Design, synthesis, and activity of a series of pyrrolidine-3-carboxylic acid-based, highly specific, orally active ET(B) antagonists containing a diphenylmethylamine acetamide side chain

Article abstract of DOI:10.1021/jm990171i

The endothelin (ET)-B receptor subtype is expressed on vascular endothelial and smooth muscle cells and mediates both vasodilation and vasoconstriction. On the basis of the pharmacophore of the previously reported ETA-specific antagonist 1, (ABT-627), we

Full text of DOI:10.1021/jm990171i

J . Med. Chem. 1999, 42, 3679-3689
3679
Design , Syn th esis, a n d Activity of a Ser ies of P yr r olid in e-3-ca r boxylic
Acid -Ba sed , High ly Sp ecific, Or a lly Active ETB An ta gon ists Con ta in in g a
Dip h en ylm eth yla m in e Aceta m id e Sid e Ch a in
Gang Liu,*,† Natasha S. Kozmina,‡ Martin Winn,† Thomas W. von Geldern,† William J . Chiou,†
Douglas B. Dixon,† Bach Nguyen,§ Kennan C. Marsh,§ and Terry J . Opgenorth†
Metabolic Disease Research and Drug Analysis Department, Pharmaceutical Products Division,
Abbott Laboratories, Abbott Park, Illinois 60064-6098
Received April 12, 1999
The endothelin (ET)-B receptor subtype is expressed on vascular endothelial and smooth muscle
cells and mediates both vasodilation and vasoconstriction. On the basis of the pharmacophore
of the previously reported ETA-specific antagonist 1, (ABT-627), we are reporting the discovery
of a novel series of highly specific, orally active ETB receptor antagonists. Replacing the
dibutylaminoacetamide group of 1 with a diphenylmethylaminoacetamide group resulted in
antagonist 2 with a complete reversal of receptor specificity. Structure-activity relationship
studies revealed that ortho-alkylation of the phenyl rings could further increase ETB affinity
and also boost the ETA/ETB activity ratio of the resulting antagonists. A similar antagonism
selectivity profile could also be achieved when one of the phenyl rings of the acetamide side
chain was replaced with an alkyl group, preferably a tert-butyl group (10h ). Combining these
features with modification of the 2-aryl group of the pyrrolidine core, we have identified a
potent antagonist (9k , A-308165) with over 27 000-fold selectivity favoring the ETB receptor
and an acceptable pharmacokinetic profile (F ) 24%) in rats.
In tr od u ction
Since 1994, a large number of potent, nonpeptide ET
antagonists have been reported, most of which exhibited
specificity toward the ETA receptor18 or nonspecificity
toward either the ETA or ETB receptor.19 However,
reports of potent ETB-specific antagonists have been
scarce, only represented by BQ-788,17 Ro 46-8443,20
RES-701-1,21 and IRL-2500.22 A more recent account of
a benzenesulfonamide-based ETB receptor-selective an-
tagonist has appeared in the literature.23 The lack of
high-quality, orally deliverable ETB-specific antagonists
has hindered the efforts of clarifying the role of the ETB
receptor. During the course of expanding the structure-
activity relationship (SAR) of pyrrolidine-3-carboxylic
acid-based ETA-specific antagonists, we noticed that
replacing the N,N-dibutylamine portion of ABT-627 (1)24
with a diphenylmethylamine led to a dramatic boost of
ETB receptor affinity (IC50 ) 8.1 nM) and a complete
reversal of the receptor specificity of the resulting
antagonist 2 (Scheme 1). This observation is consistent
with results from several previous studies by this group,
indicating the critical role played by the N-linked side
chain of 1 in determining receptor binding and selectiv-
ity. Herein, we would like to report the design, synthe-
sis, and activity of this novel series of ETB receptor-
selective antagonists, which are valuable tools for
further elucidating the role that the ETB receptor plays
in vivo.
The endothelins (ET-1, ET-2, and ET-3), potent vaso-
constrictors and mitogens, were discovered in 1988,1,2
and subsequently two subtypes of human endothelin
receptors (ETA and ETB) were cloned.3,4 ETA receptor
is abundantly expressed on vascular smooth muscle
cells, and binding of ET-1 to the ETA receptor mediates
the vasoconstrictive and mitogenic effects of endothelin
in vitro and in vivo.5 Pharmacology studies have impli-
cated ET-1 as a contributing factor in a number of
disease states where excessive vasoconstriction or smooth
muscle proliferation plays a role. These include acute
myocardial infarction,6 congestive heart failure,7 pul-
monary hypertension,8 renal failure,9 and restenosis.10
ETB receptor subtype is expressed on vascular endo-
thelial and smooth muscle cells and has high affinity
for all isoforms of endothelins. Despite the tremendous
research activity in the field of endothelins, the roles of
the ETB receptor remain poorly understood. ETB recep-
tors could not only mediate endothelium-dependent
relaxation11 through the production of nitric oxide12 but
also direct vaso- or broncho constriction.13-16 It is also
linked to the clearance of endogenous endothelin from
circulation.17 Therefore, highly potent, orally active ETB
receptor-specific antagonists are needed to advance the
understanding of the role of the ETB receptor in both
normal physiological and pathological conditions.
Ch em istr y
* Address correspondence to G. Liu, D-47R/AP-10, Abbott Labora-
tories, 100 Abbott Park Rd, Abbott Park, IL 60064-6098. E-mail:
gang.liu@abbott.com.
All of the new compounds in this report were synthe-
sized by direct analogy to our earlier work on 1 with
minor modification,18 as shown in Scheme 2. Various
â-ketoesters 4 were prepared by reacting the imida-
zolides of carboxylic acids 3 with magnesium monoeth-
† Metabolic Disease Research.
§ Department of Drug Analysis.
‡ Current address: DuPont Pharmaceuticals Co., Wilmington, DE
19880.
10.1021/jm990171i CCC: $18.00 © 1999 American Chemical Society
Published on Web 08/17/1999

3680 J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 18
Liu et al.
Sch em e 1. Reversal of Antagonist Receptor Subtype Specificity through Acetamide Side Chain Modification
Sch em e 2a
a
Reagents and conditions: (a) CDI, THF, then magnesium monoethylmalonate, rt; (b) cat. t-BuOK, THF, rt; (c) H2, Raney Ni, AcOH,
THF, rt, then TFA, rt, one pot; (d) DBU, CH3CN, reflux; (e) BrCH2CONHCH(Ar1)X (8), i-Pr2NEt, CH3CN, rt; (f) 6N aq NaOH, EtOH, rt.
Sch em e 3a
ylmalonate followed by decarboxylation25(ca. 70% yield).
Potassium tert-butoxide-catalyzed Michael addition of
â-ketoesters 4 to nitrostyrene 526 yielded two isomers
of the adducts 6 in ca. 80% yield. Raney nickel-mediated
hydrogenation of the adducts 6 in the presence of acetic
acid and further hydrogenation of the resulting cyclic
iminium TFA salts provided almost exclusively the cis,-
cis-isomers of the pyrrolidines, which were epimerized
with DBU to afford the pure trans,trans-pyrrolidines 7
in ca. 70% yield from the Michael addition. Alkylation
a
Reagents and conditions: (a) HONH2HCl, Pyr, EtOH, reflux;
of pyrrolidines 7 with bromoacetamides 8 and subse-
(b) Na, liq NH3, THF, -78 °C to rt; (c) BrCH2COBr, NEt3,
ClCH2CH2Cl, -78 °C to rt.
quent saponification of the resultant ethyl esters fur-
nished final compounds 9 and 10 in 80% yield for in
vitro assays.
details) following protection of racemic pyrrolidines 7
The synthesis of noncommercially available amines
used for the preparation of bromoacetamides 8 is shown
in Scheme 3. Condensation of N-hydroxylamine with
ketones 11 provided the oximes 12. Reduction of oximes
12 by dissolved sodium metal in liquid NH3 yielded
benzylamines 13, which were converted to the bromoace-
tamides 8 according to the literature procedure.27
For detailed evaluation, two compounds have been
prepared in optically pure form. The enantiomerically
pure pyrrolidines 14 were secured through chiral HPLC
separation (Scheme 4, see Experimental Section for
as their tert-butyl carbamates. Removal of the Boc
groups of 14, N-alkylation with appropriate bromoace-
tamides 8, and saponification provided the optically
pure antagonists 9j and 9k .
Str u ctu r e-Activity Rela tion sh ip s
The primary screening for the compounds described
in this study was a measurement of their ability to
displace endothelin from its receptors. We employed
human ETA and ETB receptors (hETA, hETB) perma-
nently expressed in CHO cells. IC50 data were recorded

Orally Active ETB Antagonists
J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 18 3681
Sch em e 4a
exceeded that of ETA affinity (4-fold). Addition of one
more phenyl group to the acetamide of 2 led to a much
less potent antagonist 9d , with no selectivity for either
receptor subtype. Apparently, diphenylmethylamine
seems to be the preferred group for ETB receptor binding
and specificity.
Next, the spatial orientation of the two phenyl groups
was fine-tuned with small alkyl substituents, which
would also probe this hydrophobic binding site in a more
detailed fashion. Initially, mono-ortho-methylation of
one of the phenyl rings led to antagonist 9e with higher
ETB receptor affinity and slightly decreased ETA affin-
ity, a 3-fold gain of the selectivity over unsubstituted
analogue 2 (Table 1). In comparison, para-methylation
of the phenyl ring was not tolerated, based on the
observation that a 1,4-dimethylated phenyl analogue
(9f) exhibited decreased affinity for both receptor sub-
types. The optimal selectivity and affinity profile was
achieved with a bis-o-tolylmethylamine in place of the
diphenylmethylamine. The optimal combination of spa-
tial orientation of the two phenyl groups and hydropho-
bic interaction with the receptor provided antagonist 9g
with 1 nM affinity for the ETB receptor and almost 150-
fold separation of affinities between the two receptor
subtypes. One-carbon homologation of one of the o-
methyl groups (9h ) decreased the newly gained ETB
receptor affinity 6-fold and slightly compromised ETB
specificity. Bis-ortho-ethylation of the diphenylmethyl-
amine (9i) attenuated the affinity for the ETB receptor
to some degree but reduced the ETB selectivity of the
antagonist 10-fold.
a
Reagents and conditions: (a) Boc2O, Et3N, CH2Cl2, rt; (b)
chiral HPLC separation; (c) neat TFA, rt; (d) BrCH2CONHCH(Ar1)-
Ar2 (8), i-Pr2NEt, CH3CN, rt; (e) 6 N aq NaOH, EtOH, rt.
by measuring the displacement of [125I]ET-1 from the
ETA receptor or [125I]ET-3 from the ETB receptor.
Analogues of particular interest were examined for their
pharmacokinetic properties using a standard protocol
which compares the time course of plasma drug levels
after dosing in rats by intravenous injection and oral
gavage.
We then explored the possibility of replacing one of
the phenyl groups of 2 with an alkyl group (Table 2).
Methylbenzylamine-derived analogue 10a offered a
slightly ETA-selective antagonist with moderate po-
tency. Ortho-methylation of the phenyl ring (10b) did
not alter the affinity for ETB receptor but decreased that
for the ETA receptor 3-fold. Antagonist 10c, derived from
R-ethylbenzylamine, exhibited low nanomolar affinity
for both ETA and ETB receptors with virtually no
discrimination against either receptor subtype. Further
elongation of the alkyl group to n-propyl (10d ) or n-butyl
(10e) did not result in any dramatic variation of the
affinity and selectivity of the antagonists.
The reversal of receptor specificity resulting from the
acetamide side chain modification (1 to 2, Scheme 1)
suggested two important features in designing an ETB-
selective antagonist. The first feature is the hydrogen-
bonding donating nature of the secondary amide present
in compound 2, which is absent in the ETA receptor-
specific antagonist 1. Our previous studies have indi-
cated that the presence of both alkyl groups of the
tertiary acetamide is required for maintaining the high
ETA selectivity of the antagonist 1. In the case of
compound 2, we suspect that hydrogen bonding of the
secondary amide with the ETB receptor is involved in
orienting the diphenylmethyl group into appropriate
hydrophobic binding pockets, which are inaccessible to
the N,N-dialkylacetamide side chain of 1. The second
feature is the hydrophobic interaction provided by the
conformationally restricted, yet somewhat flexible, bi-
phenylmethyl group. The importance of flexibility of the
two phenyl groups was confirmed when a rigid and flat
9-aminofluorene was used in place of it (Table 1). The
potency of the resulting antagonist 9a was severely
compromised, even though the marginal ETB selectivity
of 2 was still observed.
In comparison to R-propylbenzylamine-based com-
pound 10d , branching of the n-propyl group (10f) did
not provide any benefit in term of selectivity but did
improve the receptor affinity over 3-fold (Table 2). ETB
affinity improved 2-fold, while ETA affinity decreased
4-fold when the isopropyl group of 10f was elongated
to a 3-pentyl group (10g). This improvement has re-
sulted in a selectivity profile favoring the ETB receptor,
reversing the moderate ETA selectivity of this series of
compounds (10a -10f). In fact, compounds 10c, 10f, and
10g could be more appropriately categorized as very
potent, ETA/ETB receptor-mixed antagonists. Their bio-
chemical profile compares favorably with that of the
leading literature compounds.19
The size of the binding pocket for this diphenyl-
methylamine acetamide was then probed (Table 1). One-
carbon extension of one of the phenyl rings of 2
decreased ETB receptor affinity 6-fold, and the resulting
antagonist 9b favored the ETA receptor by more than 1
order of magnitude. (Mixture of diastereoisomers was
used for the primary screening and the same for the
rest of the report.) If both phenyl groups of 2 were moved
one carbon out (9c), the erosion of ETB affinity (13-fold)
The ETB receptor-favoring character of 10g was
further strengthened using a tert-butyl group to replace
one of the phenyl groups of 2 to give antagonist 10h
with subnanomolar potency against the ETB receptor
and 10-fold selectivity over the ETA receptor. Extension
of the isopropyl group of 10f to an isobutyl group (10i)

3682 J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 18
Liu et al.
Ta ble 1. Structure-Activity Relationships of Diarylmethylamine Acetamides
a
IC50 calculated using a mean of at least 2 measurements (all duplicates) for 11 concentrations from 10-10 to 10-5 M unless otherwise
noted. bExpressed as IC50(ETA)/IC50(ETB).

Orally Active ETB Antagonists
J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 18 3683
Ta ble 2. Structure-Activity Relationships of Phenylalkylamine Acetamides
a
IC50 calculated using a mean of at least 2 measurements (all duplicates) for 11 concentrations from 10-10 to 10-5 M unless otherwise
noted. bExpressed as IC50(ETA)/IC50(ETB).
resulted in over 10-fold increase of the selectivity of the
antagonist and moderate decrease of ETB affinity. By
the same analogy, elongation of the tert-butyl group of
10h to a neopentyl group provided antagonist 10j with

3684 J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 18
Liu et al.
a 3-fold increase of selectivity but a 5-fold decrease of
ETB receptor affinity. Compared to the diphenylmethyl-
amine series, the phenylalkylmethylamine series could
offer equally potent antagonism against the ETB recep-
tor (IC50 ) 0.94 nM of 10h ), even though the selectivity
was somewhat inferior to that of the diarylmethylamine
series (A/B ) 26 of 10j).
During the course of SAR studies of pyrrolidine-based
endothelin receptor antagonists, we demonstrated the
importance of the 2-aryl group in modulating the affinity
and specificity profiles of the compounds after establish-
ing the essential nature of the profile (ETA-selective,
balanced).19,24 Several variations of the p-anisyl group
of 2, such as p-methoxyethoxyphenyl and p-isopropoxy-
ethoxyphenyl groups, have been identified to offer better
specificity toward the ETB receptor. Having discovered
a novel class of ETB-selective antagonists by virtue of
side chain modification, we began to mix and match
these acetamide side chains with the more ETB-selective
pyrrolidine core modifications. And to our delight, this
exercise proved to be very fruitful in yielding potent and
highly specific ETB receptor antagonists.
of the antagonist. It is also more potent and exhibits a
comparable pharmacokinetic profile in rats. Even though
the pharmacology studies using A-192621 and other
ETB-specific antagonists29 have suggested that selective
ETB antagonists may not be suitable as agents for long-
term systemic therapy because of their hypertensive
liabilities, compound 9k could be a valuable tool for
further elucidating the role of the ETB receptor in both
normal physiological and pathological conditions.
Su m m a r y
Two novel series of pyrrolidine-3-carboxylic acid-based
potent and highly ETB receptor-selective antagonists
have been identified through modification of the N,N-
dibutylamino group of the ETA-selective antagonist 1.
In the first series, an opportunistic observation during
SAR studies led to the observation that a diarylmethyl-
amine acetamide side chain imparts ETB selectivity to
these pyrrolidine-based endothelin antagonists. Opti-
mization of the side chain and the pyrrolidine 2-aryl
group yielded compound 9k with nanomolar affinity for
the ETB receptor, over 27 000-fold selectivity for the ETB
versus ETA receptor, and good oral bioavailability.
The second series of ETB-selective antagonists was
developed by replacing one of the aryl groups in the
biarylmethylamine series with an alkyl group. Through
optimizing the size of the alkyl groups, the receptor
antagonists could be transformed from the ETA/ETB-
mixed type to the ones favoring the ETB receptor
subtype. Combining the preferred tert-butylphenyl-
methylamine acetamide side chain with 2-aryl group
modification led to antagonist 10l with subnanomolar
affinity and more than 450-fold selectivity for the ETB
receptor.
The tert-butylphenylmethylamine acetamide side chain
from compound 10h was first examined with pyrrolidine
core modifications and compared with the parent com-
pounds (Table 3). p-Methoxyethoxy substituent of the
2-aryl group boosted the ETB selectivity of the resulting
antagonist 10k to 220-fold while preserving the high
affinity for the ETB receptor. An even more ETB-specific
modification, a p-isopropoxyethoxy group, provided
antagonist 10l with subnanomolar affinity and over 450-
fold selectivity for the ETB receptor. Then, the more
ETB-selective bis-o-tolylmethylamine acetamide side
chain of 9g was combined with these 2-aryl substituent
variations. The p-methoxyethoxyphenyl-substituted pyr-
rolidine improved the selectivity of antagonist 9j 80-
fold, yielding a nanomolar antagonist with over 12 000-
fold selectivity for the ETB receptor. Parallel to the
selectivity improvement shown with 10k to 10l, another
2-fold boost of receptor selectivity was noticed with a
p-isopropoxyethoxy group replacement, resulting in one
of the most selective ETB receptor antagonists (9k )
reported to date. Combination of the less ETB-specific
acetamide side chain of compound 9h with the p-
isopropoxyethoxy-substituted pyrrolidine core (9l) re-
sulted in a 5-fold loss of receptor affinity and selectivity
in comparison to 9k .
Exp er im en ta l Section
Gen er a l. Unless otherwise specified, all solvents and
reagents were obtained from commercial suppliers and used
without further purification. All reactions were performed
under nitrogen atmosphere unless specifically noted. Flash
chromatography was performed using silica gel (230-400
mesh) from E.M. Science. Proton NMR spectra were recorded
on a General Electric QE300 instrument with Me4Si as an
internal standard and are reported as shift (multiplicity,
coupling constants, proton counts). Mass spectral analyses
were accomplished using different techniques, including de-
sorption chemical ionization (DCI), atmospheric pressure
chemical ionization (APCI), and electrospray ionization (ESI),
as specified for individual compounds. Elemental analyses
were performed by Robertson Microlit Laboratories, Madison,
NJ , and are consistent with theoretical values to within 0.4%
unless indicated.
P r ep a r a tion of Keton es 11. Most of the ketones were
purchased from commercial vendors. 2,2′-Dimethylbenzophe-
none and 2-ethyl-2′-methylbenzophenone were prepared from
commercially available methyl 2-methylbenzoate according to
the published procedure.30 3,3-Dimethyl-1-phenylbutan-1-one
was prepared from commercially available 3,3-dimethylbutyryl
chloride according to the published procedure.31
Bis-o-tolyl N-Hydr oxyoxim e (12, Ar 1 ) Ar 2 ) o-CH3C6H5).
In a 50-mL round-bottom flask were placed 2,2′-dimethylben-
zophenone (2.50 g, 10 mmol), hydroxylamine hydrochloride
(0.76 g, 11 mmol), pyridine (5 mL), and ethanol (5 mL). The
mixture was refluxed for 8 h with stirring. The reaction
mixture was then allowed to cool to ambient temperature and
extracted with 2 × 25 mL of EtOAc. The combined organic
layer was washed in turns with 15 mL of aqueous CuSO4, 15
mL of water, and 15 mL of brine, dried over magnesium
sulfate, and concentrated in vacuo. The residual oil obtained
Having identified a series of very potent and highly
selective ETB receptor antagonists, two compounds (9j
and 9k ) were prepared in enantiomerically pure form
and their pharmacokinetic profiles were evaluated in
rats (Table 4). The active enantiomer of 9j behaved
rather poorly in vivo. It has a very short half-life and is
absorbed poorly following oral administration, resulting
in a bioavailability (F) of a mere 8%. In comparison,
enantiomer 9k (A-308165) has a much more acceptable
pharmacokinetic profile in rats. It has a reasonable half-
life (4.8 h) and total drug exposure (AUC0-∞ ) 0.73 µg-
h/mL) following oral administration. The calculated oral
bioavailability (F) is 24%.
As reported in the companion article, A-192621 is a
potent and selective ETB receptor antagonist.28 In
comparison to A-192621, compound 9k has improved
substantially over its predecessor in term of specificity

Orally Active ETB Antagonists
J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 18 3685
Ta ble 3. Structure-Activity Relationships of 2-Aryl and Acetamide Modifications
a
IC50 calculated using a mean of at least 2 measurements (all duplicates) for 11 concentrations from 10-10 to 10-5 M unless otherwise
noted. bExpressed as IC50(ETA)/IC50(ETB).
was purified by silica gel column chromatography (elution with
10% EtOAc in hexanes) to give 1.31 g (73%) of white crystalline
solid.
ture, transferred to a separatory funnel, diluted with 50 mL
of water, and extracted with 3 × 50 mL of dichloromethane.
The combined organic layer was dried over sodium sulfate and
concentrated under reduced pressure to give a yellowish oil.
The residue was purified by a silica gel column chromatogra-
phy (elution with 60% EtOAc in hexanes, followed by elution
with 2% Et3N in EtOAc) to give 500 mg (66%) of the pure
amine.
Bis-o-tolylm eth yla m in e (13, Ar 1 ) Ar 2 ) o-CH3C6H5).
To a round-bottom flask with 55 mL of ammonia cooled in a
dry ice-acetone bath was added 130 mg (6.0 mmol) of sodium
metal. To the resulting blue solution at -78 °C was added
slowly 650 mg (3.0 mmol) of oxime 12 in 25 mL of anhydrous
THF. The reaction mixture was stirred for 1 h at -78 °C and
then quenched with 1 g of ammonium chloride. The resulting
colorless reaction mixture was warmed to ambient tempera-
Bis-o-tolylm eth yla m in e Br om oa ceta m id e (8, Ar 1 ) Ar 2
) o-CH3C6H5). The amine 13 (100 mg, 0.47 mmol) was
dissolved in 2 mL of 1,2-dichloroethane. To this solution at

3686 J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 18
Liu et al.
Ta ble 4. Pharmacokinetic Profiles of Compounds 9j and 9k in
The following compounds were prepared using the proce-
dures described above for compounds 9g and 9k .
Ratsa
tr a n s,tr a n s-2-(4-Meth oxyp h en yl)-4-(1,3-ben zod ioxol-5-
yl)-1-(diph en ylm eth ylam in ocar bon ylm eth yl)pyr r olidin e-
3-ca r boxylic a cid (2): white solid; 1H NMR (CDCl3, 300 MHz)
δ 3.32 (d, J ) 15.6 Hz, 1H), 3.43 (t, J ) 9.9 Hz, 2H), 3.50 (td,
J ) 6.3, 10.2 Hz, 1H), 3.68-3.83 (m, 2H), 3.77 (s, 3H), 4.51 (d,
J ) 10.2 Hz, 1H), 5.94 (dd, J ) 1.2, 3.0 Hz, 2H), 6.14 (d, J )
9.0 Hz, 1H), 6.69 (d, J ) 8.4 Hz, 1H), 6.74 (dd, J ) 2.4, 9.0 Hz,
1H), 6.82 (d, J ) 9.0 Hz, 1H), 6.88 (d, J ) 2.4 Hz, 1H), 7.11-
7.19 (m, 4H), 7.19-7.37 (m, 8H), 8.19 (d, J ) 9.0 Hz, 1H). MS
(ESI+) (M + H)+ at m/z 565. Anal. Calcd for C34H32N2O6‚
0.70TFA: C, 65.98; H, 5.11; N, 4.35. Found: C, 65.84; H, 5.10;
N, 4.17.
tr a n s,tr a n s-2-(4-Meth oxyp h en yl)-4-(1,3-ben zod ioxol-5-
yl)-1-[(flu or en yl-9-a m in o)ca r bon ylm eth yl]p yr r olid in e-3-
ca r boxylic a cid (9a ): white solid; 1H NMR (CDCl3, 300 MHz)
δ 3.30 (d, J ) 15.3 Hz, 1H), 3.34 (t, J ) 9.0 Hz, 1H), 3.49 (t, J
) 10.5 Hz, 1H), 3.60 (dd, J ) 6.3, 10.8 Hz, 1H), 3.67-3.82 (m,
3H), 3.77 (s, 3H), 3.47 (d, J ) 9.6 Hz, 1H), 5.91 (dd, J ) 1.8,
6.6 Hz, 2H), 6.07 (d, J ) 9.0 Hz, 1H), 6.57 (d, J ) 8.4 Hz, 1H),
6.70 (dd, J ) 1.8, 8.4 Hz, 1H), 6.80 (d, J ) 3.6 Hz, 1H), 6.82
(d, J ) 3.6 Hz, 1H), 7.23-7.34 (m, 2H), 7.36-7.47 (m, 5H),
7.71 (d, J ) 8.4 Hz, 2H); MS (DCI/NH3) (M + H)+ at m/z 563.
Anal. Calcd for C34H30N2O6‚0.70TFA: C, 66.18; H, 4.82; N,
4.36. Found: C, 66.24; H, 4.85; N, 4.37.
tr a n s,tr a n s-2-(4-Meth oxyp h en yl)-4-(1,3-ben zod ioxol-5-
yl)-1-[(1,2-diphenylethyl)aminocarbonylmethyl]pyrrolidine-
3-ca r boxylic a cid (9b): white solid; 1H NMR (CDCl3, 300
MHz, mixture of diastereomers) δ 2.88-3.75 (m, 7H), [3.77
(s), 3.79 (s), 3H in total], 4.47 (t, J ) 9.0 Hz, 1H), 5.11-5.37
(m, 2H), 5.96-6.03 (m, 2H), 6.72-7.37 (m, 17H); MS (ESI+)
(M + H)+ at m/z 578. Anal. Calcd for C35H34N2O6‚0.80TFA:
C, 65.62; H, 5.24; N, 4.18. Found: C, 65.53; H, 5.24; N, 4.08.
tr a n s,tr a n s-2-(4-Meth oxyp h en yl)-4-(1,3-ben zod ioxol-5-
yl)-1-[(2,2-d ip h en ylet h yl)a m in oca r b on ylm et h yl]p yr r o-
lid in e-3-ca r boxylic a cid (9c): white solid; 1H NMR (CDCl3,
300 MHz) δ 2.80 (t, J ) 10.2 Hz, 2H), 2.96 (dd, J ) 4.2, 9.6
Hz, 1H), 3.20 (d, J ) 15.0 Hz, 1H), 3.53 (td, J ) 4.2, 9.0 Hz,
1H), 3.74-4.0 (m, 3H), 3.79 (s, 3H), 4.17 (t, J ) 7.8 Hz, 1H),
6.03 (dd, J ) 1.8, 4.8 Hz, 2H), 6.50 (d, J ) 8.7 Hz, 1H), 6.74-
6.82 (m, 4H), 7.02 (d, J ) 7.2 Hz, 1H), 7.16-7.37 (m, 12H);
MS (ESI+) (M + H)+ at m/z 579. Anal. Calcd for C35H34N2O6‚
0.20TFA: C, 70.69; H, 5.73; N, 4.66. Found: C, 70.65; H, 5.83;
N, 4.55.
iv
AUCiv
oral
AUCoral
compd
T1/2 (h) (µg-h/mL) T1/2 (h) (µg-h/mL) F (%)
9j
2.9
1.8
2.50
3.03
0.55
4.8
0.20
0.73
8
(2R,3R,4S)
9k
(2R,3R,4S)
24
a
5 mg/kg dosed in both intravenous injection and oral gavage.
-78 °C were added 100 µL of Et3N (0.71 mmol) and then
bromoacetyl bromide (40 µL, 0.47 mmol in 1 mL of 1,2-
dichloroethane) dropwise. The reaction mixture was stirred
at -78 °C for 10 min, then at ambient temperature for 2 h,
diluted with 10 mL of water, and extracted with 2 × 25 mL of
1,2-dichloroethane. The combined organic layers were dried
over sodium sulfate and concentrated in vacuo to give the
bromoacetamide as a white solid (184 mg, 96%) suitable for
further use without additional purification.
tr a n s,tr a n s-2-(4-Meth oxyp h en yl)-4-(1,3-ben zod ioxol-5-
yl)-1-(bis-o-tolylm eth ylam in ocar bon ylm eth yl)pyr r olidin e-
3-ca r boxylic Acid (9g). To a stirred solution of 0.20 g (0.54
mmol) of trans,trans-pyrrolidine and N,N-diisopropylethyl-
amine (0.1 mL, 0.57 mmol) in 10 mL of CH3CN was added
the bromoacetamide 8 (184 mg, 0.42 mmol). The reaction
mixture was stirred at ambient temperature overnight. The
solvent was then removed on a rotavap, and the crude product
was purified by a flash column chromatography (elution with
40% of EtOAc in hexanes) to give 250 mg (73%) of the ethyl
ester as a colorless oil. The ester thus obtained was dissolved
in 5.0 mL of ethanol, and 0.70 mL of 6 N aqueous sodium
hydroxide was added. The mixture was stirred at ambient
temperature overnight. The solution was then diluted with 10
mL of water and extracted with 15 mL of 20% hexanes in
EtOAc to remove any unhydrolyzed ester. The aqueous phase
was acidified with 1 N aqueous H3PO4 to pH ) 5 and extracted
with 3 × 10 mL of chloroform. The combined organic layer
was dried and concentrated to get a colorless viscous oil. The
title compound was isolated by lyophilization from dilute CH3-
1
CN/TFA/H2O as an amorphous white solid: H NMR (CDCl3,
300 MHz) δ 2.14 (s, 3H), 2.20 (s, 3H), 3.02-3.33 (m, 2H), 3.40-
3.72 (m, 3H), 3.80 (s, 3H), 4.16-4.24 (brs, 1H), 5.92 (m, 2H),
6.36-6.42 (m, 1H), 6.58-6.67 (m, 2H), 6.81 (t, J ) 9.0 Hz, 4H),
6.88-7.00 (m, 2H), 7.05-7.27 (m, 8H); MS (ESI+) (M + H)+
at m/z 593. Anal. Calcd for C36H36N2O6‚0.40TFA: C, 69.25; H,
5.75; N, 4.39. Found: C, 69.20; H, 5.68; N, 4.22.
tr a n s,tr a n s-2-(4-Meth oxyp h en yl)-4-(1,3-ben zod ioxol-5-
yl)-1-(tr iph en ylm eth ylam in ocar bon ylm eth yl)pyr r olidin e-
3-ca r boxylic a cid (9d ): white solid; 1H NMR (CDCl3, 300
MHz) δ 2.92 (d, J ) 16.5 Hz, 1H), 3.04-3.19 (m, 2H), 3.37 (d,
J ) 16.5 Hz, 1H), 3.43 (dd, J ) 4.2, 9.6 Hz, 1H), 3.64 (td, J )
2.7, 9.0 Hz, 1H), 3.79 (s, 3H), 3.96 (d, J ) 9.0 Hz, 1H), 5.95
(dd, J ) 1.8, 4.8 Hz, 2H), 6.58 (d, J ) 9.0 Hz, 1H), 6.70 (dd, J
) 2.1, 9.0 Hz, 1H), 6.77 (d, J ) 9.0 Hz, 2H), 6.82 (s, 1H), 7.03-
7.14 (m, 6H), 7.19 (d, J ) 9.0 Hz, 2H), 7.23-7.34 (m, 8H), 8.33
(s, 1H); MS (ESI+) (M + H)+ at m/z 641. Anal. Calcd for
R esolu t ion of Com p ou n d s. tr a n s,tr a n s-(2R,3R,4S)-
E t h yl 2-[4-(2-Isop r op oxyet h oxy)p h en yl]-4-(1,3-b en zo-
d ioxol-5-yl)p yr r olid in e-3-ca r boxyla te (7, R1 ) i-P r OCH2-
CH2O). To a solution of amino ester 7 (500 mg, 1.14 mmol) in
3.0 mL of dichloromethane with 0.48 mL (3.4 mmol) of
triethylamine was added 0.30 g (1.4 mmol) of di-tert-butyl
dicarbonate, and the mixture was stirred at ambient temper-
ature for 2 h. Solvents were then removed in vacuo, and the
residue was purified with silica gel flash chromatography using
15% EtOAc in hexanes as eluent to give 580 mg (1.07 mmol,
94%) of N-Boc ester 14 as a colorless oil. The racemic ester 14
(580 mg, 1.07 mmol) was separated by preparative chiral
HPLC on a Regis Whelk-O2 column (5 × 25 cm; 80:20 hexane:
ethanol; 100 mL/min; ambient temperature; 210 nm UV 1.0-
mm path), to give 245 mg of the (2S,3S,4R)-isomer (tR ) 8.1
min) and 251 mg of the (2R,3R,4S)-isomer (tR ) 11.9 min),
respectively. The products are more than 99% enantiomerically
pure, as indicated by analytical HPLC analysis, using a Regis
Whelk-O column (4.6 × 250 mm; 80:20 hexane:EtOH; 1.0 mL/
min; ambient temperature; 210 nm UV). The (2S,3S,4R)-
enantiomer (tR ) 11.9 min) (75 mg, 0.17 mmol) was dissolved
in 1.0 mL of TFA and stirred at ambient temperature for 1 h.
Solvents were removed in vacuo, and the residue was evapo-
rated twice with benzene. The enantiomerically pure amino
ester 7 thus obtained was then converted to the final compound
(2R,3R,4S)-9k following the same procedure as described for
compound 9g.
C
40H36N2O6‚0.16TFA: C, 73.49; H, 5.53; N, 4.25. Found: C,
73.48; H, 5.48; N, 4.18.
tr a n s,tr a n s-2-(4-Meth oxyp h en yl)-4-(1,3-ben zod ioxol-5-
yl)-1-[[1-(2′-m eth ylp h en yl)-1-p h en ylm eth yl]a m in oca r bo-
n ylm eth yl]p yr r olid in e-3-ca r boxylic a cid (9e): white solid;
1H NMR (CDCl3, 300 MHz, mixture of diastereomers) δ [2.22
(s), 2.26 (s), 3H in total], 3.21-3.78 (m, 7H), [3.79 (s), 3.80 (s),
3H in total], 4.44-4.53 (t, J ) 9.0 Hz, 1H), 5.94-5.97 (m, 2H),
6.34 (d, J ) 9.0 Hz, 1H), 6.66-6.92 (m, 4H), 7.04-7.36 (m,
11H); MS (ESI+) (M + H)+ at m/z 578. Anal. Calcd for
C
35H34N2O6‚0.90TFA: C, 64.99; H, 5.17; N, 4.12. Found: C,
64.99; H, 5.34; N, 3.95.
tr a n s,tr a n s-2-(4-Meth oxyp h en yl)-4-(1,3-ben zod ioxol-5-
yl)-1-[[1-(2′,5′-dim eth ylph en yl)-1-ph en ylm eth yl]am in ocar -
bon ylm eth yl]p yr r olid in e-3-ca r boxylic a cid (9f): white
solid; 1H NMR (CDCl3, 300 MHz, mixture of diastereomers) δ
[2.19 (s), 2.30 (s), 6H in total], 3.27-3.66 (m, 3H), 3.72-3.84
(m, 7H), 4.57 (t, J ) 9.0 Hz, 1H), 5.92-5.97 (m, 2H), 6.29 (dd,
J ) 4.5, 9.0 Hz, 1H), 6.67-7.40 (m, 14H); MS (ESI+) (M +

Orally Active ETB Antagonists
J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 18 3687
H)+ at m/z 592. Anal. Calcd for C36H36N2O6‚0.85TFA: C, 65.80;
H, 5.40; N, 4.07. Found: C, 65.78; H, 5.61; N, 4.07.
(M + H)+ at m/z 530. Anal. Calcd for C31H34N2O6‚0.45TFA:
C, 66.07; H, 5.99; N, 4.84. Found: C, 66.10; H, 6.01; N, 4.57.
tr a n s,tr a n s-2-(4-Meth oxyp h en yl)-4-(1,3-ben zod ioxol-5-
yl)-1-[(2-e t h yl-1-p h e n ylb u t yl)a m in oca r b on ylm e t h yl]-
tr a n s,tr a n s-2-(4-Meth oxyp h en yl)-4-(1,3-ben zod ioxol-5-
yl)-1-[[1-(2′-eth ylp h en yl)-1-(2′-m eth ylp h en yl)m eth yl]a m i-
n oca r bon ylm eth yl]p yr r olid in e-3-ca r boxylic a cid (9h ):
1
p yr r olid in e-3-ca r boxylic a cid (10g): white solid; H NMR
1
white solid; H NMR (CDCl3, 300 MHz, mixture of diastere-
(CDCl3, 300 MHz, mixture of diastereomers) δ 0.77-0.91 (m,
6H), 1.08-1.66 (m, 4H), 2.87-3.48 (m, 4H), 3.60-3.75 (m, 2H),
[3.78 (s), 3.81 (s), 3H in total], 4.01-4.11 (m, 2H), 4.88-5.01
(m, 1H), 5.92-6.00 (m, 2H), 6.74-7.46 (m, 12H); MS (ESI+)
(M + H)+ at m/z 558. Anal. Calcd for C33H38N2O6‚0.22TFA:
C, 68.71; H, 6.59; N, 4.79. Found: C, 68.72; H, 6.62; N, 4.67.
tr a n s,tr a n s-2-(4-Meth oxyp h en yl)-4-(1,3-ben zod ioxol-5-
yl)-1-[(2,2-d im et h yl-1-p h en ylp r op yl)a m in oca r b on ylm e-
omers) δ 1.08-1.20 (m, 3H), 2.20 (brs, 3H), 2.43-2.54 (m, 2H),
3.40-3.87 (m, 10H), 4.48-4.60 (m, 1H), 5.96 (s, 2H), 6.48-
7.40 (m, 15H); MS (ESI+) (M + H)+ at m/z 606. Anal. Calcd
for C37H38N2O6‚1.00TFA: C, 64.97; H, 5.45; N, 3.87. Found:
C, 65.01; H, 5.47; N, 3.47.
tr a n s,tr a n s-2-(4-Meth oxyp h en yl)-4-(1,3-ben zod ioxol-5-
yl)-1-[[1,1-bis(2′-eth ylph en yl)m eth yl]am in ocar bon ylm eth -
yl]p yr r olid in e-3-ca r boxylic a cid (9i): white solid; 1H NMR
(CDCl3, 300 MHz) δ 1.12 (t, J ) 7.5 Hz, 6H), 2.28-2.59 (brm,
4H), 3.43-3.95 (m, 10H), 4.61-4.73 (brs, 1H), 5.97 (s, 2H),
6.52-7.42 (m, 15H). MS (ESI+) (M + H)+ at m/z 621. Anal.
Calcd for C38H40N2O6‚1.15TFA: C, 64.36; H, 5.51; N, 3.72.
Found: C, 64.36; H, 5.51; N, 3.73.
1
th yl]p yr r olid in e-3-ca r boxylic a cid (10h ): white solid; H
NMR (CDCl3, 300 MHz, mixture of diastereomers) δ [0.86 (s),
0.89 (s), 9H in total], 3.10-3.77 (m, 5H), [3.78 (s), 3.82 (s), 3H
in total], 4.32-4.52 (m, 2H), 4.69-4.77 (m, 1H), 5.96-6.02 (m,
2H), 6.78-7.47 (m, 12H); MS (ESI+) (M + H)+ at m/z 544. Anal.
Calcd for C32H36N2O6‚0.67TFA: C, 64.45; H, 5.95; N, 4.51.
Found: C, 64.40; H, 6.18; N, 4.71.
tr a n s,tr a n s-2-(4-Meth oxyp h en yl)-4-(1,3-ben zod ioxol-5-
yl)-1-[(1-p h en yleth yl)a m in oca r bon ylm eth yl]p yr r olid in e-
tr a n s,tr a n s-2-(4-Meth oxyp h en yl)-4-(1,3-ben zod ioxol-5-
yl)-1-[(3-m et h yl-1-p h en ylb u t yl)a m in oca r b on ylm et h yl]-
1
3-ca r boxylic a cid (10a ): white solid; H NMR (CDCl3, 300
1
MHz, mixture of diastereomers) δ [1.43 (d), 1.48 (d), J ) 7.5
Hz, 3H in total], 2.70-3.48 (m, 4H), 3.55-3.72 (m, 1H), [3.78
(s), 3.82 (s), 3H in total], 3.88-4.01 (m, 2H), 4.97-5.11 (m 1H),
5.93-6.00 (m, 2H), 6.65-6.94 (m, 5H), 7.17-7.47 (m, 7H); MS
(ESI+) (M + H)+ at m/z 502. Anal. Calcd for C29H30N2O6‚
0.22TFA: C, 67.02; H, 5.77; N, 5.31. Found: C, 67.08; H, 5.57;
N, 4.97.
p yr r olid in e-3-ca r boxylic a cid (10i): white solid; H NMR
(300 MHz, CDCl3) δ 0.78-0.96 (m, 6H), 1.34-1.50 (m, 1H),
1.51-1.77 (m, 2H), 3.30-3.92 (m, 8H), 4.67-4.95 (m, 3H),
5.89-6.03 (m, 2H), 6.68-7.47 (m, 12H); MS (ESI+) (M + H)+
at m/z 544. Anal. Calcd for C32H36N2O6‚0.50TFA: C, 66.07; H,
6.14; N, 4.68. Found: C, 66.10; H, 5.89; N, 4.68.
tr a n s,tr a n s-2-(4-Meth oxyp h en yl)-4-(1,3-ben zod ioxol-5-
yl)-1-[(3,3-d im eth yl-1-p h en ylbu tyl)a m in oca r bon ylm eth -
yl]p yr r olid in e-3-ca r boxylic a cid (10j): white solid; 1H NMR
(CDCl3, 300 MHz, mixture of diastereomers) δ [0.84 (s), 0.89
(s), 9H in total], 1.68 (t, J ) 7.5 Hz, 2H), 3.05-3.30 (m, 2H),
3.34-3.53 (m, 2H), 3.62-3.74 (m, 1H), 3.77 (s, 2H), 3.80 (s,
3H), 4.92-5.02 (m, 1H), 5.97-6.01(m, 2H), 6.77 (t, J ) 6.0 Hz,
2H), 6.88 (q, J ) 7.5, 18.0 Hz, 2H), 6.97 (d, J ) 6.0 Hz, 1H),
7.10-7.40 (m, 7H); MS (ESI+) (M + H)+ at m/z 559. Anal. Calcd
for C33H38N2O6‚0.45TFA: C, 66.75; H, 6.35; N, 4.59. Found:
C, 66.69; H, 6.32; N, 4.46.
tr a n s,tr a n s-2-(4-Meth oxyp h en yl)-4-(1,3-ben zod ioxol-5-
yl)-1-[1-(2′-m eth ylp h en yl)eth yl]a m in oca r bon ylm eth yl]-
1
p yr r olid in e-3-ca r boxylic a cid (10b): white solid; H NMR
(CDCl3, 300 MHz, mixture of diastereomers) δ [1.38 (d), 1.42
(d), J ) 7.5 Hz, 3H in total], [2.27 (s), 2.32 (s), 3H in total],
2.77-3.42 (m, 3H), 3.52-3.93 (m, 4H), [3.77 (s), 3.81 (s), 3H
in total], 5.15-5.30 (m, 1H), 5.90-5.98 (m, 2H), 6.60-6.96 (m,
7H), 7.06-7.38 (m, 4H); MS (ESI+) (M + H)+ at m/z 516. Anal.
Calcd for C30H32N2O6‚0.20TFA: C, 67.69; H, 6.02; N, 5.19.
Found: C, 67.56; H, 5.89; N, 5.16.
tr a n s,tr a n s-2-(4-Meth oxyp h en yl)-4-(1,3-ben zod ioxol-5-
yl)-1-[(1-ph en ylpr opyl)am in ocar bon ylm eth yl]pyr r olidin e-
3-ca r boxylic a cid (10c): white solid; H NMR (CDCl3, 300
MHz, mixture of diastereomers) δ [0.83 (t), 0.87 (t), J ) 7.5
Hz, 3H in total], 1.71-1.84 (m, 2H), 2.85-4.16 (m, 7H), [3.77
(s), 3.81 (s), 3H in total], 4.72-4.86 (m, 1H), 5.95-6.03 (m,
2H), 6.68-7.42 (m, 12H); MS (ESI+) (M + H+) at m/z 516. Anal.
Calcd for C30H32N2O6‚0.10TFA: C, 68.73; H, 6.13; N, 5.31.
Found: C, 68.74; H, 6.13; N, 5.22.
tr a n s,tr a n s-2-[4-(2-Meth oxyeth oxy)p h en yl]-4-(1,3-ben -
zodioxol-5-yl)-1-[(2,2-dim eth yl-1-ph en ylpr opyl)am in ocar -
bon ylm eth yl]p yr r olid in e-3-ca r boxylic a cid (10k ): white
solid; 1H NMR (CDCl3, 300 MHz, mixture of diastereomers) δ
[0.85 (s), 0.88 (s), 9H in total], 3.44 (s, 2H), 3.10-3.42 (m, 3H),
3.46 (s, 3H), 3.51-3.75 (m, 4H), 4.06-4.13 (m, 2H), 4.72 (m,
1H), 5.97 (m, 2H), 6.77-7.45 (m, 12H); MS (ESI+) (M + H)+
at m/z 589. Anal. Calcd for C34H40N2O7‚0.75TFA: C, 63.24; H,
6.09; N, 4.15. Found: C, 63.33; H, 6.18; N, 4.05.
tr a n s,tr a n s-2-(4-Meth oxyp h en yl)-4-(1,3-ben zod ioxol-5-
yl)-1-[(1-p h en ylbu tyl)a m in oca r bon ylm eth yl]p yr r olid in e-
3-ca r boxylic a cid (10d ): white solid; H NMR (CDCl3, 300
tr a n s,tr a n s-2-[4-(2-Isop r op oxyet h oxy)p h en yl]-4-(1,3-
ben zod ioxol-5-yl)-1-[(2,2-d im eth yl-1-p h en ylp r op yl)a m i-
n oca r b on ylm et h yl]p yr r olid in e-3-ca r boxylic a cid (10l):
1
1
MHz, mixture of diastereomers) δ 0.82-0.96 (m, 3H), 1.10-
1.31 (m, 2H), 1.63-1.77 (m, 2H), 2.94-3.84 (m, 9H), 4.13-
4.22 (m, 1H), 4.79-4.89 (m, 1H), 5.98 (s, 2H), 6.69-7.47 (m,
12H); MS (ESI+) (M + H)+ at m/z 530. Anal. Calcd for
white solid; H NMR (CDCl3, 300 MHz, mixture of diastere-
omers) δ [0.83 (s), 0.88 (s), 3H in total], 1.19 (d, J ) 7.0 Hz,
6H), 3.14-3.83 (m, 9H), 4.07 (p, J ) 4.5, 10.5 Hz, 2H), 4.27-
4.47 (m, 1H), 4.70 (t, J ) 9.0 Hz, 1H), 5.93-6.00 (m, 2H), 6.73-
7.38 (m, 12H); MS (ESI+) (M + H)+ at m/z 617. Anal. Calcd
for C36H44N2O7‚0.60TFA: C, 65.21; H, 6.56; N, 4.09. Found:
C, 65.15; H, 6.59; N, 4.01.
tr a n s,tr a n s-2-[4-(2-Meth oxyeth oxy)p h en yl]-4-(1,3-ben -
zod ioxol-5-yl)-1-(bis-o-t olylm et h yla m in oca r bon ylm et h -
yl)p yr r olid in e-3-ca r boxylic a cid (9j): white solid; 1H NMR
(CDCl3, 300 MHz) δ 2.13 (s, 3H), 2.20 (s, 3H), 2.94-3.23 (m,
3H), 3.32-3.51 (m, 2H), 3.47 (s, 3H), 3.58-3.69 (brs, 2H), 3.76
(dd, J ) 1.5, 6.0 Hz, 4H), 4.09 (t, J ) 4.5 Hz, 1H), 5.93 (m,
2H), 6.34-6.41 (d, J ) 7.5 Hz, 2H), 6.58 (brs, 2H), 6.72-6.98
(m, 3H), 7.05-7.28 (m, 8H); MS (ESI+) (M + H)+ at m/z 637.
Anal. Calcd for C38H40N2O7‚0.20TFA: C, 69.93; H, 6.14; N,
4.25. Found: C, 70.03; H, 6.08; N, 4.21.
C
31H34N2O6‚0.30TFA: C, 67.12; H, 6.11; N, 4.95. Found: C,
67.15; H, 5.88; N, 4.97.
tr a n s,tr a n s-2-(4-Meth oxyp h en yl)-4-(1,3-ben zod ioxol-5-
yl)-1-[(1-ph en ylpen tyl)am in ocar bon ylm eth yl]pyr r olidin e-
1
3-ca r boxylic a cid (10e): white solid; H NMR (CDCl3, 300
MHz, mixture of diastereomers) δ [0.79 (t), 0.87 (t), J ) 7.5
Hz, 3H in total], 1.10-1.38 (m, 4H), 1.66-1.80 (m, 2H), 2.91-
3.83 (m, 6H), [3.75 (s), 3.80 (s), 3H in total], 4.03-4.12 (m,
1H), 4.79-4.89 (m, 1H), 5.96-5.99 (m, 2H), 6.70-6.99 (m, 5H),
7.08-7.38 (m, 7H); MS (ESI+) (M + H)+ at m/z 544. Anal. Calcd
for C32H36N2O6‚0.25TFA: C, 67.94; H, 6.36; N, 4.87. Found:
C, 68.00; H, 6.18; N, 4.51.
tr a n s,tr a n s-2-(4-Meth oxyp h en yl)-4-(1,3-ben zod ioxol-5-
yl)-1-[(2-m eth yl-1-p h en ylp r op yl)a m in oca r bon ylm eth yl]-
tr a n s,tr a n s-2-[4-(2-Isopr opoxyeth oxy)ph en yl]-4-(1,3-ben -
zod ioxol-5-yl)-1-(bis-o-t olylm et h yla m in oca r bon ylm et h -
yl)p yr r olid in e-3-ca r boxylic a cid (9k ): white solid; 1H NMR
(CDCl3, 300 MHz) δ 1.21 (d, J ) 6.6 Hz, 6H), 2.16 (s, 3H),
2.20 (s, 3H), 3.17 (d, J ) 15.6 Hz, 1H), 3.26 (t, J ) 10.0 Hz,
1H), 3.33-3.55 (m, 3H), 3.66 (brs, 1H), 3.70 (quintet, J )
1
p yr r olid in e-3-ca r boxylic a cid (10f): white solid; H NMR
(CDCl3, 300 MHz, mixture of diastereomers) δ 0.77-0.95 (m,
6H), 1.96-2.07 (m, 1H), 2.80-3.45 (m, 4H), 3.60-3.76 (m, 1H),
[3.76 (s), 3.80 (s), 3H in total], 3.98-4.04 (m, 2H), 4.67 (t, J )
9.0 Hz, 1H), 5.89-6.00 (m, 2H), 6.68-7.42 (m, 12H); MS (ESI+)

3688 J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 18
Liu et al.
(8) (a) Underwood, D. C.; Bochnowicz, S.; Osborn, R. R.; Luttmann,
M. A.; Hay, D. W. Nonpeptide Endothelin Receptor Antagonists.
X. Inhibition of Endothelin-1- and Hypoxia-induced Pulmonary
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6.0 Hz, 2H), 3.78 (t, J ) 4.8 Hz, 2H), 4.07 (t, J ) 4.8 Hz, 2H),
4.34 (d, J ) 9.9 Hz, 1H), 5.94 (s, 2H), 6.38 (d, J ) 8.7 Hz, 1H),
6.65 (dd, J ) 8.4, 9.9 Hz, 2H), 6.82 (s, 2H), 6.86 (s, 1H), 6.91
(d, J ) 7.8 Hz, 1H), 6.95 (d, J ) 7.8 Hz, 1H), 7.04-7.34 (m,
6H), 7.71 (d, J ) 8.4 Hz, 1H); MS (ESI+) (M + H)+ at m/z 665.
Anal. Calcd for C40H44N2O7‚0.69TFA: C, 66.85; H, 6.06; N,
3.77. Found: C, 66.85; H, 6.01; N, 3.63.
tr a n s,tr a n s-2-[4-(2-Isop r op oxyet h oxy)p h en yl]-4-(1,3-
ben zod ioxol-5-yl)-1-[[1-(2′-eth ylp h en yl)-1-(2′-m eth ylp h e-
n yl)m eth yl]a m in oca r bon ylm eth yl]p yr r olid in e-3-ca r box-
ylic a cid (9l): white solid; 1H NMR (CDCl3, 300 MHz, mixture
of diastereomers) δ 1.04-1.28 (m, 9H), 2.20 (s, 3H), 2.53 (brs,
2H), 2.94-3.23 (m, 3H), 3.35-3.87 (m, 6H), 4.08 (brs, 3H), 4.52
(brs, 1H), 5.96 (s, 2H), 6.48-7.35 (m, 15H); MS (ESI+) (M +
H)+ at m/z 678. Anal. Calcd for C41H46N2O7‚0.95TFA: C, 65.46;
H, 6.01; N, 3.46. Found: C, 65.47; H, 6.00; N, 3.10.
tr a n s,tr a n s-(2R,3R,4S)-2-[4-(2-Meth oxyeth oxy)ph en yl]-
4-(1,3-ben zod ioxol-5-yl)-1-(bis-o-tolylm eth yla m in oca r bo-
n ylm eth yl)p yr r olid in e-3-ca r boxylic a cid (9j): white solid;
1
[R]23 +14.0° (c 0.0015, CH3OH); H NMR (CDCl3, 300 MHz)
D
δ 2.13 (s, 3H), 2.20 (s, 3H), 2.94-3.23 (m, 3H), 3.32-3.51 (m,
2H), 3.47 (s, 3H), 3.58-3.69 (brs, 2H), 3.76 (dd, J ) 1.5, 6.0
Hz, 4H), 4.09 (t, J ) 4.5 Hz, 1H), 5.93 (m, 2H), 6.34-6.41 (d,
J ) 7.5 Hz, 2H), 6.58 (brs, 2H), 6.72-6.98 (m, 3H), 7.05-7.28
(m, 8H); MS (ESI+) (M + H)+ at m/z 637. Anal. Calcd for
C
38H40N2O7‚0.66TFA: C, 66.33; H, 5.76; N, 3.93. Found: C,
66.57; H, 5.36; N, 3.68.
tr a n s,tr a n s-(2R,3R,4S)-2-[4-(2-Isop r op oxyeth oxy)p h e-
n yl]-4-(1,3-ben zodioxol-5-yl)-1-(bis-o-tolylm eth ylam in ocar -
bon ylm eth yl)p yr r olid in e-3-ca r boxylic a cid (9k ): white
1
solid; [R]23 +10.3° (c 0.0016, CH3OH); H NMR (CDCl3, 300
D
MHz) δ 1.21 (d, J ) 6.6 Hz, 6H), 2.16 (s, 3H), 2.20 (s, 3H),
3.17 (d, J ) 15.6 Hz, 1H), 3.26 (t, J ) 10.0 Hz, 1H), 3.33-3.55
(m, 3H), 3.66 (brs, 1H), 3.70 (quintet, J ) 6.0 Hz, 2H), 3.78 (t,
J ) 4.8 Hz, 2H), 4.07 (t, J ) 4.8 Hz, 2H), 4.34 (d, J ) 9.9 Hz,
1H), 5.94 (s, 2H), 6.38 (d, J ) 8.7 Hz, 1H), 6.65 (dd, J ) 8.4,
9.9 Hz, 2H), 6.82 (s, 2H), 6.86 (s, 1H), 6.91 (d, J ) 7.8 Hz,
1H), 6.95 (d, J ) 7.8 Hz, 1H), 7.04-7.34 (m, 6H), 7.71 (d, J )
8.4 Hz, 1H); MS (ESI+) (M + H)+ at m/z 665. Anal. Calcd for
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C
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68.68; H, 6.15; N, 3.87.
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Receptor Bin din g Assays an d P h ar m acokin etic An aly-
sis. See the previously published Experimental Section.18
Ack n ow led gm en t. The authors thank the Abbott
1
Analytical Department for assistance in acquiring H
NMR and mass spectra and Mr. Michael Fitzgerald of
D-45L for performing the chiral HPLC separation of the
enantiomers.
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