Synthesis and thermally stable helix-dimer formation of amidohelicene oligomers

Article abstract of DOI:10.1246/bcsj.20100041

Optically active amidohelicene monomer to nonamer were synthesized in high yields by a two-directional method. The CD spectra in chloroform exhibited a large difference between dimer and the higher homologs, and vapor pressure osmometry studies revealed the formation of dimeric aggregates for the latter. It is noted that amidohelicene oligomers possessing two-atom linking groups between helicene and m-phenylene spacer formed helix-dimers in solution as were ethynylhelicene oligomers. The helix-dimer of the amidohelicene octamer in chloroform was very stable, and did not dissociate at 5 × 10^-8M on heating to 60 °C. The dissociation of the amidohelicene oligomers to random-coil state took place in hydrogen-bonding breaking solvents, DMSO or THF. The equilibrium between helix-dimer and random-coil changed by varying the ratio in the mixed solvents of chloroform and DMSO. Notably, the equilibriums were not affected by temperature for various mixtures of helix-dimer and random-coil. Thus, the sensitivity toward the environment was quite different between the amido- and ethynylhelicene oligomers.

Full text of DOI:10.1246/bcsj.20100041

© 2010 The Chemical Society of Japan
Bull. Chem. Soc. Jpn. Vol. 83, No. 7, 809–815 (2010)
809
Synthesis and Thermally Stable Helix-Dimer Formation
of Amidohelicene Oligomers
Ryo Amemiya,1 Wataru Ichinose,1 and Masahiko Yamaguchi*1,2
1Department of Organic Chemistry, Graduate School of Pharmaceutical Sciences, Tohoku University,
6-3 Aoba, Aramaki, Aoba-ku, Sendai 980-8578
2WPI Advanced Institute for Materials Research, Tohoku University, Aoba, Sendai 980-8577
Received February 16, 2010; E-mail: yama@mail.pharm.tohoku.ac.jp
Optically active amidohelicene monomer to nonamer were synthesized in high yields by a two-directional method.
The CD spectra in chloroform exhibited a large difference between dimer and the higher homologs, and vapor pressure
osmometry studies revealed the formation of dimeric aggregates for the latter. It is noted that amidohelicene oligomers
possessing two-atom linking groups between helicene and m-phenylene spacer formed helix-dimers in solution as were
ethynylhelicene oligomers. The helix-dimer of the amidohelicene octamer in chloroform was very stable, and did not
dissociate at 5 © 10¹8 M on heating to 60 °C. The dissociation of the amidohelicene oligomers to random-coil state took
place in hydrogen-bonding breaking solvents, DMSO or THF. The equilibrium between helix-dimer and random-coil
changed by varying the ratio in the mixed solvents of chloroform and DMSO. Notably, the equilibriums were not affected
by temperature for various mixtures of helix-dimer and random-coil. Thus, the sensitivity toward the environment was
quite different between the amido- and ethynylhelicene oligomers.
Molecular double-helixes are aggregates formed by two
linear molecules through intra- and intermolecular non-cova-
lent bond interactions. Well-known double-strand DNA is
constructed via hydrogen-bonding between complementary
bases and ³-³ interactions between aromatic bases, and its
reversible association/dissociation plays an important role in
the biological function. Thus, it was considered interesting to
study synthetic double-helix forming molecules, since the
comparison of their aggregation properties would deepen our
understanding of the properties of natural double-helixes. In
addition, synthetic double-helix molecules can have various
applications in materials. Recently, such synthetic oligomers
were reported. Lehn and others investigated oligobipyridine
ligands coordinated to metal ions forming double-helixes.1 We
reported that ethynylhelicene oligomers form double-helix via
³-³ interactions.2 Yashima synthesized two complementary
strands linked with amidinium-carboxylate salt bridges,3 and
also oligoresorcinols.4 Huc showed that oligoamidopyridines
formed double-helixes via hydrogen-bonds and ³-³ interac-
tions.5 Pyridine-thiazine oligomers associated through self-
complementary hydrogen-bonds were also reported.6 Among
the compounds, pyridine-pyrimidine oligomers,1c ethynyl-
helicene oligomers,2 salts,3c oligoresorcinols,4a,4b,4d and oligo-
amidopyridines5a,5b changed structure between double-helix
and random-coil in response to temperature change, solvent
change, or complexation with other molecules. However, such
reversible structure change systems are still rare, and the
development of novel synthetic double-helix molecules is
desired. In particular, it is critical to understand the relationship
between the oligomer structure and the double-helix forming
property.
We previously synthesized optically active acetylene oligo-
mers containing helicene and m-phenylene units. The heptamer
(P)-2 was found to form a double-helix in solution,2a and ³-³
interactions between the non-planar aromatic system of the
helicene was considered to play an important role in aggregate
formation: (P)-2 changed between random-coil by increasing
temperature or decreasing concentration;2b the hardness and
softness of aromatic solvents affected the stability of the
double-helix, and the ³-³ interactions were related to the
HSAB (hard soft acid base) principle.
We then decided to examine various derivatives of the
ethynylhelicene oligomers to know the relationship between
the structure and double-helix formation. It was expected that
the systematic study would provide a diversity of double-helix
molecules, and comparison of their structures and properties
would be used to design molecular systems, which respond to
change of environment. We recently reported derivatives, in
which the decyloxycarbonyl substituent in the m-phenylene
units of the ethynylhelicene oligomers was replaced with a
perfluorooctyl group.2d The pentamer (P)-3 formed a double-
helix in solution, but with an inverted twist double-helix from
pentamer (P)-1 and heptamer (P)-2. It was also observed that
(P)-3 formed hetero-double-helix with the ethynylhelicene
pentamer (M)-1 but not with (P)-1. Compounds possessing two
parts of the ethynylhelicene oligomers were synthesized, which
formed intramolecular helix-dimers.2c They exhibited different
kinetic properties than the intermolecular aggregates.
In the present study, the effect of the linking group in the
ethynylhelicene oligomers was examined using amidohelicene
oligomers, in which the acetylene moiety of the ethynyl-
helicene oligomers was replaced with amide group. Both amide
Published on the web June 30, 2010; doi:10.1246/bcsj.20100041

810
Bull. Chem. Soc. Jpn. Vol. 83, No. 7 (2010)
(P)-Ethynylhelicene Oligomers
Helix-Dimer Formation of Helicene Oligoamides
(P)-14
1) coupling with
C
C
C
C
C
C
C
C
Me3Si
H
SiMe3
n-1
H
H
H
H
H
H2N
N
NH2
N
N
N
N
N
Boc
Boc
R
O
O
O
O
R
R
R
R
n
(P)-1 (n = 5) R = CO2n-C10H21
(P)-2 (n = 7) R = CO2n-C10H21
(P)-3 (n = 5) R = n-C8F17
n
diamine (n = 1-7)
( )-4 to ( )-12 (n = 1-9)
P
P
2) deprotection
(P)-Amidohelicene Oligomers: A Two-Atom Analog
H
(P)-13 X = OH
(P)-14 X = Cl
N
NHBoc
X
R = CO2n-C10H21
H
H
H
H
NHBoc
N
BocHN
N
N
N
O
O
O
O
O
O
R
R
n-1
R
R
Even number series
Odd number series
(P)-4 (n = 1)
(P)-5 (n = 2)
(P)-6 (n = 3)
(P)-7 (n = 4)
(P)-8 (n = 5)
(P)-9 (n = 6)
(P)-10 (n = 7)
(P)-11 (n = 8)
(P)-12 (n = 9)
R = CO2n-C10H21
NH2
H2N
NHBoc
H2N
+
P
( )-14
+
Cl
Cl
R
R
O
O
17
15
(P)-16
97%
92%
(P)-5 (n = 2)
(P)-4 (n = 1)
72%
92%
(P)-7 (n = 4)
85%
(P)-6 (n = 3)
80%
Chart 1.
(P)-9 (n = 6)
(P)-8 (n = 5)
85%
86%
and acetylene are two-atom groups. However, acetylene has
a rigid, straight, and non-polar structure, whereas amide
has a bond angle of 120° with polar heteroatoms capable
of hydrogen-bonding. It was considered interesting to know
whether the amidohelicene oligomers could form double-helix,
and if this was the case, to know the differences in the double-
helix formation.
(P)-10 (n = 7)
43%
(P)-11 (n = 8)
(P)-12 (n = 9)
Scheme 1.
Amidohelicene monomer (P)-4 to nonamer (P)-12 were
synthesized (Chart 1), and trimer and higher oligomers formed
helix-dimers in non-polar solvents (see Supporting Informa-
tion). The dimeric structures of the oligomers were very stable,
and did not dissociate by heating even at low concentrations.
However, they readily dissociated in hydrogen-bond breaking
polar solvents. It was noted that the equilibrium between helix-
dimer and random-coil were little affected by temperature. The
results contrasted the double-helix of ethynylhelicene oligo-
mers, which readily dissociated on heating.2
of (P)-14. Diamine formed by deprotection of (P)-5 was then
subjected to the coupling sequence giving tetramer (P)-7,
hexamer (P)-9, and octamer (P)-11 possessing even numbers of
the helicene.
Helix-Dimer Formation. The CD spectra of (P)-4 to (P)-12
(5 © 10¹6 M, 25 °C) were taken in dimethyl sulfoxide (DMSO)
and chloroform (Figure 1). In DMSO, the intensity of the
Cotton effect increased linearly with increasing number of
helicene units. In chloroform, similar spectra to those in DMSO
were obtained for the monomer (P)-4 and dimer (P)-5.
However, the trimer and higher oligomers (P)-6 to (P)-12
provided quite different spectra, which exhibited strong positive
and negative Cotton effects at 324 and 297 nm, respectively,
indicating the formation of ordered chiral structures. Such chiral
structure of (P)-11 was also formed in toluene but not in THF
(Figure 2). VPO study in chloroform at 35 °C indicated that
tetramer (P)-7 at 1, 5, and 10 © 10¹3 M and octamer (P)-11 at
1 © 10¹3 M formed bimolecular aggregates, while they were
monomeric in THF (5 © 10¹3 M) (Figure 3). The infrared
spectra of (P)-7 (1 © 10¹3 M) provided an amide I carbonyl
Results and Discussion
Synthesis. Amidohelicene oligomers were synthesized by
repeated amide formation (Scheme 1).7b Acid chloride building
block (P)-14 was obtained from carboxylic acid (P)-13 by
treating with potassium hydroxide and sulfinyl chloride
followed by rapid silica gel chromatography. The purification
was critical to obtain reproducible results in the subsequent
amide formation. Amidohelicene monomer (P)-4 was synthe-
sized by the coupling of 2 equivalents of decyl 3-amino-5-
(t-butoxycarbonylamino)benzoate 15 and diacid dichloride (P)-
16 in 92% yield. Removal of the t-butoxycarbonyl group with
trifluoroacetic acid and coupling with (P)-14 then gave the
trimer (P)-6 in 72% yield in 2 steps. The sequence of synthesis
starting from (P)-6 provided pentamer (P)-8, heptamer (P)-10,
and nonamer (P)-12. The dimer (P)-5 was obtained by the
coupling of decyl 3,5-diaminobenzoate 17 and 2 equivalents
¹1
¹1
absorption at 1682 cm in THF, and 1654, 1647 cm in
chloroform. Amide carbonyls were reported to shift to lower
frequencies by 20-40 cm¹1 by forming hydrogen-bonds.8 It was
concluded that amidohelicene oligomers (P)-6 to (P)-12 formed
helix-dimers in chloroform and toluene, and random-coil mono-
mers in DMSO and THF. The effect of soft aromatic solvent was
small, and no dissociation was observed in C6H5CF3, C6H5F,

R. Amemiya et al.
Bull. Chem. Soc. Jpn. Vol. 83, No. 7 (2010)
811
Figure 1. CD spectra (5 © 10¹6 M, 25 °C). (a) (P)-4-12 (n = 1-9) in DMSO. (b) (P)-4-12 (n = 1-9) in chloroform.
Figure 3. Degree of aggregation determined by VPO. (P)-7
(n = 4) in chloroform at 35 °C (red dots), in THF at 45 °C
(green dot), and (P)-11 (n = 8) in chloroform at 35 °C
(yellow dot), in THF at 45 °C (blue dot).
Figure 2. CD spectra (5 © 10¹6 M, 25 °C) of octamer
(P)-11 in various solvents.
Figure 4. CD spectra of octamer (P)-11 (5 © 10¹6 M, 25 °C) in mixed solvents: (a) in DMSO/CHCl3 in various ratios and (b) in
2,2,2-trifluoroethanol/toluene in various ratios.
C6H6, C6H5CH3, C6H5Cl, and C6H5I (5 © 10¹6 M) at 60 °C,
which compared with ethynylhelicene oligomers.2a
The effect of the mixed solvent system of a nonpolar solvent
and a hydrogen-bond breaking solvent was examined using
(P)-11 at 5 © 10¹6 M concentration. The equilibrium between
helix-dimer and random-coil shifted by changing the ratio of
chloroform and DMSO, and the Cotton effect at 325 nm was
reduced to a half in 10% DMSO/chloroform compared to that
in chloroform (Figure 4a). Another hydrogen-bond breaking
solvent however, 2,2,2-trifluoroethanol, did not show notable
effect on the CD spectra even at 50% content in toluene
(Figure 4b). The driving force of the helix-dimer formation of
the amidohelicene olgomers was at least partly ascribed to
hydrogen-bonding.

812
Bull. Chem. Soc. Jpn. Vol. 83, No. 7 (2010)
Helix-Dimer Formation of Helicene Oligoamides
Figure 5. CD spectra of tetramer (P)-7 (5 © 10¹6 M, 25 °C) in mixed solvents: (a) in DMSO/CHCl3 in various ratios and (b) in
2,2,2-trifluoroethanol/toluene in various ratios.
It was also observed in the CD spectra under different
H
H
H
H
conditions that ¦¾ peaks were obtained at 324 nm with
NHBoc
N
BocHN
N
N
N
¹1
540 cm¹1 M and at 297 nm with ¹631 cm¹1 M¹1. It may
O
O
O
O
R
n-1
R
R
reasonably be concluded that these are the spectra of the pure
helix-dimer.
R = CO2n-C10H21
amidohelicene oligomers
helix-dimer
sheet
The stability of the helix-dimer of octamer (P)-11 and
tetramer (P)-7 was compared. In 10% DMSO/chloroform, the
CD spectra of (P)-7 was similar to that in DMSO exhibiting
random-coil state (Figure 5a), which contrasted to the partial
dissociation of (P)-11 in the same solvents. In 50% 2,2,2-
trifluoroethanol/toluene, the equilibrium of (P)-7 considerably
shifted to random-coil compared to (P)-11 (Figure 5b). The
helix-dimer complexation became stronger as the oligomer
elongated.
H
H
H
H
N
N
N
N
O
O
O
O
n
n
Kevlar
Nomex
Me
O
Me
O
H
H
N
N
N
O
H
OMe
H
MeO
H
Boc
N
H
N
N
Boc
O
N
N
H
N
3
O
O
1-4
single-helix
double-helix
pyridine oligomers
single strand
anthranilamide oligomers
Several related aromatic amide oligomers were compared in
regard to the aggregate formation (Chart 2). Kevlar and Nomex
are amide polymers with m- and p-linked benzenedioic acids
and benzenediamines, respectively,9 and their high thermal
resistance is ascribed to sheet formation by intermolecular
hydrogen-bonding. Anthranilamide oligomers possessing the
trimethoxylated Kevlar structure are monomeric in solution,10
in which intermolecular hydrogen-bonding is inhibited by
intramolecular hydrogen-bonding between the amide protons
and the methoxy oxygens. A pyridine version of Kevlar forms
a single-helix, in which intrastrand hydrogen-bonding by the
pyridine nitrogen and amide proton play an important role.5b
In nonpolar solvent, the compound forms a double-helix via
spring-like extension.5h The amidohelicene oligomers in the
present work can be regarded as a helicene derivative of
Kevlar. The helix-dimer formation and not the polymeric
sheet formation of the helicene amides may be ascribed to
the chirality. Alternatively, the different distance between
two carboxylate groups might also be important. It may be
interesting that the change in the aromatic moiety of aromatic
amides causes dramatic changes in the aggregate structures.
We previously synthesized amidohelicene monomer to
decamer possessing 1,1-dianilinocyclohexyl spacer,7a,7b and
observed the higher oligomers not to form hydrogen-bonded
structure in chloroform. When compared with the present
amidohelicene oligomers, the structure of the aniline moiety
was shown to be critical for the helix-dimer formation.
Notably, using the same dianiline compound, m-phenylenedi-
H
N
H
N
no aggregation
H2N
NH2
O
O
dianilinocyclohexyl helicene
oligomers
n
H
N
H
NH2
H2N
N
zipper
O
O
dianilinocyclohexyl
m-phenylenedicarbonyl oligomers
2
Chart 2.
carbonyl oligomers were reported to form double-strand zipper
complexes in solution.11 The diversity of hydrogen-bonded
structures formed from oligomeric aromatic amides indicated
the delicate balance between oligomer structure and aggregate
structure.
It should also be emphasized that both amidohelicene
oligomers and ethynylhelicene oligomers possessing the two-
atom linkers, formed helix-dimers in solution. This suggests
that chiral oligomers obtained by connecting the helicene and
the m-phenylene with two-atom linkers could form various
helix-dimers.
Equilibrium between Helix-Dimer and Random-Coil.
Amidohelicene oligomers formed very strong dimeric aggre-
gates in nonpolar solvents. The CD spectra of octamer (P)-11

R. Amemiya et al.
Bull. Chem. Soc. Jpn. Vol. 83, No. 7 (2010)
813
in chloroform at 25 °C did not largely change between the
The effect of temperature was examined for various
equilibrated states of helix-dimer and random-coil. In 3, 5,
and 10% DMSO/chloroform, (P)-11 (5 © 10¹6 M) formed
¹6
concentrations of 5 © 10 and 5 © 10¹8 M (Figure 6). The
¹1
association constant was estimated to be K > 109 M by the
dimerization at 5 © 10¹8 M assuming 90% binding. It com-
mixtures of helix-dimer and random-coil as indicated by the
¹1
pared with the strong dimerization in the pyridinedicarbox-
¦¾ values (25 °C) at 324 nm: 470, 380, and 310 cm¹1 M
,
¹1 5h
amide oligomers by Huc with the estimated K > 107 M
.
respectively (Figure 8), being smaller than the value 540
¹1
The temperature dependence of the aggregation was next
examined. Little change was observed in the CD spectra of
octamer (P)-11 between 60 and 5 °C in chloroform at
concentration ranging from 1 © 10¹6 to 5 © 10¹8 M (Figure 7).
Such insensitiveness to temperature was observed in toluene at
5 © 10¹6 M (Figure S1).
cm¹1 M of pure helix-dimer noted above. Notably, essen-
tially no change was observed with these mixtures between 5
and 60 °C, which indicated no change of the equilibrium.
The CD experiments of (P)-7 in mixtures of 5 and 10%
CF3CH2OH/chloroform and 3% DMSO/chloroform between 5
and 60 °C exhibited little temperature dependence (Figures 9
and S2). Thus, the helix-dimer/random-coil equilibrium of the
amidohelicene oligomers in solution turned out to be insensi-
tive to temperature, which was a characteristic feature of these
chiral oligomers. This contrasted greatly with the temperature
sensitive structure change of ethynylhelicene oligomers.2
The structure of ethynylhelicene oligomers and amidoheli-
cene oligomers differed only at the two-atom component
linking helicene and m-phenylene moieties. Although both
formed helix-dimers, their aggregate forming properties were
quite different. The helix-dimers of the amidohelicene oligo-
mers were dissociated by hydrogen-bond breaking solvents,
and the equilibria were temperature-independent; those of the
ethynylhelicene oligomers were dissociated by soft aromatic
solvents, and the equilibrium highly temperature-dependent.
The temperature-dependent equilibrium in the bimolecular
aggregation/deaggregation of the ethynylhelicene oligomers
was ascribed to large entropy changes, ¦S exceeding 100
Figure 6. CD spectra of octamer (P)-11 at 25 °C in CHCl3
in various concentrations.
Figure 7. CD spectra of octamer (P)-11 in CHCl3 at various temperatures: (a) 1 © 10¹6, (b) 0.5 © 10¹6, (c) 0.1 © 10¹6, and
(d) 0.05 © 10¹6 M.

814
Bull. Chem. Soc. Jpn. Vol. 83, No. 7 (2010)
Helix-Dimer Formation of Helicene Oligoamides
Figure 8. CD spectra of octamer (P)-11 at 5 © 10¹6 M at various temperatures: (a) in CHCl3 97% and DMSO 3%, (b) in CHCl3 95%
and DMSO 5%, (c) in CHCl3 90% and DMSO 10%, and (d) in DMSO 100%.
Figure 9. CD spectra of tetramer (P)-7 at 5 © 10¹6 M at various temperatures: (a) in CHCl3 95% and CF3CH2OH 5%, (b) in CHCl3
90% and CF3CH2OH 10%, and (c) in CHCl3 80% and CF3CH2OH 20%.

R. Amemiya et al.
Bull. Chem. Soc. Jpn. Vol. 83, No. 7 (2010)
815
¹1
J mol¹1 K based on the equation ¦G = ¦H ¹ T¦S.2c The
Yamaguchi, J. Am. Chem. Soc. 2004, 126, 14858. b) H. Sugiura,
M. Yamaguchi, Chem. Lett. 2007, 36, 58. c) H. Sugiura, R.
Amemiya, M. Yamaguchi, Chem. Asian J. 2008, 3, 244. d) R.
Amemiya, N. Saito, M. Yamaguchi, J. Org. Chem. 2008, 73, 7137.
origin of the temperature-independence in the case of amido-
helicene oligomers is notable. Several examples of the
association/dissociation equilibrium with small temperature-
dependences are known in biomolecules such as proteins,12
nucleic acids,13 or oligosugars14 as well as synthetic oligoace-
tylenes15 or oligoamides.5c The phenomena were in some cases
ascribed to small entropy changes ¦S by solvation/desolva-
tion14,15 or by formation of preorganized structure in the
deaggregated state.5c,13 Alternatively, temperature dependences
of entropy change ¦S and enthalpy change ¦H were
discussed.12 In the present study, preorganized structure for
monomeric amidohelicene oligomers may not be likely: The
effect of the chain length of the oligomers was not appreciable
in CD and 1H NMR spectra in DMSO. If preorganized
structures were formed by hydrogen-bonding, their spectra
probably exhibited the dependences of oligomer length
reflecting the weaker preorganization of smaller oligomers.
Solvation/desolvation may not also be appreciable in non-
aqueous solvents. The present phenomena of the amidohelicene
oligomers probably are a delicate balance of the temperature-
dependent ¦H and ¦S, which cancel the effect of temperature.
3
a) Y. Tanaka, H. Katagiri, Y. Furusho, E. Yashima, Angew.
Chem., Int. Ed. 2005, 44, 3867. b) M. Ikeda, Y. Tanaka, T.
Hasegawa, Y. Furusho, E. Yashima, J. Am. Chem. Soc. 2006, 128,
6806. c) T. Maeda, Y. Furusho, S. Sakurai, J. Kumaki, K. Okoshi,
E. Yashima, J. Am. Chem. Soc. 2008, 130, 7938. d) H. Ito, Y.
Furusho, T. Hasegawa, E. Yashima, J. Am. Chem. Soc. 2008, 130,
14008.
4
a) H. Goto, H. Katagiri, Y. Furusho, E. Yashima, J. Am.
Chem. Soc. 2006, 128, 7176. b) H. Goto, H. Furusho, E. Yashima,
J. Am. Chem. Soc. 2007, 129, 109. c) H. Goto, Y. Furusho, E.
Yashima, J. Am. Chem. Soc. 2007, 129, 9168. d) H. Goto, Y.
Furusho, K. Miwa, E. Yashima, J. Am. Chem. Soc. 2009, 131,
4710.
5
a) V. Berl, I. Huc, R. G. Khoury, M. J. Krische, J.-M. Lehn,
Nature 2000, 407, 720. b) V. Berl, I. Huc, R. G. Khoury, J.-M.
Lehn, Chem.®Eur. J. 2001, 7, 2810. c) H. Jiang, V. Maurizot, I.
Huc, Tetrahedron 2004, 60, 10029. d) C. Dolain, C. Zhan, J.-M.
Légar, L. Daniels, I. Huc, J. Am. Chem. Soc. 2005, 127, 2400. e) C.
Zhan, J.-M. Légar, I. Huc, Angew. Chem., Int. Ed. 2006, 45, 4625.
f) D. Haldar, H. Jiang, J.-M. Légar, I. Huc, Angew. Chem., Int. Ed.
2006, 45, 5483. g) D. Haldar, H. Jiang, J.-M. Légar, I. Huc,
Tetrahedron 2007, 63, 6322. h) E. Berni, B. Kauffmann, C. Bao, J.
Lefeuvre, D. M. Bassani, I. Huc, Chem.®Eur. J. 2007, 13, 8463.
Conclusion
To summarize, amidohelicene trimer to nonamer formed
helix-dimer in non-polar solvents, which dissociated in the
presence of hydrogen-bond breaking solvents, DMSO and
trifluoroethanol. The aggregation in chloroform was very
strong, and the helix-dimer did not dissociate even at low
concentrations. Notably, the equilibrium was not affected by
temperature, which contrasted to the ethynylhelicene oligomer
previously reported. Design of the molecules may be interest-
ing using such different properties in the helix-dimer forma-
tion.
6
3267.
7
J. Li, J. A. Wisner, M. C. Jennings, Org. Lett. 2007, 9,
a) H. Okubo, M. Yamaguchi, C. Kabuto, J. Org. Chem.
1998, 63, 9500. b) H. Okubo, M. Yamaguchi, J. Org. Chem. 2001,
66, 824.
8
a) M. Beer, H. B. Kessler, G. B. B. M. Sutherland, J. Chem.
Phys. 1958, 29, 1097. b) R. D. McLachlan, R. A. Nyquist,
Spectrochim. Acta 1964, 20, 1397. c) H. Torii, T. Tatsumi, T.
Kanazawa, M. Tasumi, J. Phys. Chem. B 1998, 102, 309. d) M.-E.
Lee, S. Y. Lee, S.-W. Joo, K.-H. Cho, J. Phys. Chem. B 2009, 113,
6894.
Supporting Information
General methods, synthetic procedure and characterization
data for (P)-4-12, 13-20, and diamine (n = 1-7), CD spectra of
(P)-7 and (P)-11 (Figures S1 and S2). This material is available
free of charge on the web at http://www.csj.jp/journals/bcsj/.
9
K. Tashiro, M. Kobayashi, H. Tadokoro, Macromolecules
1977, 10, 413.
10 J. Zhu, X.-Z. Wang, Y.-Q. Chen, X.-K. Jiang, X.-Z. Chen,
Z.-T. Li, J. Org. Chem. 2004, 69, 6221.
11 A. P. Bisson, F. J. Carver, D. S. Eggleston, R. C.
Haltiwanger, C. A. Hunter, D. L. Livingstone, J. F. McCabe, C.
Rotger, A. E. Rowan, J. Am. Chem. Soc. 2000, 122, 8856.
12 C. S. Raman, M. J. Allen, B. T. Nall, Biochemistry 1995,
34, 5831.
References
1
a) J.-M. Lehn, A. Rigault, J. Siegel, J. Harrowfield, B.
Chevrier, D. Moras, Proc. Natl. Acad. Sci. U.S.A. 1987, 84, 2565.
b) U. Koert, M. M. Harding, J.-M. Lehn, Nature 1990, 346, 339.
c) M. Barboiu, G. Vaughan, N. Kyritsakas, J.-M. Lehn, Chem.®
Eur. J. 2003, 9, 763. d) C. R. Woods, M. Benaglia, J. S. Siegel, F.
Cozzi, Angew. Chem., Int. Ed. Engl. 1996, 35, 1830. e) A. Orita, T.
Nakano, D. L. An, K. Tanikawa, K. Wakamatsu, J. Otera, J. Am.
Chem. Soc. 2004, 126, 10389. f) H. Katagiri, T. Miyagawa, Y.
Furusho, E. Yashima, Angew. Chem., Int. Ed. 2006, 45, 1741.
13 H. Shindo, H. Torigoe, A. Sarai, Biochemistry 1993, 32,
8963.
14 H. Viernstein, P. Weiss-Greiler, P. Wolschann, J. Inclusion
Phenom. Macrocyclic Chem. 2002, 44, 235.
15 T. Kawase, Y. Nishiyama, T. Nakamura, T. Ebi, K.
Matsumoto, H. Kurata, M. Oda, Angew. Chem., Int. Ed. 2007,
46, 1086.
2
a) H. Sugiura, Y. Nigorikawa, Y. Saiki, K. Nakamura, M.