Synthesis of a polyprenyl-type library containing 1,4-disubstituted-1,2,3-triazoles with anti-biofilm activities against Pseudoalteromonas sp.

Article abstract of DOI:10.1016/j.tetlet.2009.01.125

A terpenoid-like library containing 1,4-disubstituted-(1H)-1,2,3-triazoles was prepared by means of 1,3-dipolar cycloaddition of geranyl and farnesyl azides with a set of terminal alkynes, in order to design a new class of potentially active anti-biofilm

Full text of DOI:10.1016/j.tetlet.2009.01.125

Tetrahedron Letters 50 (2009) 1645–1648
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Tetrahedron Letters
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Synthesis of a polyprenyl-type library containing 1,4-disubstituted-1,2,3-triazoles
with anti-biofilm activities against Pseudoalteromonas sp.
*
Annie Praud-Tabaries, Linda Dombrowsky, Olivier Bottzek, Jean-Francois Briand, Yves Blache
Laboratoire MAPIEM, EA 4323, UFR Sciences et Techniques, Université du Sud Toulon-Var, 83957 La Garde Cedex, France
a r t i c l e i n f o
a b s t r a c t
Article history:
A terpenoid-like library containing 1,4-disubstituted-(1H)-1,2,3-triazoles was prepared by means of
1,3-dipolar cycloaddition of geranyl and farnesyl azides with a set of terminal alkynes, in order to design
a new class of potentially active anti-biofilm compounds. Reactions were optimized to proceed under
mild conditions and in high yields. Two compounds were found to possess interesting activity against
Pseudoalteromonas sp. biofilm. This process is suitable for combinatorial chemistry of marine natural
product-like compounds.
Received 10 December 2008
Revised 20 January 2009
Accepted 23 January 2009
Available online 29 January 2009
Ó 2009 Elsevier Ltd. All rights reserved.
Biofilms are agglomerates of bacteria on a surface that is sur-
rounded or held together by extracellular polymeric substances.
Bacteria produce these, in part, to help them attach to surfaces
and bind to one another. Such biofilms cause persistent infections
in humans and serious corrosion and equipment failure in indus-
trial settings.1 In continuation of our program aimed at establish-
ing the potentiality of marine natural products as potential
antifouling compounds,2 our group recently isolated a series of
meroditerpenes from brown alga Halidrys siliquosa.3 These com-
pounds were derivatives of geranylgeranyltoluquinol and repre-
sent an interesting class of biologically active compounds
exhibiting antifouling properties against marine bacteria. In addi-
tion, meroditerpenes were also found in diverse marine organisms
such as brown alga Cystoseira crinita,4 and were reported to possess
anticancer and anti-oxidant activities. Furthermore, 3-(40-geranyl-
oxy-30-methoxyphenyl)-2-trans propenoic acid isolated from Acr-
onychia baueri Schott5 was reported for its capacity to inhibit the
formation of P. gingivalis biofilm. In an effort to probe antifouling
structure–activity relationships of natural products, we felt that
the relatively simple structure of these compounds invited the syn-
thesis of analogs. In this context, we needed to develop a rapid and
efficient synthesis of libraries of analogs. The general structure of
the targeted library, as well as the retrosynthetic analysis is pre-
sented in Figure 1.
for combinatorial chemistry.6 In addition, a number of compounds
containing 1,2,3-triazoles have shown a broad spectrum of biolog-
ical activities such as antibiofilm inhibitors,7 antibacterial,8 antimi-
crobial,9 and anticancer.10 In general, the copper(I)-catalyzed 1,3-
dipolar cycloaddition namely Huisgen–Fokin–Sharpless usually
proceeds to completion in 6–36 h at ambient temperature in water
with a variety of organic co-solvents, such as tert-butanol, ethanol,
DMSO, THF, or CH3CN, and this reaction is useful for large classes of
azides and alkynes.6 However, since the particular allylazides exist
as an equilibrating mixture of regioisomers,11 the reaction should
be expected to be complex and might lead at least to mixtures of
three 1,2,3-triazole species resulting from rearrangements of start-
ing azides. In this context, we have first focused our interest on the
feasibility of the one-pot reaction between geranyl bromide, prop-
argyl methyl ether, and sodium azide, sodium ascorbate in DMF/
H2O in the presence of CuSO4–H2O as the catalyst. Formation of
azide in dimethylformamide was first monitored by 1H NMR (linal-
yl form 10%). The three-component reaction was then investigated
following the process given in Scheme 1.
Under these conditions, two compounds were isolated and
identified as 1-geranyl-4-methoxymethyl-1H-1,2,3-triazole 1a
and 1-neryl-4-methoxymethyl-1H-1,2,3-triazole 1b in a 35/65
Z/E ratio. Assignment of the stereochemistry of 1a and 1b was
unambiguously determined by 13C NMR and by comparison with
the parent compound geraniol and nerol: chemical shift of the
methyl group attached to the isomeric double bond is of
17.8 ppm in the case of 1a,12 and of 23.5 ppm in the case of 1b.13
In this reaction, no formation of the 1-linalyl-1H-1,2,3-triazole
derivative was found. However, since the yield of the reaction
(66%) was not sufficient enough for our purpose, we decided to
investigate a two-step procedure as follows (Scheme 2): azide
was first prepared in refluxing acetonitrile, and was treated in
order to eliminate excess of sodium azide and other salts (washed
with brine and extracted with ethyl acetate). The resulting
Conjugation of the aromatic moiety to the lipophilic chain was
planned to be achieved by click reaction between two different azi-
do derivatives of terpenes and aromatic-alkyne derivatives. The
copper(I)-catalyzed 1,3-dipolar cycloaddition of organic azides
and alkynes resulting in the formation of 1,2,3-triazoles has
become an increasingly attractive area because it is a highly
efficient process in bond formations among diverse building blocks
* Corresponding author.
E-mail address: blache@univ-tln.fr (Y. Blache).
0040-4039/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2009.01.125

1646
A. Praud-Tabaries et al. / Tetrahedron Letters 50 (2009) 1645–1648
Figure 1. Structure of targeted library.
Scheme 1. Three-component synthesis of triazoles.
Scheme 2. Two-step procedure for the synthesis of triazoles.
non-purified mixture of the three allylic azides was monitored by
1H NMR and then submitted to a set of diverse conditions in order
to optimize copper source, co-solvent, and temperature. Results
are reported in Scheme 2 and Table 1.
context, further optimization of reaction conditions indicated that
using acetonitrile as co-solvent at 70 °C led exclusively to the
5-alkynyl-1,2,3-triazoles 2a,b in 71% yield (entry 5). To our knowl-
edge, this method using Cu wire was not described previously, and
finally represent the simplest way to obtain 5-alkynyl-1,2,3-tria-
zoles in good yields. Furthermore, we found that the synthesis of
1a,b was better assumed using CuSO4–5H2O with sodium ascor-
bate and dimethylformamide as co-solvent (entry 1).16 In addition
whatever the conditions used, no derivatives possessing the linalyl
skeleton were found. Finally, conditions used in entry 1 were re-
tained for designing a small library of terpenoid-like compounds
by using geranylbromide and farnesylbromide as the source of
terpenoid units and some ethynylmethoxybenzene derivatives as
the source of terminal alkynes (Table 2).
The reported results clearly indicated the influence of the nat-
ure of catalyst. When using Cu wire, compounds 1a,b were ob-
tained admixed with the unexpected trisubstituted triazoles 2a,b
(entries 3 and 4). Such side reactions have been reviewed.6 For
example, Sharpless and co-workers have observed such derivatives
in the direct synthesis of trisubstituted triazoles via addition of
bromomagnesium acetylides to azides.14 More recently, formation
of such 5-alkynyl-1,2,3-triazoles from azides and alkynes was re-
ported by Baudouin et al.15 by use of tetrakisacetonitrile cop-
per(I)hexafluorophosphate with a diamine ligand. However, in
this study, the expected 1,4,5-trisubstituted triazoles were always
obtained admixed with their 1,4-disubstituted derivatives. In this
As in the case of geranylazide, farnesylazide underwent the
allylic rearrangement (monitored by 1H NMR) without effect on
Table 1
Copper (I)-catalyzed synthesis of 1,2,3-triazoles 1 and 2 in various conditionsa
Entry
Cu source
Solvent/H2O
(temp)
Compounds
1a,b (%, Z:E ratio)
2a,b (%, Z:E ratio)
1
2
3
4
5
CuSO4/sodium ascorbate
CuSO4/sodium ascorbate
Cu wire
Cu wire
Cu wire
DMF (rt)
CH3CN (rt)
DMF (rt)
CH3CN (rt)
CH3CN (70 °C)
96% (32/68)b
80% (48/52)b
57% (50/50)c
44% (40/60)c
0%
0%
0%
43% (50/50)c
56% (40/60)c
71% (31/69)b
a
16
All experiments were achieved in the same conditions of concentrations of reactants, catalyst, volume of solvents as referenced for entry 1 in Ref.
.
b
c
Calculated after purification.
Calculated from 1H NMR spectra of crudes mixtures.

A. Praud-Tabaries et al. / Tetrahedron Letters 50 (2009) 1645–1648
1647
Table 2
Synthesis of selected 1,2,3-triazolesa
N
R
N
N
Br
R
n
n
Compounds a(Z),b(E)
n
R
Yield (%)
Z/E ratio
3a,b
4a,b
5a,b
6a,b
7a,b
8a,b
9a,b
10a,b
11a,b
12a,b
1
1
1
1
1
2
2
2
2
2
2-Methoxy
3-Methoxy
4-Methoxy
3,5-Dimethoxy
3-Hydroxy
2-Methoxy
3-Methoxy
4-Methoxy
3,5-Dimethoxy
3-Hydroxy
83
92
68
45
94
78
69
94
82
88
20/80
36/64
38/62
41/59
58/42
37/63
40/60
36/64
35/65
35/65
a
16
All experiments were achieved in the same conditions of concentration of reactants, catalyst, volume of solvents as referenced for entry 1 in Ref.
.
the final composition. As observed (Table 2), independently of the
structural differences within the azide precursors (geranyl or far-
nesyl), the 1,2,3-triazole derivatives were obtained as Z/E mixtures
in good to excellent yields.
All compounds were tested as Z/E mixtures at a concentration of
500 lM for their capacity to inhibit biofilm formation by Pseudoal-
more, the potential of the Cu(I)-catalyzed Huisgen reaction as a
successful strategy to explore new diversity space and address
the structural decoration of privileged scaffolds has been estab-
lished in this area. Although we did not obtain any antibacterial
activity with the newly constructed terpenoid-like compounds, it
can be concluded that this class of compounds provide interesting
lead in our search for new potential inhibitors of bacterial biofilm
formation that should be used as environmentally-friendly anti-
fouling biocides. Further studies in this field by using others bacte-
rial strains are actually under way.
teromonas sp. D41. (Table 3).17 Farnesol (the parent sesquiterpene
of 8–12 and SEANINEÒ (a commercial biocide used in antifouling
coatings) were used as references. The results showed that all far-
nesyl derivatives presented mild to good anti-adhesion activities,
while only two geranyl derivatives were potentially active.
The most active compounds 5a,b and 11a,b were selected to
evaluate the EC50 of each isomer (EC50 is expressed as the effective
concentration to inhibit 50% of the bacterial adhesion). Results
showed that both isomers of the farnesyl derivative are active.
All compounds were also evaluated as the Z/E mixtures for their
potential antibacterial activities, in order to correlate inhibition
of biofilm to an antibacterial activity. Using the disk diffusion assay
methods,18 compounds were tested for their antibacterial activities
against various strains of bacteria, including Pseudoalteromonas sp.
(D41), Pseudomonas aeruginosa (ATCC A22), Staphylococcus aureus
(ATCC 53.156), Bacillus cereus (ATCC 78.3), and Escherichia coli
(ATCC 54.8 T). Interestingly, no significant inhibitory activities
were observed when compared to norfloxacin.
Acknowledgment
The pseudoalteromonas sp. strain was gracefully supplied by
IFREMER; Service Interfaces et Capteurs, IFREMER Brest, France.
References and notes
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127, 13444; Padwa, A.; Marcus, M. Tetrahedron Lett. 1997, 38, 5087.
12. 1-Geranyl-4-methoxymethyl-1H-1,2,3-triazole (1a): Yellow oil, MS (ESI), 250
(M+1), 272(M+23), 1H NMR (400 MHz, CDCl3) d 1.58 (s, 3H, CH3), 1.66 (s, 3H,
CH3), 1.76 (s, 3H, CH3), 2.12 (m, 4H), 3.39 (s, 3H, OCH3), 4.55 (s, 2H), 4.94
In summary, a simple and efficient procedure allowing the rapid
assembly of libraries of bioactive valuable 1,2,3-triazoles contain-
ing terpenoid mimetic structures has been developed. Further-
Table 3
Pseudoalteromonas sp. D41 biofilm inhibition of compounds 1–12
Compoundsa
(%) of adhesionb
EC50 (lM)
Z/E (a,b)
E (a)
Z (b)
5a,b
7a,b
8a,b
9a,b
10a,b
11a,b
12a,b
Farnesol
SeanineÒ
3
30
25
15 39
46
0
34
25
19
8
6
7
400.0 5.9
298.0 1.2
71.0 1.2
188.0 1.2
7
7
2
9
6
99.0 1.2
53.0 1.2
188.0 1.2
135.0 2.0
a
No activity was observed with other compounds (3, 4, 6).
Percentage of adhesion at a concentration of 500 lM (% of adhesion).
b

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A. Praud-Tabaries et al. / Tetrahedron Letters 50 (2009) 1645–1648
(d, J = 7.33, 2H), 5.04 (m, 1H), 5.41 (t, J = 7.59, 1H), 7.47, (s, 1H); 13C NMR
(100 MHz, CDCl3) d: 16.3, 17.6, 25.6, 26.0, 39.3, 47.7, 58.2, 66.0, 116.9, 121.5,
123.4, 132.1, 143.3, 145.0.
The organic layers were then dried over Na2SO4 and evaporated. The resulting
oil was added to a solution of H2O/DMF (1.5 mL/1.5 mL) containing CuSO4–
5H2O (0.07 mmol), propargyl methyl ether (1.1 mmol), and sodium ascorbate
(0.2 mmol). The resulting mixture was stirred 12 hours at rt. A saturated
solution of Na2CO3 was added, and the resulting solution was extracted three
times with ethyl acetate. The organic layers were then dried over Na2SO4 and
evaporated to give the corresponding triazoles, which were purified by flash
13. 1-Neryl-4-methoxymethyl-1H-1,2,3-triazole (1b): Yellow oil, 250 (M+1),
272(M+23), 1H NMR: (400 MHz, CDCl3) d:1.60 (s, 3H, CH3), 1.67 (s, 3H, CH3),
1.79 (s, 3H, CH3), 2.17 (m, 4H), 3.39 (s, 3H, OCH3), 4.56 (s, 2H), 4.92 (d, J = 7.33,
2H), 5.08 (m, 1H), 5.41 (t, J = 7.59, 1H), 7.49, (s,1H). 13C NMR (100 MHz, CDCl3)
d 17.6, 23.3, 25.6, 26.2, 32.0, 47.6, 58.2, 66.0, 117.7, 121.6, 123.1, 132.6, 143.0,
145.0.
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15. Baudouin, G.; Ryan, J.; Beeler, A.-B.; Porco, J.-A., Jr. Tetrahedron 2006, 62, 6405.
16. Entry 1: A solution of geranyl bromide (0.78 mmol), and NaN3 (2.8 mmol) in
CH3CN (1.5 mL) was stirred at 70 °C for 2 h. A saturated solution of Na2CO3 was
added, and the resulting solution was extracted three times with ethyl acetate.
chromatography on silica gel (Si60 15–40 lm, n-hexane/ethyl acetate (70:30)).
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