Preparation of a New Chiral Stationary Phase Based on Macrocyclic Amide Chiral Selector for the Liquid Chromatographic Chiral Separations

Article abstract of DOI:10.1002/chir.22569

A new chiral stationary phase (CSP) based on macrocyclic amide receptor was prepared starting from (1R,2R)-1,2-diphenylethylenediamine. The new CSP was successfully applied to the resolution of various N-(substituted benzoyl)-α-amino amides with reasonably good separation factors and resolutions (α = 1.75 ~ 2.97 and R_S = 2.89 ~ 6.82 for 16 analytes). The new CSP was also applied to the resolution of 3-substituted 1,4-benzodiazepin-2-ones and some diuretic chiral drugs including bendroflumethiazide and methylchlothiazide and metolazone. The resolution results for 3-substituted 1,4-benzodiazepin-2-ones and some diuretic chiral drugs were also reasonably good. Chirality 28:253-258, 2016.

Full text of DOI:10.1002/chir.22569

CHIRALITY 28:253–258 (2016)
Preparation of a New Chiral Stationary Phase Based on Macrocyclic
Amide Chiral Selector for the Liquid Chromatographic Chiral
Separations
*
JI YEONG SUNG, SEUNG HYUCK CHOI, AND MYUNG HO HYUN
Department of Chemistry, Pusan National University, Busan, Republic of Korea
ABSTRACT
A new chiral stationary phase (CSP) based on macrocyclic amide receptor was
prepared starting from (1R,2R)-1,2-diphenylethylenediamine. The new CSP was successfully
applied to the resolution of various N-(substituted benzoyl)-α-amino amides with reasonably
good separation factors and resolutions (α = 1.75 ~ 2.97 and RS = 2.89 ~ 6.82 for 16 analytes). The
new CSP was also applied to the resolution of 3-substituted 1,4-benzodiazepin-2-ones and some
diuretic chiral drugs including bendroflumethiazide and methylchlothiazide and metolazone.
The resolution results for 3-substituted 1,4-benzodiazepin-2-ones and some diuretic chiral drugs
were also reasonably good. Chirality 28:253–258, 2016. © 2016 Wiley Periodicals, Inc.
KEY WORDS: chiral stationary phase; enantiomer separation; liquid chromatography; macrocyclic
amide chiral selector
1 (2.32 g, 88% yield). 1H NMR (CDCl3) (ppm) 1.83–1.99 (m, 2H),
2.20–2.30 (m, 2H), 3.93 (s, 6H), 4.04 (t, 2H), 4.98–5.11 (m, 2H), 5.75–5.95
(m, 1H), 7.73 (s, 2H), 8.25 (s, 1H).
Liquid chromatographic chiral stationary phases (CSPs)
have attracted quite a lot of attention because CSPs can be
used in the preparative-scale separation of the two enantio-
mers and in the exact determination of the enantiomeric com-
position of chiral compounds in a very accurate, convenient,
and cost-effective way.1–3 Various liquid chromatographic
CSPs have been developed by bonding appropriate chiral se-
lectors to column supporting materials. For example, polysac-
charide derivatives,4,5 macrocyclic antibiotics,6,7 macrocyclic
oligosaccharides,8 chiral crown ethers,9–14 proteins,15 and
other chiral molecules16,17 bonded to silica gel have been
used as liquid chromatographic CSPs.
Macrocyclic amide chiral selectors bonded to silica gel
have also been used as liquid chromatographic CSPs. In
particular, a CSP based on a macrocyclic amide receptor
prepared from (1R,2R)-1,2-diphenylethylenediamine and
5-allyloxyisophthalic acid was very successful in the resolution
of N-3,5-dinitrobenzoyl amino acid amides and some other
racemic compounds.18 Another CSP based on a macrocyclic
amide receptor prepared from bi-β-naphthol was also utilized
for the resolution of some racemic compounds.19 We also have
been interested in the development of CSPs based on a macro-
cyclic amide receptor. In this study we report the preparation of
a new CSP (CSP 1, Fig. 1) based on a macrocyclic amide recep-
tor prepared from (1R,2R)-1,2-diphenylethylenediamine and its
application to the resolution of some chiral compounds.
5-(4-Pentenyloxy)isophthalic Acid 2. Compound 1 (2.0 g, 7.2
mmole) was added to 1 M KOH solution of methanol (100 ml) in
250 ml round bottom flask. The mixture was heated to reflux for
5 h. After cooling the reaction mixture, methanol was removed by
using a rotary evaporator. The residue was dissolved in ethyl ace-
tate and then the solution was treated with 1 N HCl solution. The
separated organic solution was dried over anhydrous Na2SO4 and
then solvent was removed by using a rotary evaporator to afford
5-(4-pentenyloxy)isophthalic acid 2 (1.78 g, 99% yield). 1H NMR
(Acetone d6) (ppm) 1.88–1.98 (m, 2H), 2.24–2.34 (m, 2H), 4.16
(t, 2H), 4.97–5.11 (m, 2H), 5.84–5.98 (m, 1H), 7.77 (s, 2H), 8.28
(s, 1H), 11.03 (broad s, 2H).
N-t-Boc-(1R,2R)-Diphenylethylenediamine 3. (1R,2R)-1,2-Diphe-
nylethylenediamine (0.5 g, 2.4 mmole) was dissolved in chloroform
(40 ml). To the stirred solution was added di-tert-butyl dicarbonate
(0.54 ml, 2.4 mmole) through a dropping funnel slowly for 1 h at 0 °C
and then the whole mixture was stirred for 4 h at 0 °C. To the reaction
mixture was added saturated NaHCO3 solution. After shaking well, the
organic layer was separated and then dried over anhydrous Na2SO4. Sol-
vent was removed by using a rotary evaporator. The residue was purified
by flash column chromatography on silica gel (ethyl acetate/hexane/
methanol: 1/3/0.1) to afford compound 3 (0.36 g, 48% yield). 1H NMR
(CDCl3) (ppm) 1.32 (s, 9H), 4.34 (s, 1H), 4.84 (s, 1H), 5.76 (s, 1H),
7.21–7.38 (m, 10H).
Preparation of Compound 4. The mixture of 5-(4-pentenyloxy)isophthalic
acid 2 (1.50 g, 6.0 mmole) and thionyl chloride (20 ml) in 100 ml
round bottom flask was heated to reflux for 6 h under an argon
atmosphere. Excess thionyl chloride was removed by using a rotary
evaporator and then the residue was dissolved in methylene
chloride (50 mL). The methylene chloride solution was slowly
added through a cannula to another methylene chloride solution
(90 ml) containing N-t-Boc-(1R,2R)-diphenylethylenediamine 3 (3.74 g, 12.0
mmole) and triethylamine (1.82 ml, 13.2 mmole) in 250 ml round
bottom flask at –78 °C. The whole mixture was stirred at –78 °C
MATERIALS AND METHODS
Preparation of CSP 1 and Column Packing
CSP 1 was prepared according to the scheme shown in Figure 1.
Dimethyl 5-(4-Pentenyloxy)isophthlatae 1. Dimethyl 5-hydroxy-
isophthalate (2.0 g, 9.5 mmole) was dissolved in acetonitrile (100 ml) in
a 250 ml round bottom flask. To the solution was added K2CO3 (2.0 g,
14.5 mmole). After stirring the solution for 30 min, 5-bromo-1-petene
(1.35 ml, 11.4 mmole) was added. The whole mixture was heated to reflux
for 5 h. After cooling the solution, acetonitrile was removed by using a ro-
tary evaporator. The residue was dissolved in dichloromethane and then
the solution was washed with 1 N NaOH solution. The organic solution
was dried over anhydrous Na2SO4 and then solvent was removed by
using a rotary evaporator to afford dimethyl 5-(4-pentenyloxy)isophthalate
*Correspondence to: M.H. Hyun, Department of Chemistry, Pusan National
University, Busan 609-735, Republic of Korea. E-mail: mhhyun@pusan.ac.kr
Received for publication 6 October 2015; Accepted 20 November 2015
DOI: 10.1002/chir.22569
Published online 4 January 2016 in Wiley Online Library
(wileyonlinelibrary.com).
© 2016 Wiley Periodicals, Inc.

254
SUNG ET AL.
Fig. 1. Scheme for the synthesis of CSP 1. a) 5-Bromo-1-pentene, K2CO3, acetonitrile, reflux. b) KOH, methanol, reflux. c) Di-tert-butyl dicarbonate, CHCl3,
0 °C. d) (1) SOCl2, reflux. (2) Compound 3, triethylamine, methylene chloride, –78 °C and then 0 °C. e) (1) CF3COOH, methylene chloride. (2) Isophthaloyl
chloride, N,N-diisopropylethylamine, tetrahydrofuran (THF), 0 °C and then room temperature. f) (1) Trichlorosilane, Pt/C (10 wt%), methylene chloride,
toluene. (2) Ethanol/triethylamine (1:1, v/v), methylene chloride. (3) Silica gel, toluene, Dean-Stark trap.
for 1 h and then at 0 °C for 10 h. The reaction mixture was washed with
1 N HCl solution and then with 1 N NaOH solution. Finally, the organic
solution was dried over anhydrous Na2SO4. Solvent was removed by
using a rotary evaporator. The residue was purified by flash column
chromatography on silica gel (ethyl acetate/hexane: 1/3) to afford
compound 4 (2.67 g, 53% yield). 1H NMR (DMSO d6) (ppm) 1.23
(s, 18H), 1.81–1.89 (m, 2H), 2.17–2.24 (m, 2H), 3.99–4.03 (m, 2H),
4.98-5.02 (m, 2H), 5.03–5.16 (m, 2H), 5.45–5.51 (m, 2H), 5.80-5.92
(m, 1H), 7.10–7.36 (m, 22 H), 7.64–7.71 (m, 3H), 8.78 (d, 2H).
was dissolve in methylene chloride. The methylene chloride solution
was washed with 1 N HCl solution and 1 N NaOH solution. The organic
solution was dried over anhydrous Na2SO4. Solvent was removed by
using a rotary evaporator. The residue was purified by flash column
chromatography on silica gel (ethyl acetate/hexane, 1/3, v/v) to afford
compound 5 (1.50 g, 65% yield). 1H NMR (acetone d6) (ppm) 1.76–1.83
(m, 2H), 2.12–2.19 (m, 2H), 3.94–4.05 (m, 2H), 4.89–5.02 (m, 2H),
5.61–5.69 (m, 4H), 5.77-5.87 (s, 1H), 7.17–7.47 (m, 23 H), 7.86–7.89
(m, 2H), 8.20 (s, 1H), 8.58–8.65 (m, 5H).
Preparation of Compound 5. Compound 4 (2.5 g, 3.0 mmole)
was dissolved in methylene chloride (80 ml). To the stirred solution was
added trifluoroacetic acid (2.23 ml, 30 mmole). The whole mixture was
stirred at room temperature for 3 h. Solvent and trifluoroacetic acid were
removed by using a rotary evaporator. The residue was dissolved in
methylene chloride and then the solution was washed with 1 N NaOH
solution. The organic solution was dried over anhydrous Na2SO4. Solvent
was removed by using a rotary evaporator to afford corresponding di-
amine compound, N1,N3-bis((1R,2R)-2-amino-1,2-diphenylethyl)-5-(pent-
4-en-1-yloxy)isophthalamide. Without further purification, the diamine
compound was dissolved in tetrahydrofuran (THF) (300 ml). To the solu-
tion was added N,N-diisopropylethylamine (1.15 ml, 6.6 mmole). The
whole mixture was stirred for 30 min at 0 °C under an argon atmosphere.
To the stirred solution was added a solution of isophthaloyl chloride
(0.63 g, 3.1 mmole) in THF (30 ml) through a cannula at 0 °C. The reac-
tion mixture was stirred at room temperature for 24 h. The reaction
mixture was concentrated by using a rotary evaporator. The residue
Preparation of CSP 1 and Column Packing. Compound 5 (1.40 g,
1.8 mmole) was dissolved in the mixed solvent of methylene chloride
(20 ml) and toluene (10 ml) in a 100 ml two neck round bottom flask. To
the solution was added platinum on activated carbon (Pt/C, 10 wt%)
(10 mg). The heterogeneous solution was stirred for 30 min and then
tricholosilane (20 ml) was added. The whole mixture was stirred for
30 h in an oil bath maintained at 80 °C. After cooling, solvent and excess
trichlorosilane were removed by using a rotary evaporator. The residue
was dissolved in methylene chloride (20 ml). To the solution was slowly
added 10 mL of the mixed solvent of ethyl alcohol and triethylamine
(10 ml, 1:1, v/v) at 0 °C. The whole mixture was stirred at room
temperature for 30 min and then evaporated. The residue was purified
by flash column chromatography on silica gel (ethyl acetate/hexane,
1/3, v/v) to afford triethoxysilyl compound (1.18 g, 70%). 1H NMR
(CDCl3) (ppm) 0.54–0.60 (m, 2H), 1.13 (t, 9H), 1.35–2.02 (m, 6H), 3.73
(q, 6H), 3.82–3.90 (m, 2H), 5.52–5.56 (m, 4H), 7.00 (s, 2H), 7.19–7.31
(m, 20 H), 7.46-7.49 (m, 2H), 7.68 (s, 1H), 8.15 (s, 1H), 8.34–8.42 (m, 5H).
Chirality DOI 10.1002/chir

NEW CSP BASED ON MACROCYCLIC AMIDE CHIRAL SELECTOR
255
For the preparation of CSP 1, Kromasil silica gel (4.2 g, 5 μm, 100 Å) avail-
able from Eka Chemicals was added to toluene (100 ml) in a 250 ml flask
equipped with a Dean-Stark trap, a condenser, and a magnetic stirring
bar. The mixture was heated to reflux until the complete azeotropic re-
moval of water. After cooling, triethoxysilyl compound (1.10 g, 1.2 mmole)
dissolved in toluene (10 ml) was added. The whole mixture was heated to
reflux for 72 h. After cooling, the modified silica gel (CSP 1) was filtered
and then washed successively with toluene, methanol, acetone, ethyl
acetate, methylene chloride, hexane, and diethyl ether. Elemental
analysis of CSP 1 (Found: C, 7.31%; H, 1.44%; N, 0.59%) showed a
loading of 0.12 mmole of selector (based on C) or 0.11 mmole of
selector (based on N) per gram of stationary phase. CSP 1 thus
prepared was slurried in methanol and packed into a 250 x 4.6 mm I.
D. stainless-steel HPLC column using a conventional slurry packing
method with an Alltech slurry packer.
first, CSP 1 was applied to the resolution of various
N-(substituted benzoyl)-α-amino amides 6 with the use of
20% 2-propanol in hexane as an optimized mobile phase. In
the resolution of secondary amide derivatives of N-(3,5-
dinitrobenzoyl)leucine (analytes 6a–6 h in Table 1) on CSP
1, the retention factors (k1) for the first eluted enantiomers
decreased continuously as the amide alkyl group (R2 in
Table 1) of analytes increased in length. As the length of
the amide alkyl group of analytes is increased, the interaction
between the analyte and the CSP decrease and, conse-
quently, the retention of analytes should decrease. However,
the separation factors (α) and resolutions (RS) were found to
show the maximum values when the amide alkyl group (R2
group in Table 1) is the propyl group, indicating the optimum
length of the amide alkyl group is the three methylene unit.
Other N-(3,5-dinitrobenzoyl)-α-amino n-propyl amides includ-
ing valine derivative (analyte 6 m in Table 1), phenylglycine
derivative (analyte 6n in Table 1), phenylalanine derivative
(analyte 6o in Table 1), and tyrosine derivative (analyte 6p
in Table 1) were resolved very well.
In order to see the role of the N-H hydrogen of the second-
ary amide group of analytes in the chiral recognition, the N-H
hydrogen was replaced with n-hexyl or phenyl group and the
resulting tertiary amides were resolved on CSP 1. As shown
in Table 1, N-(3,5-dinitrobenzoyl)leucine N-hexyl N-propyl
amide (analyte 6i in Table 1) and N-(3,5-dinitrobenzoyl)leucine
N-hexyl N-phenyl amide (analyte 6j in Table 1) were resolved
very well on CSP 1 with similar separation factor for analyte
6i or even better separation factor for analyte 6j. These results
indicate that the N-H hydrogen of the secondary amide group
of analytes does not play any role in the chiral recognition. By
replacing the N-H hydrogen of the secondary amide group of
analytes with hexyl or phenyl group, the resolution (RS) is in-
creased quite a lot. While the N-H hydrogen of the secondary
amide group of analytes does not play any role in the chiral rec-
ognition, it seems to improve only the affinity for the stationary
phase and, consequently, leads to peak broadening. However,
tertiary amides of N-(3,5-dinitrobenzoyl)leucine seem to mini-
mize the peak broadening. In this instance, the resolution
(RS) should be increased.
Chromatography
An HPLC system consisting of a Waters model 515 HPLC pump
(Milford, MA), a Rheodyne model 7125 injector (Rohnert Park, CA)
with a 20 μl sample loop, a Waters 2487 tunable absorbance detector
and a YoungLin Autochro data module (Software: YoungLin Autochro-
WIN 2.0 plus) was used for the liquid chromatography. The chiral col-
umn temperature was controlled by using a JEIO TECH VTRC-620
cooling circulator (Daejeon, Korea).
N-(Substituted benzoyl)-α-amino amides 6 (Fig. 2) used as analytes
were prepared by treating N-(substituted benzoyl)-α-amino acids
suspended in methylene chloride with the appropriate alkylamine in the
presence of 1-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ) at
room temperature as described in the previous report.20 N-(Substituted
benzoyl)-α-amino acids were prepared by treating substituted benzoyl
chloride with α-amino acids in the presence of propylene oxide in THF
at room temperature, as reported.21 3-Substituted 1,4-benzodiazepin-
2-ones 7 and 8 (Fig. 2) prepared by coupling o-aminobenzophenones
with N-t-Boc-α-amino acids followed by deprotection and cyclization in
the presence of trifluoroacetic acid via the known procedure22 were avail-
able from a prior study.23 Other analytes including bendroflumethiazide
(9, Fig. 2), methylchlothiazide (10, Fig. 2) and metolazone (11, Fig. 2)
are available commercially from Alfa Chemistry (Stony Brook, NY) or Ad-
vanced Technology & Industrial Co. (Hong Kong), but the actual samples
were available from a prior study24 or from laboratory stock. Injection
samples were prepared by dissolving each analyte in methanol at a con-
centration of 1.0 mg/mL and an injection volume was typically 2.0 μl.
RESULTS AND DISCUSSION
The role of the N-(3,5-dinitrobenzoyl) group of analytes in
the chiral recognition was also checked by resolving N-(3,5-
dimethylbenzoyl)leucine n-propyl amide (analyte 6 k in
Table 1) and N-(3,5-dimethoxybenzoyl)leucine n-propyl
CSP 1 contains hydrogen-bonding donor and acceptor sites
and aromatic π–π interaction sites. Consequently, CSP 1 is ex-
pected to be able to resolve various racemic compounds. At
Fig. 2. Structures of N-(substituted benzoyl)-α-amino amides (6), 3-substituted 1,4-benzodiazepin-2-ones (7 and 8), bendroflumethiazide (9), methylchlothiazide
(10), and metolazone (11).
Chirality DOI 10.1002/chir

256
SUNG ET AL.
TABLE 1. Resolution of N-(substituted benzoyl)-α-amino amides 6 on CSP 1a
Anal.
R1
R2
R3
R4
k1
α
RS
6a
6b
6c
6d
6e
6f
(CH3)2CHCH2
(CH3)2CHCH2
(CH3)2CHCH2
(CH3)2CHCH2
(CH3)2CHCH2
(CH3)2CHCH2
(CH3)2CHCH2
(CH3)2CHCH2
(CH3)2CHCH2
(CH3)2CHCH2
(CH3)2CHCH2
(CH3)2CHCH2
(CH3)2CH
CH3
CH2CH3
H
H
H
H
H
H
H
H
NO2
NO2
NO2
NO2
NO2
NO2
NO2
NO2
NO2
NO2
CH3
OCH3
NO2
NO2
NO2
NO2
1.46 (D)
1.45 (D)
0.89 (D)
0.82 (D)
0.78 (D)
0.77 (D)
0.75 (D)
0.71 (D)
0.93 (D)
0.46 (D)
0.29 (D)
0.74 (D)
0.91 (D)
1.96 (D)
1.53 (D)
2.85 (D)
1.94
1.94
2.04
1.89
1.76
1.75
1.79
1.79
1.78
2.63
2.29
2.66
1.76
1.67
1.71
2.97
3.26
3.52
3.85
3.69
3.62
3.32
2.89
2.95
5.04
6.82
3.88
4.74
3.25
2.97
3.21
4.56
(CH2)2CH3
(CH2)3CH3
(CH2)4CH3
(CH2)5CH3
(CH2)6CH3
(CH2)7CH3
(CH2)2CH3
(CH2)2CH3
(CH2)2CH3
(CH2)2CH3
(CH2)2CH3
(CH2)2CH3
(CH2)2CH3
(CH2)2CH3
6 g
6 h
6i
(CH2)5CH3
C6H5
H
H
H
H
H
H
6j
6 k
6 l
6 m
6n
6o
6p
C6H5
(C6H5)CH2
4-OH(C6H5)CH2
aMobile phase: 20% 2-propanol in hexane. Flow rate: 1.0 ml/min. Detection: 254 nm UV. Temperature: 20 °C. Column size: 250 x 4.6 mm I.D. k1: Retention factor of
the first eluted enantiomer. In the parentheses, the absolute configuration of the first eluted enantiomer is presented. α: Separation factor. RS: Resolution.
amide (analyte 6 l in Table 1) on CSP 1. The separation fac-
tors and resolutions for 6 k and 6 l were even greater than
those for 6c. These results indicate that the π–π interaction
between the electron-rich N-(3,5-dimethylbenzoyl) or N-(3,5-
dimethoxybenzoyl) group of analyte and the aromatic group
of the CSP is more significant than that between the
electron-deficient N-(3,5-dinitrobenzoyl) group of analyte
and the aromatic group of the CSP. Consequently, the
isophthalamide group of the CSP instead of the phenyl group
is expected to be involved in the chiral recognition as an aro-
matic π–π interaction site.
3-Substituted 1,4-benzodiazepin-2-ones such as camazepam,
lorazepam, lormetazepam, and oxazepam have been widely
used as anxiolytics and/or tranquilizers and their two enantio-
mers have been known to show different pharmaceutical
activity.25 In this instance, the exact determination of the
enantiomeric composition of 3-substituted 1,4-benzodiazepin-
2-ones is important. Previously, Pirkle-type CSPs have been
successfully used for the resolution of 3-substituted 1,4-
benzodiazepin-2-ones.23,26 However, CSPs based on macrocy-
clic amide chiral selectors have not been used. In this study,
CSP 1 was successfully applied to the resolution of racemic
3-substituted 1,4-benzodiazepin-2-ones. For the resolution of
racemic 3-substituted 1,4-benzodiazepin-2-ones 7 and 8 on
CSP 1, we tested 20%, 10%, and 5% 2-propanol in hexane as a
mobile phase. As an example, Figure 3 shows the representa-
tive chromatograms for the resolution of analytes 7c and 8c
on CSP 1 with the variation of the content of 2-propanol in hex-
ane in the mobile phase. As the content of 2-propanol in hex-
ane increased from 5% to 10% and then to 20%, the retention
factors were found to decrease significantly. The separation
factors (α) were found to decrease slightly as the content of
Fig. 3. Chromatograms for the resolution of 3-substituted 1,4-
2-propanol in hexane increased from 5% to 10% and then to
benzodiazepin-2-ones 7c (a) and 8c (b). Mobile phase: 5%, 10% and 20%
20%, but the resolutions were found to show the maximum
value when 10% 2-propanol in hexane was used as a mobile
phase. The chromatographic results for the resolution of race-
mic 3-substituted 1,4-benzodiazepin-2-ones 7 and 8 on CSP 1
with the use of 10% 2-propanol in hexane as a mobile phase are
summarized in Table 2. In every case, type 8 analytes contain-
ing chloride-substituted benzo ring were found to show higher
Chirality DOI 10.1002/chir
2-propanol in hexane. Flow rate: 1.0 ml/min. Detection: 254 nm UV. Tem-
perature: 20 °C.
separation factors and resolutions than the corresponding
type 7 analytes containing nonsubstituted benzo ring, but
the reason is not clear yet.

NEW CSP BASED ON MACROCYCLIC AMIDE CHIRAL SELECTOR
257
RS
TABLE 2. Resolution of 3-substituted 1,4-benzodiazepin-2-ones 7 and 8 on CSP 1a
Entry
R
k1
k2
α
7a
7b
7c
7d
7e
7f
8a
8b
8c
8d
8e
8f
CH3
3.13 (S)
2.42 (S)
3.25 (S)
2.16 (S)
2.26 (S)
2.86 (S)
2.56 (S)
1.89 (S)
2.82 (S)
1.83 (S)
1.91 (S)
2.46 (S)
3.51 (R)
2.73 (R)
4.45 (R)
2.31 (R)
2.55 (R)
3.75 (R)
3.15 (R)
2.15 (R)
4.23 (R)
1.92 (R)
2.29 (R)
3.99 (R)
1.12
1.13
1.37
1.07
1.13
1.31
1.23
1.14
1.50
1.15
1.20
1.62
1.57
0.94
3.33
0.87
1.73
2.41
2.15
1.50
4.61
1.06
2.81
4.70
(CH2)3CH3
(CH2)2SCH3
CH(CH3)2
CH2CH(CH3)2
CH2C6H5
CH3
(CH2)3CH3
(CH2)2SCH3
CH(CH3)2
CH2CH(CH3)2
CH2C6H5
aMobile phase: 10% 2-propanol in hexane. Flow rate: 1.0 ml/min. Detection: 254 nm UV. Temperature: 20 °C. Column size: 250 x 4.6 mm I.D. k1 and k2: Retention
factor of the first and second eluted enantiomer, respectively. In the parentheses, the absolute configuration is presented. α: Separation factor. RS: Resolution.
As another example for the application of CSP 1, chiral drugs
including thiazide diuretics such as bendroflumethiazide
(9) and methylchlothiazide (10) and thiazide-like diuretic
metolazone (11), were resolved on CSP 1. Even though
the two enantiomers of thiazide diuretics have been known
to show different biological activity,27 their chiral
separations on CSPs are not common. Previously, only
Pirkle-type CSPs have been utilized for the separation of
the enantiomers of thiazide diuretics.28,29 However, CSP
1 was found to be also successful for the resolution of
thiazide diuretics. The chromatograms for the resolution
of bendroflumethiazide (9) and methylchlothiazide (10) and
thiazide-like diuretic metolazone (11) on CSP 1 are presented
in Figure 4. Bendroflumethiazide (9) was resolved quite well
with a separation factor of 1.34 and resolution of 2.70 when
20% isopropanol in hexane was used as a mobile phase. Under
identical chromatographic conditions, methylchlothiazide
(10) was also found to be baseline resolved with a separation
factor of 1.20 and resolution of 1.50. However, metolazone
(11) was resolved only slightly, with a separation factor of
1.14 and resolution of 0.84.
CONCLUSION
A new CSP (CSP 1) based on macrocyclic amide receptor
prepared from (1R,2R)-1,2-diphenylethylenediamine was pre-
pared. CSP 1 was successfully applied to the resolution of var-
ious N-(substituted benzoyl)-α-amino amides, 3-substituted
1,4-benzodiazepin-2-ones, and some diuretic chiral drugs with
reasonably good separation factors and resolutions. All of the
analytes resolved on CSP 1 contain at least one aromatic func-
tional group. Consequently, CSP 1 is concluded to be useful
in the resolution of various racemic compounds containing
aromatic functional groups. Further application of CSP 1 is
under way in our laboratory.
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