Hydrogen-bonded benzylidenebenzohydrazide macrocycles and oligomers: Testing the robust capacity of an amide chain in promoting the formation of vesicles

Article abstract of DOI:10.1016/j.tetlet.2010.05.076

This Letter describes 2-(2-(dioctylamino)-2-oxoethyl-amino)-2-oxoethoxyl (DOAOE)-tuned self-assembly of vesicles from rigid macrocycles and foldamer-like oligomers. The molecules are prepared through the formation of reversible hydrazone bonds from aldehy

Full text of DOI:10.1016/j.tetlet.2010.05.076

Tetrahedron Letters 51 (2010) 3830–3835
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Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Hydrogen-bonded benzylidenebenzohydrazide macrocycles and oligomers:
testing the robust capacity of an amide chain in promoting the formation
of vesicles
Ben-Ye Lu a, Guang-Jun Sun b, Jian-Bin Lin a, Xi-Kui Jiang a, Xin Zhao a, Zhan-Ting Li a,
*
a State Key Laboratory of Bioorganic and Natural Products Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 345 Lingling Lu, Shanghai 200032, China
b Anyang Kebang Chemical Industrial Co., Ltd, Anyang 455000, China
a r t i c l e i n f o
a b s t r a c t
Article history:
This Letter describes 2-(2-(dioctylamino)-2-oxoethyl-amino)-2-oxoethoxyl (DOAOE)-tuned self-assem-
bly of vesicles from rigid macrocycles and foldamer-like oligomers. The molecules are prepared through
the formation of reversible hydrazone bonds from aldehyde and benzo-hydrazide precursors, which are
further facilitated by intramolecular NÁ Á ÁH–O hydrogen bonding. SEM, AFM, and fluorescent encapsula-
tion studies reveal that the molecules all self-assemble into vesicular structures in methanol, while sim-
ilar molecules bearing the triethylene glycol or n-decyl chains do not. The results illustrate that DOAOE is
robust in promoting the formation of vesicles for aromatic systems in polar solvents.
Ó 2010 Elsevier Ltd. All rights reserved.
Received 21 April 2010
Revised 14 May 2010
Accepted 18 May 2010
Available online 3 June 2010
The self-assembly of aromatic systems into vesicular architec-
tures is controlled not only by the backbones themselves, but also
by their appended flexible chains.1 For example, the formation of
vesicles by m-phenylene ethynylene-based macrocycle, oligo(p-
phenylenevinylene), or sexithiophene derivatives in polar media
is tuned by their amphiphilic triethylene glycol chains,2–4 while
the generation of vesicles by oligo(p-phenyleneethynylene) in dec-
ane is modulated by the appended dodecyl groups.5 We recently
reported that hydrogen bonding-induced aromatic hydrazide
foldamers are capable of forming vesicular architectures in metha-
nol or its aqueous solution.6 Instead of using the hydrophilic oligo-
glycol groups that have been widely employed to balance the
amphiphilicity of many rigid aromatic segments,2–4 we developed
a new aliphatic amide chain, that is, 2-(2-(dioctylamino)-2-oxoeth-
yl-amino)-2-oxoethoxyl unit (DOAOE),7 to facilitate the formation
of the new three-dimensional entities. Previously, we found that
this family of chains that are attached with two n-octyl units at
the end possesses the maximum capacity of inducing vesicles in
polar organic solvents.7 To further test if DOAOE works for other
kinds of aromatic backbones, we have synthesized new DOAOE-
bearing macrocyclic and linear molecules through the multicom-
ponent formation of the hydrazone bonds from simple aldehyde
and benzo-hydrazide precursors. This dynamic covalent approach
has been chosen because it enabled a quick access to molecules
of different shapes or conformations and thus remarkably simpli-
fied the synthesis of the investigated molecules.
RX (3)
HO
OH
RO
OR
4a (67%)
4b (85%)
4c (90%)
K2CO3, DMF
OHC
CHO
50 °C, 10 h
OHC
CHO
2
RO
MeO2C
OR
RO
OR
N2H4, MeOH
O
O
50 °C, 6 h
70%
CO2Me
H2NHN
OR
NHNH2
5a-c
6a (70%)
6b (86%)
6c (75%)
RO
H
N
O
N
H
RO
N
N
OR
O
O
4a-c
RO
H
OR
H
CHCl3-DMSO
(1:1)
N
O
N
O
N
N
N
N
60 °C, 20 h
>95%
RO
OR
O
N
H
N
H
OR
OR
O
R
O
R
1a-c
3a: X = Cl, 3b, 3c: X = Ts
The a series: R = CH2CONHCH2CON(n-C8H17 2
)
The b series: R = (CH2CH2O)3Me, the c series: R = n-C10H21
Scheme 1. The synthesis of macrocycles 1a–c.
* Corresponding author. Tel.: +86 21 54925122; fax: +86 21 64166128.
E-mail address: ztli@mail.sioc.ac.cn (Z.-T. Li).
0040-4039/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2010.05.076

B.-Y. Lu et al. / Tetrahedron Letters 51 (2010) 3830–3835
3831
Furthermore, the intramolecular NÁ Á ÁH–O hydrogen bonding
has been used to facilitate the synthesis and to induce the linear
molecules to adopt different conformations. Scanning electron
(SEM), atom force (AFM), and fluorescent microscope studies re-
vealed that both new kinds of molecules formed vesicles in meth-
anol. The results are described in this Letter.
stage, which gradually became simpler and finally exhibited only
one set of signals. These signals could be assigned to those of the
macrocycles by comparing with those of the spectra of the pure
samples, reflecting the DCC feature of the reactions.
Trimer 7 was prepared from 88 and 9 (1:2 molar ratio),7a while
10a was obtained from the reaction of 2 and 9 (1:2 molar ratio)
(Scheme 2). For the preparation of 10b, analogue of 10a, 1110
was first coupled with n-butylamine to afford 12, which was fur-
ther treated with hydrazine to produce 13. The latter was then re-
acted with 2 (0.5 molar amount) to give 10b in 95% yield. Due to
the electrostatic repulsion between the ether oxygen and imine
nitrogen,15 7 was expected to have a crescent conformation, while
10a and 10b should have an extended conformation owing to the
two intramolecular hydrogen bonds of the hydroxyl groups.16 By
using the similar procedures,17 straight trimers 14 and 19, whose
ends were attached with six DOAOE groups, were also prepared,
as shown in Scheme 3.
To get deep insight into the feature of DOAEO in inducing the
formation of vesicular structures, we prepared three macrocyclic
and six linear molecules. Macrocycles 1a–c were prepared accord-
ing to the routes shown in Scheme 1. Compounds 1b and 1c were
prepared for the sake of comparison. Thus, isophthalaldehydes
4a–c were first obtained from the alkylation of 28 in the presence
of potassium carbonate in hot DMF. Then, diester 5a-c9,10 were
treated with an excess amount of hydrazine in hot methanol to
give intermediates 6a–c. Finally, macrocycles 1a–c were obtained
from the reactions of 6a–c with 4a–c in the mixture of chloroform
and DMSO in nearly quantitative yields.11 We and others have pre-
viously used the similar 3+3 strategy to prepare imine-based mac-
rocycles.12 This dynamic covalent approach13 was facilitated by the
intramolecular hydrogen bonding14 as well as the two alkyl groups,
through the steric hindrance,15 in 4a–c, which forced the resulting
hydrazone bonds to adopt the conformation shown in Scheme 1.
The 1H NMR tracking experiments in CDCl3/DMSO-d6 (1:1 v/v)
showed that the solutions gave rise to complicated spectra at early
Although the hydrazone bonds are theoretically reversible, 1H
NMR spectra showed that all the molecules were stable in polar
DMSO-d6 or CD3OD (3 mM). The 1H NMR of macrocycles 1a–c in
CDCl3 (in 99.5% purity) gradually gave rise to new small signals
after one week, implying that other linear products were formed,
presumably due to the existence of water in the solvent. When
the solvent was treated with aluminum oxide, no such peaks were
observed, implying that trace hydrochloric acid in the solvent
could slowly catalyze their isomerization. The stacking of the aro-
matic backbones should be responsible for the increased stability
of these macrocycles in polar solvents. An evidence for this came
from the observation that the signals of the aromatic segments in
1H NMR shifted upfield notably (0.07 ppm) in DMSO-d when the
concentration was increased from 0.25 mM to 5 mM.
RO
OR
MeO
OHC
OMe
CHO
n-BuOH
O
O
+
reflux, 12 h, 90%
NHBu-n NHNH2
MeO
8
9
OMe
SEM was then used to investigate the self-assembling behavior
of the samples. The images of all the DOAOE-attached macrocycle
and linear trimers showed the formation of vesicular structures for
their samples obtained by evaporating the methanol solutions
H
O
N
O
N
O
H
O
RO
N
N
OR
RO
H
OR
H
OH
OR
3a
HO
OH
RO
OR
K2CO3, KI, acetone
N
7
N
Bu-n
Bu-n
60 °C, 5 h, 71%
n-BuOH
reflux, 12 h, 95%
CO2CH3
CO2CH3
CHO
15
16
2
+ 9
OR
O
O
O
O
H
N
H
N
O
O
RO
OR
NH2NH2, MeOH
60 °C, 6 h, 60%
18
OHC
n-BuN
H
N
H
N
H
NBu-n
H
MeOH, r.t., 12 h
95%
10a
O
R
O
R
O
R
O
R
17
CONHNH2
RO
RO
7, 9, 10a: R = CH2CONHCH2CON(C8H17-n)2
O
HN
N
RO
OR
n-BuNH2
RO
MeO2C
OR
RO
OR
OR
OR
EDCI, DMAP
NH
N
O
O
THF, r.t., 12 h
90%
14
CO2H
OMe
NHBu-n
12
O
11
HO
OHC
CHO
17, MeOH
RO
OR
2, n-BuOH
NH2NH2, MeOH
50 °C, 6 h, 90%
r.t., 16 h, 85%
O
O
reflux, 12 h
95%
OH
RO
2018
NHBu-n NHNH2
13
O
O
O
RO
H O
O
O
H
H
N
O
O
HN
N
N
n-BuN
N
H
N
H
NBu-n
RO
OR
19
H
O
R
H
N
NH
O
R
O
R
O
10b
R = (CH2CH2O)3Me
Scheme 2. The synthesis of trimers 7, 10a, and 10b.
H
O
OR
R
O
R = CH2CONHCH2CON(C8H17-n)2
OR
Scheme 3. The synthesis of trimers 14 and 19.

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B.-Y. Lu et al. / Tetrahedron Letters 51 (2010) 3830–3835
Figure 1. SEM images on mica of (a) 1a, (b) 1b, (c) 7, (d) 10a, (e) 14, (f) 19, (g) 22, and (h) the mixture of 17, 20, and 21 (2:3:2). The samples were obtained from their
methanol solution (1 mg/mL) upon evaporation of the solvent. For 1b, a 1:1 solution of methanol and water was used.
(Fig. 1). In contrast, macrocycle 1b did not form similar structures
in methanol. The image obtained from the solution of 1b in the
mixture of methanol and water (1:1 v/v) showed the formation
of smaller vesicles of lower density (Fig. 1b). We might propose
that the increase of the polarity of the medium enhanced the stack-
ing tendency of its aromatic backbone and thus promoted it to
form the ordered structures.2 SEM also revealed that macrocycle
1c did not form vesicles in methanol or its mixture with water,
chloroform, or n-hexane.
same measurement conditions, SEM of 10b did not exhibit any
vesicular structures. Similar trimers, prepared from the reactions
of compound 13 with 8, 2,3-, or 2,5-dihydroxy- terephthalaldehyde
(20), did not either. All these observations supported that DOAEO
as a side chain is much more robust than the glycol oligomer in
inducing the formation of vesicles by aromatic systems in
methanol.
To further expand the scope of target molecules, we also per-
formed the reactions of compounds 17, 20, and 2,5-dim-
ethoxyterephthalohydrazide (21)7b in methanol under similar
conditions. Their molar ratios were controlled to be 2:2:1 and
2:3:2, respectively. For both reactions, 1H NMR spectra of the crude
products in CDCl3 showed that all the starting materials were con-
sumed. MALDI-TOF mass spectrometry exhibited the peaks of 19 at
2552 [M+Na]+, pentamer 22 at 2936 [M+Na]+, and heptamer 23 at
The SEM images of trimers 7, 10a, 14, and 19 are also provided
in Figure 1. Their average diameters, obtained by measuring 50
vesicles in a randomly selective square area, are 1.3, 4.5, 5.0, and
4.8
larger than that of 7 and also 1a (1.7
ing of their aromatic backbone was of higher order. Under the
lm, respectively. The value of linear 10a, 14, and 19 is notably
l
m), implying that the stack-

B.-Y. Lu et al. / Tetrahedron Letters 51 (2010) 3830–3835
3833
RO
RO
O
H O
N
HN
RO
H OMe
O
N
N
N
O H
H O
N
22: n = 1
23: n = 2
O
OR
OR
OR
MeO H
NH
O
N
O
O H
RO
RO
NHNH2
n
O
OMe
OMe
OR
24: R =
O
O
N
O
O
O
O
Figure 2. AFM images (the width is 20 lm) on mica of (a) 14, (b) 19, and (c) 22. The samples were obtained from their methanol solution (0.1 mg/mL) upon evaporation of the
solvent.
3221 [M+Na]+. Pentamer 22 could be separated in 10% yield from
the mixture of the first reaction.19 Although the reactions gave rise
to oligomers of different lengths, SEM images showed that both the
mixtures and pure 22 could form vesicles in methanol (Fig. 1g and
h). In contrast, the mixtures prepared from the reaction of 2420
with 20 and 21 did not generate vesicular structures. Compound
24 was prepared from the corresponding ester21 and excessive
hydrazine in hot methanol. The result again demonstrated the ver-
satility of DOAEO in inducing the formation of vesicles.
surface, which reflected the evaporation of solvent molecules from
the hollow spheres.
Dye-encapsulation experiments were also performed in metha-
nol for compounds 14, 19, and 22 (Fig. 3). In the presence of rhoda-
mine B, the vesicles could entrap the dye. After dialysis for
5 days,7a the dye in the solution was removed, while the entrapped
dye could be kept in the cavity of the vesicles. This result again
supported their hollowness and also showed that the membranes
of the vesicles were quite stable.
AFM also supported the formation of the vesicles in methanol.
As examples, the images obtained for 14, 19, and 22 are shown
in Figure 2. The ratios of the diameter and height of their vesicles
were estimated to be about 10, 10, and 5, respectively, indicating
important flattening upon being transferred from solution to mica
In conclusion, we have described the 2-(2-(dioctylamino)-2-
oxoethyl-amino)-2-oxoethoxy (DOAEO)-modulated self-assembly
of vesicles by both macrocyclic and linear hydrazone-based aro-
matic systems in methanol. The linear oligomers have different
conformations and their DOAEO chains have been appended at dif-

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B.-Y. Lu et al. / Tetrahedron Letters 51 (2010) 3830–3835
Figure 3. Fluorescence micrographs of vesicles of (a) 14, (b) 19, and (c) 22, formed in methanol (1 mg/mL) in the presence of rhodamine B (1%) after being purified by dialysis
for 5 days.
9. Cai, W.; Wang, G.-T.; Du, P.; Wang, R.-X.; Jiang, X.-K.; Li, Z.-T. J. Am. Chem. Soc.
2008, 130, 13450–13459.
10. Yuan, L.; Sanford, A. R.; Feng, W.; Zhang, A.; Zhu, J.; Zeng, H.; Yamato, K.; Li, M.;
ferent positions. Therefore, their stacking patterns may be differ-
ent—to form membranes of mono- or multi-layered structures.
However, the results, together with our previous studies, well
demonstrate that DOAEO is a new, unique, and useful amphiphilic
amide-alkane-hybridized chain for the formation of vesicular
structures in polar organic solvents. Because DOAEO can modulate
the self-assembly of aromatic backbones of varying shape, in the
future we will design new large electron-rich and deficient conju-
gated disc or linear backbones to assemble vesicular structures,
which are expected to exhibit new interesting electron or energy
transfer properties within their membranes.
Ferguson, J. S.; Gong, B. J. Org. Chem. 2005, 70, 10660–10669.
11. Typical procedure: A solution of compounds 4b (92 mg, 0.20 mmol) and 6b
(0.10 g, 0.20 mmol) in the mixture of chloroform (5 mL) and DMSO (5 mL) was
stirred at 60 °C for 12 h and then concentrated with a rotavapor. The obtained
slurry was dissolved in chloroform (10 mL). The solution was washed with
water (5 mL Â 2) and brine (5 mL) and dried over sodium sulfate. Upon
removal of the solvent, the crude product was recrystallized from ether and
petroleum ether to give macrocycle 1b as a yellow solid (0.18 g, 95%). 1H NMR
(300 MHz, CDCl3) d: 11.10 (s, 6H), 9.07 (s, 6H), 9.02 (s, 6H), 8.21 (s, 6H), 6.68 (s,
6H), 6.39 (s, 6H), 4.17–3.23 (m, 180H). 13C NMR (75 MHz, CDCl3) d: 160.7,
160.5, 159.5, 140.8, 137.6, 125.7, 116.5, 113.9, 97.8, 96.5, 71.8, 70.6, 70.4, 70.3
(d), 69.8, 69.4, 68.5, 68.0, 58.9, 58.8. MS (MALDI-TOF): m/z 2845.2 [M+Na]+.
HRMS (MALDI-TOF): calcd for
2844.34782.
C132H204N12O54Na: 2844.3475. Found:
Acknowledgments
12. (a) Lin, J.-B.; Xu, X.-N.; Jiang, X.-K.; Li, Z.-T. J. Org. Chem. 2008, 73, 9403–9410;
(b) Lin, J.-B.; Wu, J.; Jiang, X.-K.; Li, Z.-T. Chin. J. Chem. 2009, 27, 117–122; (c) Xu,
X.-N.; Wang, L.; Lin, J.-B.; Wang, G.-T.; Jiang, X.-K.; Li, Z.-T. Chem. Eur. J. 2009,
15, 5763–5774; (d) Xu, X.-N.; Wang, L.; Li, Z.-T. Chem. Commun. 2009, 6634–
6636.
13. (a) Rowan, S. J.; Cantrill, S. J.; Cousins, G. R. L.; Sanders, J. K. M.; Stoddart, J. F.
Angew. Chem., Int. Ed. 2002, 41, 899–952; (b) Corbett, P. T.; Leclaire, J.; Vial, L.;
West, K. R.; Wietor, J.-L.; Sanders, J. K. M.; Otto, S. Chem. Rev. 2006, 106, 3652–
3711.
We thank National Natural Science Foundation of China
(20921091, 20732007, 20974118), Ministry of Science and Tech-
nology of China (2007CB808001), and Science and Technology
Commission of Shanghai Municipality (09XD1405300) for financial
support.
14. Ferguson, J. S.; Yamato, K.; Liu, R.; He, L.; Zeng, X. C.; Gong, B. Angew. Chem., Int.
Ed. 2009, 48, 3150–3154.
References and notes
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17. Typical procedure: A solution of compounds 17 (0.16 g, 0.12 mmol) and 2018
(11 mg, 0.06 mmol) in methanol (8 mL) was stirred at room temperature for
16 h and then concentrated with
a rotavapor. The resulting residue was
recrystallized from methanol to give compound 19a as a yellow solid (0.13 g,
85%). 1H NMR (300 MHz, CDCl3) d: 11.43 (s, 2H), 10.92 (s, 2H), 8.51(s, 2H),
8.41(s, 2H), 7.40 (d, J = 12 Hz, 4H), 6.80 (s, 2H), 4.81 (s, 4H), 4.75 (s, 8H), 4.15 (s,
12H), 3.31 (s, 12H), 3.19 (s, 12H). 13C NMR (75 MHz, CDCl3): 169.6, 168.5,
167.4, 162.3, 151.0, 150.7, 149.7, 140.8, 128.6, 120.3, 117.8, 108.2, 72.9, 68.9,
47.4, 46.6, 41.2, 41.0, 32.0, 29.6, 29.5, 29.0 (d), 27.8, 27.2, 22.8, 14.3. MS
(MALDI-TOF): 2584.8 [M+K+H2O]+. HRMS (MALDI-TOF): calcd for
C
142H246N16O22Na [M+Na]+: 2550.8514. Found: 2550.8498.
18. Borisenko, K. B.; Zauer, K.; Hargittai, I. J. Phys. Chem. 1996, 100, 19303–19309.
19. Compound 22: A mixture of compounds 17 (96 mg, 0.08 mmol), 20 (13 mg,
0.08 mmol), and 21 (10 mg, 0.04 mmol) in the mixture of chloroform (6.4 mL)
and methanol (1.6 mL) was stirred at room temperature for 48 h and then
concentrated. The resulting slurry was subjected to column chromatography
(CH2Cl2/MeOH 10:1) to give a crude product, which was further recrystallized
from petroleum ether and ethyl acetate to give 22 as an orange-yellow solid
(10 mg, 10%). 1H NMR (300 MHz, CDCl3) d: 11.26 (t, J = 3.6 Hz, 2H), 10.83 (s,
4H), 10.39 (d, J = 6.0 Hz, 2H), 8.42 (s, 2H), 8.23 (d, J = 1.8 Hz, 2H), 7.84–7.80 (m,
8. Richter, D. T.; Lash, T. D. Tetrahedron 2001, 57, 3657–3672.

B.-Y. Lu et al. / Tetrahedron Letters 51 (2010) 3830–3835
3835
4H), 7.70–7.64 (m, 4H), 7.26 (s, 4H), 6.63 (t, J = 1.2 Hz, 4H), 4.70 (s, 12H), 4.17
(s, 18H), 3.25 (dd, J = 3.3 Hz, 24H), 1.51 (s, 12H), 1.28–1.22 (m, 132H), 0.87–
0.81 (m, 36H). MS (MALDI-TOF): m/z 2934.7 [M+Na]+. HRMS (MALDI-TOF):
calcd for C160H262N20O28Na [M+Na]+: 2934.9572. Found 2934.9585.
151.6, 128.0, 106.5, 71.8, 71.8, 70.7, 70.4 (t), 70.3, 70.2 (d), 70.0, 69.8, 69.2, 69.0,
68.9, 68.5, 66.8 66.0, 59.8, 58.9, 58.8, 48.1, 47.9, 47.6, 47.1, 46.4, 46.1, 45.8. MS
(MALDI-TOF): m/z 1518.2 [M+Na]+. HRMS (MALDI-TOF): calcd for
C
67H125N5O31Na [M+Na]+: 1518.8241. Found: 1518.8250.
20. Compound 24. Whitle solid. 1H NMR (300 MHz, CDCl3) d: 7.03 (s, 2H), 4.93 (s,
6H), 3.59 (s, 96H), 3.30 (s, 18H). 13C NMR (75 MHz, CDCl3): 172.4, 168.7, 168.1,
21. Xue, W.; Song, B.; He, W.; Wang, H.; Yang, S.; Jin, L.; Hu, D.; Liu, G.; Lu, P. J.
Heterocycl. Chem. 2006, 43, 867–871.