) only gave poor yields. This
was due to the competitive saponification reaction as
well as decarboxylation observed in some cases. Finally,
unprotected alcohols like the propargyl one can be used
(29) whereas propargyl amine (30) gave N-alkylated
products and can only be treated with the azide gener-
ated ex situ.
The products were then tested for their biological activ-
ity on a reference strain of S. aureus (ATCC 25923)
and resistant strains 1199B NorA and RN4220
pUL5054 MsrA.8 Solutions were prepared in DMSO
and added to the strains in Mueller–Hinton broth in
96-well plates. The growth and its inhibition were mea-
sured by the optical density followed over 24 h. The re-
sults of the inhibition on the three strains are presented
in Table 2.
For the C4 phthalimidomethyl derivatives (1–9), some
of them showed a moderate inhibition of S. aureus
strains. The derivative bearing an octyl chain on N1
(1) inhibited the growth of MsrA strain at 40%. A dode-
cyl chain at this position (2) gave an inhibition of 40%
for NorA strain and an almost equivalent (43%) for
MsrA. An allyl (3) substituent made the activity drop
to lower values. A benzyl (4) group gave a triazole with
a better activity against the NorA strain (57%). For the
compound substituted by a phenyl ring (5), the activity
on all the strains was low. Introduction of a para-nitro
(6) group on the aromatic ring gave a product more spe-
cific for S. aureus MsrA (48.1%), while a methoxy (7)
one lowered the potency. A pyridine nucleus on the
N1 gave a compound with a moderate inhibition of
the MsrA strain (46%).

M. Aufort et al. / Bioorg. Med. Chem. Lett. 18 (2008) 1195–1198
1197
Table 2. Inhibition of the growth of strains of S. aureus by triazoles 1–30 at 0.1 mg mLÀ1 after 24 h
Triazole
% Inhibitiona
S. aureus ATCC
25923
% Inhibitiona
S. aureus 1199B
NorA
% Inhibitiona
S. aureus RN4220
MsrA
% Inhibitiona,b
S. aureus 1199B
NorA+cip
% Inhibitiona,b
S. aureus RN4220
MsrA+ery
1
na
27.4 ( 0.4)
40 ( 2)
18 ( 4)
57 ( 10)
17 ( 3)
35 ( 3)
15 ( 6)
22 ( 1)
15 ( 3)
21 ( 6)
11 ( 2)
18 ( 3)
11 ( 3)
22 ( 4)
na
40 ( 2)
43 ( 3)
33 ( 16)
30 ( 4)
24 ( 4)
48.1 ( 0.1)
24.1 ( 0.7)
46 ( 1)
32 ( 2)
32.7 ( 0.2)
11 ( 2)
34 ( 3)
21 ( 3)
30 ( 3)
6 ( 2)
25 ( 1)
45 ( 6)
23 ( 2)
36 ( 1)
17 ( 3)
38 ( 3)
18 ( 5)
26.6 ( 0.1)
20 ( 9)
20 ( 8)
26 ( 1)
24 ( 2)
16( 2)
56 ( 5)
na
24 ( 9)
65 ( 4)
36 ( 11)
44 ( 9)
41 ( 13)
72 ( 4)
48 ( 3)
71 ( 2)
38 ( 5)
43 ( 4)
41 ( 11)
56 ( 19)
39 ( 7)
58 ( 22)
40 ( 3)
28 ( 13)
na
2
20 ( 4)
na
na
3
4
5
na
6
22 ( 3)
24 ( 3)
24 ( 1)
16 ( 3)
12 ( 3)
31 ( 4)
27 ( 4)
10 ( 4)
22 ( 3)
17 ( 2)
32 ( 7)
na
7
8
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
6 ( 1)
na
19 ( 11)
na
9 ( 2)
8 ( 2)
na
na
na
11 ( 4)
6.3 ( 0.3)
na
71 ( 10)
na
25 ( 8)
na
na
na
na
na
na
6 ( 1)
9 ( 3)
15 ( 1)
24 ( 5)
24 ( 8)
16 ( 3)
18 ( 7)
na
8 ( 1)
31 ( 2)
54 ( 2)
38 ( 1)
52.6 ( 0.1)
44 ( 1)
15 ( 2)
11 ( 4)
na
22 ( 2)
74.9 ( 0.8)
45.8 ( 0.6)
78 ( 1)
71 ( 1)
33 ( 3)
78.3 ( 0.6)
na
na
na
18.0 ( 0.7)
21 ( 6)
23 ( 9)
16 ( 2)
15 ( 6)
na
14 ( 5)
21 ( 2)
25 ( 7)
16 ( 4)
6.1 ( 0.3)
6 ( 3)
na
a Values are means of two experiments; standard deviation is given in parentheses (na, not active; nm, not measured).
b Measured in the presence of ciprofloxacin (cip) at 4 mg LÀ1, and erythromycin (ery) at 16 mg LÀ1 (antibiotics not active at this concentration).
In the case of the C4 phenyloxymethyl substituted tria-
zoles (10–15) and the C4 formyl diethyl acetal deriva-
tives (16–20), all compounds had quite low inhibition
on the strains (630%). In the case of the C4-carboxy
bearing triazoles (21–25), the derivatives with the N1-
phenyl (21), p-methoxyphenyl (24) and pyridine (25)
were moderately active on the MsrA strain, with 54%,
38% and 53% inhibition, respectively. The methoxycar-
bonyl derivatives 26–28 were not as active as their car-
boxy parents; only the allyl substituted product 26
gave 44% inhibition of growth on S. aureus MsrA.
The C4-hydroxymethyl compound 29 was not active at
all on all tested strains.
For the strain RN4220 MsrA and erythromycin, almost
all compounds were found to be more active using this
protocol. For the C4-phthalimidomethyl series (1–9),
while the triazole 1 lost its activity and 3 stayed at the
same level, all other derivatives were up to two times
more potent. An increase of around 50% was observed
for the triazoles 2 (43–65%), 4 (30–44%), 6 (48–72%)
and 8 (46–71%), while the derivatives 5 and 7 have
shown a important rise around 100%, going up from
24% to 41% and 24% to 48%, respectively. In the series
of C4-phenoxymethyltriazoles (10–15), a similar effect
was encountered and the inhibitions were increased by
50% for 11 (33–43%) and 13 (34–56%), by two times
for 14 (21–39%) and 15 (30–58%), and up to four times
for the triazole 12 (11–41%). For the C4-formyl diethy-
lacetal derivatives (16–20), significant increases of inhi-
bition of three times for 19 (9–25%) and seven times
for 16 (6–40%) were observed. In the case of the carbox-
ylic acids (21–25), the triazoles 23 (54–75%) and 25 (53–
78%) were found to be 50% more active. For the methyl
ester analogues (26–28), a similar increase was observed
for the compound 26 (44–71%) while it was of two to six
times for 27 (15–33%) and 28 (11–78%).
The triazole library was then tested on the resistant
strains but in the presence of the antibiotic for which
the strain has lost its sensitivity, in order to evaluate
any possible synergetic effects (Table 2). The tests
were conducted using doses of antibiotics below the
inhibition concentration: namely ciprofloxacin (cip)
at 4 mg LÀ1 for NorA, and erythromycin (ery) at
16 mg LÀ1 for MsrA.
In the case of S. aureus 1199B NorA and ciprofloxacin,
only a few compounds were found to have an effect.
While the triazole 2 is giving an equivalent inhibition va-
lue (45% vs 40%), 4-phenoxymethyl-1-(3-pyridyl)triazole
(15) and 4-(diethoxymethyl)-1-(4-methoxyphenyl)tria-
zole (19) gave a two to six time increase of growth inhi-
bition: from 22% to 56% and 11% to 71%, respectively.
We presented in this communication our results for the
synthesis and antibiotic activity measurements of a
thirty compounds library of 1,4-disubstituted-1,2,3-tria-
zoles. The triazoles were not very active on a reference
(ATCC 25923) and two resistant strains (1199B NorA,
RN4220 MsrA) of S. aureus.

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M. Aufort et al. / Bioorg. Med. Chem. Lett. 18 (2008) 1195–1198
However, a few products were found to have a moderate
activity on the NorA strain in the presence of ciproflox-
acin. This phenomenon was even more important while
testing the triazoles on the MsrA strain in the presence
of erythromycin. In this case, several compounds of
the library have shown a good inhibition in the presence
of this antibiotic, some of them reaching levels up to 70–
80% growth inhibition.
pUL5054 MsrA (at 16 and 256 mg LÀ1). The plates were
incubated at 37 °C and optical densities read over a 24 h
time.
Acknowledgments
This work was made possible by grants from CNRS
(7573 and 8151) and INSERM (U640). The authors also
wish to thank for their financial support SESAME and
CPER programs (Ile-de-France) and Pr. Jean-Marc
Paris for helpful discussions.
These results seem to demonstrate that 1,2,3-triazoles
could be interesting candidates for further antibiological
activity testing. Investigations on other members of this
class of compounds, as well as on their mode of action,
will be reported in due course.
References and notes
Typical procedures for triazole synthesis and tests. 1-
Benzyl-4-(N-phthalimidomethyl)-1,2,3-triazole (4): In
a 10 mL Schlenk tube was placed 185 mg (1 mmol) of
N-propargylphthalimide in 2 mL of DMSO/water 9:1.
Under stirring was introduced successively 119 lL
(1 mmol, 1 equiv) of benzyl bromide, 23 mg (0.2 mmol,
0.2 equiv) of D,L-proline, 21 mg (0.2 mmol, 0.2 equiv)
de Na2CO3, 78 mg de NaN3 (1.2 mmol, 1.2 equiv),
100 lL of freshly prepared 1 M sodium ascorbate
(0.1 mmol, 10 mol%) and 50 lL of 1 M CuSO4Æ5H2O
(0.05 mmol, 5 mol%). The tube was capped with a sep-
tum and the mixture stirred at 65 °C overnight. The
mixture was poured into 20 mL of ice-cold water and
stirred for 0.5 h. The resulting solid was filtered,
washed with water and dried under vacuum. The crude
product was purified on a short pad silica gel column
using a heptane to ethyl acetate gradient. 1-Benzyl-4-
(N-phthalimidomethyl)-1,2,3-triazole (4) (260 mg, 82%)
was isolated as a white solid.
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1402 cmÀ1
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3110, 3076, 3038, 2849, 1708, 1432,
.
1H NMR (300 MHz, CDCl3): d 4.97 (s,
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7.70–7.85 (m, 4H) ppm. 13C NMR (75.5 MHz, CDCl3):
d 33.1, 54.2, 122.7, 123.4, 128.1, 128.7, 129.1, 132.0,
134.1, 134.5, 143.1, 167.6 ppm. LC–MS. Rt = 9.10 min,
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Inhibition tests. Four isolated colonies of the strain were
suspended in Mueller–Hinton broth (1 mL) and incu-
bated at 37 °C for 18 h. This inoculum (100 lL) was di-
luted in 10 mL of the same medium to be used in
inhibition tests. Solutions of the compounds to be tested
were prepared in DMSO (10 mg mLÀ1). The tests were
run in 96-well format microplates using a Biomek 2000
(Beckman-Coulter). Two microliters of the compound
solution was added to 198 lL of each inoculum (for a fi-
nal concentration of 0.1 mg mLÀ1 of the molecule).
Three blanks were also prepared by adding 2 lL DMSO
and 2 lL of Mueller–Hinton medium, both to 198 lL of
inoculum, and the third one made from 200 lL of Muel-
ler–Hinton medium alone. Controls were also made
using antibiotics known to inhibit the strains’ growth:
ampicillin for S. aureus ATCC 25923 (at 0.25 mg LÀ1),
ciprofloxacin for S. aureus 1199B NorA (at 4 and
32 mg LÀ1) and erythromycin for S. aureus RN4220