Synthesis and biological evaluation of new N-acyl-homoserine-lactone analogues, based on triazole and tetrazole scaffolds, acting as LuxR-dependent quorum sensing modulators

Article abstract of DOI:10.1016/j.bmc.2012.06.007

New analogues of N-acyl-homoserine-lactone (AHL), in which the amide was replaced by a triazole or tetrazole ring, were prepared and tested for their activity as LuxR-dependent QS modulators. Several compounds showed a level of antagonistic or agonistic activity, notably some 1,4-triazolic and 1,5-tetrazolic derivatives, whereas the 2,5-tetrazolic compounds were inactive. In 1,5-tetrazoles, substituted with butyrolactone and an alkyl chain, the activity was reversed, depending on the connection between the lactone and the tetrazole. The C-N connected compounds were agonists whereas the C-C connected ones were antagonists.

Full text of DOI:10.1016/j.bmc.2012.06.007

Bioorganic & Medicinal Chemistry 20 (2012) 4727–4736
Contents lists available at SciVerse ScienceDirect
Bioorganic & Medicinal Chemistry
journal homepage: www.elsevier.com/locate/bmc
Synthesis and biological evaluation of new N-acyl-homoserine-lactone
analogues, based on triazole and tetrazole scaffolds, acting as
LuxR-dependent quorum sensing modulators
Mohamad Sabbah a,b, Fanny Fontaine a,b, Lucie Grand a,b, Mohamed Boukraa a,b,c, Mohamed L. Efrit c,
a,b,
Alain Doutheau a,b, Laurent Soulère a,b, , Yves Queneau
⇑
⇑
a INSA Lyon, ICBMS, Bât J. Verne, 20 av A. Einstein, 69621 Villeurbanne Cedex, France
b CNRS, UMR 5246, ICBMS, Université Lyon 1, INSA-Lyon, CPE-Lyon, Bât CPE, 43 bd du 11 novembre 1918, 69622 Villeurbanne Cedex, France
c Laboratoire de Synthèse Organique et Hétérocyclique, Faculté des Sciences de Tunis, Campus Universitaire, 2092 Manar II, Tunis, Tunisia
a r t i c l e i n f o
a b s t r a c t
Article history:
Available online 9 June 2012
New analogues of N-acyl-homoserine-lactone (AHL), in which the amide was replaced by a triazole or tet-
razole ring, were prepared and tested for their activity as LuxR-dependent QS modulators. Several com-
pounds showed a level of antagonistic or agonistic activity, notably some 1,4-triazolic and 1,5-tetrazolic
derivatives, whereas the 2,5-tetrazolic compounds were inactive. In 1,5-tetrazoles, substituted with
butyrolactone and an alkyl chain, the activity was reversed, depending on the connection between the
lactone and the tetrazole. The C–N connected compounds were agonists whereas the C–C connected ones
were antagonists.
Keywords:
Quorum sensing
Inhibition
Induction
AHL
Ó 2012 Elsevier Ltd. All rights reserved.
Triazole
Tetrazole
1. Introduction
transcriptional factors.12–14 In recent years we have reported sev-
eral classes15–22 of QS inhibitors in Vibrio fischeri bacteria. Among
Bacterial quorum sensing (QS) refers to a cell-to-cell communi-
cation system which allows bacteria to synchronize the expression
of specific genes, encoding for phenotype expression, as a function
of their population density.1–5 This communication is based on the
synthesis and release of small diffusible signal molecules, known
as autoinducers, which bind to their cognate transcriptional regu-
latory proteins. QS regulates diverse phenotypes, such as biolumi-
nescence, antibiotic production, symbiosis, biofilm formation or
virulence factors, in a variety of microorganisms found in plants,
animals and humans. Thus, QS modulation is considered as a
promising new strategy for controlling both pathogenesis and
symbiosis, which have important impacts on human health and
the environment,6–11 either by stimulation or inhibition of commu-
nication. Therefore, the development of synthetic ligands, which
are able to behave as antagonists of autoinducers, constitutes an
important research strategy for the design of potential antibacte-
rial drugs.
those showing close structural analogy with AHLs, we have inves-
tigated, in particular, the effect of replacing the amide function
with amide bioisosteres, such as sulfonamide,19 urea,20 sulfonyl-
urea21 or reverse-amides.22
Heterocycles, containing several nitrogen atoms, are scaffolds
that are frequently considered when designing bioactive com-
pounds and some of them behave as biomimetics. However, within
the field of QS modulation, very few AHL analogues built on a cen-
tral multi-nitrogen heterocycle have been reported to date, with
the exception of one series of tetrazolic compounds described by
Greenberg’s group23 and one family of imidazolium compounds
O
H
N
R
O
O
X
AHLs
In Gram negative bacteria, N-acyl-homoserine lactones (AHLs)
(Fig. 1) are the main autoinducers and LuxR-type proteins are the
X = H, OH
R = alkyl
O
H
N
R
O
⇑
Corresponding authors. Tel.: +33 4 72 43 83 42; fax: +33 4 72 43 88 96 (L.S.);
O
tel.: +33 4 72 43 61 69; fax: +33 4 72 43 88 96 (Y.Q.).
E-mail addresses: laurent.soulere@insa-lyon.fr (L. Soulère), yves.queneau@
insa-lyon.fr (Y. Queneau).
O
Figure 1. Structures of AHLs.
0968-0896/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.bmc.2012.06.007

4728
M. Sabbah et al. / Bioorg. Med. Chem. 20 (2012) 4727–4736
O
O
N
O
N
C11H23
a)
N
N
N
N
O
O
N3
HO
N
tetrazole PD12 (ref. 23)
1a
2
O
N3
O
3
b)
-
Br
+
C11H23
N
N
O
N
N
N
R2
R1
C5H11 C12H23
R1
R2
Imidazolium salt (ref. 18)
N
1b c
,
(79, 89 %)
1b
1c
1e
EtO
c)
1d
1f
HO
O
1d,e
(96 %)
X
N
H2N
O
d)
e)
N
alkyl chain
1f
(95 %)
(75 %)
1b
1g
HOHN
X = C, N
Triazolic and tetrazolic new targets
1g
Scheme 1. Preparation of triazole 1a–1g. Reagents and conditions: (a) hept-1-yne,
CuI, H2O/CH3CN (1:1), rt, 72 h; (b) CuIsupp, CH2Cl2, rt, 12 h; (c) KOH, Ethanol, rt, 4 h;
(d) NH3, methanol, À30 °C to rt, 16 h; (e) NH2OHaq, KCN, THF/MeOH (1:1), rt, 24 h.
Figure 2. Known and targeted QS modulators constructed on a central multi-
nitrogen heterocyclic scaffold.
inverted triazoles of type 2, isomers of type 1 compounds, were
synthesized in order to evaluate any effects on the biological activ-
ity due to the position of the nitrogen atoms with respect to the
substituents on the triazole ring.
described by some of us (Fig. 2).18 Pursuing our efforts to identify
new QS inhibitors by replacing the amide of AHLs with various
functions, we report here the synthesis and the biological evalua-
tion of new AHL analogues, based on the 1,2,3-triazole or 1,2,3,4-
tetrazole scaffolds ( Fig. 2), as LuxR-dependent QS agonists or
antagonists.
2.1. Synthesis
Racemic 1,2,3-triazole 1a was prepared from a 1,3-dipolar
cycloaddition reaction between the known32 racemic azido-lac-
2. Triazoles
tone
2 and hept-1-yne, using copper iodide as a catalyst
(Scheme 1).28 Triazoles 1b–g were obtained from known33 ethyl-
2-azidoacetate 3. Huisgen’s 1,3 dipolar cycloaddition reaction of
3 with hept-1-yne or tetradec-1-yne, in the presence of a poly-
mer-supported copper catalyst,34 led to the desired triazoles 1b,c
in 79–89% of isolated yields. Triazoles with an acid function, 1d
and 1e, were obtained by saponification of the corresponding ethyl
esters, 1b and 1c. The reaction of 1b with ammonia in methanol35
or in aqueous hydroxylamine, using potassium cyanide as a cata-
lyst,36 produced the triazole-amide 1f and triazole-hydroxamate
1g, respectively (Scheme 1).
The triazole ring displays some similarity with amide bonds, in
terms of distance and planarity, and has been known for a long
time as an amide bond mimic.24–26 This motif can be easily ob-
tained using Huisgen’s 1,3-dipolar cycloaddition between an azide
and an alkyne.27 Using improved experimental conditions, this
reaction can result in good to excellent yields and complete regi-
oselectivity,28–30 making this strategy attractive for the design of
bioactive compounds.31 In this context, we decided to prepare an
AHL analogue of type 1, in which a 1,2,3-triazole ring is introduced
in place of the amide function of AHLs (Fig. 3). The first targeted tri-
azole derivative in the series was 1a, in which the lactone ring is
retained and equipped with an alkyl chain of 5 carbon atoms, an
appropriate length according to our previous studies.19–21 Since
this compound was active (vide infra), and inspired by Greenberg’s
results23 showing that a carboxylic acid was a possible substitution
in tetrazolic compounds bearing a long alkyl chain (although the
activity was demonstrated in another biological assay related to
Pseudomonas aeruginosa), triazoles 1b–g, lacking the lactone ring
and bearing longer alkyl chains, were then prepared. Finally,
Type 2 triazoles were prepared in three or four steps (Scheme 2).
The reaction of pentyl bromide, 4a, and dodecyl bromide, 4b, with
sodium azide resulted in azidoalkanes 5a and 5b in 36% and 80%
isolated yields, respectively.33 Also, a good yield of triazoles 6
was obtained by reacting azidoalkanes 5 with 3-butyn-1-ol, under
the same cycloaddition conditions as stated above. Oxidation of
compounds 6 with Jones reagent led to the desired triazoles 2c
and 2d in 66% and 69% yields, respectively, which could then be
transformed into the corresponding esters 2a,b (Scheme 2).
O
O
O
N
N
N
N
N
N
N
N
N
R1
O
R1
R2
C5H13
R2
1a
1b-g
2a-d
R1 = EtO, HO, H2N, HOHN
R2 = C5H11 C12H23
R1 = EtO, HO
R2 = C5H11, C12H23
,
Figure 3. Structure of triazoles of type 1 and 2.

M. Sabbah et al. / Bioorg. Med. Chem. 20 (2012) 4727–4736
4729
O
N
N
N
N
N
N
a)
b)
c)
d)
R2N3
R2Br
R1
R2
R2
HO
4a
4b
5a
6a
(73 %)
6b (81 %)
(36 %)
2c
2d
(68 %)
(69 %)
R1 = HO
5b (80 %)
a, c
b, d
= C12H23
R2:
= C5H11
;
2a
(40 %)
R1 = EtO
2b (59 %)
Scheme 2. Preparation of triazole 2a–d. Reagents and conditions: (a) NaN3, acetone/H2O (3:1), rt, 1 h; (b) 3-butyn-1-ol, CuIsupp, CH2Cl2, rt, 12 h; (c) chromic acid, sulfuric
acid, acetone, 0 °C, 12 h; (d) sulfuric acid, ethanol, 0 °C to rt, 4 h.
2.2. Biological evaluation of triazoles
the amide 1f and hydroxamate 1g were active. The longer chain
compounds 1c and 1e, as well as all type 2 triazoles, were found
to be inactive.
Compounds 1 and 2 were first tested for their ability to induce
luminescence in an Escherichia coli biosensor strain containing a
plasmid that couples the luxR and luxICDABE promoter region of
Vibrio fischeri to the luxCDABE operon of Photorhabdus lumines-
cens.15 Neither of them displayed any agonistic activity at concen-
2.3. Molecular modeling of triazole 1a
The proposed binding mode of the triazole derived compound,
1a, was obtained as a result of flexible docking in the ligand bind-
ing site of the LuxR model37 (Fig. 4), constructed on the basis of the
X-ray structure of TraR.38
trations up to 200 lM. QS inhibition was then evaluated by
measuring the decrease in bioluminescence induced by 3-oxo-
C6-HSL (200 nM), the main QS autoinducer in Vibrio fischeri. The
lactone 1a proved to be active, with significant antagonist activity
This binding mode suggests that compound 1a has a similar po-
sition in the active site to the natural ligand 3-oxo-hexanoyl homo-
serine lactone (OHHL),16,38 with the triazole ring located in the
same area of the active site as the amide function in the autoinduc-
er (Fig. 4A). Three hydrogen bonds are shown in the model, two of
which are similar to those observed in the case of the natural li-
gand,16 involving Trp66 and the carbonyl function of the lactone
ring and Tyr62 and the nitrogen atoms of the triazolyl moiety,
respectively. The third H-bond indicated in this model, which in-
volves the triazole ring and Ser137, might explain the antagonist
activity of triazole 1a (Fig. 4B).
(IC50 = 51
1b, equipped with
(IC50 = 94 M) whereas neither the corresponding acid 1d, nor
2
lM). Among the non-lactonic analogues, ethyl ester
a
short alkyl chain, displayed activity
4
l
3. Tetrazoles
Tetrazoles are often important in biology and medicine.39 In
particular, 5-substituted tetrazoles are nonclassical isosteres of
the carboxyl group and 1,5-disubstituted tetrazoles can be used
as isosteres of the cis-amide bond of peptides.40–42 Although they
have been studied less, examples of biologically active 2,5-disub-
stituted tetrazoles have also been reported.43–45 Notably, among
the tetrazoles reported by Greenberg and colleagues as being QS
inhibitors in Pseudomonas aeruginosa, the most potent was the
2,5-disubstituted derivative PD12 (Fig. 2). In the present study,
we have focused our attention on new butyrolactone–tetrazole hy-
brids in which the lactone moiety is connected either to the carbon
atom of the tetrazole ring (7a and 8a,d,e) or to the nitrogen atom
(9a–d). All the compounds in this series are racemic. Analogues
with an ethyl ester (7b,c and 8b,c) were also prepared in view of
our previous results in the triazole series, as were the carboxylic
acids (7d,e) for comparison purposes (Fig. 5).
3.1. Synthesis
The reaction of the known46 racemic lactone 10 with sodium
azide, in the presence of ammonium chloride,47 gave a moderate
yield of the tetrazole 11. Subsequent alkylation with hexyl bromide
led to a mixture of the racemic tetrazoles 7a and 8a in 66% yield
(Scheme 3), which were then separated by silica gel column chro-
matography. Compounds 7b,c and 8b,c, were obtained in good
yields by the same method, from the known48 tetrazole 12 using
hexyl or dodecyl chloride. The corresponding acids, 7d and 7e,
were obtained by saponification of the ester-tetrazoles 7b and
7c, in almost quantitative yields.
Figure 4. Proposed binding mode of compound 1a in the ligand binding site of the
LuxR model: (A) Overview of compound 1a and 3-oxo-hexanoyl homoserine
lactone (OHHL) within the binding site; (B) magnification and simplification of the
binding mode showing interactions with conserved residues.

4730
M. Sabbah et al. / Bioorg. Med. Chem. 20 (2012) 4727–4736
C6H13
O
R1
O
N
N
2
N
O
N
N
N
N
N
1
O
2
5
N
5
N
1
O
N
N
5
N
1
N
5
EtO
O
N
O
N
N
5
N
O
R2
N
O
N
R1
R1
R1
7a
7b-e
8a,d,e
8b,c
9a-d
R1 = alkyle R2 = H, Et
Figure 5. Structure of tetrazoles 7, 8 and 9.
O
O
O
C6H13
O
a)
b)
N
N
O
N
N
O
N
O
N
N
O
NH
N
C N
+
N
N
N
C6H13
10
11 (42%)
7a (46%)
8a (20%)
R1
NH
N
O
N
N
O
N
N
O
b)
N
N
N
N
+
O
N
R2
R2
N
12
(50 %)
R1
7b R1 = C6H13 R2 = EtO (54%)
8b
R1 = C6H13 R2 = EtO (38%)
7c
R1 = C12H23 R2 = EtO (53%)
8c R1 = C12H23 R2 = EtO (34%)
c)
7d
R1 = C6H13 R2 = H (94%)
7e (PD12) R1 = C12H23 R2 = H (93%)
Scheme 3. Simultaneous preparation of tetrazoles 7a–e and 8a–c. Reagents and conditions: (a) NaN3, NH4Cl, DMF, 105 °C, 6 h, then HClconc (b) alkyl bromide, Et3N,
acetonitrile, reflux, 18 h; (c) KOH, ethanol, rt, 4 h.
O
O
O
O
N N
a)
b)
R
N
O
COOH
O
N
H
O
N
R
14a
8d
R = C4H9
R = C4H9 (35 %)
13
14b R = C5H11
8e R = C5H11 (45 %)
Scheme 4. Preparation of tetrazole 8d and 8e. Reagents and conditions: (a) butylamine/pentylamine, DCC, DMAP, CH2Cl2, 0 °C to rt, 14 h; (b) NaN3, Tf2O, CH3CN, rt, 10 h.
Tetrazoles 8d and 8e were obtained from a two step reaction
(Scheme 4). Reaction of the known49 racemic butyrolactone 13
with butylamine and hexylamine led to amides 14a and 14b (re-
verse amide AHL analogues previously described by our group).22
A subsequent reaction with sodium azide, in the presence of triflic
anhydride,50 led to the corresponding tetrazoles 8d and 8e.
Tetrazoles 9 were prepared from reactions of the racemic
aminolactone 15 with diverse acyl chlorides, under basic condi-
tions, resulting in the intermediate amides 16. A further reaction
with sodium azide50 (Scheme 5) led to the racemic tetrazoles
9a–d in yields ranging from 35% to 80%.
O
O
O
N
N
H
N
b)
a)
NH2.HBr
N
O
3.2. Biological evaluation
O
R
N
O
O
R
The series of 14 new tetrazoles was evaluated using the same
biological assay, as described above, for triazoles. All 2,5-disubsti-
tuted compounds of type 7 proved to be inactive in this test, which
relates to the QS system of Vibrio fischeri. It is interesting to note that
compound 7e was reported, by Greenberg, to be active in another QS
system, that of Pseudomonas aeruginosa which involves a different
type of receptor protein.23 This is another example amongst many
15
16a
16b
16c
a: R = C4H9
9a
(98 %)
(35 %)
(80 %)
(54 %)
b
9b
9c
(62 %) : R = C5H11
(90 %) c: R = C6H13
16d (67 %) d: R = C7H15 9d (56 %)
Scheme 5. Preparation of tetrazole 9a to 9d. Reagents and conditions: (a) acyl
chloride, pyridine, CHCl3, 0 °C to rt, 16 h; (b) NaN3, Tf2O, CH3CN, rt, 10 h.

M. Sabbah et al. / Bioorg. Med. Chem. 20 (2012) 4727–4736
4731
Table 1
3.3. Molecular modeling of tetrazoles 8a and 9b
Inhibition or induction of bioluminescence obtained with compounds 8a, b, d, e and
9b, c
The proposed binding modes of tetrazole 8a and 9b, obtained
with the protein LuxR, are depicted in Figure 6.
a,b
c,d
Compounds IC50
(l
M) Compounds EC50
(l
M) Biolum.
(RLU)
max
Compounds 9b and 8a are shown to occupy the same general
area within the active site as the autoinducer. According to this
model, compound 9b, which exhibits agonistic activity, would dis-
play similar interactions as the natural ligand, with hydrogen bonds
involving Trp 66 and Tyr 62.16 For compound 8a, which exhibits
antagonistic activity, the same two hydrogen bonds with Trp66
would appear to be possible, whereas the heterocycle would now
interact tightly with Tyr70 instead of Tyr 62. It is suggested that
the difference of activity between the two compounds is mainly dri-
ven by these interactions, either with Tyr62 or with Tyr70.
8a
8b
8d
8e
74 ( 1)
>200
>200
9b
9c
10 ( 1)
35 ( 1)
59 ( 2)
102 ( 3)
80 ( 2)
a
Concentration (lM) required to reduce the bioluminescence, induced by
200 nM of 3-oxo-C6-HSL, to a level of 50% intensity (IC50).
Values are the means of three experiments; standard deviation is given in
brackets.
b
c
Concentration (
lM) required to induce 50% intensity of bioluminescence.
d
Values are the means of two experiments; standard deviation is given in
brackets.
compounds which exhibit a distinct activity, sometimes even re-
verse activity, when applied to one bacterium species or an-
other.12–14,51
4. Conclusion
Several new compounds with a triazolic or tetrazolic core, to
which a lactone is attached, are shown to behave as LuxR-depen-
dent QS modulators, with activity levels within the moderate 10–
Among the 1,5-disubstitued tetrazoles, only compounds substi-
tuted with a short alkyl chain displayed significant activity, either
antagonistic (8a and 8e) or agonistic (9b and 9c) (Table 1). Thus,
just a slight modification in the structure, namely the position of
the nitrogen atoms in the tetrazole ring, is enough to convert the
antagonist tetrazoles 8a and 8e into the agonist isomeric tetrazoles
9c and 9b, respectively. It should be noted that the tetrazole 9c,
which displays a much higher EC50 than the autoinducer (3-oxo-
100 lM range. Modeling of the most active compounds in the study
suggests that the triazolic or tetrazolic rings are located where the
amide function of the autoinducer normally sits. Apart from one
triazolic compound, which bears an ethyl ester motif instead of
the lactone, all active compounds in this study retain the lactone
moiety. Among the tetrazolic compounds, only the 1,5-systems
have shown any activity whereas the 2,5-ones proved to be inactive,
possibly due to the relative ability, or inability, of such linkages to
serve as amide mimics. In the case of the active 1,5-tetrazoles, the
way in which the lactone is connected to the tetrazole appears to
C6-HSL, EC50 = 0.2
concentrations (P100
l
M),15 is nevertheless quite active since at high
M) these two compounds induce the same
l
bioluminescence intensity, that is 99 ( 3) and 102 ( 3) RLU,
respectively.
Figure 6. Proposed binding mode of agonist 9b (top) and antagonist 8a (bottom) in the ligand binding site of the LuxR model: (A) Overview of compounds 9b and 8a with all
the residues of the binding site; (B) magnification and simplification of the binding mode showing interactions with conserved residues.

4732
M. Sabbah et al. / Bioorg. Med. Chem. 20 (2012) 4727–4736
be critical, as the C–N connected compounds are agonists whereas
the C–C connected ones are antagonists. Overall, this study confirms
that multi-nitrogen heterocycles can serve as scaffolds for designing
new QS modulators.
5.1.2.1.
(1b).
Ethyl
2-(4-pentyl-1H-1,2,3-triazol-1-yl)acetate
Following the general procedure A, compound 1b
(481 mg, 79%) was obtained as a green oil from ethyl azidoacetate
3 (349 mg, 2.7 mmol) and hept-1-yne (354 L, 3.24 mmol). Eluent:
l
pentane/ dichloromethane (8/2). 1H NMR (300 MHz, CDCl3): d 0.89
(m, 3H); 1.30 (m, 7H); 1.69 (m, 2H); 2.74 (t, J = 7.7 Hz, 2H); 4.26 (q,
J = 7.2 Hz, 2H); 5.11 (s, 2H); 7.41 (s, 1H). 13C NMR (75 MHz, CDCl3):
d 14.0; 14.0; 22.4; 25.6; 29.0; 31.4; 50.8; 62.3; 122.0; 148.9; 166.6.
HRMS ESI+ calculated for C11H19N3O2 H+: 226.1550; found: MH+,
226.1547.
5. Experimental section
5.1. Synthesis
The solvents were distilled and dried prior to use: dichloro-
methane from calcium hydride and tetrahydrofuran from sodium
benzophenone ketyl. Organic solutions were dried over anhydrous
sodium sulfate. The reactions were performed under a constant
flow of nitrogen. The reactions were monitored, by t.l.c., on Silica
Gel 60 F254 (Merck) and detection was carried out by UV light
(254 nm) and/or charring with a 5% phosphomolybdic acid solu-
tion in ethanol containing 10% of H2SO4, or a 1% potassium per-
manganate solution in water. Silica gel (Kieselgel 60, 70–
230 mesh ASTM, Merck) was used for column chromatography.
Melting points were determined on a Kofler block apparatus.
The 1H NMR (300 MHz or 400 MHz) and 13C NMR (75 MHz or
100 MHz) spectra were recorded with Brucker ALS300, DRX300,
and DRX400 spectrometers. Chemical shifts are given in ppm. Cou-
pling constants are expressed in Hertz and splitting pattern abbre-
viations are: s, singlet; d, doublet; t, triplet; q, quartet; quint,
quintuplet; m, multiplet; M, massif, p, pseudo; br, broad. Multiplic-
ity (13C NMR) was determined by DEPT sequences. High resolution
mass spectra were obtained using an electro spray technique, in
positive mode with a ThermoFinnigan MAT 95 XL spectrometer.
Amides 14a,b,22 and amides 1652 were obtained following the pro-
cedures reported in the literature.
5.1.2.2.
(1c).
Ethyl
2-(4-dodecyl-1H-1,2,3-triazol-1-yl)acetate
Following the general procedure A, compound 1c
(753 mg, 89%) was obtained as a white solid from ethyl azidoace-
tate 3 (338 mg, 2.6 mmol) and tetradec-1-yne (966 L, 3.9 mmol).
l
Mp = 75–76 °C, Eluent: pentane/dichloromethane (8/2). 1H NMR
(300 MHz, CDCl3): d 0.88 (t, J = 6.7 Hz, 3H); 1.30 (m, 21H); 1.68
(m, 2H); 2.73 (t, J = 7.8 Hz, 2H); 4.26 (q, J = 7.1 Hz, 2H); 5.12 (s,
2H); 7.41 (s, 1H). 13C NMR (75 MHz, CDCl3): d 14.1; 14.2; 22.7;
25.7; 29.3; 29.4 (2C); 29.4; 29.6; 29.7 (2C); 29.7; 32.0; 50.8;
62.3; 122.0; 149.0; 166.6. HRMS ESI+ calculated for C18H33N3O2
H+: 324.2646; found: MH+, 324.2647.
5.1.2.3. 2-(1-Pentyl-1H-1,2,3-triazol-4-yl)ethanol (6a).
lowing the general procedure A, compound 6a (670 mg, 73%) was
obtained as green oil from 1-azidopentane 5a (500 mg,
4.42 mmol) and 3-butyn-1-ol (402 L, 5.3 mmol). Eluent: metha-
Fol-
a
l
nol/ethyl acetate (5/95). 1H NMR (300 MHz, CDCl3): d 0.89 (t,
J = 6.9 Hz, 3H); 1.32 (m, 4H); 1.89 (quint, J = 7.5 Hz, 2H); 2.31 (M,
2H); 2.93 (t, J = 5.9 Hz, 2H); 3.99 (M, 1H, OH); 4.31 (t, J = 7.2 Hz,
2H); 7.43 (m, 1H). HRMS ESI+ calculated for C9H17N3O Na+:
206.1264; found: MNa+, 206.1259.
5.1.1. 3-(4-Pentyl-1H-1,2,3-triazol-1-yl)dihydrofuran-2(3H)-one
(1a)
5.1.2.4.
(6b).
2-(1-Dodecyl-1H-1,2,3-triazol-4-yl)ethanol
Following the general procedure A, compound 6b
Copper(I) iodide (30 mg, 0.15 mmol) and hept-1-yne (394 lL,
(920 mg, 83%) was obtained as a white solid from 1-azidododecane
5b (853 mg, 4.03 mmol) and 3-butyn-1-ol (366 L, 4.84 mmol).
3 mmol) were added to a stirred solution of 3-azidodihydrofuran-
2(3H)-one32 2 (381 mg, 3 mmol) in 12 mL of acetonitrile/water
(1:1). The mixture was stirred at room temperature for 72 h, washed
with water (50 mL) and then extracted with ethyl acetate
(2 Â 100 mL). The organic phase was dried, filtered, and concen-
trated, under reduced pressure, to provide the compound 1a
(288 mg, 43%), after purification by flash chromatography using
pentane/ethyl acetate (4/6) as the eluent. White solid mp = 75–
76 °C. 1H NMR (300 MHz, CDCl3): d 0.90 (t, J = 7.2 Hz, 3H); 1.35 (m,
4H); 1.69 (m, 2H); 2.73 (t, J = 7.5 Hz, 2H); 2.94–3.15 (m, 2H); 4.53–
4.57 (m, 1H); 4.65–4.72 (dt, J = 3.6 Hz et 8.1 Hz, 1H); 5.29 (t,
J = 9.6 Hz, 1H); 7.54 (s, 1H). 13C NMR (75 MHz, CDCl3): d 14.1;
22.5; 25.7; 29.0; 29.4; 31.5; 57.6; 66.4; 120.9; 149.1; 171.4. HRMS
ESI+ calculated for C11H17N3O2 H+: 224.1394; found: MH+, 224.1391.
l
Mp = 67–68 °C, eluent: methanol/ethyl acetate (1/9). 1H NMR
(300 MHz, CDCl3): d 0.88 (t, J = 6.7 Hz, 3H); 1.28 (m, 18H); 1.61
(s, 1H); 1.89 (quint, J = 6.8 Hz, 2H); 2.61 (t, J = 5.9 Hz, 1H); 2.95 (t,
J = 5.6 Hz, 2H); 3.96 (m, 2H); 4.32 (t, J = 7.2 Hz, 2H); 7.36 (s, 1H).
HRMS ESI+ calculated for C16H32N3O H+: 282.2540; found: MH+,
282.2539.
5.1.3. 2-(4-Pentyl-1H-1,2,3-triazol-1-yl)acetamide (1f)
Triazole 1b (200 mg, 0.89 mmol) was added to a saturated solu-
tion of NH3 in MeOH (10 mL) at À30 °C. The mixture was stirred for
16 h at room temperature. After evaporation, the residue was puri-
fied by recrystallisation (MeOH/pentane) to produce pure 1f
(166 mg, 95%) as
a
white solid. Mp = 164–165 °C, 1H NMR
5.1.2. General procedure A for the preparation of triazoles (1b,
1c, 6a, 6b), using a polymer supported catalyst34
(300 MHz, DMSO-d6): d 0.87 (t, J = 6.6 Hz, 3H); 1.29 (m, 4H); 1.59
(m, 2H); 2.60 (t, J = 7.5 Hz, 2H); 4.98 (s, 2H); 7.34 (s, 1H, NH);
7.67 (s, 1H, NH); 7.76 (s, 1H). 13C NMR (75 MHz, DMSO-d6): d
13.9; 21.9; 24.9; 28.7; 30.8; 51.3; 123.3; 146.6; 167.5. HRMS
ESI+ calculated for C9H16N4O Na+: 219.1216; found: MNa+,
219.1217.
Dry Amberlyst A-21 (1.0 g, 4.8 mmol amine) was added to a
solution of copper(I) iodide (381 mg, 2.00 mmol) in acetonitrile
(15 mL) and gently shaken on an orbital stirrer for 17 h. The sol-
vent was filtered, the resin was washed with CH3CN (2 Â 15 mL)
and CH2Cl2 (2 Â 15 mL), and then dried in vacuum (0.01 mm Hg)
at 40 °C. The increase in weight was 0.307 g (1.61 mmol CuI),
5.1.4. N-Hydroxy-2-(4-pentyl-1H-1,2,3-triazol-1-yl)acetamide
(1g)
which gave the polymer a loading of 1.23 mmol CuI gÀ1
.
The polymer supported catalyst (Amberlyst A-21ÁCuI,
0.076 equiv) was added to a solution of azides (1 equiv) and al-
kynes (1.2 equiv) in dichloromethane. The suspension was orbital-
ly stirred for 12 h at room temperature. The solution was filtered
and the reactors and polymers were washed with CH2Cl2. The ex-
tracts were evaporated under reduced pressure and the products
dried in vacuum.
Aqueous hydroxylamine (1.1 mL, 17.7 mmol) and KCN (4 mg,
0.062 mmol) were added to a solution of triazole 1b (400 mg,
1.77 mmol) in a THF/methanol mixture (3 mL, 1:1). The mixture
was stirred at room temperature for 24 h. The reaction was diluted
with EtOAc (50 mL) and washed with saturated NaHCO3
(2 Â 30 mL) and brine (30 mL). The organic layer was then dried
and concentrated in vacuum. The product 1g (282 mg, 75%) was

M. Sabbah et al. / Bioorg. Med. Chem. 20 (2012) 4727–4736
4733
obtained as a white solid after purification by silica gel chromatog-
raphy, using ethyl acetate/methanol (95:5) as the eluent.
0.2). 1H NMR (300 MHz, acetone-d6): d 0.87 (t, J = 6.7 Hz, 3H);
1.30 (m, 18H); 1.91 (p, J = 7.2 Hz, 2H); 3.76 (s, 2H); 4.39 (t,
J = 7.2 Hz, 2H); 7.87 (s, 1H); 9.49 (br, 1H). 13C NMR (75 MHz,
DMSO-d6): d 13.9; 22.1; 25.9; 28.5; 28.8; 28.9; 29.0; 29.1 (2C);
29.8; 31.3; 31.5; 49.2; 123.3; 140.6; 171.5. HRMS ESI+ calculated
for C16H29N3O2 H+: 296.2333; found: MH+, 296.2340.
Mp = 159–160 °C, 1H NMR (300 MHz, DMSO-d6):
d 0.87 (t,
J = 6.6 Hz, 3H); 1.30 (m, 4H); 1.59 (m, 2H); 2.60 (s, J = 7.5 Hz,
2H); 4.90 (s, 2H); 7.79 (s, 1H); 9.10 (s, 1H); 11.00 (s, 1H). 13C
NMR (101 MHz, DMSO-d6): d 13.9; 21.8; 24.9; 28.6; 30.8; 49.2;
123.1; 146.7; 171.5. HRMS ESI+ calculated for C9H16N4O2 Na+:
235.1165; found: MNa+, 235.1165.
5.1.7. General procedure D for the esterification of triazoles
with a carboxylic acid function (2a, 2b)
5.1.5. General procedure B for saponification
A few drops of sulfuric acid (18 M) were added to a solution of
triazole (2c and 2d) in ethanol (5 mL/1 mmol of triazole). The reac-
tion mixture was stirred at 80 °C for 4 h. The solvent was removed
under pressure and the residue was dissolved in water, then ex-
tracted with ether. The organic solution was washed with a satu-
rated solution of NaHCO3, dried and evaporated under reduced
pressure.
A solution of potassium hydroxide (2 equiv) was added to a
solution of the corresponding ester (1b, 1c) (1 equiv) in ethanol.
The reaction mixture was stirred at room temperature for 4 h.
The solvent was removed under pressure, the residue was dis-
solved in water and the pH of this solution was adjusted to 2, by
adding 1 N hydrochloric acid, and extracted with ethyl acetate.
The combined ethyl acetate extract was washed with saturated
NaCl solution, dried and concentrated.
5.1.7.1.
(2a).
Ethyl
2-(1-pentyl-1H-1,2,3-triazol-4-yl)acetate
Following the general procedure D, compound 2a
5.1.5.1.
(1d).
2-(4-Pentyl-1H-1,2,3-triazol-1-yl)acetic
Following the general procedure B, compound 1d
acid
(441 mg, 40%) was obtained as a green oil from triazole-acid 2c
(1 g, 5.02 mmol). Eluent: ethyl acetate/pentane (3/7). 1H NMR
(300 mg, 96%) was obtained as a white solid from triazole 1b
(357 mg, 1.58 mmol). Mp = 124–125 °C. 1H NMR (300 MHz,
DMSO-d6): d 0.86 (t, J = 6.9 Hz, 3H); 1.30 (m, 4H); 1.59 (q,
J = 7.3 Hz, 2H); 2.61 (t, J = 7.5 Hz, 2H); 5.19 (s, 2H); 7.81 (s, 1H);
13.31 (br, 1H). 13C NMR (75 MHz, DMSO-d6): d 13.9; 21.9; 24.9;
28.7; 30.9; 50.4; 123.2; 147.1; 168.8. HRMS ESI+ calculated for
C9H15N3O2 H+: 198.1237; found: MH+, 198.1232.
(300 MHz, CDCl3):
d 0.89 (t, J = 6.6 Hz, 3H); 1.24–1.38 (t,
J = 7.2 Hz, 3H)-(m, 4H); 1.9 (quint, J = 7.2 Hz, 2H); 3.82 (s, 2H);
4.18 (q, J = 7.2 Hz, 2H); 4.33 (t, J = 7.2 Hz, 2H); 7.58 (s, 1H). RMN
13C (75 MHz, CDCl3): d 13.8; 14.1; 22.1; 28.1; 29.9; 31.9; 50.3;
61.1; 122.3; 140.5; 170.3. HRMS ESI+ calculated for C11H19N3O2
H+: 226.155; found: MH+, 226.1547.
5.1.7.2.
(2b).
Ethyl
2-(1-dodecyl-1H-1,2,3-triazol-4-yl)acetate
5.1.5.2.
(1e).
2-(4-Dodecyl-1H-1,2,3-triazol-1-yl)acetic
Following the general procedure B, compound 1e
acid
Following the general procedure D, compound 2b
(197 mg, 59%) was obtained as a colorless oil from triazole-acid
2d (308 mg, 1.04 mmol). Eluent: ethyl acetate/pentane (3/7). 1H
NMR (300 MHz, CDCl3): d 0.87 (t, J = 6.7 Hz, 3H); 1.27 (m, 21H);
1.89 (quint, J = 7.0 Hz, 2H); 3.81 (s, 2H); 4.18 (q, J = 7.2 Hz, 2H);
4.32 (t, J = 7.2 Hz, 2H); 7.58 (s, 1H). RMN 13C (75 MHz, CDCl3): d
14.1; 14.2; 22.7; 25.7; 29.3; 29.4 (2C); 29.4; 29.6; 29.7 (2C);
29.7; 32.0; 50.8; 62.3; 122.0; 149.2; 166.6. HRMS ESI+ calculated
for C18H33N3O2 H+: 324.2646; found: MH+, 324.2643.
(300 mg, 96%) was obtained as a white solid from triazole 1c
(342 mg, 1.02 mmol). Mp = 135–136 °C. 1H NMR (300 MHz,
DMSO-d6): d 0.85 (t, J = 6.7 Hz, 3H); 1.24 (M, 18H); 1.58 (m, 2H);
2.60 (t, J = 7.5 Hz, 2H); 5.19 (s, 2H); 7.80 (s, 1H); 13.32 (br, 1H).
13C NMR (75 MHz, DMSO-d6): d 14.0; 22.2; 25.1; 28.8; 28.9;
29.0; 29.1 (2C); 29.2; 29.3 (2C); 31.5; 49.2; 123.2; 147.1; 168.9.
HRMS ESI+ calculated for C16H29N3O2 H+: 296.2333; found: MH+,
296.2331.
5.1.6. General procedure C for Jones oxidation (2c, 2d)
A solution of the corresponding alcohol 6 (1 equiv), in acetone,
was added dropwise to a stirred solution of chromium trioxide
(2 equiv) in H2SO4 (5 M, 3 mL/1 mmol of alcohol), at 0 °C. The reac-
tion mixture was allowed to warm to room temperature and stir-
ring was continued for 12 h. The mixture was diluted with water
and extracted with ethyl acetate. The organic phase was washed
with brine, dried over Na2SO4, filtered and then concentrated un-
der reduced pressure.
5.1.8. 3-(2H-Tetrazol-5-yl)dihydrofuran-2(3H)-one (11)
A mixture of cyanolactone 10 (800 mg, 7.2 mmol), sodium
azide (586 mg, 9 mmol), and ammonium chloride (485 mg,
9 mmol) in dimethylformamide (7 mL) was maintained at
100 °C for 7 hrs. After cooling to room temperature, the solution
was concentrated and was co-evaporated with water. Finally, it
was dissolved in water (10 mL) and the pH of this solution was
adjusted to 1.8, by adding hydrochloric acid, and extracted with
ethyl acetate (3 Â 20 mL). The combined ethyl acetate extract
was washed with saturated NaCl solution, dried over Na2SO4
and concentrated. The crude product was purified by flash chro-
matography on silica gel, with ethyl acetate-methanol (9/1) as
the eluent, producing compound 11 (252 mg, 23%) as a colorless
5.1.6.1.
(2c).
2-(1-Pentyl-1H-1,2,3-triazol-4-yl)acetic
Following the general procedure C, compound 2c
acid
(800 mg, 68%) was obtained as a white solid from triazole 6a
(1.1 g, 6 mmol) and chromium trioxide (1.19 g, 10 mmol).
Mp = 75–76 °C, eluent: ethyl acetate/methanol (95/5). 1H NMR
(300 MHz, CDCl3): d 0.89 (m, 3H); 1.33 (m, 4H); 1.19 (m, 2H);
4.35 (t, J = 7.6 Hz, 2H); 5.32 (s, 2H); 7.63 (s, 1H); 9.46 (br, 1H).
13C NMR (75 MHz, DMSO-d6): d 14.1; 26.2; 30.8; 31.4; 32.5;
51.6; 123.2; 139.2; 170.9. HRMS ESI+ calculated for C9H15N3O2
H+: 198,1237; found: MH+, 198,1239.
oil. 1H NMR (300 MHz, CDCl3):
d 2.90 (m, 2H); 4.28 (t,
J = 9.4 Hz, 1H); 4.46 (m, 1H); 4.63 (m, 1H); 5.87 (br, 1H). HRMS
ESI+ calculated for C5H6N4O2 H+: 155.0569; found: MH+,
155.0571.
5.1.9. General procedure E for the alkylation of tetrazoles 11, 12
Triethylamine (1.5 equiv) was added to different solutions of al-
kyl bromide (1.5 equiv) with tetrazole 11 or 12 (l equiv) in acetoni-
trile. The reaction mixture was refluxed for 16 h and the solvent
was then removed under vacuum after filtration. Flash chromatog-
raphy on the crude product allowed us to purify and separate the
two regioisomers.
5.1.6.2.
(2d).
2-(1-Dodecyl-1H-1,2,3-triazol-4-yl)acetic
Following the general procedure C, compound 2d
acid
(635 mg, 69%) was obtained as a white solid from triazole 6b
(875 mg, 3.1 mmol) and chromium trioxide (622 mg, 6.2 mmol).
Mp = 94–95 °C, eluent: ethyl acetate/pentane/CH3COOH (60/40/

4734
M. Sabbah et al. / Bioorg. Med. Chem. 20 (2012) 4727–4736
5.1.9.1. 3-(2-Hexyl-2H-tetrazol-5-yl)dihydrofuran-2(3H)-one 7a
2H); 11.1 (br, 1H). 13C NMR (75 MHz, CDCl3): d 14.2, 22.8, 26.4,
28.9, 29.3, 29.4 (2C), 29.6, 29.7 (2C), 31.6, 32.0, 53.5, 159.6,
173.6. HRMS ESI+ calculated for C15H28N4O2Na+: 319.2104; found:
MNa+, 319.2103.
and
8a.
3-(1-hexyl-1H-tetrazol-5-yl)dihydrofuran-2(3H)-one
Following the general procedure E, the reaction between
tetrazole 11 (140 mg, 0.91 mmol) and bromohexane (192 lL,
1.37 mmol) gave the compounds 7a (99 mg) and 8a (42 mg) as
yellow oils, in a 65% total yield. Eluent: ethyl acetate–dichloro-
methane (2/8). 1H NMR of 7a (300 MHz, CDCl3): d 0.81 (m,
3H), 1.26 (m, 6H), 1.19 (m, 2H), 2.75 (m, 2H), 4.18 (t,
J = 9.33 Hz, 1H), 4.38 (m, 1H), 4.51 (m, 3H). 13C NMR of 7a
(75 MHz, CDCl3): d 13.9, 22.3, 25.9, 28.7, 29.1, 30.9, 37.7, 53.4,
67.2, 162.2, 174.1. 1H NMR of 8a (300 MHz, CDCl3): d 0.86 (m,
3H), 1.32 (m, 6H), 1.96 (m, 2H), 2.78 (m, 1H), 3.17 (m, 1H),
4.06 (t, J = 8.8 Hz, 1H), 4.4–4.5 (m, 3H), 4.7 (m, 1H). 13C NMR
of 8a (75 MHz, CDCl3): d 14, 22.5, 26.3, 27.4, 29.6, 31.2, 36.1,
48.1, 68, 152.4, 172.3. HRMS CI + calculated for C11H18N4O2
H+: 239.1508; found: MH+, 239.1507.
5.1.12. General procedure F for the synthesis of tetrazole (8d, 8e
and 9)
Triflic anhydride (4 equiv) was added to a stirred suspension of
amide (1 equiv) and sodium azide (3 equiv) in acetonitrile, under a
nitrogen atmosphere. The mixture rapidly resulted in a homoge-
nous solution. After 20 h, the mixture was poured into a 5% NaH-
CO3 solution and extracted with EtOAc. The combined organic
phases were washed with brine, dried over MgSO4 and concen-
trated under reduced pressure. The crude residue was then puri-
fied, by silica gel chromatography, using AcOEt/ether (1:1) to
yield the desired tetrazole.
5.1.9.2. Ethyl 2-(2-hexyl-2H-tetrazol-5-yl)acetate (7b) and ethyl
5.1.12.1.
(8d).
3-(1-Butyl-1H-tetrazol-5-yl)dihydrofuran-2(3H)-one
Following the general procedure F, compound 8d
2-(1-hexyl-1H-tetrazol-5-yl)acetate (8b).
Following the gen-
eral procedure E, the reaction between tetrazole 12 (1 g,
6.49 mmol) and bromohexane (1.2 mL, 8.5 mmol) gave the com-
pounds 7b (811 mg) and 8b (525 mg) as colorless oils, in an 86%
total yield. Eluent: pentane/ether (6:4). 1H NMR of 7b (300 MHz,
DMSO-d6): d 0.83 (m, 3H), 1.17 (t, J = 7.1 Hz, 3H), 1.24 (m, 6H),
1.18 (m, 2H), 4.04 (s, 2H), 4.10 (q, J = 7.1 Hz, 2H), 4.65 (t,
J = 6.9 Hz, 2H). 13C NMR of 7b (75 MHz, CDCl3): d 14.0, 14.1,
22.4, 26.0, 29.3, 31.1, 32.0, 53.3, 61.6, 160.1, 168.4. 1H NMR of
8b (300 MHz, DMSO-d6): d 0.85 (m, 3H), 1.19 (t, J = 7.1 Hz, 3H),
1.27 (m, 6H), 1.79 (m, 2H), 4.13 (q, J = 7.1 Hz, 2H), 4.26 (s, 2H),
4.34 (t, J = 7.2 Hz, 2H). 13C NMR of 8b (75 MHz, CDCl3): d 14.0,
14.1, 22.5, 26.2, 29.4, 29.9, 31.2, 47.9, 62.4, 148.9, 166.6. HRMS
(118 mg, 35%) was obtained from amide 14a (prepared as in Ref.
22) (300 mg, 1.61 mmol) as a yellow oil. 1H NMR (300 MHz,
CDCl3): d 0.94 (t, J = 7.4, 3H), 1.36 (m, 2H), 1.93 (m, 2H), 2.77 (m,
1H), 3.13 (m, 1H), 4.13 (t, J = 9 Hz, 1H), 4.46 (m, 3H), 4.66 (m,
1H). 13C NMR (75 MHz, CDCl3): d 13.5, 19.8, 27.4, 31.5, 36.0, 47.7,
68.0, 150.8, 172.5 HRMS CI + calculated for C9H14N4O2 H+:
211.1195; found: MH+, 211.1197.
5.1.12.2. 3-(1-Pentyl-1H-tetrazol-5-yl)dihydrofuran-2(3H)-one
(8e).
Following the general procedure F, compound 8e
(151 mg, 45%) was obtained from amide 14b (prepared as in Ref.
22) (300 mg, 1.5 mmol) as a yellow oil. 1H NMR (300 MHz, CDCl3):
d 0.88 (t, J = 6.8 Hz, 3H), 1.34 (m, 4H), 1.99 (m, 2H), 2.78 (m, 1H),
3.14 (m, 1H), 4.10 (t, J = 8.9 Hz, 1H), 4.47 (m, 3H), 4.66 (m, 1H).
13C NMR (75 MHz, CDCl3): d 13.9, 22.4, 27.4, 28.6, 29.3, 36.0,
48.0, 68.0, 150.7, 172.4. HRMS CI + calculated for C10H16N4O2 H+:
225.1352; found: MH+, 225.1355.
ESI+ calculated for
263.1479.
C
11H20N4O2Na+: 263.1478; found: MNa+,
5.1.9.3. Ethyl 2-(2-dodecyl-2H-tetrazol-5-yl)acetate (7c) and
ethyl 2-(1-dodecyl-1H-tetrazol-5-yl)acetate (8c). Following
the general procedure E, the reaction between tetrazole 12
(997 mg, 6.43 mmol) and bromododecane (2 mL, 8 mmol) gave
the compounds 7c (1.12 g), as a colorless oil, and 8c (780 mg) as
a white solid, in a 92% total yield. Eluent: pentane/ether (9:1). 1H
5.1.12.3.
(9a).
3-(5-Butyl-1H-tetrazol-1-yl)dihydrofuran-2(3H)-one
Following the general procedure F, compound 9a
(193 mg, 68%) was obtained from amide 16a (prepared as in Ref.
52) (250 mg, 1.35 mmol) as a yellow oil. 1H NMR (300 MHz,
CDCl3): d 0.97 (t, J = 7.3 Hz, 3H), 1.45 (m, 2H), 1.86 (m, 2H), 2.90
(m, 3H), 3.18 (m, 1H), 4.55 (m, 1H), 4.76 (m, 1H), 5.18 (t,
J = 9.1 Hz, 1H). 13C NMR (75 MHz, CDCl3): d 13.6, 22.2, 22.8, 28.7,
NMR of 7c (300 MHz, DMSO-d6):
d 0.85 (m, 3H), 1.17 (t,
J = 7.1 Hz, 3H), 1.22 (m, 18H), 1.88 (m, 2H), 4.03 (s, 2H), 4.10 (q,
J = 7.1 Hz, 2H), 4.64 (t, J = 6.9 Hz, 2H). 13C NMR of 7c (75 MHz,
CDCl3): d 14.2, 14.2, 22.8, 26.4, 28.9, 29.3, 29.4 (2C), 29.6, 29.7
(2C), 31.9, 32.0, 53.3, 61.6, 160.1, 168.4. Mp of 7c = 77 °C. 1H
NMR of 8c (300 MHz, DMSO-d6): d 0.85 (m, 3H), 1.11–1.40 (m,
21H), 1.79 (m, 2H), 4.12 (q, J = 7.15 Hz, 2H), 4.25 (s, 2H),, 4.33 (t,
J = 7.2 Hz, 2H). 13C NMR of 8c (75 MHz, CDCl3): d 14.1, 14.1, 22.7,
26.5, 29.0, 29.3, 29.4 (2C), 29.5, 29.6 (2C), 29.8, 31.9, 47.8, 62.3,
148.8, 166.6. HRMS ESI+ calculated for C17H32N4O2Na+: 347.2417;
found: MNa+, 347.2427.
29.1, 54.9, 66.5, 156.5, 170.5. HRMS CI
+ calculated for
C9H14N4O2 H+: 211.1195; found: MH+, 211.1194.
5.1.12.4. 3-(5-Pentyl-1H-tetrazol-1-yl)dihydrofuran-2(3H)-one
(9b). Following the general procedure F, compound 9b
(179 mg, 80%) was obtained from amide 16b (prepared as in
Ref. 52) (200 mg, 1 mmol) as an orange solid. Mp = 63 °C. 1H
NMR (300 MHz, CDCl3): d 0.91 (t, J = 7.2 Hz, 3H), 1.37 (m, 4H),
1.86 (m, 2H), 2.90 (m, 3H), 3.16 (m, 1H), 4.52 (m, 1H), 4.76
(m, 1H), 5.22 (t, J = 9.2 Hz, 1H). 13C NMR (75 MHz, CDCl3): d
14.0, 22.3, 23.3, 26.9, 28.6, 31.3, 54.9, 66.6, 156.3, 170.1. HRMS
5.1.10. 2-(2-Hexyl-2H-tetrazol-5-yl)acetic acid (7d)
Following the general procedure B, compound 7d (348 mg, 98%)
was obtained as
a white solid from tetrazole 7b (404 mg,
1.69 mmol). Mp = 67 °C. 1H NMR (300 MHz, CDCl3): d 0.80 (m,
3H), 1.25 (m, 6H), 1.93 (m, 2H), 3.99 (s, 2H), 4.53 (t, J = 7.1 Hz,
2H), 10.92 (s, 1H). 13C NMR (75 MHz, CDCl3): d 13.8, 22.3, 25.9,
29.1, 30.9, 31.4, 53.3, 159.5, 172.9. HRMS ESI+ calculated for
C9H16N4O2Na+: 235.1165; found: MNa+, 235.1168.
CI +: calculated for
225.1356.
C
10H16N4O2 H+: 225.1352; found: MH+,
5.1.12.5. 3-(5-Hexyl-1H-tetrazol-1-yl)dihydrofuran-2(3H)-one
(9c). Following the general procedure F, compound 9c
(258 mg, 53%) was obtained from amide 16c (prepared as in Ref.
52) (400 mg, 1.88 mmol) as an orange solid. Mp = 76 °C. 1H NMR
(300 MHz, CDCl3): d 0.89 (t, 3H), 1.38 (m, 6H), 1.87 (m, 2H), 2.92
(m, 3H), 3.16 (m, 1H), 4.54 (m, 1H), 4.78 (m, 1H), 5.17 (t,
J = 9.1 Hz, 1H). 13C NMR (75 MHz, CDCl3): d 14.0, 22.4, 23.1, 27.0,
5.1.11. 2-(2-Dodecyl-2H-tetrazol-5-yl)acetic acid (7e)
Following the general procedure B, compound 7e (392 mg, 87%)
was obtained as
a white solid from tetrazole 7c (495 mg,
1.53 mmol). Mp = 72 °C. 1H NMR (300 MHz, CDCl3): d 0.87 (m,
3H), 1.24 (m, 18H), 1.20 (m, 2H), 4.03 (s, 2H), 4.59 (t, J = 7.1 Hz,

M. Sabbah et al. / Bioorg. Med. Chem. 20 (2012) 4727–4736
4735
28.7, 28.75, 31.3, 54.9, 66.5, 156.5, 170.4. HRMS CI + calculated for
11H18N4O2 H+: 225.1352; found: MH+, 225.1357.
Supplementary data
C
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.bmc.2012.06.007.
5.1.12.6. 3-(5-Heptyl-1H-tetrazol-1-yl)dihydrofuran-2(3H)-one
9d. Following the general procedure F, compound 9d
(187 mg, 56%) was obtained from amide 16d (prepared as in
Ref. 52) (300 mg, 1.32 mmol) as an orange solid. Mp = 58–
60 °C. 1H NMR (300 MHz, CDCl3): d 0.86 (t, J = 7.2 Hz, 3H), 1.35
(m, 8H), 1.85 (m, 2H), 2.91 (m, 3H), 3.13 (m, 1H), 4.53 (m,
1H), 4.74 (m, 1H), 5.24 (t, J = 9.2 Hz, 1H). 13C NMR (75 MHz,
CDCl3): d 14.1, 22.7, 23.3, 27.2, 28.6, 28.9, 29.2, 31.7, 54.9,
66.6, 156.3, 170.1. HRMS CI + calculated for C12H20N4O2 H+:
253.1664; found: MH+, 253.1664.
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The financial support from MESR, CNRS, and the ‘Cluster de
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support from the ANR project ECORUM. We owe many thanks to
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throughout the biological evaluation stage.

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