New non-peptide endothelin-a receptor antagonists: Synthesis, biological properties, and structure-activity relationships of 5-(dimethylamino)-N- pyridyl-, -N-pyrimidinyl-, -N-pyridazinyl-, and -N-pyrazinyl-1- naphthalenesulfonamides

Article abstract of DOI:10.1021/jm9604585

Use of automated synthesis led to the discovery of several 6-membered nitrogen heterocycles as replacements for the N-isoxazolyl substituent present in the 1-naphthalenesulfonamide endothelin-A (ETA) antagonist 5- (dimethylamino)-N-(3,4-dimethyl-5-isoxazolyl)-1-naphthalenesulfonamide (BMS 182874). In each of these heterocycles, a small substituent such as halogen para to the position of attachment to the sulfonamide nitrogen atom was found to be advantageous for ETA receptor affinity. Of these heterocycles, 2- pyrazines offered the greatest scope for improving receptor affinity. Optimization of the substituents at the 3- and 5-positions in the pyrazine ring led to potent, ET(A)-selective compounds such as 5-(dimethylamino)-N- (5-chloro-3-methoxy-2-pyrazinyl)-1-naphthalenesulfonamide (7m, ET(A) pIC₅₀ 8.1). When dosed orally at 10 mg/kg to conscious, normotensive rats infused with big ET-1, compounds such as 7m showed significant inhibition of the pressor response with a duration of effect lasting for the 5-h course of the experiment.

Full text of DOI:10.1021/jm9604585

996
J . Med. Chem. 1997, 40, 996-1004
New Non -P ep tid e En d oth elin -A Recep tor An ta gon ists: Syn th esis, Biologica l
P r op er ties, a n d Str u ctu r e-Activity Rela tion sh ip s of
5-(Dim eth yla m in o)-N-p yr id yl-, -N-p yr im id in yl-, -N-p yr id a zin yl-, a n d
-N-p yr a zin yl-1-n a p h th a len esu lfon a m id es
Robert H. Bradbury,* Colin Bath, Roger J . Butlin, Michael Dennis, Christine Heys, Sarah J . Hunt,
Roger J ames, Andrew A. Mortlock, Neil F. Sumner, Eric K. Tang, Berwick Telford, Elaine Whiting, and
Campbell Wilson
Cardiovascular and Musculoskeletal Department, ZENECA Pharmaceuticals, Mereside, Alderley Park,
Macclesfield, Cheshire SK10 4TG, U.K.
Received J une 25, 1996X
Use of automated synthesis led to the discovery of several 6-membered nitrogen heterocycles
as replacements for the N-isoxazolyl substituent present in the 1-naphthalenesulfonamide
endothelin-A (ETA) antagonist 5-(dimethylamino)-N-(3,4-dimethyl-5-isoxazolyl)-1-naphtha-
lenesulfonamide (BMS 182874). In each of these heterocycles, a small substituent such as
halogen para to the position of attachment to the sulfonamide nitrogen atom was found to be
advantageous for ETA receptor affinity. Of these heterocycles, 2-pyrazines offered the greatest
scope for improving receptor affinity. Optimization of the substituents at the 3- and 5-positions
in the pyrazine ring led to potent, ETA-selective compounds such as 5-(dimethylamino)-N-(5-
chloro-3-methoxy-2-pyrazinyl)-1-naphthalenesulfonamide (7m , ETA pIC50 8.1). When dosed
orally at 10 mg/kg to conscious, normotensive rats infused with big ET-1, compounds such as
7m showed significant inhibition of the pressor response with a duration of effect lasting for
the 5-h course of the experiment.
Following the initial isolation of the vasoconstrictor
peptide endothelin-1 (ET-1) from endothelial cells,1 ET-1
and the closely-related isopeptides endothelin-2 (ET-2)
and endothelin-3 (ET-3) have been implicated in a
number of disease states.2-5 Thus, blockade of the
endothelin receptor may be of use in treating conditions
such as renal failure,6 cerebral vasospasm,7 and pul-
monary hypertension.8
In mammalian tissues, two subtypes of endothelin
receptor have been identified.9,10 The endothelin-A
(ETA) receptor binds ET-1 and ET-2 with greater affinity
than ET-3 and is found mainly in vascular smooth
muscle, where it mediates vasoconstriction11-13 and
smooth muscle proliferation.14 The endothelin-B (ETB)
receptor binds ET-1, ET-2, and ET-3 with equal affinity
and mediates both vasoconstriction and vasodilatation
in certain vascular beds.11,15,16 The pharmacological
significance of the ETB subtype in mammalian tissues
is the subject of continuing debate.17-20
The endothelin antagonists reported initially were
peptidic in nature. The cyclic pentapeptide BQ-12321
and the tripeptide FR13931722 are ETA-selective, whereas
the tripeptide BQ-78823 is ETB-selective, and hexapep-
tides such as PD 14289324 and PD 14506525 display
antagonism at both ETA and ETB receptors. Of these
compounds, the prototype ETA-selective antagonist BQ-
123 has been shown to be effective in animal models,
most notably by hypertension26 and acute renal fail-
ure.27
More recently, the first non-peptide endothelin an-
tagonists have been described. These include the sul-
fonamides Ro 46-2005,28 Ro 47-0203 (Bosentan),29 and
BMS 182874,30,31 the 1,3-diarylindan-2-carboxylic acid
SB 209670,32 the related diaryl pyrrolidine A-127722,33
and the butenolide PD 156707.34 Of these compounds,
BMS 182874, A-127722, and PD 156707 are ETA-
selective, whereas the remainder are mixed ETA/ETB
antagonists. All of these non-peptide antagonists have
been shown to be effective in endothelin-dependent
disease models.
It appears that these non-peptide antagonists were
derived by optimization of leads found through either
directed32 or high-throughput28,30,34 screening of phar-
maceutical-company compound collections. Our own
screening program produced no attractive starting
points for optimization, and we therefore turned our
attention to non-peptide endothelin antagonists recently
described in the literature.
Of the non-peptide antagonists reported at the time
of starting the work described in this paper, the ETA-
selective BMS 182874 (1)30,31 seemed a particularly
attractive starting point for several reasons. Firstly, we
sought an ETA-selective antagonist to maintain ETB-
mediated vasodilatation and because the contractile
response to endothelin in vascular tissue is thought to
be predominantly ETA-mediated.35 Secondly, as de-
scribed below, in our biological test cascade 1 showed
antihypertensive activity after oral dosing at 10 mg/kg
in rats challenged with big ET-1. Thirdly, a pharma-
cokinetic study in rats showed 1 to be rapidly absorbed
through the lower intestine. Finally, sulfonamides such
as 1 are simply prepared from the appropriate naph-
thalenesulfonyl chloride and aminoisoxazole, and we
envisaged that using automated synthesis36 a wide
range of analogs of 1 could rapidly be made from readily-
available aryl or heteroaryl sulfonyl chlorides and amino
heterocycles.
Of these two structural parameters, varying the
amino heterocycle part of the structure led to com-
pounds with the more interesting biological properties.
X Abstract published in Advance ACS Abstracts, February 15, 1997.
S0022-2623(96)00458-X CCC: $14.00 © 1997 American Chemical Society

New Non-Peptide ETA Receptor Antagonists
J ournal of Medicinal Chemistry, 1997, Vol. 40, No. 6 997
Sch em e 2a
F igu r e 1. Structure of BMS 182874 (1).
Sch em e 1
a
Reagents: (i) NaH/MeI/DMF (9a ,c); (ii) POCl3/MeCN/sul-
folane/70 °C; (iii) NaH/2-amino-5-bromo-3-methoxypyrazine/DME;
(iv) TMSI/MeCN; (v) B2H6/THF.
(method C) or prior deprotonation of the amino hetero-
cycle using sodium hydride as base (method D).
The majority of amino heterocycles needed for this
work were commercially available or were prepared by
published methods.37-49 Characterization data for the
remaining, novel aminohalopyrazines 3a -e synthesized
during the course of this work are given in Table 6. A
small number of compounds synthesized for biological
testing (6e-g, 7i) were obtained by manipulation of
preformed N-heteroaryl 1-naphthalenesulfoanmides as
detailed in the Experimental Section.
The compounds 11a -d listed in Table 5 were pre-
pared to investigate the effect of varying the 5-substitu-
ent in the naphthalene ring. The unsubstituted 1-naph-
thalenesulfonamide 11d was prepared (method B) by
reaction of 1-naphthalenesulfonyl chloride with 2-amino-
5-bromo-3-methoxypyrazine,48 while the remaining com-
pounds 11a -c were obtained as outlined in Scheme 2,
starting from the acylated 5-aminonaphthalene-1-sul-
fonic acids 8a ,50b.51
In this paper, we describe how this approach resulted
in the discovery of several 6-membered nitrogen het-
erocycles as replacements for the isoxazole moiety in 1
and led to a series of N-heteroaryl 1-naphthalene-
sulfonamides that are potent, selective endothelin ETA
antagonists both in vitro and in vivo.
Ch em istr y
The naphthalenesulfonamides 4-7 and 11 prepared
during the course of this work are listed in Tables 1-5.
The majority of these compounds (4a -1, 5a -d , 6a -
d ,h ,i, 7a -h ,j-n ) were obtained as shown in Scheme 1
by reaction of 5-(dimethylamino)-1-naphthalenesulfonyl
chloride (2, dansyl chloride) with the appropriate amino
heterocycle 3.
Three sets of reaction conditions were used to effect
sulfonamide formation. Initially, we required conditions
for automated synthesis from dansyl chloride and a
range of commercially-available, 5- and 6-membered
amino heterocycles, chosen on the basis of structural
diversity, lack of other functionality that might interfere
under the reaction conditions, and a molecular weight
of less than 200. Use of stoichiometric amounts of
dansyl chloride, amino heterocycle, and pyridine and a
catalytic amount of 4-(dimethylamino)pyridine in dichlo-
romethane (method A) proved effective for automation
on a Zymate XP robot.36 Of 40 amino heterocycles tried
under these conditions, 25 cleanly gave the correspond-
ing dansyl sulfonamides, the products being isolated
directly by either filtration or bond elute chromatogra-
phy. The remaining amino heterocycles did not react
cleanly with dansyl chloride, presumably due to either
poor solubility or low reactivity of the amino group, or
both.
As described below, application of automated synthe-
sis gave two pyridine derivatives (4b,i) that showed
endothelin antagonist activity in vitro. To improve on
the activity of these compounds, a range of analogs
incorporating various 6-membered nitrogen heterocycles
was prepared using conventional laboratory synthesis.
The initial 2- and 3-pyridyl analogs 4c-g were obtained
using essentially the procedure employed for robotic
synthesis (method B). For preparation of analogs 5a -
d , 6a -d ,h ,i, and 7a -h ,j-n derived from less reactive
amino diazines, more forcing conditions were needed,
involving either reaction in pyridine at 70-80 °C
En d oth elin Recep tor Affin ity
The compounds listed in Tables 1-5 were evaluated
as endothelin antagonists in a radioligand binding assay
involving displacement of [125I]ET-1 from membranes
prepared from cloned human ETA receptors9 expressed
in mouse erythroleukemic (MEL) cells. The pIC50 for 1
in this assay is included in Table 1 for comparison. A
similar assay was used to measure affinity for the
human ETB receptor10 (data not shown).
Of the 25 initial analogs of 1 prepared by automated
synthesis from dansyl chloride and a variety of amino
heterocycles, only the 2- and 3-pyridyl derivatives 4b,i
(Table 1) showed affinity for the ETA receptor, although
at a lower level than the prototype 1. To explore further
the activity of the para-substituted 2-pyridyl compound
4b, the corresponding halopyridines 4c-e were pre-
pared and found to show similar affinity. Whereas
further substitution at the 6-position resulted in lower
affinity (compound 4f), introduction of a methyl group
at the 3-position led to increased affinity (compound 4g).
For 3-pyridyl derivatives, replacement of chlorine by
bromine increased affinity (compound 4j).
The importance of the substituent at the position para
to the position of attachment to the sulfonamide nitro-
gen atom was shown by the reduced activity of the
parent 2- and 3-pyridyl compounds 4a ,h , possibly

998 J ournal of Medicinal Chemistry, 1997, Vol. 40, No. 6
Bradbury et al.
Ta ble 1. Characterization Data and ETA Receptor Affinity for N-Pyridyl- and N-Phenyl-1-naphthalenesulfonamides 4a -l
no.
X
Y
R1
R2
R3
methoda
mp, °C
formulab
% inhibtn at 10 µMc
pIC50 (n)c
1
98
<30
79
95
91
84
54
94
<30
81
95
30
7.3 ( 0.1 (7)
4a
4b
4c
4d
4e
4f
4g
4h
4i
N
N
N
N
N
N
N
CH
CH
CH
CH
CH
CH
CH
CH
CH
CH
CH
CH
N
N
N
CH
CH
H
H
H
H
H
H
Me
H
H
H
H
H
H
H
H
H
H
H
H
Me
H
H
H
H
H
A
A
B
B
C
B
B
A
A
B
B
B
235-237
209-211
160-162
176-177
211-212
155-156
foam
230-232
145-146
164-165
foam
C
C
C
C
C
C
C
C
C
C
C
C
17H17N3O2S
18H19N3O2S
Me
Cl
Br
I
Br
Br
H
Cl
Br
Cl
Br
5.8 (1)
5.7 ( 0.1 (6)
5.8 (1)
5.3 (1)
5.0 (1)
6.5 ( 0.0 (2)
17H16ClN3O2S
17H16BrN3O2S
17H16IN3O2Sd
18H18BrN3O2Se
18H18BrN3O2Sf
17H17N3O2S‚HCl
17H16ClN3O2S
17H16BrN3O2S
18H17ClN2O2Sg
18H17BrN2O2S
5.9 (1)
6.6 ( 0.1 (2)
5.1 (1)
4j
4k
4l
foam
72
5.5 (1)
a
Method A: 2/DMAP/CH2Cl2 (XP Zymate robot). Method B: 2/DMAP/CH2Cl2. Method C: 2/DMAP/pyridine/70-80 °C. Method D:
2/NaH/DME. Analyses for C, H, N were correct within (0.4% unless otherwise stated. c pIC50 for inhibition of specific binding of [125I]ET-
b
1 to human ETA receptor (n ) no. of replicate determinations). H, N; C: calcd, 45.6; found, 45.0. e H, N; C: calcd, 51.4; found, 50.4.f H,
d
g
N; C: calcd, 51.4; found, 49.7. H, N; C: calcd, 59.9; found, 59.0.
Ta ble 2. Characterization Data and ETA Receptor Affinity for N-Pyrimidyl-1-naphthalenesulfonamides 5a -d
no.
X
Y
R
methoda
mp, °C
formulab
% inhibtn at 10 µMc
pIC50 (n)c
5a
5b
5c
5d
N
N
N
CH
CH
CH
CH
N
H
C
C
C
C
235-237
189
197-199
177-179
C16H16N4O2S
54
84
80
88
5.2 (1)
5.8 (1)
5.7 (1)
6.2 ( 0.1 (3)
Cl
Br
Br
C
C
C
16H15ClN4O2S
16H15BrN4O2Sd
16H15BrN4O2S
d
a-c See Table 1. H, N; C: calcd, 47.2; found, 46.2.
consistent with a specific role for the substituent in
binding to the human ETA receptor. To determine the
importance of the ring nitrogen atom, para-substituted
aniline derivatives 4k ,l were prepared and found to
show only weak activity. A variety of aniline derivatives
with a wide range of substituents was subsequently
prepared by robotic synthesis (data not shown), but none
showed increased affinity.
stituent led to compounds with electron-withdrawing
(6e) and -releasing (6f,g) substituents at the position
para to the sulfonamide nitrogen atom. Of these
compounds, only 6f, in which a methoxy substituent was
introduced at the 6-position, was comparable in affinity
to the corresponding halopyridazines 6c,d . Further ring
substitution either maintained (6i) or reduced (6h )
receptor affinity.
To investigate the effect of introducing a second ring
nitrogen atom and to give access to substitution patterns
that might be difficult to introduce in a precursor 2- or
3-aminopyridine, the diazine derivatives listed in Tables
2-4 were prepared. Like the corresponding pyridines,
the parent pyrimidine and pyridazine derivatives 5a
and 6a showed reduced affinity, whereas substitution
with halogen or methyl at the para position gave a range
of compounds with moderate affinity (5b,c, 6b-d ). The
unsubstituted pyrazine 7a showed modest affinity, and
again this was enhanced by halogen substitution at the
para position (7c,d ).
Based on the reference 5-bromopyrazine derivative
7d , a more detailed study of the effect of substitution
was carried out at the 3-position in the pyrazine series
of antagonists (Table 4). Introduction of alkyl, cyano,
and hydroxyl groups (7e-i) all resulted in diminished
affinity, but introduction of a methoxy group gave
compound 7j with comparable affinity to the prototype
antagonist 1. The importance of the 3-methoxy group
in binding of 7j to the human ETA receptor was evident
from the reduced activity seen on increasing the bulk
of the alkoxy substituent (7k ,l). Replacement of the
5-bromo substituent with a chloro or methyl substituent
led to compounds 7m ,n with optimized ETA receptor
affinity. Like the prototype 1, at a concentration of 10
µM none of the compounds 7j,m ,n showed measurable
The effect of further substitution was examined in the
pyridazine and pyrazine series of antagonists. In the
pyridazine series (Table 3), manipulation of the 6-sub-

New Non-Peptide ETA Receptor Antagonists
J ournal of Medicinal Chemistry, 1997, Vol. 40, No. 6 999
Ta ble 3. Characterization Data and ETA Receptor Affinity for N-Pyridazinyl-1-naphthalenesulfonamides 6a -i
no.
R1
R2
R3
methoda
mp, °C
formulab
C16H16N4O2Sd
% inhibtn at 10 µMc
pIC50 (n)c
6a
6b
6c
6d
6e
6f
6g
6h
6i
H
Me
Cl
H
H
H
H
H
H
H
Me
H
H
H
H
H
H
H
H
H
C
C
C
C
g
h
h
D
D
117-120
113-115
153-154
151-153
160-165
125-127
194-198
110-112
182-186
<30
68
70
95
<30
92
64
64
89
C
C
C
C
C
C
C
C
17H18N4O2Se
5.8 (1)
6.7 ( 0.2 (3)
6.6 (1)
16H15ClN4O2S
Br
16H15BrN4O2Sf
17H15N5O2S‚0.25Me2NCHO
17H18N4O3S
CN
OMe
OEt
Cl
6.5 (1)
5.4 (1)
5.3 (1)
6.4 ( 0.2 (3)
18H20N4O3S
17H17ClN4O2Si
17H17ClN4O2Sj
Cl
Me
d
a-c See Table 1. C, H; N: calcd, 17.1; found, 15.9. e H; C: calcd, 59.6; found, 58.8. N: calcd, 16.4; found, 15.5. f H; C: calcd, 47.2;
g
h
found, 47.7. N: calcd, 13.8; found, 12.6. Prepared via corresponding 6-iodopyridazine (see the Experimental Section). Prepared from
i
j
6a (see the Experimental Section). H; C: calcd, 54.2; found, 53.3. N: calcd, 14.9; found, 14.2. C, H; N: calcd, 14.9; found, 13.9.
Ta ble 4. Characterization Data and ETA Receptor Affinity for N-Pyrazinyl-1-naphthalenesulfonamides 7a -n
no.
R1
R2
methoda
mp, °C
formulab
% inhibtn at 10 µMc
pIC50 (n)c
7a
7b
7c
7d
7e
7f
7g
7h
7i
7j
7k
7l
7m
7n
H
H
H
H
H
B
D
D
C
D
D
D
D
g
C
D
C
D
D
206-207
153-154
112-113
161-163
171-172
171-172
144-146
180-182
123-126
166-167
179-181
145-147
137-138
126-127
C16H16N4O2Sd
58
91
97
96
96
6.0 ( 0 (2)
5.9 (1)
6.8 (1)
6.9 ( 0.2 (2)
6.2 (1)
Me
Cl
Br
Br
Br
Br
Br
Br
Br
Br
Br
Cl
Me
C
C
C
C
C
C
C
C
C
C
C
C
C
17H18N4O2Se
16H15ClN4O2S
16H15BrN4O2S
17H17BrN4O2S
118H19BrN4O2S
19H21BrN4O2S
17H14BrN5O2Sf
Me
Et
Pr
CN
OH
OMe
OEt
OBn
OMe
OMe
68
5.6 (1)
<30
<30
81
93
92
<30
97
98
h
16H15BrN4O3
5.3 (1)
7.2 ( 0.2 (7)
6.3 (1)
17H17BrN4O3S
18H19BrN4O3S
23H21BrN4O3S
17H17ClN4O3S
18H20N4O3S
8.0 ( 0.1 (6)
8.1 ( 0.1 (10)
d
a-c See Table 1. H; C: calcd, 58.5; found, 59.5. N: calcd, 17.1; found, 16.1. e H, N; C: calcd, 59.6; found, 58.9. f H; C: calcd, 47.2;
g
h
found, 45.6. N: calcd, 16.2; found, 15.5. Prepared from 7j (see the Experimental Section). C, N; H: calcd, 3.6; found, 4.4.
affinity for the ETB receptor, nor did any of the other
ETA antagonists listed in Tables 1-5.
In a guinea pig portal vein preparation, compound 7m
showed functional antagonism of the ETA-induced con-
tractile response with a pA2 value of 7.20 ( 0.05 (n )
6). The corresponding value in this assay for the
prototype 1 was 6.20 ( 0.06 (n ) 3).
groups gave compounds 11a -c with similar affinity for
the ETA receptor to the 5-(dimethylamino) compound
7j, removal of the substituent resulted in ca. 100-fold
loss of affinity (11d vs 7j) and highlighted the impor-
tance of the 5-substituent in binding to the ETA receptor,
similarly to previously-reported structure-activity re-
lationships for the prototype 1.31
The key role of the acidic sulfonamide NH in binding
of compounds related to 1 to the ETA receptor has been
reported previously.31 pKa measurements on represen-
tative examples of the above N-heteroaryl 1-naphtha-
lenesulfonamides showed the acidity of these com-
pounds to be similar to that of 1 (e.g., pKa 5.0 for 7m vs
4.5 for 1).
Finally, with 7j as reference compound a limited
investigation was carried out to study the effect of
varying the 5-(dimethylamino) substituent in the naph-
thalene ring (Table 5). While fine tuning of the N-alkyl
P h a r m a cologica l Eva lu a tion
Selected compounds listed in Tables 1-5 were evalu-
ated for endothelin antagonism in vivo by determining
their mean dose ratios for inhibition of the pressor
response induced by infusion of big ET-1 in conscious,
normotensive rats. Data for 7m as a representative
member of this series of compounds are shown in Table
7, together with the corresponding data for 1 as a
comparison.

1000 J ournal of Medicinal Chemistry, 1997, Vol. 40, No. 6
Bradbury et al.
Ta ble 5. Characterization Data and ETA Receptor Affinity for
N-Pyrazinyl-1-naphthalenesulfonamides 11a -d
cycles as replacements for the isoxazole moiety. Like
the prototype 1, 1-naphthalenesulfonamides incorporat-
ing these heterocycles showed good ETA selectivity.
In each of these heterocycles, a small substituent such
as halogen para to the position of attachment to the
sulfonamide nitrogen atom was found to be advanta-
geous for receptor affinity. Of these heterocycles,
2-pyrazines offered the greatest scope for improving
affinity. Optimization of the substituents at the 3- and
5-positions in the pyrazine ring led to ETA-selective
compounds such as 7m (pIC50 8.1).
When dosed orally at 10 mg/kg to conscious, normo-
tensive rats infused with big ET-1, compounds such as
7m showed significant inhibition of the pressor response
with a duration of effect lasting for the 5-h course of
the experiment. Further work leading to more potent,
ETA-selective antagonists with improved pharmacologi-
cal profiles will be described in subsequent publications.
% inhibtn
no.
R
mp, °C
formulaa
at 10 µMb
pIC50 (n)b
11a NHMe
11b NHEt
11c N(Me)Et foam
171-173 C16H15BrN4O3Sc
216-218 C17H17BrN4O3S
100
95
99
7.8 ( 0.2 (2)
8.6 ( 0.1 (3)
7.9 (1)
C18H19BrN4O3S
11d 169-171 C15H12BrN3O3S
H
83
5.7 (1)
a,b
See Table 1. c H; C: calcd, 45.4; found, 46.1. N: calcd, 13.2;
found, 12.1.
Ta ble 6. Characterization Data for Aminopyrazine
Intermediates 3a -e
Exp er im en ta l Section
All operations were carried out at room temperature unless
otherwise stated. All evaporations were carried out at below
50 °C using a rotary evaporator. Flash chromatography was
performed on silica gel (Merck Kieselgel, Art. 9385). Bond
elute chromatography was performed on silica gel using 20-g
Mega Bond Elut cartridges (Varian, part no. 1225-6042).
Melting points were taken on a Buchi apparatus in glass
capillary tubes and are uncorrected. Automated synthesis was
carried out on a Zymate XP robot (Zymark Corp., Hopkinton,
MA 01748). 1H NMR spectra were recorded on a Bruker
WM200, WM250, or WM400 instrument and are reported as
δ values (parts per million) relative to Me4Si as internal
standard. Chemical ionization mass spectra (CIMS) were
recorded on a VG 70-250 SE spectrometer. Positive or negative
fast atom bombardment spectra (FABMS) were determined
on a VG ZAB 2-SE spectrometer.
no.
R1
R2
Et
mp, °C
formulaa
3a
3b
3c
3d
3e
Br
Br
Br
Cl
75-76
52-54
89-90
132-133
74-75
C6H8BrN3
C7H10BrN3
C11H10BrN3O
C5H6ClN3O
C6H9N3O
Pr
OBn
OMe
OMe
Me
a
See Table 1.
2-Am in o-5-br om o-3-eth ylp yr a zin e (3a ). A solution of
Br2 (0.21 mL, 640 mg, 4.0 mmol) in CHCl3 (40 mL) was added
dropwise over 1 h to a stirred solution of 2-amino-3-ethylpyra-
zine52 (492 mg, 4.0 mmol) and pyridine (0.32 mL, 316 mg, 4.0
mmol) in CHCl3 (100 mL) shielded from light. The solution
was stirred for a further 30 min and then washed with water
(50 mL) and dried (MgSO4). The solvent was removed by
evaporation, and the residue was purified by flash chroma-
tography, eluting with 25% EtOAc/isohexane to give 3a (660
mg, 82%): mp 75-76 °C (after recrystallization from isohex-
As can be seen from Table 7, following intravenous
administration at a dose of 10 mg/kg, compound 7m
showed a greater effect in this animal model than the
prototype 1. After oral administration at the same dose,
7m demonstrated a significant effect on the pressor
response for the 5-h time course of the experiment. The
magnitude and duration of effect seen for this compound
exceeded the effect of 1 at the same oral dose. Further
work using N-heteroaryl sulfonamides such as 7m as a
starting point and leading to potent, selective ETA
antagonists with improved pharmacological profiles will
be described in subsequent publications.
1
ane); H NMR (DMSO-d6) δ 1.15 (t, 3H), 2.55 (q, 2H), 6.4 (s,
2H), 7.9 (s, 1H). Anal. (C6H8BrN3) C, H, N.
A similar procedure starting from 2-amino-3-propylpyrazine
(obtained analogously to the preparation of 2-amino-3-eth-
ylpyrazine52 from 2-chloro-3-propylpyrazine53) gave 3b.
2-Am in o-3-(ben zyloxy)-5-br om op yr a zin e (3c). NaH (oil
free; 192 mg, 8.0 mmol) was added to a solution of benzyl
alcohol (864 mg, 8.0 mmol) in THF (10 mL), and the mixture
was stirred for 30 min. 2-Amino-3,5-dibromopyrazine47 (1.01
g, 4.0 mmol) was added, and the solution was heated under
reflux for 4 h. Water (50 mL) was added, and the mixture
Su m m a r y
Use of automated synthesis to explore variation of the
N-isoxazolyl substituent in the 1-naphthalenesulfona-
mide endothelin ETA antagonist BMS 182874 (1) led to
the discovery of several 6-membered nitrogen hetero-
Ta ble 7. Effects of Compounds 1 (BMS 182874) and 7m after Intravenous and Oral Dosing to Rats Infused with Big ET-1
oral MDRc
iv MDRb
1.03
0.5 h
1.09
1 h
1.03
3 h
1.05
5 h
1.28
a
no.
pIC50
vehicle
(0.60-1.75)
(0.98-1.22)
(0.94-1.13)
(0.89-1.24)
(1.13-1.44)
1
7.3
8.0
2.68**
3.37***
2.28**
2.18**
1.55
(2.21-3.26)
8.87***
(2.38-4.77)
3.91***
(1.45-3.56)
4.42***
(1.38-3.46)
2.54***
(0.91-2.61)
2.07***
7m
(3.65-21.55)
(2.92-5.24)
(3.29-5.94)
(1.64-3.90)
(1.55-2.76)
a
b
See Table 1. Mean dose ratio for inhibition of pressor response 5 min after intravenous administration of compound at 10 mg/kg to
pithed rats (n ) 4); 95% confidence limits are in parentheses. c Mean dose ratio for inhibition of pressor response at time points shown
after oral administration of compound at 10 mg/kg to conscious, normotensive rats (n ) 6); 95% confidence limits are in parentheses. **p
< 0.01, ***p < 0.001 vs vehicle-treated group (unpaired Student’s t-test).

New Non-Peptide ETA Receptor Antagonists
J ournal of Medicinal Chemistry, 1997, Vol. 40, No. 6 1001
was extracted with EtOAc (2 × 25 mL). The extracts were
washed with water (25 mL) and saturated NaCl (25 mL) and
dried (MgSO4). Volatile material was removed by evaporation,
and the residue was purified by flash chromatography, eluting
with 35% EtOAc/isohexane. The appropriate fractions were
combined and concentrated, and the residue was triturated
into two equal portions, and each portion was purified by bond
elute chromatography, eluting with CH2Cl2. The appropriate
fractions were concentrated, and the residue was triturated
with ether to give 4c (0.77 g, 43%): mp 160-162 °C; 1H NMR
(DMSO-d6) δ 2.85 (s, 6H), 7.05 (d, 1H), 7.3 (d, 1H), 7.6-7.8
(m, 3H), 8.1 (d, 1H), 8.3 (dd, 1H), 8.4 (d, 1H), 8.5 (d, 1H);
FABMS m/e 362 (M + H)+. Anal. (C17H16ClN3O2S) C, H, N.
5-(Dim eth ylam in o)-N-(5-br om o-3-m eth oxy-2-pyr azin yl)-
1-n a p h th a len esu lfon a m id e (7j) (Meth od C). 5-(Dimethyl-
amino)-1-naphthalenesulfonyl chloride (15.2 g, 56.0 mmol) and
2-amino-5-bromo-3-methoxypyrazine48 (9.5 g, 47.0 mmol) were
mixed intimately and added to pyridine (150 mL) at 0 °C. The
solution was kept at 0 °C for 1 h and then heated at 80 °C for
18 h. Volatile material was removed by evaporation, and CH2-
Cl2 (250 mL) was added to the residue. Insoluble material
was removed by filtration, and the filtrate was washed with
water (100 mL) and saturated NaCl (100 mL). The solution
was treated with charcoal and dried (MgSO4). The solvent was
removed by evaporation, and the residue was purified by flash
chromatography, eluting with 20% EtOAc/isohexane. The
resulting solid was triturated with ether and recrystallized
1
with isohexane to give 3c (570 mg, 51%): mp 89-90 °C; H
NMR (DMSO-d6) δ 5.4 (s, 2H), 6.5 (br s, 2H), 7.3-7.45 (m,
3H), 7.5-7.6 (m, 2H), 7.65 (s, 1H). Anal. (C11H10BrN3O) C,
H, N.
2-Am in o-5-ch lor o-3-m eth oxyp yr a zin e (3d ). Reaction of
2-amino-5-chloropyrazine44 with bromine by an analogous
procedure to that used for the preparation of 3a gave in 74%
yield 2-amino-3-bromo-5-chloropyrazine: mp 102-105 °C (af-
1
ter trituration with isohexane); H NMR (DMSO-d6) δ 7.0 (s,
2H), 8.1 (s, 1H).
2-Amino-3-bromo-5-chloropyrazine (78.0 g, 0.374 mol) was
added to a solution of sodium methoxide (30.3 g, 0.56 mol) in
methanol (1.66 L), and the solution was heated under reflux
for 6 h. The solvent was removed by evaporation, and water
(1 L) was added to the residue. The mixture was extracted
with CH2Cl2 (3 × 1 L), and the extracts were washed with
water (1 L) and dried (MgSO4). The solvent was removed by
evaporation, and the residue was triturated with isohexane
1
from EtOH to give 4j (4.7 g, 23%): mp 166-167 °C; H NMR
(DMSO-d6) δ 2.8 (s, 6H), 3.9 (s, 3H), 7.25 (d, 1H), 7.55-7.7
(m, 2H), 7.8 (s, 1H), 8.3 (d, 1H), 8.4-8.5 (m, 2H), 11.5 (br s,
1H); CIMS m/e 437 (M + H)+. Anal. (C17H17BrN4O3S) C, H,
N.
1
to give 3d (56.5 g, 95%): mp 132-133 °C; H NMR (DMSO-
d6) δ 3.9 (s, 3H), 6.45 (br s, 2H), 7.5 (s, 1H). Anal. (C6H9N3O)
C, H, N.
5-(Dim eth ylam in o)-N-(5-ch lor o-3-m eth oxy-2-pyr azin yl)-
1-n a p h th a len esu lfon a m id e (7m ) (Meth od D). NaH (60%
dispersion in oil; 2.38 g, 59.6 mmol) was freed from oil and
suspended in DME (20 mL) under Ar. A solution of 3d (3.78
g, 23.8 mmol) in DME (80 mL) was added, and the mixture
was stirred for 30 min. A solution of 5-(dimethylamino)-1-
naphthalenesulfonyl chloride (6.43 g, 23.8 mmol) in DME (60
mL) was added over 30 min, and the mixture was stirred for
19 h. Aqueous citric acid (40%; 200 mL) was added, and the
mixture was extracted with EtOAc (3 × 200 mL). The extracts
were washed with water (200 mL), dried (MgSO4), and
concentrated. The residue was recrystallized from EtOH to
2-Am in o-3-m eth oxy-5-m eth ylp yr a zin e (3e). Reaction of
2-amino-3-bromo-5-methylpyrazine46 with sodium methoxide
by an analogous procedure to that used for the preparation of
3d gave 3e in 78% yield: mp 74-75 °C (after trituration with
1
isohexane); H NMR (DMSO-d6) δ 2.55 (s, 3H), 3.95 (s, 3H),
4.75 (s, 2H), 7.4 (s, 1H). Anal. (C5H6ClN3O) C, H, N.
All other amino heterocycles used as precursors of 1-naph-
thalenesulfonamides were commercially available or were
prepared by published methods: 2-amino-5-iodopyridine,37
5-amino-2-bromopyrimidine,38 3-aminopyridazine,39 3-amino-
6-methylpyridazine,40 3-amino-6-bromopyridazine,39 3-amino-
6-chloro-4-methylpyridazine,41 3-amino-6-chloro-5-methyl-
pyridazine,42 2-amino-5-methylpyrazine,43 2-amino-5-chloro-
pyrazine,44 2-amino-5-bromopyrazine,45 2-amino-5-bromo-3-
methylpyrazine,46 2-amino-5-bromo-3-cyanopyrazine,47 2-amino-
5-bromo-3-methoxypyrazine,48 and 2-amino-5-bromo-3-ethoxy-
pyrazine.49
1
give 4m (4.26 g, 46%): mp 137-138 °C; H NMR (DMSO-d6)
δ 2.8 (s, 6H), 3.9 (s, 3H), 7.25 (d, 1H), 7.55-7.7 (m, 2H), 7.75
(s, 1H), 8.3 (d, 1H), 8.4 (d, 1H), 8.5 (d, 1H), 11.5 (br s, 1H);
FABMS m/e 393 (M + H)+. Anal. (C17H17ClN4O3S) C, H, N.
N-(6-Cya n o-3-p yr id a zin yl)-5-(d im eth yla m in o)-1-n a p h -
t h a len esu lfon a m id e (6e). Reaction of 3-amino-6-iodo-
pyridazine54 with 5-(dimethylamino)-1-naphthalenesulfonyl
chloride according to method C, but carrying out the reaction
at 20 °C, gave in 55% yield 5-(dimethylamino)-N-(6-iodo-3-
P r oced u r e for P r ep a r a tion of 5-(Dim eth yla m in o)-1-
n a p h t h a len esu lfon a m id es Usin g Zym a t e XP R ob ot
(Meth od A). A 0.33 M stock solution of 5-(dimethylamino)-
1-naphthalenesulfonyl chloride and pyridine in CH2Cl2 was
prepared, and 4-(dimethylamino)pyridine (0.05 equiv) was
added. Samples of 40 commercially-available amino hetero-
cycles (1 mmol) were placed in tubes in a rack on a Zymate
XP robot, and 3-mL aliquots of the stock solution were added
to each tube via the robot arm. The tubes were checked
visually, and insoluble amino heterocycles were noted. The
tubes were agitated overnight. Insoluble solids were filtered
off and checked against starting amino heterocycles by TLC.
In tubes where no precipitate was formed, the solution was
analyzed by TLC and any product formed isolated by bond
elute chromatography, eluting with MeOH/CH2Cl2 in the range
0-5% as appropriate. Of the 40 commercially-available amino
heterocycles used, 25 gave products in yields in the range 10-
90%. Compounds were tested for endothelin antagonist af-
finity in vitro without full characterization. Compounds
showing activity (4b,i) and representative inactive compounds
(e.g., 4a ,h ) were then characterized and generally found to give
satisfactory analytical data, e.g., 4i: mp 145-146 °C; 1H NMR
(DMSO-d6) δ 2.85 (s, 6H), 7.3 (dd, 2H), 7.45 (dd, 1H), 7.45-
7.6 (m, 3H), 8.05 (d, 1H), 8.25 (dd, 1H), 8.35 (d, 1H), 8.5 (d,
1H); FABMS m/e 362 (M + H)+. Anal. (C17H16ClN3O2S) C,
H, N.
1
pyridazinyl)-1-naphthalenesulfonamide: mp 177-178 °C; H
NMR (DMSO-d6) δ 2.8 (s, 6H), 7.2 (d, 1H), 7.55-7.7 (m, 3H),
7.9 (d, 1H), 8.3 (d, 1H), 8.4 (d, 1H), 8.9 (d, 1H).
A mixture of 5-(dimethylamino)-N-(6-iodo-3-pyridazinyl)-1-
naphthalenesulfonamide (227 mg, 0.5 mmol), KCN (130 mg,
2.0 mmol), and CuI (10 mg) in DMF (2 mL) was heated at 160
°C for 4 h. The solvent was removed by evaporation, and water
(10 mL) was added to the residue. Aqueous citric acid (8%)
was added to pH 5, and the precipitated solid was filtered off.
The solid was purified by bond elute chromatography, eluting
with MeOH/CH2Cl2 on a gradient from 0 to 7%, to give 6e (60
mg, 34%): mp 160-165 °C; 1H NMR (DMSO-d6) δ 2.8 (s, 6H),
7.2 (d, 1H), 7.55-7.7 (m, 3H), 8.0 (d, 1H), 8.4 (d, 2H), 8.5 (d,
1H), 13.7 (br s, 1H); FABMS m/e 353 (M + H)+. Anal.
(C17H15N5O2S‚0.25Me2NCHO) C, H; N: calcd, 19.2; found, 18.6.
5-(Dim e t h yla m in o)-N -(6-m e t h oxy-3-p yr id a zin yl)-1-
n a p h th a len esu lfon a m id e (6f). A mixture of compound 6c
(362 mg, 1.0 mmol) and sodium methoxide (162 mg, 3.0 mmol)
in N-methylpyrrolidone (1 mL) was heated under reflux for 4
h. The solvent was removed by evaporation under high
vacuum, and the residue was purified by flash chromatogra-
phy, eluting with 1% MeOH/CH2Cl2, to give 6f (140 mg, 33%):
mp 125-127 °C; 1H NMR (DMSO-d6) δ 2.9 (s, 6H), 3.8 (s, 3H),
7.2-7.3 (2d, 2H), 7.5-7.7 (m, 2H), 7.8 (d, 1H), 8.3 (d, 1H), 8.4-
8.6 (m, 2H); CIMS m/e 359 (M + H)+. Anal. (C17H18N4O3S)
C, H, N.
5-(Dim eth yla m in o)-N-(5-ch lor o-2-p yr id yl)-1-n a p h th a -
len esu lfon a m id e (4c) (Met h od B). A solution of 5-(di-
methylamino)-1-naphthalenesulfonyl chloride (1.35 g, 5.0 mmol),
2-amino-5-chloropyridine (0.64 g, 5.0 mmol), pyridine (0.40 g,
5.0 mmol), and 4-(dimethylamino)pyridine (20 mg) in CH2Cl2
(20 mL) was left to stand for 3 days. The solution was split
5-(Dim eth ylam in o)-N-(5-br om o-3-h ydr oxy-2-pyr azin yl)-
1-n a p h th a len esu lfon a m id e (7i). A solution of 7j (218 mg,
0.5 mmol) and sodium thiomethoxide (105 mg, 1.5 mmol) in

1002 J ournal of Medicinal Chemistry, 1997, Vol. 40, No. 6
Bradbury et al.
DMF (5 mL) was heated at 130 °C for 4 h. Aqueous citric acid
(8%; 20 mL) was added, and the mixture was extracted with
EtOAc (2 × 20 mL). The extracts were washed with water (3
× 20 mL), dried (MgSO4), and concentrated. The residue was
purified by bond elute chromatography, eluting with MeOH/
CH2Cl2 on a gradient from 0 to 2%, to give 7i (69 mg, 33%):
mp 123-126 °C; 1H NMR (DMSO-d6) δ 2.8 (s, 6H), 7.2 (d, 1H),
7.35-7.45 (br, 1H), 7.55-7.7 (m, 2H), 8.3 (dd, 1H), 8.5 (t, 2H);
FABMS m/e 423 (M + H)+. Anal. (C16H15BrN4O3S) C, N; H:
calcd, 3.6; found, 4.4.
(6.65 mL, 6.65 mmol) was added to a solution of 10b (725 mg,
1.66 mmol) in dry THF (60 mL) at 0 °C under Ar. The solution
was heated under reflux for 24 h, and then volatile material
was removed by evaporation. The residue was purified by
flash chromatography, eluting with 35% EtOAc/isohexane, to
give 11b (230 mg, 32%): mp 216-218 °C (after trituration with
1
ether); H NMR (DMSO-d6) δ 1.3 (t, 3H), 3.25 (q, 2H), 3.9 (s,
3H), 6.6 (d, 1H), 7.4-7.6 (m, 2H), 7.75 (s, 1H), 7.95 (d, 1H),
8.25 (d, 1H), 8.5 (d, 1H), 11.4 (br s, 1H); FABMS m/e 437 (M
+ H)+. Anal. (C17H17BrN4O3S) C, H, N.
5-[(Ben zyloxyca r bon yl)m eth yla m in o]-1-n a p h th a len e-
su lfon yl Ch lor id e (9a ). NaH (60% dispersion in oil; 2.89 g,
72.4 mmol) was added over 5 min to a solution of sodium
5-[(benzyloxycarbonyl)amino]-1-naphthalenesulfonate (8a )50
(11.0 g, 29.0 mmol) in DMF (110 mL). The mixture was stirred
for 30 min, and then iodomethane (4.15 g, 29.2 mmol) was
added dropwise over 30 min. The mixture was stirred for 20
h and then added to water (300 mL). Volatile material was
removed by evaporation under high vacuum, and the residue
was dissolved in water (100 mL). The solution was washed
with EtOAc (100 mL) and acidified to pH 3 with concentrated
HCl. The mixture was extracted with CH2Cl2 (3 × 100 mL),
and the extracts were dried (MgSO4). The solvent was
removed by evaporation, and the residue was purified by flash
chromatography, eluting with AcOH/MeOH/CH2Cl2 (0.1:20:80),
to give 5-[(benzyloxycarbonyl)methylamino]-1-naphthalene-
5-(N-Meth yla ceta m id o)-1-n a p h th a len esu lfon yl Ch lo-
r id e (9c). Use of a similar procedure to that described for
the preparation of 9a , but starting from sodium 5-acetamido-
1-naphthalenesulfonate (8b),51 gave 9c as an oil in 42% overall
yield: 1H NMR (DMSO-d6) δ 1.6 (s, 3H), 3.2 (s, 3H), 7.45-
7.65 (m, 3H), 7.7 (dd, 1H), 8.05 (dd, 1H), 8.9 (dd, 1H); CIMS
m/e 298 (M + H)+.
5-(N -Me t h y la c e t a m id o )-N -(5-b r o m o -3-m e t h o x y -2-
p yr a zin yl)-1-n a p h th a len esu lfon a m id e (10c). Reaction of
9c with 2-amino-5-bromo-3-methoxypyrazine48 according to
method D and purifying the crude product by flash chroma-
tography, eluting with MeOH/CH2Cl2 on a gradient from 1 to
10%, gave 10c as a foam in 21% yield: 1H NMR (DMSO-d6) δ
1.6 (s, 3H), 3.2 (s, 3H), 3.9 (s, 3H), 7.6-7.7 (m, 4H), 8.1 (d,
1H), 8.35-8.45 (m, 1H), 8.8-8.9 (m, 1H), 11.6 (br s, 1H);
FABMS m/e 465 (M + H)+.
5-(E t h y lm e t h y la m i n o )-N -(5-b r o m o -3-m e t h o x y -2-
p yr a zin yl)-1-n a p h th a len esu lfon a m id e (11c). Use of a
similar procedure to that described for the preparation of 11b,
but starting from 10c and purifying the crude product by bond
elute chromatography (1% MeOH/CH2Cl2), gave 11c as a foam
in 41% yield: 1H NMR (DMSO-d6) δ 1.1 (t, 3H), 2.8 (s, 3H),
3.1 (q, 2H), 3.9 (s, 3H), 7.3 (d, 1H), 7.6-7.7 (m, 2H), 7.7 (s,
1H), 8.3-8.4 (m, 1H), 8.5 (t, 2H), 11.5 (br s, 1H); FABMS m/e
451 (M + H+). Anal. (C18H19BrN4O3S) C, H, N.
Deter m in a tion of Affin ity for Clon ed Hu m a n En d o-
th elin ETA a n d ETB Recep tor s Exp r essed in Mou se
Er yth r oleu k em ic Cells. The cDNAs for the ETA and ETB
receptors were obtained by polymerase chain reaction (PCR)
of a human kidney cDNA library or a human placental cDNA
template, respectively. The cDNAs were subcloned and ex-
pressed in MEL-C88 cells using standard published methodol-
ogy.55 MEL cell membranes (cloned human ETA and ETB)
were incubated with [125I]ET-1 (30 pM final) and competing
ligands, in a final incubation volume of 225 µL. Samples were
incubated for 180 min at 30 °C, and the incubation was
terminated by filtering through GF/B filters using a Brandel
cell harvester. [125I]ET-1 binding was quantified by gamma
counting.
sulfonic acid (6.5 g, 60%) as a foam: 1H NMR (DMSO-d6
+
CD3CO2D) δ 3.3 (s, 3H), 5.0 (s, 2H), 7.05 (br s, 1H), 7.25 (br s,
2H), 7.4-7.6 (m, 4H), 7.8 (d, 1H), 7.95 (s, 1H), 8.05 (d, 1H),
8.9 (d, 1H).
POCl3 (0.73 mL) was added to a solution of 5-[(benzyloxy-
carbonyl)methylamino]-1-naphthalenesulfonic acid (741 mg,
2.0 mmol) in MeCN (2 mL) and sulfolane (2 mL), and the
solution was heated at 70 °C for 2 h under Ar. The solution
was added to ice-water (30 mL) and extracted with EtOAc (2
× 20 mL). The extracts were washed with water (20 mL),
dried (MgSO4), and concentrated. The residue was purified
by flash chromatography, eluting with 30% EtOAc/isohexane,
to give 9a (510 mg, 66%) as a foam: 1H NMR (DMSO-d6) δ
3.3 (s, 3H), 4.9-5.3 (m, 2H), 6.9-7.6 (m, 8H), 7.75 (d, 1H), 8.0
(dd, 1H), 8.85 (dd, 1H); FABMS m/e 390 (M + H)+. Anal.
(C19H16ClNO4S) C, H, N.
5-[(Ben zyloxyca r b on yl)m et h yla m in o]-N-(5-b r om o-3-
m eth oxy-2-p yr a zin yl)-1-n a p h th a len esu lfon a m id e (10a ).
Reaction of 9a with 2-amino-5-bromo-3-methoxypyrazine48
according to method D and purifying the crude product by bond
elute chromatography (40% EtOAc/isohexane) gave 12a as a
foam in 50% yield: 1H NMR (DMSO-d6) δ 3.3 (s, 3H), 3.9 (s,
3H), 4.9-5.3 (m, 2H), 6.9-7.6 (m, 9H), 8.1 (d, 1H), 8.35 (dd,
1H), 8.6 (d, 1H).
An ta gon ism of ETA-In d u ced Con tr a ctile Resp on se in
Gu in ea P ig P or ta l Vein . Guinea pigs of either sex and
weight > 250 g (n ) 3-6) were killed by cervical dislocation.
A 1-cm length of portal vein was removed and put into
oxygenated (95% O2/5% CO2) Krebs solution (118 mM NaCl,
4.75 mM KCl, 2.54 mM CaCl2, 1.2 mM MgCl2, 25 mM
NaHCO3, 0.93 mM KH2PO4, 11 mM glucose). The portal vein
was cleared of connective tissue and an approximately 4-mm
length set up for isometric recording of the circular muscle by
inserting two fine stainless steel wires through the lumen. The
tissue was suspended in a 20-mL organ bath containing
oxygenated Krebs solution at 32 °C. After an equilibration
time of approximately 1.5 h, a cumulative partial dose-
response curve to big ET-1 was constructed using a 3-fold
concentration increment to the point where a tension increase
of >100 mg was produced. Big ET-1 was washed out, and a
time period of 2 h was allowed to elapse. The tissue was again
washed, and a partial dose-response curve to big ET-1 in the
presence of the test antagonist was determined. The dose-
ratio shift was calculated and the pA2 value determined.
An ta gon ism of ETA-In d u ced P r essor Resp on ses by
Com p ou n d s Ad m in ister ed In tr a ven ou sly to P ith ed Ra ts.
Male Alderley Park Wistar rats (280-320 g, n ) 4) were pithed
under halothane anesthesia, and arterial and venous catheters
were implanted for measurement of blood pressure and
administration of big ET-1, respectively. Repeated cumulative
dose-response curves to big ET-1 (0.1-4.0 nmol/kg) were
5-(Meth yla m in o)-N-(5-br om o-3-m eth oxy-2-p yr a zin yl)-
1-n aph th alen esu lfon am ide (11a). Iodotrimethylsilane (0.20
mL, 282 mg, 1.41 mmol) was added over 1 min to a solution of
10a (330 mg, 0.60 mmol) in MeCN (6 mL), and the solution
was stirred for 30 min. MeOH (10 mL) was added, and the
solution was concentrated. The residue was purified by bond
elute chromatography, eluting with EtOAc/isohexane on a
gradient from 0 to 100%, to give 11a (30 mg, 12%): mp 171-
173 °C (after trituration with 50% ether/isohexane); 1H NMR
(DMSO-d6) δ 2.85 (s, 3H), 3.9 (s, 3H), 6.55 (d, 1H), 7.4-7.5
(m, 2H), 7.7 (s, 1H), 7.95 (d, 1H), 8.25 (dd, 1H), 8.45 (d, 1H),
11.3 (br s, 1H); FABMS m/e 425 (M + H)+. Anal. (C16H15
-
BrN4O3S) H; C: calcd, 45.4; found, 46.1. N: calcd, 13.2; found,
12.1.
5-Ace t a m id o-N-(5-b r om o-3-m e t h oxy-2-p yr a zin yl)-1-
n a p h th a len esu lfon a m id e (10b). Reaction of 5-acetamido-
1-naphthalenesulfonyl chloride (9b)51 with 2-amino-5-bromo-
3-methoxypyrazine48 according to method C and purifying the
crude product by flash chromatography, eluting with MeOH/
CH2Cl2 on a gradient from 3 to 5%, gave 10b in 8% yield: mp
221-225 °C; 1H NMR (DMSO-d6) δ 2.2 (s, 3H), 3.9 (s, 3H),
7.5-7.75 (m, 3H), 7.8 (s, 1H), 8.3-8.4 (m, 2H), 8.65 (d, 1H),
10.05 (s, 1H), 11.5 (br s, 1H); FABMS m/e 451 (M + H)+. Anal.
(C17H15BrN4O4S) C, H, N.
5-(Eth yla m in o)-N-(5-br om o-3-m eth oxy-2-p yr a zin yl)-1-
n a p h th a len esu lfon a m id e (11b). Diborane (1.0 M) in THF

New Non-Peptide ETA Receptor Antagonists
J ournal of Medicinal Chemistry, 1997, Vol. 40, No. 6 1003
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Endothelin and Angiotensin Receptors in Human Resistance
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constructed both prior to and 5 min after intravenous admin-
istration of test compound. The dose of big ET-1 to induce a
rise in mean arterial pressure of 30 mmHg was estimated for
each curve and the dose-ratio shift calculated.
An ta gon ism of ETA-In d u ced P r essor Resp on ses by
Com p ou n d s Ad m in ister ed Or a lly to Con sciou s, Nor m o-
ten sive Ra ts. Male Alderley Park Wistar rats (220-260 g,
n ) 6) were prepared under Saffan (alphaxalone/alphadolone)
anesthesia with indwelling arterial and venous catheters for
measurement of blood pressure and administration of big ET-
1, respectively. Repeated cumulative dose-response curves
to big ET-1 (0.1-4.0 nmol/kg) were constructed both prior to
and at time points following oral administration of test
compound. The dose of big ET-1 to induce a rise in mean
arterial pressure of 30 mmHg was estimated for each curve
and the dose-ratio shift calculated.
Ack n ow led gm en t. We thank the following for as-
sistance with some of the experimental work: E. Brian
Ellison, Paul K. Humphrey, Richard Hunt, Mukesh
Patel, Alan C. Reid, Kevin Rogers (Chemistry), David
A. Rudge (Robotics), Elizabeth Kelly, and Susan Mellor
(Pharmacology).
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