Glycosyl-nucleoside fluorinated amphiphiles as components of nanostructured hydrogels

Article abstract of DOI:10.1016/j.tetlet.2009.12.042

The synthesis of two novel glycosyl-nucleoside fluorinated amphiphiles (GNFs) derived from the 2H,2H,3H,3H-perfluoro-undecanoyl hydrophobic chain is described. The GNF amphiphiles, which feature either β-d-glucopyranosyl or β-d-lactopyranosyl moieties linked to a thymine base via a 1,2,3 triazole linker, were prepared using a 'double click' chemistry route. Surface tension measurements, gelation properties, and TEM studies show that GNFs spontaneously assemble into supramolecular structures. Similarly to their hydrocarbon analogues (GNLs), the GNFs have unique gelation properties in water. A minimum hydrogelation concentration of 0.1% (w/w), was determined in the case of the β-d-glucopyranosyl derivative. Cell viability studies indicate that fluorocarbon GNF 5 was not toxic for human cells (Huh7), whereas hydrocarbon analogue GNL is toxic above 100 μm.

Full text of DOI:10.1016/j.tetlet.2009.12.042

Tetrahedron Letters 51 (2010) 1012–1015
Contents lists available at ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Glycosyl-nucleoside fluorinated amphiphiles as components
of nanostructured hydrogels
*
Guilhem Godeau, Christophe Brun, Hélène Arnion, Cathy Staedel, Philippe Barthélémy
Université de Bordeaux, 146 rue léo Saignat, F-33076, Bordeaux Cedex, France
Inserm, U-869, Bordeaux, F-33076, France
a r t i c l e i n f o
a b s t r a c t
Article history:
The synthesis of two novel glycosyl-nucleoside fluorinated amphiphiles (GNFs) derived from the
Received 12 November 2009
Revised 5 December 2009
Accepted 9 December 2009
Available online 28 December 2009
2H,2H,3H,3H-perfluoro-undecanoyl hydrophobic chain is described. The GNF amphiphiles, which feature
either b-D-glucopyranosyl or b-D-lactopyranosyl moieties linked to a thymine base via a 1,2,3 triazole lin-
ker, were prepared using a ‘double click’ chemistry route. Surface tension measurements, gelation prop-
erties, and TEM studies show that GNFs spontaneously assemble into supramolecular structures.
Similarly to their hydrocarbon analogues (GNLs), the GNFs have unique gelation properties in water. A
minimum hydrogelation concentration of 0.1% (w/w), was determined in the case of the b-
osyl derivative. Cell viability studies indicate that fluorocarbon GNF 5 was not toxic for human cells
(Huh7), whereas hydrocarbon analogue GNL is toxic above 100 m.
D-glucopyran-
l
Ó 2009 Elsevier Ltd. All rights reserved.
Owing to their unique properties, hydrogels have attracted much
attention for potential applications in nanoscale devices or sys-
tems.1 These soft materials are present in numerous fields of re-
search including chemistry, biology, and biomedicine.2 For
example, hydrogels can provide scaffolds for cell cultures,3,4 matrix
for tissue engineering,5,6 or drug delivery systems.7–9 Among the
gelator molecules investigated so far, low molecular weight gelators
(LMWGs)10 are of particular interest for biomedical applications.
Hence, due to their intrinsic properties, in particular the non-cova-
lent nature of the molecular interactions at work, LMWGs feature
several advantages to macromolecules such as polymers. Thus due
to their supramolecular structure, the water gelation by small mol-
ecules is sensitive to external stimuli. These systems also allow an
easier clearance from the body compared to polymeric gel. In this
context, a critical challenge facing this field is how to develop non-
toxic LMWGs, which can provide biocompatible supramolecular
hydrogel scaffolds at low concentration. This is critical to develop
new materials suitable for drug delivery and/or tissue engineering
applications.
To this end, amphiphilic molecules derived from natural chem-
ical structures appear as suitable small molecular building blocks
to construct supramolecular hydrogels. Recently, bio-inspired-
amphiphiles derived from amino acids have been reported to form
supramolecular networks capable to stabilize gels.11 Likewise, we
have described that amphiphilic building blocks, appropriately
functionalized with nucleoside and/or nucleotide moieties, form
well-defined supramolecular systems with tunable physico-chem-
ical properties and functions.12 The combination of nucleic acids
chemistry with supramolecular principles has been explored by
several groups to prepare nucleoside-amphiphile based gels.13–17
As hydrophobic parts, fluorocarbon chains can be inserted in the
building blocks. An appealing part of the perfluorinated or semiflu-
orinated hydrocarbon chains lies in their special properties related
to the characteristics of the fluorine atom. It is well established
that fluorinated chains are highly hydrophobic, chemically, and
biologically stable and feature segregation behavior toward perhy-
drogenated compounds.18–20 Numerous examples of fluorocarbon
amphiphiles have been reported for different purposes, including
gel stabilization,21–24 and biomedical applications.25–30 We previ-
ously reported that the combination of fluorocarbon chains with
nucleoside has a significant impact on the properties of the supra-
molecular assemblies observed compared to their hydrocarbon
analogues.31 In parallel, we demonstrated that glycosyl-nucleo-
side-lipids (GNLs) self-assemble to give highly organized struc-
tures, which can stabilize hydrogels.32,33 In the present study, we
report the synthesis of two novel glycosyl-nucleoside fluorinated
amphiphiles (GNFs), their self-assembly properties, the formation
of hydrogels, and a study of their possible cytotoxicity.
We hypothesized that the use of a GNF based amphiphile would
allow for the stabilization of non-toxic hydrogels. For this purpose,
the 2H,2H,3H,3H-perfluoroundecanoyl chain was selected to pro-
vide a similar hydrophobicity character as the palmitoyl/stearoyl
hydrocarbon chains.34 This choice was also motivated by the
non-detergency toward cell membranes of this fluorocarbon
chain,35 which may lead to a poor cytotoxicity.
The GNFs based amphiphiles 5 and 6 were synthesized in three
steps starting from N-propargyl-2H,2H,3H,3H-perfluoroundecana-
* Corresponding author. Tel.: +33 5 57 57 48 53; fax: +33 5 57 57 10 15.
E-mail address: philippe.barthelemy@inserm.fr (P. Barthélémy).
0040-4039/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2009.12.042

G. Godeau et al. / Tetrahedron Letters 51 (2010) 1012–1015
1013
mide 1 and 50-azido-20-deoxythymidine 2 following a route as de-
tailed in Scheme 1. Following a first ‘click’ reaction, the N-propar-
gylated fluorocarbon 1 was reacted with the azido derivative 2 in
the presence of CuSO4 in a THF/H2O mixture to afford the expected
2H,2H,3H,3H-perfluoroundecanamide-triazolyl-thymidine inter-
mediate 3. This fluorocarbon nucleoside (FN) intermediate 3 was
treated at room temperature in the presence of potassium carbon-
ate with 2 equiv of propargyl bromide to lead to N-propargylated
thymidine derivative 4. Then, either 1-azido-b-D-glucopyranosyl
or 1-azido-b-lactosyl moieties were reacted with the N-propargyl
derivative 4 in the presence of CuSO4 following a second ‘click’
reaction to provide the expected non-ionic GNFs based amphi-
philes (GNFs, compounds 5 and 6).
One of the goals of the present study was to determine the
self-assembly properties of GNFs 5 and 6. The critical aggregation
concentrations (CAC’s) of GNFs were determined by air-solution
Figure 1. Air–water interfacial tension
(blue diamond) and compound 6 (red square) at 25 °C.
c
versus concentration for compound 5
3.65 0.16 lM, respectively. Note that CAC values for GNFs are
surface tension (
centration c. Example of (
are shown in Figure 1. The GNF amphiphiles 5 and 6 gave breaks
in versus Log (c) characteristic of CAC’s of 5.89 1.39 and
c) measurements as a function of amphiphile con-
similar in magnitude to the ones reported for GNLs bearing C18
c
) versus (c) curves, measured at 25 °C,
hydrocarbon chains.32 The surface tension measured at the CAC
(ccac) indicates the effectiveness of the amphiphiles to stabilize
c
Scheme 1. Three step synthesis of the GNFs (5) and (6). Reagents and conditions: (i) 10 mol % CuSO4, 20 mol % sodium ascorbate, THF/H2O (50/50), 65 °C, 10 h; (ii) 2 equiv
propargyl bromide, 2 equiv K2CO3, DMF, rt, overnight; (iii) 1 equiv 1-azido-b- -glucopyranoside, 10 mol % CuSO4, 20 mol % sodium ascorbate, THF/H2O (50/50), 65 °C, 10 h;
(iii0) 1 equiv 1-azido-b-lactoside , 10 mol % CuSO4, 20 mol % sodium ascorbate, THF/H2O (50/50), 65 °C, 10 h.
D

1014
G. Godeau et al. / Tetrahedron Letters 51 (2010) 1012–1015
Figure 2. TEM images of supramolecular assemblies formed by GNFs 5 (a) and 6 (b) in water (scales: 100 nm).
the water–air interface. As expected the fluorocarbon chain de-
creases the ccac values (ccac ꢀ 27 and 25 mN mꢁ1, for 5 and 6,
respectively) compared to the C18 hydrocarbon GNLs
(
ccac ꢀ 35 mN mꢁ1).
Given our interest in LMWGs the gelation abilities of GNFs were
studied both in pure water and in tissue culture medium (Dulbecco’s
modified Eagle medium, DMEM). Interestingly, clear gels were
formed both in water and in DMEM for GNFs 5 and 6 (see Fig. SI5).
The hydrogels obtained were stable at room temperature for several
weeks. In water, the minimum gelation concentration was found to
vary with the sugar moiety of the polar head. Similarly to its satu-
Figure 3. Cell viability in percent versus concentrations of GNF 5 and GNL (see
Fig. SI6 for GNL structure).
rated C18 hydrocarbon analogue, the b-D-glucopyranoside GNF 5 is
an excellent hydrogelator with a minimum gelation concentration
of 0.1% w/w, whereas GNF 6 is less effective with a minimum gela-
tion concentration of 2.5% w/w. Note that, contrary to hydrocarbon
GNLs, which were not able to stabilize the hydrogels at low concen-
trations in the presence of DMEM, fluorocarbon GNFs stabilize gels
at low concentrations in DMEM (0.1% and 1% w/wfor 5 and 6, respec-
tively), indicatingthat these fluorocarbon derivatives can be used for
cell culture environments. However, both GNFs 5 and 6 are not able
to stabilize a gel in organic solvents such as n-hexane, n-butan-1-ol,
toluene chloroform, DMSO, and perfluorohexane.
non-toxicity of GNFs demonstrate the great potential of these fluo-
rocarbon amphiphiles for biomedical applications.
Acknowledgments
P.B. acknowledges financial support from the Army Research
Office. The authors thank the ‘Conseil Régional d’Aquitaine’ for
financial support.
The morphology of the supramolecular network formed by GNFs
was investigated through transmission electronic microscopy
(TEM). GNFs gelators displayed different organization networks of
Supplementary data
varying morphologies (Fig. 2). In water, gelator 5 having b-D-gluco-
Experimental procedures (synthesis of compounds 1–6, Surface
tension measurements, cells culture, cells survival), HRMS spectra
for compounds 5 and 6, TEM images, gel in water and DMEM
images). Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/j.tetlet.2009.12.042.
pyranoside polar head formed entangled nanofibers of roughly 10–
20 nm in diameter (Fig. 2a). A very compact system showing fibers
helically organized reminiscent to springs (see Fig. SI4d for magnifi-
cation of TEM images) was observed for b-D-lactopyranoside
derivative 6 (Fig. 2b). These observations underline that the polar
head structure has an impact on supramolecular organisations,
and consequently on hydrogel macroscopic properties.
References and notes
Another goal of this study was to determine the cytotoxicity of
GNFs as compared to that of GNLs. The cell viability was assessed
after a 5-day incubation of growing human cells (Huh-7, human
hepatocarcinoma cell line) with increasing concentrations of GNF
5 or C18 GNL hydrocarbon analogue (see Fig. SI6 for GNL structure).
Importantly, cell viability data presented in Figure 3 indicate that
fluorocarbon GNF 5 are not toxic for these human cells at any of
the tested concentrations, whereas hydrocarbon GNL becomes
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