Bridged bicyclic vasopressin receptor antagonists with V2-selective or dual V1a/V2 activity

Article abstract of DOI:10.1016/S0960-894X(02)00649-2

The synthesis and biological testing of a novel series of nonpeptide vasopressin receptor antagonists, containing a bridged bicyclic nucleus, are reported. Variation of substituents (R₁-R₃) in general formula 3, and the configuration

Full text of DOI:10.1016/S0960-894X(02)00649-2

Bioorganic & Medicinal Chemistry Letters 12 (2002) 3081–3084
Bridged Bicyclic Vasopressin Receptor Antagonists with
V2-Selective or Dual V1a/V2 Activity
Alexey B. Dyatkin,a,* William J. Hoekstra,a Dennis J. Hlasta,a
Patricia Andrade-Gordon,a Lawrence de Garavilla,a
b
b
KeithT. Demarest, JosephW. Gunnet, William Hageman,a
Richard Lookb and Bruce E. Maryanoff a,*
aDrug Discovery, Johnson and Johnson Pharmaceutical Research and Development, Spring House, PA 19477-0776, USA
bDrug Discovery, Johnson and Johnson Pharmaceutical Research and Development, Raritan, NJ 08869-0602, USA
Received 5 June 2002; accepted 2 August 2002
Abstract—The synthesis and biological testing of a novel series of nonpeptide vasopressin receptor antagonists, containing a
bridged bicyclic nucleus, are reported. Variation of substituents (R1–R3) in general formula 3, and the configuration of the stereo-
center, resulted in potent V2-selective (e.g., 4) and balanced dual V1a/V2 (e.g., 10) compounds. Data from receptor binding, cell-
based functional, and in vivo assays are presented.
# 2002 Elsevier Science Ltd. All rights reserved.
Arginine vasopressin (AVP), a nonapeptide hormone
that is secreted mainly from the posterior pituitary
gland, exerts its biological action through two major
G-protein-coupled receptors, V1a and V2.1,2 The V1a
receptor subtype, which exists predominantly in vas-
cular smoothmuscle cells, platelets, the liver, adrenal
glands, and the uterus, is responsible for the cardio-
vascular effects of AVP, suchas vasoconstriction. The
V2 receptor subtype, which exists in the kidneys, is
responsible for controlling water reabsorption and salt
(NaCl) balance. Thus, there is therapeutic potential for
vasopressin V2-selective and dual V1a/V2 receptor
antagonists, suchas in treating congestive heart failure,
hypertension, renal disease, edema, and hyponatremia.3
The goal for this work was the discovery of both types of
agents.
rat aquaresis studies. We supposed that the introduction
of a basic amino group might improve physicochemical
properties of the target compounds. Saturation of the
pyrrole portion of the molecule, as in 2, also changes the
steric aspects of the tricyclic template to modulate
potency and selectivity. Although both the R and S
isomers of 2 are selective V2 receptor antagonists, the
enantiomer derived from (S)-proline exhibits lower affi-
nity. We envisioned the replacement of proline in the
synthesis of 2 by bridged bicyclic amino acids to afford
compounds of type 3, which might exhibit good potency
and in vivo efficacy as V2-selective and dual V1a/V2
agents. Indeed, this approach was successful as exem-
plified by derivatives 4 and 10. Compound 4, withthe R
absolute configuration, shows potent V2-selective activ-
ity and compound 10, withthe S configuration, shows
potent, balanced V1a/V2 activity.
Benzodiazepine heterocycles have been employed suc-
cessfully as a scaffold in several nonpeptide vasopressin
receptor antagonists. Representative compounds are 1
(VPA-985; lixivaptan)4 and 2 (VP-365)5 (Fig. 1), as well
as OPC-31260 (not shown),6 which exhibit high selectiv-
ity for V2 receptors in vitro and good in vivo efficacy in
The synthetic methodology for preparation of the
requisite bridged bicyclic amino acids in enantiomeri-
cally enriched form is well developed.7,8 The general
approachto these intermediates is presented in Scheme 1.
Diels–Alder cycloaddition of a cyclic diene to an activated
imine, formed from a-methyl-benzylamine and ethyl
glyoxalate, was catalyzed by CF3CO2H (TFA) for cyclo-
pentadiene or TFA-BF3 for 1,3-cyclohexadiene. The
cycloadducts were obtained withhighdiastereoselectivity,
*Corresponding authors. Tel.: +1-215-628-5008; email: adyatkin@
prdus.ini.com (A. B. Dyatkin); tel.: +1-215-628-5530; fax: +1-215-
628-4985; e-mail: bmaryano@prdus.jnj.com (B. E. Maryanoff);
0960-894X/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved.
PII: S0960-894X(02)00649-2

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A. B. Dyatkin et al. / Bioorg. Med. Chem. Lett. 12 (2002) 3081–3084
Further chemical modification of the benzodiazepine,
involving acylation with4-nitrobenzoyl chloride, reduc-
tion of the nitro group, and acylation of the aniline,
provided the desired target molecules (Scheme 3).
In Vitro Activity
We evaluated a series of bridged benzodiazepine targets
for binding to human V1a and V2 receptors and for cell-
based functional activity (Table 1). In general, the
(S)-enantiomers demonstrated high V2 activity along
Figure 1. Nonpeptide vasopressin receptor antagonists.
withV activity. In contrast, 4 (the R-enantiomer of 5)
1a
was V2-selective. Introduction of Cl atoms in the
2-position of benzodiazepine ring also increased affinity
of compounds toward V1a receptors.
We introduced substituted 4-aminobenzoic acids that
have been favorable with other benzodiazepine-based
vasopressin receptor antagonists.1 Variations of R2 and
R3 groups did not significantly affect the potency or
V1a/V2 selectivity of the compounds.
Scheme 1. (i) Toluene, reflux (–H2O).ꢀ (ii) TFA (n=1) or TFA/
.
BF3 Et2O (n=2), CH2Cl2 or DMF, ꢁ20 C. (iii) H2, Pd/C, EtOH.
Bioavailability and Metabolism
withthe ( R)-(+)-amine providing the (S)-cycloadduct.
The diastereomers were separated by flash-column
chromatography and hydrogenated to reduce the
alkene. During the hydrogenation step, the nitrogen was
deprotected, as well, to yield the bicyclic amino esters in
good yields.
In rats, 4–6 exhibited modest bioavailability and plasma
clearance rates. Selected pharmacokinetic properties are
given in the Table 2.
Compounds 4 and 6 were tested in a cytochrome P450
inhibition screen involving recombinant enzymes. Com-
pound 4 was A potently inhibitor of CYP3A4, whereas
6 had a small effect on CYP3A4 and no effect on
CYP1A2, CYP2C19 or CYP2D6; 6 was most active on
CYP2C9 (IC50=7.4 mM).10
For the preparation of the benzodiazepines, we
employed the method of Carabateas.9 Acylation of the
bicyclic amino esters with2-nitrobenzoyl chloride, fol-
lowed by tandem reduction-cyclization, provided ben-
zodiazepinediones, which were reduced by LiAlH4 in
THF (Scheme 2). These reactions occurred without loss
of the stereochemical integrity at the original stereo-
genic center. The commercial availability of substituted
2-nitrobenzoic allowed us to prepare 3-substituted benzo-
diazepines in this way.
Aquaretic Activity in Rats
We investigated some potent derivatives for in vivo
aquaretic activity in conscious hydrated male Sprague–
Dawley rats. Urine volume and osmolality were mea-
sured 4 hafter oral administration of the test com-
pounds. The results are presented in Table 3 for 4
Target compounds were prepared in 45–60% overall
yield based on the amino acid component.
Scheme 2. (i) CH2Cl2, Et3N, 0 ꢀC; (ii) Fe, AcOH, reflux; (iii) LAH,
THF, 0 ꢀC.
Scheme 3. (i) CH2Cl2, Et3N, 0 ꢀC. (ii) Zn dust, NH4Cl, MeOH, reflux.
(iii) CH2Cl2, Et3N, ArCOCl, 0 ꢀC.

A. B. Dyatkin et al. / Bioorg. Med. Chem. Lett. 12 (2002) 3081–3084
Table 1. Vasopressin V2 and V1a binding and functional data
3083
Compda
R1
R2
R3
n
Configb
V2 IC50, mMc
V1a IC50, mMc
hV2funct., Ki, mMd
hV1a funct., Ki, mMd
4
5
6
7
8
9
10
11
12
13
14
H
H
Cl
Cl
H
Cl
H
H
H
H
Cl
Cl
H
H
2-Ph1
2-Ph1
Se
Rf
S
S
S
S
S
R/S
R/S
S
0.004
0.015
0.005
0.003
0.026
0.010
0.007
0.006
0.004
0.019
0.013
0.072
0.005
0.028
0.024
7%g
0.009
0.03
0.013
—
0.180
0.032
0.009
—
—
—
0.52
—
0.13
—
0.023
—
2.6
0.13
0.04
—
—
—
Cl
Cl
Cl
Cl
Cl
H
H
H
Cl
Cl
2-(40-MeC6H4)
2-(40-MeC6H4)
2-F
1
1
1
1
1
0.024
0.035
0.068
0.005
0.004
ꢂ0.1
30%g
15%g
0.035
0.059
0.15
2-Cl
2-CF3
2-Ph2
2-Ph2
3-F-5-Me
2-Cl
2-(40-MeC6H4)
2
2
2
S
S
0.62
—
—
0.89
15
VPA-985h
OPC-31260h
0.09
0.16
0.25
aTarget compounds were purified by flash-column chromatography and crystallized as HCl salt hydrates (EtOAc). Purities were judged by reverse-
phase HPLC/MS at 215 nm and 254 nm; all compounds were analyzed by 300-MHz 1H NMR and MS; compounds tested in vivo gave satisfactory
elemental analyses. Enantiomeric purity (>99% ee) was confirmed by chiral HPLC.
bAbsolute configuration for the stereocenter designated by an asterisk (*).
cInhibition of [3H]-Arg-vasopressin binding to recombinant human vasopressin V1a and V2 receptors. IC50 values unless noted otherwise.
dInhibition of vasopressin receptor activation caused by AVP was determined in HEK-293 cells expressing human V1a or V2 receptors; changes in
intracellular Ca2+ (V1a) or cAMP (V2) concentra-tions were measured.
20
½ꢀꢃD +188ꢀ (c 0.175, MeOH).
e
20
½ꢀꢃD ꢁ206ꢀ (c 0.193, MeOH).
f
gPercentage inhibition value, determined at 0.1 mM.
hReference standards within-house data.
Table 2. Oral pharmacokinetic properties of 4–6a
Table 3. In vivo diuretic effect in rats
Dose, po
(mg/kg)
No. of
animals
Urine volume
(mL)a
Urine osmolality
(mOsm/kg)a
Compd
Oral
t1/2 (h)
F
(%)
Clearance, iv
(mg/kg/mM-h)
Oral Cmax
(mM)
4
Vehicle
0.3
1
3
10
5
Vehicle
0.3
1
3
10
6
Vehicle
1
4
5
6
5
2.5
2.5
14
10
7
1.2
3.3
2.1
0.65
0.23
0.32
10
9
10
10
10
1.1ꢄ0.2
2.5ꢄ0.3
6.0ꢄ0.7
15.1ꢄ1.4
29.9ꢄ2.0
663ꢄ62
444ꢄ79
299ꢄ34
180ꢄ9
aMature male rats (250–300 g) were used. Eachcompound was admin-
istered at a dose of 30 mg/kg, p.o. (N=3) and 3 mg/kg, iv (N=3). The
plasma levels for the compounds were determined by LC-MS.
138ꢄ11
10
9
10
10
10
0.6ꢄ0.1
1.4ꢄ0.1
3.4ꢄ0.4
9.4ꢄ1.1
19.5ꢄ1.4
892ꢄ70
408ꢄ37
303ꢄ29
238ꢄ19
172ꢄ9
(10-fold V2-selective), 5 (V2-selective), and 6 (balanced
V1a/V2).
It is evident that 4–6 have significant aquaretic activity,
as they strongly increased urine volume and decreased
urine osmolality in a dose-dependent manner. The salt-
sparing activity of 6 and OPC-31260 were shown by the
small amount of sodium and potassium lost through the
urine (Table 4), as compared to the large volume of
urine produced.
10
10
10
10
2.3ꢄ0.3
2.9ꢄ0.2
5.8ꢄ0.5
17.8ꢄ1.3
441ꢄ30
387ꢄ15
226ꢄ9
159ꢄ9
3
10
OPC-31260
Vehicle
1
3
10
30
16
8
10
9
2.1ꢄ0.4
2.3ꢄ0.5
5.4ꢄ0.7
12.2ꢄ1.0
21.5ꢄ3.0
608ꢄ50
530ꢄ42
372ꢄ39
238ꢄ18
165ꢄ17
8
aMeanꢄSE.
Reversal of AVP-Induced Hypertension in Rats
Vasopressin plays an important role in regulating blood
pressure by means of the V1a receptors in the cardio-
vascular system. Activation of V1a receptors on arterial
smoothmuscle cells results in vasoconstriction and an
increase in blood pressure. In this assay, we assessed the
ability of VPA-985, 4, 6, and 10 to reverse exogenous
AVP-induced hypertension in pentobarbital-anesthe-
tized male Long–Evans rats. AVP was diluted in saline

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A. B. Dyatkin et al. / Bioorg. Med. Chem. Lett. 12 (2002) 3081–3084
Table 4. Na, K, and creatinine excretion
variation of substituents and absolute configuration
resulted in V2-selective (e.g., 4) and balanced V1a/V2
(e.g., 10) vasopressin receptor antagonists, some of
which have good efficacy in vitro and in vivo.
Dose, po
(mg/kg)
Na
(mEq/4 h)a
K
Creatinine
(mg/dL) a
(mEq/4 h)a
6
Vehicle
1
3
10
0.05ꢄ0.01
0.07ꢄ0.01
0.16ꢄ0.02
0.52ꢄ0.04
0.28ꢄ0.03
0.30ꢄ0.02
0.34ꢄ0.02
0.64ꢄ0.03
36.6ꢄ2.9
31.4ꢄ1.5
16.2ꢄ1.0
7.7ꢄ0.6
Acknowledgements
We thank Eric Ericson, Gail Thompson, Barbara
Haertlein, and Pat Sasso for technical assistance; Dr.
Zhengyin Yan for cytochrome P450 inhibition data; and
Mary Evangelisto for determinations of enantiomeric
purity.
OPC-31260
Vehicle
3
10
30
0.05ꢄ0.01
0.17ꢄ0.04
0.42ꢄ0.08
0.50ꢄ0.09
0.35ꢄ0.02
0.52ꢄ0.04
0.62ꢄ0.04
0.74ꢄ0.03
56.1ꢄ8.6
30.5ꢄ5.4
14.1ꢄ2.2
9.2ꢄ0.9
aMeanꢄSE; N=8–10.
References and Notes
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withED
values of 217ꢄ43 mg/kg (N=6), 172ꢄ119
50
mg/kg (N=8), and 380ꢄ286 mg/kg (N=5), respectively.
Note that 6 tended to be the most potent of the bicyclic
compounds and that this correlates with the relative
potency in the V1a functional assay. Although 10 was
more potent than 4 in the functional assay, this differ-
ence could not be detected in the blood pressure assay in
rats. Because of specific differences in the vasopressin
receptors, it may be difficult to draw a direct compar-
ison between the blood pressure assay in rats and the
functional assay in cells expressing the human receptor,
especially withteh limited number of compounds
involved.
Summary
We have identified a novel series of nonpeptide vaso-
pressin receptor antagonists comprised of a benzodia-
zepine ring that is fused to a bridged bicyclic amine. The