Butenolide endothelin antagonists with improved aqueous solubility

Article abstract of DOI:10.1021/jm980504w

Continued development around our ET(A)-selective endothelin (ET) antagonist 1 (CI-1020) has led to the synthesis of analogues with improved aqueous solubility profiles. Poor solubility characteristics displayed by 1 required a complex buffered formulation

Full text of DOI:10.1021/jm980504w

2162
J . Med. Chem. 1999, 42, 2162-2168
Bu ten olid e En d oth elin An ta gon ists w ith Im p r oved Aqu eou s Solu bility
William C. Patt,*,† Xue-Min Cheng,† J oseph T. Repine,† Chet Lee,† Bill R. Reisdorph,† Mark A. Massa,†
Annette M. Doherty,† Kathleen M. Welch,‡ J ohn W. Bryant,‡ Michael A. Flynn,‡ Donnelle M. Walker,‡
Richard L. Schroeder,‡ Stephen J . Haleen,‡ and J oan A. Keiser‡
Departments of Chemistry and Vascular and Cardiac Diseases, Parke-Davis Pharmaceutical Research Division,
Warner-Lambert Company, 2800 Plymouth Road, Ann Arbor, Michigan 48105
Received August 31, 1998
Continued development around our ETA-selective endothelin (ET) antagonist 1 (CI-1020) has
led to the synthesis of analogues with improved aqueous solubility profiles. Poor solubility
characteristics displayed by 1 required a complex buffered formulation in order to conduct iv
studies. To overcome the use of specific iv formulations for preclinical studies on additional
drug candidates, analogues with improved aqueous solubility were desired. Several analogues
were synthesized with substitution patterns that allowed for the formation of either acid or
base addition salts. These derivatives had dramatically improved aqueous solubility. In addition,
these analogues retained equivalent or improved ETA receptor selectivity and antagonist
potency, versus 1, both in vitro and in vivo. Compound 29, which contains as a substituent the
sodium salt of a sulfonic acid, has an ETA IC50 ) 0.38 nM, ETA selectivity of 4200-fold, and
ETA functional activity of KB ) 7.8, all of which are similar or superior to those of 1. Compound
29 also has vastly superior aqueous solubility and solubility duration, compared to 1.
Furthermore, 29 after iv infusion displays improved activity to 1 in preventing acute hypoxia-
induced pulmonary hypertension in rats with an ED50 ) 0.3 µg/kg/h.
In tr od u ction
compound. While 1 has good oral activity,4 displaying
the ability to counteract the effects of an exogenous dose
of the ET agonist ET-1, its iv use is limited by the
insolubility of the closed-form butenolide tautomer,
which precipitates out of aqueous solutions, without the
use of a specific and complex buffered formulation.
Our goal in this project was to develop water-soluble
closed-form γ-hydroxy butenolides that would not re-
quire specific formulations for parenteral uses. Toward
that end, two general series of analogues were synthe-
sized which retained the desired ETA antagonist selec-
tivity and potency while greatly improving the aqueous
solubility of the drug candidates at physiological pH.
The endothelins (ETs) are a family of peptides that
display a variety of physiological activities. These
peptides exert their actions via activation of two distinct
receptor subtypes, ETA and ETB. Antagonists of these
receptors have received numerous citations in the recent
pharmaceutical literature.1-3 Both ETA- and ETB-selec-
tive, as well as nonselective, receptor antagonists
demonstrating wide therapeutic potential have been
described.4-6 Our first clinical candidate in this field, 1
(CI-1020), exemplifies an ETA-selective antagonist.4
Compound 1 is an extremely potent antagonist of the
human recombinant ETA receptor with an IC50 ) 0.30
nM. It is also 2600-fold selective for the ETA receptor
over the ETB receptor (ETB IC50 ) 780 nM). Chemically
1 is rather interesting in that it exists, in solution, as
an equilibrium mixture of two tautomers, Figure 1. At
acidic pH’s the equilibrium resides predominantly in the
γ-hydroxy butenolide structure, 1, while at basic pH’s
the equilibrium favors the ring-opened γ-keto acid salt
structure, 1a . This equilibrium allows for isolation of
either form as a stable solid. However in aqueous
solution, at physiological pH, both tautomers are present.
In fact, due to solution-phase equilibration, both tau-
tomers are always present, to some extent, regardless
of pH. While one can easily synthesize and isolate the
water-soluble salts of the keto acid forms, once they are
placed in aqueous solutions the equilibrium determines
how much of each tautomer is present. In fact, if the
γ-hydroxy butenolide tautomer is sufficiently water-
insoluble, it can precipitate out of solution and the
equilibrium can drive the complete precipitation of the
Ch em istr y
The synthetic route to these compounds has been
previously published,4,7 and the general approach is
depicted in Scheme 1. Noncommercial aldehydes 8
employed in step iv were obtained by the alkylation of
the corresponding phenols 7 (3-hydroxybenzaldehyde
and 3,4-dimethoxy-5-hydroxybenzaldehyde) with a halo-
alkylamine, using standard methodology. The crude
aldehydes were generally used without extensive puri-
fication in the subsequent condensation reaction.
Resu lts a n d Discu ssion
Two series of compounds are shown in Table 1, and
both contain the p-methoxyphenyl substituent at the
γ-position and the 3,4-(methylenedioxy)phenyl moiety
at the R-position on the butenolide structure. These two
substituents impart high ETA potency to the butenolide
series.4 The SAR presented here has been restricted to
the “central” benzylic group. This position is known to
accept a wide variety of substitution patterns while
retaining potency.4
† Department of Chemistry.
‡ Department of Vascular and Cardiac Diseases.
10.1021/jm980504w CCC: $18.00 © 1999 American Chemical Society
Published on Web 05/21/1999

Butenolide Endothelin Antagonists
J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 12 2163
F igu r e 1. Tautomerization of butenolides.
Sch em e 1a
a
(i) NaOH, EtOH; (ii) KCN, HOAc, 2-ethoxyethanol, 100 °C; (iii) p-TsOH, MeOH, reflux; (iv) NaOMe, MeOH, 8; (v) HOAc; (vi) NaOH;
(vii) Cs2CO3, X-(CH2)n-Cl, DMF.
pholinylpropoxy compound 13 is the most potent of the
Compounds 9-22 in Table 1 contain basic groups that
monosubstituted basic compounds with an ETA IC50
2.0 nM.
)
allow the formation of acid addition salts, expected to
improve the aqueous solubility of the closed butenolide
form. The compounds were tested for their ability to
inhibit specific [125I]ET-1 binding to recombinant human
ETA and ETB receptors as previously described.8
Compounds 16-20 contain 3,4-dimethoxy substitu-
tions, on the benzyl, in addition to the m-aminoalkoxy
moiety. This trialkoxy substitution pattern induces a
10-50-fold improvement in receptor binding affinity, as
expected from previous work.4 The (dimethylamino)-
ethoxy and -propoxy compounds 16 and 17 have 2.8 and
1.0 nM binding affinities, respectively, at the ETA
receptor. Again the morpholinyl compounds are more
potent as exemplified by compound 19 which has a
binding affinity of IC50 ) 0.2 nM (ETA) which is just
slightly more potent than 1. Compounds 21 and 22
contain two morpholinylethoxy substituents, and both
are substantially less active indicating some steric
limitations around the central benzylic site. Few of these
compounds had measurable ETB inhibition, which is
consistent with our earlier report in that most buteno-
lides are extremely ETA-selective.
The first seven analogues, 9-15, are monosubstituted
with aminoalkoxy groups. From previous work, we know
that long chains at the para position have a negative
effect on ET receptor potency while meta substitution
is unaffected. This is borne out in this series as exempli-
fied by compounds 9 and 11. The p-(dimethylamino)-
propoxy compound 9 was essentially inactive, while the
otherwise identical meta derivative 11 had an ETA IC50
) 28 nM.
Chain length at the meta position, while not explored
to a great extent, appears to be unimportant, with
regard to binding potency. The (dimethylamino)ethoxy
and -propoxy analogues 10 and 11, as well as the
morpholinylethoxy and -propoxy compounds 12 and 13,
were both equipotent within their own series. The cyclic
amines were more potent than the dimethylamino
derivatives. The morpholinyl (13), methylpiperazinyl
(14), and pyrrolidinyl (15) analogues all had improved
activity over the dimethylamino compounds. The mor-
Compounds 23-29, in Table 1, contain acidic substi-
tutions as well as some of their immediate ester precur-
sors. The acidic functionalities on these analogues
allowed for the formation of “metal” salts to attempt to
improve the aqueous solubility of the butenolides. The
three carboxylic acid compounds 24, 26, and 28 were

2164 J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 12
Ta ble 1. Biological Data for Butenolides
Patt et al.
IC50 (nM)
KB
a
a
b
compd
R2
ETA
ETB
ETA
1
9
3,4,5-(OMe)3
0.30
780
>2500
2400
7.5
6.2
7.0
4-O-(CH2)3-NMe2
3-O-(CH2)2-NMe2
3-O-(CH2)3-NMe2
3-O-(CH2)2-(N-morpholinyl)
3-O-(CH2)3-(N-morpholinyl)
>25000
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
27
28
>250
>2500
>2500
>2500
>2500
>2500
>2500
>2500
2300
>250
>2500
>2500
600
4500
200
1200
900
2100
1600
4.0
2.0
12
10
2.8
1.0
2.0
0.2
0.7
3-O-(CH2)3-(N′-Me-N-piperazinyl)
3-O-(CH2)2-(N-pyrrolidinyl)
3,4-(OMe)2-5-O-(CH2)2-NMe2
3,4-(OMe)2-5-O-(CH2)3-NMe2
3,4-(OMe)2-5-O-(CH2)3-(N′-Me-N-piperazinyl)
3,4-(OMe)2-5-O-(CH2)2-(N-morpholinyl)
3,4-(OMe)2-5-O-(CH2)3-(N-morpholinyl)
4-OMe-3,5-[O-(CH2)2-(N-morpholinyl)]2
3,5-[O-(CH2)2-(N-morpholinyl)]2
3,4-(OMe)2-5-OCH2CO2Me
3,4-(OMe)2-5-OCH2CO2H
3,4-(OMe)2-5-O(CH2)3CO2Me
3,4-(OMe)2-5-O(CH2)3CO2H
3,4-(OMe)2-5-O(CH2)4CO2Me
3,4-(OMe)2-5-O(CH2)4CO2H
3,4-(OMe)2-5-O(CH2)3SO3Na
6.9
6.8
2000
>10
0.2
8.5
0.09
0.29
0.05
0.30
0.38
7.5
7.4
7.8
7.8
a
IC50 values were determined as described using six concentrations of inhibitor (0.01-2500 nM), depending on inhibitor and n ) 2.
Inhibition of ET-1-induced contraction in rabbit femoral artery rings; KB determined from n ) 2.
b
Ta ble 2. Solubility Data for Selected Butenolides
derived from their corresponding esters 23, 25, and 27
by base hydrolysis. The acids were less potent at the
ETA receptor than their esters by 5-40-fold but still
retained significant activity since the esters were some
of the most potent analogues we have synthesized in
aqueous
solubility
compd
salt form
solubilitya
durationb
1
1a
parent
Na
<0.01
g125
not determined
precipitatesc
12
12
16
20
26a
29
parent
isethionic
isethionic
isethionic
di Na
<0.25
<0.25
g250
g250
g250
not determined
not determined
soluble for >120 h
soluble for >120 h
soluble for >120 h
soluble for >120 h
this program. Ester derivative 27 has an ETA IC50
)
50 pM, 6 times more potent than that of 1. These esters
are, unfortunately, virtually insoluble in aqueous sys-
tems and were unsuitable for in vivo testing, and
consequently further development was prohibited. The
most potent of the carboxylic acids, 26, has an ETA IC50
) 0.3 nM, equivalent to that of 1. The final acidic
analogue in this study, 29, contains a sulfonic acid group
which was isolated solely as a sodium salt due to the
strongly acidic nature of the sulfonic acid moiety. This
derivative is also rather potent with an ETA IC50 ) 0.38
nM, identical to that of 1.
Na
g250
a
b
In mg/mL, determined in pH 7.4 phosphate buffer. Visual
observation of a 50 mg/mL solution in pH 7.4 phosphate buffer.
c Turns cloudy within minutes, and a noticeable precipitate is
observed within 2 h.
no solubility, while the sodium salt 1a has good im-
mediate solubility (g125 mg/mL), but exposure to
physiological pH quickly drives the equilibrium to the
poorly soluble closed-form butenolide. Thus, in 10 min
an initial 50 mg/mL solution of 1a starts to turn hazy,
and after 2 h a definite precipitate is observed. It should
be noted that even a 1.0 mg/mL solution of 1a precipi-
tates out of solution rapidly.
Numerous acid addition salts were examined (e.g.,
citric acid, hydrochloric acid, acetic acid, methane-
sulfonic acid...) for their ability to increase aqueous
solubility of the base-containing derivatives, and the
isethionic acid salt was found to give the greatest degree
of improvement. All of the γ-hydroxy butenolides (closed
form) containing basic groups had very poor aqueous
solubility without an acid addition salt. The monoamino-
alkoxy-substituted derivative 12 has low aqueous solu-
bility, <0.25 mg/mL, as both a free base and its
Functional activity due to ETA receptor antagonism
was then determined, for selected compounds from
Table 1. This arterial ring contraction assay was run
in isolated rabbit femoral arteries, an ETA tissue, using
ET-1 as the agonist as previously disclosed.8,9 As
expected, antagonist activity correlated with receptor
binding affinity. The clinical lead 1 has a KB value of
7.5 in this assay. The base-containing compounds have
KB values of 6.2-7.0, while the more potent esters and
acids had potencies equivalent with the potency of 1.
The sulfonic acid analogue 29 had a KB value of 7.8,
slightly more potent than that of 1.
In Table 2 the solubility data for several of the
compounds in pH 7.4 phosphate buffer is presented. The
parent ring-closed butenolide version of 1 has essentially

Butenolide Endothelin Antagonists
J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 12 2165
F igu r e 3. Pulmonary hypertensive response for 29.
F igu r e 2. Pulmonary hypertensive response for 16.
isethionic acid salt. Salts of the more potent dimethoxy
derivatives had greatly improved aqueous solubility
characteristics. The isethionic acid salts of 16 and 20
had excellent aqueous solubility (g250 mg/mL respec-
tively). More importantly a 50 mg/mL solution of either
did not cause precipitation for >120 h after dissolution.
Finally, two of the derivatives containing acidic sub-
stituents were examined. The carboxylic acid 26a was
tested as a bis-sodium salt in the open form similar to
1. This salt had initial solubility similar to that of 1,
g250 mg/mL. Fortunately, the duration of solubility was
greatly enhanced versus that of 1. A 50 mg/mL solution
showed no evidence of precipitation after >120 h in
solution. The more potent antagonist 29 was tested as
its monosodium salt in the closed form, and it had
excellent aqueous solubility (g250 mg/mL). This deriva-
tive also showed no evidence of precipitating out of
solution even upon standing for >120 h.
Two of the potent water-soluble salts, 16 and 29, were
then tested in vivo for activity against acute hypoxic
pulmonary hypertension.10,11 In this model male Spra-
gue-Dawley rats were surgically instrumented with
pulmonary artery and femoral vein cannulae. The day
after surgery the instrumented rats were given either
vehicle or drug by iv infusion from 1 h before and
throughout 4 h of hypoxia (10% oxygen). This hypoxic
regimen produced more than a 2-fold increase in pul-
monary arterial pressure (13 ( 1 to 30 ( 4 mmHg) in
vehicle-treated rats.
F igu r e 4. Pulmonary hypertension data for 29 (black) and
16 (gray). Pulmonary arterial hypertensive response in con-
scious Sprague-Dawley rats to hypoxia (10% O2). This area-
under-the-curve representation is the hypertensive response
above prehypoxic baseline levels accumulated over 4 h.
Ta ble 3. Acute Pulmonary Hypertension Data
compd
ED50 (µg/kg/h)a
1
16
29
1.5
6.0
0.3
a
Determined using the AUC data from Figure 4.
Con clu sion s
We have been able to synthesize analogues closely
related to 1 that retain similar ETA receptor potency
and selectivity. Several analogues containing salts of
either acidic or basic groups had increased aqueous
solubility and solution duration, a prerequisite for
parenteral administration. Of particular note are the
isethionic acid salt of the (dimethylamino)ethoxy ana-
logue 16 and the sodium salt of the sulfonic acid 29.
Compound 16 had an ETA IC50 ) 2.8 nM (>900-fold
selective) and a KB value of 7.0 in the in vitro ETA
functional assay, while 29 had an ETA IC50 ) 0.38 nM
(4200-fold selective) and a KB value of 7.8 in the in vitro
ETA functional assay. Both compounds exhibit high
aqueous solubility and did not precipitate out of solution
upon prolonged exposure to aqueous solutions at physi-
ological pH. Additionally, 16 and 29 were active in
preventing acute hypoxia-induced pulmonary hyperten-
sion in the conscious rat. Compound 16 was slightly less
potent than 1, in this assay, with an ED50 ) 6.0 µg/kg/
The data obtained for 16 and 29 are displayed
graphically in Figures 2-4. Figure 2 gives the actual
blood pressure response observed with 16, and Figure
3 is the raw data obtained with 29. Both compounds
gave a good dose response, and both lowered pulmonary
arterial pressure versus vehicle-treated rats over the
entire infusion period. Figure 4 depicts the potency of
16 and 29 using area under the curve (AUC) methodol-
ogy. The ED50’s that were determined via the AUC
method are displayed in Table 3 and compared to the
published data for 1. These two novel analogues bracket
the potency of 1 (ED50 ) 1.5 µg/kg/h). The single-digit
nanomolar receptor binding compound 16 gave an ED50
) 6.0 µg/kg/h, while the more potent subnanomolar
binding analogue 29 gave an ED50 ) 0.3 µg/kg/h, 5 times
as potent as that of 1.
h, while 29 was slightly more potent with an ED50
0.3 µg/kg/h. Several of these compounds are undergoing
)
preclinical evaluation.

2166 J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 12
Patt et al.
3-Ben zo[1,3]dioxol-5-yl-4-[3-(2-(dim eth ylam in o)eth oxy)-
Exp er im en ta l Section
b e n zyl]-5-h yd r oxy-5-(4-m e t h oxyp h e n yl)-5H -fu r a n -2-
1
Gen er a l Ch em ica l P r oced u r es. All reagents were either
purchased from common commercial sources or synthesized
according to literature references using commercial sources.
Melting points were determined on a Thomas-Hoover capillary
melting point apparatus and are reported uncorrected. Proton
NMR (1H NMR) were obtained on a Varian Unity 300- or 400-
MHz spectrometer and are referenced to internal TMS. Mass
spectra were recorded on a Varian VG 7070 spectrometer at
nominal 500 resolution, a Finnigan MAT 900Q spectrometer,
or a Micromass platformLC using MassLynx 2.3 data system
and OpenLynxLC open access software. Microanalyses were
determined under contract with Robertson Analytical Services.
on e, 10. H NMR: (DMSO-d6) δ 2.23 (s, 6H), 2.66 (t, J ) 5.5
Hz, 2H), 3.71 (s, 2H), 3.75 (s, 3H), 3.89 (t, J ) 5.5 Hz, 2H),
5.95 (s, 2H), 6.47 (d, J ) 7.4 Hz, 1H), 6.58 (m, 2H), 6.78 (m,
3H), 6.96 (m, 3H), 7.41 (m, 2H), butenolide OH missing.
Microanalysis (C29H29NO7‚1.3H2O) C, H, N. MS: (CI) M+ + 1
) 504.
3-Ben zo[1,3]d ioxol-5-yl-4-[3-(3-(d im et h yla m in o)p r o-
p oxy)ben zyl]-5-h yd r oxy-5-(4-m eth oxyp h en yl)-5H-fu r a n -
1
2-on e, 11. H NMR: (DMSO-d6) δ 1.93 (m, 2H), 2.38 (s, 6H),
2.69 (t, J ) 7.6 Hz, 2H), 3.62 (s, 2H), 3.75 (s, 3H), 3.85 (t, J )
6.0 Hz, 2H), 5.92 (s, 2H), 6.58 (m, 3H), 6.74 (d, J ) 8.0 Hz,
1H), 6.81 (m, 2H), 6.95 (m, 3H), 7.4 (m, 2H), butenolide OH
missing. Microanalysis (C30H31NO7‚2.2H2O): C, H, N. MS: (CI)
M+ + 1 ) 518.
Gen er a l Exa m p le for Com p ou n d s
1 a n d 9-29.
3 -B e n z o [1 ,3 ]d i o x o l -5 -y l -4 -[3 -(2 -(d i m e t h y l a m i n o )-
eth oxy)-4,5-d im eth oxyben zyl]-5-h yd r oxy-5-(4-m eth oxy-
p h en yl)-5H-fu r a n -2-on e, 16. In DMF (45 mL) were stirred
3,4-dimethoxy-5-hydroxybenzaldehyde (1.82 g, 10 mmol) and
cesium carbonate (8.14 g, 25 mmol). To this was added
(dimethylamino)ethyl chloride hydrochloride (1.73 g, 12 mmol).
The mixture was stirred at 50 °C for 18 h. The mixture was
filtered free of insolubles and evaporated in vacuo to give an
oil. This was partitioned between ether (100 mL) and water
(100 mL). The ether layer was dried over magnesium sulfate
and evaporated in vacuo to give 1.75 g (69%) of crude
3,4-dimethoxy-5-[(dimethylamino)ethoxy]benzaldehyde, which
was used as is. In methanol (10 mL) was dissolved sodium
metal (97 mg, 4.2 mmol). To this solution were added 6 (2-
benzo[1,3]dioxol-5-yl-4-(4-methoxyphenyl)-4-oxobutyric acid
methyl ester7) (1.37 g, 4.0 mmol) and 3,4-dimethoxy-5-[(dim-
ethylamino)ethoxy]benzaldehyde (1.04 g, 4.1 mmol). The solu-
tion was warmed to 60 °C and stirred for 24 h. The mixture
was treated with acetic acid (1 mL) and stirred at reflux for
an additional 24 h. The mixture was cooled to room temper-
ature and evaporated free of solvents. The residue was
partitioned between ethyl acetate (75 mL) and water (50 mL).
The organic phase was separated and the aqueous phase
extracted with methylene chloride (2 × 50 mL). The methylene
chloride washes were combined and dried over magnesium
sulfate. The solvents were evaporated in vacuo to give a foam.
The foam was purified by flash chromatography (150 g silica
gel, 10-15% methanol in methylene chloride). The appropriate
fractions were evaporated in vacuo to give 1.05 g (47%) of pure
compound. 1H NMR: (DMSO-d6) δ 2.34 (s, 6H), 2.79 (d, J )
5.8 Hz, 2H), 3.64-3.67 (m, 2H), 3.66 (s, 3H), 3.69 (s, 3H), 3.77
(s, 3H), 4.06 (t, J ) 5.8 Hz, 2H), 5.93 (s, 2H), 6.08 (s, 1H), 6.36
(s, 1H), 6.75-6.94 (m, 5H), 7.45-7.49 (m, 2H), butenolide OH
3-Ben zo[1,3]dioxol-5-yl-5-h ydr oxy-5-(4-m eth oxyph en yl)-
4-[3-(2-m or p h olin -4-yleth oxy)ben zyl]-5H-fu r a n -2-on e, 12.
1H NMR: (DMSO-d6) δ 2.62 (m, 4H), 2.78 (t, J ) 5.5 Hz, 2H),
3.69 (s, 2H), 3.73 (m, 4H), 3.80 (s, 3H), 4.02 (t, J ) 5.5 Hz,
2H), 5.96 (s, 2H), 6.53 (m, 2H), 6.64 (m, 1H), 6.77 (m, 1H),
6.85 (m, 2H), 6.96 (m, 2H), 7.06 (t, J ) 8.0 Hz, 1H), 7.40 (m,
2H), butenolide OH missing. Microanalysis (C31H31NO8‚
1.5H2O) C, H, N. MS: (CI) M+ + 1 ) 546.
3-Ben zo[1,3]dioxol-5-yl-5-h ydr oxy-5-(4-m eth oxyph en yl)-
4-[3-(2-m or p h olin -4-yleth oxy)ben zyl]-5H-fu r a n -2-on e, 12,
Iseth ion ic Acid Sa lt. 1H NMR: (DMSO-d6) δ 2.50 (m, 4H),
2.60 (t, J ) 7.0 Hz, 2H), 3.19 (m, 1H), 3.72-3.40 (m, 6H), 3.74
(s, 3H), 3.96 (m, 2H), 4.5 (m, 2H), 6.02 (s, 2H), 6.48 (s, 1H),
6.50 (d, J ) 7.7 Hz, 1H), 6.67 (m, 1H), 6.91 (m, 6H), 7.36 (m,
2H), 8.16 (s, 1H), 9.83 (br.s, 1H), acid protons missing.
Microanalysis (C30H31NO7‚C2H6SO4‚0.57H2O) C, H, N. MS:
(CI) M+ + 1 ) 546.
3-Ben zo[1,3]dioxol-5-yl-5-h ydr oxy-5-(4-m eth oxyph en yl)-
4-[3-(3-m or ph olin -4-ylpr opoxy)ben zyl]-5H-fu r an -2-on e, 13.
1H NMR: (DMSO-d6) δ 2.10 (m, 2H), 2.50 (m, 4H), 3.05 (m,
2H), 3.35 (br.s, 1H), 3.42 (m, 2H), 3.64 (m, 2H), 3.75 (s, 3H),
3.81 (m, 2H), 3.96 (m, 2H), 6.03 (s, 2H), 6.29 (s, 1H), 6.42 (d,
J ) 7.7 Hz, 1H), 6.58 (m, 1H), 6.88 (m, 5H), 7.35 (d, J ) 9.2
Hz, 2H), 8.17 (s, 1H). Microanalysis (C32H33NO8‚2.3H2O) C,
H, N. MS: (CI) M+ + 1 ) 560.
3-Ben zo[1,3]dioxol-5-yl-5-h ydr oxy-5-(4-m eth oxyph en yl)-
4-{3-[3-(4-m e t h ylp ip e r a zin -1-yl)p r op oxy]b e n zyl}-5H -
fu r a n -2-on e, 14. 1H NMR: (DMSO-d6) δ 1.85 (m, 2H), 2.22
(s, 3H), 2.48 (m, 10H), 3.68 (s, 2H), 3.77 (s, 3H), 3.79 (m, 2H),
5.95 (s, 2H), 6.48 (m, 2H), 6.61 (m, 1H), 6.81(m, 3H), 6.94 (m,
2H), 7.00 (t, J ) 8.0 Hz, 1H), 7.46 (d, J ) 8.9 Hz, 2H),
butenolide OH missing. Microanalysis (C33H36N2O7‚0.65H2O)
C, H, N. MS: (CI) M+ + 1 ) 573.
3-Ben zo[1,3]dioxol-5-yl-5-h ydr oxy-5-(4-m eth oxyph en yl)-
4-[3-(2-p yr r olid in -1-yleth oxy)ben zyl]-5H-fu r a n -2-on e, 15.
1H NMR: (DMSO-d6) δ 1.89 (br.m, 4H), 2.96 (m, 4H), 3.06 (t,
J ) 5.3 Hz, 2H), 3.68 (s, 2H), 3.78 (s, 3H), 4.7 (t, J ) 5.3 Hz,
2H), 5.92 (s, 2H), 6.57 (m, 2H), 6.73 (m, 2H), 6.83 (m, 2H),
6.93 (m, 2H), 7.0 (t, J ) 7.9 Hz, 1H), 7.45 (m, 2H), butenolide
OH missing. Microanalysis (C31H31NO7‚1.7H2O) C, H, N. MS:
(CI) M+ + 1 ) 530.
3-B e n zo [1,3]d io x o l-5-y l-4-[3-(3-(d im e t h y la m in o )-
p r op oxy)-4,5-d im eth oxyben zyl]-5-h yd r oxy-5-(4-m eth oxy-
p h en yl)-5H-fu r a n -2-on e, 17. 1H NMR: (DMSO-d6) δ 2.17-
2.24 (m, 2H), 2.75 (s, 6H), 3.11-3.15 (m, 2H), 3.61 (s, 2H), 3.65
(s, 3H), 3.69 (s, 3H), 3.79 (s, 3H), 3.97-4.00 (m, 2H), 5.93 (s,
2H), 6.03 (s, 1H), 6.33 (s, 1H), 6.75-6.93 (m, 5H), 7.42-7.45,
(m, 2H), butenolide OH missing. Microanalysis (C32H35NO9)
Calcd: C, 66.54; H, 6.11; N, 2.42. Found: C, 60.99; H, 5.94;
N, 2.17. High-resolution ESI-MS (resolution 19 000 FWHH):
measured, 578.2360; theory, 578.2390; difference, -5.2 ppm.
MS: (CI) M+ ) 578.
missing. Microanalysis (C31H33NO9) C, H, N. MS: (CI) M+
564.
)
3-Ben zo[1,3]dioxol-5-yl-4-[3-(2-(dim eth ylam in o)eth oxy)-
4,5-d im et h oxyb en zyl]-5-h yd r oxy-5-(4-m et h oxyp h en yl)-
5H-fu r a n -2-on e, 16, Iseth ion ic Acid Sa lt. To 16 (3.62 g, 6.4
mmol) in methanol (75 mL) was added isethionic acid (15.2
mL of 0.42 M solution in water, 6.4 mmol). The mixture was
stirred for 30 min and evaporated in vacuo to give a foam.
This was treated with methanol (2 × 25 mL) and again
evaporated. The residue was triturated with ether (50 mL) and
the resultant solid collected by filtration to give 3.95 g (90%)
of the pure salt. 1H NMR: (DMSO-d6) δ 2.60 (t, J ) 6.8 Hz,
2H), 2.89 (s, 6H), 3.43-3.49 (m, 2H), 3.53 (s, 3H), 3.54 (s, 3H),
3.56-3.58 (m, 4H), 3.73 (s, 3H), 3.98-4.04 (m, 2H), 6.01 (s,
2H), 6.08 (s, 2H), 6.87-6.95 (m, 5H), 7.36 (d, J ) 7.7 Hz, 2H),
8.2 (br.s, ex, 1H), 9.53 (br.s, ex, 1H), butenolide OH missing.
Microanalysis (C31H33NO9‚C2H6SO4‚0.6H2O) C, H, N, S, H2O-
(KF). MS: (CI) M+ ) 564.
3-Benzo[1,3]dioxol-5-yl-4-[4-(3-(dimethylamino)propoxy)-
b e n zy l]-5-h y d r o x y -5-(4-m e t h o x y p h e n y l)-5H -fu r a n -
1
2-on e, 9. H NMR: (DMSO-d6) δ 2.03-2.08 (m, 2H), 2.75 (s,
3-Ben zo[1,3]d ioxol-5-yl-4-{3,4-d im eth oxy-5-[3-(4-m eth -
ylp ip er a zin -1-yl)p r op oxy]ben zyl}-5-h yd r oxy-5-(4-m eth -
oxyp h en yl)-5H-fu r a n -2-on e, 18. 1H NMR: (DMSO-d6) δ
1.89-1.96 (m, 2H), 2.27 (s, 3H), 2.50-2.70 (m, 10H), 3.63 (m,
2H), 3.66 (s, 3H), 3.74 (s, 3H), 3.80 (s, 3H), 3.88-3.92 (m, 2H),
5.96 (s, 2H), 6.06 (s, 1H), 6.26 (s, 1H), 6.79-6.96 (m, 5H), 7.44-
6H), 3.11-3.15 (m, 2H), 3.55-3.60 (m, 2H), 3.75 (s, 3H), 3.89-
3.92 (m, 2H), 6.02 (s, 2H), 6.59 (d, J ) 8.6 Hz, 2H), 6.71 (d, 8.6
Hz, 2H), 6.88-6.94 (m, 5H), 7.32 (d, J ) 8.8 Hz, 2H), 8.11 (s,
1H), 10.31 (br.s, 1H). Microanalysis (C30H31NO7‚HCl‚1.3H2O)
C, H, N, Cl-. MS: (CI) M+ ) 518.

Butenolide Endothelin Antagonists
J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 12 2167
7.46 (m, 2H), butenolide OH missing. Microanalysis (C35H40N2O9‚
H2O) C, H, N. MS: (CI) M+ ) 633.
δ 2.04-2.11 (m, 2H), 2.52-2.55 (m, 2H), 3.57-3.80 (m, 2H),
3.67 (s, 3H), 3.74 (s, 3H), 3.81 (s, 3H), 3.85-3.88 (m, 2H), 5.96
(s, 2H), 6.07 (s, 1H), 6.17 (s, 1H), 6.78-6.96 (m, 5H), 7.39-
7.41 (m, 2H), butenolide OH and acid proton missing. Mi-
croanalysis (C31H30O11‚0.5EtOAc (by NMR)) C, H, N. MS: (CI)
M+ ) 578.
3-Ben zo[1,3]d ioxol-5-yl-4-[3,4-d im eth oxy-5-(2-m or p h o-
lin -4-yleth oxy)ben zyl]-5-h yd r oxy-5-(4-m eth oxyp h en yl)-
5H-fu r a n -2-on e, 19. 1H NMR: (DMSO-d6) δ 2.55-2.57 (m,
4H), 2.74 (t, J ) 5.8 Hz, 2H), 3.65 (s, 3H), 3.65-3.73 (m, 6H),
3.74 (s, 3H), 3.79 (s, 3H), 3.92 (t, J ) 5.8 Hz, 2H), 5.97 (s, 2H),
6.04 (s, 1H), 6.10 (s, 1H), 6.79-6.97 (m, 5H), 7.39-7.42 (m,
2-Ben zo[1,3]d ioxol-5-yl-3-[3-(3-ca r b oxyp r op oxy)-4,5-
d im eth oxyben zyl]-4-(4-m eth oxyp h en yl)-4-oxobu t-2-en o-
1
2H), butenolide OH missing. Microanalysis (C33H35NO10
‚
ic Acid , 26, Disod iu m Sa lt. H NMR: (D2O) δ 190-1.94 (m,
0.6H2O) C, H, N. MS: (CI) M+ ) 606.
2H), 2.27-2.31 (m, 2H), 3.48 (s, 2H), 3.60 (s, 3H), 3.64 (s, 3H),
3.84 (s, 3H), 3.75-3.79 (m, 2H), 6.04 (s, 2H), 6.06 (s, 1H), 6.10
(s, 1H), 6.89-6.93 (m, 4H), 7.00-7.02 (m, 1H), 7.61-7.63 (m,
2H), butenolide OH exchanged. Microanalysis (C31H28O11Na2‚
2.1H2O) C, H, N, Na, H2O(KF). MS: (CI) M+ ) 577.
3-Ben zo[1,3]d ioxol-5-yl-4-[3,4-d im eth oxy-5-(3-m or p h o-
lin -4-ylp r op oxy)ben zyl]-5-h yd r oxy-5-(4-m eth oxyp h en yl)-
5H-fu r a n -2-on e, 20. 1H NMR: (DMSO-d6) δ 1.89-1.96 (m,
2H), 2.47-2.54 (m, 6H), 3.66 (s, 3H), 3.66-3.72 (m, 6H), 3.75
(m, 3H), 3.80 (m, 3H), 3.83-3.87 (m, 2H), 5.97 (s, 2H), 6.04 (s,
1H), 6.12 (s, 1H), 6.80-6.98 (m, 5H), 7.38-7.42 (m, 2H),
butenolide OH missing. Microanalysis (C34H37NO10‚0.3H2O) C,
H, N. MS: (CI) M+ ) 620.
3-Ben zo[1,3]d ioxol-5-yl-4-[3,4-d im eth oxy-5-(3-m or p h o-
lin -4-ylp r op oxy)ben zyl]-5-h yd r oxy-5-(4-m eth oxyp h en yl)-
5H-fu r a n -2-on e, 20, Iseth ion ic Acid Sa lt. 1H NMR: (DMSO-
d6) δ 2.0-2.1 (m, 2H), 2.58-2.62 (m, 2H), 3.05-3.18 (m, 2H),
3.18-3.25 (m, 2H), 3.3-3.6 (m, 4H), 3.51 (s, 3H), 3.52 (s, 3H),
3.6-3.85 (m, 6H), 3.74 (m, 3H), 3.99-4.02 (m, 2H), 5.95 (s,
1H), 6.02 (s, 2H), 6.88-6.95 (m, 5H), 7.35-7.37 (m, 2H), 8.17
(br.s, ex, 1H), 9.5 (br.s, ex, 1H), butenolide OH missing.
Microanalysis (C34H37NO10‚C2H6SO4‚0.5H2O): C, H, N, S, H2O-
(KF). MS: (CI) M+ ) 620.
3-Ben zo[1,3]d ioxol-5-yl-5-h yd r oxy-4-[4-m et h oxy-3,5-
bis(2-m or ph olin -4-yleth oxy)ben zyl]-5-(4-m eth oxyph en yl)-
5H-fu r a n -2-on e, 21, Diiseth ion ic Acid Sa lt. 1H NMR: (D2O)
δ 3.16 (t, J ) 6.5 Hz, 4H), 3.4-3.6 (m, 8H), 3.63-3.66 (m, 4H),
3.71 (s, 3H), 3.7-3.8 (m, 2H), 3.81 (s, 3H), 3.96 (t, J ) 6.5 Hz,
4H), 3.9-4.15 (m, 8H), 4.15-4.2 (m, 4H), 5.99 (s, 2H), 6.08 (s,
2H), 6.83-6.93 (m, 5H), 7.41-7.43 (m, 2H), both hydroxys,
both acid OH’s, and butenolide OH exchanged. Microanalysis
(C38H44N2O11‚2(C2H6SO4)‚0.8H2O) C, H, N, S, H2O(KF). MS:
(CI) M+ ) 705.
3-Ben zo[1,3]d ioxol-5-yl-4-[3,5-bis(2-m or p h olin -4-yleth -
o x y )b e n z y l ]-5 -h y d r o x y -5 -(4 -m e t h o x y p h e n y l )-5 H -
fu r a n -2-on e, 22. 1H NMR: (DMSO-d6) δ 2.53 (m, 8H), 2.71 (t,
J ) 5.6 Hz, 4H), 3.66 (s, 2H), 3.71 (m, 8H), 3.79 (s, 3H), 3.91
(t, J ) 5.6 Hz, 4H), 5.97 (s, 2H), 6.07 (d, J ) 2.2 Hz, 2H), 6.22
(t, J ) 2.2 Hz, 1H), 6.81 (m, 1H), 6.83 (dd, J ) 2.0, 6.9 Hz,
2H), 6.97 (m, 2H), 7.40 (dd, J ) 2.0, 6.9 Hz, 2H), butenolide
OH missing. Microanalysis (C37H42N2O10‚0.5H2O) C, H, N.
MS: (CI) M+ + 1 ) 675.
{5-[4-Ben zo[1,3]d ioxol-5-yl-2-h yd r oxy-2-(4-m et h oxy-
p h e n y l )-5 -o x o -2 ,5 -d i h y d r o fu r a n -3 -y l m e t h y l ]-2 ,3 -
d im eth oxyp h en oxy}a cetic Acid Meth yl Ester , 23. 1H
NMR: (CDCl3) δ 3.54-3.79 (m, 2H), 3.65 (s, 3H), 3.76 (s, 3H),
3.79 (s, 3H), 3.80 (s, 3H), 3.90 (s, 1H), 4.50-4.51 (m, 2H), 5.98
(s, 2H), 6.02 (s, 1H), 6.06 (s, 1H), 6.80-6.95 (m, 5H), 7.34-
7.38 (m, 2H). Microanalysis (C30H28O11) C, H, N. MS: (CI) M+
) 564.
{5-[4-Ben zo[1,3]d ioxol-5-yl-2-h yd r oxy-2-(4-m et h oxy-
p h e n y l )-5 -o x o -2 ,5 -d i h y d r o fu r a n -3 -y l m e t h y l ]-2 ,3 -
d im eth oxyp h en oxy}a cetic Acid , 24. 1H NMR: (CDCl3) δ
3.56-3.79 (m, 2H), 3.64 (s, 3H), 3.79 (s, 6H), 4.49 (s, 2H), 5.96
(s, 2H), 6.07 (s, 2H), 6.78-6.92 (m, 5H), 7.33-7.37 (m, 2H),
butenolide OH and acid proton missing. Microanalysis
(C29H26O11‚1.4H2O) C, H, N. MS: (CI) M+ ) 551.
5-{5-[4-Be n zo[1,3]d ioxol-5-yl-2-h yd r oxy-2-(4-m e t h -
o x y p h e n y l )-5 -o x o -2 ,5 -d i h y d r o fu r a n -3 -y l m e t h y l ]-
2,3-d im eth oxyp h en oxy}p en ta n oic Acid Meth yl Ester , 27.
1H NMR: (CDCl3) δ 1.76-1.78 (m, 4H), 2.37-2.41 (m, 2H),
3.56-3.75 (m, 2H), 3.63 (s, 3H), 3.66 (s, 3H), 3.66-3.75 (m,
2H), 3.73 (s, 3H), 4.33 (s, 1H), 5.96 (s, 2H), 6.00 (s, 1H), 6.79-
6.95 (m, 5H), 7.37-7.41 (m, 2H), butenolide OH missing.
Microanalysis (C33H34O11): C, H, N. MS: (CI) M+ ) 606.
5-{5-[4-Be n zo[1,3]d ioxol-5-yl-2-h yd r oxy-2-(4-m e t h -
o x y p h e n y l )-5 -o x o -2 ,5 -d i h y d r o fu r a n -3 -y l m e t h y l ]-
2,3-d im et h oxyp h en oxy}p en t a n oic Acid , 28. 1H NMR:
(CDCl3) δ 1.77-1.80 (m, 4H), 2.42-2.46 (m, 2H), 3.47-3.75
(m, 2H), 3.64 (s, 3H), 3.73 (s, 3H), 3.75-3.85 (m, 2H), 3.79 (s,
3H), 5.96 (s, 2H), 6.01 (s, 1H), 6.07 (s, 1H), 6.78-6.94 (m, 5H),
7.37-7.41 (m, 2H), butenolide OH and acid proton missing.
Microanalysis (C32H32O11‚0.25H2O) C, H, N, H2O(KF). MS: (CI)
M+ ) 592.
3-{5-[4-Be n zo[1,3]d ioxol-5-yl-2-h yd r oxy-2-(4-m e t h -
o x y p h e n y l )-5 -o x o -2 ,5 -d i h y d r o fu r a n -3 -y l m e t h y l ]-
2,3-d im eth oxyp h en oxy}p r op a n e-1-su lfon ic Acid , 29. 1H
NMR: (DMSO-d6) δ 2.10-2.14 (m, 2H), 2.99-3.29 (t, 2H), 3.43
(s, 2H), 3.53 (s, 3H), 3.58 (s, 3H), 3.73-3.76 (t, 2H), 3.78 (s,
3H), 5.80 (s, 2H), 5.97 (s, 2H), 6.78 (s, 1H), 6.78-6.89 (m, 4H),
7.18 (s, 1H), 7.38-7.40 (d, 2H). Microanalysis (C30H29O12SNa‚
1.0H2O) C, H, N, S, Na, H2O(KF). MS: (ES) M+ ) 613.
Refer en ces
(1) Lago, M. A.; Luengo, J . I.; Peishoff, J . D.; Elliott, J . D. Chapter
9. Endothelin Antagonists. In Annual Reports in Medicinal
Chemistry; Bristol, J . A., Ed.; Academic Press: New York, 1996;
Vol. 31, pp 81-90.
(2) Peishoff, C. E.; Lago, M. A.; Ohlstein, E. H.; Elliott, J . D.
Endothelin receptor antagonists. Curr. Pharm. Des. 1995, 1,
425-440.
(3) Webb, M. L.; Meek, T. D. Inhibitors of Endothelin. Med. Res.
Rev. 1997, 17, 17-67.
(4) Patt, W. C.; Edmunds, J . J .; Repine, J . T.; Berryman, K. A.;
Reisdorph, B. R.; Lee, C.; Plummer, M. S.; Shahripour, A.;
Haleen, S. J .; Keiser, J . A.; Flynn, M. A.; Welch, K. M.; Reynolds,
E. E.; Rubin, R.; Tobias, B.; Hallak, H.; Doherty, A. M.
Structure-activity relationships in
a series of orally active
γ-hydroxy butenolide endothelin antagonists. J . Med. Chem.
1997, 40, 1063-1074.
(5) Ishikawa, K.; Ihara, M.; Noguchi, K.; Mase, T.; Mino, N.; Saeki,
T.; Fukuroda, T.; Fukami, T.; Ozaki, S.; Nagase, T.; Nishikibe,
J .; Yano, M. Biochemical and Pharmacological profile of a potent
and selective endothelin B-receptor antagonist BQ-788. Proc.
Natl. Acad. Sci. U.S.A. 1994, 91, 4892-4896.
(6) Raju, B.; Okun, I.; Stavros, F.; Chan, M. F. Search for sur-
rogates: a study of endothelin receptor antagonist structure
activity relationships. Bioorg. Med. Chem. Lett. 1997, 7, 933-
938.
4-{5-[4-Be n zo[1,3]d ioxol-5-yl-2-h yd r oxy-2-(4-m e t h -
o x y p h e n y l )-5 -o x o -2 ,5 -d i h y d r o fu r a n -3 -y l m e t h y l ]-
2,3-d im et h oxyp h en oxy}b u t yr ic Acid Met h yl E st er , 25.
1H NMR: (CDCl3) δ 1.98-2.05 (m, 2H), 2.47-2.50 (m, 2H),
3.58-3.80 (m, 2H), 3.68 (s, 3H), 3.71 (s, 3H), 3.74 (s, 3H), 3.82
(s, 3H), 3.85-3.88 (m, 2H), 5.96 (s, 2H), 6.09 (s, 1H), 6.23 (s,
1H), 6.78-6.80 (m, 1H), 6.87-6.89 (m, 2H), 6.94-6.97 (m, 2H),
7.41-7.43 (m, 2H), butenolide OH missing. Microanalysis
(C32H32O11) C, H, N. MS: (CI) M+ ) 551.
(7) Doherty, A. M.; Patt, W. C.; Edmunds, J . J .; Berryman, K. A.;
Reisdorph, B. R.; Plummer, M. S.; Shahripour, A.; Lee, C.;
Cheng, X.; Walker, D.; Haleen, S. J .; Keiser, J . A.; Flynn, M. A.;
Welch, K. M.; Hallak, H.; Taylor, D. G.; Reynolds, E. E. Discovery
of a novel series of orally active non-peptide endothelin-A (ETA)
receptor-selective antagonists. J . Med. Chem. 1995, 38, 1259-
1263.
(8) Reynolds, E. E.; Keiser, J . A.; Haleen, S. J .; Walker, D. M.; Davis,
L. S.; Olszewski, B.; Taylor, D. G.; Hwang, O.; Welch, K. M.;
Flynn, M. A.; Thompson, D. M.; Edmunds, J . J .; Berryman, K.
A.; Lee, C.; Reisdorph, B. R.; Cheng, X.-M.; Patt, W. C.; Doherty,
A. M. Pharmacological characterization of PD156707, an orally
active ETA receptor antagonist. J . Pharmacol. Exp. Ther. 1994,
273, 1410-1417.
4-{5-[4-Be n zo[1,3]d ioxol-5-yl-2-h yd r oxy-2-(4-m e t h -
o x y p h e n y l )-5 -o x o -2 ,5 -d i h y d r o fu r a n -3 -y l m e t h y l ]-
2,3-d im eth oxyp h en oxy}bu tyr ic Acid , 26. 1H NMR: (CDCl3)

2168 J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 12
Patt et al.
(9) Doherty, A. M.; Cody, W. L.; He, J .; DePue, P. L.; Waite, L. A.;
Leonard, D. M.; Leitz, N. L.; Dudley, D. T.; Rapundalo, S. T.;
Hingorani, G. P.; Haleen, S. J .; LaDouceur, D. M.; Hill, K. E.;
Flynn, M. A.; Reynolds, E. E. Design of C-terminal peptide
antagonists of endothelin: structure-activity relationships of
ET-1[16,21,D-His]. J . Med. Chem. 1993, 36, 2585-2594.
(10) Keiser, J .; Schroeder, R.; Hallak, H.; Uprichard, A. C. G.;
Doherty, A. M.; Haleen, S. J . Pharmacodynamics of PD156707,
A selective endothelin receptor-A (ETA) antagonist, in acute
hypoxic pulmonary hypertension (PH). FASEB J . 1997, 11 (3),
A36.
(11) Haleen, S.; Schroeder, R.; Walker, D.; Quenby-Brown, E.; Welch,
K.; Hallak, H.; Uprichard, A.; Keiser, J . Efficacy of 1, an
endothelin-A receptor antagonist, in hypoxic pulmonary hyper-
tension. J . Cardiol. Pharmacol. 1998, 31, S331-S335.
J M980504W