Supermolecular Chiral Mesogenic Tripedes

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 liquid crystalline tripedes Glucoside and Mannoside derivatives Gn and Mn (n = 1–3) have been synthesised. The inner cores consist of methyl a-d-Glucoside G or methyl a-d-Mannoside M, regioselectively functionalised at the less hindered position C6, with tert-butyldimethylsilyl (TBDMS), hydroxyl or

carboxylic acid moieties. The cores, which can acquire several flexible conformations, are attached to rod-like smectogenic-preferring cyanobiphenyl Keywords: carbohydrates · chirality transfer · liquid crystals · mesogens · tripedes

Introduction Mesogens are the building blocks of liquid crystalline mesophases, which combine fluid mobility and anisotropic ordering properties in a single material. Typically, low molar mass liquid-crystals are composed of a relatively rigid shape anisometric mesogenic core to which one or two terminal flexible spacers, most commonly alkyl chains, are attached (Figure 1).

Figure 1. Typical low molar mass mesogens consisting of a shape-anisometric 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 calamitic 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 overall molecular anisometry and consequently have limited influence on their structural phase type. However, conformational isomerism can critically affect the thermodynamic stability 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: [email protected] [b] Dr. X. Zeng Department of Materials Science and Engineering The University of Sheffield, Sheffield, S1 3JD (UK) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201102193.

2366

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 characteristics are discussed.

On the other hand, conventional dendritic-like supermolecular 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 structure(s) in the bulk. In contrast to low molar mass mesogens, there is a strong interdependence between the conformational properties and the phase type of supermolecular liquid crystals. However, the statistical probability of the condensed phase dominant conformer(s) is dictated primarily by the space filling efficiency.[2] Thus, the dominant conformational 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 incorporating 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 mesomorphic properties of supermolecular liquid crystals with carbohydrate-based cores and mesogenic units attached at the periphery.[6, 7] Moreover, in nature, hydrogen bonding interactions are considered of crucial importance in inducing aggregation.

 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Chem. Eur. J. 2012, 18, 2366 – 2373

FULL PAPER Here, we report the synthesis of supermolecular chiral liquid crystalline tripedes, incorporating either methyl a-dglucopyranoside or methyl ad-mannopyranoside as chiral cores, linked to three smectogenic 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 Figure 2. Schematic representation of primary structures of a globular supermolecular liquid crystalline tetrapede exhibiting conformational isomerism. The dominant conformer(s) determines the mesophase structural with R configuration for the type. methyl a-d-Glucoside and S for the methyl a-d-Mannoside. Functional groups were incorporated within the inner core For instance, in biological systems, intermolecular hydrogen in order to add structural functional diversity and fine tune bonding plays a critical role in stabilising the double helical the macroscopic behaviour without modifying their stereostructure of nucleic acids.[8] genic properties. We demonstrate the effect of the associatMany carboxylic acids have been found to exhibit liquid ed conformational and orientational properties of the core crystalline behaviour.[9] These compounds dimerise through chirality, in addition to some incorporated specific functionintermolecular hydrogen bonds, generating supramolecular al groups on their liquid crystalline properties. structures and therefore affecting the overall molecular shape anisometry, which can influence critically the mesomorphic properties. In this context, we incorporated enantiomerically pure Results and Discussions carbohydrate derived units, as inner cores within supermolecular structures, to investigate the directional effect of the Synthesis: Similarly to the synthesis of tetrapedes that we scaffold and how the chirality, encoded at molecular level as have reported previously,[6] the supermolecular tripedes Gn structural information inherent to the core, is transmitted and Mn (n = 1–3) were accessible via the convergent apthrough the geometry of the mesogenic arms to the periphproach, which consists of assembling the pre-synthesised ery, and is expressed at macromolecular level in terms of arms with the functionalised cores. The synthetic routes are mesophase behaviour. Furthermore, the glycosic carbon C6 outlined in Scheme 1. was functionalised with three different groups, a micro-segThe etherification reaction of 4-cyano-4’-hydroxybiphenyl regating and sterically hindering tert-butyldimethylsilyl 1 with 6-bromo-1-hexanol in butanone in the presence of (TBDMS), hydrogen bonding donor-acceptors hydroxyl and potassium carbonate K2CO3, afforded 6-(4-cyanobiphenylcarboxylic acid moieties (Figure 3). Each functional group 4’-yloxy)hexanol 2. The oxidation of 2 with Jones reagent in induces specific interactions which ultimately affect the mesacetone yielded the corresponding carboxylic acid 6-(4-cyaomorphic behaviour. 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 glycosides as the simplest sugars with the advantage of an efficient control of the core stereogenicity. In addition, they are highly abundant in nature with an important biological significance.[11] The bulky tert-butyldimethylsilyloxy (TBDMSO) group is considerably more hydrolytically stable than trimethylsilyloxy ethers,[12] which are too sensitively susceptible to solvolysis to be considered as protecting groups. Hence, the tertbutyldimethylsilyl (TBDMS) ether is one of the most commonly used silyl protecting groups, particularly in carbohydrate chemistry, where the steric bulk of the TBDMS ether allows their high yielding chemoselective coupling,[13] in addition 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 Figure 3. Molecular structures of functional chiral supermolecular carbohydrate-based liquid crystalline tripedes (Gn and Mn, n = 1–3). methyl pyranosides of a-d-Glucose and a-d-Mannose, was

Chem. Eur. J. 2012, 18, 2366 – 2373

 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.chemeurj.org

2367

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 (TBDMSCl) in pyridine, to afford the mono-silylated compounds Glucoside[15] 5 g and Mannoside[16] 5 m in good yields. The esterification reactions of the C6-O-monosilylated derivatives methyl a-d-Glucoside 5 g and methyl a-d-Mannoside 5 m 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 kinetically 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 potassium 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-butyldimethylsilyl ethers can be achieved in Iodine-Methanol system.[20] No strong bases or acids are used and the anomeric moieties and ester groups are stable in these mild reac-

2368

www.chemeurj.org

tion conditions. However, I2-MeOH mediated cleavage of tert-butyldimethylsilyl (TBDMS) ether groups from G1 and M1 were unsuccessful and only the unreacted starting materials were recovered. A milder and selective deprotection of tert-butyldimethylsilyl (TBDMS) ethers using iodine monobromide 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 1 m dichloromethane solution of iodine monobromide IBr yielded the corresponding tripedes G2 and M2 with free hydroxyl group C6-OH in relatively good yields. However, the reaction does not go to completion and the unreacted starting materials G1 and M1 were readily recovered by column chromatography. Subsequent oxidation of the primary hydroxy groups at C6 position of the Methyl glycoside derivatives G2 and M2 with chromium trioxide-sulfuric acid in acetone gave the corresponding carboxylic acids G3 and M3 in very good yields. 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.

 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Chem. Eur. J. 2012, 18, 2366 – 2373

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 60 8C, exhibiting typical fingerprint texture of N* mesophase. c) G2 sheared at 78 8C displays N* phase, slightly uncrossed polarisers showing the helical nature of the phase. d) G3 with carboxylic acid functional group, sheared at 106.9 8C showing N* (left) and SmA textures with homogeneous and homeotropic domains (right).

Figure 5. DSC thermograms of functional Me-a-d-Glucoside mesogenic tripedes Gn (n = 1–3).

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-6TBDMS-a-d-Glucoside central core, after annealing, exhibits poorly defined smectic A texture with streaks where the

Chem. Eur. J. 2012, 18, 2366 – 2373

focal conic domains were sheared with the flow and homeotropic domains at room temperature (Figure 4 a). 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 10 8C. On the other hand, POM micrographs of G2 with free hydroxyl group C6-OH, after slow cooling from isotropic displays a typical fingerprint texture of a chiral nematic phase with left handed helicity (Figure 4 b,c). The tripede G3 with a carboxylic acid functional group, exhibits a typical fingerprint texture of a chiral nematic mesophase at 100 8C 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 4 d). However, the examination of mesophase structures of Mannoside derivatives were inconclusive by POM, therefore other evidences must be incorporated to assign their mesomorphic properties. 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 10 8C min 1. 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 transitions were observed. The first endothermic transition at lower temperature region corresponds to the glass-smectic A obtained at midpoint 18.6 8C and a second with the signal onset at 47.8 8C (DH = 3.10 Jg 1) allocated to smectic A-isotropic transition. The anisotropic-isotropic phase transition peaks exhibit broad asymmetric profile during the heating and cooling cycles. The broadness reveals slow phase transition kinetics, attributed to the gradual conformational changes affecting the packing properties of the Glucoside and Mannoside bulks during their corresponding smectic Aisotropic transitions.

 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.chemeurj.org

2369

A. Belaissaoui et al.

Table 1. Transition temperatures (8C) and enthalpic data (in italics between brackets, Jg 1) obtained for functional 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 G1 Iso 54.9 ( 2.53) SmA 17.2 G M1 Iso 24.6 G can critically influence the G 18.6 SmA 47.8 (3.10) Iso G 20.0 SmA 27.5 (1.11) Iso phase behaviour and the associated thermal properties. M2 Iso 60.6 ( 0.40) Cr 32.7 G G2 Iso 94.1 ( 1.03) N*-SmA 37.1 G Thus, fine-tuning of the mesoG 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 morphic properties of these M3 Iso 67.4 ( 0.76) N*-SmA 44.2 G G3 Iso 113.7 ( 0.40) N* 103.9 ( 0.15) SmA 45.0 G glyco-supermolecules can be 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 stereogenic features of the core In the heating cycle of M1 (Figure 6), a glass transition and the nature of the incorporated functional groups. was characterised at midpoint 20.0 8C, followed by a broad transition at 27.5 8C (DH = 1.11 Jg 1). Upon cooling, only X-ray: The mesomorphic behaviours of the Mannoside and one broad shoulder at midpoint 24.6 8C attributed to a glass Glucoside derivatives have been characterised by X-Ray diftransition was detected. fraction measurements (Figure 7). Unfortunately, XRD on For G2, the phase sequence while heating displays four powder samples cannot tell the difference between chiral endothermic transitions. A glass transition at lower temperanematic and isotropic phases, as both of them show only difture at midpoint 23 8C, followed by a broad melting shoulder fuse scattering. All the samples generally gave very weak reflections and only one sharp diffraction peak can be obwith an onset at 37.7 8C (DH = 0.49 Jg 1), a broad weak served for the smectic phase. smectic A-chiral nematic transition (DH = 0.14 Jg 1) with an The compounds G1 and M1 bearing tert-butyldimethylsilyl onset at 68.0 8C and an extremely weak and broad peak with an onset at 93.7 8C (DH = 0.05 Jg 1), which is attributed to (TBDMS) group at C6 position, were examined at 25 8C and the chiral nematic-isotropic transition. On cooling, only two exhibited one sharp diffraction peak, associated with lateral transitions have been observed. In addition to the glass at packing at 2q = 2.248 and 2.358 respectively, corresponding midpoint 37.1 8C, the sample displays very broad range to interlayer d-spacing 3.94 nm and 3.75 nm, suggesting smectic A mesophases. transition from 94.1 8C to 68 8C, corresponding to two For the compounds with free hydroxyl groups, no diffracoverlapping transitions, which couldn’t be resolved and tion peak has been observed for the Mannoside M2, even were allocated to isotropic-chiral nematic-smectic A transiafter long exposure. This result is consistent with POM obtions. servations and DSC measurements. However, for the GlucoIn contrast, DSC traces of the Mannoside M2 exhibited no side G2, a weak but sharp diffraction peak is observed at liquid crystalline mesophase. The heating and cooling curves show broad transition peaks. On heating, in addition to a 40 8C with 2q = 2.908 (d = 3.04 nm), consistent with that exglass at midpoint 33.3 8C, a broad endotherm has been obpected for a smectic structure. At 55 8C only diffuse scatterserved at an onset 55.1 8C (DH = 0.66 Jg 1) attributed to the ing were observed, possibly a chiral nematic phase. For the carboxylic acid derivatives, sharp diffraction peak isotropic transition. was observed up to 65 8C (2q = 2.878 d = 3.08 nm) for G3 and The heating curve of the glycopyranuronic acid derivative G3 shows a similar profile to G2, but with all four transitions 50 8C (2q = 2.868, d = 3.09 nm) for M3. For higher temperaglass, melt, smectic A, chiral nematic and isotropic observed tures only diffuse scattering were observed, suggesting chiral at higher temperatures. nematic or isotropic phases. M3 exhibits fairly broad transitions on heating and cooling. Firstly, the heating curve displays three partially overEffect of core conformational properties on the mesomorlapping transitions, a melt onset at 45.2 8C (DH = 3.1 Jg 1) phic behaviours: The conformational diversity associated with the Glucoside and Mannoside chiral cores confers corresponding to a smectic A transition, a second endothem high versatility and flexibility. Pyranosic monosacchartherm which can be attributed to a nematic transition and a ides can access a large number of low energy conformations, third ascribed to the isotropisation with a peak at 67.1 8C. as a result of their conformationally dynamic nature Overall, upon changing the chiral core structure from (Figure 8), thus affecting their phase behaviours. Glucoside Gn to Mannoside Mn (n = 1–3), an increase in When comparing the Glucosides Gn and Mannosides Mn Tg values have been observed, associated simultaneously with depression of the clearing-point temperatures. For both (n = 1–3), they differ only in configuration at the stereogenic Glucosides and Mannosides, the glass transition Tg and centre C2 corresponding to R and S respectively (Figure 3). clearing point temperatures are critically influenced by the The resulting spatial orientation of the arms in relation to nature of moieties at C6 position and their values increase the chiral core constitutes the structural basis underlying the concurrently with the strength of the hydrogen bonding formation and the stabilisation of their corresponding ordonor-acceptor interactions, in ascending order in this sedered phases. The higher thermal stability of mesophases of quence tert-butyldimethylsilyl (TBDMS) < hydroxyl OH < Glucosides, in comparison to their corresponding Mannoside carboxylic acid CO2H. analogues, is owing to the expression of the chirality[22] from the central core to the periphery, inducing specific three-di-

2370

www.chemeurj.org

 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Chem. Eur. J. 2012, 18, 2366 – 2373

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.

Figure 8. Conformational diversity associated with Glucoside and Mannoside 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 equatorial.

mensional conformational properties (Figure 8) associated with each core, hence affecting their corresponding anisometric 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 conformations, as shown in Figure 8. Each chair conformer displays 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), hydrogen bonding donor-acceptors OH and carboxylic acid, considerably affect the phase behaviours of these materials. This is owing to the type of interactions induced by each functional group at C6 position. 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-

Chem. Eur. J. 2012, 18, 2366 – 2373

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 Glucosides (G2, G3) and Mannosides (M2, M3) with the inner core in the two chair conformations (A, E) underlay the structural and conformational basis of the combined molecular expression of the chirality and hydrogen bonding interactions on phase behaviours.

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 several flexible conformations. The effects of the chiral cores and the incorporated functional groups on the liquid crystalline 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 mesophases, M2 shows no fluid anisotropic phase. G3 bearing carboxylic acid functional group displays similar profile to G2 with higher transition temperatures, while the corresponding

 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.chemeurj.org

2371

A. Belaissaoui et al.

Mannoside M3 exhibits similar phase behaviour, with a depression in the melting point. In summary, tailoring the thermo-mesomorphic behaviours 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-butyldimeth-ylsilyl-a-d-glucopyranoside G1: Under nitrogen atmosphere, to an oven-dried round-bottomed flask containing a solution of 6-(4-cyanobiphenyl-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 resulting mixture was stirred for 14 days at room temperature and the reaction 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) to give G1 (100 %); 1H 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, 2 H), 3.80– 3.87 (m, 1 H), 3.88–4.05 (m, 3CH2), 4.87–4.92 (m, 1 H), 4.93–4.97 (d, 1 H), 5.06 (t, 1 H), 5.52 (t, 1 H), 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 = 5.46 (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. Methyl-2,3,4-tri-O-[6-(4-cyanobiphenyl-4’-yloxy)hexanoyl]-6-O-tert-butyldimethy-lsilyl-a-d-mannopyranoside M1: Using methyl-6-O-tert-butyldimethylsilyl-a-d-mannoyranoside 5 m as starting material, the same procedure as for the preparation of G1 was carried out. The oily crude was submitted 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), 3.40ACHTUNGRE(s, MeO), 3.65–3.76 (m, 2 H), 3.77–3.85 (m, 1 H), 3.88–4.05 (m, 3CH2), 4.67–4.71 (d, 1 H), 5.23–5.28 (m, 1 H), 5.28–5.41 (m, 2 H), 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 = 5.57 (Me), 5.51 (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-glucopyranoside 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, 1 m in CH2Cl2) at room temperature, and the whole mixture was stirred for 1 h. The reaction was quenched with saturated sodium thiosul-

2372

www.chemeurj.org

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 chromatography on silica gel (AcOEt/CH2Cl2/Hexane 1:2:3) to recover the unreacted 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, 1 H), 3.67-3.85 (m, 2 H), 3.88-4.05 (m, 3 OCH2), 4.88-4.94 (m, 1 H), 4.97-5.00 (m, 1 H), 5.07 (t, 1 H), 5.60 (t, 1 H), 6.90-7.00 (m, 6CH), 7.44-7.54 (m, 6CH), 7.55-7.70 ppm (m, 12CH); 13 C 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 (CqCN), 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. Methyl-2,3,4-tri-O-[6-(4-cyanobiphenyl-4’-yloxy)hexanoyl]-a-d-mannopyranoside M2 : Using methyl-6-O-tert-butyldimethylsilyl-a-d-mannoyranoside 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, 1 H), 3.68-3.83 (m, 2 H), 3.89-4.04 (m, 3 OCH2), 4.72-4.75 (d, 1 H), 5.25-5.35 (m, 2 H), 5.40-5.47 (m, 1 H), 6.90-7.00 (m, 6 H), 7.44-7.54 (m, 6 H), 7.557.70 ppmACHTUNGRE(m, 12 H); 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 %); elemental 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-glucopyranuronic acid G3 : To a stirred and cooled (0 8C) solution of G2 (2.32 g, 1.96 mmol) in acetone (150 mL), was added dropwise Jones reagent (2.67 m, 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 product 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. 1 H 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, 1 H), 4.90-4.97 (dd, 1 H), 5.05-5.10 (d, 1 H), 5.27 (t, 1 H), 5.58 (t, 1 H), 6.88-7.02 (m, 6CH), 7.44-7.54 (m, 6CH), 7.557.70 (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]-a-d-mannopyranuron-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

 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Chem. Eur. J. 2012, 18, 2366 – 2373

Supermolecular Chiral Mesogenic Tripedes

procedure as for the preparation of G3 was carried out. The crude product 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. 1 H 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), 4.364.41 (d, 1 H), 4.83-4.87 (d, 1 H), 5.28-5.31 (m, 1 H), 5.39-5.46 (m, 1 H), 5.46-5.54 (m, 1 H), 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.

FULL PAPER

[8] [9]

[10]

[11]

[12]

Acknowledgements

[13]

This work has been financed by EPSRC within the EUROCORES Programme SONS II of the European Science Foundation. We also thank the EPSRC Mass Spectrometry Service at Swansea for provision of services.

[14] [15]

[1] a) I. M. Saez, J. W. Goodby, Struct. Bonding 2008, 128, 1 – 62; b) B. Donnio, S. W. Buathong, I. Bury, D. Guillon, Chem. Soc. Rev. 2007, 36, 1495 – 1513; c) C. T. Imrie, P. A. Henderson, Chem. Soc. Rev. 2007, 36, 2096 – 2124; d) M. Lehmann, Chem. Eur. J. 2009, 15, 3638 – 3651. [2] a) M. Lehmann, M. Jahr, F. C. Grozema, R. D. Abellon, L. D. A. Siebbeles, M. Mller, Adv. Mater. 2008, 20, 4414 – 4418; b) M. Lehmann, M. Jahr, B. Donnio, R. Graf, S. Gemming, I. Popov, Chem. Eur. J. 2008, 14, 3562 – 3576; c) P. J. Stackhouse, M. Hird, Liq. Cryst. 2008, 35, 597 – 607. [3] J. W. Goodby, V. Gortz, S. J. Cowling, G. Mackenzie, P. Martin, D. Plusquellec, T. Benvegnu, P. Boullanger, D. Lafont, Y. Queneau, S. Chambert, J. Fitremann, Chem. Soc. Rev. 2007, 36, 1971 – 2032, and references therein. [4] a) C. M. Paleos, Mol. Cryst. Liq. Cryst. 1994, 243, 159 – 183; b) C. Tschierske, Prog. Polym. Sci. 1996, 21, 775 – 852; c) G. A. Jeffrey, L. M. Wingert, Liq. Cryst. 1992, 12, 179 – 202. [5] a) P. Sears, C. H. Wong, Proc. Natl. Acad. Sci. USA 1996, 93, 12086 – 12093; b) A. Ltzen in Encyclopedia of Supramolecular Chemistry, (Eds.: J. L. Atwood, J. W. Steed), Taylor & Francis, London, 2004, pp. 169 – 177, ; c) J. W. Goodby, Liq. Cryst. 1998, 24, 25 – 38; d) J. W. Goodby, Liq. Cryst. 2006, 33, 1229 – 1237; e) H. A. Van Doren, E. Smits, J. M. Pestman, J. B. F. N. Engberts, R. M. Kellog, Chem. Soc. Rev. 2000, 29, 183 – 199. [6] A. Belaissaoui, S. J. Cowling, I. M. Saez, J. W. Goodby, Soft Matter 2010, 6, 1958 – 1963. [7] a) M. Tian, B. Y. Zhang, Y. H. Cong, N. Zhang, D. S. Yao, J. Mol. Struct. 2009, 923, 39 – 44; b) H. Akiyama, A. Tanaka, H. Hiramatsu,

Chem. Eur. J. 2012, 18, 2366 – 2373

[16]

[17] [18]

[19] [20] [21] [22]

J. Nagasawa, N. Tamaoki, J. Mater. Chem. 2009, 19, 5956 – 5963; c) B. Zhang, W. Xiao, Y. Cong, Y. Zhang, Liq. Cryst. 2007, 34, 1129 – 1136; d) W. Q. Xiao, B. Y. Zhang, Y. H. Cong, Chem. Lett. 2007, 36, 938 – 939; e) M. Tian, B.-Y. Zhang, Y.-H. Cong, X.-Z. He, H.-S. Chu X.-Y. Zhang, Liq. Cryst. 2010, 37, 1373 – 1379. J. D. Watson, F. H. Crick, Nature 1953, 171, 737 – 738. a) G. W. Gray, Molecular Structure and Liquid Crystals, Academic Press, London, 1967. p. 161, and references therein; b) Handbook of Liquid Crystals, (Eds.: H. Kelker, R. Hatz), Verlag Chemie, Weinheim, 1980, and references therein; c) C. M. Paleos, D. Tsiourvas, Angew. Chem. 1995, 107, 1839 – 1855; Angew. Chem. Int. Ed. Engl. 1995, 34, 1696 – 1711. a) D. Horton, Carbohydrate Chemistry, Biology and Medical Applications, ELSEVIER, 2008, pp. 1 – 28; b) H. G. Fletcher, J. Chem. Educ. 1940, 17, 153 – 156. a) A glycoside consists of a sugar group bonded through its anomeric carbon to no sugar group via a (O, N, S, or C) glycosidic bond; b) B.-A. Marco, Synthesis and Characterization of Glycosides, Springer, 2007. T. W. Green, P. G. M. Wuts, Greenes Protective Groups in Organic Synthesis Vol. 4, Wiley-Interscience, 2006. ISBN: 978 – 0 – 471 – 69754 – 1. a) K. K. Ogilvie, S. L. Beaucage, A. L. Schifman, N. Y. Theriault, K. L. Sadana, Can. J. Chem. 1978, 56, 2768 – 2780; b) K. K. Ogilvie, A. L. Schifman, C. L. Penney, Can. J. Chem. 1979, 57, 2230 – 2238. a) T. D. Nelson, R. D. Crouch, Synthesis 1996, 1031 – 1069; b) R. D Crouch, Tetrahedron 2004, 60, 5833 – 5871. a) N. Moitessier, P. Englebienne, Y. Chapleur, Tetrahedron 2005, 61, 6839 – 6853; b) A. Bartoszewicz, M. Kalek, J. Stawinski, Tetrahedron 2008, 64, 8843 – 8850; c) V. H. Brandstetter, E. Zbiral, Helvetica Chimica Acta 1980, 63, 327 – 343. a) V. Belakhov, E. Dovgolevsky, E. Rabkin, S. Shulami, Y. Shohamb, T. Baasov, Carbohydr. Res. 2004, 339, 385 – 392; b) M. H. El-Badri, D. Willenbring, D. J Tantillo, J. Gervay-Hague, J. Org. Chem. 2007, 72, 4663 – 4672; c) D. Lee; M. S. Taylor, J. Am. Chem. Soc. 2011, 133, 3724 – 3727; M. S. Taylor, J. Am. Chem. Soc. 2011, 133, 3724 – 3727; d) E. Mark, E. Zbiral, H. H. Brandstetter, Monatsh. Chem. 1980, 111, 289 – 307; e) S. Akhtar, A. Routledge, R. Patel, J. M Gardiner, Tetrahedron Lett. 1995, 36, 7333 – 7336. B. E. Blass, C. L. Harris, D. E. Portlock, Tetrahedron Lett. 2001, 42, 1611 – 1613. a) E. J. Corey, A. Venkateswarlu, J. Am. Chem. Soc. 1972, 94, 6190 – 6191; b) E. J. Corey, B. B. Snider, J. Am. Chem. Soc. 1972, 94, 2549 – 2550. A. H. Haines, Adv. Carbohydr. Chem. Biochem. 1976, 33, 11 – 109. A. R. Vaino, W. A. Szarek, Chem. Commun. 1996, 2351 – 2352. K. P. R. Kartha, R. A. Field, Synlett 1999, 3, 311 – 312 a) Themed issue: Nanoscale chirality, Chem. Soc. Rev. 2009, 3, 657852; b) R. Eelkema, B. L. Feringa, J. Am. Chem. Soc. 2005, 127, 13480 – 13481; c) B. N. Thomas, C. M. Lindemann, N. A. Clark, Phys. Rev. E 1999, 59, 3040 – 3047; d) A. Ajayaghosh, P. Chithra, R. Varghese, Angew. Chem. Int. Ed. 2007, 46, 230 – 233.

 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Received: July 17, 2011 Published online: January 19, 2012

www.chemeurj.org

2373