Resolution of Rac-Bambuterol via Diastereoisomeric Salt Formation with o-Chloromandelic Acid and Differences in the Enantiomers' Pharmacodynamical Effects in Guinea Pigs and Beagles

Article abstract of DOI:10.1002/chir.22573

In this study an enantioseparation method for rac-bambuterol (5-(2-(tert-butylamino)-1-hydroxyethyl)-1,3-phenylene bis(dimethylcarbamate)) via diastereoisomeric salt formation with o-chloromandelic acid was developed. The enantiomeric excess (ee) values and chemical purities of the desired products were confirmed by high-performance liquid chromatography (HPLC) using chiral stationary phase and reverse-phase HPLC analyses, respectively. The ee values and the chemical purities both exceeded 99%. Animal experiments showed that (R)-bambuterol was a potent inhibitor for histamine-induced asthma reactions. (S)-bambuterol was ineffective in relaxing the airways. Both enantiomers increased heart rates in beagles. Therefore, replacing rac-bambuterol with (R)-bambuterol could be beneficial for asthma patients.

Full text of DOI:10.1002/chir.22573

CHIRALITY 28:306–312 (2016)
Resolution of Rac-Bambuterol via Diastereoisomeric Salt Formation
with o-Chloromandelic Acid and Differences in the Enantiomers’
Pharmacodynamical Effects in Guinea Pigs and Beagles
1
JIE WU,1 FEI LIU,1 SHANPING WANG,1 HONGJUN WANG,1 QING LIU,1 XINGHAN SONG,1 JUNXIAO LI,1 LING XU,2 AND WEN TAN
*
1School of Bioscience and Bioengineering, South China University of Technology; Pre-Incubator for Innovative Drug and Medicine, South China
University of Technology; Guangdong Provincial Key Laboratory of Fermentation and Enzyme Engineering, South China University of Technology,
Guangzhou, Guangdong, China
2Keypharma Biomedical Inc., Songshan Lake Science & Technology Industry Park, Dongguan, Guangdong, China
ABSTRACT
In this study an enantioseparation method for rac-bambuterol (5-(2-(tert-
butylamino)-1-hydroxyethyl)-1,3-phenylene bis(dimethylcarbamate)) via diastereoisomeric salt
formation with o-chloromandelic acid was developed. The enantiomeric excess (ee) values and
chemical purities of the desired products were confirmed by high-performance liquid chroma-
tography (HPLC) using chiral stationary phase and reverse-phase HPLC analyses, respectively.
The ee values and the chemical purities both exceeded 99%. Animal experiments showed that
(R)-bambuterol was a potent inhibitor for histamine-induced asthma reactions. (S)-bambuterol
was ineffective in relaxing the airways. Both enantiomers increased heart rates in beagles.
Therefore, replacing rac-bambuterol with (R)-bambuterol could be beneficial for asthma patients.
Chirality 28:306–312, 2016. © 2016 Wiley Periodicals, Inc.
KEY WORDS: enantioseparation; bambuterol; o-chloromandelic acid; enantiomer; pharmacodynamical
effects
Bambuterol is a long-acting β-agonist that has been used to
treat asthma for over 20 years.1,2 It is a biscarbamate ester
prodrug that can be hydrolyzed mainly by butyrylcholinester-
ase (BChE) to slowly generate the active parent drug terbuta-
line, a β2-adrenergic receptor agonist.2–5 Bambuterol is a
chiral drug consisting of equal amounts of (R)- and (S)-enan-
tiomers. Enantiomers of chiral drugs can exhibit stereo-
selectivity in their interactions with their targets and may
have different therapeutic effects.6–10 Previous studies have
demonstrated that the inhibition of BChE by the (R)-enantio-
mer was five times more potent than the (S)-enantiomer,
indicating that the enantiomers of bambuterol have signifi-
cantly different biological effects.11–13 Bambuterol is a widely
prescribed drug for the treatment of asthma. It is possible that
(R)-bambuterol and (S)-bambuterol may have different
pharmacodynamical effects. Thus, the chiral separation of rac-
bambuterol is of great importance for its use in clinical settings.
Three methods have been reported for the production of single
enantiomers of rac-bambuterol. The first method was reported in
2006 and used a high-performance liquid chromatography (HPLC)
system to separate each of the enantiomers.11 The second method,
which was reported in 2008, was a chemical synthesis method that
used 1-(3, 5-dihydroxyphenyl) ethanone as a starting material. (ꢀ)-
DIP-chloride was used as an asymmetric reducing agent in the
asymmetric reduction reaction to produce the (R)-enantiomer,
and (+)-DIP-chloride could be used to produce the (S)-enantio-
mer via the same synthetic sequence.14 The last method, which
was reported in 2013, was a chemo-enzymatic method to pro-
duce the (R)-enantiomer. Whole cells of Williopsis californica
JCM 3600 were used for the asymmetric reduction and
1-[3,5-bis(dimethylcarbamoyloxy)phenyl]-2-chloroethanone was
used as the asymmetric reducing agent.15 However, these
methods were either designed only for laboratory use or re-
quired an expensive chiral catalytic agent. (ꢀ)-DIP-chloride,
which contains borane, is an environmentally hazardous
reagent.
In this study we describe an ecofriendly and cost-
effective method to resolve single enantiomers of rac-
bambuterol by using chiral o-chloromandelic acid and re-
crystallization techniques. The optical purities of (R)- and
(S)-bambuterol were determined using chiral HPLC
methods. Pharmacological differences between (R)- and
(S)-bambuterol were investigated in guinea pigs and
beagles.
MATERIALS AND METHODS
General
Optical rotation data were obtained on an autopol automatic polarime-
ter at ambient temperature. ESI-MS (HRMS) chromatograms were
recorded on a Bruker (Billerica, MA) maXis impact mass spectrometer.
Materials used in the resolution procedure were obtained from commer-
cial suppliers (AR grade) and all other analytical-grade chemicals were
purchased from Sigma-Aldrich (Shanghai, PRC). HPLC-grade solvents
were obtained from Fisher Scientific (Guangzhou, PRC). The histamine
used in the animal experiments was purchased from Sigma-Aldrich (Lot
#BCBC2083 V).
Preparation of Rac-Bambuterol
Rac-bambuterol hydrochloride (30 g, 74.3 mmol) was dissolved in
120 mL of H2O. Anhydrous potassium carbonate (10.25 g, 74.3 mmol)
in 30 mL of H2O was added dropwise to the suspension of rac-bambuterol
hydrochloride. After 0.5 h, the aqueous phase was extracted with ethyl
acetate three times (100 mL, 50 mL, and 30 mL). The combined organic
*Correspondence to: Wen Tan, School of Bioscience and Bioengineering,
South China University of Technology; Pre-Incubator for Innovative Drug
and Medicine, South China University of Technology;Guangdong Provincial
Key Laboratory of Fermentation and Enzyme Engineering, South China Uni-
versity of Technology, Guangzhou, 510006, Guangdong, China.
E-mail: went@scut.edu.cn
Received for publication 17 October 2015; Accepted 11 December 2015
DOI: 10.1002/chir.22573
Published online 25 January 2016 in Wiley Online Library
(wileyonlinelibrary.com).
© 2016 Wiley Periodicals, Inc.

RESOLUTION OF RAC-BAMBUTEROL
layer was dried over anhydrous Na2SO4, filtered, and concentrated to
307
Chiral HPLC Analyses
remove most of the solvent. The product was then dissolved in ethyl ace-
tate and used in the next reaction without further purification. 27.02 g,
yield: 99.01% (not dry).
The chiral HPLC used for the analyses was an SPD 20A system
(Shimadzu, Japan) that comprised a Shimadzu SPD 20A UV detector, a
Shimadzu LC-20AT pump, and a Shimadzu LC solution workstation.
The column used for the purification was a Daicel CHIRALCEL OJ-H
coated on 5 μm silica particles. The column dimensions were 4.6 mm
ø × 250 mm. UV detection was performed at 263 nm. The mobile phase
was a hexane/ethanol/diethyl-amine =230:20:0.75 (v/v/v) mixture. The
flow rate was 1.0 mL/min. The analyses were conducted at ambient
temperature.
Preparation of (S)-Bambuterol (S)-o-Chloromandelic Acid
or (R)-Bambuterol (R)-o-Chloromandelic Acid
(S)-bambuterol (S)-o-chloromandelic acid: The solution of rac-
bambuterol in ethyl acetate was treated dropwise with (S)-o-
chloromandelic acid (13.86 g, 74.3 mmol) in 20 mL of ethyl acetate at
50 °C. Then the solution was stirred at 60 °C for 2 h and cooled to room
temperature. Four hours later, the suspension was filtered and the white
solid was recrystallized twice with ketone and once with a solvent mixture
(ethyl acetate: ethanol =2:1). The product was used in the next step.
8.18 g, yield: 19.87%. (R)-bambuterol (R)-o-chloromandelic acid was ob-
tained via the same procedure but by using (R)-o-chloromandelic acid.
10.58 g, yield: 25.70%.
Animals
Healthy guinea pigs of either sex (200 20 g, CV) were purchased from
the Laboratory Animal Center of Guangdong (China). All guinea pigs
were kept in a specific pathogen-free animal facility under controlled con-
ditions at a temperature of (22 2 °C) and humidity of (50 15%) with a
12 h light–dark cycle. Six dogs (~6–9 months) were selected for this
study and weighed ~6 1.5 kg. Each dog was identified by a unique num-
ber tattooed on its chest. The dogs were kept in a specific pathogen-free
animal facility under controlled conditions at a temperature of (24 2 °C)
and humidity of (50 15%) with a 12 h light–dark cycle. Approximately
300 g of extruded food and enough water were given to each dog twice
a day (8:30 to 10:30 a.m. and 17: 30 to 19: 30 p.m.). All of the animal exper-
imental procedures in this study were performed in accordance with a
protocol approved by the Ethics Committee for Animal Welfare at the
South China University of Technology, in accordance with National Insti-
tutes of Health and Nutrition Guidelines for the Care and Use of Labora-
tory Animals.
Preparation of (S)- or (R)-Bambuterol Hydrochloride
A
suspension of the enantiomer o-chloromandelic acid (7.92 g,
14.29 mmol) prepared using the procedure described above was dis-
solved in 30 mL of H2O and was treated dropwise with anhydrous
potassium carbonate (1.97 g, 14.29 mmol) in 6 mL of H2O. After 0.5 h,
the aqueous phase was extracted with ethyl acetate three times (90 mL,
60 mL and 50 mL). The combined organic layer was dried over anhy-
drous Na2SO4, filtered, and concentrated to give a yellow oil. The oil
was dissolved in 8 mL of ethanol. Hydrochloric acid in ethanol was added
dropwise to the resulting solution in an ice-bath to adjust the solution to
pH = 1. After 1 h, the reaction mixture was filtered and the white solid
was recrystallized once using anhydrous ethanol. (S)-bambuterol hydro-
chloride: White powder; 3.7 g, Yield: 24.67% (based on half quality of
racemate); HRMS (ESI, m/z): calculated for ([M + H]+) 368.2180, found
368.2183; [α]2D9 = +26.39 (C = 0.1, methanol). (R)-bambuterol hydrochlo-
ride: White powder; 5.48 g, Yield: 36.53% (based on half quality of
racemate); HRMS (ESI, m/z): calculated for ([M + H]+) 368.2180, found
368.2184; [α]2D9 = ꢀ27.95 (C = 0.1, methanol).
Histamine-Induced Bronchospasm in Conscious Guinea
Pigs
Animals were randomly divided into three groups: saline, R-BMB, and
S-BMB, which were treated with the vehicle, (R)-bambuterol hydrochlo-
ride, and (S)-bambuterol hydrochloride, respectively. Each group
contained six animals of either sex. Bronchospasm responses were
induced and evaluated following a previously reported method.16 Briefly,
a guinea pig was in a sealed box (4 L), which was connected to the output
port of an ultrasonic nebulizer that had a speed of 0.5 ml/min (particle
size 1–5 μm, Model YLS-8A, Medical Science Equipment Station,
Shandong, China). The concentration of histamine solution and the
output of the nebulizer were adjusted to produce a control collapse time
of 120 s (100–140 s) in the guinea pigs. (R)-bambuterol hydrochloride
and (S)-bambuterol hydrochloride were dissolved in saline solutions
and were then given to the animals (4 mg/kg) by intragastric lavage
2 h before the histamine bisphosphate monohydrate aerosol challenge
(0.6% w/v, 15 s); the control group was treated with a blank saline
solution. The time to collapse was then measured. Animals that did not
collapse 3 min after exposure to the histamine aerosol were considered
“completely protected.”
RP-HPLC Analyses
The HPLC system used to investigate the chemical purity of the
compounds was an SPD-M20A (Shimadzu, Japan) that comprised a
Shimadzu SPD-M20A detector, a Shimadzu CBM-20A controller, two
Shimadzu LC-20AT pumps, and a Shimadzu LC Labsolution workstation.
The column used for the purification was an Agilent (Palo Alto, CA)
ZORBAX Eclipse XDB-C18 coated on 5 μm silica particles. The column
dimensions were 4.6 mm ø × 150 mm. UV detection was performed at
220 nm. The mobile phase was a phosphate buffer (pH = 3, 500 mL con-
taining 3.4 g NaH2PO4 and 1.0908 g sodium heptanesulfonate)/metha-
nol/acetonitrile =500:309:100 (v/v/v) mixture. The flow rate was
1.0 mL/min. The temperature was 40 °C.
Fig. 1. Protocol of this program.
Chirality DOI 10.1002/chir

308
WU ET AL.
dosage was 0.08 mg/kg. The drug dosage was 0.7 mg/kg.18 Each dog in
this experiment was subjected to the same protocol (Fig. 1). This protocol
was previously used by Tan et al.17
Histamine-Induced Bronchospasm in Anesthetized Beagles
The method used to measure the dogs’ lung functions was based on a
histamine-induced dog asthma model.17 This model utilized a facemask
to measure the airway flow. A wireless-telemetry implant was placed into
the pleural cavity of the dogs to directly measure their real pleural
pressures. The data for intrathoracic pressure and ECG were obtained
from animals using a telemetry system. The flow rates were measured
using a signal converter on the respiratory masks. The airway resistance
(Raw) was counted using the following equation:
Statistical Analyses
Data are presented as the mean SD using SPSS19.0 software (Chicago,
IL). One-way analysis of variance (ANOVA) followed by Student-Newman-
Keuls (SNK) test were used to determine significant differences between
the means of multiple samples. The critical level for significance was set
at α = 0.05.
Raw ¼ ΔPR=f
(1)
RESULTS AND DISCUSSION
Preparation of Bambuterol Hydrochloride Enantiomers
The animals were randomly divided into two groups: R-BMB and
S-BMB, which were treated with (R)-bambuterol hydrochloride and (S)-
bambuterol hydrochloride, respectively. Histamine was dissolved in
sterilized normal saline and diluted to a final volume of 2 ml and the final
In our experiment, we chose commercially available rac-
bambuterol hydrochloride as
a starting material. Salt
Scheme 1. The route of enantioseparating (R)- and (S)-bambuterol hydrochloride from rac-bambuterol hydrochloride via diastereoisomeric salt formation with
enantiopure o-chloromandelic acid.
Chirality DOI 10.1002/chir

RESOLUTION OF RAC-BAMBUTEROL
309
formation was carried out using free rac-bambuterol with
enantiopure o-chloromandelic acid. The synthetic route is
shown in Scheme 1. For the preparation of free rac-
bambuterol, the reaction time was limited to ensure that rac-
bambuterol was not hydrolyzed. In the recrystallization
step, ketone and a combined solvent system (ethyl acetate:
ethanol =2:1) was used to resolve rac-bambuterol. Three re-
crystallization steps using this method afforded compounds
with ee values of up to 99%. Usually, the dosage of the
resolving agent, reaction temperature, duration of heating
and cooling time were key factors for improving separation
efficiencies.19–21
bambuterol hydrochloride were 7.041 min and 8.857 min,
respectively, and were longer than previously obtained
results. The value of the resolution factor was 3.57 and the
theoretical plates were 4162 for (R)-bambuterol hydrochlo-
ride and 3723 for (S)-bambuterol hydrochloride, which were
also larger than previously obtained results. These data
showed that a Daicel CHIRALCEL OJ-H column facilitated
better separation than a CHIRALCEL-OJ column. (R)-
bambuterol hydrochloride was obtained with 99.888% ee and
(S)-bambuterol hydrochloride was obtained with 99.070% ee
(Fig. 2). The chemical purity of the enantiomers was
investigated by HPLC analysis using an Agilent ZORBAX
Eclipse XDB-C18 column. The results showed that the
chemical purities of the enantiomers were higher than 99%
(Fig. 3).
Optical Rotation
20
The specific rotation [α]D
value of (R)-bambuterol
hydrochloride has been previously reported to be ꢀ26.1°.14
In our study, the specific rotation [α]2D9 values of (R)-
bambuterol hydrochloride and (S)-bambuterol hydrochloride
were ꢀ27.95 and +26.39, respectively (C = 0.1, methanol).
The result for (R)-bambuterol hydrochloride was consistent
with a previous study, which validated our conclusions.
Animal Experiment with Conscious Guinea Pigs
An animal experiment was conducted to evaluate the
different effects of the two enantiomers in guinea pigs. In
the saline control group, animals generally collapsed ~100 s
after 15 s of exposure to the histamine aerosol. The potency
of the two enantiomers was determined by intragastric la-
vage. (R)-Bambuterol hydrochloride inhibited the histamine-
induced bronchoconstrictive response and prolonged the
time to collapse compared to the saline control group
(169.83 10.15 versus 108.00 16.30, respectively). However,
the maximum reaction time for the histamine attack of (S)-
bambuterol hydrochloride-treated group was less than
100 s, which was almost half the time observed for the (R)-
HPLC Analyses
The ee values of (R)-bambuterol hydrochloride and (S)-
bambuterol hydrochloride were determined with a chiral
HPLC system equipped with a Daicel CHIRALCEL OJ-H
column instead of a CHIRALCEL-OJ column, as reported in
2008 (Fig. 2).14 Results of the rac-bambuterol hydrochloride
HPLC run showed that (R)-bambuterol hydrochloride and
(S)-bambuterol hydrochloride were well separated. The
retention times for (R)-bambuterol hydrochloride and (S)-
bambuterol hydrochloride-treated group (96.00
30.72
versus 169.83 10.15, respectively). This group did not show
Fig. 2. Chiral HPLC analyses of rac-bambuterol hydrochloride, (R)-bambuterol hydrochloride and (S)-bambuterol hydrochloride. (a) Rac-bambuterol hydrochlo-
ride. (b) (R)-bambuterol hydrochloride. (c) (S)-bambuterol hydrochloride.
Chirality DOI 10.1002/chir

310
WU ET AL.
Fig. 3. RP HPLC analyses of (R)-bambuterol hydrochloride and (S)-bambuterol hydrochloride (a) (R)-bambuterol hydrochloride (b) (S)-bambuterol
hydrochloride.
relaxation effects but also slight airway constriction effects.
The results are shown in Figure 4. There are many reports
regarding the proconstrictory and proinflammatory effects
of (S)-enantiomers, but most of these studies have focused
on the effects of (S)-salbutamol.22–24 It has been suggested
that (S)-salbutamol could increase the sensitivity of human
bronchial smooth muscle cells (hBSMCs) toward antigens,25
which is consistent with our results demonstrating that (S)-
bambuterol hydrochloride may cause hyperresponsiveness
to histamine.
dogs are presented in Table 1. There was no change during
the process of administering saline. The mean changes in per-
centage values upon administration of 0.08 mg/kg of
histamine were 254 36% for the R-BMB group and 221 52%
for the S-BMB group. There was a significant difference com-
pared to the corresponding saline-administered groups
(P < 0.01). The results showed that histamine could evoke
hyperresponsiveness in airways. However, after i.v. injections
of (R)-bambuterol hydrochloride, the mean change in percent-
age value upon the administration of 0.08 mg/kg histamine was
only 133 25%, indicating the full protection of (R)-bambuterol
hydrochloride against histamine attacks. During the same pro-
cess using (S)-bambuterol hydrochloride, the mean change in
percentage value was 280 83%, indicating that (S)-bambuterol
hydrochloride was ineffective in relaxing the airways.
Animal Experiment with Anesthetized Beagles
An animal experiment was conducted to evaluate the differ-
ent effects of the two enantiomers in beagles. The results
following the administration of different drugs to anesthetized
The effects of (R)-bambuterol hydrochloride and (S)-
bambuterol hydrochloride on airway resistance after i.v.
administration of histamine for the second time demonstrated
TABLE 1. Results of airway resistance changing in different
status
R-BMB
S-BMB
Before saline
After saline
Before histamine
After histamine
Before histamine secondly
After histamine secondly
1.00 0.00
1.03 0.07
0.99 0.06
2.54 0.36**
1.14 0.19
1.33 0.25##
1.00 0.00
1.02 0.04
0.98 0.08
2.21 0.52**
0.92 0.17
2.80 0.83
Fig. 4. Effects of (R)-bambuterol hydrochloride and (S)-bambuterol hydro-
chloride on collapse times after the histamine aerosol challenge in guinea
pigs. In the same doses, the (R)-bambuterol hydrochloride group displayed
apparent bronchodilation effects compared to the (S)-bambuterol hydrochlo-
ride-treated group. Data are expressed as the mean SD, n = 6. ##P < 0.01
versus (R)-bambuterol hydrochloride, **P < 0.01 versus saline.
Data are expressed as mean SD, n = 6.
**P < 0.01 versus after saline.
##P < 0.01 versus after histamine.
Chirality DOI 10.1002/chir

RESOLUTION OF RAC-BAMBUTEROL
311
Fig. 5. Bronchodilation effects of (R)-bambuterol hydrochloride and (S)-bambuterol hydrochloride. At the same dosage, (R)-bambuterol hydrochloride displayed
apparent bronchodilation effects compared to (S)-bambuterol hydrochloride, in accordance with the table presented above. Data are expressed as themean SD,
n = 6. **P < 0.01 versus histamine.
obvious differences in beagles (Fig. 5). At the same
dosage, (R)-bambuterol hydrochloride displayed apparent
bronchodilation effects compared to the administration of (S)-
bambuterol hydrochloride (133 25% versus 280 83%, respec-
tively). Moreover, (S)-bambuterol hydrochloride elicited slight
airway constriction effects. These results were consistent with
the conclusions obtained from the experiments using guinea
pigs.
bronchoconstriction induced by histamine, indicating an
improvement of lung function during an asthmatic attack. In
contrast, the same dosage of (S)-bambuterol caused airway
constriction rather than relaxation. Both of the enantiomers
increased heart rates after administration. It is obvious that
(S)-bambuterol is responsible for at least part of the adverse
effects of rac-bambuterol observed in clinics, even though it
has no therapeutic benefit.
Both (R)-bambuterol hydrochloride and (S)-bambuterol
hydrochloride increased the heart rates of beagles. No
significant differences were found between the enantiomers.
After administration of the enantiomers, the heart rates
increased compared to those prior to administration of the
drugs. In the R-BMB group, a significant difference was
found 15 min after i.v. administration of (R)-bambuterol
hydrochloride. However, significant differences were noted
35 min after administration for the S-BMB group (Fig. 6). It
is commonly known that bambuterol is hydrolyzed primarily
by BChE to slowly generate the active parent drug, terbuta-
line. Enantiomers of bambuterol have been shown to exhibit
different potencies for inhibiting BChE.26 Thus, the time re-
quired for the terbutaline enantiomers to reach effective con-
centrations may be different. Moreover, it has been reported
that both rac-bambuterol and (R)-bambuterol could increase
heart rates at doses of 30 mg/kg.27 During the recovery pe-
riod, 20 min after the treatment, the heart rates of rats treated
with rac-bambuterol returned toward control levels and were
significantly higher than the heart rates of rats treated with
(R)-bambuterol. We predicted that (S)-bambuterol in the ra-
cemate caused this phenomenon.
CONCLUSION
In conclusion,
a convenient and simple method to
enantioseparate rac-bambuterol has been developed by using
chiral o-chloromandelic acid and a common crystallization
technique. This method is able to yield either single (R)- or
(S)-bambuterol with high optical purity (ee > 99%) and
chemical purity (>99%).
Animal experiments indicated that (R)-bambuterol was the
eutomer and had antiasthmatic effects. Meanwhile, (S)-
bambuterol was shown to be the distomer, which did not
exhibit effects similar to (R)-bambuterol. In addition, (S)-
bambuterol showed an unexpected bronchoconstriction
effect. This may explain the superresponsiveness or the
exacerbation of asthma symptoms, which are well-known
adverse effects observed in patients who use racemic β2
agonist therapy. Furthermore, we found that (S)-bambuterol
had significant positive chronotropic effects on the heart rates
of animals that was more potent than (R)-bambuterol.
Our findings demonstrate that a chiral switch using (R)-
bambuterol to replace rac-bambuterol is beneficial. It may
increase the potency of the drug while reducing adverse
effects for patients in need.
From the results of the animal experiments, we found
that (R)-bambuterol was potent enough to inhibit
ACKNOWLEDGMENTS
This work was supported by the Major Science and Technol-
ogy Project of Guangdong Province, which was funded by the
Ministry of Science & Technology of Guangdong Province,
China (Grant No. 2012A080204001).
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Chirality DOI 10.1002/chir