Synthesis and chiral recognition of helical poly(phenylacetylene)s bearing L-phenylglycinol and its phenylcarbamates as pendants

Article abstract of DOI:10.1002/pola.27506

A series of novel stereoregular one-handed helical poly(phenylacetylene) derivatives (PPA-1 and PPA-1a-g) bearing L-phenylglycinol and its phenylcarbamate residues as pendants was synthesized for use as chiral stationary phases (CSPs) for HPLC, and their chiral recognition abilities were evaluated using 13 racemates. The phenylcarbamate residues include an unsubstituted phenyl, three chloro-substituted phenyls (3-Cl, 4-Cl, 3,5-Cl₂), and three methyl-substituted phenyls (3-CH₃, 4-CH₃, 3,5-(CH₃)₂). The acidity of the phenylcarbamate N-H proton and the hydrogen bonds formed between the N-H groups of the phenylcarbamate residues were dependent on the type, position, and the number of substituents on the phenylcarbamate residues. The chiral recognition abilities of these polymers significantly depended on the dynamic helical conformation of the main chain with more or less regularly arranged pendants. The chiral recognition abilities seem to be improved by the introduction of substituents on the phenylcarbamate residues, and PPA-1d bearing the more acidic N-H groups due to the 3,5-dichloro substituents, exhibited a higher chiral recognition than the others. PPA-1d showed an efficient chiral recognition for some racemates, and baseline separation was possible for racemates 5, 11, 12, and 15.

Full text of DOI:10.1002/pola.27506

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Synthesis and Chiral Recognition of Helical Poly(phenylacetylene)s
Bearing L-Phenylglycinol and its Phenylcarbamates as Pendants
Chunhong Zhang,1 Hailun Wang,1 Taotao Yang,1 Rui Ma,1 Lijia Liu,1 Ryosuke Sakai,2
Toshifumi Satoh,3 Toyoji Kakuchi,3 Yoshio Okamoto1,4
1Polymer Materials Research Center, Key Laboratory of Superlight Materials and Surface Technology of Ministry of Education,
College of Materials Science and Chemical Engineering, Harbin Engineering University, Harbin 150001, China
2Department of Materials Chemistry, Asahikawa National College of Technology, Asahikawa 071-8142, Japan
3Division of Biotechnology and Macromolecular Chemistry, Graduate School of Chemical Sciences and Engineering,
Faculty of Engineering, Hokkaido University, Sapporo 060-8628, Japan
4Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan
Correspondence to: C. Zhang (E-mail: zhangchunhong97@163.com) or Y. Okamoto (E-mail: okamoto@apchem.nagoya-u.ac.jp)
Received 14 August 2014; accepted 2 December 2014; published online 31 December 2014
DOI: 10.1002/pola.27506
ABSTRACT: A series of novel stereoregular one-handed helical
poly(phenylacetylene) derivatives (PPA-1 and PPA-1a~g)
bearing L-phenylglycinol and its phenylcarbamate residues as
pendants was synthesized for use as chiral stationary phases
(CSPs) for HPLC, and their chiral recognition abilities were
evaluated using 13 racemates. The phenylcarbamate residues
include an unsubstituted phenyl, three chloro-substituted phe-
nyls (3-Cl, 4-Cl, 3,5-Cl2), and three methyl-substituted phenyls
(3-CH3, 4-CH3, 3,5-(CH3)2). The acidity of the phenylcarbamate
N-H proton and the hydrogen bonds formed between the N-H
groups of the phenylcarbamate residues were dependent on
the type, position, and the number of substituents on the phe-
nylcarbamate residues. The chiral recognition abilities of these
polymers significantly depended on the dynamic helical con-
formation of the main chain with more or less regularly
arranged pendants. The chiral recognition abilities seem to be
improved by the introduction of substituents on the phenylcar-
bamate residues, and PPA-1d bearing the more acidic N-H
groups due to the 3,5-dichloro substituents, exhibited a higher
chiral recognition than the others. PPA-1d showed an efficient
chiral recognition for some racemates, and baseline separation
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was possible for racemates 5, 11, 12, and 15. 2014 Wiley Peri-
odicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 809–
821
KEYWORDS: chiral; chiral recognition; helical conformation; high
performance liquid chromatography (HPLC); L-phenylglycinol;
molecular recognition; phenylcarbamate; polyacetylenes;
poly(phenylacetylene)
CSPs for a wide range of chiral compounds,4,6,7 various opti-
cally active synthetic polymers with a controllable helical
sense have also been applied as the CSPs for the HPLC separa-
tion of enantiomers in the last two decades.7–16 Among the
synthetic polymers, the helical poly(phenylacetylene) deriva-
tives bearing chiral pendants have been proved to be good
candidates as novel CSPs for the HPLC separation of enantiom-
ers due to their helical structures induced by chiral pend-
ants.16–21 Up to now, there have been only a few reports on
the poly(phenylacetylene) derivatives as CSPs for HPLC, their
chiral recognition mechanism as CSPs and the influencial fac-
tors for chiral recognition are still not so totally clarified.
INTRODUCTION Chiral compounds often exhibit different
physiological and metabolic activities in organisms between
enantiomers, though most of their chemical and physics prop-
erties are identical. Therefore, the chirality of compounds is an
important issue, in particular, for chiral drugs and food addi-
tives, and it is valuable to prepare pure enantiomers of various
chiral compounds.1,2 Chiral separation, especially direct enan-
tioseparation by high-performance liquid chromatography
(HPLC) has been recognized as one of the most efficient tech-
niques to obtain pure enantiomers on analytical and prepara-
tive scales.3–5 One of the key points of this separation
technique is to design and prepare the efficient chiral station-
ary phases (CSPs) with high chiral recognition abilities.
Although polysaccharide derivatives, especially the phenylcar-
bamates and benzoates of cellulose and amylose with high chi-
ral recognition abilities have been developed as the popular
The poly(phenylacetylene)s possessing dynamic helical confor-
mations can be internally tuned and externally manipulated,
resulting in the change of the helical pitch and inversion of the
helicity. The former is usually achieved by changing their
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molecular structures, especially their functional pendants, while
the latter is accomplished by applying external stimuli, such as
temperature and solvent. Previously, we reported a series of
the poly(phenylacetylene)s bearing different L-amino acid ethyl
ester pendants with different linkages, and discussed the influ-
ences of the main chain helicity, linkage group between the
main chain and chiral pendants, coating solvents on silica gel,
polymerization conditions, and structures of the amino acids
on their chiral recognition abilities.20–22 To the best of our
knowledge, the helical poly(phenylacetylene)s bearing phenyl-
carbamate derivatives of L-amino alcohols as pendants have
never been reported. In this study, based on our previous stud-
ies, a series of novel stereoregular one-handed helical poly(-
phenylacetylene) derivatives bearing L-phenylglycinol and its
phenylcarbamate residues as pendants was designed and syn-
thesized, and their chiral recognition abilities as CSPs for HPLC
were evaluated. The main focus was on the influence of unsub-
stituted and substituted phenylcarbamate residues on the heli-
cal structures of the stereoregular main chain and the chiral
recognition abilities of these poly(phenylacetylene) derivatives.
The influence of the position and the number of chloro-
substituents and methy L-substituents on the phenyl group of
the phenylcarbamate residues was investigated in detail.
grade. Hexane and 2-propanol used in the chromatographic
experiments were of HPLC grade. The racemates were com-
mercially available or were prepared by the usual methods.
Instrumentation
The NMR spectra were recorded using a Bruker AVANCE III-
500 instrument. The number-average molecular weight (Mn),
the weight-average molecular weight (Mw), and the polydis-
persity (Mw/Mn) of the polymers were determined by size
exclusion chromatography (SEC) calibrated with standard
polystyrenes at 40 ꢀC using a JASCO SEC system (PU-980
Intelligent pump, CO-965 column oven, RI-930 Intelligent RI
detector, and Shodex DEGAS KT-16) equipped with a Shodex
Asahipak GF-310 HQ column (linear, 7.6 mm 3 300 mm;
pore size, 20 nm; bead size, 5 lm; exclusion limit, 4 3 104)
and a Shodex Asahipak GF-7 M HQ column (linear, 7.6 mm
3 300 mm; pore size, 20 nm; bead size, 9 lm; exclusion
limit, 4 3 107) in DMF containing lithium chloride (0.01 M)
at the flow rate of 0.4 mL min21. The optical rotation was
measured in CHCl3 at room temperature using a Perkin-
Elmer Model 341 polarimeter. The circular dichroism (CD)
and ultraviolet visible (UV-Vis) spectra were measured in a
1-mm path length cell using a JASCO J-815 spectropolarime-
ter. All the enantioseparation experiments were performed
using a JASCO PU-2089 high performance liquid chromato-
graph (HPLC) system equipped with UV-Vis (JASCO-UV-2070)
and circular dichroism (JASCO-CD-2095) detectors. A solu-
tion of a racemate (3 mg/mL) was injected into the chro-
matographic system through an intelligent sampler (JASCO
AS-2055). The thermogravimetric analyses (TGA) were per-
formed using a TGA Q 50 (TA) instrument.
EXPERIMENTAL
Materials
L-Phenylglycinol (purity 99%) was purchased from Shanghai
Jingchun Reagent Co., Ltd. (Shanghai, China). 4-(4,6-Dime-
thoxy-1,3,5-triazin-2-yl)-4-methyl morpholinium chloride
(DMT-MM) (purity 98%) was purchased from Sahn Chemical
Technology Co., Ltd. (Shanghai, China). Triphenylphosphine
(purity 99%) was purchased from J&K Chemical Co., Ltd.
(Beijing, China). 4-Ethynylbenzoic acid was synthesized
Monomer Synthesis
Synthesis of N-(4-Ethynylbenzoyl)-L-Phenylglycinol (PA-1)
PA-1 was synthesized by the amidation reaction between 4-
ethynylbenzoic acid and L-phenylglycinol. A typical procedure
is described as follows. To a solution of 4-ethynylbenzoic
acid (5.00 g, 34.21 mmol) and DMT-MM (10.41 g, 37.64
mmol) in MeOH (175 mL) was added L-phenylglycinol
(4.69 g, 34.21 mmol). After stirring at room temperature for
18 h, the reaction mixture was purified by column chroma-
tography on silica gel with hexane/acetone (5/4, v/v) to give
PA-1 as white crystals.
according to
a
previously reported method.23 3-
Chlorophenylisocyanate (purity 98%) was purchased from
Tokyo Chemical Industry Co., Ltd. (Shanghai, China). Phenyl
isocyanate, 4-chlorophenyl isocyanate, 3,5-dichlorophenyl
isocyanate, 3-methylphenyl isocyanate, 4-methylphenyl iso-
cyanate, and 3,5-dimethylphenyl isocyanate (purity 98%)
were purchased from Puyang Hongda Shengdao Mew Materi-
als Co., Ltd. (Henan, China). Rh1(2,5-norbornadiene)[(g6-
C6H5)B(C6H5)3] (Rh(nbd)BPh4) was prepared based on a
previous report.24 All the solvents used in the reactions
were of analytical grade, carefully dried, and distilled before
use. The solvents (methanol (MeOH), tetrahydrofuran (THF),
N,N-dimethylformide (DMF), dimethyl sulfoxide (DMSO), and
N,N-dimethylacetamide (DMAc)) for the solubility test of the
polymers were commercially available and used without fur-
ther purification. Silica gel with a mean particle size of 37 to
56 lm for column chromatography was purchased from
Qingdao Haiyang Chemical Co., Ltd. (Qingdao, China). The
porous spherical silica gel with a mean particle size of 7 lm
and a mean pore diameter of 100 nm (Daiso gel SP-
100027) for HPLC was kindly supplied by Daiso Chemicals
(Osaka, Japan), then silanized with (3-aminopropyl)triethoxy-
1
ꢀ
Yield: 6.93 g (76.3%). H NMR (500 MHz, CDCl3, TMS, 20 C,
ppm): d 5 7.78–7.76 (d, Ar-H, 2H), 7.57–7.55 (d, Ar-H, 2H),
7.42–7.35 (m, Ar-H, 4H), 7.35–7.30 (m, Ar-H, 1H), 6.84–6.82 (d,
Ar-NH-, 1H), 5.29-5.25 (q, Ar-CH-, 1H), 4.06-3.98 (m, -O-CH2-,
2H), 3.20 (s, CꢁCH, 1H), 2.40 (s, -OH, 1H). 13C NMR (125 MHz.
DMSO-d6, 20 ꢀC, ppm): d 5 165.3 (2CO2 (amino)), 141.2 (aro-
matic), 134.7 (aromatic), 131.5 (aromatic), 128.1 (aromatic),
127.7 (aromatic), 126.9 (aromatic), 126.8 (aromatic), 124.3
(aromatic), 82.9 (2CꢁCH), 82.7 (2CꢁCH), 64.4 (2CH22O),
56.0 (2CH2NH-). ANAL. CALCD. for C17H15NO2 (265.31): C,
76.96; H, 5.70; N, 5.28. Found: C, 76.93; H, 5.72; N, 5.25.
Synthesis of PA-1a-g
Seven carbamate derivatives PA-1a-g were synthesized via
the reaction between PA-1 and unsubstituted phenyl
ꢀ
silane in toluene at 80 C before use. All solvents used in the
preparation of the chiral stationary phases were of analytical
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isocyanate or a series of substituted phenyl isocyanates. A
typical procedure is described as follows. To a solution of
the PA-1 (1.00 g, 3.77 mmol) in THF (38 mL) was added
phenyl isocyanate (0.53 g, 4.52 mmol) under a nitrogen
atmosphere. After stirring at 35 ꢀC for 10 h, the reaction
mixture was purified by column chromatography on silica
gel with hexane/ethyl acetate (5/2, v/v) to give (S)-2-(4-
ethynylbenzamino)22-phenylethyl phenylcarbamate (PA-1a)
as white crystals.
matic), 132.1 (aromatic), 129.1 (aromatic), 129.0 (aromatic),
128.1 (aromatic), 128.0 (aromatic), 127.4 (aromatic), 126.6
(aromatic), 125.1 (aromatic), 120.3 (aromatic), 120.2 (aro-
matic), 83.3 (2CꢁCH), 83.2 (2CꢁCH), 66.7 (2CH22O-), 53.1
(2CH2NH-). ANAL. CALCD. for C24H19ClN2O3 (418.87): C,
68.82; H, 4.57; Cl, 8.46; N, 6.69. Found: C, 68.90; H, 4.58; Cl,
8.49; N, 6.61.
Based on the above procedure, (S)-2-(4-ethynylbenzamino)-
2-phenylethyl 3,5-dichlorophenylcarbamate (PA-1d) was suc-
cessfully synthesized and purified by column chromatogra-
phy on silica gel with hexane/ethyl acetate (5/2, v/v) to give
white crystals. Yield: 1.21 g (70.9%). 1H NMR (500 MHz,
CDCl3, TMS, 20 ꢀC, ppm): d 5 7.76–7.74 (d, Ar-H, 2H), 7.53-
7.51 (d, Ar-H, 2H), 7.41–7.35 (m, Ar-H, 4H), 7.35–7.28 (m,
Ar-H, 3H), 7.19 (s, Ar-NH-, 1H), 7.13-7.08 (d, -CO-NH-, 1H),
7.05 (s, Ar-H, 1H), 5.5,6–5.49 (m, Ar-CH, 1H), 4.76–4.70 (q, -
O-CH2-, 1H), 4.41–4.35 (q, -O-CH2-, 1H), 3.19 (s, CꢁCH, 1H).
13C NMR (125 MHz, DMSO-d6, 20 ꢀC, ppm): d 5 165.3
(2CO2 (ester)), 153.1 (2CO2 (amino)), 141.6 (aromatic),
139.5 (aromatic), 134.2 (aromatic), 131.7 (aromatic), 128.5
(aromatic), 127.7 (aromatic), 127.6 (aromatic), 127.0 (aro-
matic), 124.7 (aromatic), 121.7 (aromatic), 116.3 (aromatic),
83.0 (2CꢁCH), 82.9 (2CꢁCH), 66.6 (2CH22O-), 52.6
(2CH2NH-). ANAL. CALCD. for C24H18Cl2N2O3 (453.32): C,
63.59; H, 4.00; Cl, 15.64; N, 6.18. Found: C, 63.68; H, 3.96;
Cl, 15.59; N, 6.22.
1
ꢀ
Yield: 1.05 g (72.7%). H NMR (500 MHz, CDCl3, TMS, 20 C,
ppm): d 5 7.78–7.76 (d, Ar-H, 2H), 7.52-7.50 (d, Ar-H, 2H),
7.37–7.41 (m, Ar-H, 4H), 7.28–7.37 (m, Ar-H, 5H; -CO-NH-,
1H), 7.67–7.12 (m, Ar-H, 1H), 6.74 (s, Ar-NH-, 1H), 5.50–5.43
(m, Ar-CH-, 1H), 4.74–4.68 (q, -O-CH2-, 1H), 4.40–4.36 (q, -O-
CH2-, 1H), 3.18 (s, CꢁCH, 1H). 13C NMR (125 MHz, DMSO-d6,
20 ꢀC, ppm): d 5 165.3 (2CO2 (ester)), 153.4 (2CO2
(amino)), 139.7 (aromatic), 139 (aromatic), 134.3 (aromatic),
131.7 (aromatic), 128.7 (aromatic), 128.5 (aromatic), 127.7
(aromatic), 127.5 (aromatic), 127 (aromatic), 124.6 (aro-
matic), 122.5 (aromatic), 118.3 (aromatic), 118.2 (aromatic),
83.0 (2CꢁCH), 82.9 (2CꢁCH), 66.2 (2CH22O), 52.7
(2CH2NH-). ANAL. CALCD. for C24H20N2O3 (384.43): C, 74.98;
H, 5.24; N, 7.29. Found: C, 74.96; H, 5.26; N, 7.28.
Based on the above procedure, (S)-2-(4-ethynylbenzamino)-
2-phenylethyl 3-chlorophenylcarbamate (PA-1b) was suc-
cessfully synthesized and purified by column chromatogra-
phy on silica gel with chloroform/ethyl acetate (9/1, v/v) to
give white crystals. Yield: 1.18 g (74.7%). 1H NMR (500
MHz, CDCl3, TMS, 20 ꢀC, ppm): d 5 7.77–7.75 (d, Ar-H, 2H),
7.53–7.51 (d, Ar-H, 2H), 7.47 (s, Ar-H, 1H), 7.42–7.35 (m,
Ar-H, 4H), 7.35–7.28 (m, Ar-H, 1H), 7.24–7.19 (m, Ar-H, 1H),
7.19-7.11 (m, Ar-H, 2H), 7.08–7.03 (d, -CO-NH -, 1H), 6.74 (s,
Ar-NH-, 1H), 5.55–5.47 (m, Ar-CH-, 1H), 4.74-4.69 (q, -O-
CH2-, 1H), 4.42–4.38 (q, -O-CH2-, 1H), 3.19 (s, CꢁCH, 1H).
13C NMR (125 MHz, DMSO-d6, 20 ꢀC, ppm): d 5 165.8
(2CO2 (ester)), 153.7 (2CO2 (amino)), 141.1 (aromatic),
140.1 (aromatic), 134.7 (aromatic), 133.6 (aromatic), 132.1
(aromatic), 130.9 (aromatic), 128.9 (aromatic), 128.1 (aro-
matic), 128.0 (aromatic), 127.4 (aromatic), 125.1 (aromatic),
122.6 (aromatic), 118.0 (aromatic), 117.1 (aromatic), 83.4
(2CꢁCH), 83.3 (2CꢁCH), 66.8 (2CH22O-), 53.1 (2CH2NH-
). ANAL. CALCD. for C24H19ClN2O3 (418.87): C, 68.82; H, 4.57;
Cl, 8.46; N, 6.69. Found: C, 68.88; H, 4.55; Cl, 8.51; N, 6.64.
Based on the above procedure, (S)-2-(4-ethynylbenzamino)-
2-phenylethyl 3-methylphenylcarbamate (PA-1e) was suc-
cessfully synthesized and purified by column chromatogra-
phy on silica gel with chloroform/ethyl acetate (15/1, v/v)
to give white crystals. Yield: 1.23 g (81.6%). 1H NMR (500
MHz, CDCl3, TMS, 20 ꢀC, ppm): d 5 7.78–7.76 (d, Ar-H, 2H),
7.52–7.50 (d, Ar-H, 2H), 7.42–7.33(m, Ar-H, 4H; -CO-NH-,
1H), 7.33–7.28 (m, Ar-H, 1H), 7.20-7.14 (m, Ar-H, 3H), 6.92–
6.90 (d, Ar-H, 1H), 6.69 (s, Ar-NH-, 1H), 5.48–5.44 (m, Ar-
CH, 1H), 4.74–4.69 (q, -O-CH2-, 1H), 4.39–4.35 (q, -O-CH2-,
1H), 3.19 (s, CꢁCH, 1H), 2.33(s, -CH3, 3H). 13C NMR (125
MHz, DMSO-d6, 20 ꢀC, ppm): d 5 165.8 (2CO2 (ester)),
153.8 (2CO2 (amino)), 140.2 (aromatic), 139.4 (aromatic),
138.3 (aromatic), 134.8 (aromatic), 132.1 (aromatic), 129.0
(aromatic), 128.9 (aromatic), 128.2 (aromatic), 128.0 (aro-
matic), 127.4 (aromatic), 125.1 (aromatic), 123.7 (aromatic),
119.3 (aromatic), 83.4 (2CꢁCH), 83.3 (2CꢁCH), 66.6
(2CH22O-), 53.2 (2CH2NH-), 21.7 (-CH3). ANAL. CALCD. for
Based on the above procedure, (S)-2-(4-ethynylbenzamino)-
2-phenylethyl 4-chlorophenyl- carbamate (PA-1c) was suc-
cessfully synthesized and purified by column chromatogra-
phy on silica gel with chloroform/ethyl acetate (10/1, v/v)
to give white crystals. Yield: 1.23 g (77.8%). 1H NMR (500
MHz, CDCl3, TMS, 20 ꢀC, ppm): d 5 7.77–7.75 (d, Ar-H, 2H),
7.53–7.51 (d, Ar-H, 2H), 7.47 (s, Ar-H, 1H), 7.40-7.36 (m, Ar-
H, 4H), 7.35–7.30 (m, Ar-H, 1H), 7.30–7.26 (m, Ar-H, 4H),
7.22–7.20 (d, -CO-NH-, 1H), 6.77 (s, Ar-NH-, 1H), 5.50-5.45
(m, Ar-CH-, 1H), 4.74-4.68 (q, -O-CH2-, 1H), 4.42–4.36 (q, -O-
CH2-, 1H), 3.20 (s, CꢁCH, 1H). 13C NMR (125 MHz, DMSO-d6,
20 ꢀC, ppm): d 5 165.8 (2CO2 (ester)), 153.8 (2CO2
(amino)), 140.1 (aromatic), 138.4 (aromatic), 134.8 (aro-
C
25H22N2O3 (398.45): C, 75.36; H, 5.57; N, 7.03. Found: C,
75.43; H, 5.65; N, 6.91.
Based on the above procedure, (S)-2-(4-ethynylbenzamino)-
2-phenylethyl 4-methylphenylcarbamate (PA-1f) was suc-
cessfully synthesized and purified by column chromatogra-
phy on silica gel with chloroform/ethyl acetate (13/1, v/v)
to give white crystals. Yield: 1.33 g (88.7%). 1H NMR (500
MHz, CDCl3, TMS, 20 ꢀC, ppm): d 5 7.78–7.76 (d, Ar-H, 2H),
7.52–7.50 (d, Ar-H, 2H), 7.44–7.34 (m, Ar-H, 4H; -CO-NH-,
1H), 7.28–7.33 (m, Ar-H, 1H), 7.21 (Ar-H, 2H), 7.11–7.09 (d,
Ar-H, 2H), 6.72 (s, Ar-NH-, 1H), 5.47–5.42 (m, Ar-CH, 1H),
4.72-4.68 (q, -O-CH2-, 1H), 4.36–4.33 (q, -O-CH2-, 1H), 3.19
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SCHEME 1 Synthesis of poly(phenyacetylene)s bearing L-phenylglycinol derivatives as pendants PPA-1 and PPA-1a~h. [Color fig-
ure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]
(s, CꢁCH, 1H), 2.31(s, -CH3, 3H). 13C NMR (125 MHz, DMSO-
d6, 20 ꢀC, ppm): d 5 165.8 (2CO2 (ester)), 153.8 (2CO2
(amino)), 140.2 (aromatic), 136.9 (aromatic), 134.8 (aro-
matic), 132.1 (aromatic), 131.7 (aromatic), 129.6 (aromatic),
129.5 (aromatic), 128.9 (aromatic), 128.1 (aromatic), 128.0
(aromatic), 127.4 (aromatic), 125.1 (aromatic), 118.7 (aro-
matic), 83.4 (2CꢁCH), 83.3 (2CꢁCH), 66.5 (2CH22O-), 53.2
(2CH2NH-), 20.8 (-CH3). ANAL. CALCD. for C25H22N2O3
(398.45): C, 75.36; H, 5.57; N, 7.03. Found: C, 75.40; H, 5.55;
N, 6.96.
mer]0/[Rh(nbd)BPh4]0 5 50.
A
typical procedure is
described as follows. PA-1 (0.50 g, 1.88 mmol) was weighed
into a flask and dissolved in dry DMF (50.3 mL) before a
solution of Rh(nbd)BPh4 (19.4 mg, 37.7 lmol) in dry DMF
(12.5 mL) was added. After stirring at room temperature for
24 h, triphenylphosphine (19.8 mg, 75.4 lmol) was added to
the reaction mixture. The solution was concentrated and
then poured into a large amount of MeOH (1000 mL). The
precipitates were purified by reprecipitation using MeOH
and then dried under reduced pressure to give PPA-1 as a
yellow solid.
Based on the above procedure, (S)-2-(4-ethynylbenzamino)-
2-phenylethyl 3,5-dimethylphenyl- carbamate (PA-1g) was
successfully synthesized and purified by column chromatog-
raphy on silica gel with chloroform/ethyl acetate (10/1, v/v)
to give white crystals. Yield: 1.14 g (73.6%). 1H NMR (500
MHz, CDCl3, TMS, 20 ꢀC, ppm): d 5 7.79–7.77 (d, Ar-H, 2H),
7.53–7.51 (d, Ar-H, 2H), 7.35–7.42 (m, Ar-H, 4H), 7.28–7.34
(m, Ar-H, 1H; -CO-NH-, 1H), 6.94 (s, Ar-H, 2H), 6.74 (s, Ar-H,
1H), 6.55 (s, Ar-NH-, 1H), 5.48-5.44 (m, Ar-CH, 1H), 4.73-
4.68 (q, -O-CH2, 1H), 4.38-4.35 (q, -O-CH2, 1H), 3.18 (s,
CꢁCH, 1H), 2.28(s, -CH3, 6H). 13C NMR (125 MHz, DMSO-d6,
20 ꢀC, ppm): d 5 165.7 (2CO2 (ester)), 153.8 (2CO2
(amino)), 140.2 (aromatic), 139.3 (aromatic), 138.2 (aro-
matic), 138.1 (aromatic), 134.8 (aromatic), 132.1 (aromatic),
128.9 (aromatic), 128.1 (aromatic), 128.0 (aromatic), 127.4
(aromatic), 125.1 (aromatic), 124.5 (aromatic), 116.5 (aro-
matic), 83.4 (2CꢁCH), 83.3 (2CꢁCH), 66.6 (2CH22O-), 53.2
(2CH2NH-), 21.6 (-CH3). ANAL. CALCD. for C26H24N2O3
(412.48): C, 75.71; H, 5.86; N, 6.79. Found: C, 75.74; H, 5.92;
N, 6.76.
Yield: 0.49 g (98%). Mn 5 4.15 3 105; Mw/Mn 5 3.88. Based
on the above procedure, the other monomers (PA-1a-g)
were polymerized to give the corresponding polymers (PPA-
1a-g).
Preparation of Chiral Stationary Phases (CSPs)
The poly(phenylacetylene) derivatives (PPA-1 and PPA-
1a~g) (0.20 g each) were first dissolved in a coating solvent
(5 mL) and then coated on aminopropyl silanized silica gel
(0.80 g) according to a previous method.25 The polymer-
coated silica gels were then packed in a stainless-steel tube
(25 cm 3 0.20 cm i.d.) by the slurry method. The plate num-
bers of the packed columns were 1600 to 3000 for benzene
using a hexane/2-propanol (95/5, v/v) mixture as the eluent
at the flow rate of 0.1 mL/min at 25 ꢀC. The dead time (t0)
of the columns was estimated using 1,3,5-tri-tert-butylben-
zene as the nonretained compound.26
RESULTS AND DISCUSSION
Synthesis of Polymers, PPA-1 and PPA-1aꢂg
Polymerization
The monomers and polymers were synthesized via the reac-
tion route illustrated in Scheme 1. The amidation reaction of
4-ethynylbenzoic acid with the L-phenylglycinol proceeded
using 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methyl morpholi-
nium chloride (DMT-MM) as a catalyst in good yields to pro-
duce a novel monomer bearing the L-phenylglycinol pendant
The polymerizations of the phenylacetylenes bearing the L-
phenylglycinol pendants (PA-1, PA-1a-g) were carried out in
dry DMF using Rh1(2,5-norbornadiene)[(g6-C6H5)B-(C6H5)3]
(Rh(nbd)BPh4) as the catalyst under a nitrogen atmosphere
for 24 h at 28 ꢀC with [monomer]0 5 0.03 M, and [mono-
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2-(4-ethynylbenzamino)-2-phenylethyl 3,5-dichlorophenylcar-
bamate (PA-1d), (S)-2-(4-ethynylbenzamino)-2-phenylethyl
3-methylphenylcarbamate (PA-1e), (S)-2-(4-ethynylbenza-
mino)-2-phenylethyl 4-methylphenylcarbamate (PA-1f), and
(S)-2-(4-ethynylbenzamino)-2-phenylethyl 3,5-dimethylphe-
nylcarbamate (PA-1g). The 1H NMR spectra were used to
characterize the monomer structure (see Experimental Sec-
tion for details). The acetylenyl protons of these monomers
appeared at about 3.18-3.20 ppm. Compared with the 1H
NMR spectrum of PA-1, the proton resonance signals on the
chiral carbon atom of PA-1a~g shifted downfield and the
proton signals of the methyne adjacent to the chiral carbon
atom split after the introduction of the phenylcarbamate
groups to PA-1 (Fig. 1). The optical rotations of the phenyla-
cetylene derivitives also varied with the change in the mono-
mer structures (Table 1); PA-1 showed a high levorotatory
20
optical rotation ([a]D 5 287.0ꢀ) in DMF, while the optical
rotation values of PA-1a~g were quite low ([a]D20 5 29 to
216ꢀ in DMF, though the sense of the optical rotations was
the same.
To obtain the stereoregular poly(phenylacetylene)s and to
investigate the influence of the various phenylcarbamate
pendants on the helical conformation and chiral recognition
abilities, the monomers were polymerized using
Rh(nbd)BPh4 as the catalyst and the polymerization results
are shown in Table 2. PPA-Phg-1 and PPA-Phg-1a~g were
synthesized in DMF using the corresponding monomers with
0.03 M as the monomer concentration. The SEC profiles of
all the polymers were monomodal with high molecular
weights. Figure 2 depicts the 1H NMR spectra of PPA-1 and
PPA-1a in DMSO-d6 at 80 ꢀC. The 1H NMR spectra showed
the characteristic signals due to the main chain proton at
5.78 ppm for PPA-1 and at 5.66 ppm for PPA-1a, respec-
tively. These signals suggest the formation of the highly cis-
transoidal stereoregular structure of the poly(phenylacety-
lene) main chain.27–30 For PPA-1a, there are two resonances
assigned to the N-H protons; the signal in the lower field at
9.20 ppm was due to the N-H of the phenylcarbamate resi-
dues, while the signal at 8.41 ppm was attributed to the N-H
of the amide groups, which shifted downfield after the intro-
duction of a phenylcarbamate group. Figures 3 and 4 show
the 1H NMR spectra of the polymers bearing phenylcarba-
mate pendants (PPA-1a~g) in DMSO-d6 at 80 ꢀC. The 1H
NMR spectra of these polymers showed the characteristic
signals due to the main chain proton at 5.55 to 5.70 ppm,
indicating the stereoregular cis-transoid configuration in the
main chains of these poly(phenylacetylene)s. As shown in
Figure 3, the N-H proton signals of the amide groups in PPA-
1a~d showed no obvious shift, while the N-H proton signals
assigned to the phenylcarbamate residues in PPA-1b~d
shifted downfield compared with PPA-1a. In Figure 4, the
FIGURE 1 1H NMR spectra of chiral carbon atom (-CH-) and the
methyne (-CH2-) adjacent to the chiral carbon atom region of
phenylacetylene derivatives (PA-1 and PA-1a~g) at 20 ꢀC in
CDCl3. [Color figure can be viewed in the online issue, which is
available at wileyonlinelibrary.com.]
with an active hydroxyl group, N-(4-ethynylbenzoyl)-L-phe-
nylglycinol (PA-1). Various phenyl isocyanates (phenyl iso-
cyanate,
3-chlorophenyl
isocyanate,
4-chlorophenyl
isocyanate, 3,5-dichlorophenyl isocyanate, 3-methylphenyl
isocyanate, 4-methylphenyl isocyanate, and 3,5-dimethyl-
phenyl isocyanate) were then used to react with the active
hydroxyl of PA-1 in good yields respectively, to produce a
series of novel monomers with various phenylcarbamate
groups, (S)-2-(4-ethynylbenzamino)-2-phenylethyl phenylcar-
bamate (PA-1a), (S)-2-(4-ethynylbenzamino)- 2-phenylethyl
3-chlorophenylcarbamate (PA-1b), (S)-2-(4-ethynylbenza-
mino)-2-phenylethyl 4-chlorophenylcarbamate (PA-1c), (S)-
TABLE 1 Specific Rotations of PA-1 and PA-1a~g in DMF
PPA-1
PPA-1a
PPA-1b
PPA-1c
PPA-1d
PPA-1e
PPA-1f
PPA-1g
20
[a]D
287.0
215.6
215.3
210.4
29.7
213.7
212.0
214.3
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TABLE 2 Polymerization Results of PA-1 and PA-1a~g
a
b
b
Polymer
Yield/%
Mn (31025
)
PDI
PPA-1
97.0
97.3
90.0
97.0
99.3
92.5
93.3
93.2
4.15
3.29
4.05
3.32
3.95
4.40
3.85
4.64
3.88
5.03
3.95
4.29
4.76
3.24
2.98
3.10
PPA-1a
PPA-1b
PPA-1c
PPA-1d
PPA-1e
PPA-1f
PPA-1g
a
Polymerization condition: catalyst, Rh(nbd)BPh4; solvent, DMF; [Mono-
mer]/[Rh(nbd)BPh4] 5 50/1; [Monomer] 5 0.03 M; temperature, 28 ꢀC;
time, 24 h.
b
Determined by SEC in DMF containing lithium chloride (0.01 M) at the
flow rate of 0.4 mL min21, and using polystyrene standards.
phenylcarbamate N-H proton signals in PPA-1e~g shifted to
a high field compared with PPA-1a, though the amide N-H
proton signals showed almost no shift. This means that the
phenylcarbamate N-H protons shifted downfield when the
aromatic rings of the phenylcarbamates have an electron-
withdrawing substituent (chloro group) (PPA-1b~d), and
shifted to a high field when the aromatic rings of the phenyl-
carbamates have an electron-donating substituent (methyl
group) (PPA-1e~g). The chemical shifts of the phenylcarba-
mate N-H resonances significantly depended on the acidity
of the N-H protons and shifted downfield with an increase in
the acidity of the N-H groups of the phenylcarbamate resi-
dues.25,31 Therefore, the acidity of the phenylcarbamate N-H
protons of these polymers may be as follows: PPA-1d > PPA-
FIGURE 3 1H NMR spectra of poly(phenylacetylene) derivatives
bearing chloro-substituted phenylcarbamate pendants in
DMSO-d6 at 80 ꢀC ((A) PPA-1a, (B) PPA-1b, (C)PPA-1c, (D) PPA-
1d). [Color figure can be viewed in the online issue, which is
available at wileyonlinelibrary.com.]
FIGURE 4 1H NMR spectra of poly(phenylacetylene) derivatives
bearing methyl-substituted phenylcarbamate pendants in
DMSO-d6 at 80 ꢀC ((A) PPA-1a, (B) PPA-1e, (C) PPA-1f, (D) PPA-
1g). [Color figure can be viewed in the online issue, which is
available at wileyonlinelibrary.com.]
FIGURE 2 1H NMR spectra of (A) PPA-1 and (B) PPA-1a in
DMSO-d6 at 80 ꢀC.
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TABLE 3 Solubility of PPA-1 and PPA-1a~g
Polymer
MeOH
CHCl3
acetone
THF
DMF
DMAc
DMSO
Hexane
2-Propanol
PPA-1
2
2
2
2
2
2
2
2
2
2
2
1
2
2
2
2
2
1
1 1
1 1
1 1
1 1
1
1 1
1 1
1 1
1 1
1 1
1 1
1 1
1 1
1 1
1 1
1 1
1 1
1 1
1 1
1 1
1 1
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
PPA-1a
PPA-1b
PPA-1c
PPA-1d
PPA-1e
PPA-1f
PPA-1g
1
1
1 1
1
11
11
1
1
1 1
1
1
1 1
1 1
1 1
1 1
1 1
1 1
1 1, soluble, 1, partly soluble, 2, insoluble.
20
1c
ꢃ
PPA-1b > PPA-1a > PPA-1e > PPA-1f > PPA-1g. Fur-
on the solvents. Moreover, the [a]D values of the different
polymers in the same solvent also varied with the unsubsti-
tuted or substituted phenylcarbamate residues as pendants,
indicating that the chiral structures of these poly(phenylace-
tylene)s changed by altering the functional pendants.
thermore, the more acidic N-H protons of the phenylcarba-
mate groups probably have a much stronger interaction with
the adjacent L-phenylglycinol or phenylcarbamate residues
via hydrogen bonds, which induce and maintain a stable
arrangement of the polymer main chain and the pendants. In
addition, the specific association of the N-H group with
DMSO, a typical hydrogen bonding solvent, should also not
be ignored in this case.32,33
The chiroptical properties of PPA-1 and PPA-1a~g were also
investigated using circular dichroism (CD) to confirm their
helical structures. Figure 5 shows the CD and UV-Vis absorp-
tion spectra of the polymers in various solvents at room
temperature. All the polymers exhibited intense Cotton
effects biased by the covalently bonded L-phenylglycinol or
its phenylcarbamate derivatives as pendants in the UV-Vis
wavelength range from 300 nm to 550 nm, in which the p-
conjugation of the polymer backbone typically appears.
These distinctive Cotton effects clearly indicated that these
polymers definitely possess a predominantly one-handed hel-
ical conformation induced by the chiral pendants of L-phenyl-
glycinol or its phenylcarbamate derivatives.21,38,39 These
results suggest that the side groups of the polymers must be
regularly arrayed in the helical structures.
The solubilities of all the obtained polymers in several
organic solvents are shown in Table 3. All the polymers were
essentially soluble in polar solvents, such as DMAc, DMSO,
and DMF, and insoluble in MeOH, hexane, and 2-propanol.
Moreover, the solubility of these polymers in CHCl3, acetone,
and THF is somewhat different probably due to the different
polarity of the carbamate groups depending on the substitu-
ent groups on the phenylcarbamate pendants.
Chiroptical Properties of the Polymers
The specific optical rotations ([a]D20) of the obtained poly-
mers (PPA-1 and PPA-1a~g) in different solvents were
determined in order to investigate the chiroptical properties
of these polymers, and the results are shown in Table 4. As
expected, the polymers exhibited high optical rotations in
good solvents, especially in DMF. The optical rotations of all
the polymers were positive in the tested solvents, though the
corresponding monomers showed low negative optical rota-
20
Similar to the [a]D values, the chain helicity of the poly-
mers were also sensitive to solvents and exhibited obvious
changes in their CD spectral patterns and intensities.
TABLE 4 Specific Rotations of PPA-1 and PPA-1a~g in Different
Solvents
20
tions in DMF. As examples, PPA-1 and PPA-1b showed [a]D
values of 1443ꢀ and 1360ꢀ, respectively, in DMF, while the
optical rotations of the corresponding monomers PA-1 and
PPA-1b were 287.0ꢀ and 215.3ꢀ, respectively, in the same
solvent. The opposite and high optical rotations of the poly-
mers suggest that a new structure, most likely a secondary
helical structure, must be formed in the polymer chains.34–37
The optical activities of the polymers were influenced by the
Polymer In DMF In DMAc In CHCl3 In THF Monomera
PPA-1
1443
1268
1360
1268
—
1163
1123
158
—
—
287.0
215.6
215.3
210.4
29.70
213.7
212.0
214.3
PPA-1a
PPA-1b
PPA-1c
PPA-1d
PPA-1e
PPA-1f
PPA-1g
—
—
1169
—
1102
128
—
141
159
—
20
helicity of the polymer backbones. Furthermore, the [a]D
1283
1206
1312
175
1273
—
—
values of the polymers obviously varied with the solvents.
This may be attributed to the polarity and hydrogen-bonding
ability of the solvents. The optical activities of the polymers
were dependent on the solvents, suggesting that the poly-
mers possess a dynamic helical structure highly dependent
1130
1105
14.7
198
1115
a
Solvent: DMF. “—” means solubility of the polymer in the solvent is
not sufficient for the measurement.
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FIGURE 5 CD (upper) and UV-Vis (lower) spectra of PPA-1 and PPA-1a~g in various solvents at 25 ꢀC (c 5 1 mg/mL) ((A) PPA-1, (B)
PPA-1a, (C) PPA-1b, (D) PPA-1c, (E) PPA-1d, (F) PPA-1e, (G) PPA-1f, (H) PPA-1g). [Color figure can be viewed in the online issue,
which is available at wileyonlinelibrary.com.]
Although most polymers induced similar split-type Cotton
effects in DMF, DMSO, and DMAc (i.e., the first negative Cot-
ton effect at 465 to 450 nm, the second positive Cotton
effect at 395–375 nm and the third negative Cotton effect at
335–315 nm), they showed quite different split-type Cotton
effects in tetrahydrofuran (THF) and chloroform (CHCl3) (i.e.,
the first negative Cotton effect at 338ꢂ330 nm, the second
positive Cotton effect at 300 nm or lower than 300 nm) with
a large blue-shift in the UV-Vis absorption spectra. These
results mean that PPA-1 and PPA-1a~g actually have
dynamic helical conformations in the different solvents. The
variation in the Cotton effects may originate from the
polarity and hydrogen-bonding ability of the solvents. The
solvents may have an important influence on the hydrogen-
bond formation of L-phenylglycinol or its phenylcarbamate
derivatives arrayed with a predominant screw-sense along
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FIGURE 6 IR spectra of N–H region of PPAs bearing phenylcarbamate residues (A) PPA-1a~d, (B) PPA-1a, and PPA-1e~g.
the polymer backbones. The blue-shifts in the UV-Vis absorp-
tion spectra can be ascribed to a change in the twist angle of
the conjugated double bonds, and the polymers may have a
tightly twisted helical conformation in THF and CHCl3.40,41
intramolecular hydrogen bonding between the adjacent
amide groups, which induce and stabilize the dynamic helical
conformation of the polymer main chain. The results in Fig-
ure 6(B) indicate that the methyl-substituents showed more
steric hindrance by the phenylcarbamate residues than the
corresponding chloro-substituents (except for the meta-posi-
tion). The significantly lower amount of hydrogen bonding
N-Hs of PPA-1e also suggests the greater steric hindrance of
the substituents at the meta-position.
Intramolecular Hydrogen Bonding in the Polymers PPA-
1aꢂg
The IR spectra of the phenylcarbamate N-H of the polymers
PPA-1a~g are depicted in Figure 6. Two N-H peaks were
observed in the IR spectra of these polymers. One peak in
the higher wavenumber region was assigned to a free N-H
bond and the other peak in the lower wavenumber region
was due to an N-H group involved in the intramolecular
hydrogen bond between the adjacent phenylcarbamate resi-
dues or amide groups arrayed along the polymer back-
bones.27,28 Figure 6(A) shows that PPA-1a, PPA-1c, and
PPA-1d possess a significant amount of hydrogen bonding
N-Hs and a lower amount of free N-Hs, while PPA-1b pos-
sesses a low amount of hydrogen bonding N-Hs. The hydro-
gen bond may make the phenylcarbamate residues arrayed
with a predominant screw-sense along the polymer helical
main chains, leading to the formation of a regular arrange-
ment of phenylcarbamate residues. The low content of the
hydrogen bonding N-H in PPA-1b is probably due to the sig-
nificant steric hindrance of the chloro-substituents at the
meta-position, which prevents the intramolecular hydrogen
bonding between the adjacent phenylcarbamate residues,
resulting in the less regular arrangement of the phenylcarba-
mate residues along the polymer helical main chain. The
hydrogen bonding N-H of PPA-1b may be assigned to the
Chiral Recognition of PPA-1 and PPA-1aꢂg
PPA-1 and PPA-1a~g are expected to exhibit chiral recogni-
tion abilities, because these polymers not only have a chiral-
ity at the pendants, but also possess a predominantly one-
handed helical conformation at the main chains. Their chiral
recognition abilities were evaluated as the CSPs by HPLC
using the thirteen tested racemates shown in Figure 7.
The resolution results of the thirteen racemates (3–15) on
PPA-1 and PPA-1a are summarized in Table 5. The pendant
of PPA-1a is an unsubstituted phenylcarbamate derivative of
PPA-1. These two polymers showed different chiral recogni-
tion abilities under the same chromatographic conditions.
The retention factor, k1’ [5(t1 2 t0)/t0], for the first eluted
enantiomer in Table 5 is the factor indicating the interaction
strength between a CSP and the corresponding enantiomer,
and can be obtained from its elution time t1 and the dead
time t0. PPA-1a showed different k1’ values compared with
those of PPA-1 due to the introduction of the unsubstituted
phenylcarbamate residue. The separation factor a, which is
directly correlated to the chiral recognition ability of a CSP,
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FIGURE 7 Structures of racemates.
is an important factor for evaluating a CSP. If a is equal to
1.00, this means no chiral recognition, and the higher the a
value, the better chiral recognition ability of a CSP. As shown
in Table 5, PPA-1 bearing L-phenylglycinol as pendents
exhibited an efficient chiral recognition for racemates 4, 5, 7,
11, 12, and 15, while PPA-1a with the phenylcarbamate res-
idue seems to show much lower recognition abilities.
Although the reason for the low chiral recognition ability of
PPA-1a is not clear at present, it may be ascribed to the
change in the chiral recognition sites as described below.
The helical structure of the poly(phenylacetylene)s consists
of the main chain helicity and the regular arrangement of
the side chains along the main chain, and the side chain
groups probably form hydrogen bonds between each other.
The hydrogen bonds and steric hindrance of the side chain
groups can alter the conformation of the helical structure,
accompanying the change in the chiral recognition abilities.
The helical grooves exist along the main chain of PPA-1 and
PPA-1a. For PPA-1, the phenyl amide groups should be
arrayed inside of the helical grooves, and the L-phenylglyci-
nol residues should be arrayed outside of the helical
grooves.42,43 The chiral recognition sites of PPA-1 are mainly
on the amide and L-phenylglycinol residue. The side chain of
PPA-1a is longer than that of PPA-1. For PPA-1a, the phenyl-
carbamate residues should be arrayed outside of the helical
grooves,42,43 and the enantiomers may predominantly inter-
act with the phenylcarbamate residues outside the grooves
through the formation of intermolecular hydrogen bonds.
The difference in the chiral recognition sites of PPA-1 and
PPA-1a must lead to the different chiral recognition abilities.
phenylcarbamate residues on chiral recognition abilities, the
poly(phenylacetylene)s, PPA-1b~d, with chlorosubstituted
phenylcarbamate residues as pendants and PPA-1e~g with
methyl-substituted phenylcarbamate residues as pendants
were synthesized. Their chiral recognition abilities were
evaluated using the thirteen tested racemates. The resolution
results of the racemates on PPA-1a~d are summarized
in Table 6. As already discussed, the introduction of the
TABLE 5 Resolution of Racemates on PPA-1 and PPA-1aa
PPA-1
PPA-1a
Racemates
k0
a
k0
a
1
1
3
0.50 (-)
0.33 (-)
5.02 (-)
ꢂ1
1.42
1.08
ꢂ1
1.33
1
0.88
0.60
1
4
1
5
4.20 (-)
7.93 (-)
3.91
ꢂ1
ꢂ1
1
6
1.39 (1)
7.99 (-)
2.42
7
8
5.31
1
9
1.64
1
3.01 (-)
0.53
ꢂ1
1
10
11
12
13
14
15
0.46 (1)
14.82 (-)
8.04 (-)
1.15
ꢂ1
1.14
1.04
1
2.44 (-)
8.81 (-)
0.72
ꢂ1
1.04
1
3.12
1
1.29
1
6.60 (-)
1.07
6.22 (-)
1.11
a
Column: 25 cm 3 0.20 cm id. Coating solvent: DMF. Eluent: hexane/2-
propanol (95/5, v/v). Flow rate: 0.1 mL/min. The signs in parentheses
represent the optical rotation of the first-eluted enantiomer.
In order to clarify the influence of the electron-withdrawing
substituents and the electron-donating substituents of the
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TABLE 6 Resolution of Racemates on Helical Poly(phenylacetylene)s Bearing Phenylcarbamate and Chloro Substituted Phenylcar-
bamate Residues (PPA-1a~d)a
PPA-1d (3,5-Cl2)b
PPA-1c (4-Cl)c
PPA-1b (3-Cl)c
PPA-1a (H)c
Racemates
k0
a
k0
a
k0
a
k0
1
a
1
1
1
3
1.28(1)
0.30
1.13
1
0.93(2)
0.47
ꢂ1
1
0.90(2)
0.41
ꢂ1
1
0.88
0.60
1
4
1
5
3.11(2)
1.61
1.79
1
4.74(2)
2.05
ꢂ1
1
3.78
1
4.20(2)
7.93(2)
3.91
ꢂ1
ꢂ1
1
6
1.47
1
7
1.48
1
4.60(1)
9.14(1)
2.28(2)
0.35
ꢂ1
1.50
ꢂ1
1
3.17
1
8
8.08(1)
1.34
1.11
1
3.35(1)
1.94
ꢂ1
1
5.31
1
9
3.01(2)
0.53
ꢂ1
1
10
11
12
13
14
15
0.19
1
0.31
1
8.93(2)
2.99(2)
0.47
1.52
1.28
1
16.84(2)
7.59(2)
0.72(2)
0.77
1.07
1.03
ꢂ1
1
14.46(2)
7.92
ꢂ1
1
2.44(2)
8.81(2)
0.72
ꢂ1
1.04
1
0.76(2)
0.83
ꢂ1
1
0.68
1
1.29
1
4.49(2)
1.71
6.17(2)
ꢂ1
5.54
1
6.22(2)
1.11
a
b
Column: 25 cm 3 0.20 cm i.d. Eluent: hexane/2-propanol (95/5, v/v).
Flow rate: 0.1 mL/min. The signs in parentheses represent the optical
rotation of the first-eluted enantiomer.
Coating solvent: DMAc.
Coating solvent: DMF.
c
chloro-substituent (electron-withdrawing) may increase the
acidity of the phenylcarbamate N-H groups, i.e., the acidity of
these four polymers may be as follows: PPA-1d > PPA-1c ꢃ
PPA-1b > PPA-1a. In Table 6, the polymers from left to right
are listed in the order of decreasing acidity of the N-H
groups of the phenylcarbamate residues. As can be seen
from Table 6, PPA-1a~d showed different chiral recognition
abilities under the same chromatographic conditions. Their
chiral recognition abilities varied with the position and the
number of chloro-substituents. It seems that the chiral recog-
nition abilities were improved with the increase in the acid-
ity of N-H groups, probably because stronger interactions
were formed between the polymers and some racemic
compounds via hydrogen bonds. PPA-1d with the most
acidic N-H groups due to the 3,5-dichlorophenylcarbamate
residues among the four polymers, exhibited a higher chiral
recognition than the others. PPA-1d showed an efficient chi-
ral recognition for racemates 3, 5, 8, 11, 12, and 15. More-
over, the racemates 5, 11, 12, and 15 were resolved with a
baseline separation or nearly baseline separation. Figure 8
shows the chromatograms for racemates 5 and 15 on PPA-
1d. The enantiomers were completely separated with the
separation factors of 1.79 for 5 and 1.71 for 15. Compared
with PPA-1d, PPA-1c with the lower acidic N-H groups
showed lower recognition abilities. Although the acidity of
the phenylcarbamate N-H groups of PPA-1b is similar to that
of PPA-1c, it exhibited a much lower chiral recognition than
PPA-1c, and PPA-1b resolved only 8, 11, and 12 with a very
FIGURE 8 Chromatograms for the resolution of (A) benzoin (5) and (B) 2,2’-dimethyl-6,6’-dinitrobiphenyl (15) on PPA-1d with hex-
ane/2-propanol (95/5) as eluent.
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TABLE 7 Resolution of Racemates on Helical Poly(phenylacetylene)s Bearing Phenylcarbamate and Methyl Substituted Phenylcar-
bamate Residues (PPA-1a and PPA-1e~g)
PPA-1a (H)
PPA-1e (3-CH3)
PPA-1f (4-CH3)
PPA-1g (3,5-(CH3)2)
Racemates -
k0
a
k0
a
k0
a
k0
a
1
1
1
1
3
0.88
0.60
1
0.72(2)
0.50(1)
2.72(2)
1.13(1)
4.62(1)
3.76(1)
2.17(2)
0.34
ꢂ1
ꢂ1
ꢂ1
1.32
ꢂ1
1.27
ꢂ1
1
0.59(2)
0.46(1)
4.20(2)
1.80(1)
5.06(1)
4.27(1)
2.21(2)
0.49
ꢂ1
ꢂ1
ꢂ1
1.07
1.07
ꢂ1
ꢂ1
1
0.69(2)
0.57(1)
3.29
ꢂ1
ꢂ1
1
4
1
5
4.20(2)
7.93(2)
3.91
ꢂ1
ꢂ1
1
6
1.26(1)
4.16
1.06
1
7
8
5.31
1
3.88(2)
1.57(2)
0.27
ꢂ1
ꢂ1
1
9
3.01(2)
0.53
ꢂ1
1
10
11
12
13
14
15
2.44(2)
8.81(2)
0.72
ꢂ1
1.04
1
26.92(2)
1.87
1.07
1
27.26(2)
2.43
ꢂ1
1
17.35(2)
1.34
1.25
1
0.68(2)
0.98
ꢂ1
1
0.82
1
0.72
1
1.29
1
0.87
1
1.27
1
6.22(2)
1.11
6.56
1
7.01
1
5.06
1
Column: 25 cm 3 0.20 cm i.d. Coating solvent: DMF. Eluent: hexane/2-propanol (95/5, v/v). Flow rate: 0.1 mL/min. The signs in parentheses represent
the optical rotation of the first-eluted enantiomer.
CONCLUSIONS
low chiral recognition. The reason for this low ability is not
clear at present, but it may be ascribed to the irregular
structure of the phenylcarbamate residues along the helical
A series of novel poly(phenylacetylene) derivatives, PPA-1
and PPA-1a~g, with an amide linkage bearing L-phenylglyci-
main chain induced by the greater steric hindrance of the
nol and its phenylcarbamate derivatives as pendants, respec-
chlorosubstituents at the meta-position as discussed for the
tively, were synthesized to evaluate their chiral recognition
IR spectra analysis.
as CSPs in HPLC using the thirteen racemates. The main
chains of these polymers possessed helical conformations,
and the pendants are arrayed along polymer main chains
Table 7 shows the resolution results of the racemates on PPA-
1 and PPA-1e~g bearing the methyl-substituted phenylcarba-
depending on the pendants including L-phenylglycinol and
mate residues. Similar to the chloro derivatives, these poly-
its unsubstituted or substituted phenylcarbamate residues.
mers exhibited different recognition abilities depending on
The chain helicities of the polymers were tunable by chang-
the position and the number of methyl-substituents. The
ing the pendants and solvents. The results of the IR and 1H
introduction of methyl-substituents (electron-denoting) seems
NMR spectra indicated that the N-H groups of the phenylcar-
to improve the chiral recognition abilities for some racemates,
bamate residues formed more or less hydrogen bonds, which
though the acidity of the N-H groups of the phenylcarbamate
varied with the type, position, and the number of substitu-
residues decreased. This is probably relevant to the
ents on the phenylcarbamate residues. The acidity of the
substituted phenylcarbamate pendants arrayed along the
phenylcarbamate N–H proton of the polymers was also influ-
helical main chains. The derivatives with the 3-
enced by the various substituents on the phenylcarbamate
methylphenylcarbamate residues can be explained as follows.
residues. The hydrogen bonds and the acidity of the phenyl-
As previously discussed regarding the IR spectra, the free N-H
carbamate N-H proton significantly influenced the arrange-
groups of the phenylcarbamate residues increased after the
ments of the phenylcarbamate pendants and the main chain
introduction of the 3-methyl groups, suggesting that the
helicity, and the chiral recognition abilities of the polymers
hydrogen bonds between the phenylcarbamate pendants
depended on these stereochemical arrangements.
were partly disturbed by the steric hindrance of the 3-methyl
substituents and the main chains became less regular. How-
ever, new chiral recognition sites should be formed at the
same time, resulting in the improvement of the chiral recogni-
ACKNOWLEDGMENTS
tion abilities for some racemates. As shown in Table 7, PAA-
1e with the 3-methylphenylcarbamate residues as pendants
exhibited a higher chiral recognition than the others, and
showed an efficient chiral recognition on racemates 6, 8, and
11. In addition, comparing PPA-1e to PPA-1b, it is also indi-
cated that a methyl group is probably more preferable than a
chloro group as the meta-substituent of PAA-1a.
This work was financially supported by the National Natural
Science Foundation of China (Grant No. 51373044 and
21204014), the Scientific Research Foundation for the
Returned Overseas Chinese Scholars, State Education Ministry
(Grant No. 20111568), the Special Fund for Scientific and
Technological Innovative Talents in Harbin City (Grant No.
2012RFLXG001), and the Fundamental Research Funds for
820
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23 E. Yashima, T. Matsushima, Y. Okamoto, J. Am. Chem. Soc.
1997, 119, 634526359.
the Central Universities, China (Grant No. HEUCFT1009,
HEUCF20130910004, HEUCF201403008, HEUCFQ1417). This
work was also partially supported by Daicel Corporation
(Tokyo, Japan). The authors are grateful for the support.
24 Y. Kishimoto, M. Itou, T. Miyatake, T. Ikariya, R. Noyori,
Macromolecules 1995, 28, 666226666.
25 Y. Okamoto, M. Kawashima, K. Hatada, J. Chromatogr.
1986, 363, 1732186.
REFERENCES AND NOTES
26 Y. Okamoto, R. Aburatani, T. Fukumoto, K. Hatada, Chem.
Lett. 1987, 185721860.
1 Y. Zhang, S. Yao, H. Zeng, H. Song, Curr. Pharm. Anal. 2010,
6, 1142130.
27 C. I. Simionescu, V. Percec, S. Dumitrescu, J. Polym. Sci.,
Polym. Chem. Ed. 1977, 15, 2497–2509.
2 N. M. Maier, P. Franco, W. Lindner, J. Chromatogr. A 2001,
906, 3–33.
28 C. I. Simionescu, V. Percec, Prog. Polym. Sci. 1982, 8, 133–
3 C. Ravelet, E. Peyrin, J. Sep. Sci. 2006, 29, 132221331.
4 Y. Okamoto, T. Ikai, Chem. Soc. Rev. 2008, 37, 259322608.
214.
29 Y. Kishimoto, P. Eckerle, T. Miyatake, M. Kainosho, A. Ono,
T. Ikariya, R. Noyori, J. Am. Chem. Soc. 1999, 121, 12035–
12044.
5 C.Yamamoto, Y. Okamoto, Bull. Chem. Soc. Jpn. 2004, 77,
2272257.
6 Y. Okamoto, J. Polym. Sci., Part A: Polym. Chem. 2009, 47,
1731–1739.
30 V. Percec, M. Obata, J. G. Rudick, B. B. De, M. Glodde, T.
K. Bera, S. N. Magonov, V. S. K. Balagurusamy, P. A.
Heiney, J. Polym. Sci., Part A: Polym. Chem. 2002, 40, 3509–
3533.
7 T. Ikai, Y. Okamoto, Chem. Rev. 2009, 109, 6077–6101.
8 Y. Okamoto, T. Ikai, J. Shen, Isr. J. Chem. 2011, 51,
109621106.
31 J. Shen, Y. Zhao, S. Inagaki, C. Yamamoto, Y. Shen, S. Liu,
Y. Okamoto, J. Chromatogr. A 2013, 1286, 41–46.
9 H. Yuki, Y. Okamoto, I. Okamoto, J. Am. Chem. Soc.1980,
102, 635626358.
32 R. J. Abraham, J. J. Byrne, L. Griffiths, M. Perez, Magn.
Reson. Chem. 2006, 44, 491–509.
10 T. Nakano, J. Chromatogr. A 2001, 906, 2052225.
11 T. Nakano, Y. Okamoto, Chem. Rev. 2001, 101, 401324038.
33 J. S. Lomas, A. Adenier, J. Chem. Soc. Perkin Trans. 2,
2001, 1051–1057.
12 K. Morioka, Y. Isobe, S. Habaue, Y. Okamoto, Polym. J.
2005, 37, 2992308.
34 K. Akagi, S. Guo, T. Mori, M. Goh, G. Piao, M. Kyotani, J.
Am. Chem. Soc. 2005, 127, 14647–14654.
13 T. Miyabe, H. Iida, A. Ohnishi, E. Yashima, Chem. Sci. 2012,
3, 8632867.
35 T. Fukushima, K. Takachi, K. Tsuchihara, Macromolecules
2006, 39, 3103–3105.
14 T. Aoki, K. Shinohara, T. Kaneko, E. Oikawa, Macromole-
cules 1996, 29, 419224198.
36 T. Iwasaki, H. Nishide, Curr. Org. Chem. 2005, 9, 1665–1684.
15 K. Tamura, T. Miyabe, H. Iida, E. Yashima, Polym. Chem.
2011, 2, 91–98.
37 H. C. Zhao, F. Sanda, T. Masuda, J. Polym. Sci., Part A:
Polym. Chem. 2005, 43, 5168.
16 Y. Naito, Z. Tang, H. Iida, T. Miyabe, E. Yashima, Chem.
Lett. 2012, 41, 8092811.
38 R. Kakuchi, S. Nagata, Y. Tago, R. Sakai, I. Otsuka, H.
Nakade, T. Satoh, T. Kakuchi, Macromolecules 2009, 42,
147621481.
17 M. Teraguchi, K. Mottate, S. Kim, T. Aoki, T. Kaneko, S.
Hadano, T. Masuda, Macromolecules 2005, 38, 636726373.
18 E. Yashima, S. Huang, Y. Okamoto, J. Chem. Soc. Chem.
Commun. 1994, 6, 181121812.
39 R. Sakai, B. E. Barasa, N. Sakai, S. Sato, T. Satoh, T.
Kakuchi, Macromolecules 2012, 45, 822128227.
19 E. Yashima, T. Matsushima, T. Nimura, Y. Okamoto, Kor.
Polym. J. 1996, 4, 1392146.
40 G. M. Miyake, H. Iida, H. Y. Hu, Z. Tang, E. Y. X. Chen, E.
Yashima, J. Polym. Sci., Part A: Polym. Chem. 2011, 49, 5192–
5198.
20 C. Zhang, F. Liu, Y. Li,; X. Shen, X. Xu, R. Sakai, T. Satoh, T.
Kakuchi, Y. Okamoto, J. Polym. Sci. Part A: Polym. Chem.
2013, 51, 227122278.
41 R. Kakuchi, S. Nagata, R. Sakai, I. Otsuka, H. Nakade, T.
Satoh, T. Kakuchi, Chem. Eur. J. 2008, 14, 10259–10266.
21 C. Zhang, H. Wang, Q. Geng, T. Yang, L. Liu, R. Sakai, T. Satoh,
T. Kakuchi, Y. Okamoto, Macromolecules 2013, 46, 8406–8415.
42 E. Yashima, S. Huang, T. Matsushima, Y. Okamoto, Macro-
molecules 1995, 28, 4184–4193.
22 C. Zhang, H. Wang, F. Liu, X. Shen, L. Liu, R. Sakai, T.
Satoh, T. Kakuchi, Y. Okamoto, ACTA Polym. Sin. 2013, 6,
8112816.
43 T. Nishimura, K. Maeda, S. Ohsawa, E. Yashima, Chem. Eur.
J. 2005, 11, 1181–1190.
WWW.MATERIALSVIEWS.COM
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