Supermolecular chiral mesogenic tripedes

Article abstract of DOI:10.1002/chem.201102193

A novel series of chiral liquid crystalline tripedes Glucoside and Mannoside derivatives G_n and M_n (n=1-3) have been synthesised. The inner cores consist of methyl α-D-Glucoside G or methyl α-D-Mannoside M, regioselectively functiona

Full text of DOI:10.1002/chem.201102193

DOI: 10.1002/chem.201102193
Supermolecular Chiral Mesogenic Tripedes
Abdelhak Belaissaoui,*[a] Isabel M. Saez,[a] Stephen J. Cowling,[a] Xiangbing Zeng,[b] and
John W. Goodby[a]
Abstract:
A
novel series of chiral
carboxylic acid moieties. The cores,
which can acquire several flexible con-
formations, are attached to rod-like
smectogenic-preferring cyanobiphenyl
units, by means of a flexible hexanoyl
spacer. These Glyco-Supermolecules
exhibit chiral nematic (N*) and smectic
A (SmA) phases. The combined effects
of core chirality and functional groups
on thermal and mesomorphic charac-
teristics are discussed.
liquid crystalline tripedes Glucoside
and Mannoside derivatives Gn and Mn
(n=1–3) have been synthesised. The
inner cores consist of methyl a-d-Glu-
coside G or methyl a-d-Mannoside M,
regioselectively functionalised at the
less hindered position C6, with tert-bu-
tyldimethylsilyl (TBDMS), hydroxyl or
Keywords: carbohydrates · chirality
transfer · liquid crystals · mesogens ·
tripedes
Introduction
On the other hand, conventional dendritic-like supermo-
lecular liquid crystals[1] consist of a number of mesogenic
units attached to an inner core via flexible spacers
(Figure 2). The associated conformational properties give
rise to a number of different molecular anisometric shapes.
Hence, the mesophase type of supermolecular liquid crystals
strongly depends on the dominant conformational struc-
ture(s) in the bulk. In contrast to low molar mass mesogens,
there is a strong interdependence between the conforma-
tional properties and the phase type of supermolecular
liquid crystals. However, the statistical probability of the
condensed phase dominant conformer(s) is dictated primari-
ly by the space filling efficiency.[2] Thus, the dominant con-
formational structure(s) may differ from the minimum
energy conformers in the single-molecule state. Overall, the
core-shell structure is the key component controlling the
three-dimensional orientation of the mesogenic units and
consequently the supermolecular conformational properties
and their associated packing characteristics.
In addition, the self-assembly in mesophases of globular
supermolecular liquid crystals can be tuned further by incor-
porating specific functional moieties within the central core
structural components to add site specific interactions, such
as hydrogen bonding or nanosegregation.
Carbohydrate-based mesogens represent a large class of
liquid crystals that exhibit lyotropic as well as thermotropic
phase behaviours.[3,4] The growing interest in such materials,
as a promising source of novel liquid crystalline materials,
has arisen as a result of their profound importance in many
biological and molecular recognition processes.[3,5] Yet, there
have been very few reports on the synthesis and mesomor-
phic properties of supermolecular liquid crystals with carbo-
hydrate-based cores and mesogenic units attached at the pe-
riphery.[6,7]
Mesogens are the building blocks of liquid crystalline meso-
phases, which combine fluid mobility and anisotropic order-
ing properties in a single material. Typically, low molar mass
liquid-crystals are composed of a relatively rigid shape ani-
sometric mesogenic core to which one or two terminal flexi-
ble spacers, most commonly alkyl chains, are attached
(Figure 1).
Figure 1. Typical low molar mass mesogens consisting of a shape-aniso-
metric core and one or two flexible end-chains.
In essence, the nature of the liquid crystal behaviour is
dictated primarily by the anisometry of the mesogenic core.
For example, rod-like molecules induce the formation of ca-
lamitic mesophases while disc-like molecules self-organize
to give columnar mesophases.
Molecular conformational properties of low molar mass
mesogens have limited impact on their corresponding over-
all molecular anisometry and consequently have limited in-
fluence on their structural phase type. However, conforma-
tional isomerism can critically affect the thermodynamic sta-
bility of the mesophases.
[a] Dr. A. Belaissaoui, Dr. I. M. Saez, Dr. S. J. Cowling,
Prof. J. W. Goodby
Department of Chemistry, University of York
Heslington Road, York, YO10 5DD (UK)
E-mail: abdel.belaissaoui@york.ac.uk
[b] Dr. X. Zeng
Department of Materials Science and Engineering
The University of Sheffield, Sheffield, S1 3JD (UK)
Moreover, in nature, hydrogen bonding interactions are
considered of crucial importance in inducing aggregation.
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201102193.
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FULL PAPER
Here, we report the synthe-
sis of supermolecular chiral
liquid crystalline tripedes, in-
corporating either methyl a-d-
glucopyranoside or methyl a-
d-mannopyranoside as chiral
cores, linked to three smecto-
genic cyanobiphenyl groups in
branching configuration by
means of hexanoyl spacers
(Figure 3). It is noteworthy
that the two carbohydrate
cores differ only at C2 position
with R configuration for the
methyl a-d-Glucoside and S
for the methyl a-d-Mannoside.
Figure 2. Schematic representation of primary structures of a globular supermolecular liquid crystalline tetra-
pede exhibiting conformational isomerism. The dominant conformer(s) determines the mesophase structural
type.
For instance, in biological systems, intermolecular hydrogen
bonding plays a critical role in stabilising the double helical
structure of nucleic acids.[8]
Many carboxylic acids have been found to exhibit liquid
crystalline behaviour.[9] These compounds dimerise through
intermolecular hydrogen bonds, generating supramolecular
structures and therefore affecting the overall molecular
shape anisometry, which can influence critically the meso-
morphic properties.
Functional groups were incorporated within the inner core
in order to add structural functional diversity and fine tune
the macroscopic behaviour without modifying their stereo-
genic properties. We demonstrate the effect of the associat-
ed conformational and orientational properties of the core
chirality, in addition to some incorporated specific function-
al groups on their liquid crystalline properties.
In this context, we incorporated enantiomerically pure
carbohydrate derived units, as inner cores within supermo-
lecular structures, to investigate the directional effect of the
scaffold and how the chirality, encoded at molecular level as
structural information inherent to the core, is transmitted
through the geometry of the mesogenic arms to the periph-
ery, and is expressed at macromolecular level in terms of
mesophase behaviour. Furthermore, the glycosic carbon C6
was functionalised with three different groups, a micro-seg-
regating and sterically hindering tert-butyldimethylsilyl
(TBDMS), hydrogen bonding donor-acceptors hydroxyl and
carboxylic acid moieties (Figure 3). Each functional group
induces specific interactions which ultimately affect the mes-
omorphic behaviour.
Results and Discussions
Synthesis: Similarly to the synthesis of tetrapedes that we
have reported previously,[6] the supermolecular tripedes Gn
and Mn (n=1–3) were accessible via the convergent ap-
proach, which consists of assembling the pre-synthesised
arms with the functionalised cores. The synthetic routes are
outlined in Scheme 1.
The etherification reaction of 4-cyano-4’-hydroxybiphenyl
1 with 6-bromo-1-hexanol in butanone in the presence of
potassium carbonate K2CO3, afforded 6-(4-cyanobiphenyl-
4’-yloxy)hexanol 2. The oxidation of 2 with Jones reagent in
acetone yielded the corresponding carboxylic acid 6-(4-cya-
nobiphenyl-4’-yloxy)hexanoic acid 3 in excellent yield.[6]
Due to mutarotation,[10] free carbohydrate substrates were
not employed in this work. Instead, we used methyl glyco-
sides as the simplest sugars with the advantage of an effi-
cient control of the core stereogenicity. In addition, they are
highly abundant in nature with an important biological sig-
nificance.[11]
The bulky tert-butyldimethylsilyloxy (TBDMSO) group is
considerably more hydrolytically stable than trimethylsily-
loxy ethers,[12] which are too sensitively susceptible to solvol-
ysis to be considered as protecting groups. Hence, the tert-
butyldimethylsilyl (TBDMS) ether is one of the most com-
monly used silyl protecting groups, particularly in carbohy-
drate chemistry, where the steric bulk of the TBDMS ether
allows their high yielding chemoselective coupling,[13] in ad-
dition to the good balance between their stability under
acidic or basic conditions and ease of selective removal.[14]
Thus, a regioselective silylation of the C6 hydroxyl group in
methyl pyranosides of a-d-Glucose and a-d-Mannose, was
Figure 3. Molecular structures of functional chiral supermolecular carbo-
hydrate-based liquid crystalline tripedes (Gn and Mn, n=1–3).
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A. Belaissaoui et al.
Scheme 1. Reagents and conditions: a) K2CO3/KI, butanone b) Jones reagent, acetone c) TBDMSCl, pyridine/DMAP d) DCC/CH2Cl2/DMAP e) IBr/
CH2Cl2/MeOH f) Jones Reagent, acetone.
accomplished
using
tert-butyldimethylsilyl
chloride
tion conditions. However, I2-MeOH mediated cleavage of
tert-butyldimethylsilyl (TBDMS) ether groups from G1 and
M1 were unsuccessful and only the unreacted starting mate-
rials were recovered. A milder and selective deprotection of
tert-butyldimethylsilyl (TBDMS) ethers using iodine mono-
bromide IBr in methanol constitutes an effective alternative
method for their facile cleavage and has the advantage to
tolerate base labile groups such as esters and amides.[21]
Thus, treatment of a solution of C6-O-TBDMS derivatives
of Me-a-d-Glucoside G1 and Me-a-d-Mannoside M1 in
MeOH/CH2Cl2 mixture with a 1m dichloromethane solution
of iodine monobromide IBr yielded the corresponding tri-
pedes G2 and M2 with free hydroxyl group C6-OH in rela-
tively good yields. However, the reaction does not go to
completion and the unreacted starting materials G1 and M1
were readily recovered by column chromatography. Subse-
quent oxidation of the primary hydroxy groups at C6 posi-
tion of the Methyl glycoside derivatives G2 and M2 with
chromium trioxide-sulfuric acid in acetone gave the corre-
sponding carboxylic acids G3 and M3 in very good yields.
(TBDMSCl) in pyridine, to afford the mono-silylated com-
pounds Glucoside[15] 5g and Mannoside[16] 5m in good
yields.
The esterification reactions of the C6-O-monosilylated de-
rivatives methyl a-d-Glucoside 5g and methyl a-d-Manno-
side 5m with the carboxylic acid 3 in CH2Cl2 using DCC as
coupling reagent in the presence of a catalytic amount of
DMAP, afforded the corresponding trimers G1 and M1 as
monodisperse structures in quantitative yields. The kinetical-
ly slow reactions were monitored by GPC to completion for
two weeks.
One of the most widely used methods for the cleavage of
silyl ethers are the fluoride anion based reagents, such as po-
tassium fluoride (KF)[17] or tetrabutylammonium fluoride
(TBAF),[18] as a result of the high affinity between silicon
and fluoride ions. However, these methods suffer from the
strong basicity of fluoride anion, making them incompatible
with substrates prone to elimination. Furthermore, esters
are known to migrate under basic conditions in the case of
polyhydroxy compounds, with hydroxyl groups protected as
esters.[19] Alternatively, a facile and mild removal of tert-bu-
tyldimethylsilyl ethers can be achieved in Iodine-Methanol
system.[20] No strong bases or acids are used and the anome-
ric moieties and ester groups are stable in these mild reac-
Mesomorphic properties: The mesomorphic properties were
investigated by thermal polarising optical microscopy
(POM) (Figure 4), differential scanning calorimetry (DSC)
(Figure 5 & Figure 6) and X-Ray (Figure 7) measurements.
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Supermolecular Chiral Mesogenic Tripedes
FULL PAPER
Figure 7. X-ray patterns of Gn (n=1–3) and Mn (n=1, 3). No diffraction
peak has been observed for the Mannoside M2.
Figure 4. POM of the molecular tripedes: a) G1 at RT, after annealing,
shows streaks and homeotropic domains of the SmA texture. b) G2 after
slow cooling down from isotropic to 608C, exhibiting typical fingerprint
texture of N* mesophase. c) G2 sheared at 788C displays N* phase, slight-
ly uncrossed polarisers showing the helical nature of the phase. d) G3
with carboxylic acid functional group, sheared at 106.98C showing N*
(left) and SmA textures with homogeneous and homeotropic domains
(right).
focal conic domains were sheared with the flow and homeo-
tropic domains at room temperature (Figure 4a). Despite
being monodisperse, the sample behaves very similar to
polymers such that the isotropisation transition appears to
be very broad in a range of over 108C. On the other hand,
POM micrographs of G2 with free hydroxyl group C6-OH,
after slow cooling from isotropic displays a typical finger-
print texture of a chiral nematic phase with left handed hel-
icity (Figure 4b,c). The tripede G3 with a carboxylic acid
functional group, exhibits a typical fingerprint texture of a
chiral nematic mesophase at 1008C after annealing for one
hour. It was difficult to observe the chiral nematic-smectic
A transition, but upon shearing, the transition between the
two phases can be observed (Figure 4d).
However, the examination of mesophase structures of
Mannoside derivatives were inconclusive by POM, therefore
other evidences must be incorporated to assign their meso-
morphic properties.
Figure 5. DSC thermograms of functional Me-a-d-Glucoside mesogenic
tripedes Gn (n=1–3).
Thermal properties: differential scanning calorimetry: The
phase transition temperatures of Gn and Mn (n=1–3) were
analysed by DSC and their traces were recorded during the
third heating and cooling run at
a scanning rate of
108CminÀ1. The thermograms are shown in Figures 5 and 6
and transition temperatures are listed in Table 1
On the heating curve of G1, two endothermic phase tran-
sitions were observed. The first endothermic transition at
lower temperature region corresponds to the glass-smectic
A obtained at midpoint 18.68C and a second with the signal
onset at 47.88C (DH=3.10 JgÀ1) allocated to smectic A-iso-
tropic transition. The anisotropic-isotropic phase transition
peaks exhibit broad asymmetric profile during the heating
and cooling cycles. The broadness reveals slow phase transi-
tion kinetics, attributed to the gradual conformational
changes affecting the packing properties of the Glucoside
and Mannoside bulks during their corresponding smectic A-
isotropic transitions.
Figure 6. DSC thermograms of functional Me-a-d-Mannoside mesogenic
tripedes Mn (n=1–3).
Polarised Optical Microscopy: The optical defect textures of
the tripede G1, consisting of three 6-(4-cyanobiphenyl-4’-
yloxy)hexanoate mesogenic arms and
a methyl O-6-
TBDMS-a-d-Glucoside central core, after annealing, exhib-
its poorly defined smectic A texture with streaks where the
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A. Belaissaoui et al.
Table 1. Transition temperatures (8C) and enthalpic data (in italics between brackets, JgÀ1) obtained for func-
tional mesogenic tripedes Me-a-d-Glucosides Gn & Me-a-d-Mannosides Mn (n=1–3).
It is noteworthy that the
functional group at C6 position
can critically influence the
phase behaviour and the asso-
G1 Iso 54.9 (À2.53) SmA 17.2 G
M1 Iso 24.6 G
G 20.0 SmA 27.5 (1.11) Iso
G 18.6 SmA 47.8 (3.10) Iso
ciated
thermal
properties.
G2 Iso 94.1 (À1.03) N*-SmA 37.1 G
M2 Iso 60.6 (À0.40) Cr 32.7 G
Thus, fine-tuning of the meso-
morphic properties of these
glyco-supermolecules can be
G 23.0 Cr 37.7 (0.49) SmA 68.0 (0.14) N* 93.7 (0.05) Iso
G 33.3 Cr 55.1 (0.66) Iso
G3 Iso 113.7 (À0.40) N* 103.9 (À0.15) SmA 45.0 G
M3 Iso 67.4 (À0.76) N*-SmA 44.2 G
G 32.3 Cr 45.30 (0.94) SmA 94.7 (0.32) N* 113.30 (0.30) Iso
Cr 45.2 (3.1) SmA-N* 60.7 (3.0) Iso
achieved by controlling the ste-
reogenic features of the core
In the heating cycle of M1 (Figure 6), a glass transition
was characterised at midpoint 20.08C, followed by a broad
transition at 27.58C (DH=1.11 JgÀ1). Upon cooling, only
one broad shoulder at midpoint 24.68C attributed to a glass
transition was detected.
and the nature of the incorporated functional groups.
X-ray: The mesomorphic behaviours of the Mannoside and
Glucoside derivatives have been characterised by X-Ray dif-
fraction measurements (Figure 7). Unfortunately, XRD on
powder samples cannot tell the difference between chiral
nematic and isotropic phases, as both of them show only dif-
fuse scattering. All the samples generally gave very weak re-
flections and only one sharp diffraction peak can be ob-
served for the smectic phase.
The compounds G1 and M1 bearing tert-butyldimethylsilyl
(TBDMS) group at C6 position, were examined at 258C and
exhibited one sharp diffraction peak, associated with lateral
packing at 2q=2.248 and 2.358 respectively, corresponding
to interlayer d-spacing 3.94 nm and 3.75 nm, suggesting
smectic A mesophases.
For the compounds with free hydroxyl groups, no diffrac-
tion peak has been observed for the Mannoside M2, even
after long exposure. This result is consistent with POM ob-
servations and DSC measurements. However, for the Gluco-
side G2, a weak but sharp diffraction peak is observed at
408C with 2q=2.908 (d=3.04 nm), consistent with that ex-
pected for a smectic structure. At 558C only diffuse scatter-
ing were observed, possibly a chiral nematic phase.
For the carboxylic acid derivatives, sharp diffraction peak
was observed up to 658C (2q=2.878 d=3.08 nm) for G3 and
508C (2q=2.868, d=3.09 nm) for M3. For higher tempera-
tures only diffuse scattering were observed, suggesting chiral
nematic or isotropic phases.
For G2, the phase sequence while heating displays four
endothermic transitions. A glass transition at lower tempera-
ture at midpoint 238C, followed by a broad melting shoulder
with an onset at 37.78C (DH=0.49 JgÀ1), a broad weak
smectic A-chiral nematic transition (DH=0.14 JgÀ1) with an
onset at 68.08C and an extremely weak and broad peak with
an onset at 93.78C (DH=0.05 JgÀ1), which is attributed to
the chiral nematic-isotropic transition. On cooling, only two
transitions have been observed. In addition to the glass at
midpoint 37.18C, the sample displays very broad range
transition from 94.18C to 688C, corresponding to two
overlapping transitions, which couldn’t be resolved and
were allocated to isotropic-chiral nematic-smectic A transi-
tions.
In contrast, DSC traces of the Mannoside M2 exhibited no
liquid crystalline mesophase. The heating and cooling curves
show broad transition peaks. On heating, in addition to a
glass at midpoint 33.38C, a broad endotherm has been ob-
served at an onset 55.18C (DH=0.66 JgÀ1) attributed to the
isotropic transition.
The heating curve of the glycopyranuronic acid derivative
G3 shows a similar profile to G2, but with all four transitions
glass, melt, smectic A, chiral nematic and isotropic observed
at higher temperatures.
M3 exhibits fairly broad transitions on heating and cool-
ing. Firstly, the heating curve displays three partially over-
lapping transitions, a melt onset at 45.28C (DH=3.1 JgÀ1)
corresponding to a smectic A transition, a second endo-
therm which can be attributed to a nematic transition and a
third ascribed to the isotropisation with a peak at 67.18C.
Overall, upon changing the chiral core structure from
Glucoside Gn to Mannoside Mn (n=1–3), an increase in
Tg values have been observed, associated simultaneously
with depression of the clearing-point temperatures. For both
Glucosides and Mannosides, the glass transition Tg and
clearing point temperatures are critically influenced by the
nature of moieties at C6 position and their values increase
concurrently with the strength of the hydrogen bonding
donor-acceptor interactions, in ascending order in this se-
quence tert-butyldimethylsilyl (TBDMS) <hydroxyl OH <
carboxylic acid CO2H.
Effect of core conformational properties on the mesomor-
phic behaviours: The conformational diversity associated
with the Glucoside and Mannoside chiral cores confers
them high versatility and flexibility. Pyranosic monosacchar-
ides can access a large number of low energy conformations,
as
a result of their conformationally dynamic nature
(Figure 8), thus affecting their phase behaviours.
When comparing the Glucosides Gn and Mannosides Mn
(n=1–3), they differ only in configuration at the stereogenic
centre C2 corresponding to R and S respectively (Figure 3).
The resulting spatial orientation of the arms in relation to
the chiral core constitutes the structural basis underlying the
formation and the stabilisation of their corresponding or-
dered phases. The higher thermal stability of mesophases of
Glucosides, in comparison to their corresponding Mannoside
analogues, is owing to the expression of the chirality[22] from
the central core to the periphery, inducing specific three-di-
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Supermolecular Chiral Mesogenic Tripedes
FULL PAPER
Figure 9. Computed low energy conformers of Glucosides (G2, G3) and
Mannosides (M2, M3) inner cores in the two chair conformations (A, E)
displaying the core orientational properties induced by intramolecular
hydrogen-bonding interactions. Parts of the structures are hidden for
clarity.
etry, thus critically influencing their packing characteristics.
Moreover, the intrinsic conformational distribution in the
bulk state is likely to be influenced by the contribution of
both specific intra- and inter-molecular hydrogen bonding
interactions.
As shown in Figure 9, the computed conformers of Gluco-
sides (G2, G3) and Mannosides (M2, M3) with the inner core
in the two chair conformations (A, E) underlay the structur-
al and conformational basis of the combined molecular ex-
pression of the chirality and hydrogen bonding interactions
on phase behaviours.
Figure 8. Conformational diversity associated with Glucoside and Manno-
side confers high versatility and flexibility to the chiral cores (arms are
hidden for clarity). (1) Glucoside chair conformations with three arms.
a) All equatorials. b) All axials. (2) Mannoside chair conformations with
three arms. c) Two equatorials and one axial. d) Two axials and one equa-
torial.
mensional conformational properties (Figure 8) associated
with each core, hence affecting their corresponding aniso-
metric shapes and associated packing properties.
At the macroscopic level, nanosegregation of building
blocks and their space filling efficiency in the condensed
phase are two competing driving forces for the molecular
self-assembly in liquid-crystalline phases. However, both
Glucoside and Mannoside cores can adopt two chair confor-
mations, as shown in Figure 8. Each chair conformer dis-
plays differently the resulting spatial orientation of the arms
in relation to the chiral core. Therefore, the molecular shape
anisometry may vary from rod-like to disk-like depending
on predominant chair conformer(s) in the condensed phase,
thus determining the structural phase type.
However, the functionalisation of the carbon C6 with
three different functional groups, a microsegregating and
sterically hindering tert-butyldimethylsilyl (TBDMS), hydro-
gen bonding donor-acceptors OH and carboxylic acid, con-
siderably affect the phase behaviours of these materials.
This is owing to the type of interactions induced by each
functional group at C6 position.
Conclusion
A novel series of carbohydrate-based chiral liquid crystalline
tripedes have been synthesised. The inner cores consist of
Glucoside or Mannoside derivatives, which can acquire sev-
eral flexible conformations. The effects of the chiral cores
and the incorporated functional groups on the liquid crystal-
line properties were investigated.
Typically and independently of the chiral core structure,
higher glass transitions and clearing temperatures are found
to be associated with the strength of the hydrogen bonding
character of the functional group incorporated within the
inner core. In addition, Glucoside derivatives Gn (n=1–3)
exhibit wider temperature range mesophases as a result of
lower Tgs and higher melting temperatures than in the case
of the corresponding Mannosides Mn (n=1–3).
G1 and M1, incorporating tert-butyldimethylsilyl
(TBDMS) moiety, display the smectic A mesophase at RT
with broad isotropisation transitions. For tripede derivatives
G2 and M2 bearing free hydroxyl groups at C6, while the
Glucoside exhibits chiral nematic and smectic A mesophas-
es, M2 shows no fluid anisotropic phase. G3 bearing carbox-
ylic acid functional group displays similar profile to G2 with
higher transition temperatures, while the corresponding
While G1 and M1 are highly flexible, Gn and Mn (n=2–3)
are relatively conformationally restricted as a result of the
hydrogen bonding interaction of the hydroxyl or carboxylic
acid functional groups at C6 position with the ester group
attached to the pyranosic carbon C4 (Figure 9). This affects
the topological orientation of the arms relative to the inner
core and consequently their overall molecular shape anisom-
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A. Belaissaoui et al.
fate Na2S2O3 solution and extracted with CHCl3. The organic layer was
washed with brine, dried over MgSO4, and concentrated to dryness under
reduced pressure. The resulting residue was submitted to column chroma-
tography on silica gel (AcOEt/CH2Cl2/Hexane 1:2:3) to recover the un-
reacted starting material G1, followed by(AcOEt/CH2Cl2 1:1) to afford
G2 (72%) as a colourless oil. 1H NMR (CDCl3, 400 MHz): d=1.38-1.55
(m, 3CH2), 1.55-1.72 (m, 3CH2), 1.72-1.86 (m, 3CH2), 2.20-2.48 (m, 3CH2
+ OH), 3.41 (s, MeO), 3.55-3.64 (m, 1H), 3.67-3.85 (m, 2H), 3.88-4.05
(m, 3 OCH2), 4.88-4.94 (m, 1H), 4.97-5.00 (m, 1H), 5.07 (t, 1H), 5.60 (t,
1H), 6.90-7.00 (m, 6CH), 7.44-7.54 (m, 6CH), 7.55-7.70 ppm (m, 12CH);
13C NMR (CDCl3, 100 MHz): d=24.11 (CH2), 24.13 (CH2), 24.22 (CH2),
25.04 (CH2), 25.12 (CH2), 28.37 (CH2), 28.41 (CH2), 33.43 (CH2), 33.48
(CH2), 33.56 (CH2), 54.96 (MeO), 60.54 (CH2O), 67.19 (CH2O), 68.31
(CH), 69.02 (CH), 69.31 (CH), 70.53 (CH), 96.33 (CHO2), 109.41 (Cq-
CN), 114.54 (CH), 114.56 (CH), 118.62 (CN), 126.43 (CH), 126.45 (CH),
127.80 (CH), 130.59 (Cq), 130.60 (Cq), 132.06 (CH), 144.43 (Cq), 144.48
(Cq), 159.17 (Cq-O), 171.99 (CO2), 172.21 (CO2), 172.44 ppm (CO2);
HRMS (MALDI): m/z 1067.3 ([M]+, 51%), 1090.3 ([M+Na]+, 100%),
1106.3 ([M+K]+, 8%); elemental analysis calcd for C64H65N3O12: C
71.96, H 6.13, N 3.93, found: C 68.94, H 5.89, N 3.76.
Mannoside M3 exhibits similar phase behaviour, with a de-
pression in the melting point.
In summary, tailoring the thermo-mesomorphic behav-
iours of the tripedes Gn and Mn (n=1–3) were achieved by
combining the stereogenic properties of carbohydrate-based
conformationally dynamic chiral cores and the functional
properties of the incorporated moieties.
Experimental Section
Methyl-2,3,4-tri-O-[6-(4-cyanobiphenyl-4’-yloxy) hexanoyl]-6-O-tert-bu-
tyldimeth-ylsilyl-a-d-glucopyranoside G1: Under nitrogen atmosphere, to
an oven-dried round-bottomed flask containing a solution of 6-(4-cyano-
biphenyl-4’-yloxy)hexanoic acid 3 (9.41 g, 30.41 mmol, 4.18 equiv) and
methyl-6-O-tert-butyldimethylsilyl-a-d-glucopyranoside
5g
(2.34 g,
7.27 mmol) in dry CH2Cl2 (250 mL) were added DCC (9.41 g,
45.62 mmol), N,N-dimethylaminopyridine (371 mg, 3.04 mmol). The re-
sulting mixture was stirred for 14 days at room temperature and the reac-
tion progress was monitored by gel permeation chromatography (GPC).
The resulting solution was filtered and the DCU washed with CH2Cl2.
The solvent was evaporated in vacuo to afford an oily crude residue,
which was purified by column chromatography (EtOAc/CH2Cl2/Hexane)
Methyl-2,3,4-tri-O-[6-(4-cyanobiphenyl-4’-yloxy)hexanoyl]-a-d-manno-
pyranoside M2: Using methyl-6-O-tert-butyldimethylsilyl-a-d-mannoyra-
noside M1 as starting material, same procedure as for the preparation of
G2 was carried out to afford a colourless oil M2 in 72% yield. 1H NMR
(CDCl3, 400 MHz): d=1.38-1.90 (m, 9CH2), 2.22-2.31 (m, CH2), 2.31-2.39
(m, CH2), 2.39-2.55 (m, CH2 + OH,), 3.40 (s, MeO), 3.56-3.68 (m, 1H),
3.68-3.83 (m, 2H), 3.89-4.04 (m, 3 OCH2), 4.72-4.75 (d, 1H), 5.25-5.35
(m, 2H), 5.40-5.47 (m, 1H), 6.90-7.00 (m, 6H), 7.44-7.54 (m, 6H), 7.55-
1
to give G1 (100%); H NMR (CDCl3, 400 MHz): d=0.04 (s, Me), 0.05 (s,
Me), 0.89 (s, tBu), 1.35–1.54 (m, 3CH2), 1.54–1.70 (m, 3CH2), 1.70–1.86
(m, 3CH2), 2.20–2.45 (m, 3CH2), 3.40 (s, MeO), 3.65–3.71 (d, 2H), 3.80–
3.87 (m, 1H), 3.88–4.05 (m, 3CH2), 4.87–4.92 (m, 1H), 4.93–4.97 (d, 1H),
5.06 (t, 1H), 5.52 (t, 1H), 6.90–7.00 (m, 6CH), 7.46–7.54 (m, 6CH), 7.55–
7.70 ppm (m, 12CH); 13C NMR (CDCl3, 100 MHz): d=À5.46 (Me), 18.24
(Cq, tBu), 24.48 (CH2), 24.54 (CH2), 25.45 (CH2), 25.53 (CH2), 25.56
(CH2), 25.76 (3Me, tBu), 28.79 (CH2), 33.86 (CH2), 33.93 (CH2), 33.99,
(CH2), 55.08 (MeO), 62.07 (CH2O), 67.57 (CH2O), 68.71 (CH), 69.84
(CH), 70.28 (CH), 70.89 (CH), 96.42 (CHO2), 109.97 (Cq-CN), 114.90
(CH), 114.92 (CH), 118.99 (CN), 119.01 (CN), 126.92 (CH), 126.95 (CH),
128.22 (CH), 128.24 (CH), 131.22 (Cq), 131.25 (Cq), 132.49 (CH), 144.99
(Cq), 145.05 (Cq), 159.51 (Cq-O), 171.95 (CO2), 172.50 (CO2), 172.63 ppm
(CO2); HRMS (MALDI): m/z 1199.6 ([M+NH4]+, 100%); elemental
analysis calcd (%) for C70H79N3O12Si: C 71.10, H 6.73, N 3.55; found: C
70.14, H 6.67, N 3.43.
7.70 ppmACHTUNGTRNEUNG
(m, 12H); 13C NMR (CDCl3, 100 MHz): d=24.13 (CH2), 24.32
(CH2), 24.40 (CH2), 25.18 (CH2), 25.19 (CH2), 25.27 (CH2), 28.51 (CH2),
28.54 (CH2), 33.57 (CH2), 33.68 (CH2), 54.93 (MeO), 60.97 (CH2O), 65.93
(CH), 67.30 (CH2O), 67.35 (CH2O), 67.44 (CH2O), 68.68 (CH), 69.09
(CH), 70.27 (CH), 98.33 (CHO2), 109.57 (Cq-CN), 109.59 (Cq-CN), 114.67
(CH), 114.72 (CH), 118.74 (CN), 126.59 (CH), 126.61 (CH), 127.91 (CH),
127.94 (CH), 130.77 (Cq), 130.79 (Cq), 130.85 (Cq), 132.18 (CH), 144.65
(Cq), 144.70 (Cq), 159.26 (Cq-O), 159.29 (Cq-O), 159.34 (Cq-O), 171.93
(CO2), 172.22 (CO2), 172.85 ppm (CO2); HRMS (MALDI): m/z 1067.4
([M]+, 100%), 1090.4 ([M+Na]+, 79%), 1106.4 ([M+K]+, 18%); ele-
mental analysis calcd for C64H65N3O12: C 71.96, H 6.13, N 3.93; found: C
68.16, H 5.84, N 3.65.
Methyl-2,3,4-tri-O-[6-(4-cyanobiphenyl-4’-yloxy)hexanoyl]-a-d-glucopyr-
anuronic acid G3: To a stirred and cooled (08C) solution of G2 (2.32 g,
1.96 mmol) in acetone (150 mL), was added dropwise Jones reagent
(2.67m, 2.5 mL). The mixture was stirred at room temperature for 1 h
and the reaction was then quenched with iPrOH. The reaction mixture
was diluted with CHCl3 (250 mL), washed with brine 50 mL, and dried
over MgSO4. The solvent was then removed in vacuo and the crude prod-
uct was purified by flash column chromatography on silica gel (AcOEt)
to recover the unreacted starting material G2, followed by (AcOEt/
AcOH 99/1) to give the carboxylic acid product G3 in 98% yield.
1H NMR (CDCl3, 400 MHz): d=1.38-1.55 (m, 3CH2), 1.55-1.71 (m,
3CH2), 1.71-1.87 (m, 3CH2), 2.23-2.45 (m, 3CH2), 3.45 (s, MeO), 3.88-4.05
(m, 3 CH2O), 4.35-4.40 (d, 1H), 4.90-4.97 (dd, 1H), 5.05-5.10 (d, 1H),
5.27 (t, 1H), 5.58 (t, 1H), 6.88-7.02 (m, 6CH), 7.44-7.54 (m, 6CH), 7.55-
7.70 (m, 12CH), 9.11 ppm (Broad s, CO2H); 13C NMR (CDCl3,
100 MHz): d=24.28 (CH2), 24.45 (CH2), 24.53 (CH2), 25.34 (CH2), 25.43
(CH2), 25.49 (CH2), 28.69 (CH2), 28.75 (CH2), 33.68 (CH2), 33.75 (CH2),
33.88 (CH2), 56.04 (MeO), 67.55 (CH2O), 67.72 (CH2O), 69.11 (CH),
70.26 (CH), 97.01 (CH), 109.90 (Cq-CN), 114.89 (CH), 114.91 (CH),
114.96 (CH), 118.93 (CN), 126.89 (CH), 126.92 (CH), 128.22 (CH),
131.22 (Cq), 131.25 (Cq), 131.27 (Cq), 132.47 (CH), 144.97 (Cq), 145.02
(Cq), 159.43 (Cq), 159.48 (Cq-O), 170.95 (CO2), 172.11 (CO2), 172.25
(CO2), 172.55 ppm (CO2); HRMS (MALDI): m/z 1099.5 ([M+NH4]+,
100%); elemental analysis calcd (%) for C64H63N3O13: C 71.03, H 5.87, N
3.88; found: C 68.88, H 5.73, N 3.65.
Methyl-2,3,4-tri-O-[6-(4-cyanobiphenyl-4’-yloxy)hexanoyl]-6-O-tert-butyl-
dimethy-lsilyl-a-d-mannopyranoside M1: Using methyl-6-O-tert-butyldi-
methylsilyl-a-d-mannoyranoside 5m as starting material, the same proce-
dure as for the preparation of G1 was carried out. The oily crude was sub-
mitted to column chromatography (EtOAc/CH2Cl2/Hexane) to give M1
(100%). 1H NMR (CDCl3, 400 MHz): d=0.05 (s, Me), 0.06 (s, Me), 0.90
(s, tBu), 1.35–1.90 (m, 9CH2), 2.18–2.36 (m, 2CH2), 2.36–2.52 (m, CH2),
3.40ACHTUNGTRENNUNG(s, MeO), 3.65–3.76 (m, 2H), 3.77–3.85 (m, 1H), 3.88–4.05 (m,
3CH2), 4.67–4.71 (d, 1H), 5.23–5.28 (m, 1H), 5.28–5.41 (m, 2H), 6.90–
7.00 (m, 6CH), 7.46–7.54 (m, 6CH), 7.55–7.70 ppm (m, 12CH); 13C NMR
(CDCl3, 100 MHz): d=À5.57 (Me), À5.51 (Me), 18.04 (Cq, tBu), 24.22
(CH2), 24.48 (CH2), 24.56 (CH2), 25.30 (CH2), 25.33 (CH2), 25.43 (CH2),
25.64 (3Me, tBu), 28.67 (CH2), 33.73 (CH2), 33.88 (CH2), 54.79 (MeO),
62.05 (CH2O), 66.01 (CH), 67.45 (CH2O), 67.47 (CH2O), 67.56 (CH2O),
69.35 (CH), 71.04 (CH), 98.19 (CHO2), 109.76 (Cq-CN), 109.78 (Cq-CN),
109.80 (Cq-CN), 114.79 (CH), 114.85 (CH), 118.84 (CN), 126.74 (CH),
126.77 (CH), 128.04 (CH), 128.07 (CH), 130.95 (Cq), 130.97 (Cq), 131.03
(Cq), 132.31 (CH), 144.83 (Cq), 144.89 (Cq), 159.40 (Cq-O), 159.42 (Cq-O),
159.49 (Cq-O), 171.86 (CO2), 172.15 (CO2), 172.38 ppm (CO2); HRMS
(MALDI): m/z 1199.6 ([M+NH4]+, 100%); elemental analysis calcd (%)
for C70H79N3O12Si: C 71.10, H 6.73, N 3.55; found: C 68.94, H 6.50, N
3.40.
Methyl-2,3,4-tri-O-[6-(4-cyanobiphenyl-4’-yloxy)hexanoyl]-a-d-glucopyr-
anoside G2: To a solution of G1 (903 mg, 0.764 mmol) in MeOH (10 mL)
and CH2Cl2 (6 mL) was added iodine monobromide IBr solution
(1.3 mL, 1m in CH2Cl2) at room temperature, and the whole mixture was
stirred for 1 h. The reaction was quenched with saturated sodium thiosul-
Methyl-2,3,4-tri-O-[6-(4-cyanobiphenyl-4’-yloxy)hexanoyl]-a-d-manno-
pyranuron-ic acid M3: Using methyl-2,3,4-tri-O-[6-(4-cyanobiphenyl-4’-
yloxy)hexanoyl]-a-d-mannopyrano-side M2 as starting material, same
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ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2012, 18, 2366 – 2373

Supermolecular Chiral Mesogenic Tripedes
FULL PAPER
procedure as for the preparation of G3 was carried out. The crude prod-
uct was submitted to flash column chromatography on silica gel (AcOEt)
to recover the unreacted starting material M2, followed by (AcOEt/
AcOH 99/1) to afford the carboxylic acid derivative M3 in 90% yield.
1H NMR (CDCl3-D2O, 400 MHz): d=1.38-1.59 (m, 3CH2), 1.59-1.90 (m,
6CH2), 2.23-2.50 (m, 3CH2), 3.46 (s, MeO), 3.88-4.05 (m, 3 OCH2), 4.36-
4.41 (d, 1H), 4.83-4.87 (d, 1H), 5.28-5.31 (m, 1H), 5.39-5.46 (m, 1H),
5.46-5.54 (m, 1H), 6.90-7.00 (m, 6CH), 7.44-7.54 (m, 6CH), 7.55-7.70 ppm
(m, 12CH);13C NMR (CDCl3, 100 MHz): d=24.41 (CH2), 24.66 (CH2),
25.42 (CH2), 25.52 (CH2), 25.55 (CH2), 28.76 (CH2), 28.86 (CH2), 28.87
(CH2), 33.80 (CH2), 33.83 (CH2), 33.95 (CH2), 56.09 (MeO), 66.42 (CH),
66.44 (CH), 67.68 (CH2O), 67.73 (CH2O), 67.86 CH2O), 68.40 (CH),
68.80 (CH), 68.87 (CH), 98.89 (CH), 110.04 (Cq-CN), 110.07 (Cq-CN),
110.10 (Cq-CN), 114.99 (CH), 115.04 (CH), 119.04 (CN), 127.01 (CH),
127.03 (CH), 128.32(CH), 128.34 (CH), 131.34 (Cq),131.36 (Cq), 132.58
(CH), 145.07 (Cq), 145.08 (Cq), 145.14 (Cq), 159.43 (Cq-O), 159.55 (Cq-O),
159.62 (Cq-O), 172.12 (CO2), 172.25 (CO2), 172.52 ppm (CO2); HRMS
(MALDI): m/z 1099.5 ([M+NH4]+, 100%); elemental analysis calcd for
C64H63N3O13: C, 71.03; H, 5.87; N, 3.88; found: C, 70.32; H, 5.89; N, 3.89.
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Received: July 17, 2011
Published online: January 19, 2012
Chem. Eur. J. 2012, 18, 2366 – 2373
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
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