Characterization of orally active nonpeptide vasopressin V2 receptor agonist. Synthesis and biological evaluation of both the (5R)- and (5S)-enantioisomers of 2-[1-(2-chloro-4-pyrrolidin-1-yl-benzoyl)- 2,3,4,5-tetrahydro-1H-1-benzazepin-5-yl]-N

Article abstract of DOI:10.1021/jm020133q

The synthesis and evaluation of both the (R)- and (S)-enantioisomers about the 5-position on a tetrahydro-1H-1-benzazepine derivative were described. The absolute configuration of the (R,R)-isomer (10) was determined by x-ray crystallographic analysis. Af

Full text of DOI:10.1021/jm020133q

J . Med. Chem. 2002, 45, 3805-3808
3805
Brief Articles
Ch a r a cter iza tion of Or a lly Active Non p ep tid e Va sop r essin V2 Recep tor Agon ist.
Syn th esis a n d Biologica l Eva lu a tion of Both th e (5R)- a n d (5S)-En a n tioisom er s
of 2-[1-(2-Ch lor o-4-p yr r olid in -1-yl-ben zoyl)-2,3,4,5-tetr a h yd r o-1H-1-ben za zep in -
5-yl]-N-isop r op yla ceta m id e
Kazumi Kondo,* Keizo Kan, Yoshihisa Tanada, Masahiko Bando, Tomoichi Shinohara, Muneaki Kurimura,
Hidenori Ogawa, Shigeki Nakamura, Takahiro Hirano, Yoshitaka Yamamura, Masaru Kido, Toyoki Mori, and
Michiaki Tominaga
Second Tokushima Institute of New Drug Research, Otsuka Pharmaceutical Company, 463-10 Kagasuno Kawauchi-cho,
Tokushima 771-0192, J apan
Received March 25, 2002
The synthesis and evaluation of both the (R)- and (S)-enantioisomers about the 5-position on
a tetrahydro-1H-1-benzazepine derivative were described. The absolute configuration of the
(R,R)-isomer (10) was determined by X-ray crystallographic analysis. After evaluation of both
enantiomers (compounds R-2, S-2) for binding affinity, cAMP accumulation, and an in vivo
study using Brattleboro rats, R-2 showed more potent activity as a V2 receptor agonist than
S-2.
In tr od u ction
V2 receptor and potent activity as an agonist (IC50 ) 9
nM, 64.5% to maximal cAMP accumulation at a con-
centration of 10-6 M).2 The antidiuretic effect of com-
pound 1 was also confirmed by po administration using
Brattleboro rats for reduced urine volume (7.3% to
control, 1 mg/kg, 0-2 h) and increased urine osmolality
(4.76-fold to control, 1 mg/kg), though the binding
affinity of 1 for the rat V2 receptor was less potent than
for the human receptor (IC50 rat V2 ) 0.15 µM). After
optimization and evaluation of the functional groups on
the structure of 1, the N-isopropylacetamide-substituted
analogue 2 showed more potent activity by po admin-
istration than compound 1. Further characterization of
both the (5R)- and (5S)-enantiomers of 2 gave us some
interesting results for the binding affinity and agonist
activity. The syntheses of both enantiomers were
achieved by optical resolution to form esters with
optically active alcohols.
The cyclic nonapeptide arginine vasopressin (AVP) is
a well-known hormone that exerts its major actions
through three well-defined receptor subtypes: the V1a,
V1b, and V2 receptors.1 The V1a receptor subtype, which
mainly exists in vascular smooth muscle cells, platelets,
liver, the adrenal gland, and uterus, causes contraction
and proliferation of the vascular smooth muscle, platelet
aggregation, coagulation factor (factor VIII) release, and
glycogenolysis. The V1b receptor is found in the pituitary
that is involved in the corticotropic response to stress
through regulation of ACTH secretion and the potenti-
ating effect on the corticotropin-releasing hormone
(CRH). The V2 receptor is present in the collecting duct
of the kidney. Vasopressin-induced antidiuresis, medi-
ated by the renal epithelial V2 receptors, helps to
maintain normal plasma osmolality, blood volume, and
blood pressure.
Desmopressin (1-desamino-8-D-Arg vasopressin,
DDAVP) is a peptide analogue of AVP, which is an
agonist of the AVP V2 receptor. It is used for the treat-
ment of central diabetes insipidus and the control of
nocturnal enuresis and may also be of use for the con-
trolling of nocturia. However, DDAVP is a peptide ana-
logue with variable bioavailability even via the intra-
nasal route or oral formulation. Therefore, the discovery
and the development of an orally effective nonpeptide
V2 agonist may be particularly useful in all respects.
As we have reported for nonpeptide V2 agonists, 1-(2-
chloro-4-pyrrolidin-1-ylbenzoyl)-2,3,4,5-tetrahydro-1H-
1-benzazepine (1) showed a high affinity for the human
Ch em istr y
The synthesis of compound 2 (racemate), the (5R)-
enantioisomer, and the 5S-enantioisomer are shown in
Scheme 1. An R,â-unsaturated ester group was intro-
duced by the Horner-Emmons reaction to give com-
pound 4. The reduction of the olefin and removal of the
1-tosyl group were simultaneously done by reacting with
Mg in methanol to afford 5. After condensing benz-
azepine 5 with 2-chloro-4-pyrrolidin-1-yl benzoic acid
(6),2 the ester group was hydrolyzed to give the car-
boxylic acid 8. The N-isopropylacetamide derivative (2)
was obtained by the condensation of 8 with isopropy-
lamine using BOP-Cl.
A mixture of diastereoisomers 10 and 11 was obtained
by the condensation of 8 with (R)-(-)-2-heptanol (9)
using WSC and DMAP. After a brief separation of both
* To whom correspondence should be addressed. Phone: +81-88-
665-2126. Fax: +81-88-665-6031. E-mail: k_kondo@research.otsuka.
co.jp.
10.1021/jm020133q CCC: $22.00 © 2002 American Chemical Society
Published on Web 07/16/2002

3806 J ournal of Medicinal Chemistry, 2002, Vol. 45, No. 17
Brief Articles
Sch em e 1a
a
Reagents: (a) (EtO)2P(O)CH2CO2Et, NaH, THF; (b) Mg, MeOH; (c) SOCl2, NMP, CH2Cl2; (d) 6 N NaOH, MeOH; (e) isopropylamine,
BOP-Cl, Et3N, CH2Cl2; (f) (R)-2-heptanol (9), WSC, DMAP; (g) 5 N NaOH, MeOH; (h) isopropylamine, diethyl cyanophosphonate, DMF;
(i) 6 N NaOH, MeOH; (j) WSC, DMAP, (S)-2-heptanol (13), DMF; (k) 5 N NaOH, MeOH; (l) isopropylamine, diethyl cyanophosphonate,
DMF.
isomers by silica gel column chromatography, two
fractions of both isomer-rich mixtures were obtained.
Crystals were formed in a mixture of the polar substrate-
enriched fraction. After several recrystallizations and
analysis by X-ray crystallography, the absolute config-
uration of the polar substrate was determined on the
basis of the configuration of the alcohol (9). The chiral
centers of this compound (10) were assigned to have the
(R,R)-configuration. The hydrolysis of the ester group
(10) was achieved by heating with 5 N NaOH for 5 h at
50 °C to provide the carboxylic acid (12). The condensa-
tion of 12 with isopropylamine afforded the compound
R-2. The absolute configuration at the 5-position of the
resulting compound is suggested to be R.
The less polar substrate-enriched fraction, which was
obtained as a mixture of 10 and 11, was hydrolyzed,
and the subsequent condensation with (S)-(+)-2-hep-
tanol then gave a mixture of 14 and 15. The formation
of crystals was definitely expected for the isomer having
the (S,S)-configuration. Actually, the (S,S)-isomer, com-
pound 14, was easily isolated after purification by
several recrystallizations. After the hydrolysis of the
ester group, the condensation of 16 with isopropylamine
provided S-2.
Resu lts a n d Discu ssion
The binding affinity for the human V2 receptors of R-2
is 0.33 ( 0.03 (IC50, µM) and that of S-2 is 0.98 ( 0.09.
The binding affinity for the rat V2 receptors of R-2 is
0.23 ( 0.07 and that of S-2 is 0.39 ( 0.04. Although
the substitution of N-isopropylacetamide at the 5-posi-
tion did not affect the binding affinity for the rat
receptor, it caused a detrimental effect on the binding
affinity for the human receptor. The binding affinity of
R-2 was 36.7-fold less potent than compound 1 for the
human receptor, and S-2 was 108.9-fold less potent than
compound 1. The binding affinity of R-2 was 3 times
more potent than S-2 for the human receptor. This
discrepancy in the binding affinity of the (R)- and (S)-
isomers was small for the rat receptor (1.7-fold). Figure
1 shows the concentration-dependent percentage of the
maximal cAMP accumulation for 2, R-2, and S-2 in the
human receptor. R-2 showed the accumulation of cAMP
to be 52% at a concentration of 10-6 M. S-2 showed a
cAMP accumulation of 22% at a concentration of 10-4
M. Both isomers did not reach 100% of the maximal
response with AVP; therefore, these compounds were
determined to be partial agonists. Although the binding

Brief Articles
J ournal of Medicinal Chemistry, 2002, Vol. 45, No. 17 3807
at a dose of 0.01 mg/kg. An increase in the urine
osmolarity was also seen under the same conditions. The
same magnitude of antidiuretic action was observed
using compound S-2 by po administration at a dose of
0.1 mg/kg. Both compounds had an antidiuretic action
in a dose-dependent manner.
Con clu sion
We have prepared a series of benzazepine derivatives
as AVP V2 receptor agonists.2 Although additional
functional groups on the 5-position enhanced the oral
activity, the binding affinity for the human receptor was
dramatically affected by the difference in configuration
at this position. R-2 (OPC-51803) showed a more potent
agonist activity both in vitro and in vivo than S-2.4 This
compound is the first reported example of an orally
potent nonpeptide agonist for the AVP V2 receptor and
is expected to be an orally effective drug for treating
patients with low circulating levels of AVP.5
Exp er im en ta l Section
The radioligand binding assay and measurement of the
cyclic AMP production using HeLa cells expressing the human
AVP V2 receptors were performed according to the reported
method.4,6
An im a ls. Homozygous Brattleboro rats (weighing 180-300
g) were bred in our animal house (Otsuka Pharmaceutical Co.,
Ltd., Tokyo, J apan). The rats were housed in a temperature-,
humidity-, and light-controlled room and given free access to
food (MF; Oriental Yeast, Osaka, J apan) and water. The care
and handling of these animals were in accordance with The
Guidelines for Animal Experimentation at Otsuka Pharma-
ceutical Co., Ltd., October 1, 1994.
F igu r e 1. cAMP accumulation in response to nonpeptide
compounds at the given concentration expressed as per-
cent with standard error of the response obtained by stimula-
tion with AVP (1 nM) in HeLa cells expressing human V2
receptors.
Ack n ow led gm en t. The authors thank Dr. Y. Yab-
uuchi and Dr. T. Sumida for their valuable comments
and continuing encouragement. We also thank Ms. M.
Murakami for her technical support with the in vitro
assay.
Su p p or tin g In for m a tion Ava ila ble: General experimen-
tal procedure for syntheses of compounds, single-crystal X-ray
analysis of 10, physical and spectral characterizations (1H
NMR, mass spectrometry) and physicochemical parameters,
and tables listing crystal data and structure refinement,
atomic coordinates, bond lengths and angles, anisotropic
displacement parameters, hydrogen coordinates, and isotropic
displacement parameters of 10. This material is available free
of charge via the Internet at http://pubs.acs.org.
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