Protonated amino acid-induced one-handed helicity of polynorbornene having monoaza-18-crown-6 pendants

Article abstract of DOI:10.1021/ma1014726

Upon complexation with protonated amino acids, one-handed helical polynorbornenes appended with monoaza-18-crown-6 (7a) are obtained. The cooperativity is observed as revealed by the sergeant-soldier effect and the majority rule. When sterically hindered

Full text of DOI:10.1021/ma1014726

Macromolecules 2010, 43, 8813–8820 8813
DOI: 10.1021/ma1014726
Protonated Amino Acid-Induced One-Handed Helicity of Polynorbornene
Having Monoaza-18-crown-6 Pendants
Renjie Ji,†,‡ Chih-Gang Chao,‡ Yen-Chin Huang,‡ Yi-kang Lan,§ Cheng-Lu Lu,† and
Tien-Yau Luh*,‡,§
†Shanghai Institute of Organic Chemistry, 354 Ling Ling Lu, Shanghai 200032, China,
‡Department of Chemistry, National Taiwan University, Taipei, Taiwan 106, and
§Institute of Polymer Science and Engineering, National Taiwan University, Taipei, Taiwan 106
Received October 30, 2009; Revised Manuscript Received September 23, 2010
ABSTRACT: Upon complexation with protonated amino acids, one-handed helical polynorbornenes
appended with monoaza-18-crown-6 (7a) are obtained. The cooperativity is observed as revealed by the
sergeant-soldier effect and the majority rule. When sterically hindered amino acids such as phenylalanine,
isovaline or proline, esters of amino acids, and aminoalcohols are used, the Δε values in CD spectra
are significantly reduced. The protonated ammonium ion may form complex with a crown ether moiety
whereas the carboxylic acid may form hydrogen bonding with the adjacent crown ether pendant resulting in
unidirectional orientation of the pendants leading to a helical scaffold. The corresponding dimer 10 with the
same isotactic stereochemistry as that of polynorbornene 7a behaves similarly to exhibit bisignate CD curve
upon treatment with protonated alanine. On the other hand, polynorbornene with monoaza-15-crown-5 (7b)
does not exhibit any CD response under the same conditions.
Introduction
cooperative interactions in the polymer backbone.15,16 These
studies has not only addressed the formation of one-handed
Polynorbornenes obtained by metal-catalyzed ring-opening
metathesis polymerization (ROMP)1 of the corresponding nor-
bornene derivatives having different kinds of pending groups
have been demonstrated to be useful for catalysis,2 light harvest-
ing and photoinduced electron transfer,3 ion conductivity,4 and
optoelectronic applications.5-9 We recently established that
ROMPs of nobornenes having 5,6-endofused N-arylpyrrolidine
catalyzed by the first generation Grubbs catalyst give iso-
tactic single stranded polynorbornenes with all double bonds
in trans configuration and all pendants aligned coherently
towardthesamedirection(eq1).10,11 Presumably, π-πinteractions
between these pending aryl groups might take place during the
course of the polymerization and would be responsible for
the stereoselectivity.12 This protocol has been successfully used
for the synthesis of relatively rigid polynorbornene-based double
stranded polymeric ladderphanes13 and for the replication of
a single stranded polynorbornene into the corresponding com-
plementary polynorbornene.14 Amalgamation of chiral auxilia-
ries into the polymer through hydrogen bonding has offered a
powerful platform for the one-handed helical polymers.15-18
Incorporation of chiral linkers is known to afford one-handed
helical double stranded ladderphane 1.13b Alternatively, the
use of bisamidic chiral alanine linkers between the pending
porphyrins and the polynorbornene backbone has been shown
to induce one-handed helical structures for these polymers 2
owing to hydrogen bonding between the adjacent linkers.18
Both polymers 1 and 2 exhibit characteristic exciton coupling
between adjacent aminobenzoate pendants as revealed by the
circular dichroitic (CD) profiles.13b,18 A stereoregular poly-
(phenylacetylene) bearing the azacrown ether pendants forms
a one-handed helix upon complexation with protonated amino
acids as revealedbythe enhanced CDattributedbythe significant
helical polymers through complexation, but also provided useful
information on the stereoregularity of the polymers.15-17 We
now wish to report the first one-handed single stranded helical
polynorbornene having crown ethers as pendants.
Results and Discussion
Synthesis. Monoaza-18-crown-6 appended norbornene
monomer 3a was obtained in 40% yield from the reaction
*Corresponding author. Fax þ886-2-2364-4971. E-mail: tyluh@
ntu.edu.tw.
r 2010 American Chemical Society
Published on Web 10/13/2010
pubs.acs.org/Macromolecules

8814 Macromolecules, Vol. 43, No. 21, 2010
Ji et al.
of 4a with acid chloride 5-Cl. Treatment of 3a with excess
LiAlH4 gave the corresponding amine 6a in 61% yield.
ROMPof 6awith3 mol% of(Cy3P)2Cl2Ru=CHPhfollowed
by quenching with EtOCHdCH2 afforded the corresponding
amines are shown in the Supporting Information. The
second Cotton wavelengths and the corresponding Δε
values of these complexes are summarized in Table 1.
A positive Cotton effect was observed with protonated
L-amino acids and vice versa, and the wavelength region
was consistent with the absorption maximum of the
4-aminobenzyl chromophore. In addition, the CD curves
were reversibly temperature dependent (Figure 1c), the
intensities decreasing with increasing temperature. It
is noteworthy that a mixture monomer 6a and protonated
L-alanine prepared under the same conditions was CD
inactive.
polymer 7a in 90% yield (Mn = 14 700, PDI = 1.18). The 13
C
NMR spectrum of 7a showed two peaks of equal intensity at
δ 36.1 and 36.3 ppm attributed to C7,19 which is characteristic
for isotactic polynorbornene with endofused N-arylpyrrolidine
pendants having all double bonds in trans configuration.11b
In a similar manner, 7b was obtained in overall 32% yield
from 4b, and the details are described in the Experimental
Section.
As shown in Figure 1 and Table 1, mirror image CD
curves were obtained for a pair of enantiomeric proton-
ated alanines. The Δε values were comparable but had
opposite sign. It is interesting to note that neutral (entries
1-4), basic (entries 5 and 6), acidic (entries 7 and 8), and
hydroxyl-substituted (entry 9) amino acids gave similar
Δε values.
Crown ethers are known to form one to one complexes
with protonated amines.20 The stoichiometry of the complex
formed from 7a and D-alanine-HClO4 in CF3CH2OH was
examined.21 A plot of Δε values against the molar ratio of
D-alanine-HClO4 versus total crown ether in 7a is shown in
Figure 2 and the details are shown in Figure S2 in the
Supporting Information. The Δε values reached a plateau
when the molar ratio of alanine and crown ether reached 1. A
similar plot using D-valine-HClO4 is also shown in Figure 2.
These results indicate that each of the crown ether moieties in
7a would form one to one complex with the ammonium ion.
It is noteworthy that the Δε values for the complexes formed
from protonated D-alanine and D-valine and 7a under these
conditions were comparable to those obtained by the extrac-
tion procedure shown in Table 1. In addition, when CD2Cl2
was employed as the solvent for the extraction of protonated
1
D-alanine, the organic solution was analyzed by H NMR
(Figure S21). The ratio of the methyl protons of D-alanine
to those of aminobenzyl moieties in 7a suggests that a one
to one complex between 7a and protonated alanine was
formed. Furthermore, certain protons of the crown ether
moieties in this complex shifted to lower field, presumably
due to complexation.
The presence of sterically bulky substituent(s) of the
amino acids such as phenylalanine or isovaline (entries
10 and 11) somewhat reduced the Δε values. As mentioned
above, the spacing occupied by each of the monomeric units
would be around 0.5-0.6 nm.11 Presumably, these amino
acids may be more difficult to insert into the space between
two adjacent crown ethers resulting in decrease in Δε values.
Protonated proline also gave poor CD response (entry 12).
Unlike other protonated amino acids, protonated proline
has only two N-H bonds for hydrogen bonding to the
crown ether moiety in 7a. Complexation of protonated
proline with 7a would therefore be less selective, leading to
small Δε value.
Hydrogen bonding to the adjacent crown ether module
appeared to be essential to control the helicity of the poly-
mer. Amino alcohols behaved similarly, albeit the Δε inten-
sities were about 50% of those for the corresponding amino
acids (entries 13 and 14). The Δε values were significantly
reduced when the methyl esters of the amino acids were used
(entries 15-18).
In order to scrutinize the helicity of the complex of 7 with
different protonated amino acids, dimer 10 was synthesized
from 818 in 48% overall yield and the details are described in
the Experimental Section.
Reactions of 7a with Protonated Amino Acids. An equal
volume (10 mL) of 7a (4.1 mM based on the molecular weight
of 6a) in CH2Cl2 and an aqueous solution of HClO4 (0.1 M)
containing 82 mM of amino acid was stirred at room
temperature for 18 h. The organic phase was separated and
subjected to CD measurements. The absorption spectra of 6a
and 7a are shown in Figure 1a. Like all polynorbornenes with
N-arylpyrrolidine pendants,11 the λmax for 7a appeared at
slightly shorter wavelength than that of the corresponding
monomer 6a. The CD curves for the alanine-7a complexes
are shown in Figure 1b and those of the complexes with other
amino acids, amino esters and aminoalcohols and chiral
Chiral alkyl amines 11 and 12 gave very low CD responses
(entries 19 and 20). These results suggest that the presence of
the other protic substituents would be essential to direct the
orientation of the adjacent crown ether pendants leading to
one handed helicity.

Article
Macromolecules, Vol. 43, No. 21, 2010 8815
Figure 1. (a) Absorption spectra of monomer 6a (black) and polymer 7a (red) in CH2Cl2. (b) CD curves of complexes of
-alanine-HClO4 (red) with 7a in CH2Cl2. (c) Reversible temperature dependent CD profiles of -alanine-HClO4 with 7a in CH2Cl2. All spectra were
measured at the [7a] = 2 mg/mL equivalent to 4.1 μmol of monomer units per milliliter.
L-alanine-HClO4 (black) and
D
D
Table 1. Signs and Differences of the Second Cotton (Δε2nd) for the
Complexes of 7a with Protonated Amino Acids, Amino Esters,
Amino Alcohols, and Chiral Amines in CH2Cl2
entry
protonated amine
Δεsecond (M-1 cm-1)/λ(nm)
1
2
3
4
5
6
7
8
L-Ala
D-Ala
L-Val
D-Val
L-Lys
D-Lys
L-Asp
D-Asp
L-Ser
L-Phe
L-isoval
L-Pro
L-valinol
L-alaninol
L-Ala-OMe
D-Ala-OMe
L-Val-OMe
D-Val-OMe
11
-3.97/260
þ4.02/260
-4.87/260
þ4.73/260
-3.57/260
þ3.51/260
-4.35/260
þ4.37/260
-4.09/260
-2.80/260
-0.90/260
-0.30/260
-2.13/260
-2.03/260
-1.38/261
þ1.42/261
-1.49/261
þ1.48/261
-0.35/260
þ0.50/259
9
10
11
12
13
14
15
16
17
18
19
20
The similar shape of the CD profiles indicates that the
nature of binding of the protonated amino acids and the 7a
may be similar. The helicity of the complexes between 7a and
protonated amino acids can be understood within the frame-
work of exciton chirality method.22 In other words, exciton
coupling between pending aminobenzyl moieties would re-
flect the helicity of the complexes. The exciton couplet
amplitudes among these complexes would be related to the
interchromophore distance as well as the dihedral angle of
the interacting moments.22 As menionted earlier, all pending
groups in 7a would align coherently toward the similar direc-
tion, and the spacing occupied by each of the monomeric
units in polynorbornenes would be about 0.5-0.6 nm.10,11
The dihedral angle of the interacting chromophores would
likely offer a platform to dictate the intensity of the couplet.
The uniformity of the orientation of these interacting chro-
mohores in these complexes would determine the amplitude
of the CD curves.
12
follows the majority rule23,24 and there is cooperative effect
in the complex formation of 7a with protonated amino acids.
In a similar manner, a plot of the Δεsecond values of
the complexed 7a against the molar ratio of protonated
D-alanine in a mixture of D-alanine and glycine is shown in
Figure 4. Again, the nonlinear relationship because of the
sergeant-soldier effect23,24 further supports the cooperative
effect in the complex formation between 7a and protonated
amino acids.
Reaction of 10 with Protonated Alanines. Treatment of 10
in CH2Cl2 with L- and D-alanine in perchloric acid under the
same conditions as described above gave the corresponding
organic solution which was subjected to CD analysis and the
results are shown in Figure 5. It is worthy noting that the
Majority Rule and Sergeant-Soldier Effect. In order to
establish the cooperative effect toward helicity, the Δεsecond
values using different enantionmeric mixtures of L-valine and
of D-alanine were measured and the results are shown in
Figure 3 and details are shown in Figure S3. The nonlinear
relationship suggests that the helicity of these complexes

8816 Macromolecules, Vol. 43, No. 21, 2010
Ji et al.
profiles exhibited same Cotton effect as those of the com-
plexes of 7a with alanines (cf. Figure 1) but with lower
intensities.25 The exciton coupling due to the adjacent amino-
benzyl pendants would be responsible for the CD properties
for both 7a and 10. These results offer convincing evidence to
show that the helicity would be arisen from the complexation
of protonated amino acid with the crown ether pendants in
7a and 10.
ether pendant. It is noteworthy that these two oxygen atoms
0
(O7 and O130) would be diastereotopic. The total energy
difference between these two distereomers was 16.7 kcal/mol
in favor of 14a. The center to center distance between two
˚
crown ethers in 14a was around 7.3 A. The projected
torsional angle of the two pendants defined by two lines
from the center of the cyclopentane ring and the center of the
crown ethers in 14a was about 27° with a right handed
rotation which is consistent with the experimental observa-
tion described above based on exciton chirality method.22
Apparently, the configuration at the chiral center of the
amino acid would direct the orientation of the carboxylic
þ
DFT Calculations of 14. In general, the -NH3 moiety
may form symmetrically hydrogen bonding with three
alternating oxygen atoms of the 18-crown-6.26 The rela-
tive hydrogen-bond acceptor abilities of amino nitrogen
and ethereal oxygen depend not only on the basicity of the
heteroatoms, but also on the relative orientation of the
nonbonding orbital.27 The crystal structures indicate that
the substituent on nitrogen in monoaza-18-crown-6 ethers in
general locates at the axial position.28 The lone pair electrons
on nitrogen of the crown ether moiety would likely orient
along the equatorial position toward the center of the crowþn
ether ring. In this regard, it seems likely that the -NH3
moiety may preferentially form hydrogen bonding with O4,
O
10 and O16 in a N-substituted monoaza 18-crown-6. On the
basis of this assumption, density function theory (DFT)
calculations were carried out to examine the possible con-
formations of 14 obtained from 13 and two equivalents of
protonated L-alanine.29
þ
As shown in Figure 6, the -NH3 moiety would form
hydrogen bonding with O4, O10, and O16 of one crown ether
pendant and the0 carboxylic a0cid group would hydrogen-
bond to either O7 (14a) or O13 (14b) of the adjacent crown
Figure 4. Changes in ICD intensity (Δεsecond) of 7a against the molar
ratio of D-alanine in a mixture of D-alanine and glycine.
Figure 2. Plot of Δεsecond values against the molar ratio of
D
-alanine-
HClO4 (open circle and solid line) and -valine (solid circle and dotted
D
Figure 5. CD curves of complexes of
-alanine-HClO4 (red) with 10 in CH2Cl2. [10] = 2.36 (4.1 μmol
monomer units) mg/mL.
L-alanine-HClO4 (black) and
line) versus momomeric crown ether unit in in 7a. [7a]=2 mg/mL in
CF3CH2OH.
D
Figure 3. Changes in ICD intensity (Δεsecond) of 7a against enantiomeric excess (%) of
20 (black) and -10 °C (red) respectively. [7a]=2 mg/mL in CH2Cl2.
L-Val (a) and D-Ala (b) during the complexation with 7a at

Article
Macromolecules, Vol. 43, No. 21, 2010 8817
oxygen atoms of the crown ether as revealed by the crystal
structure.30 The complex formation might therefore be
unselective because no diastereotopic oxygen atoms would
be present for hydrogen bonding with the carboxylic acid end
of the complexed amino acid.
Conclusion
In summary, we have addressed for the first time one-handed
helicity of single stranded polynorbornenes appended with mono-
aza-18-crown-6 7a and the corresponding isotactic dimer 10
induced by protonated amino acids. The protonated ammonium
ion may form complex with a monoaza-18-crown-6 whereas the
carboxylic acid may form hydrogen bonding with the adjacent
crown ether resulting in unidirectional orientation of the pendants
leading to a helical scaffold. A homogeneous stereochemistry
(double bonds and tacticity) of 7a would be crucial for the helical
formation. It is striking to note that polynorbornene with mono-
aza-15-crown-5 7b does not exhibit any CD response under the
same conditions. The uniqueness of monoaza-18-crown-6 pen-
dants in 7a and 10 appeared to be consistent with the model based
on DFT calculations.
Expermental Section
General Data. Gel permeation chromatography (GPC)
was performed on a Waters GPC machine using an isocratic
HPLC pump (1515) and a refractive index detector (2414).
THF was used as the eluent (flow rate =1.0 mL/min).
Melting points were measured on a SPSIC WRS-2A melting
point apparatus and were uncorrected. CD spectra were
taken at 20 °C unless otherwise specified on a JASCO
J-810 spectropolarimeter in a 3 mL cell. Absorption spectra
were measured with a Hitachi U-331 spectrophotometer.
Monomer 3a. To a mixture of 4a31 (0.80 g, 3.0 mmol) and
Na2CO3 (2.12 g, 20.0 mmol) in CH2Cl2 (30 mL) was added
the freshly prepared 5-Cl (1.22 g, 4.5 mmol) in CH2Cl2
(30 mL) at 0 °C. The mixture was gradually warmed to room
temperature and stirred for 17 h. After filtration, the solvent
was removed in vacuo and the residue was chromato-
graphed on silica gel (CH2Cl2/MeOH = 19:1) to give 3a
Figure 6. DFT calculationsof14a (righthanded) and 14b (lefthanded).
1
˚
˚
(0.60 g, 40%) as a solid: mp 165-166 °C; H NMR (400
Seleced distances for 14a: 0H1O4, 1.86 A; H2O10, 2.00 A; H3O16
,
,
,
0
0
0
0
0
0
0
˚
˚
˚
˚
MHz, CDCl3) δ 1.51 (d, J = 8.4 Hz, 1 H; H7 on norbornene),
2.01 A; H4O7 , 1.79 A; H1 O4 , 1.89 A; H2 O10 , 2.02 A; H3 O16
˚
˚
˚
˚
2.00 A; 14b: H1O4, 2.02 A; H2O10, 1.94 A; H3O16, 1.99 A; H4O13
0
1.61 (d, J = 8.4 Hz, 1 H; H7 on norbornene), 2.89-2.97
0
0
0
0
0
0
˚
˚
˚
˚
1.82 A; H1 O4 , 1.99 A; H2 O10 , 1.82 A; H3 O16 , 1.83 A.
(m, 4 H), 3.07-3.11 (m, 2 H), 3.21-3.27 (m, 2 H), 3.62-3.77
(m, 24 H; H on crown ether), 6.16 (s, 2 H; olefinic-H), 6.38 (d,
J = 8.4 Hz, 2 H; Ar H), 7.29 (d, J = 8.4 Hz, 2 H; Ar H); 13C
NMR (100 MHz, CDCl3) δ 45.3, 46.4, 50.3, 51.9, 53.3, 69.7,
70.3, 70.5, 70.6, 110.9, 122.6, 128.5, 135.6, 148.1, 172.7; MS
(ESI, m/z) 501 (Mþ þ H). Anal. Calcd: C, 67.18; H, 8.05; N,
5.60. Found: C, 67.09; H, 8.05; N, 5.58.
acid groups so that the pending groups in 7a may oriented
uniformly leading to a helical scaffold.
Reaction of 7b with with Protonated L-Alanine. In order to
establish the importance of the diastereoselective formation
of hydrogen bonding predicted by DFT calculations, poly-
mer 7b having monoaza-15-crown-5 ether pendants was
synthesized. Interestingly, no CD response was observed
when 7b was treated with protonated L-alanine under the
same conditions as described above. These results are differ-
ent from those of poly(phenyleneacetylene)derivative bear-
Monomer 6a. Under argon atmosphere, a solution of
3a (0.5 g, 1.0 mmol) in CH2Cl2 (8 mL) was added dropwise
to LiAlH4 (152 mg, 4.0 mmol) in ether (4 mL) at 0 °C. The
mixture was allowed to warm to room temperature and
stirred for an additional 18 h, quenched with H2O (1 mL)
and filtered. The organic layer was dried (MgSO4) and
evaporated in vacuo to give the residue which was chromato-
graphed on silica gel (CH2Cl2/MeOH=15:1) to give 6a
(296 mg, 61%) as a white solid: mp 152-153 °C; 1H NMR
(400 MHz, CDCl3) δ 1.47 (d, J = 10.8 Hz, 1 H), 1.57 (d, J =
10.8 Hz, 1 H), 2.75 (br, 4 H), 2.83-2.86 (m, 2 H), 2.92 (br,
2 H), 3.01 (br, 2 H), 3.15-3.17 (m, 2 H), 3.54-3.65 (m, 22 H),
6.12 (s, 2 H), 6.36 (d, J = 8.4 Hz, 2 H), 7.10 (d, J = 8.4 Hz,
2 H); 13C NMR (100 MHz, CDCl3) δ 45.2, 46.2, 50.3, 50.4,
51.9, 59.3, 69.7, 70.1, 70.51, 70.59, 111.3, 125.4, 129.6, 135.5,
146.5; LRMS (ESI, m/z) 487 ([M þ H]þ). Anal. Calcd: C,
69.11; H, 8.70; N, 5.76. Found: C, 69.12; H, 8.68; N, 5.76.
1
ing same monoaza-15-crown-5 ether pendants.16d The H
NMR experiment using CD2Cl2 as the extracting solvent
indicates that only less than 25% of protonated D-alanine
was extracted from the aqueous layer into the organic phase
(Figure S21). This organic solution again showed no CD
response (Figure S22).
Unlike 18-crown-6 ethers, the crown ether pendant in 7b
has only five heteroatoms (four O’s and 1 N) available for
hydrogen bonding. It is worthy noting that the complex
between a chiral N-benzylmonoaza-15-crown-5 and the
-NH3þ moiety is held together by hydrogen bonds between
the two protons of the ammonium ion and nitrogen and three

8818 Macromolecules, Vol. 43, No. 21, 2010
Ji et al.
Polymer 7a. Under argon atmosphere, a solution of (Cy3P)2-
Cl2RudCHPh (190 mg, 0.24 mmol) in CH2Cl2 (30 mL) was
added to 6a (3.5 g, 0.72 mmol) in CH2Cl2 (15 mL). The mixture
was stirred at room temperature for 80 min, quenched with
ethyl vinyl ether (5 mL) and poured into Et2O (25 mL).
The solid was collected and washed with EtOAc and Et2O to
afford 7a as a tan solid (2.7 g, 90%): Mn = 14700; Mw = 17300;
PDI = 1.18; 1H NMR (400 MHz, CDCl3) δ 1.24 (br, 1 H), 1.47
(br, 1 H), 2.75-2.89 (br, 8 H), 3.14 (br, 4 H), 3.62-3.67 (m,
22 H), 5.48 (br, 2 H), 6.57 (br, 2 H), 7.17 (br, 2 H); 13C NMR
(100 MHz, CDCl3) δ 36.0, 36.3, 45.0, 45.2, 46.3, 46.5, 50.3,
53.3, 59.3, 69.7, 70.1, 70.5, 70.6, 112.7, 126.4, 128.2, 129.6,
131.3, 131.5, 147.3, 147.4; IR (KBr) ν=3060, 2928, 2853,
1612, 1518, 1480, 1450, 1366, 1357, 1331, 1115, 967, 951,
Dimer 9. To a solution of 617 (230 mg, 0.32 mmol) in THF
(20 mL) and MeOH (5 mL) at 0 °C was added NaOH (55 mg,
1.37 mmol). The mixture was heated at reflux for 10 h and
cooled to room temperature. After most of the solvent was
removed, Et2O (20 mL) and H2O (30 mL) was added, and the
aqueous layer was separated, and then acidified with 10%
HCl (until pH = 6). The solid was filtered to give the diacid
as a white solid, which was used for the next reaction without
further purification.
To a solution of the diacid (100 mg, 0.15 mmol) in CH2Cl2
(10 mL) at 0 °C was added oxalyl chloride (0.2 mL, 2.3 mmol)
and DMF (one drop). The mixture was gradually warmed to
room temperature and stirred for 1 h. The solvent was
removed in vacuo to give crude acid chloride, which was
taken up in CH2Cl2 (6 mL) and added to a cooled (0 °C)
solution of 4a (76 mg, 0.29 mmol), NEt3 (0.5 mL) in CH2Cl2
(10 mL). The mixture was stirred at room temperature for
17 h. Saturated NaHCO3 was added and the organic layer
was washed with water, brine and then dried (MgSO4). The
solvent was removed in vacuo, and the residue was chromato-
graphed on silica gel (CH2Cl2/MeOH/NEt3 = 19:1:0.05)
818, 735, 720, 527 cm-1
.
Monomer 3b. To a mixture of 4b32 (1.0 g, 4.5 mmol), NEt3
(1 mL, d = 0.728, 1.4 mmol) and a catalytic amount of
DMAP in CH2Cl2 (15 mL) was added 5-Cl [freshly prepared
from 5-OH (1.28 g, 5.0 mmol) and oxalyl chloride (1 mL, d =
1.478, 11.7 mmol) in CH2Cl2 (10 mL)] at 0 °C. The mixture
was gradually warmed to room temperature and stirred for
24 h, poured into water and extracted with CH2Cl2. The
organic layer was dried (MgSO4), filtered, and the filtrate
was evaporated in vacuo to give the residue which was
chromatographed on silical gel (CH2Cl2/EtOAc = 1/2) to
give 3b as a yellow liquid (1.5 g, 71%): 1H NMR (400 MHz,
CDCl3) δ 1.51 (d, J = 8.4 Hz, 1 H), 1.61 (d, J = 8.4 Hz, 1 H),
2.88-2.90 (m, 2 H), 2.91-2.92 (m, 2 H), 3.00-3.08 (m, 2 H),
3.20-3.26 (m, 2 H), 3.61-3.68 (m, 18), 3.76 (t, J = 6.0 Hz,
4 H), 6.15(s, 2H), 6.36 (d, J= 8.2 Hz, 2 H) 7.29 (d, J = 8.2 Hz,
2 H); 13C NMR (100 MHz, CDCl3) δ 45.5, 46.6, 50.5, 52.1,
69.9, 70.27, 70.29, 71.1, 110.9, 122.6, 128.5, 135.6, 148.1, 172.6;
IR (KBr) ν 3053, 2914, 2850, 1608, 1523, 1460, 1411, 1316,
1293, 1252, 1194, 1125, 982, 933, 823, 764, 729 cm-1. HRMS
(FAB) m/z: calcd for C26H36N2O5, 456.2624; found, 456.2626.
Polymer 7b. Under nitrogen, a solution of 3b (200 mg,
0.44 mmol) and (Cy3P)2Cl2RudCHPh (16 mg, 0.05 equiv) in
dried CH2Cl2 (5 mL) was stirred at room temperature for 1 h.
The mixture was quenched with ethyl vinyl ether (1 mL)
and then poured into pentane (20 mL). The solid was
collected and redissolved in CH2Cl2 and precipitated again
with pentane. This procedure was repeated twice to afford
the polymer as a grayish solid. (150 mg, 75%) Mn = 6800,
1
to give 9 as an oil (102 mg, 59%): H NMR (400 MHz,
CDCl3) δ 1.59-1.65 (m, 2 H), 1.90-1.95 (m, 2 H), 2.81-2.83
(m, 2 H), 2.89-3.05 (m, 6 H), 3.17-3.29 (m, 8 H), 3.61-3.70
(m, 48 H), 5.47-5.50 (m, 2 H), 6.18 (dd, J = 7.2, 15.8 Hz,
1 H), 6.21 (dd, J = 7.2, 15.8 Hz, 1 H), 6.41 (d, J = 15.8 Hz,
1 H), 6.42 (d, J = 15.8 Hz, 1 H), 6.53 (d, J = 8.4 Hz, 2 H),
6.55 (d, J = 8.4 Hz, 2 H), 7.18-7.33 (m, 14 H); 13C NMR
(100 MHz, CDCl3) δ 36.16, 36.24, 44.9, 45.1, 45.3, 45.4, 46.4,
46.67, 46.73, 49.84, 49.87, 50.0, 53.4, 69.7, 70.4, 70.6, 70.7,
111.94, 111.97, 125.8, 126.9, 128.31, 128.33, 128.5 130.4,
130.7, 131.6, 131.7, 137.1, 148.74, 148.77, 172.37, 172.39; IR
(KBr) ν 3024, 2914, 2859, 1736, 1607, 1522, 1455, 1413, 1367,
1290, 1193, 1117, 965, 825 cm-1. HRMS (FAB) m/z: calcd
for C70H92N4O12 (Mþ þ H), 1180.6716; found, 1180.6726.
Dimer 10. To a slurry of LiAlH4 (30 mg, 0.79 mmol) in
Et2O (5 mL) was added slowly 9 (100 mg, 0.088 mmol) in
CH2Cl2 (5 mL), and the mixture was stirred at room tem-
perature for 1 h. EtOAc was carefully added, water (0.5 mL)
was then introduced. The resulting suspension was filtered,
and the organic layer was evaporated in vacuo to give a
residue, which was triturated with CH2Cl2 repeatedly.
The CH2Cl2 solution was dried (MgSO4) and filtered. The
solvent was removed in vacuo to give 10 as a oil (81 mg,
1
Mw = 8100, PDI = 1.18; H NMR (400 MHz, CDCl3) δ
1
1.38-1.54 (br, 1 H), 1.78-1.90 (br, 1 H), 2.60-2.80 (br, 2 H),
2.80-3.00 (br, 2 H), 3.00-3.40 (br, 4 H) 3.50-4.00 (br, 20
H), 5.30-5.40 (br, 2 H), 6.30-6.60 (br, 2 H), 7.10-7.30 (br,
2 H); 13C NMR (100 MHz, CDCl3) δ 36.4, 36.7, 44.9, 45.1,
46.5, 46.9, 49.8, 67.9, 69.7, 70.2, 71.0, 111.8, 123.6, 125.9,
128.5, 131.6, 131.9, 148.8, 172.5.
82%): H NMR (400 MHz, CDCl3) δ 1.61-1.65 (m, 2 H),
1.85-1.90 (m, 2 H), 2.74-2.77 (m, 10 H), 2.86-3.02 (m,
6 H), 3.56-3.68 (m, 40 H), 5.54 (m, 2 H), 6.24 (dd, J = 7.6,
15.6 Hz, 1 H), 6.26 (dd, J = 7.6, 15.6 Hz, 1 H), 6.41 (d, J =
15.6 Hz, 1 H), 6.43 (d, J = 15.6 Hz, 1 H), 6.56 (d, J = 8.4 Hz,
2 H), 6.59 (d, J = 8.4 Hz, 2 H), 7.11-7.36 (m, 14 H); 13C
NMR (100 MHz, CDCl3) δ 36.38, 36.46, 45.5, 45.7, 45.90,
45.96, 46.8, 46.9, 47.01, 47.05, 50.82, 50.87, 50.91, 50.96,
59.8, 70.2, 70.6, 71.01, 71.03, 71.11, 113.33, 113.34, 126.2,
127.2, 128.7, 130.05, 130.08, 130.6. 131.3, 131.76, 131.9,
137.65, 137.67, 147.86, 147.90; IR (KBr) ν 3024, 2918,
To a slurry of LiAlH4 (33 mg, 0.88 mmol) in Et2O (10 mL)
was added slowly the above polymer (100 mg, 0.22 mmol) in
CH2Cl2 (5 mL), and the mixture was stirred at room tem-
perature for 2 h. The reaction was quenched by water (1 mL)
and the resulting suspension was filtered, and the organic
layer was evaporated in vacuo to give the residue which
was dissolved in CH2Cl2. The organic solution was dried
(MgSO4) and filtered, and the residue poured into pentane
(20 mL). The solid was collected to afford 7b as grayish
solid. (36 mg, 36%) Mn = 6100, Mw = 6700, PDI = 1.10; IR
(KBr) ν 2954, 2917, 2850, 1597, 1522, 1459, 1377, 1252, 1169,
1122, 1024, 948, 850, 805 cm-1; 1H NMR (400 MHz, CDCl3)
δ 1.40-1.60 (br, 1 H), 1.70-1.90 (br, 1 H) 2.60- 3.00 (br,
8 H), 3.05-3.30 (br, 4 H) 3.50-3.80 (br, 18 H), 5.40-5.60
(br, 2 H), 6.50-6.70 (br, 2 H), 7.05-7.20 (br, 2 H); 13C NMR
(100 MHz, CDCl3) δ = 46.3, 46.6, 47.2, 50.3, 53.6, 60.0, 69.5,
70.1, 70.3, 70.8, 112.8, 125.8, 128.3, 129.9, 131.3, 147.6.
1613, 1518, 1479, 1354, 1280, 1197, 1107, 952, 821 cm-1
.
HRMS (FAB) m/z: calcd for C70H96N4O10, (Mþ þ H),
1152.7167; found, 1152.7158.
Preparation of L-Ala Solution and Helicity Induction
of Polymer 7a. A stock solution of 7a in CH2Cl2 (2 mg/mL
(4.1 mM, 10 mL) and a stock solution of L-Ala (7.3 mg/mL,
82 mM, 10 mL) in aqueous HClO4 (0.1 M) were prepared. To
a flask was added an equal volume (10 mL) of the above two
solutions and the resulting mixture was thoroughly stirred
for 18 h, then allowed to stand for 8 h and the organic phase
was separated for the CD measurement (Figures 1 and S1
(Supporting Information)).

Article
CD Titration Experiment. Stock solutions of 7a (4 mg/mL,
Macromolecules, Vol. 43, No. 21, 2010 8819
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20 mL) in CF3CH2OH and D-alanine-HClO4 in CF3CH2OH
(19.4 mg/mL, 5 mL) were prepared. To a flask a stock solu-
tion of 7a (1 mL) were added different volumes of the solu-
tion of D-alanine-HClO4 and the resulting solutions were
diluted with CF3CH2OH to keep the concentration of
7a at 2 mg/mL. The CD spectra are shown in Figure S-2
(Supporting Information). The Hill plot analysis33 of the data
gave the binding constant of 6.6 ꢀ 102 M-1 with D-alanine. In
a similar manner, a stock solution of D-valine was employed
for a similar measurements and CD spectra were recorded.
The binding constant with D-valine was 6.4 ꢀ 102 M-1 (see
Figure S3 (SupportingInformation) for the Hill plotanalysis).
1H NMR Experiments for the Complex Formation between
7 and Protonated D-Alanine. A stock solution of 7a in CD2Cl2
(2 mg/mL, 4.1 mM, 8 mL) and D-Ala (7.3 mg/mL (82 mM),
25 mL) in aqueous HClO4 (0.1 M) were prepared. To a flask
were mixed equal volumes of 7a in CD2Cl2 (4 mL) and D-Ala
solution (4 mL), and the mixture was thoroughly stirred for
15 h then stand for 8 h. The organic phase was separated for
1H NMR measurement. A similar procedure was used for the
complexation of 7b with protonated D-Ala. The results are
shown in Figure S21 (Supporting Information).
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DFT Calculations. DFT calculations were based on the
GGA/BLYP/DNP level and implemented with the DMol3
program package.34 The electronic configuration of molecular
systems was described by a double-numerical plus polarization
(DNP) basis set-comparable to the Gaussian 6-31G** basis
sets.34 The local exchange-correlation potential35 was aug-
mented in a self-consistent manner with Becke exchange36
and Lee-Yang-Parr correlation37 gradient corrections, giving
a generalized gradient approximation (GGA/BLYP) for the
evaluation of energies and geometries. Convergence criteria for
geometry optimizations were based on the threshold values:
2ꢀ10-5 hartree, 0.004 hartree/A, 0.005 A, and 1ꢀ 10-5 hartree
for energy, force, displacement, and self-consistent field (SCF)
density, respectively. In order to obtain precise results, neither
direct inversion of iterative subspace (DIIS) to accelerate
convergence of the SCF algorithm nor smearing techniques
were used.
˚
˚
Acknowledgment. We thank Shanghai Institute of Organic
Chemistry, the National Science Council, Taipei, National Taiwan
University, and the National Natural Science Foundation of
China, Beijing (in part) for support.
Supporting Information Available: Figures showing 1H and
13C NMR spectra of all new compounds, the CD profiles of the
complexes, and titration curves. This material is available free of
charge via the Internet at http://pubs.acs.org.
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