Design, synthesis and evaluation of racemic 1-(4-hydroxyphenyl)-2-[3- (substituted phenoxy)-2-hydroxy-1-propyl]amino-1-propanol hydrochlorides as novel uterine relaxants

Article abstract of DOI:10.1016/j.bmcl.2005.05.047

Novel 1-(4-hydroxyphenyl)-2-[3-(substituted phenoxy)-2-hydroxy-1-propyl] amino-1-propanol hydrochlorides were designed based on the pharmacophore for potent uterine relaxant activity and by utilizing the principles of structural hybridization. The designed molecules were synthesized as racemates by a novel route and were evaluated for uterine relaxant activity in vitro on isolated rat uterus and in vivo in pregnant rats. Their cAMP-releasing potential was studied using rat uterus tissue homogenates by the cAMP [³H] assay, and cardiac stimulant potential was evaluated on isolated guinea pig right atrium. All compounds exhibited potent uterine relaxant activity in vitro and produced a significant delay in the onset of labour in pregnant rats; their cAMP-releasing potential was slightly less, while their cardiac stimulant potential was insignificant as compared to isoxsuprine hydrochloride.

Full text of DOI:10.1016/j.bmcl.2005.05.047

Bioorganic & Medicinal Chemistry Letters 15 (2005) 3532–3535
Design, synthesis and evaluation of racemic
1-(4-hydroxyphenyl)-2-[3-(substituted phenoxy)-2-hydroxy-
1-propyl]amino-1-propanol hydrochlorides as novel
uterine relaxants
C. L. Viswanathan,* M. M. Kodgule and A. S. Chaudhari
Department of Pharmaceutical Chemistry, Bombay College of Pharmacy, Kalina, Santacruz (E), Mumbai 400 098, India
Received 26 December 2004; revised 15 May 2005; accepted 19 May 2005
Available online 20 June 2005
Abstract—Novel 1-(4-hydroxyphenyl)-2-[3-(substituted phenoxy)-2-hydroxy-1-propyl]amino-1-propanol hydrochlorides were
designed based on the pharmacophore for potent uterine relaxant activity and by utilizing the principles of structural hybridization.
The designed molecules were synthesized as racemates by a novel route and were evaluated for uterine relaxant activity in vitro on
isolated rat uterus and in vivo in pregnant rats. Their cAMP-releasing potential was studied using rat uterus tissue homogenates by
the cAMP [3H] assay, and cardiac stimulant potential was evaluated on isolated guinea pig right atrium. All compounds exhibited
potent uterine relaxant activity in vitro and produced a significant delay in the onset of labour in pregnant rats; their cAMP-releas-
ing potential was slightly less, while their cardiac stimulant potential was insignificant as compared to isoxsuprine hydrochloride.
ꢀ 2005 Elsevier Ltd. All rights reserved.
Premature labour is the leading cause of neonatal mor-
bidity and perinatal mortality.1 b2-adrenoceptor agonists
are the drugs of choice for treating premature labour.1
They relax the uterine smooth muscle by inhibiting the
rate and force of myometrial contractions and this pro-
cess involves the intracellular release of cAMP.2 This
leads to a gradual rise in plasma progesterone levels
and maintenance of pregnancy. b2-Adrenoceptor ago-
nists, such as isoxsuprine and ritodrine, when used in
clinical practice for treating premature labour, also pro-
duce tachycardia3 due to cardiac b1-adrenoceptor stimu-
lation. To reduce this side effect, co-administration of
cardioselective b-blockers is recommended.4
designing novel molecules using the principle of struc-
tural hybridization, and synthesizing and evaluating
them.
The present work was aimed towards developing novel
molecules with improved uterine relaxant property
and with decreased cardiac stimulant activity. It is
proposed to achieve this aim by generating a pharma-
cophore for potent b2-adrenoceptor stimulant activity,
Keywords: Uterine relaxants; b2-Adrenoceptor stimulants; cAMP [3H]
assay.
*
Corresponding author. Tel.: +91 22 26670871; fax: +91 22
26670816; e-mail addresses: chelakara_viswanathan@yahoo.com;
atulsc@rediffmail.com
Figure 1. Structures of isoxsuprine, ritodrine, and nylidrin.
0960-894X/$ - see front matter ꢀ 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2005.05.047

C. L. Viswanathan et al. / Bioorg. Med. Chem. Lett. 15 (2005) 3532–3535
3533
A four-point pharmacophore was developed by using the
structures of potent b2-adrenoceptor stimulants like isox-
suprine, ritodrine and nylidrin (Fig. 1). The study was
carried out using the Chem-X5 software on a Pentium
IV 1.6 GHz computer. The conformers of each molecule
were generated by using dynamics simulations at a tem-
perature of 310 ꢁC and the sampling time was 5 · 10ꢀ4 s.
Lowest energy conformations were identified for each
molecule and were then used for arriving at the pharma-
cophore (Fig. 2). Based on the pharmacophore, four
novel molecules with the general structure 1-(4-hydroxy-
phenyl)-2-[3-(substituted phenoxy)-2-hydroxy-1-pro-
pyl]amino-1-propanol were designed.
Reacting phenylpropionate 1 with anhydrous AlCl3 in
nitrobenzene at 30 ꢁC yielded 4-hydroxypropiophenone
2 (mp 147 ꢁC). This was condensed with benzyl chloride
in aqueous NaOH to yield 4-benzyloxypropiophenone 3
(mp 102–103 ꢁC), which, on bromination with Br2 in
glacial acetic acid at room temperature, gave 2-bromo-
40-benzyloxypropiophenone 4 (mp 75–76 ꢁC). The reac-
tion of substituted phenols (5a–d) with epichlorohydrin
in aqueous NaOH at room temperature yielded the cor-
responding substituted phenoxymethyloxiranes (6a–d),
which were then reacted with benzylamine in ethanol
Figure 2. Pharmacophoric points (distances in Angstrom units).
Scheme 1. Synthesis of compounds 9a–d.

3534
C. L. Viswanathan et al. / Bioorg. Med. Chem. Lett. 15 (2005) 3532–3535
at room temperature to yield substituted phenoxypropa-
nolamines (7a–d).
contractions was recorded at different concentrations
(Table 2).6,7
Finally, heating compound 4, in turn, with compounds
7a–d in dioxane in the presence of K2CO3, followed by
treatment with dry HCl, gave compounds 8a–d, which
were then reduced catalytically using H2 and 10%
Pd/C in ethanol at room temperature to get compounds
9a–d as racemates (Scheme 1).
Compounds 9a–d were then evaluated in pregnant
Sprague–Dawley rats by a method developed by us.8
Each dose was evaluated in a group of six rats. The
dose of standard drug isoxsuprine hydrochloride used
was 10 mg/kg body weight/day and was administered
orally from day 13 to 21 of gestation. Similarly com-
pounds 9a–d were evaluated at doses 10 and 15 mg/
kg/day. The rats were weighed daily until parturition
and on delivery, the delay in onset of labour was calcu-
lated for each rat by comparing with control (see Table
2). Litter size and average weight of pup were also
noted.
All compounds were purified by silica gel column chro-
matography. The physical constants and spectral char-
acteristics of the final compounds are given in Table 1.
Fries rearrangement of compound 1 in nitrobenzene at
30 ꢁC gave a higher yield (60%) of para isomer than
the reaction in CS2 and reactions at higher temperatures.
In the final step, the reduction of keto function to
secondary alcohol, and simultaneous N- and O-debenz-
ylations were achieved in a single step at a hydrogen
pressure of 2 bar.
Compounds 9a–d and isoxsuprine hydrochloride were
administered p.o. to Sprague–Dawley female virgin rats
in an oestrus phase. Three hours later, the rats were sac-
rificed and the uterine strips were isolated, weighed,
placed in 2 ml Tris–EDTA buffer and homogenized
using Kinematica AG, Polytron. The homogenates were
centrifuged at 12,000g using Hetlich Zentrifugan, Uni-
versal 16 R. The supernatants were deproteinised using
Final compounds 9a–d were evaluated for uterine relax-
ant activity in isolated rat uterus preparation. The point
where the inhibition of oxytocin induced sustained
Table 1. Physical constants and spectral data of the final compounds
Compound R1
R2
Melting point % Yield 1H NMR (d in ppm)
(free base)
9a
–NHCOCH3
–H
57–58 ꢁC
62%
d 1.0 (d, 3H, –CH3), d 2.2 (2s, 2H, 2 –OH),
d 2.9 (m, 1H, –CH–), d 3.1 (s, 3H, –COCH3),
d 3.3 (m, 4H, OCH2, HO–C–CH2), d 3.9 (m, 2H, 2 CHOH),
d 4.2 (s, 1H, –NH), d 4.6 (2s, 2H, Ar-OH, NHCO),
d 6.8–7.3 (m, 8H, Ar-H)
9b
9c
9d
–CH2CONH2
–H
47–49 ꢁC
85–87 ꢁC
60%
58%
60%
d 1.0 (d, 3H, –CH3), d 2.1 (2s, 2H, 2 –OH), d 2.5 (m, 1H, –CH–),
d 3.4 (s, 2H, –CH2CO), d 3.7 (m, 4H, OCH2, –COHCH2),
d 3.9 (m, 2H, 2 –CHOH), d 4.2 (s, 1H, –NH), d 4.6 (s, 1H, Ar-OH),
d 5.0 (s, 2H, –NH2), d 6.8–7.3 (m, 8H, Ar-H)
d 1.2 (d, 3H, –CH3), d 2.0 (2s, 2H, 2 –OH), d 2.5 (m, 1H, –CH–),
d 3.2 (m, 5H, CH2COCH3), d 3.6 (t, 2H, ArCH2–),
d 3.8 (m, 4H, OCH2, HO–C–CH2), d 3.9–4.2 (m, 2H, 2 –CHOH),
d 5.1 (m, 2H, ArOH, N–H), d 6.8–8.0 (m, 8H, Ar-H)
d 1.2 (d, 3H, –CH3), d 2.0 (2s, 2H, 2 –OH), d 3.3 (2s, 6H, 2 –COCH3),
d 3.7 (m, 4H, –OCH2, HO–C–CH2), d 4.2 (m, 2H, 2 –CHOH),
d 4.7 (s, 1H, –NHCO), d 5.1 (m, 2H, –N–H, ArOH),
d 7–8 (m, 7H, Ar-H).
–CH2CH2OCH3 –H
–NHCOCH3
–COCH3 78–79 ꢁC
Table 2. In vitro, in vivo uterine relaxant activity and cAMP assay
Compound
Inhibition of oxytocin
induced contraction IC50 (lmol)
Delayed onset of labour (h)
cAMP released (pmol)
at 10 mg (lmol)
10 mg (lmol)
15 mg (lmol)
9a
9b
6.07
6.32
6.02
6.58
9.15
25.0 (24.3)
24.02 (24.3)
27.05 (24.3)
23.70 (22.0)
31.63 (29.6)
31.78 (36.5)
31.70 (36.5)
33.67 (36.4)
30.07 (33.1)
—
3.48 (24.3)
3.56 (24.3)
3.66 (24.3)
3.53 (22.0)
5.03 (29.6)
9c
9d
Isoxsuprine HCl

C. L. Viswanathan et al. / Bioorg. Med. Chem. Lett. 15 (2005) 3532–3535
3535
Table 3. In vitro cardiac activity
Compound
Heart rate at different doses (beats per minute)
Control
10 lmol
25 lmol
50 lmol
100 lmol
9a
9b
9c
9d
62
65
62
65
60
64
60
63
58
64
56
59
55
60
53
58
55
57
50
55
Control
62
0.5 lmol
0.75 lmol
1.0 lmol
1.25 lmol
84
Isoxsuprine HCl
70
74
79
trichloroacetic acid (TCA) and the tubes were centri-
fuged again. The supernatants were freed from TCA
by repeated extractions with ether and then the pH
was adjusted to 7.5. The cAMP (3H) assay system
(TRK 432) from Amersham International plc, UK,
was used as per the procedure listed in their booklet.9
To assay tubes placed in an ice bath was added standard
cAMP in concentrations of 0, 1, 2, 4, 8 and 16 pmol/
50 ll Tris–EDTA buffer, 50 ll (0.9 pmol) cAMP [3H]
and 100 ll of binding protein. Tubes were vortex-mixed
for 5 s and allowed to stand in a refrigerator at 2–8 ꢁC
for 2 h. Charcoal suspension (100 ll) was then added
to each tube, vortex-mixed and centrifuged. Two hun-
dred microlitres of supernatant was removed from each
tube and was placed in scintillation vials for counting.
to the development of novel uterine relaxants free from
cardiac stimulation side effects.
Acknowledgments
The authors thank the Indian Council of Medical
Research (ICMR), New Delhi, for the financial support
and Dr. S. B. Moodbidri, Deputy Director, Institute for
Research in Reproduction (IRR), Parel, Mumbai 400
012, for assistance in pharmacological evaluation.
References and notes
1. Caritis, S. N. Drugs 1983, 26, 243.
2. Gabbe, S. G.; Niebyl, J. R.; Simpson, J. L. In Obstetrics:
Normal and Problem Pregnancies; Churchill Livingstone:
New York, 1991, p 829.
3. Schenken, R. S.; Hayashi, R. H.; Valenzuela, G. V.;
Castillo, M. S. Am. J. Obstet. Gynecol. 1980, 137, 773.
4. Mahon, W. A.; Reid, D. W. J. J. Pharmacol. Exp. Ther.
1967, 156, 178.
5. Chem-X, Chemical Design Ltd, Oxon, England, Jan. 1997.
6. Gaddum, J. H.; Peart, W. S.; Vost, M. J. Physiol.
(London) 1949, 108, 467.
Fifty microliters of supernatants obtained after tissue
extractions (for samples) was similarly analyzed. The
counts were recorded as counts per minute (cpm) using
b-scintillation counter. From a plot of C0/Cx vs c, where
C0 and Cx are the cpm in the absence and presence of
standard cAMP, respectively, and c is the concentration
of standard cAMP, the amount of cAMP present in
samples was determined (see Table 2).
7. Selected Topics in Experimental Pharmacology; Sheth, U.
K., Dadkar, N. K., Kamat, U. G, Eds.; Shri Mohanlal B.
Kothari Publishers: Bombay, 1972, p 160.
Compounds 9a–d and isoxsuprine hydrochloride were
evaluated in an isolated guinea pig right atrium.10
8. Kodgule, M. M.; Viswanathan, C. L.; Moodbidri, S. B.;
Vanage, G. Indian J. Pharm. Sci 1997, 59, 42.
Test compounds 9a–d exhibited potent inhibition of
oxytocin induced sustained contractions of rat uterus
and produced a significant delay in the onset of labour
(24–34 h) in pregnant rats and their activity is compara-
ble to that of isoxsuprine hydrochloride. Increase in ges-
tation period led to a significant increase in the average
weight of the pups, but no effect was observed on the
mean litter size. No mortality was recorded in pregnant
rats or in the pups delivered. The cAMP release study
showed that the test compounds were slightly less po-
tent. Test compounds inhibited an ISP induced increase
in the heart rate and exhibited an insignificant cardiac
depression at higher doses studied, while isoxsuprine
hydrochloride, even at much lower doses, exhibited sig-
nificant cardiac stimulation. The present work thus led
9. Cyclic AMP [3H] assay system (code TRK 432), Amer-
sham International plc, Amersham, UK.
10. Black J. W.; Duncan W. A. M.; Shanks R. G. Br. J.
Pharmacol. 1965, 25, 577. The atrium was mounted in a
jacketed organ bath filled with Ringer–Locke solution
under a resting tension of 1 g. Carbogen gas was bubbled
and the temperature was maintained at 37 ꢁC and the
tissue was allowed to equilibrate for 45 min. Ten micro-
mole of isoproterenol sulfate (ISP, Ref. Std) was added to
the organ bath and the heart rate was recorded using a
force transducer on a polygraph. Compounds 9a–d at
doses of 10, 25, 50 and 100 lmol were added to the bath
and incubated for 3 min, then 1 lmol ISP was added and
the heart rate was recorded (Table 3). In a similar manner
isoxsuprine hydrochloride was evaluated at 0.5, 0.75, 1.0
and 1.25 lmol doses.