Synthesis and Application of C2 and C3 Symmetric (R)-Phenylglycinol-Derived Chiral Stationary Phases

Article abstract of DOI:10.1002/chir.22572

A C3 symmetric (R)-phenylglycinol N-1,3,5-benzenetricarboxylic acid-derived chiral stationary phase (CSP) and three C2 symmetric (R)-phenylglycinol CSPs were newly synthesized using o-, m-, and p-phthaloyl dichlorides.

Full text of DOI:10.1002/chir.22572

CHIRALITY 28:186–191 (2016)
Special Issue Article
Synthesis and Application of C2 and C3 Symmetric (R)-Phenylglycinol-
Derived Chiral Stationary Phases
2
JEONGJAE YU,1 DONG HYUN RYOO,1 JUNG MI LEE,1 AND JAE JEONG RYOO
*
1Department of Chemistry, Kyungpook National University, Daegu, Korea
2Department of Chemistry Education, Kyungpook National University, Daegu, Korea
ABSTRACT
A C3 symmetric (R)-phenylglycinol N-1,3,5-benzenetricarboxylic acid-derived
chiral stationary phase (CSP) and three C2 symmetric (R)-phenylglycinol CSPs were newly syn-
thesized using o-, m-, and p-phthaloyl dichlorides.
These CSPs were used to compare the resolution of 25 chiral samples using a previously re-
ported 3,5-dinitrobenzoyl (R)-phenylglycinol-derived CSP. Even though all CSPs have the same
chiral moiety, the C3 symmetric CSP showed the best resolution. Chirality 28:186–191, 2016.
© 2016 Wiley Periodicals, Inc.
KEY WORDS: 1,3,5-benzenetricarboxylic acid; C2 symmetry; C3 symmetry; (R)-phenylglycinol
CSP; chiral HPLC
Various types of high-performance liquid chromatography
(HPLC) chiral stationary phases (CSPs) such as brush/Pirkle-
type stationary phases,1 crown ethers,2 ligand exchange,3 pro-
teins,4 polysaccharides,5 cyclodextrin,6 and cyclofructan7 have
been developed.8,9 Many amino acid-based CSPs have been
reported as chiral selectors; for example, (S)-leucine and
(R)-phenylglycine-derived brush/Pirkle-type CSP,10 (S)-proline-
and (S)-lysine-derived ligand-exchange CSPs,11 and a protein
CSP.12 Various aminoalcohol-derived CSPs have also been
synthesized using (R)-phenylglycinol, (S)-alaninol, (S)-leucinol,
and (S)-tert-leucinol. These aminoalcohol-derived CSPs have
some merits compared with amino acid-derived CSPs in short
and simple synthetic processes. Among the various amino-alco-
hol-derived CSPs, (R)-phenylglycinol- and (S)-leucinol-derived
CSPs showed better results in the resolution of many chiral
samples.13–16 A CSP derived from a synthetic amino alcohol,
(S)-1-anilino-3-propyl-2-propanol, has also been reported.17
Some compounds with both chirality and a symmetric
element have been used as chiral catalysts in the Diels-Alder
reaction,18,19 ethylation of benzaldehyde,20 and addition reac-
tion of β-ketoester.21 Mechanistic studies of the asymmetric
synthesis process of some of these compounds have been
reported.22,23 Many studies have investigated the simulta-
neous application of cyclodextrins as a chiral selector and a
chiral catalyst.24,25 Many chiral symmetric compounds have
also been used as chiral catalysts18–23; it is assumed that
these compounds can also be used as powerful chiral selector
candidates.
C3 symmetric CSP in 1995.31 Tichy et al. reported a C2
symmetric CSP for the resolution of chiral amino alcohol de-
rivatives in 1994.32 In this study, a new (R)-phenylglycinol
N-1,3,5-benzenetricarboxylic acid-derived CSP (CSP 2) with
C3 symmetry was synthesized and used for the resolution
of various chiral samples. In addition, three C2 symmetric
CSPs were prepared by using both (R)-phenylglycinol and
o-, m-, and p-phthaloyl dichlorides. The previously reported
CSP 1 was also prepared for comparison with newly pre-
pared CSPs (CSP 2–5) using the same chiral samples under
the same separation conditions. Twenty-five chiral samples
(five π-basic, six π-acidic, and 14 antibiotic oxazolidinones)
were used in this study.
MATERIALS AND METHODS
General Methods
1H-NMR spectra were measured with a Bruker (Billerica, MA)
AVANCE digital 400 spectrometer (400 MHz). Elemental analysis
data were obtained using
a ThermoFisher (Waltham, MA) Flash
2000 Elemental analyzer. All reagents used in this study were pur-
chased from Tokyo Chemical Industry (Tokyo, Japan). The spherical
silica gel (5 μm) was purchased from Fuji Silysia Chemical (Tokyo,
Japan).
Preparation of CSP 2
N1,N3,N5-Tris(2-hydroxy-1-phenylethyl)benzene-1,3,5-
tricarboxamide (2a). Thionyl chloride (7.00 mmol) and 3 drops of
dimethylformamide (DMF) were gradually added to a stirred solution
of 1,3,5-benzenetricarboxylic acid (2.26 mmol) in 40 mL of tetrahydrofu-
ran (THF), and the mixture was refluxed for 18 h. After reaction, the
solvent and excess thionyl chloride in the reaction mixture were re-
moved by a rotary evaporator.33 The resulting product was gradually
1,3,5-Benzenetricarboxylic acid has been used as an impor-
tant cross-linker for fabricating metal-organic frameworks
(MOFs).26,27 Recently, we reported the preparation of some
chiral MOFs by using 1,3,5-benzenetricarboxylic acid as a
cross-linker and used them in chiral recognition tests.28–30
(R)-Phenylglycinol N-3,5-dinitrobenzoyl amide-derived CSP
(CSP 1) has been used in the resolution of various chiral
analytes with moderate efficiency.14,15 There are only two re-
ports related to symmetric CSPs. Gasparrini et al. reported
the chiral separation of several amino acid derivatives on a
© 2016 Wiley Periodicals, Inc.
*Correspondence to: Jae Jeong Ryoo, Department of Chemistry Education,
Kyungpook National University, Daegu 702-701, Korea. E-mail: jjryoo@knu.
ac.kr
Received for publication 21 October 2015; Accepted 3 December 2015
DOI: 10.1002/chir.22572
Published online 20 January 2016 in Wiley Online Library
(wileyonlinelibrary.com).

C2 AND C3 SYMMETRIC (R)-PHENYLGLYCINOL-DERIVED CSPS
187
added to a solution of (R)-phenylglycinol (1.76 mmol) and triethylamine
(1 mL) in 30 mL of methylene chloride at 0°C. The reaction mixture was
stirred at room temperature under nitrogen for 36 h, and then washed
successively with 1.2 N HCl and saturated NaHCO3. The solvent was re-
moved after drying over anhydrous MgSO4. The reaction mixture was
first dissolved in a solution of methanol and methylene chloride, and
then n-hexane was added to it. A white solid product was obtained, which
was recrystallized and dried in a vacuum oven. 2a; Yield 48.2%, 1H NMR
(DMSO-d6) δ: 3.63–3.67 (dd, 1H), 3.71–3.76 (dd, 1H), 5.07–5.12 (m, 2H),
7.21–7.25 (tt, 1H), 7.30–7.33 (t, 2H), 7.38–7.40 (d, 2H), 8.49 (s, 1H),
9.09–9.12 (d, 1H).
was stirred at reflux for 72 h. After cooling, the mixture was evaporated
under reduced pressure, and directly added to a flask containing 5-μm
silica gel (4.00 g) in 100 mL of toluene dehydrated by the Dean-Stark
trap. The mixture was heated to reflux for 72 h with stirring magneti-
cally. The modified silica gel was washed with toluene, methylene
chloride, ethyl acetate, ethyl alcohol, and ethyl ether, and then dried in
a vacuum oven.
Preparation of CSP 3–5
N,N-Bis((R)-2-hydroxy-1-phenylethyl)phthalamide (3a–5a). To
a stirred solution of each phthaloyl chloride (ortho-, meta-, para-; 3.21
mmol) and triethylamine (7.85 mmol), 30 mL of methylene chloride was
considerately added to a solution of (R)-phenylglycinol (7.14 mmol) in
70 mL of methylene chloride at 0°C. The reaction mixture was stirred
for 24 h and then washed with 1.2 N HCl and saturated NaHCO3. The
solvent was removed after drying over anhydrous MgSO4. The reaction
product was first dissolved in a small amount of the mixed solution of
N1,N3,N5-Tris(2-hydroxy-1-phenylethyl)benzene-1,3,5-tricarboxamide
(triethoxysilyl) propyl carbamate (2b) and CSP 2.
A solution of
3-(triethoxysilyl)propyl isocyanate (5.81 mmol), N1,N3,N5-tris(2-hydroxy-1-
phenylethyl)benzene-1,3,5-tricarboxamide (triethoxysilyl) propyl carba-
mate (1.76 mmol), and triethylamine (1 mL) in 100 mL of 1,4-dioxane
Fig. 1. Structure of racemic analytes investigated in this study.
Chirality DOI 10.1002/chir

188
YU ET AL.
Scheme 1. Synthetic procedures for CSP 2-5.
methanol and methylene chloride, and then n-hexane was added to the
solution. A white solid product appeared, which was recrystallized and
filtered and dried in a vacuum oven. 3a; Yield 69.0%, 1H NMR
(DMSO-d6) δ: 3.57–3.66 (m, 2H), 4.82–4.85 (t, 1H), 5.00–5.06 (q, 1H),
7.22–7.25 (tt, 1H), 7.28–7.32 (tt, 2H), 7.38–7.40 (d, 2H), 7.52–7.55
(m, 1H), 7.56–7.59 (m, 1H), 8.70–8.72 (d, 1H).4a; Yield 64.5%, 1H
NMR (DMSO-d6) δ: 3.65–3.78 (m, 4H), 4.97–5.00 (t, 2H), 5.01–5.13
(td, 2H), 7.22–7.26 (tt, 2H), 7.30–7.35 (t, 4H), 7.40–7.42 (d, 4H),
7.57–7.61 (t, 1H), 8.04–8.06 (dd, 2H), 8.40–8.41 (s, 1H), 8.88–8.90
(d, 2H). 5a; Yield 69.0%, 1H NMR (DMSO-d6) δ: 3.64–3.77 (m, 2H),
4.97–5.00 (t, 1H), 5.06–5.12 (m, 1H), 7.22–7.26 (tt, 1H), 7.31–7.35
(t, 2H), 7.40–7.41 (d, 2H), 8.00 (s, 2H), 8.85–8.86 (d, 1H).
N,N-Bis((R)-2-hydroxy-1-phenylethyl)phthalamide (triethoxysilyl)
propylcarbamate (3b–5b). A solution of 3-(triethoxysily)propyl isocya-
nate (2.48 mmol), (N,N-bis((R)-2-hydroxy-1-phenylethyl)phthalamide
(3a–5a) (5.46 mmol), and triethylamine (5.46 mmol) in 100 mL of
1,4-dioxane was stirred at reflux for 72 h. After cooling, the mixture was
evaporated under reduced pressure, and directly added to a flask contain-
ing 5-μm silica gel (4.00 g) in 100 mL of toluene dehydrated by the
Chirality DOI 10.1002/chir

C2 AND C3 SYMMETRIC (R)-PHENYLGLYCINOL-DERIVED CSPS
189
TABLE 1. Elemental analysis of chiral stationary phases
(CSPs)
The obtained compounds were identified by comparing the
obtained NMR data with those of previously prepared similar
compounds. Elemental analyses were carried out to deter-
mine the extent of bonding between chiral selectors and the
silica gel; the results are shown in Table 1.
As shown in Table 1, silica gel in CSP 2 and CSP 3
contained more than 0.1 mmol/g of chiral selectors, whereas
CSP 4 and CSP 5 contained only 0.02–0.04 mmol/g. Even
though we conducted additional synthetic experiments for
CSP 4 and CSP 5, the extent of covalent binding ratio between
each chiral selector to silica gel did not increase. It is believed
that the low covalent binding ratio was caused by the low
solubility of the precursors of CSP 4 and CSP 5.
C (%)
N (%)
Based on C
Based on N
CSP 1
CSP 2
CSP 3
CSP 4
CSP 5
2.055
12.65
6.156
2.173
0.959
0.528
1.679
0.923
0.380
0.111
0.086 mmol/g
0.167 mmol/g
0.122 mmol/g
0.043 mmol/g
0.019 mmol/g
0.094 mmol/g
0.200 mmol/g
0.165 mmol/g
0.068 mmol/g
0.020 mmol/g
Dean-Stark trap. The mixture was heated to reflux for 72 h with stirring
magnetically. The modified silica gel was washed with toluene, methy-
lene chloride, ethyl acetate, ethyl alcohol, and ethyl ether, and dried in
a vacuum oven.
Several chromatograms for the resolution of the first sample,
6,6′-dibromo-1,1′-bi-2-naphthol (S1), on CSP 1–5 are shown in
Figure 2. S1 separated on CSP 2 and CSP 3, but not on others.
Analyses were performed with the remaining 24 samples,
and the results are shown in Table 2.
Chromatography
The HPLC system comprised a Waters 2690 Separation Module, which
consists of a Waters 996 photodiode array detector and an auto sampler
(Waters, Milford, MA). HPLC-grade solvents were obtained from J.T.
Baker (Phillipsburg, NJ). The mobile phase consisted of 2-propanol:
n-hexane (10:90) and 2-propanol:n-hexane:trifluoroacetic acid (10:90:0.1)
at a flow rate of 1.2 mL/min. Twenty-five samples (S1–S25) were used
in this study. Samples S1–S5 are π-basic, samples S6–S11 are π-acidic
amino acid derivatives, and samples S12–S25 are oxazolidinone series
of chiral medicines. The sample structures are shown in Figure 1. The
chiral samples were purchased from Sigma-Aldrich (Seoul, Korea) and
Tokyo Chemical Industry (Tokyo, Japan). The sample structures are
shown in Figure 1.
It was expected that π-acidic CSP 1 would perform better
than the others in the resolution of the π-basic chiral samples
(S1–S5). However, all of the π-basic chiral samples separated
on CSP 2, but only two (S4, S5) separated on π-acidic CSP 1,
one each on CSP 4 and CSP 5, and none on CSP 3. Therefore,
some structural interactions occur between CSP 2 and S1–S5
that are more important than the general face-to-face π–π
interactions between π-acidic CSP and π-basic samples.
In the chiral resolution of the π-acidic amino acid deriva-
tives (S6–S11) on CSP 1–5, S9–S11 separated on both CSP 1
and CSP 2, but only S8 separated on CSP 3, and none on
CSP 4 and CSP 5. CSP 1 showed a slightly better resolution
from the selectivity point of view than CSP 2 for the separa-
tion of S9–S11, which have a phenyl group in common.
In the case of 14 oxazolidinone samples (S12–S25), three
samples (S20, S21, and S24) resolved on CSP 1, six (S13,
S14, S18, S21, S23, S24, and S25) on CSP 2, only S12 on
CSP 3, and S16 and S22 on CSP 4 and CSP 5, respectively.
Chiral separation results on CSP 2 are much better than those
on CSP 1 and are slightly worse than those obtained with the
RESULTS AND DISCUSSION
Synthetic procedures for CSP 2–5 are shown in Scheme 1.
CSP 1 was prepared using a previously reported method.15
The synthesis of CSP 2 includes four steps, including acyla-
tion, whereas the synthesis of CSP 3–5 requires only three
steps. All products (2b, 3a, 4a, and 5a) were in the form
of a white solid, with very poor solubility in all solvents except
for DMF and DMSO. Because of the poor solubility, the
product yields were low.
Fig. 2. Representative chromatograms of 6,6′-dibromo-1,1′-bi-2-naphthol (S1) on (a) CSP 1, (b) CSP 2, (c) CSP 3, (d) CSP 4, and (e) CSP 5 (CSP: chiral stationary
phase).
Chirality DOI 10.1002/chir

190
YU ET AL.
TABLE 2. Resolution of chiral samples on chiral stationary phases (CSPs)
CSP 1
CSP 2
CSP 3
CSP 4
CSP 5
Sample
k1
α
k1
α
k1
α
k1
α
k1
α
No.b
π-Basic compounds
S1
S2
S3
S4
S5
S6
S7
S8
1.35
1.08
1.07
2.56
0.82
0.95
0.97
1.64
2.52
3.32
2.26
5.19
5.20
9.49
7.60
9.14
4.82
1.00
1.00
1.00
1.08
1.16
1.00
1.00
1.00
1.47
1.16
1.14
1.00
1.00
1.00
1.00
1.00
1.00
1.00
1.00
1.16
1.11
1.00
1.00
1.10
1.00
9.53a
6.47a
3.16
1.17a
1.13a
1.10
5.31
3.66
1.62
4.83
2.51
2.16
2.16
3.85
6.57
2.90
6.52
2.81a
5.90a
5.35a
5.31a
3.35a
5.93a
5.44a
5.90a
2.87a
5.93a
5.53a
1.44
3.07a
3.86a
3
1.03
1.00
1.00
1.00
1.00
1.00
1.00
1.02
5.04
3.49
1.78
1.74
3.06
1.70
1.71
2.82
3.35
4.57
3.62
2.26
4.72
4.10
3.52
2.30
5.40
5.42
4.74
5.90
3.23
2.32
3.80
ND
1.00
1.17
1.00
1.00
1.00
1.00
1.00
1.00
1.00
1.00
1.00
1.00
1.00
1.00
1.00
1.04
1.00
1.00
1.00
1.00
1.00
1.04
1.00
ND
2.06
1.70
1.48
2.77
1.50
1.54
1.58
2.46
2.74
3.56
2.92
2.02
4.47
3.83
3.02
2.00
4.48
4.55
4.49
4.00
2.96
2.26
3.23
ND
1.00
1.00
1.00
1.00
1.00
1.00
1.00
1.00
1.00
1.00
1.00
1.00
1.00
1.00
1.00
1.02
1.00
1.00
1.00
1.00
1.00
1.03
1.00
ND
2
2
1
2
2
0
0
1
2
2
2
1
1
1
0
2
0
1
0
1
2
2
1
2
1
31
8.70a
3.34a
4.34a
4.28a
4.52a
9.64
1.07a
1.07a
1.00a
1.00a
1.00a
1.06
π-Acidic compounds
S9
1.00
1.00
1.00
S10
S11
S12
S13
S14
S15
S16
S17
S18
S19
S20
S21
S22
S23
S24
S25
9.89
1.11
7.57
1.06
Oxazolidinone
6.58a
8.67a
6.21
1.00a
1.03a
1.03
1.02a
1.00a
1.00a
1.00a
1.00a
1.00a
1.00a
1.00a
1.00a
1.00a
1.00a
1.00
2.21a
5.76a
7.01a
4.44a
4.00a
6.78a
7.95
1.00a
1.00a
1.00a
1.14a
1.00a
1.00a
1.17
15.4
2.29
4.64
9.25
2.23
5.76
9.05
8.08
7.26
1.00
1.11
1.11
1.11
16.2
16.7
26.5
8
1.00a
1.00a
2.13
3
1.00
1.79
2
1.00
No.c
15
Detection at 210–400 nm; flow rate, 1.2 mL/min; eluent, IPA:n-hexane = 10:90.
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cNumber of separated samples.
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A C3 symmetric (R)-phenylglycinol N-1,3,5-benzenetricar-
boxylic acid-derived chiral stationary phase (CSP 2) and three
C2 symmetric (R)-phenylglycinol CSPs (CSP 3–5) prepared
with o-, m-, p-phthaloyl dichlorides were synthesized to com-
pare the resolution of 25 chiral samples with a previously
reported 3,5-dinitrobenzoyl (R)-phenylglycinol-derived CSP
(CSP 1). Eight enantiomeric samples were separated on
CSP 1, 15 on CSP 2, 3 on CSP 3 and CSP 4 each, and 2 on
CSP 5. Even though all CSPs have the same chiral moiety,
C3 symmetric CSP 2 showed the best resolution among all
the 25 chiral samples. It is believed that a structural
interaction derived from the C3 symmetry led to an additional
interaction between the CSP and chiral samples, which in
turn led to improved resolution. Chiral symmetric CSPs
should be further investigated to understand their properties.
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Chirality DOI 10.1002/chir