Azole endothelin antagonists. 2. Structure-activity studies

Article abstract of DOI:10.1021/jm950592+

Structure-activity studies have been performed in an attempt to improve the potency of a novel series of azole-based endothelin-A (ET(A)) selective antagonists. Modifications of the hydrophobic group on the terminal urea produced substantial effects on receptor affinity; in particular, the choice of cyclohexyl- or arylureas led to substantial improvements in activity. Conformational restriction of these groups provides an additional benefit. N- Methylation of the indole moiety which is part of the heterocyclic dipeptide surrogate also improves potency. The effects of these two modifications appear to be synergistic, with the best of the resultant doubly modified analogs (e.g. 14q, 15y, and 15ff) exhibiting an 80-200-fold improvement over the original leads.

Full text of DOI:10.1021/jm950592+

968
J . Med. Chem. 1996, 39, 968-981
Azole En d oth elin An ta gon ists. 2. Str u ctu r e-Activity Stu d ies
Thomas W. von Geldern,* J effrey A. Kester, Radhika Bal, J inshyun R. Wu-Wong, William Chiou,
Douglas B. Dixon, and Terry J . Opgenorth
Aging and Degenerative Diseases Research Department, Pharmaceutical Products Research, Abbott Laboratories,
Abbott Park, Illinois 60064
Received August 8, 1995X
Structure-activity studies have been performed in an attempt to improve the potency of a
novel series of azole-based endothelin-A (ETA) selective antagonists. Modifications of the
hydrophobic group on the terminal urea produced substantial effects on receptor affinity; in
particular, the choice of cyclohexyl- or arylureas led to substantial improvements in activity.
Conformational restriction of these groups provides an additional benefit. N-Methylation of
the indole moiety which is part of the heterocyclic dipeptide surrogate also improves potency.
The effects of these two modifications appear to be synergistic, with the best of the resultant
doubly modified analogs (e.g. 14q, 15y, and 15ff) exhibiting an 80-200-fold improvement over
the original leads.
In tr od u ction
to the production of nitric oxide and to the clearance of
endogenous ET. Because these latter effects might be
beneficial in a number of the diseases described above,
it has been suggested3 that a selective ETA antagonist
may provide some therapeutic advantage over a non-
selective agent.
We evaluated compounds 14-19 in competitive bind-
ing assays, using MMQ cell homogenates as a source of
ETA and porcine cerebellar membranes as a source of
ETB receptor. These receptors are highly homologous
with the human receptor sequence, and we have dem-
onstrated (unpublished results) that receptor affinities
measured these systems correlate well with those
recorded using human ETA,B expressed in CHO cells.
The results of these two assays not only provide receptor
affinities (indicated in Tables 1-3 as IC50 values) but
also give an indication of the relative selectivity of the
compounds for the ETA subtype.
To confirm that our analogs are functioning as
antagonists to block the actions of the endothelins, we
have also established an assay which evaluates receptor
activation by measuring the hydrolysis of inositol
phosphates. We measure both agonist (compound-
stimulated) and antagonist (ET-1 stimulation) profiles
for a selected set of compounds in the MMQ cell line.
All of the analogs tested act as antagonists, with EC50
values that are comparable to their binding IC50s.
Importantly, none of our compounds exhibits any sig-
nificant level of agonist activity; rather they appear to
act as relatively pure functional antagonists.
In the preceding article1 we have described our
strategy for the development of a novel class of endo-
thelin-A (ET-A) receptor antagonists, prepared (Scheme
1) through modification of the amide framework of the
known peptide antagonists BQ-485 and FR-139317. Our
preliminary structure-activity studies in this new
series suggested that, while the peptidic and peptido-
mimetic compounds appear to be closely related, they
differ significantly in the manner in which they interact
with the ETA receptor. We have been able to rationalize
several unusual aspects of the activity profile of com-
pounds 1 by applying a generalized model of GPCR
binding, developed at Abbott, to the specific case of the
endothelin receptor.
The initial set of compounds 1, prepared as a pre-
liminary test of our design concept, exhibit only a
modest ability to bind to the receptor of interest. In
retrospect this is not a surprising result. The structures
of BQ-485 and FR-139317 have been optimized by
workers at Banyu and Fujisawa, respectively, through
extensive analog studies;2 the shift in binding mode
which we encounter upon rigidification of the C-terminal
dipeptide is likely to influence the steric and electronic
requirements for various substituents along its back-
bone. We thus viewed 1 as a lead structure which would
require further optimization to maximize ETA affinity,
and accordingly initiated a study to probe the structure-
activity profile of this new series.
Recep tor Bin d in g a n d Selectivity; F u n ction a l
An a lysis
Ch em istr y
Endothelin acts by binding to a family of membrane-
associated, G-protein coupled receptors.3 Binding to the
ETA receptor subtype, which predominates in vascular
smooth muscle cells, triggers a cascade of events which
lead, via the hydrolysis of inositol phosphates and the
release of calcium ions, to the observed vasoconstrictive
and proliferative responses. The results of binding to
ETB, which is the major receptor on endothelial cells,
are less clearly understood; while this receptor mediates
constriction in some tissue beds, it has also been linked
The majority of the analogs described in this article
were prepared by the basic strategy described in our
previous article (Schemes 2-4).1 Briefly, the core azoles
are assembled in a manner similar to that described by
Gordon and co-workers4 (Scheme 2) through cyclization
of key intermediate 3, itself prepared by sequential C-
and N-acylation of glycine anion equivalent 2. By
proper choice of cyclization conditions4 we are able to
prepare either imidazoles 4 or oxazoles 5 from ketoa-
mide 3. Deprotection of 4/5, followed by coupling with
a urea prepared from leucine and hydrolysis of the
terminal ester, provides target molecules 14/15.
X Abstract published in Advance ACS Abstracts, J anuary 15, 1996.
0022-2623/96/1839-0968$12.00/0 © 1996 American Chemical Society

Azole Endothelin Antagonists
J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 4 969
Sch em e 1. Heterocyclic Dipeptide Surrogates
Sch em e 2. Synthesis of Azole Coresa
a
(i) LiHMDS, THF, -78 °C; CH3COCl; (ii) HCl-H2O; (iii) P-D-Trp(R′)-OCOOiBu, THF, -20 °C; NMM (dropwise); (iv) RNH3OAc,
HOAc, reflux; (v) PPh3, CCl4, pyr, CH3CN.
Several modifications of our original route should be
noted. We have reported that hydrolysis of the C-
terminal ethyl ester to give our final product acid often
requires vigorous conditions and sometimes leads to
some loss of stereochemical integrity. To avoid this
difficulty, and to simplify purification at this final stage,
most of the analogs discussed here were prepared via
the corresponding benzyl ester. This modification al-
lows for hydrogenolytic esterolysis, a process which
occurs without detectable stereomutation. Unfortu-
nately this change also leads to a re-evaluation of our
overall protecting group strategy. Ideally, the N-ter-
minus of 3 (and thus of 4 and 5) might now be
orthogonally protected with a tert-butyloxycarbonyl
(Boc) group, which is readily removable with anhydrous
trifluoroacetic or hydrochloric acids. This strategy is
successfully applied in the synthesis of oxazoles 5.
However, the Boc group proves labile to the conditions
(acetic acid, heat) employed in preparing imidazoles 4.
After exploring several possibilities, we have found it
most efficient to return to the original choice of the
carbobenzoxy (Cbz) group for protecting the primary
amine of 4. Deprotection may be accomplished using
HBr in acetic acid, for relatively short periods of time,
with minimal cleavage of the benzyl ester.
The majority of leucylureas 8 (Scheme 3) prepared
for this study derive by reacting 1,1′-carbonyldiimida-
zole sequentially with leucine benzyl ester and the
relevant primary or secondary amine. Removal of the
benzyl ester is accomplished through hydrogenolysis;
the resultant acid is coupled (Scheme 4) with a depro-
tected heterocyclic core to assemble the analog skeleton.
Hydrogenolysis of the remaining ester provides the final
product. Alternatively, ureas 8 may be assembled
(Scheme 3) by condensing leucine benzyl ester with
preformed carbamoyl chlorides or isocyanates; similarly
sulfonylureas 11 are prepared using the corresponding
sulfamoyl chloride. Less reactive amines, e.g. anilines,
react more efficiently with the isocyanate prepared by
reacting the leucyl ester with phosgene. Finally, indole
derivative 13 arises by direct coupling of leucine benzyl
ester with the symmetrical anhydride derived from
indole-1-carboxylic acid.5 In this latter case, it is
important that both hydrogenolysis steps are performed
under transfer-hydrogenation conditions to avoid over-
reduction of the acylindole moiety.
A number of acid derivatives may also be elaborated
at a later stage in the synthesis. Thus, the acid chloride
derived from oxazole 15a may be reacted with a variety
of amines to produce amides 16. Alternatively the
dipeptide mimetic 17 can be homologated via an Arndt-
Eistert sequence to give (after further assembly) the
oxazoleacetic acid 19.
Str u ctu r e-Activity Rela tion sh ip s
Our previous preliminary structure-activity study1
of the heterocyclic dipeptide mimic incorporated in 1
resulted in two significant observations: first, that
imidazole and oxazole are dramatically superior to
thiazole as the heterocyclic core moiety, and second, that
small alkyl groups are strongly preferred as substitu-
ents on this heteroring (Table 1). These preliminary
studies led to the identification of compounds 14a and
15a as lead structures for further study. We thus began
our secondary SAR studies by conducting a cursory
examination of the remainder of the molecule in order
to identify potential sites for modification.
One such site was revealed through studies of the
urea moiety. The critical importance of the urea car-
bonyl was suggested by the lack of activity of sulfony-
lureas 14/15b. On the other hand, a scan of several
hydrophobic amines led to the identification of cyclo-
hexylamine (compounds 14/15e) as a valuable replace-
ment for the perhydroazepinyl group. The use of this
amine leads to a 2-fold increase in ETA binding affinity
in the oxazole series (compare 15e vs 15a ) and >7-fold
in the imidazole series (14e vs 14a ). Other amines
chosen in this initial scan (e.g. diethylamine or benzy-
lamine) were inferior to perhydroazepine.
We next examined the effect of heteroalkylation of the
indole and imidazole heterocycles. Indole N-methyla-
tion is well tolerated in the peptidic antagonist series;
in fact, the state of the indole nitrogen represents the
primary difference between Banyu’s (unsubstituted) and
Fujisawa’s (indole N-alkylated) contributions in this

970 J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 4
Sch em e 3. Synthesis of N-Terminal Substituentsa
von Geldern et al.
a
(i) CDl, Et3N, THF; (ii) R1R2NH; (iii) R1R2NCOCl, Et3N, THF; (iv) R1NCO, Et3N, THF (R2 ) H); (v) H2-10% Pd-C, EtOH; (vi)
triphosgene, tol. reflux; (vii) ArNH2; (viii) PhaSO2Cl, i-Pr2NEt, DMF; (ix) n-BuLi, THF, -78 °C; (x) CO2; (xi) H+; (xii) EDC, CH2Cl2; (xiii)
9; (xiv) 10% Pd-C; cyclohexadiene, EtOH-EtOAc.
Sch em e 4. Analog Assemblya
a
(i) TFA; (ii) H2-10% Pd-C, EtOH; (iii) 30% HBr-HOAc; (iv) EDC, HOBt, NMM, THF-DMF; (v) NaOH, EtOH-H2O; (vi) 10% Pd-
C; cyclohexadiene; EtOH-EtOAc; (vii) (COCl)2, cat. DMF, THF; (viii) RNH2; (ix) i-BuOCOCl, NMM, THF, -40 °C; (x) CH2N2-Et2O; (xi)
AgOBz, Et3N, CH3OH; (xii) RNHCOCl or RNCO, NEt3, THF.
area. In our own example, methylation of the indole
improves ETA binding by a factor of 2 in both hetero-
cyclic series (viz. 14f vs 14a and 15f vs 15a ). When
N3 of the imidazole is methylated (as in 14r ) or benzy-
lated (as in 14s), the resultant analogs show substan-
tially reduced activity.
A series of replacements for the carboxylic acid
functionality of 1 were also studied. Although none of
the replacements examined were as potent as the parent
acid 15a , amides 16b and 16c and hydroxamate 16a
all show significant levels of activity. On the other
hand, ester 16d and homologated acid 19 are substan-

Azole Endothelin Antagonists
J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 4 971
Ta ble 1. Preliminary SAR Studies
tially less potent. In the model for endothelin receptor
binding described in the preceding article, we propose
that this carboxylate provides a critical interaction with
lysine residue 166 on helix III. Consistent with that

972 J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 4
Ta ble 2. Aliphatic Ureas
von Geldern et al.

Azole Endothelin Antagonists
J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 4 973
Ta ble 2 (Continued)
model, the relative binding affinities of these acid
replacements correlate qualitatively with the electron
density at the carbonyl oxygen.
tions were well tolerated, and led to compounds which
were more active than the original perhydroazepinyl
ureas 14/15f, neither was as effective as cyclohexy-
lamine. To probe the steric environment around the six-
membered ring, we placed a methyl group sequentially
at the 1-, 2-, 3-, and 4-positions (compounds 15w , 14l-
n , and 15l-n ). Because the methylcyclohexylamines
were incorporated as racemic cis/trans mixtures, ana-
logs 14l-n and 15l-n each comprise a number of
isomeric compounds. Despite this complication, the
results of the binding studies are clear, indicating that
substitution is tolerated at the 1-, 2-, and 3-positions,
while 4-substitution results in a >10-fold decrease in
activity. To confirm this latter result, we also prepared
trans-(4-hydroxycyclohexyl)ureas 14/15k . Again, these
analogs had only one-tenth of the activity of unsubsti-
tuted 14/15g.
These preliminary studies additionally serve to rein-
force two important aspects of the structure-binding
profile of compounds related to 1. While the ETA
affinities reported in Table 1 vary over 3 orders of
magnitude, the compounds all show minimal activity
at the ETB receptor. Thus, despite the apparent changes
in the binding mode of these compounds as compared
with FR-139317, it appears that the high degree of
receptor selectivity inherent in the peptidic series has
been translated to this new structural class. Addition-
ally, the pairwise comparison of identically-substituted
oxazoles and imidazoles indicates that the latter are
consistently more active at ETA, by a factor of 2-8. This
difference in potency may indicate that the imidazole
ring is better able to mimic the H-bonding pattern of
the amide bond which it replaced.
The above studies identified two modifications of our
lead structure, the choice of cyclohexylurea and indole
N-methylation, which independently provide significant
improvements in ETA affinity. These two substitutions
were combined in compounds 14/15g (Table 2) to see if
their effects might be additive. In fact, the two modi-
fications appear to act synergistically; imidazole 14g has
an IC50 of 11 nM, a 7-fold improvement over 14e, while
the corresponding oxazole 15g binds at 220 nM, 3 times
better than 15e. Compounds 14g and 15g define new
standards of potency for this structural class and
highlight the urea and indole as profitable sites for
modification.
None of the alkyl substitutions provide a significant
improvement in ETA affinity; however, they do suggest
the possibility of examining larger substituents, or of
employing multiple points of attachment to the ring. A
number of analogs were prepared to explore these ideas.
At position 1 of the cyclohexane, we find that a car-
bomethoxy substituent (as in 15x) is superior either to
methyl (15w ) or to the unsubstituted parent. The
1-position may also be used as the attachment point for
a spirocyclic aminal, as in 15y. This conformationally
restricted analog is approximately 40 times more potent
than the flexible 15g, 15w , and 15x, a result which may
also indicate some advantage for N-alkylation. Fusion
of an aryl ring to the 2,3-positions of the cyclohexane
(as in 15t) is well tolerated, but offers no advantage.
Surprisingly a variety of bicyclic (endo- and exo-nor-
bornyl) and tricyclic (1- and 2-adamantyl) systems are
also acceptable; at best, however, the activities of these
analogs are equivalent to 14/15g.
To expand on these new leads, we first examined
whether increasing the size of the Ni-alkyl substituent
led to further improvements in binding affinity. In fact,
N-ethylindoles 14h and 15h are 60-fold less active than
14/15g, suggesting that the space in this region of the
receptor is quite limited.
Another series of analogs was prepared to further
examine the hydrophobic domain at the urea terminus
(Table 2). To study the effect of ring size, we incorpo-
rated cyclopentylamine (analogs 14/15i) and cyclohep-
tylamine (14/15j) into the urea. While both substitu-
Another possible replacement for the cycloalkyl sub-
stituent on the urea is an aryl group. In practice the
use of aniline leads to a set of analogs (14z, 15z, Table
3) that are more active (IC50 ) 7.6 and 16 nM against
ETA) than the corresponding cyclohexylureas 14/15g.
Phenyl substitution seems to offer a particular advan-
tage in the oxazole series (14-fold improvement over

974 J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 4
Ta ble 3. Aromatic Ureas
von Geldern et al.
cyclohexyl) as opposed to the imidazole series (1.4-fold
increase in ETA affinity); this provides the first example
in which these two series exhibit similar levels of
activity with a given urea substituent.
than the simple 4-fluoro-substituted analog, but it is
clear from the relative activities of these two compounds
that it is the 4-substituent which provides the major
deficit.
To take advantage of the unique boost provided to the
oxazole-based antagonists by the phenyl substituent, a
series of oxazoles containing aromatic ureas were
prepared and examined in the binding assays (Table 3).
Replacement of the benzene ring with pyridine was
detrimental to activity; 2- and 3-pyridyl analogs 15a a
and 15bb were 10- and 20-fold less potent than 15z.
The placement of fluorine atoms on the aromatic ring
causes a decrease in activity which is remarkably
position-dependent. While the 2-fluoroanilide 15cc is
equipotent with 15z, the 3- and 4-substituted analogs
15d d and 15ee are 4-fold and 120-fold less active,
respectively. This activity profile is reminiscent of that
observed with methyl substitution on the cyclohexy-
lurea. Pentafluoranilide 15ff is somewhat less active
Several conformationally-restricted aromatics were
also examined. Of these, indoline 15gg is the most
effective with an IC50 of 5.9 nM against the ETA
receptor. The increased activity of 15gg when compared
with 15z suggests that it may be desirable for the
aromatic ring to exist in the plane of the urea carbonyl.
This result is in sharp contrast to that observed with
aminal 15y, in which a significant boost in potency was
realized when the cyclohexane ring was restricted
orthogonally to the plane of the carbonyl π-system.
However, the difference in activity between 15gg and
15z is small; additionally, the fact that the anilide is
N-alkylated in 15gg may complicate our analysis.
Another explanation is possible, however. Our receptor
modeling work suggests that this hydrophobic pocket

Azole Endothelin Antagonists
J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 4 975
ride; HOBt, 1-hydroxybenzotriazole hydrate; LiHMDS, lithium
hexamethyldisilazide; NMM, N-methylmorpholine; Pha, hex-
amethyleneimine (perhydroazepine); PPh3, triphenylphos-
phine; pyr, pyridine; TFA, trifluoroacetic acid; THF, tetrahy-
drofuran; pTsOH, p-toluenesulfonic acid.
is actually rather large and that aminal 15y and
indoline 15gg fit it in different ways; the observation
that a variety of norbornyl- and adamantylamines are
tolerated at the urea terminus is consistent with this
suggestion. Indoline may be replaced with indole
(15h h ) or with 1,2,3,4-tetrahydroquinoline (15ii) with
some success, but the resultant analogs are inferior to
either 15z or 15gg.
Syn th esis of Cor e Heter ocycles 4 a n d 5. Compounds 4
(P ) Cbz, R ) Et, R1 ) H or P ) Cbz, R ) Bn, R1 ) CH3) and
5 (P ) Cbz, R ) Et, R1 ) H or P ) Boc, R ) Bn, R1 ) CH3)
were prepared from the appropriate starting materials, includ-
ing Ni-methyl D-tryptophan6 using the procedures described
in the previous article.1
Con clu sion s
Syn th esis of Leu cin e Der iva tives. Leucine-derived urea
acids were prepared from the appropriate starting materials
according to the procedures described in the previous article1
or using the following methods:
Our structure-activity studies have served to identify
a number of modifications of imidazole 14a and oxazole
14b which lead to improved affinity for the ETA recep-
tor. Compounds with an imidazole core are consistently
more active than the corresponding oxazoles, and all of
the analogs reported in this work are highly selective
(up to 6000-fold) for ETA over ETB. In particular we
observe that N-methylation of the indole moiety leads
to improved analogs, and that modification of the
hydrophobic urea dramatically affects interactions with
the receptor. In this latter case, both cyclohexyl- and
arylamines appear to be quite well accepted, with the
anilines appearing to provide a selective boost to the
oxazole series, thus closing the “activity gap” between
imidazoles and oxazoles. A variety of minor modifica-
tions of the cyclohexyl and phenyl rings are tolerated;
however, the only changes which lead to further im-
provements in binding affinity involve conformational
restriction.
The results of these SAR studies are essentially
consistent with the model we described in the previous
article in this series. In particular the model suggests
that there may be additional hydrophobic space in the
N-terminal and indole binding pockets to accomodate
the preferred methylations; in the former case the
predicted available space is great enough to allow a
convenient explanation for the acceptability of two
orthogonal conformational restrictions of this N-termi-
nal group. On the other hand, it is difficult for us to
rationalize the strong preference for methyl over larger
alkyl groups at these two positions using our current
model, suggesting that some refinement may be neces-
sary.
N-((P h en yla m in o)ca r bon yl)leu cin e (8, R1 ) P h , R2
)
H) (Gen er a l P r ep a r a tion of Ar yla n ilin es). Leu-OBn‚p-
TsOH (2.0 g) was suspended in THF (5 mL). N-Methylmor-
pholine (0.56 mL, 0.51 g) and phenyl isocyanate (0.55 mL, 0.6
g) were added, and the solution was stirred at ambient
temperature for 4 h. The solvent was evaporated and the
residue dissolved in EtOAc (20 mL). The solution was washed
with saturated NaHCO3 solution, 1 N H3PO4, and brine, dried
with MgSO4, and evaporated under reduced pressure to give
a colorless oil which was dissolved in EtOH (25 mL); 10%
palladium on carbon (200 mg) was added. The flask was fitted
with a three-way stopcock connected to a hydrogen-filled
balloon and a nitrogen/vacuum manifold. The flask was
evacuated, filled with nitrogen, evacuated again, and then put
under a hydrogen atmosphere. The mixture was stirred at
ambient temperature for 14 h. The hydrogen was evacuated
and the flask filled with nitrogen. The catalyst was removed
by filtration through a pad of Celite and the solvent removed
in vacuo to give a colorless oil which solidified upon standing
(1.08 g, 85% yield).
N-(((1-Meth ylcycloh exyl)a m in o)ca r bon yl)leu cin e (8,
R1 ) 1-CH3-c-C6H11, R2 ) H). To a solution of 1.06 g (7.5
mmol) of 1-methylcyclohexane-1-carboxylic acid in 40 mL of
toluene were added 1.61 mL of diphenyl phosphorazidate (2.06
g, 1 equiv) and 1.65 mL (1.52 g, 15 mmol) of N-methylmor-
pholine. The resultant mixture was heated at 70 °C for 2 h,
cooled to room temperature, and added dropwise to a solution
of 1.97 g (5 mmol) of Leu-OBn‚TsOH and 1.1 mL of N-
methylmorpholine in 20 mL of toluene. The reaction mixture
was stirred overnight at ambient temperature, washed with
sodium bicarbonate solution, 1 N H3PO4, and brine, and
concentrated in vacuo. The crude product (2.5 g) was dissolved
in 50 mL of EtOH, 50 mg of 10% palladium on carbon was
added, and the mixture was purged with nitrogen. The
nitrogen line was exchanged for a balloon of hydrogen, and
the mixture was stirred at ambient temperature for 4 h. The
catalyst was removed by filtration through a pad of Celite, and
the solvents were removed in vacuo to give the title compound
which was used without further purification.
Most importantly, the above studies have resulted in
the availability of a number of highly active, ETA-
selective antagonists containing our heterocyclic dipep-
tide mimic. With these compounds in hand, it is
possible to begin to explore the effects of this core
modification on pharmacokinetics. The results of such
a study are reported in the next article in this series.
N-((2-(P yr id yla m in o)ca r bon yl)leu cin e (10, Ar ) 2-p yr )
(Used To P r ep a r e P yr id yl a n d F 5-P h en yla n ilin es). Leu-
cine benzyl ester (2.4 g) was dissolved in toluene (25 mL).
Triphosgene (1.1 g) was added and the solution heated at
reflux for 2.5 h. The solution was allowed to cool to ambient
temperature and the solvent evaporated. The residue was
dissolved in CHCl3 (25 mL) and cooled to 0 °C in an ice bath.
2-Aminopyridine (1.2 mL) was added and solution stirred cold
for 30 min. The bath was removed and the solution allowed
to stir at ambient temperature for 5 h. The solution was
washed with saturated sodium bicarbonate solution, 1 N H3-
PO4, and brine, dried with MgSO4, and evaporated to give an
orange oil which was purified by flash chromatography on
silica gel eluting with 20% EtOAc-hexane to give a light
yellow oil which solidified on standing (3.65 g, 95%). The
resultant benzyl ester was dissolved in EtOH (150 mL), the
solution was purged of oxygen, 10% Pd/C (150 mg) was added,
and the mixture was stirred under hydrogen for 2 h. The
solvent was removed in vacuo, and the residue was taken up
in EtOAc and filtered through Celite to remove the catalyst.
The solvent was evaporated in vacuo to give the carboxylic
acid as a colorless oil (2.62 g, 96%).
Exp er im en ta l Section
Unless otherwise specified, all solvents and reagents were
obtained from commercial suppliers and used without further
purification. THF was dried over sodium and purified by
distillation. All reactions were performed under a nitrogen
atmosphere unless specifically noted. All final products are
analyzed for purity by analytical HPLC using a 25-cm Vydac
Protein and Peptide C18 column, and are >95% pure unless
otherwise stated. 1H-NMR spectra were recorded at 300 MHz;
all values are referenced to tetramethylsilane as internal
standard and are reported as shift (multiplicity, coupling
constants). Mass spectral analysis is accomplished using fast
atom bombardment (FAB-MS) or direct chemical ionization
(DCI-MS) techniques. All elemental analyses are consistent
with theoretical values to within (0.4% unless indicated.
Abbr evia tion s: CDI, 1,1′-carbonyldiimidazole; DBU, 1,8-
diazabicyclo[5.4.0]undec-7-ene; DMF, dimethylformamide; EDC,
1-ethyl-3-(3-(dimethylamino)propyl)carbodiimide hydrochlo-

976 J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 4
von Geldern et al.
1
N-(P er h yd r oa zep in -1-ylsu lfon yl)leu cin e (11). Perhy-
droazepine (6 mL) was dissolved in diethyl ether (250 mL) and
cooled to 0 °C in an ice bath. HCl gas was bubbled through
the solution and the resulting white solid collected by filtration
and dried in vacuo. The solid was taken up in sulfuryl chloride
(20 mL) and the mixture heated at reflux. The reaction
became very thick, additional sulfuryl chloride (10 mL) was
added, and reflux was continued for 16 h. The remaining
sulfuryl chloride was evaporated and the residue distilled (90-
100 °C, 0.1 mm) to give homopiperidinesulfonyl chloride as a
colorless oil (9.06 g, 86%). To the sulfonyl choride (0.97 g)
dissolved in DMF (10 mL) were added Leu-OBn‚p-TsOH (2.03
g), Hu¨nig’s base (1.75 mL), and then DMAP (0.2 g), and the
mixture was stirred at room temperature for 16 h. The
solution was diluted with ethyl acetate, washed with water, 2
N HCl, saturated NaHCO3 solution, and brine, dried, and
evaporated. Purification by flash chromatography (10% EtOAc-
hexane) gave N-(homopiperidin-1-ylsulfonyl)leucine benzyl
ester as a white solid (0.88 g, 47%). The benzyl ester (0.85 g)
was dissolved in MeOH (20 mL), and 10% Pd/C (0.75 g) was
added. The mixture was stirred at room temperature under
an H2 atmosphere for 2.5 h. The catalyst was filtered off and
the solvent evaporated to give the product as a colorless oil
(0.66 g, 100%).
N-(In d ol-1-ylca r bon yl)leu cin e (13). Indole-1-carboxylic
acid5 (12; 0.64 g, 4.0 mmol) was dissolved in 20 mL of
dichloromethane, EDC (0.58 g, 3 mmol) was added, and the
solution was stirred at ambient temperature for 30 min. Leu-
OBn (0.55 g, 2.5 mmol) was added, and the solution was stirred
for 16 h at ambient temperature. The solvents were removed
in vacuo, and the residue was taken up in EtOAc, washed with
water, sodium bicarbonate solution, 1 N H3PO4, and brine, and
concentrated in vacuo. The product was purified by flash
chromatography on silica gel. A sample of this material (170
mg, 0.49 mmol) was added to a suspension of 87 mg of 10%
Pd-C in 1.5 mL of MeOH, the mixture was purged with
nitrogen, and 0.1 mL of cyclohexadiene was added. The
resultant suspension was stirred at ambient temperature for
1 h. The catalyst was removed by filtration through a pad of
Celite, and the solvents were removed in vacuo to give a
product which was used without further purification.
Com p ou n d Assem bly. The following compounds were
prepared from the appropriate core heterocycle and leucine
derivative according to the coupling strategy described in the
previous article,1 employing the following deprotection strate-
gies:
(14e): H NMR (CD3OD, 300 MHz) for the major tautomer δ
0.78 (d, 3H, J ) 7 Hz), 0.80 (d, 3H, J ) 7 Hz), 1.2-1.85 (m,
14H), 2.53 (s, 3H), 3.35-3.6 (m, 4H), 4.04 (m, 1H), 5.42 (t, 1H,
J ) 8 Hz), 7.00 (t, 1H, J ) 7 Hz), 7.10 (s, 1H), 7.12 (t, 1H, J
) 7 Hz), 7.36 (d, 1H, J ) 8 Hz), 7.45 (d, 1H, J ) 8 Hz);
MS (DCI/NH3) m/ e 523 (M
C28H38N6O4‚1.5TFA: C, H, N.
2-{1(R)-[(P er h yd r oa zep in -1-ylca r bon yl)leu cyla m in o]-
2-(1-m eth ylin dol-3-yl)eth yl}-5-m eth ylim idazole-4-car box-
+
H)+.
Anal.
for
1
ylic a cid (14f): H NMR (CD3OD, 300 MHz) δ 0.93 (d, 3H, J
) 7 Hz), 0.96 (d, 3H, J ) 7 Hz), 1.30 (m, 2H), 1.52 (m, 5H),
1.66 (m, 4H), 2.52 (s, 3H), 3.4 (m, 5H), 3.59 (dd, 1H, J ) 7, 15
Hz), 3.75 (s, 3H), 4.07 (dd, 1H, J ) 7, 8 Hz), 4.35 (dd, 1H, J )
6, 10 Hz), 5.42 (dd, 1H, J ) 6, 8 Hz), 7.04 (s, 1H), 7.05 (ddd,
1H, J ) 1, 7, 8 Hz), 7.18 (ddd, 1H, J ) 1, 7, 8 Hz), 7.35 (d, 1H,
J ) 8 Hz), 7.47 (d, 1H, J ) 8 Hz); MS (DCI/NH3) m/ e 537 (M
+ H)+; HRMS calcd for C29H41N6O4 537.3189, found 537.3191.
2-{1(R)-[(P er h yd r oa zep in -1-ylca r bon yl)leu cyla m in o]-
2-(in d ol-3-yl)eth yl}-1,5-d im eth ylim id a zole-4-ca r boxylic
a cid (14r ): H NMR (CD3OD, 300 MHz) δ 0.89 (d, 3H, J ) 7
1
Hz), 0.91 (d, 3H, J ) 7 Hz), 0.78-1.74 (m, 11H), 2.35 (s, 3H),
3.20 (s, 3H), 3.38 (m, 4H), 3.50 (m, 2H), 4.27 (dd, 1H, J ) 5, 7
Hz), 5.36 (dd, 1H, J ) 5, 7 Hz), 6.96 (t, 1H, J ) 7 Hz), 7.07 (s,
1H), 7.09 (t, 1H, J ) 7 Hz), 7.27 (d, 1H, J ) 7 Hz), 7.34 (d, 1H,
J ) 7 Hz); MS (FAB) m/ e 537 (M + H)+, 599 (M + Cu)+. Anal.
for C29H40N6O4‚1.25TFA‚1.8H2O: C, H; N: calcd, 11.81; found,
12.36.
2-{1(R)-[(P er h yd r oa zep in -1-ylca r bon yl)leu cyla m in o]-
2-(in d ol-3-yl)et h yl}-1-b en zyl-5-m et h ylim id a zole-4-ca r -
boxylic a cid (14s): 1H NMR (CD3OD, 300 MHz) δ 0.86 (d,
3H, J ) 7 Hz), 0.88 (d, 3H, J ) 7 Hz), 1.32 (m, 1H), 1.50 (m,
6H), 1.67 (br m, 4H), 2.25 (s, 3H), 3.3-3.5 (m, 6H), 4.23 (dd,
1H, J ) 6, 8 Hz), 5.06 (dd, 2H, J ) 8, 20 Hz), 5.40 (t, 1H, J )
8 Hz), 6.88 (m, 3H), 7.02 (s, 1H), 7.10 (m, 2H), 7.25 (m, 3H),
7.34 (d, 1H, J ) 8 Hz); MS (FAB) m/ e 613 (M + H)+, 635 (M
+ Na)+. Anal. for C35H44N6O4‚1.5TFA: C, H, N.
Prepared from 4 (Cbz, R ) Bn, R′ ) CH3):
2-{(1R)-1-[N-((Cycloh exylam in o)car bon yl)leu cylam in o]-
2-(1-m eth ylin dol-3-yl)eth yl}-5-m eth ylim idazole-4-car box-
ylic a cid (14g): 1H NMR (CD3OD, 300 MHz) of major
tautomer δ 0.75 (d, 3H, J ) 7 Hz), 0.78 (d, 3H, J ) 7 Hz),
1.1-1.4 (m, 8H), 1.5-1.9 (m, 6H), 2.53 (s, 3H), 3.33 (m, 1H),
3.50 (m, 2H), 3.77 (s, 3H), 4.03 (t, 1H, J ) 8 Hz), 5.40 (dd, 1H,
J ) 6, 10 Hz), 7.04 (ddd, 1H, J ) 1, 7, 8 Hz), 7.06 (s, 1H), 7.18
(ddd, 1H, J ) 1, 7, 8 Hz), 7.35 (d, 1H, J ) 8 Hz), 7.47 (d, 1H,
J ) 8 Hz); MS (FAB/NBA) m/ e 599 (M + Cu)+. Anal. for
C29H40N6O4‚1.7TFA: C, H, N.
2-{(1R)-1-[N-((Cycloh exylam in o)car bon yl)leu cylam in o]-
2-(1-eth ylin d ol-3-yl)eth yl}-5-m eth ylim id a zole-4-ca r boxy-
lic a cid (14h ): 1H NMR (CD3OD/CDCl3, 300 MHz) for the
major tautomer δ 0.78 (d, 3H, J ) 7 Hz), 0.80 (d, 3H, J ) 7
Hz), 1.1-1.4 (m, 8H), 1.2 (s, 3H), 1.5-1.9 (m, 6H), 2.45 (s, 3H),
3.3 (m, 2H), 4.08 (m, 1H), 4.15 (q, 2H, J ) 8 Hz), 5.25 (m, 1H),
7.00 (t, 1H, J ) 7 Hz), 7.05 (t, 1H, J ) 7 Hz), 7.15 (t, 1H, J )
7 Hz), 7.35 (d, 1H, J ) 8 Hz), 7.50 (d, 1H, J ) 8 Hz); HRMS
(FAB) calcd for C30H43N6O4 551.3355, found 551.3346.
core
core
N-protecting C-protecting N-deprotection
C-deprotection
conditions
group
Cbz
group
Et
conditions
H2, 10% Pd-C, LiOH, H2O/THF, heat
EtOH
Cbz
Boc
Bn
Bn
HBr/HOAc
neat TFA
H2, 10% Pd-C, EtOH
H2, 10% Pd-C, EtOH
Prepared from 4 (P ) Cbz, R ) Et, R′ ) H):
2-{1(R)-[(P er h yd r oa zep in -1-ylca r bon yl)leu cyla m in o]-
2-(in d ol-3-yl)eth yl}-5-m eth ylim id a zole-4-ca r boxylic Acid
(14a ). Compound 14a was prepared according to the proce-
dures described in the preceding article:1 1H NMR (CD3OD,
300 MHz) δ 0.77 (d, 3H, J ) 7 Hz), 0.82 (d, 3H, J ) 7 Hz),
1.30 (m, 2H), 1.52 (m, 5H), 1.66 (m, 4H), 2.52 (s, 3H), 3.4 (m,
6H), 3.59 (dd, 1H, J ) 7, 15 Hz), 4.07 (dd, 1H, J ) 5, 9 Hz),
5.42 (dd, 1H, J ) 6, 8 Hz), 7.01 (ddd, 1H, J ) 1, 7, 8 Hz), 7.11
(ddd, 1H, J ) 1, 7, 8 Hz), 7.12 (s, 1H), 7.36 (d, 1H, J ) 8 Hz),
7.45 (d, 1H, J ) 8 Hz); MS (DCI/NH3) m/ e 523 (M + H)+. Anal.
for C28H38N6O4‚1.5TFA: C, H, N.
2-{(1R )-1-[N -((Cyclop e n t yla m in o)ca r b on yl)le u cyl-
a m in o]-2-(1-m eth ylin d ol-3-yl)eth yl}-5-m eth ylim id a zole-
4-ca r boxylic a cid (14i): 1H NMR (CD3OD, 300 MHz) of major
tautomer δ 0.72 (d, 3H, J ) 7 Hz), 0.75 (d, 3H, J ) 7 Hz),
1.1-1.5 (m, 6H), 1.5-1.8 (m, 5H), 2.48 (s, 3H), 2.72 (s, 3H),
3.18 (m, 1H), 3.58 (m, 2H), 3.72 (s, 3H), 4.05 (t, 1H, J ) 8 Hz),
5.36 (dd, 1H, J ) 6, 10 Hz), 6.95 (s, 1H), 7.00 (t, 1H, J ) 8
Hz), 7.15 (t, 1H, J ) 8 Hz), 7.30 (d, 1H, J ) 8 Hz), 7.54 (d, 1H,
J
) 8 Hz); MS (DCI) m/ e 523 (M + H)+. Anal. for
C28H38N6O4‚1.55H2O, 1.1 TFA: C, H, N.
2-{1(R)-[(P er h yd r oa zep in -1-ylsu lfon yl)leu cyla m in o]-2-
(in d ol-3-yl)et h yl}-5-m et h ylim id a zole-4-ca r b oxylic a cid
2-{(1R )-1-[N -((Cycloh e p t yla m in o)ca r b on yl)le u cyl-
a m in o]-2-(1-m eth ylin d ol-3-yl)eth yl}-5-m eth ylim id a zole-
4-ca r boxylic a cid (14j): 1H NMR (CD3OD, 300 MHz) of major
tautomer δ 0.72 (d, 3H, J ) 7 Hz), 0.75 (d, 3H, J ) 7 Hz),
1.1-1.5 (m, 10H), 1.5-1.8 (m, 5H), 2.48 (s, 3H), 2.72 (s, 3H),
3.18 (m, 1H), 3.58 (m, 2H), 3.72 (s, 3H), 4.05 (t, 1H, J ) 8 Hz),
5.36 (dd, 1H, J ) 6, 10 Hz), 6.95 (s, 1H), 7.01 (t, 1H, J ) 8
Hz), 7.15 (t, 1H, J ) 8 Hz), 7.30 (d, 1H, J ) 8 Hz), 7.54 (d, 1H,
1
(14b): H NMR (CD3OD, 300 MHz) for the major tautomer δ
0.82 (d, 3H, J ) 7 Hz), 0.85 (d, 3H, J ) 7 Hz), 1.2-1.4 (m,
3H), 1.5-1.65 (m, 8H), 2.48 (s, 3H), 3.15 (q, 4H, J ) 7 Hz),
3.45 (d, 2H, J ) 8 Hz), 3.75 (m, 1H), 5.34 (m, 1H), 7.00 (t, 1H,
J ) 7 Hz), 7.10 (s, 1H), 7.12 (t, 1H, J ) 7 Hz), 7.33 (d, 1H, J
) 8 Hz), 7.42 (d, 1H, J ) 8 Hz); MS (DCI/NH3) m/ e 559 (M +
H)+. Anal. for C27H38N6O5S‚1.2TFA: C, H, N.
2-{1(R)-[(Cycloh exyla m in oca r b on yl)leu cyla m in o]-2-
(in d ol-3-yl)et h yl}-5-m et h ylim id a zole-4-ca r b oxylic a cid
J
) 8 Hz); MS (ESI) m/ e 551 (M + H)+. Anal. for
C30H42N6O4‚1.5H2O, 0.5 TFA: C, H, N.

Azole Endothelin Antagonists
J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 4 977
2-{(1R)-1-[N-(((tr a n s-4-Hyd r oxycycloh exyl)a m in o)ca r -
bon yl)leu cyla m in o]-2-(1-m eth ylin d ol-3-yl)eth yl}-5-m eth -
ylim id a zole-4-ca r boxylic a cid (14k ): 1H NMR (CD3OD, 300
MHz) of major tautomer δ 0.75 (d, 3H, J ) 6 Hz), 0.77 (d, 3H,
J ) 6 Hz), 1.1-1.4 (m, 7H), 1.8-2.0 (m, 4H), 2.52 (s, 3H), 3.33
(dd, 1H, J ) 12, 15 Hz), 3.49 (m, 2H), 3.56 (dd, 1H, J ) 7, 15
Hz), 3.77 (s, 3H), 4.03 (t, 1H, J ) 7 Hz), 5.40 (dd, 1H, J ) 6,
9 Hz), 7.04 (dt, 1H, J ) 1, 7 Hz), 7.06 (s, 1H), 7.17 (dt, 1H, J
) 1, 7 Hz), 7.35 (d, 1H, J ) 8 Hz), 7.47 (d, 1H, J ) 8 Hz);
7.37 (d, 1H, J ) 8 Hz); MS (DCI/NH3) m/ e 524 (M + H)+, 541
(M + NH4)+. Anal. for C28H37N5O5‚0.4TFA: C, H, N.
2-{1(R)-[(P er h yd r oa zep in -1-ylsu lfon yl)leu cyla m in o]-2-
(in d ol-3-yl)et h yl}-5-m et h yloxa zole-4-ca r b oxylic
a cid
(15b): 1H NMR (CD3OD, 300 MHz) δ 0.80 (d, 3H, J ) 6 Hz),
0.83 (d, 3H, J ) 6 Hz), 1.0 (m, 2H), 1.25 (m, 1H), 1.5-1.7 (m,
8H), 2.56 (s, 3H), 3.08 (m, 4H), 3.35 (m, 2H), 3.7 (m, 1H), 5.43
(m, 1H), 6.98 (dd, 1H, J ) 1, 8 Hz), 7.07 (s, 1H), 7.08 (dd, 1H,
J ) 1, 8 Hz), 7.30 (d, 1H, J ) 8 Hz), 7.50 (d, 1H, J ) 8 Hz);
MS (DCI/NH3) m/ e 560 (M + H)+, 577 (M + NH4)+. Anal. for
C27H37N5O6S‚0.6TFA: C, H, N.
MS (FAB/NBA) m/ e 553 (M
C29H40N6O5‚1.5TFA: C, H, N.
+
H)+.
Anal. for
2-{(1R)-1-[N-(((2-Met h ylcycloh exyl)a m in o)ca r b on yl)-
leu cyla m in o]-2-(1-m eth ylin d ol-3-yl)eth yl}-5-m eth ylim i-
d a zole-4-ca r boxylic a cid (14l): 1H NMR (CD3OD, 300 MHz)
consistent with mixture of four isomers δ 2.50 (s, 3H), 3.77 (s,
3H), 7.03 (t, 1H, J ) 8 Hz), 7.06 (s, 1H), 7.17 (t, 1H, J ) 8 Hz),
7.33 (d, 1H, J ) 8 Hz), 7.48 (d, J ) 8 Hz); MS (FAB/NBA)
m/ e 551 (M + H)+. Anal. for C30H42N6O4‚1.6TFA: C, H, N.
2-{(1R)-1-[N-(((3-Met h ylcycloh exyl)a m in o)ca r b on yl)-
leu cyla m in o]-2-(1-m eth ylin d ol-3-yl)eth yl}-5-m eth ylim i-
d a zole-4-ca r boxylic a cid (14m ): 1H NMR (CD3OD, 300
MHz) consistent with mixture of four isomers δ 2.50 (s, 3H),
3.76 (s, 3H), 7.0 (t, 1H, J ) 8 Hz), 7.03 (s, 1H), 7.16 (t, 1H, J
) 8 Hz), 7.32 (d, 1H, J ) 8 Hz), 7.50 (d, J ) 8 Hz); MS (FAB/
NBA) m/ e 551 (M + H)+. Anal. for C30H42N6O4‚1.5TFA: C,
H, N.
2-{(1R)-1-[N-(((4-Met h ylcycloh exyl)a m in o)ca r b on yl)-
leu cyla m in o]-2-(1-m eth ylin d ol-3-yl)eth yl}-5-m eth ylim i-
d a zole-4-ca r boxylic a cid (14n ): 1H NMR (CD3OD, 300
MHz) of mixture δ 0.76 (m, 6H), 0.91 (apparent t, 3H), 1.0-
1.9 (m, 12H), major isomer 2.52 (s, 3H), 3.33 (m, 1H), 3.56 (dd,
1H, J ) 7, 15 Hz), 3.76 (s, 3H), 3.78 (m, 1H), 4.03 (m, 1H),
5.20 (dd, 1H, J ) 6, 9 Hz), 7.04 (dt, 1H, J ) 1, 7 Hz), 7.05 (s,
1H), 7.18 (dt, 1H, J ) 1, 7 Hz), 7.35 (d, 1H, J ) 8 Hz), 7.47 (d,
1H, J ) 8 Hz); MS (DCI/NH3) m/ e 551 (M + H)+. Anal. for
C30H42N6O4‚1.1TFA: C, H, N.
2-{(1R )-1-[N -((en d o-2-N o r b o r n y la m in o )c a r b o n y l)-
leu cyla m in o]-2-(1-m eth ylin d ol-3-yl)eth yl}-5-m eth ylim i-
d a zole-4-ca r boxylic a cid (14o): 1H NMR (CD3OD, 300 MHz)
of one diastereomer δ 0.76 (d, 3H, J ) 6 Hz), 0.78 (d, 3H, J )
6 Hz), 1.2-1.6 (m, 10H), 2.00 (m, 1H), 2.17 (m, 1H), 2.34 (m,
1H), 2.51 (s, 3H), 3.32 (dd, 1H, J ) 10, 15 Hz), 3.55 (dd, 1H,
J ) 6, 15 Hz), 3.76 (s, 3H), 3.91 (m, 1H), 4.03 (dt, 1H, J ) 3,
7 Hz), 5.38 (ddd, 1H, J ) 3, 7, 9 Hz), 7.04 (ddd, 1H, J ) 1, 7,
8 Hz), 7.06 (s, 1H), 7.18 (dt, 1H, J ) 1, 7 Hz), 7.35 (d, 1H, J )
8 Hz), 7.46 (d, 1H, J ) 8 Hz); MS (FAB/NBA) m/ e 549 (M +
H)+. Anal. for C30H40N6O4‚1.6TFA: C, H, N.
2-{(1R )-1-[N -((exo-2-N o r b o r n y la m i n o )c a r b o n y l)-
leu cyla m in o]-2-(1-m eth ylin d ol-3-yl)eth yl}-5-m eth ylim i-
d a zole-4-ca r boxylic a cid (14p ): 1H NMR (CD3OD, 300 MHz)
of one diastereomer δ 0.75 (d, 3H, J ) 6 Hz), 0.77 (d, 3H, J )
6 Hz), 1.1-1.5 (m, 10H), 1.70 (m, 1H), 2.13 (m, 1H), 2.24 (m,
1H), 2.53 (s, 3H), 3.33 (dd, 1H, J ) 10, 15 Hz), 3.49 (m, 1H),
3.57 (m, 1H), 3.77 (s, 3H), 4.02 (dt, 1H, J ) 1, 7 Hz), 5.39 (ddd,
1H, J ) 2, 6, 8 Hz), 7.04 (dt, 1H, J ) 1, 7 Hz), 7.06 (s, 1H),
7.17 (dt, 1H, J ) 1, 7 Hz), 7.35 (d, 1H, J ) 8 Hz), 7.46 (d, 1H,
J ) 8 Hz); MS (FAB/NBA) m/ e 549 (M + H)+. Anal. for
C30H40N6O4‚1.9TFA: C, H, N.
2-{1(R)-[((Cycloh exyla m in o)ca r bon yl)leu cyla m in o]-2-
(in d ol-3-yl)et h yl}-5-m et h yloxa zole-4-ca r b oxylic
a cid
(15e): 1H NMR (CD3OD, 300 MHz) δ 0.78 (d, 3H, J ) 7 Hz),
0.79 (d, 3H, J ) 7 Hz), 1.0-1.8 (m, 13H), 2.58 (s, 3H), 3.42
(m, 3H), 4.20 (t, 1H, J ) 7 Hz), 5.42 (d, 1H, J ) 7 Hz), 6.96 (t,
1H, J ) 7 Hz), 7.03 (s, 1H), 7.06 (t, 1H, J ) 7 Hz), 7.31 (d, 1H,
J ) 7 Hz), 7.44 (d, 1H, J ) 7 Hz); MS (DCI/NH3) m/ e 524 (M
+ H)+. Anal. for C28H37N5O5‚0.8TFA: C, H, N.
2-{1(R)-[(P er h yd r oa zep in -1-ylca r bon yl)leu cyla m in o]-
2-(1-m eth ylin d ol-3-yl)eth yl}-5-m eth yloxa zole-4-ca r boxy-
lic a cid (15f): 1H NMR (CD3OD, 300 MHz) δ 0.86 (d, 6H, J
) 7 Hz), 1.4 (m, 2H), 1.53 (m, 5H), 1.67 (m, 4H), 2.54 (s, 3H),
3.25-3.5 (m, 6H), 3.73 (s, 3H), 4.33 (dd, 1H, J ) 6, 10 Hz), 5.37
(t, 1H, J ) 7 Hz), 6.93 (s, 1H), 6.99 (ddd, 1H, J ) 1, 7, 8 Hz),
7.04 (ddd, 1H, J ) 1, 7, 8 Hz), 7.31 (d, 1H, J ) 8 Hz), 7.40 (td,
1H, J ) 1, 8 Hz); MS (DCI/NH3) m/ e 538 (M + H)+, 555 (M +
NH4)+. Anal. for C29H39N5O5‚1.0TFA: C, H, N.
Prepared using 5 (P ) Boc, R ) Bn, R′ ) CH3):
2-{(1R)-1-[N-((Cycloh exylam in o)car bon yl)leu cylam in o]-
2-(1-m eth ylin d ol-3-yl)eth yl}-5-m eth yloxa zole-4-ca r boxy-
lic a cid (15g): 1H NMR (CDCl3, 300 MHz) δ 0.70 (d, 3H, J )
7 Hz), 0.74 (d, 3H, J ) 7 Hz), 1.1-1.9 (m, 13H), 2.50 (s, 3H),
3.40 (m, 1H), 3.76 (s, 3H), 3.90 (m, 1H), 4.35 (dd, 1H, J ) 6, 7
Hz), 5.35 (m, 1H), 6.91 (s, 1H), 7.02 (t, 1H, J ) 8 Hz), 7.13 (t,
1H, J ) 8 Hz), 7.32 (d, 1H, J ) 8 Hz), 7.48 (d, 1H, J ) 8 Hz);
MS (FAB/NBA) m/ e 538 (M + H)+, 560 (M + Na)+, 576 (M +
K)+. Anal. for C29H39N5O5‚0.6TFA: C, H, N.
2-{(1R)-1-[N-((Cycloh exylam in o)car bon yl)leu cylam in o]-
2-(1-et h ylin d ol-3-yl)et h yl}-5-m et h yloxa zole-4-ca r b oxy-
lic a cid (15h ): 1H NMR (CD3OD/CDCl3, 300 MHz) δ 0.82 (d,
3H, J ) 7 Hz), 0.84 (d, 3H, J ) 7 Hz), 1.1-1.9 (m, 13H), 1.40
(t, 3H, J ) 7 Hz), 2.55 (s, 3H), 3.45(m, 1H), 4.14 (q, 2H, J ) 7
Hz), 4.18 (m, 1H), 5.20 (t, 1H, J ) 7 Hz), 6.95 (s, 1H), 7.02 (dt,
1H, J ) 1, 8 Hz), 7.15 (dt, 1H, J ) 1, 8 Hz), 7.30 (d, 1H, J )
8 Hz), 7.42 (d, 1H, J ) 8 Hz); MS (DCI/NH3) m/ e 552 (M +
H)+, 569 (M + NH4)+. Anal. for C30H41N5O5‚1.75H2O: C, H,
N.
2-{(1R )-1-[N -((Cyclop e n t yla m in o)ca r b on yl)le u cyl-
a m in o]-2-(1-m eth ylin d ol-3-yl)eth yl}-5-m eth yloxa zole-4-
ca r boxylic a cid (15i): 1H NMR (CDCl3, 300 MHz) δ 0.70 (d,
3H, J ) 7 Hz), 0.74 (d, 3H, J ) 7 Hz), 1.1-1.8 (m, 11H), 2.52
(s, 3H), 3.44 (m, 1H), 3.75 (s, 3H), 3.89 (m, 1H), 4.42 (dd, 1H,
J ) 6, 7 Hz), 5.35 (m, 1H), 6.96 (s, 1H), 7.03 (t, 1H, J ) 8 Hz),
7.12 (t, 1H, J ) 8 Hz), 7.30 (d, 1H, J ) 8 Hz), 7.45 (d, 1H, J )
8 Hz); MS (FAB/NBA) m/ e 524 (M + H)+, 546 (M + Na)+, 562
(M + K)+. Anal. for C28H37N5O5‚H2O‚0.5TFA: C, H, N.
2-{(1R )-1-[N -((Cycloh e p t yla m in o)ca r b on yl)le u cyl-
a m in o]-2-(1-m eth ylin d ol-3-yl)eth yl}-5-m eth yloxa zole-4-
ca r boxylic a cid (15j): 1H NMR (CDCl3, 300 MHz) δ 0.73 (d,
3H, J ) 7 Hz), 0.77 (d, 3H, J ) 7 Hz), 1.3-1.8 (m, 15H), 2.50
(s, 3H), 3.45(m, 1H), 3.75 (s, 3H), 3.92 (m, 1H), 4.45 (dd, 1H,
J ) 6, 7 Hz), 5.35 (m, 1H), 6.95 (s, 1H), 7.02 (t, 1H, J ) 8 Hz),
7.12 (t, 1H, J ) 8 Hz), 7.30 (d, 1H, J ) 8 Hz), 7.45 (d, 1H, J )
8 Hz); MS (FAB/NBA) m/ e 552 (M + H)+, 574 (M + Na)+, 590
(M + K)+. Anal. for C30H41N5O5‚H2O‚0.3TFA: C, H, N.
2-{(1R)-1-[N-((tr a n s-4-H yd r oxycycloh exyla m in o)ca r -
b on yl)leu cyla m in o]-2-(1-m et h ylin d ol-3-yl)et h yl}-5-m e-
th yloxa zole-4-ca r boxylic a cid (15k ): 1H NMR (CD3OD, 300
MHz) δ 0.81 (d, 3H, J ) 6 Hz), 0.83 (d, 3H, J ) 6 Hz), 1.1-1.5
(m, 7H), 1.8-2.0 (m, 4H), 2.53 (s, 3H), 3.3-3.6 (m, 3H), 3.56
(dd, 1H, J ) 7, 15 Hz), 3.73 (s, 3H), 4.18 (t, 1H, J ) 7 Hz),
5.36 (dd, 1H, J ) 6, 8 Hz), 6.97 (s, 1H), 7.01 (ddd, 1H, J ) 1,
7, 8 Hz), 7.13 (dt, 1H, J ) 1, 7 Hz), 7.29 (d, 1H, J ) 8 Hz),
7.45 (d, 1H, J ) 8 Hz); MS (FAB/MeOH) m/ e 554 (M + H)+,
576 (M + Na)+. Anal. for C29H39N5O6‚1.2TFA‚2H2O: C, H,
N.
2-{(1R)-1-[N-((P h en yla m in o)ca r bon yl)leu cyla m in o]-2-
(1-m eth ylin d ol-3-yl)eth yl}-5-m eth ylim id a zole-4-ca r boxy-
lic a cid (14q): 1H NMR (CD3OD, 300 MHz) of major tautomer
δ 0.80 (d, 3H, J ) 7 Hz), 0.81 (d, 3H, J ) 7 Hz), 1.34 (m, 3H),
2.43 (s, 3H), 3.33 (dd, 1H, J ) 9, 14 Hz), 3.54 (dd, 1H, J ) 6,
14 Hz), 3.72 (s, 3H), 4.14 (m, 1H), 5.38 (dd, 1H, J ) 6, 9 Hz),
7.00 (dt, 1H, J ) 1, 7 Hz), 7.03 (dt, 1H, J ) 1, 8 Hz), 7.05 (s,
1H), 7.16 (dt, 1H, J ) 1, 7 Hz), 7.26 (m, 1H), 7.28 (d, 1H, J )
8 Hz), 7.31 (m, 3H), 7.45 (d, 1H, J ) 8 Hz); MS (FAB/NBA)
m/ e 531 (M
C29H34N6O4‚1.5TFA: C, H, N.
+
H)+, 553 (M
+
Na)+. Anal. for
Prepared from 5 (P ) Cbz, R ) Et, R′ ) H):
2-{1(R)-[(P er h yd r oa zep in -1-ylca r bon yl)leu cyla m in o]-
2-(in d ol-3-yl)et h yl}-5-m et h yloxa zole-4-ca r b oxylic a cid
(15a ): 1H NMR (CD3OD, 300 MHz) δ 0.87 (d, 3H, J ) 7 Hz),
0.88 (d, 3H, J ) 7 Hz), 1.43 (m, 2H), 1.52 (m, 5H), 1.67 (m,
4H), 2.55 (s, 3H), 3.25-3.5 (m, 6H), 4.34 (dd, 1H, J ) 6, 9 Hz),
5.40 (t, 1H, J ) 7 Hz), 6.95 (ddd, 1H, J ) 1, 7, 8 Hz), 6.99 (s,
1H), 7.07 (ddd, 1H, J ) 1, 7, 8 Hz), 7.31 (td, 1H, J ) 1, 8 Hz),

978 J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 4
von Geldern et al.
2-{(1R)-1-[N-(((2-Met h ylcycloh exyl)a m in o)ca r b on yl)-
leu cyla m in o]-2-(1-m et h ylin d ol-3-yl)et h yl}-5-m et h ylox-
a zole-4-ca r boxylic a cid (15l): 1H NMR (CD3OD, 300 MHz)
consistent with structure of the four isomers δ 2.52 (s, 3H),
3.74 (s, 3H), 6.97 (s, 1H), 7.0 (t, 1H, J ) 8 Hz), 7.13 (t, 1H, J
) 8 Hz), 7.30 (d, 1H, J ) 8 Hz), 7.45 (dd, J ) 2, 8 Hz); MS
(DCI/NH3) m/ e 552 (M + H)+, 569 (M + NH4)+. Anal. for
C30H41N5O5‚H2O‚0.35TFA: C, H, N.
2-{(1R)-1-[N-(((3-Met h ylcycloh exyl)a m in o)ca r b on yl)-
leu cyla m in o]-2-(1-m et h ylin d ol-3-yl)et h yl}-5-m et h ylox-
a zole-4-ca r boxylic a cid (15m ): 1H NMR (CD3OD, 300 MHz)
consistent with structure of the four isomers δ 2.52 (s, 3H),
3.74 (s, 3H), 6.97 (s, 1H), 7.0 (t, 1H, J ) 8 Hz), 7.13 (t, 1H, J
) 8 Hz), 7.30 (d, 1H, J ) 8 Hz), 7.45 (dd, J ) 2, 8 Hz); MS
(DCI/NH3) m/ e 552 (M + H)+, 569 (M + NH4)+. Anal. for
C30H41N5O5‚1.1H2O‚0.65TFA: C, H, N.
3.4 (m, 2H), 3.73 (s, 3H) 3.76 (br s, 1H), 4.20 (dd, 1H, J ) 6,
8 Hz), 5.38 (dd, 1H, J ) 6, 8 Hz), 6.97 (s, 1H), 7.01 (dt, 1H, J
) 1, 8 Hz), 7.14 (dt, 1H, J ) 1, 8 Hz), 7.28 (d, 1H, J ) 8 Hz),
7.45 (d, 1H, J ) 8 Hz); MS (DCI/NH3) m/ e 590 (M + H)+, 607
(M + NH4)+. Anal. for C33H43N5O5‚0.8TFA: C, H, N.
2-{(1R )-1-[N -(((1-Ca r b om e t h oxycycloh e xyl)a m in o)-
ca r b on yl)leu cyla m in o]-2-(1-m et h ylin d ol-3-yl)et h yl}-5-
m eth yloxa zole-4-ca r boxylic a cid (15x): 1H NMR (CD3OD,
300 MHz) δ 0.81 (d, 3H, J ) 7 Hz), 0.82 (d, 3H, J ) 7 Hz),
1.24-1.34 (m, 3H), 1.40-1.65 (m, 6H), 1.67-1.81 (m, 2H),
1.89-1.99 (m, 2H), 2,53 (s, 3H), 3.2-3.45 (m, 2H), 3.60 (s, 3H),
3.74 (s, 3H), 4.15 (dd, 1H, J ) 6, 8 Hz), 5.35 (dd, 1H, J ) 6, 8
Hz), 6.97-7.04 (m, 2H), 7.13 (dt, 1H, J ) 1, 8 Hz), 7.3 (d, 1H,
J ) 8 Hz), 7.45 (d, 1H, J ) 8 Hz); MS (DCI/NH3) m/ e 595 (M
+ H)+. Anal. for C31H41N5O7‚0.7TFA: C, H, N.
2-{(1R)-1-[N-(1-Oxa -4-a za sp ir o[5.4]d ec-4-ylca r b on yl)-
leu cyla m in o]-2-(1-m et h ylin d ol-3-yl)et h yl}-5-m et h ylox-
a zole-4-ca r boxylic a cid (15y) was prepared as described
above, employing 1-oxa-4-azaspiro[5.4]decane:7 1H NMR (CD3-
OD, 300 MHz) δ 0.84 (m, 6H), 1.1-1.7 (m, 11H), 2.2-2.4 (m,-
2H), 2.54 (s, 3H), 3.34-3.63 (m, 4H), 3.74 (s, 3H), 3.95 (t, 2H,
J ) 6 Hz), 4.28 (m, 1H), 5.37 (t, 1H, J ) 7 Hz), 6.98 (br s, 1H),
7.01 (dt, 1H, J ) 1, 8 Hz), 7.14 (dt, 1H, J ) 1, 8 Hz), 7.30 (dd,
1H, J ) 1, 8 Hz), 7.44 (d, 1H, J ) 8 Hz); MS (DCI/NH3) m/ e
580 (M + H)+. Anal. for C31H41N5O6‚0.9TFA: C, H, N.
2-{(1R)-1-[N-(1-In d olin ylca r b on yl)leu cyla m in o]-2-(1-
m eth ylin dol-3-yl)eth yl}-5-m eth yloxazole-4-car boxylic acid
(15ff): 1H NMR (CD3OD, 300 MHz) δ 0.88 (d, 6H, J ) 7 Hz),
1.50 (m, 3H), 2.53 (s, 3H), 3.13 (m, 2H), 3.37 (d, 2H, J ) 6
Hz), 3.57 (s, 3H), 3.68 (dt, 1H, J ) 8, 10 Hz), 3.82 (dd, 1H, J
) 8, 10 Hz), 4.43 (dd, 1H, J ) 6, 8 Hz), 5.43 (t, 1H, J ) 6 Hz),
6.87 (ddd, 1H, J ) 1, 7, 8 Hz), 6.89 (s, 1H), 6.92 (dt, 1H, J )
1, 7 Hz), 7.03 (dt, 1H, J ) 1, 7 Hz), 7.12 (dt, 1H, J ) 1, 7 Hz),
7.17 (d, 1H, J ) 8 Hz), 7.23 (d, 1H, J ) 8 Hz), 7.35 (d, 1H, J
) 8 Hz), 7.83 (d, 1H, J ) 8 Hz); MS (DCI/NH3) m/ e 558 (M +
H)+, 575 (M + Na)+. Anal. for C31H35N5O5‚TFA: C, H, N.
2-{(1R)-1-[N-(1,2,3,4-Tetr a h yd r oqu in olin -1-ylca r bon yl)-
leu cyla m in o]-2-(1-m et h ylin d ol-3-yl)et h yl}-5-m et h ylox-
a zole-4-ca r boxylic a cid (15h h ): 1H NMR (CD3OD, 300 MHz)
δ 0.82 (d, 3H, J ) 7 Hz), 0.84 (d, 3H, J ) 7 Hz), 1.27-1.38 (m,
3H), 1.77-1.89 (m, 2H), 2.55 (s, 3H), 2.67 (t, 1H, J ) 7 Hz),
3.26-3.43 (m, 2H), 3.61 (t, 2H, J ) 8 Hz), 3.71 (s, 3H), 4.36
(dd, 1H, J ) 6, 9 Hz), 5.39 (dd, 1H, J ) 6, 7 Hz), 6.95 (s, 1H),
6.98-7.22 (m, 6H), 7.28 (d, 1H, J ) 8 Hz), 7.43 (d, 1H, J ) 8
Hz); MS (FAB/NBA) 572 (M + H)+, 594 (M + Na)+. Anal. for
C32H37N5O5‚0.9TFA: C, H, N.
2-{(1R)-1-[N-(((4-Met h ylcycloh exyl)a m in o)ca r b on yl)-
leu cyla m in o]-2-(1-m et h ylin d ol-3-yl)et h yl}-5-m et h ylox-
a zole-4-ca r boxylic a cid (15n ): 1H NMR (CDCl3/CD3OD, 300
MHz) consistent with mixture of two isomers δ 2.52 (s, 3H),
3.73 (s, 3H), 6.95 (s, 1H), 7.02 (dt, 1H, J ) 1, 8 Hz), 7.16 (dt,
1H, J ) 1, 8 Hz), 7.27 (d, 1H, J ) 8 Hz), 7.41 (d, J ) 8 Hz);
MS (DCI/NH3) m/ e 552 (M + H)+, 569 (M + NH4)+. Anal. for
C30H41N5O5‚0.3H2O‚0.75TFA: C, H, N.
2-{(1R)-1-[N-((en d o-n or bor n yla m in o)ca r bon yl)leu cyl-
a m in o]-2-(1-m eth ylin d ol-3-yl)eth yl}-5-m eth yloxa zole-4-
ca r boxylic a cid (15o): 1H NMR (CD3OD, 300 MHz) of one
diastereomer δ 0.81 (d, 3H, J ) 6 Hz), 0.84 (d, 3H, J ) 6 Hz),
1.1-1.6 (m, 10H), 1.99 (m, 1H), 2.15 (m, 1H), 2.32 (m, 1H),
2.54 (s, 3H), 3.35 (m, 2H), 3.73 (s, 3H), 3.86 (m, 1H), 4.20 (dt,
1H, J ) 1, 7 Hz), 5.36 (dd, 1H, J ) 6, 8 Hz), 6.97 (s, 1H), 7.00
(dt, 1H, J ) 1, 7 Hz), 7.12 (t, 1H, J ) 7 Hz), 7.28 (d, 1H, J )
8 Hz), 7.44 (d, 1H, J ) 8 Hz); MS (FAB/NBA) m/ e 550 (M +
H)+, 572 (M + Na)+. Anal. for C30H39N5O5‚0.5TFA: C, H, N.
2-{(1R)-1-[N-((exo-n or b or n yla m in o)ca r b on yl)leu cyl-
a m in o]-2-(1-m eth ylin d ol-3-yl)eth yl}-5-m eth yloxa zole-4-
ca r boxylic a cid (15p ): 1H NMR (CD3OD, 300 MHz) of one
diastereomer δ 0.81 (d, 3H, J ) 6 Hz), 0.83 (d, 3H, J ) 6 Hz),
1.1-1.5 (m, 10H), 1.70 (m, 1H), 2.08 (m, 1H), 2.22 (m, 1H),
2.53 (s, 3H), 3.3-3.5 (m, 3H), 3.72 (s, 3H), 4.19 (t, 1H, J ) 7
Hz), 5.37 (ddd, 1H, J ) 2, 6, 8 Hz), 6.99 (s, 1H), 7.00 (dt, 1H,
J ) 1, 7 Hz), 7.12 (dt, 1H, J ) 1, 7 Hz), 7.20 (d, 1H, J ) 8 Hz),
7.44 (dd, 1H, J ) 1, 8 Hz); MS (FAB/NBA) m/ e 550 (M + H)+,
572 (M + Na)+. Anal. for C30H39N5O5‚0.3TFA: C, H, N.
2-{(1R)-1-[N-((P h en yla m in o)ca r bon yl)leu cyla m in o]-2-
(1-m et h ylin d ol-3-yl)et h yl}-5-m et h yloxa zole-4-ca r b oxy-
lic a cid (15q): 1H NMR (CD3OD-CDCl3, 300 MHz) δ 0.85 (d,
3H, J ) 8 Hz), 0.88 (d, 3H, J ) 8 Hz), 1.35-1.6 (m, 3H), 2.52
(s, 3H), 3.38 (d, 2H, J ) 10 Hz), 3.56 (s, 3H), 4.32 (dd, 1H, J
) 6, 10 Hz), 5.43 (t, 1H, J ) 6 Hz), 6.90 (s, 1H), 6.98 (m, 2H),
7.11 (dt, 1H, J ) 1, 7 Hz), 7.25 (m, 3H), 7.34 (m, 3H); MS (DCI/
NH3) m/ e 532 (M + H)+, 549 (M + NH4)+. Anal. for
C29H33N5O5‚0.3TFA: C, H, N.
2-{(1R)-1-[N-(((1-Met h ylcycloh exyl)a m in o)ca r b on yl)-
leu cyla m in o]-2-(1-m et h ylin d ol-3-yl)et h yl}-5-m et h ylox-
a zole-4-ca r boxylic a cid (15w ): 1H NMR (CD3OD, 300 MHz)
δ 0.83 (d, 3H, J ) 6 Hz), 0.84 (d, 3H, J ) 6 Hz), 1.25 (s, 3H)
1.26-1.56 (m, 11H), 1.8-1.9 (m, 2H), 2.57 (s, 3H), 3.2-3.5 (m,
2H), 3.74 (s, 3H), 4.14 (dd, 1H, J ) 6, 9 Hz), 5.36 (dd, 1H, J )
6, 7 Hz), 6.97 (s, 1H), 7.05 (dt, 1H, J ) 1, 8 Hz), 7.13 (dt, 1H,
J ) 1, 8 Hz), 7.29 (d, 1H, J ) 8 Hz), 7.45 (d, 1H, J ) 8 Hz);
MS (DCI/NH3) m/ e 552 (M + H)+, 569 (M + NH4)+. Anal. for
C30H41N5O5‚0.8TFA: C, H, N.
2-{(1R)-1-[N-((1,2,3,4-Tet r a h yd r on a p h t h -1-yla m in o)-
ca r b on yl)leu cyla m in o]-2-(1-m et h ylin d ol-3-yl)et h yl}-5-
1
m eth yloxa zole-4-ca r boxylic a cid (15t): H NMR (CD3OD,
300 MHz) of one diastereomer δ 0.83 (d, 6H, J ) 6 Hz), 1.2-
1.6 (m, 3H), 1.6-2.0 (m, 4H), 2.53 (s, 3H), 2.7-2.8 (m, 2H),
3.2-3.4 (m, 3H), 3.74 (s, 3H), 4.27 (m, 1H,), 5.40 (m, 1H), 6.9-
7.2 (m, 7H), 7.26 (d, 1H, J ) 8 Hz), 7.45 (m, 1H); MS (DCI/
NH3) m/ e 586 (M + H)+, 603 (M + NH4)+. Anal. for
C33H39N5O5‚0.4TFA: C, H, N.
2-{(1R )-1-[N -((1-Ad a m a n t yla m in o)ca r b on yl)le u cyl-
a m in o]-2-(1-m eth ylin d ol-3-yl)eth yl}-5-m eth yloxa zole-4-
ca r boxylic a cid (15u ): 1H NMR (CD3OD, 300 MHz) δ 0.82
(d, 3H, J ) 6 Hz), 0.83 (d, 3H, J ) 6 Hz), 1.2-1.55 (m, 3H),
1.69 (m, 6H), 1.91 (d, 6H, J ) 3 Hz), 1.92-2.07 (m, 3H), 2.53
(s, 3H), 3.2-3.4 (m, 2H), 3.74 (s, 3H), 4.13 (dd, 1H, J ) 6, 9
Hz), 5.36 (dd, 1H, J ) 6, 8 Hz), 6.98 (s, 1H), 7.01 (dt, 1H, J )
1, 8 Hz), 7.13 (dt, 1H, J ) 1, 8 Hz), 7.23 (d, 1H, J ) 8 Hz),
7.43 (d, 1H, J ) 8 Hz); MS (DCI/NH3) m/ e 590 (M + H)+, 607
(M + NH4)+. Anal. for C33H43N5O5‚0.7TFA: C, H, N.
2-{(1R)-1-[N-((2-P yr id yla m in o)ca r bon yl)leu cyla m in o]-
2-(1-m eth ylin d ol-3-yl)eth yl}-5-m eth yloxa zole-4-ca r boxy-
lic a cid (15z): NMR is consistent with expected structure;
MS (FAB) m/ e 533 (M + H)+, 555 (M + Na)+, 571(M + K)+.
Anal. for C28H32N6O5‚0.7H2O, 0.80 TFA: C, H, N.
2-{(1R)-1-[N-((3-P yr id yla m in o)ca r bon yl)leu cyla m in o]-
2-(1-m eth ylin d ol-3-yl)eth yl}-5-m eth yloxa zole-4-ca r boxy-
lic a cid (15a a ): 1H NMR (CDCl3/CD3OD, 300 MHz) δ 0.86
(d, 3H, J ) 5 Hz), 0.88 (d, 3H, J ) 5 Hz), 1.42 (m, 2H), 1.53
(m, 1H), 2.55 (s, 3H), 3.39 (m, 2H), 3.70 (s, 3H), 3.71 (m, 1H),
4.33 (m, 1H), 5.44 (m, 1H), 6.91 (s, 1H), 7.02 (t, 1H, J ) 7 Hz),
7.13 (t, 1H, J ) 7 Hz), 7.24 (d, 1H, J ) 8 Hz), 7.46 (d, 1H, J )
8 Hz), 7.71 (dd, 1H, J ) 7, 8 Hz), 8.17 (dd, 1H, J ) 1, 8 Hz),
8.26 (d, 1H, J ) 7 Hz), 8.98 (d, 1H, J ) 1 Hz); MS (DCI/NH3)
m/ e 533 (M + H)+. Anal. for C28H32N6O5‚2.65TFA: C, H, N.
2-{(1R )-1-[N -(((2-F lu o r o p h e n y l)a m in o )c a r b o n y l)-
leu cyla m in o]-2-(1-m et h ylin d ol-3-yl)et h yl}-5-m et h ylox-
a zole-4-ca r boxylic a cid (15bb): 1H NMR (CD3OD, 300
MHz) δ 0.81 (d, 3H, J ) 4 Hz), 0.83 (d, 2H, J ) 4 Hz), 1.35 (m,
2H), 1.5 (m, 1H), 2.52 (s, 3H), 3.38 (m, 2H), 3.65 (s, 3H), 4.28
(m, 1H), 5.40 (dd, 1H, J ) 7, 8 Hz), 6.95 (m, 3H), 7.08 (m, 4H),
2-{(1R )-1-[N -((2-Ad a m a n t yla m in o)ca r b on yl)le u cyl-
a m in o]-2-(1-m eth ylin d ol-3-yl)eth yl}-5-m eth yloxa zole-4-
ca r boxylic a cid (15v): 1H NMR (CD3OD, 300 MHz) δ 0.83
(d, 3H, J ) 6 Hz), 0.84 (d, 3H, J ) 6 Hz), 1.3 (m, 2H), 1.45 (m,
1H), 1.5-1.65 (m, 3H), 1.7-1.8 (m, 11H), 2.53 (s, 3H), 3.25-

Azole Endothelin Antagonists
J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 4 979
7.25 (d, 1H, J ) 7 Hz), 7.42 (d, 1H, J ) 7 Hz); MS (DCI/NH3)
EDC (0.75 g) was added to the solution, followed by DMF (2
mL). The mixture was stirred for 20 h at room temperature.
The solvent was evaporated in vacuo and the residue taken
up in EtOAc. The solution was washed with saturated
NaHCO3 solution, 1 N H3PO4, and brine, dried with MgSO4,
and evaporated to give an orange solid that was purified by
flash chromatography (25% EtOAc-hexane) to give 1.85 g
(92%) of the title compound: 1H NMR (CDCl3, 300 MHz) δ
0.87 (d, 3H, J ) 7 Hz), 0.89 (d, 3H, H)7 Hz), 1.31 (t, 3H, J )
7 Hz), 1.45 (m, 3H), 1.52 (s, 9H), 2.46 (s, 3H), 3.27 (br s, 1H),
3.43 (m, 1H), 4.12 (m, 1H), 4.30 (q, 2H, J ) 7 Hz), 5.50 (m,
1H), 6.65 (br s, 1H), 6.80-7.10 (m, 3H), 7.12 (s, 1H), 7.40 (m,
1H), 8.26 (m, 1H); MS (DCI/NH3) m/ e 526 (M + H)+.
m/ e 550 (M
+
H)+, 567 (M
+
NH4)+. Anal. for
C29H32N5O5F‚0.35TFA: C, H, N.
2-{(1R )-1-[N -(((3-F lu o r o p h e n y l)a m in o )c a r b o n y l)-
leu cyla m in o]-2-(1-m et h ylin d ol-3-yl)et h yl}-5-m et h ylox-
a zole-4-ca r boxylic a cid (15cc): 1H NMR (CDCl3, 300 MHz)
δ 0.78 (d, 3H, J ) 6 Hz), 0.82 (d, 2H, J ) 6 Hz), 1.2-1.35 (m,
2H), 1.45-1.55 (m, 1H), 2.42 (s, 3H), 3.32 (m, 2H), 3.48 (s, 3H),
4.36 (m, 1H), 5.42 (dd, 1H, J ) 7, 8 Hz), 5.96 (m, 1H), 6.59 (dt,
1H, J ) 1, 7 Hz), 6.80 (m, 2H), 6.95 (m, 2H), 7.03 (m, 1H),
7.12 (m, 2H), 7.25 (m, 2H); MS (FAB) m/ e 550 (M + H)+, 572
(M + Na)+. Anal. for C29H32N5O5F‚1.15TFA: C, H, N.
2-{(1R )-1-[N -(((4-F lu o r o p h e n y l)a m in o )c a r b o n y l)-
leu cyla m in o]-2-(1-m et h ylin d ol-3-yl)et h yl}-5-m et h ylox-
a zole-4-ca r boxylic a cid (15d d ): 1H NMR (CDCl3/CD3OD,
300 MHz) δ 0.82 (d, 3H, J ) 4 Hz), 0.86 (d, 2H, J ) 4 Hz),
1.35 (m, 2H), 1.5 (m, 1H), 2.55 (s, 3H), 3.38 (m, 2H), 3.63 (s,
3H), 4.28 (m, 1H), 5.40 (m, 1H), 6.95 (m, 4H), 7.10 (m, 1H),
7.32 (m, 3H), 7.40 (m, 1H); MS (FAB) m/ e 550 (M + H)+, 572
(M + Na)+. Anal. for C29H32N5O5F‚2.0H2O: C, H, N.
2-{(1R)-1-[N-(((P en t a flu or op h en yl)a m in o)ca r b on yl)-
leu cyla m in o]-2-(1-m et h ylin d ol-3-yl)et h yl}-5-m et h ylox-
a zole-4-ca r boxylic a cid (15ee): 1H NMR (CD3OD, 300 MHz)
δ 0.83 (d, 3H, J ) 7 Hz), 0.84 (d, 3H, J ) 7 Hz), 1.27-1.50 (m,
3H), 2.54 (s, 3H), 3.25-3.5 (m, 2H), 3.75 (s, 3H), 4.40 (dd, 1H,
J ) 6, 8 Hz), 5.39 (dd, 1H, J ) 6, 8 Hz), 6.97 (s, 1H), 7.02 (dt,
1H, J ) 1, 8 Hz), 7.14 (dt, 1H, J ) 1, 8 Hz), 7.30 (d, 1H, J )
8 Hz), 7.44 (d, 1H, J ) 8 Hz); MS (FAB/NBA) m/ e 622 (M +
H)+, 644 (M + Na)+. Anal. for C29H28F5N5O5‚0.8TFA: C, H,
N.
2-{(1R )-1-[N -(In d ol-1-ylca r b on yl)le u cyla m in o]-2-(1-
m eth ylin dol-3-yl)eth yl}-5-m eth yloxazole-4-car boxylic Acid
(15gg). Compound 5 (P ) Boc, R ) Bn, R′ ) CH3; 110 mg)
was dissolved in 6 mL of trifluoroacetic acid and allowed to
stir at ambient temperature for 1 h. The solvents were
removed in vacuo, the residue was neutralized with bicarbon-
ate solution, and the mixture was extracted with EtOAc. The
combined organic extracts were washed with brine, dried over
Na2SO4, and concentrated under reduced pressure. The
product was dissolved in THF (4 mL) and DMF (2 mL). HOBt
(42 mg), acid 13 (90 mg), and EDC (57 mg) were added.
N-Methylmorpholine (200 µL) was added and the mixture
stirred at room temperature for 18 h. The solvent was
evaporated under reduced pressure and the residue taken up
in EtOAc. The solution was washed with saturated NaHCO3
solution, 1 N H3PO4, and brine, dried with MgSO4, and
evaporated in vacuo. The product was purified by flash
chromatography on silica gel, eluting with 4:1 going to 5:2
hexanes-EtOAc. The resultant product was added to a
suspension of 36 mg of 10% Pd-C in 1 mL of MeOH, the
mixture was purged with nitrogen, and 0.1 mL of cyclohexa-
diene was added. The resultant suspension was stirred at
ambient temperature for 2 h. The catalyst was removed by
filtration through a pad of Celite; the solvents were removed
in vacuo. The crude product was triturated with diethyl ether/
hexanes, dissolved in acetonitrile and 0.1% aqueous TFA, and
lyophilized to give the product as a white powder: 1H NMR
(CD3OD, 300 MHz) δ 0.89 (d, 3H, J ) 7 Hz), 0.90 (d, 3H, J )
7 Hz), 1.4-1.7 (m, 3H), 2.50 (s, 3H), 3.3-3.4 (m, 2H), 3.53 (s,
3H), 4.52 (dd, 1H, J ) 6, 10 Hz), 5.43 (dd, 1H, J ) 7, 8 Hz),
6.62 (d, 1H, J ) 4 Hz), 6.89-6.96 (m, 2H), 7.06 (dt, 1H, J ) 1,
8 Hz), 7.14-7.30 (m, 3H), 7.36 (d, 1H, J ) 7 Hz), 7.57 (dd, 1H,
J ) 1, 7 Hz), 7.65 (d, 1H, J ) 4 Hz), 8.16 (dd, 1H, J ) 1, 7 Hz);
MS (DCI/NH3) 556 (M + H)+, 573 (M + NH4)+. Anal. for
C31H33N5O5‚0.9TFA: C, H, N.
2-{1(R )-[((Die t h yla m in o)ca r b on yl)le u cyla m in o]-2-
(in d ol-3-yl)et h yl}-5-m et h ylim id a zole-4-ca r boxylic Acid
(14c). 2-{(1R)-1-[(N-Boc-leucyl)amino]-2-(indol-3-yl)ethyl}-5-
methylimidazole-4-carboxylic acid ethyl ester (110 mg; pre-
pared as described above) was taken up in 4 N HCl-dioxane
(2 mL) and stirred at room temperature for 1 h. The solvent
was evaporated under reduced pressure and the residue taken
up in EtOAc (10 mL). The solution was washed with saturated
NaHCO3 solution and brine, dried with MgSO4, and evapo-
rated in vacuo to give a white solid which was dissolved in
CHCl3 (2 mL). N-Methylmorpholine (27 µL, 0.24 mmol) and
diethylcarbamyl chloride (30 µL, 0.24 mmol) were added, and
the solution was stirred at room temperature for 18 h. The
solution was washed with water (10 mL), saturated sodium
bicarbonate solution (2 × 10 mL), 1 N H3PO4 (2 × 10 mL),
and brine (10 mL). The organic layer was dried with MgSO4
and evaporated to give an orange oil. This crude ester was
dissolved in 4 mL of THF. A nitrogen-purged solution of 50
mg of LiOH in 1.5 mL of water was added, and the mixture
was heated in a Carius tube at 110 °C for 15 h. Analytical
HPLC of the crude reaction mixture indicated incomplete
hydrolysis (∼20% of the starting ester remained). The organic
solvent was removed in vacuo, and the resulting solution was
acidified with 1 N H3PO4. The suspension was dissolved with
water and acetonitrile, and the product was purified by
preparative HPLC (Vydac µC18) eluting with a 10-70%
gradient of CH3CN in 0.1% TFA. Two major peaks were
collected. The fractions containing the desired acid were
lyophilized to give the product as a white solid (17.4 mg): 1H
NMR (CD3OD, 300 MHz) for the major diastereomer δ 0.79
(d, 3H, J ) 7 Hz), 0.81 (d, 3H, J ) 7 Hz), 1.08 (t, 6H, J ) 7
Hz), 1.2-1.7 (m, 3H), 2.52 (s, 3H), 3.25 (q, 4H, J ) 7 Hz), 3.4-
3.6 (m, 4H), 4.08 (m, 1H), 5.42 (dd, 1H, J ) 7, 8 Hz), 7.00 (t,
1H, J ) 7 Hz), 7.10 (s, 1H), 7.12 (t, 1H, J ) 7 Hz), 7.35 (d, 1H,
J ) 8 Hz), 7.45 (d, 1H, J ) 8 Hz); MS (DCI/NH3) m/ e 497 (M
+ H)+. Anal. for C26H36N6O4‚TFA: C, H, N.
2-{1(R)-[((Ben zylam in o)car bon yl)leu cylam in o]-2-(in dol-
3-yl)et h yl}-5-m et h ylim id a zole-4-ca r boxylic a cid (14d )
was prepared as described in 14c above, substituting benzyl
isocyanate: 1H NMR (CDCl3, 300 MHz) δ 0.87 (d, 3H, J ) 7
Hz), 0.89 (d, 3H, J ) 7 Hz), 1.31 (t, 3H, J ) 7 Hz), 1.45 (m,
3H), 1.52 (s, 9H), 2.46 (s, 3H), 3.27 (br s, 1H), 3.43 (m, 1H),
4.12 (m, 1H), 4.30 (q, 2H, J ) 7 Hz), 5.50 (m, 1H), 6.65 (br s,
1H), 6.80-7.10 (m, 3H), 7.12 (s, 1H), 7.40 (m, 1H), 8.26 (m,
1H); MS (DCI/NH3) m/ e 531 (M
+
H)+. Anal. for
C
29H34N6O4‚1.15TFA: C, H, N.
Also prepared as described in 14c:
2-{1(R)-[((Diet h yla m in o)ca r b on yl)leu cyla m in o]-2-(1-
m eth ylin dol-3-yl)eth yl}-5-m eth yloxazole-4-car boxylic acid
(15c): 1H NMR (CD3OD, 300 MHz) δ 0.84 (d, 6H, J ) 7 Hz),
1.08 (t, 6H, J ) 7 Hz), 1.42 (m, 3H), 2.54 (s, 3H), 3.26 (q, 4H,
J ) 7 Hz), 3.37 (d, 2H, J ) 8 Hz), 4.34 (dd, 1H, J ) 6, 7 Hz),
5.40 (t, 1H, J ) 6 Hz), 6.96 (dt, 1H, J ) 1, 7 Hz), 7.00 (s, 1H),
7.06 (dt, 1H, J ) 1, 7 Hz), 7.30 (d, 1H, J ) 8 Hz), 7.36 (d, 1H,
J ) 8 Hz); MS (DCI/NH3) m/ e 498 (M + H)+, 515 (M + NH4)+.
Anal. for C26H35N5O5‚0.3TFA: C, H, N.
2-{1(R)-[((Ben zyla m in o)ca r b on yl)leu cyla m in o]-2-(1-
m eth ylin dol-3-yl)eth yl}-5-m eth yloxazole-4-car boxylic acid
(15d ): 1H NMR (CD3OD, 300 MHz) δ 0.81 (d, 3H, J ) 4 Hz),
0.83 (d, 3H, J ) 4 Hz), 1.28 (t, 2H, J ) 8 Hz), 1.45 (m, 1H),
2.51 (s, 3H), 3.46 (m, 2H), 4.23 (t, 1H, J ) 7 Hz), 4.39 (s, 2H),
5.38 (m, 1H), 6.96 (t, 1H, J ) 9 Hz), 7.03 (s, 1H), 7.07 (t, 1H,
J ) 9 Hz), 7.17-7.33 (m, 6H), 7.43 (d, 1H, J ) 9 Hz); MS (DCI/
Oth er Syn th etic P r ocedu r es. 2-{(1R)-1-[(N-Boc-leu cyl)-
a m in o]-2-(in d ol-3-yl)eth yl}-5-m eth ylim id a zole-4-ca r box-
ylic Acid Eth yl Ester . 2-{(1R)-1-[(Benzyloxycarbonyl)amino]-
2-(indol-3-yl)ethyl}-5-methylimidazole-4-carboxylic acid ethyl
ester (compound 4, P ) Cbz, R ) Et, R′ ) H; 1.7 g) was
dissolved in EtOH (30 mL). The solution was purged of
oxygen, 10% Pd/C (0.5 g) was added, and the mixture was
stirred at room temperature under an atmosphere of hydrogen.
After 2 h the catalyst was removed by filtration and the solvent
evaporated in vacuo to give a white solid (1.2 g). This amino
ester was dissolved in THF (10 mL) and added to a solution
of Boc-Leu-OH‚H2O (1.0 g) and HOBt (0.5 g) in THF (10 mL).

980 J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 4
von Geldern et al.
NH3) m/ e 532 (M + H)+, 549 (M + NH4)+. Anal. for
C29H33N5O5‚TFA: C, H, N.
Synthesis of acid replacements 16:
mate. The resultant slurry was stirred at -20 °C for 45 min.
An ethereal solution of diazomethane (10 mL of ∼0.3 N) was
added dropwise, and the mixture was allowed to warm to
ambient temperature over 3.5 h. The solvents were removed
in vacuo; the residue was taken up in EtOAc and washed
sequentially with water and brine. The organic phase was
dried over Na2SO4 and stripped in vacuo. The crude product
was purified by flash chromatography on silica gel eluting with
1:1 hexanes-ethyl acetate. To the resultant diazo ketone,
dissolved in 10 mL of methanol, was added a solution of 150
mg of silver benzoate in 2 mL of triethylamine (filtered through
a short pad of Celite) over a 10-min period. After stirring for
2 h the solution had turned dark brown. The solvents were
removed in vacuo; the residue was stirred with 120 mL of a
1:1 water-ethyl acetate mixture for 10 min and then filtered
through a pad of Celite. The organic layer was washed with
brine, dried over Na2SO4, and stripped in vacuo. The crude
product was purified by flash chromatography on silica gel
eluting with a gradient of 1:1 going to 2:1 ethyl acetate-
hexanes to afford the product (13 mg, 6% yield) as a colorless
oil.
2-{1(R)-[(P er h yd r oa zep in -1-ylca r bon yl)leu cyla m in o]-
2-(in d ol-3-yl)eth yl}-5-m eth yloxa zole-4-a cetic Acid (19).
Methyl 2-{(1R)-1-(Cbz-amino)-2-(indol-3-yl)ethyl}-5-methylox-
azole-4-acetate (12 mg) was dissolved in EtOH (3 mL), and
10% Pd/C (10 mg) was added. The mixture was purged of
oxygen and stirred under a balloon of hydrogen for 5 h. The
solvent was removed in vacuo and the residue taken up in
EtOAc and filtered through Celite to remove the catalyst. The
solvent was evaporated to give the amine as a yellow oil. This
material was dissolved in THF (1 mL). HOBt (10 mg),
perhydroazepin-1-ylleucine (20 mg), and EDC (12 mg) were
added. N-Methylmorpholine (10 µL) was added, and the
mixture was stirred at room temperature for 18 h. The solvent
was evaporated under reduced pressure and the residue taken
up in EtOAc. The solution was washed with saturated
NaHCO3 solution, 1 N H3PO4, and brine, dried with MgSO4,
and evaporated in vacuo to give an orange oil which was
purified by flash chromatography on silica gel eluting with 50%
EtOAc-hexane. To this ester dissolved in THF (1 mL) was
added a solution of LiOH (15 mg) in H2O (0.5 mL) and the
mixture stirred at room temperature for 15 h. The solvents
were evaporated under reduced pressure, and the residue was
purified by preparative HPLC (Vydac µC18) eluting with a 10-
70% gradient of CH3CN in 0.1% TFA. The desired fractions
were lyophilized to give the product as a white solid: 8 mg;
1H NMR (CD3OD, 300 MHz) δ 0.85 (d, 6H, J ) 6 Hz), 0.94 (m,
1H), 1.40 (m, 1H), 1.52 (m, 5H), 1.66 (m, 4H), 2.24 (s, 3H),
3.3-3.5 (m, 6H), 3.45 (s, 2H), 4.33 (dd, 1H, J ) 6, 9 Hz), 5.37
(t, 1H, J ) 7 Hz), 6.96 (ddd, 1H, J ) 1, 7, 8 Hz), 6.97 (s, 1H),
7.07 (ddd, 1H, J ) 1, 7, 8 Hz), 7.29 (td, 1H, J ) 1, 8 Hz), 7.36
(td, 1H, J ) 1, 8 Hz); MS (DCI/NH3) m/ e 538 (M + H)+; HRMS
calcd for C29H40N5O5 538.3029, found 538.3030.
E t h yl 2-{1(R)-[(P er h yd r oa zep in -1-ylca r b on yl)leu cyl-
a m in o]-2-(in d ol-3-yl)eth yl}-5-m eth yloxa zole-4-ca r boxy-
la te (16d ). Compound 16d was prepared as an intermediate
(prior to final hydrolysis) in the synthesis of 15a : 1H NMR
(CD3OD, 300 MHz) δ 0.87 (d, 3H, J ) 7 Hz), 0.88 (d, 3H, J )
7 Hz), 1.34 (t, 3H, J ) 8 Hz), 1.43 (m, 2H), 1.52 (m, 5H), 1.67
(m, 4H), 2.55 (s, 3H), 3.25-3.5 (m, 6H), 4.32 (q, 2H, J ) 8
Hz), 4.35 (dd, 1H, J ) 5, 9 Hz), 5.39 (t, 1H, J ) 8 Hz), 6.95
(ddd, 1H, J ) 1, 7, 8 Hz), 6.98 (s, 1H), 7.07 (ddd, 1H, J ) 1, 7,
8 Hz), 7.31 (td, 1H, J ) 1, 8 Hz), 7.36 (d, 1H, J ) 8 Hz); MS
(DCI/NH3) m/ e 552 (M + H)+, 569 (M + NH4)+. Anal. for
C30H41N5O5‚0.4TFA: C, H, N.
2-{1(R)-[(P er h yd r oa zep in -1-ylca r bon yl)leu cyla m in o]-
2-(in d ol-3-yl)eth yl}-5-m eth yloxa zole-4-ca r boxylic Acid ,
Hyd r oxa m a te (16a ). Compound 15a (32 mg) was dissolved
in 1 mL of THF and cooled to 0 °C. Oxalyl chloride (6 mL)
and 10 µL of DMF were added, and the solution was stirred
for 90 min at 0 °C. Hydroxylamine hydrate (25 mg) was
dissolved in 1.2 mL of THF and cooled to 0 °C. The acid
chloride solution was added, and the mixture was allowed to
warm to room temperature and stirred overnight. The sol-
vents were evaporated, and the residue was purified by
preparative HPLC (Vydac µC18) eluting with a 10-70%
gradient of CH3CN in 0.1% TFA. The desired fractions were
lyophilized to give the title compound as a white solid: 29 mg;
1H NMR (CD3OD, 300 MHz) δ 0.84 (d, 3H, J ) 7 Hz), 0.85 (d,
3H, J ) 7 Hz), 1.4 (m, 2H), 1.52 (m, 5H), 1.67 (m, 4H), 2.53 (s,
3H), 3.25-3.5 (m, 6H), 4.29 (dd, 1H, J ) 6, 10 Hz), 5.36 (dd,
1H, J ) 7, 8 Hz), 6.97 (ddd, 1H, J ) 1, 7, 8 Hz), 7.02 (s, 1H),
7.07 (ddd, 1H, J ) 1, 7, 8 Hz), 7.31 (td, 1H, J ) 1, 8 Hz), 7.44
(td, 1H, J ) 1, 8 Hz); MS (DCI/NH3) m/ e 539 (M + H)+. Anal.
for C28H38N6O5‚0.8TFA: C, H, N .
2-{1(R)-[(P er h yd r oa zep in -1-ylca r bon yl)leu cyla m in o]-
2-(in d ol-3-yl)eth yl}-5-m eth yloxa zole-4-ca r boxylic a cid ,
N-m eth yla m id e (16b) was prepared as above for 16a ,
substituting 40% aqueous methylamine: 1H NMR (CD3OD,
300 MHz) δ 0.85 (d, 3H, J ) 7 Hz), 0.86 (d, 3H, J ) 7 Hz),
1.3-1.5 (m, 2H), 1.52 (m, 5H), 1.67 (m, 4H), 2.52 (s, 3H), 2.85
(s, 3H), 2.93 (m, 1H), 3.3-3.5 (m, 6H), 4.30 (dd, 1H, J ) 6, 10
Hz), 5.36 (dd, 1H, J ) 7, 8 Hz), 6.97 (ddd, 1H, J ) 1, 7, 8 Hz),
7.00 (s, 1H), 7.07 (ddd, 1H, J ) 1, 7, 8 Hz), 7.31 (td, 1H, J )
1, 8 Hz), 7.44 (td, 1H, J ) 1, 8 Hz); MS (DCI/NH3) m/ e 537
(M + H)+. Anal. for C29H40N6O4‚0.3TFA: C, H, N.
2-{1(R)-[(P er h yd r oa zep in -1-ylca r bon yl)leu cyla m in o]-
2-(in d ol-3-yl)eth yl}-5-m eth yloxa zole-4-ca r boxylic a cid ,
ca r boxym eth yla m id e (16c) was prepared as above for 16a ,
substituting glycine ethyl ester. The resulting product was
dissolved in THF (2 mL), a solution of LiOH (50 mg) in H2O
(1 mL) was added, and the mixture was stirred at room
temperature for 15 h. The solvents were evaporated under
reduced pressure, and the residue was purified by preparative
HPLC (Vydac µC18) eluting with a 10-70% gradient of CH3-
CN in 0.1% TFA. The desired fractions were lyophilized to
Recep tor Bin d in g Assa ys. All compounds were assayed
for binding to MMQ cell membranes (ETA receptor) or porcine
cerebellar tissues (ETB) using the protocols described in the
previous article.1
1
give the product as a white solid: 28 mg; H NMR (CD3OD,
300 MHz) δ 0.84 (d, 3H, J ) 7 Hz), 0.85 (d, 3H, J ) 7 Hz), 1.4
(m, 2H), 1.52 (m, 5H), 1.67 (m, 4H), 2.52 (s, 3H), 3.3-3.5 (m,
6H), 4.04 (s, 2H), 4.31 (dd, 1H, J ) 6, 10 Hz), 5.39 (dd, 1H, J
) 7, 8 Hz), 6.97 (ddd, 1H, J ) 1, 7, 8 Hz), 7.03 (s, 1H), 7.07
(ddd, 1H, J ) 1, 7, 8 Hz), 7.30 (td, 1H, J ) 1, 8 Hz), 7.45 (td,
1H, J ) 1, 8 Hz); MS (DCI/NH3) m/ e 581 (M + H)+. Anal. for
C30H40N6O6‚0.7TFA: C, H, N.
P h osp h oin ositid e (P I) Tu r n over Assa y. MMQ cells (0.4
× 106 cells/mL) were labeled with 10 µCi/mL of [3H]myoinositol
in RPMI for 16 h. The cells were washed with PBS and then
incubated with buffer A containing protease inhibitors and 10
mM LiCl for 60 min. The cells were incubated with test
compounds for 5 min and then challenged with 1 nM ET-1 for
30 min at 37 °C. ET-1 challenge was terminated by the
addition of 1.5 mL of 1:2 (v/v) chloroform-methanol. Total
inositol phosphates were extracted after adding chloroform and
water to give final proportions of 1:1:0.9 (v/v/v) chloroform-
methanol-water of as described by Berridge.8 The upper
aqueous phase (1 mL) was analyzed by batch chromatography
using anion-exchange resin AG1-X8 (Bio-Rad). IC50 values are
calculated using an average of at least two separate determi-
nations.
Synthesis of homologated acid 19:
Met h yl 2-{(1R)-1-(Cb z-a m in o)-2-(in d ol-3-yl)et h yl}-5-
m eth yloxa zole-4-a ceta te (18). A solution of 5 (P ) Boc, R
) Et, R′ ) H; 200 mg, 0.46 mmol; prepared as described in
previous article1) in 4 mL of THF was combined with 40 mg
of LiOH in 1 mL of water. The mixture was stirred at ambient
temperature for 65 h and then heated at 45 °C for 3 h. The
organic solvent was removed in vacuo; the aqueous solution
was neutralized with 1 N H3PO4 and then extracted with
EtOAc. The combined organic extracts were concentrated in
vacuo to give the crude acid 17. To this material, dissolved
in 5 mL of THF and cooled to -20 °C, was added 100 µL of
N-methylmorpholine, followed by 60 µL of isobutyl chlorofor-
Ack n ow led gm en t. The authors thank the Abbott
1
Analytical Department for assistance in acquiring H-
NMR and mass spectra.

Azole Endothelin Antagonists
J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 4 981
1508. Opgenorth, T. J . Endothelin Receptor Antagonism. Adv.
Pharmacol., in press.
Refer en ces
(1) von Geldern, T. W.; Hutchins, C.; Kester, J . A.; Wu-Wong, J .
R.; Chiou, W.; Dixon, D. B.; Opgenorth, T. J . J . Med. Chem. 1996,
39, 957-967.
(2) Ishikawa, K.; Fukami, T.; Hayama, T.; Niiyama, K.; Nagase, T.;
Mase, T.; Fujita, K.; Ihara, M.; Ikemoto, F.; Yano, M. Endothelin
Antagonistic Peptide Derivatives. EP 460679, 1991. Hemmi, K.;
Neya, M.; Fukami, N.; Hashimoto, M.; Tanaka, H.; Kayakiri,
N. New Endothelin Antagonists and Their Preparation. WO 93/
10144, 1993.
(3) Arai, H.; Hori, S.; Aramori, I.; Ohkubo, H.; Nakanishi, S. Cloning
and Expression of a cDNA Encoding an Endothelin Receptor.
Nature 1990, 348, 730-732. Sakurai, T. Cloning of a cDNA
Encoding a Non-isopeptide-selective Subtype of the Endothelin
Receptor. Nature 1990, 348, 732-735. For reviews of ET biology,
see: Simonson, M. S.; Dunn, M. J . The Molecular Mechanisms
of Cardiovascular and Renal Regulation by Endothelin Peptides.
J . Lab. Clin. Med. 1992, 119 (6), 622-639. Doherty, A. Endo-
thelin: A New Challenge. J . Med. Chem. 1992, 35 (9), 1493-
(4) Gordon, T. D.; Singh, J .; Hansen, P. E.; Morgan, B. A. Synthetic
Approaches to the ‘Azole’ Peptide Mimetics. Tetrahedron Lett.
1993, 34 (12), 1901-1904.
(5) Boger, D. L.; Patel, M. Indole N-Carbonyl Compounds: Prepara-
tion and Coupling of Indole-1-carboxylic Acid Anhydride. J . Org.
Chem. 1987, 52, 3934-3936.
(6) Yamada, S.-I; Shioiri, T.; Itaya, T.; Hara, T.; Matsueda, R. Ind.-
N-Alkylation of Tryptophan and Synthesis of 1-Alkyltryptophan
Hydrazides. Chem. Pharm. Bull. 1965, 13, 88-93.
(7) Bergmann, E. D.; Gil-Av, E.; Pinchas, S. The Structure of the
Products of Condensation between Primary â-Hydroxyamines
and Aliphatic Carbonyl Compounds. J . Am. Chem. Soc. 1953,
75, 358-361.
(8) Berridge, M. J .; Downes, C. P.; Manley, M. R. Lithium Amplifies
Agonist-dependent Phosphatidylinositol Responses in Brain and
Salivary Glands. Biochem. J . 1982, 206, 587-595.
J M950592+