Synthesis and liquid-crystalline properties of novel archaeal diether-type glycolipids possessing one or two furanosyl units

Article abstract of DOI:10.1016/S0008-6215(98)00291-2

Archaeal diether-type analogues possessing one or two furanosyl polar head groups and methyl branched aliphatic moieties were synthesized by glycosylation of glycerolipids with pent-4-enyl 2,3,5,6-tetra-O-acetyl-d-glycofuranosides as the donors. The produ

Full text of DOI:10.1016/S0008-6215(98)00291-2

Carbohydrate Research 314 (1998) 65–77
Synthesis and liquid-crystalline properties of novel
archaeal diether-type glycolipids possessing one or two
furanosyl units
Rachel Auze´ly-Velty a, Thierry Benvegnu a,*, Grahame Mackenzie b, Julie A. Haley b,
John W. Goodby b,1, Daniel Plusquellec a
a Laboratoire de Chimie Organique et des Substances Naturelles, associe´ au CNRS,
Ecole Nationale Supe´rieure de Chimie de Rennes, a6enue du Ge´ne´ral Leclerc, F-35700 Rennes, France
b Department of Chemistry, Faculty of Science and the En6ironment, Uni6ersity of Hull, Hull HU6 7RX, UK
Received 23 September 1998; accepted 29 October 1998
Abstract
Archaeal diether-type analogues possessing one or two furanosyl polar head groups and methyl branched aliphatic
moieties were synthesized by glycosylation of glycerolipids with pent-4-enyl 2,3,5,6-tetra-O-acetyl-D-glycofuranosides
as the donors. The products were shown to form thermotropic and lyotropic liquid crystalline mesophases, tubules
and vesicles. The self-assembling properties of the compounds prepared were found to be similar to those of naturally
occurring materials, in that they exhibited columnar thermotropic mesophases and hexagonal lyotropic phases.
© 1998 Elsevier Science Ltd. All rights reserved.
Keywords: Archaebacteria; Diethers; Glycosylation; Furanosides; Lyotropic and thermotropic liquid crystals; Tubules; Vesicles
1. Introduction
Some model diether-type amphiphiles have al-
ready been synthesized in order to investigate
their ability to form stable vesicles or planar
membranes in water [4]. The synthetic molecules
contain either straight alkyl chains or phytanyl
residues linked to glycerophosphate derivatives.
Uponsonication,thesecompoundsfurnishwell-
defined liposomes that are useful for the storage
of inorganic salts and proteins with long-term
stability and thermostability [5–7]. No study,
however, has faced the precise role of furanosyl
sugars in archaeal membranes. Here, we de-
scribe the synthesis and the evaluation of the
liquid-crystalline properties of diether-type gly-
colipids bearing one or two furanosyl units.
Some preliminary results in the preparation of
monosaccharidic diethers were recently pub-
lished [8]. We now report, with full experimental
details, the synthesis of a new range of archaeal
analogues and the study of their thermotropic
and lyotropic mesomorphic behaviour.
The lipids of methanogenic and halophilic
Archaebacteria are characterized by high pro-
portions of diether-type components with a
2,3-diphytanyl-sn-glycerol backbone [1]. Polar
groups at the sn-1 position of these lipids include
various phosphate derivatives and unusual gly-
cofuranosyl units. In particular, glycosyl head
groups in Methanospirillum hungatei, a meth-
anogen species, consist of repetitious moieties in
which the first sugar attached to glycerol is
b-D-galactofuranose (b-Galf ) and the second
one is either b-Galf or a-D-glucopyranose [2].
Thepresenceofb-D-galactofuranoseisastriking
feature since D-galactose, as well as other
hexoses, appears only in the pyranose form in
mammalian glycolipids and glycoproteins [3].
* Corresponding author. Fax: +33-2-99-871348.
E-mail address: thierry.benvegnu@ensc-rennes-fr (T. Ben-
vegnu)
1 Also corresponding author.
0008-6215/98/$ - see front matter © 1998 Elsevier Science Ltd. All rights reserved.
PII: S0008-6215(98)00291-2

66
R. Auze´ly-Velty et al. / Carbohydrate Research 314 (1998) 65–77
2. Results and discussion
The general synthetic pathway to compounds
1–7 involved the preparation of suitable di-
ether-type alcohols 8–11 followed by their
glycosylation with an appropriate furanosyl
donor derived from D-galactose, D-glucose or
D-mannose. Synthesis of the known 1,2-di-O-
alkyl-rac-glycerol 8 and 1,2-di-O-sn-glycerol
9–10 bearing either (3RS, 7R, 11R)-dihydro-
phytyl or hexadecyl chains was accomplished
from 3-O-benzyl-sn-glycerol under classical
Williamson conditions [4]. In the case of the
glycerol derivative 11, another strategy was
developed to introduce two different alkyl seg-
ments, i.e., a dihydrocitronellyl residue and a
less bulky octyl chain. (S)-1-tert-Butyldi-
phenylsilyl glycidol was readily converted into
3-O-[(R)-3,7-dimethyloctyl]-1-O-(tert-butyldi-
phenylsilyl)-sn-glycerol (12) via a borontrifl-
uoride etherate-catalysed opening of the oxi-
rane ring with (R)-3,7-dimethyloctan-1-ol [10]
(68% yield). Alkylation at the C-2 position by
octyl triflate [10] proceeded efficiently (60%) in
CH2Cl2 by heating at reflux for 48 h and using
1,8-bis(dimethylamino)naphthalene (PS) as a
base [11]. Removal of the silyl group with
tetrabutylammonium fluoride yielded the chiral
alcohol 11 in 83% yield.
Synthesis of glycolipids.—The functional
role of polar glycofuranosyl residues in natu-
ral membranes is difficult to assess, mainly
due to the absence of sufficient information
concerning the effects of hexofuranose rings
on the physical properties of the resulting
archaeal glycolipid–water systems. Although
many investigations pertaining to the
supramolecular organization of glycerophos-
phate and glyceroglycopyranoside diethers
have been undertaken [4–6], studies on the
combined effects of: (i) glycofuranosyl struc-
ture: (ii) stereochemistry of the glycerol back-
bone: and (iii) the length and nature of the
hydrocarbon chains are less common [9].
Within this context, we describe an efficient
route to the novel diether analogues 1–7 pos-
sessing: (i) either one or two furanosyl units as
polar head groups, namely b-D-galactofura-
nose, b-D-glucofuranose, a-D-mannofuranose
and
6-O-b-D-galactofuranosyl-b-D-galacto-
furanose; (ii) optically pure (R or S) or
racemic glycerol isomers; and (iii) phytanyl,
dihydrocitronellyl and/or straight alkyl chains.

R. Auze´ly-Velty et al. / Carbohydrate Research 314 (1998) 65–77
67
Table 1
Yields of glycosylation and deacetylation, optical rotation values and results of elemental analyses for diethers 1–6
Yield (%)
Rf valuea
[h]2D0 b
Elemental
C
Analysis (%)c
H
Compound
Glycosylation
Deprotection
1
2
3
4
5
6
55
82
75
69
74
75
89
90
92
89
64d
90
0.52
0.60
0.62
0.62
0.54
0.44
72.09(72.19)
72.02 (72.19)
71.96 (72.19)
71.99 (72.19)
70.32 (70.04)
63.65 (64.00)
12.23(12.11)
12.44 (12.11)
12.45 (12.11)
12.34 (12.11)
12.13 (11.76)
10.94 (10.74)
−29.2
−35.4
−48.9
a Silica Gel 60 F254 non-activated plates (E. Merck) were used. The developing solvent system is CH2Cl2–CH3OH (9:1 v/v).
b c 1.0 in CH2Cl2–CH3OH (2:3 v/v).
c The calculated values of the elemental analyses are shown in brackets.
d Yield after recrystallization of 5 in CH2Cl2–CH3OH.
methoxide in methanol resulted in effective
deprotection of the hydroxy groups to yield,
exclusively, the 1,2-trans glycofuranosides
(Table 1). The low field resonances (l 109.5–
110.1 ppm) observed for the anomeric carbon
C-1% of compounds 1–6 were similar to previ-
ously published data [13]. Moreover, the val-
ues obtained for J1%,2%B2 Hz in the gluco- and
galactofuranoside series and the J1%,2%=2.6 Hz
determined for the mannofuranoside 2 are
indicative of a trans relationship between H-1%
and H-2% (Tables 2 and 3). With the aim of
investigating the physical properties of di-
ether-type analogues which are structurally
closer to the natural archaeal lipids, we also
synthesised the glycerol diether 7 bearing a
disaccharide as a polar head group. For this
purpose, the monosaccharide diether 3 was
transformed into 2,3,5-tri-O-benzyl-b-D-galac-
tofuranoside by the application of the classical
tritylation–benzylation–detritylation sequence
of reactions [13]. By employing the galacto-
furanosyl donor 16, the disaccharidic moiety
was assembled affording, after additional de-
protection steps, the novel (1“6)-b-D-galacto-
furanoside dimer 7 (28% overall yield).
E6aluation of mesomorphic phase beha6iour
of the diethers.—The transition temperatures
and heats of transition for compounds 1–6
were determined using differential scanning
calorimetry (DSC). In addition, polarized
transmitted-light thermal microscopy was
used as the primary tool for phase identifica-
tion, classification and determination of tran-
sition temperatures. The enthalpy values and
Subsequent introduction of the furanosyl
unit on the diethers 8–11 was achieved by
n-pentenyl glycoside (NPG) glycosylation [12].
The key glycofuranosyl donors 14–16 were
prepared, in a one-pot reaction [13], by ferric
chloride promoted glycosylations of 4-penten-
1-ol with D-glucose, D-mannose and D-galact-
ose followed in situ by acetylation. Addition-
ally, the coupling reaction of the diethers 8–
11 with glycosyl donors proceeded smoothly
and quickly by using standard NPG condi-
tions [12] (NIS, 1.3 equiv, TESOTf, 0.3 equiv
with respect to donors) to afford the resulting
glycosides in moderate to high yields (Table
1). Conventional deacetylation by sodium

Table 2
1H NMR (400 MHz) data for the glyceroglycosyl moieties of 1–7
l (ppm)a (J (Hz))
Compound
Glycosyl unit
H-1%
Glyceryl moietyb
H-1a, H-1b
3.50–3.94
H-2%
H-3%
H-4%
H-5%
H-6%a, H-6%b
H-2
H-3a, H-3b
OCH2
1c
2c
3c
5.56 [B1]
5.58 [2.6]
5.58
4.85
4.93
4.98–5.01
4.63–4.66
4.85–4.87
4.79–4.84
4.80–4.85
4.53–4.57
4.33–4.37,
4.47–4.50
4.27 [6.2, 11.2],
4.45 [3.3, 11.2]
4.30–4.40,
3.50–3.94
3.90–3.93
3.92–3.95
3.50–3.94,
4.17–4.23
3.56–3.87,
4.10–4.15
3.50–3.94
3.56–3.87
3.51–3.88
4.63–4.66
4.85–4.87
4.89–4.91
4.99–5.03
3.56–3.87
/
3.51–3.88
3.51–3.88,
4.30–4.40
4.15–4.19 [4.4,
9.7]
4c
5.59 [2.0]
nda
4.87–4.90
4.79–4.81
4.85
5.03 [4.3, 6.5]
4.96 [4.2, 6.2]
5.00 [4.1, 6.4]
5.02
4.87–4.90
4.79–4.81
4.85
4.55
4.33–4.42,
4.33–4.42
4.25–4.35,
4.25–4.35
4.34, 4.34
3.52–3.83
3.46–3.78
3.92–3.97
3.90
3.88 [5.3, 10.0],
4.18 [4.8, 10.0]
3.82 [5.4, 10.4],
4.12 [4.9, 10.4]
3.53–3.78
3.52–3.83
3.46–3.78
3.53–3.78
5c
4.51
6c
5.58 [1.9]
5.65
4.55
3.83 [5.8, 10.3],
4.17 [4.7, 10.3]
3.55–3.61,
3.92
314
)
7c,d
4.84–4.87
4.71
4.58–4.63
4.15–4.21,
4.43–4.47
3.96
3.70–3.90,
4.15–4.21
3.55–3.61,
3.70–3.90
3.70–3.90
6
a Recorded in pyridine-d5+D2O; nd, not determined.
b For compounds 1–5 and 7 glycosyl units are linked to the C-3 carbon of glycerol and for 6 to the C-1 carbon.
c For compounds 1–4 and 7: l CH3 0.90–0.95, l CH, CH2 1.06–1.80; 5: l CH3 0.91, l CH2 1.32, l OCH2CH2 1.41; 6: l CH3 0.83–0.91, l CH, CH2 1.05–1.43.
d Data of the furanosyl non-reducing unit of 7 are: l H-1¦ 5.65, l H-2¦ 4.84–4.87, l H-3¦ 5.02, l H-4¦ 4.90–4.93, l H-5¦ 4.52–4.56, l H-6a¦, H-6b¦ 4.30–4.37.

Table 3
13C NMR (100 MHz) data for the glyceroglycosyl moieties of 1–7
l (ppm)a
Compound Glycosyl unit
Glyceryl moietyb
C-1
C-1%
C-2%
C-3%
C-4%
C-5%
C-6%
C-2
C-3
OCH2
/
1c
110.06, 110.10
109.58, 109.62
109.77, 109.83
109.94
109.67
109.73
81.77
78.13
83.02
83.14
82.90
83.01
82.73
77.55
72.40
78.42, 78.63
78.72
78.44
82.87, 82.91
81.15, 81.17
84.91, 84.94
85.10
84.74
84.85
71.72
71.35
72.42
72.62
72.25
72.38
70.52
65.08
64.88
64.43
64.58
64.31
64.39
70.86
68.71–71.67
68.55–71.76
68.67–71.78
68.69–71.78
70.48*
78.37–78.43
78.47–78.62
78.42–78.63
78.45, 78.52
78.36
68.04, 68.15
68.55–71.76
67.94, 68.10
67.98
67.80
69.94*
68.71–71.67
68.55–71.76
68.67–71.78
68.69–71.78
71.64*
2c
3c
4c
5c
6c
78.60
78.41
68.08
68.69–73.38
78.48
78.41, 78.47
70.57*, 71.52*
68.69–73.38
7c,d
109.72
85.02
67.94, 68.18
314
(
a Recorded in pyridine-d5+D2O; signals marked with * may be interchanged.
b For compounds 1–5 and 7 glycosyl units are linked to the C-3 carbon of glycerol and for 6 to the C-1 carbon.
c For compounds 1-4 and 7: l CH3 19.74–22.86, l CH, CH2 24.74–37.94; 5:l CH3 14.29, l CH2 22.92–32.12; 6: l CH3 14.26–22.82, l CH, CH2 22.86–39.43.
d Data of the furanosyl non reducing unit of 7 are: l C-1¦ 110.05, l C-2¦ 83.00, l C-3¦ 78.47, l C-4¦ 85.26, l C-5¦ 72.47, l C-6¦ 64.32.
6

70
R. Auze´ly-Velty et al. / Carbohydrate Research 314 (1998) 65–77
Table 4
Transition temperatures (in °C) and enthalpies (in J/g) for the various transitions exhibited for compounds 1–6
Compound
Microscopy dataa
DSC data
Melting
T
Clearing
Glass transition
DH
T
DH
T
1
2
3
4
5
6
Colh 64.4 Iso Liq
Colh 53.9 Iso Liq
Colh 70.0 Iso Liq
Colh 69.6 Iso Liq
Cryst 75.4 Colh124.8 Iso Liq
Colh102.5 Iso Liq
54.8
69.8
63.4
121.4
101.6
0.77
0.82
0.80
1.80
0.37
−54.0
−25.7
73.9
131.53
a Cryst, solid; Colh, liquid crystalline phase; Iso Liq, isotropic liquid.
the transition temperatures determined for di-
ethers 1–6 are given in Table 4. It is interest-
ing to note that only glycolipid 5, bearing two
linear (unbranched) saturated chains, exhibits
two phase transitions in the DSC which corre-
spond to the melting point and the clearing
point, whereas all of the other compounds
only exhibit enthalpies associated with their
relative isotropization points.
appearance, indicating that the structure of
the self-organised system is retained or frozen
into the solid state upon cooling. These simple
thermal cycling exercises demonstrate the
thermal stability of the self-organised struc-
tures, and they may give some insights as to
why similar glycolipids are prevalent in ex-
tremophilic Archaebacteria.
The clearing point enthalpies for all com-
pounds were found to be relatively small (B1
J/g) in comparison with the values obtained
for carbohydrates substituted with a single
lipophilic chain (around 5 J/g [9b]). These
results indicate that the thermotropic
mesophases of diether-type glycolipids have
relatively disordered structures which, in their
local appearance, are closer to the amorphous
liquid than to the solid state. Thus, it is ex-
pected that the aliphatic chains will be appre-
ciably melted, the packing of the carbohydrate
residues disordered, and the inter-molecular
hydrogen bonding dynamic.
The DSC studies also allow for a compari-
son to be made between the galactofuranose,
glucofuranose and mannofuranose systems.
We have demonstrated previously [9a] that
molecular anisotropy and availability of hy-
droxyl groups for intra- and inter-molecular
hydrogen bonding are important factors in
determining phase behaviour. Generally, it
was found that the more linear the molecular
shape is, the higher is the degree of molecular
anisotropy and the greater is the ability to
form hydrogen bonds, which in turn promotes
higher clearing temperatures. Thus, the b-
galactoside, which has a carbohydrate struc-
Glycosides 1–4 and 6, which carry
branched aliphatic moieties, showed no de-
tectable melting point over an appreciably
wide temperature range, i.e., on first heating
runs from approximately −25 °C to their
clearing points. The lack of a clear-cut melting
transition can be explained by the fact that the
branching methyl groups hinder the ordered
packing of the hydrocarbon tails, which in
turn hinders formation of the crystal state.
Consequently, materials 1–4 and 6 are in the
liquid crystal state at room temperature. Cool-
ing runs by DSC show that materials 1–3 can
be supercooled to well below −50 °C without
recrystallisation occurring. For compounds 4
and 6 (where 6 possesses mixed linear and
branched chains with an sn-2 stereochemistry
for the glycerol unit), the situation was found
to be slightly more complicated. On cooling,
compound 4 was found to have a glass transi-
tion at −54 °C and compound 6 a glass
transition just below −25 °C. Microscopy
studies on compound 6 revealed that it formed
a glassy state that retained the same defect
and textural morphology as in the liquid-crys-
talline state. Reheating returned the glassy
solid to the liquid-crystal state with the same

R. Auze´ly-Velty et al. / Carbohydrate Research 314 (1998) 65–77
71
ture that is nearest to being linear with respect
to the other members of the diether series, has
the highest clearing point. Additionally, the
similar results obtained for galactosides 3 and
4 show that the liquid crystal properties in this
case are insensitive to the stereochemistry of
the glyceryl units.
Classifications of the mesophases of the
products were made via examination of the
defect textures formed, in the polarized trans-
mitted light microscope, on cooling from the
amorphous liquid. The mesophases formed
were all classified as disordered columnar
hexagonal phases (Colhd) [14–16]. Upon cool-
ing slowly from the isotropic phase into the
liquid crystal state, fan-like defects [17,18],
without any hyperbolic or elliptical lines of
optical discontinuity associated with the
lamellar smectic state, were observed between
crossed polarizers (Fig. 1). The smoothness
associated with the fan-like domains indicates
that the columnar structure is disordered. In
addition to the fan-like domains found in
homogeneous preparations, rectilinear lines
were found in homeotropic areas of the sam-
ples. Conoscopy, however, was not able to
provide any insights into the signs of the
birefringences of the samples which would
have confirmed the structures of the
mesophases as being columnar (negative uni-
axial) rather than lamellar (positive uniaxial).
Nevertheless, the presence of homeotropy
confirms that the mesophase formed for each
of the materials is uniaxial, the absence of
Fig. 2. Schematic representation of the arrangement of glyco-
lipids 1–6 in the disordered columnar Colhd phase. The
wedge-shaped molecules pack into disc-like clusters, which
then self-assemble into columns. There is no periodic order
along the column axis.
elliptical and hyperbolic lines of optical dis-
continuity confirm that the phase is columnar,
and the fan-like texture indicates a hexagonal
packing of the columns rather than a rectan-
gular packing array.
Turn now to the question why a hexagonal
columnar phase is formed by these materials.
The molecules have wedge-shaped structures
with the polar head groups being towards the
apex of the wedge. When the wedge-shaped
sugar residues pack together via hydrogen
bonding, they will do so apex to apex, thereby
forming disordered disk-like clusters. The
disc-like aggregates will then stack in columns
where the molecules will be disordered along
the column axis (Fig. 2), and the columns
themselves will pack in a hexagonal array.
Thus, the columnar phase will have a struc-
ture where the fluid aliphatic chains are to-
wards the exterior of the columns and the
Fig. 1. Typical textures of the columnar hexagonal Dhd phase
of diethers 1–6, viewed through crossed polarizers, magnifica-
tion ca. 100X, obtained upon cooling from the isotropic
phase.

72
R. Auze´ly-Velty et al. / Carbohydrate Research 314 (1998) 65–77
Fig. 3. Schematic representation of the structure of the thermotropic columnar hexagonal phase in which the aliphatic chains are
located on the surface and in the exterior of the columns, and the sugar moieties are located towards the inside. The aliphatic
chains of neighbouring columns interpenetrate and share space thereby creating a liquid-like ‘aliphatic sea’ surrounding the sugar
columns.
rial sandwiched between a cover-slip and a
slide. The solvation process for the materials
was then observed in the polarizing micro-
scope. As the thermotropic columnar phases
of the materials were not continuously mis-
cible with water at room temperature, ly-
otropic phase formation for compounds 1–6
was observed upon heating the samples. In
each case, water penetration into the ther-
motropic phase did not occur until the clear-
ing point was approached. At the point of the
transition to the liquid, the molecular ordering
sugar moieties are located in the cores of the
columns (Fig. 3). This arrangement of the
molecules closely resembles those found in
lyotropic HII phases. The observed lack of
continuous miscibility of the thermotropic
mesophase with water supports the proposed
structural model of the phase where the
aliphatic chains located on the exteriors of the
columns would disfavour water penetration.
The lyotropic phase properties were investi-
gated by simply running a small amount of
water onto a crystalline sample of each mate-

R. Auze´ly-Velty et al. / Carbohydrate Research 314 (1998) 65–77
73
chains, myelin-type aggregates were pro-
duced after sonication (Fig. 5(b)). By con-
trast, the analysis of dispersions of 7 bearing
a more voluminous disaccharidic head group
showed the presence of spherical vesicles of
80–500 nm diameter (Fig. 5(c)).
breaks down and water penetrates immedi-
ately resulting in the formation of a hexago-
nal phase, which for each material exhibited
a classical defect texture (Fig. 4). There are
two possible structures of the hexagonal ly-
otropic phase, one where the aliphatic chains
are on the inside of the columns and the
polar head groups are towards the exterior
(i.e. HI), or alternatively the structure has a
double layer arrangement with the polar
head groups towards the centre of the
column and also on the exterior of the
column surface with the aliphatic chains ly-
ing in-between.
Self-assembling properties in dilute aqueous
media.—The diethers 1–7 were sonicated in
distilled water at 20–25 °C for 20 min. The
ratio of the amphiphiles to the solvent was
1–5 mg/mL. The resulting suspension was
centrifuged at 2000g for 10 min to give the
supernatant, which was then subjected to
transmission electron microscopic observa-
tion using 2 wt.% aqueous uranyl acetate as
a staining agent. The glycolipids were found
to self-assemble into various microstructures
depending on their structure.
These results clearly indicate that the volu-
metric ratio of the hydrophilic to the hydro-
phobic parts plays a major role in the
organization of such systems in water. Bulki-
ness of the disaccharide polar head of the
diether 7 brings to the phytanyl chains the
degree of freedom apparently necessary for
the formation of vesicles. The presence of a
decreasing hydrophilic domain favours the
formation of elongated cylindrical structures.
These aggregates made by the wedge-shaped
compounds 1–5 can be seen as multiple bi-
layers in the form of tubular vesicles [19,20].
Interestingly, the tubules formed appear to
have almost equidistantly separated parallel
defect lines running across the long axes of
the tubules, see Fig. 5(a). Lines of this na-
ture are usually associated with chirality,
and in particular helicity which results from
the way chiral molecules pack together. The
results suggest that the tubules either have a
helical multilayer structure composed of sev-
eral hundred molecular layers or else they
have a periodic defect structure that is based
on some form of helicity. Periodic defect
structures are well-known in thermotropic
liquid crystals, and are often manifested via
a competition between the need for the
molecules to form a twisted macrostructure
and some structural or space limit on their
ability to twist, e.g., Blue Phases, TGB
Phases, etc. The competition results in a
frustration which is relieved by the creation
of defects. For the lipid 6, the length reduc-
tion of the alkyl chains entails a decrease in
the steric constraints in the hydrophobic part
and, therefore, hinders the formation of
tubular structures. In fact, the polar and
non-polar parts of this rod-shaped material
are too small to participate in the stabilisa-
tion of vesicular or tubular aggregates. This
could justify why the diether 6 self-assembles
into myelin-type structures which probably
correspond to complex folding of rolled-up
multilayers [21].
Compounds 1–5 containing two identical
16 or 20 carbon atom chains and a
monosaccharidic head group exclusively ex-
hibited tubule-like structures of various sizes
(Fig. 5(a)). In the case of lipid 6, which has
comparatively shorter hydrophobic aliphatic
Fig. 4. Lyotropic hexagonal mesophase of diethers 1–6. Pho-
tomicrograph of the glycolipid–water interface at 75 °C (top
right-neat glycolipid in its liquid phase, bottom left-glyco-
lipid–water soln, centre-lyotropic hexagonal phase): Water
has penetrated the isotropic liquid sample to form a band of
hexagonal lyotropic phase.

74
R. Auze´ly-Velty et al. / Carbohydrate Research 314 (1998) 65–77
Fig. 5. Electron micrographs of aqueous aggregates of diethers 1–7 (stained by uranyl acetate). (a) Tubule-like aggregates
obtained from compounds 1–4, (b) myelins from compound 6, and (c) vesicles from diether 7.
tion of 5% H2SO4 in EtOH were used to
develop the plates. For column chromatogra-
phy, 60H (5–40 mm) Silica Gel (E. Merck)
was used. Optical rotations were measured
3. Experimental
Materials and methods.—All reactions were
performed under nitrogen in oven-dried glass-
ware. For the coupling reactions, the carbohy-
drate derivatives were dissolved in a small
quantity of toluene and placed under vacuum
for 2 h prior to use. Melting points were
determined using a Kofler apparatus and are
uncorrected. Elemental analyses were made by
the Service de Microanalyse de l’ENSCR,
Rennes (France). Thin-layer chromatography
was performed on 60F254 Silica Gel non-acti-
vated plates (E. Merck). UV light and a solu-
1
using a Perkin–Elmer 341 polarimeter. H
and 13C NMR spectra were recorded respec-
tively at 400 MHz and 100 MHz using a
Bruker ARX 400 spectrometer. Peracetylated
n-pentenyl glycofuranosides were prepared as
previously described [13]. The synthesis of the
aliphatic diethers 8–10 having two identical
chains were carried out according to literature
methods [4]. (R)-3,7-Dimethyloctan-1-ol was
prepared by Raney Ni-catalysed hydrogena-

R. Auze´ly-Velty et al. / Carbohydrate Research 314 (1998) 65–77
75
mL) and the ether suspension was filtered
through a pad of silica gel. The eluent was
removed and the crude product was purified
by column chromatography (20:1 petroleum
ether–EtOAc) to give 13 (0.79 g, 60%) as a
colourless oil; [h]2D0 −4.7 (c 1.07, CH2Cl2); Rf
tion of commercially available (R)-(+)-cit-
ronellol. The triflate ester of 1-octanol was
synthesized as described by Aoki and Poulter
[10]. Other chemicals were purchased from
Acros or Fluka Chemika. Solvents were of
reagent grade and were distilled under N2
before use: dichloromethane from phosphorus
pentoxide, tetrahydrofuran from sodium ben-
zophenone ketyl.
1
0.65 (19:1 petroleum ether–ether); H NMR
(CDCl3): l 7.70–7.67 (m, 5 H, Ph), 7.44–7.35
(m, 5 H, Ph), 3.71–3.69 (m, 2 H, CH2OSi),
3.60–3.37 [m, 7 H, CH(OCH2)CH2OCH2],
1.63–1.08 [m, 22 H, CH2CH(CH2)3CH,
(CH2)6], 1.05 [s, 9 H, (CH3)3CSi], 0.87–0.85
(m, 12 H, 4 CH3); 13C NMR (CDCl3): l
135.6–127.6 (Ph), 79.5 (OCH), 70.7, 70.6, 69.9
(CH2OCH2)CH2OCH2), 63.6 (CH2OSi), 39.3,
37.4, 36.7, 31.9, 30.2, 29.9, 29.5, 29.3, 28.0,
26.1, 24.7, 22.7 [CH2CH(CH2)3CH, (CH2)6],
26.8 [(CH3)3CSi], 22.7, 22.6, 19.7, 14.1 (4
CH3), 19.3 [(CH3)3CSi].
3-O-[(R)-3,7-Dimethyloctyl]-2-O-octyl-sn-
glycerol (11).—To a solution of 13 (0.74 g,
1.26 mmol) in dry THF (14 mL) under N2 a
1.0 M solution of Bu4NF in THF (2.6 mL,
2.60 mmol) was added. The reaction mixture
was stirred for 1 h at room temperature and
then water (20 mL) was added. After extrac-
tion with ether (3×50 mL), the combined
organic layers were dried over MgSO4 and
concentrated. Purification of the residue by
column chromatography (7:3 petroleum
ether–ether then ether) afforded 11 (0.36 g,
83%) as a colourless oil; [h]2D0 +13.3 (c 1.27,
CH2Cl2); Rf 0.26 (4:1 petroleum ether–ether);
1H NMR (CDCl3): l, 3.75–3.43 [m, 9 H,
CH2CH(OCH2)CH2OCH2], 1.66-1.46 and
1.40–1.06 [m, 22 H, CH2CH(CH2)3CH,
(CH2)6], 0.87-0.85 (m, 12 H, 4 CH3); 13C
NMR (CDCl3): l 78.3 (OCH), 70.7, 70.4, 70.1
[(CH2OCH2)CH2OCH2], 63.1 (CH2OH), 39.3,
37.3, 36.6, 31.8, 30.1, 29.8, 29.4, 29.3, 27.9,
26.1, 24.7, 22.7 [CH2CH(CH2)3CH, (CH2)6],
22.7, 22.6, 19.7, 14.1 (4 CH3). Anal. Calcd for
C21H44O3: C, 73.20; H, 12.87. Found: C,
73.43; H, 13.01.
3 - O - [(R) - 3,7 - Dimethyloctyl] - 1 - O - (tert-
butyldiphenylsilyl)-sn-glycerol (12).—A cata-
lytic amount of BF3·Et2O (0.04 mL, 0.35
mmol) was added at 0 °C to a solution of
(S)-1-tert-butyldiphenylsilyl glycidol (1.08 g,
3.45 mmol) in dry CH2Cl2 (20 mL) under N2.
The resulting mixture was stirred for 17 h at
4 °C before the addition of water (20 mL).
The resulting layers were separated and the aq
layer was extracted with CH2Cl2 (3×40 mL).
The combined organic layers were washed
with satd aq NaCl (30 mL), dried over MgSO4
and solvent was removed under reduced pres-
sure. Purification of the residue by column
chromatography (19:1 petroleum ether–
EtOAc) afforded 12 (1.10 g, 68%) as a colour-
less oil; Rf 0.4 (9:1 petroleum ether–EtOAc);
1H NMR (CDCl3): l 7.68–7.64 (m, 5 H, Ph),
7.45–7.36 (m, 5 H, Ph), 3.92–3.85 (m, 1 H,
OCH), 3.70 (d, 2 H, J 5.4 Hz, CH2OSi),
3.53–3.42 (m, 4 H, CH2OCH2), 1.65–1.10 [m,
10 H, CH2CH(CH2)3CH], 1.06 [s, 9 H,
(CH3)3CSi], 0.87–0.85 (m, 9 H, 3 CH3); 13C
NMR (CDCl3): l 135.6–127.8 (Ph), 70.7
(OCH), 71.5, 69.9 (CH2OCH2), 64.8
(CH2OSi), 39.3, 37.4, 36.6, 29.9, 24.7
[CH2CH(CH2)3CH], 26.8 [(CH3)3CSi], 22.7,
22.6, 19.7 (3 CH3), 19.3 [(CH3)3CSi].
3-O-[(R)-3,7-Dimethyloctyl]-2-O-octyl-1-O-
(tert-butyldiphenylsilyl)-sn-glycerol (13).—1,8-
Bis(dimethylamino)naphthalene (1.20 g, 5.60
mmol) was added under N2 and at room
temperature to a solution of 12 (1.05 g, 2.24
mmol) and n-octyl triflate (1.47 g, 5.60 mmol)
in dry CH2Cl2 (10 mL). The solution was
heated at reflux for 48 h. After cooling, the
mixture was diluted with CH2Cl2 (80 mL),
washed successively with 5% aq HCl (30 mL),
water (30 mL) and satd aq NaCl (30 mL). The
organic phase was dried over MgSO4 and the
solvent was evaporated under reduced pres-
sure. The residue was triturated with ether (20
General procedure for glycosylation of glyc-
erol diethers and deprotection of tetraacetylated
products.—To a solution of the aliphatic di-
ether (0.1 M, 0.8 equiv) and the pentenyl
glycoside (1.0 equiv) in dry CH2Cl2 at room
temperature was added N-iodosuccinimide
(NIS, 1.3 equiv) followed by triethylsilyl trifl-
uoromethanesulfonate (TESOTf, 0.3 equiv).

76
R. Auze´ly-Velty et al. / Carbohydrate Research 314 (1998) 65–77
tribenzylated derivative (0.417 g, 0.31 mmol).
Part of this oil (0.35 g, 0.26 mmol) was dis-
solved in AcOH (2 mL) and heated to 70 °C.
Water (0.5 mL) was then added dropwise.
This soln was stirred at 70 °C for 5 h, coevap-
orated with EtOH (4×5 mL) and chro-
matographed on silica gel using CH2Cl2 and
then a 19:1 CH2Cl2–acetone mixture to
provide the corresponding 6-O-deprotected
compound (0.195 g, 0.18 mmol) as an oil; Rf
0.28 (7:3 petroleum ether–Et2O). Glycosyla-
tion of this tribenzylated compound (0.148 g,
0.14 mmol) with pentenyl galactofuranoside
(16) (0.071 g, 0.17 mmol) was achieved follow-
ing the general procedure previously de-
scribed. The crude product was purified by
flash chromatography using a 3:2 to 2:3
petroleum ether–Et2O step-gradient mixture
to provide the corresponding disaccharide
(0.112 g, 0.079 mmol) which was then submit-
ted to Zemple`n conditions (see general proce-
dure). A solution of the resulting deacetylated
compound in EtOH–water (2:1, 3 mL) con-
taining 10% palladium on carbon (0.05 g) was
stirred under an atmosphere of hydrogen at
room temperature for 7 h. The catalyst was
removed by filtration on celite and the filtrate
was concentrated under vacuum. The residue
was chromatographed over silica gel using
CH2Cl2–CH3OH (19:1 and then 17:3) to give
compound (7) [0.039 g, 29% from (16)] as a
colorless oil; Rf 0.71 (17:3 CH2Cl2–CH3OH).
Anal. Calcd for C55H108O13: C, 67.58; H,
11.14. Found: C, 67.78; H, 11.26.
Measurements of physical properties.—
Phase identifications and determination of
phase transition temperatures were carried
out, concomitantly, by thermal polarised light
microscopy using either a Zeiss Universal or
an Olympus BH2 polarized light microscope
equipped with a Mettler FP82 microfurnace in
conjunction with an FP80 central processor.
DSC was used to determine enthalpies of tran-
sition and to confirm the phase transition
temperatures determined by optical mi-
croscopy. Differential scanning thermograms
(scan rate 10°/min) were obtained using a
Perkin Elmer DSC 7 PC system operating on
UNIX software. The results obtained were
standardised relative to indium (measured on-
The mixture was stirred under nitrogen until
TLC analysis indicated complete disappear-
ance of the starting acceptor (10–15 min).
Several drops of Et3N were added to the
reaction mixture until it turned into a yellow
solution. The resulting solution was diluted
with CH2Cl2 and washed successively with
10% aq sodium thiosulfate, 0.5% aq HCl (un-
til neutral pH) and satd aq NaCl. The com-
bined organic layers were dried over MgSO4
and the solvent was removed. The crude
residue was then subjected to flash column
chromatography, using a 9:1 to 4:1 petroleum
ether–EtOAc step-gradient mixture, to afford
the corresponding tetraacetylated glycolipid.
Hydrolysis of the tetraacetylated product (0.20
mmol) with NaOMe in MeOH (2.5 mL) in dry
MeOH (0.1 M, 2.5 mL) at room temperature
for 2 h gave the crude unprotected diether-
type furanosyl lipid which was purified by
column chromatography (19:1 CH2Cl2–
MeOH).
1,2-Di-O-[(3RS, 7R, 11R)-dihydrophytyl]-
3 - O - [6 - O - (i - D - galactofuranosyl) - i - D-
galactofuranosyl)-rac-glycerol (7).—1,2-Di-O-
[(3RS, 7R, 11R)-dihydrophytyl]-3-O-(b-D-
galactofuranosyl)-rac-glycerol (3) (0.734 g,
0.90 mmol) and DMAP (0.011 g, 0.09 mmol)
were dissolved in dry pyridine (10 mL). 4-Ani-
sylchlorodiphenylmethane (MMTrCl) (0.361
g, 1.17 mmol) in dry pyridine (5 mL) was
added at 0 °C and the reaction mixture was
stirred at room temperature for 72 h. The soln
was coevaporated with toluene and the residue
was subjected to column chromatography (9:1
CH2Cl2 –acetone) to afford the corresponding
6-O-tritylated compound (0.476 g, 0.44
mmol). To a solution of this compound (0.410
g, 0.38 mmol) in dry DMF (6 mL) was added
sodium hydride (60% dispersion in mineral oil,
0.091 g, 2.28 mmol) at 0 °C. After stirring for
15 min, benzyl bromide (0.27 mL, 2.28 mmol)
was introduced dropwise. The reaction mix-
ture was stirred for 6 h. Methanol (2 mL) was
added and the mixture was evaporated to
dryness. The residue was redissolved in
CH2Cl2 (150 mL), extracted with water (3×
20 mL) and brine (20 mL), dried (MgSO4),
evaporated and chromatographed on silica gel
using a 19:1 to 4:1 petroleum ether–Et2O
step-gradient mixture to give the resulting

R. Auze´ly-Velty et al. / Carbohydrate Research 314 (1998) 65–77
77
set 156.68 °C, DH 28.47 J/g, literature values
References
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the transition temperatures determined by
optical microscopy and DSC show some
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Acknowledgements
We are grateful to the CNRS and the Re-
gion Bretagne for a grant to R.V.; to M.
Lefeuvre and C. Penverne for assistance, re-
spectively, in NMR experiments and micro-
analyses. We also thank J.P. Rolland and D.
Thomas for electron microscopic analyses.
.