Vasopeptidase inhibitors: Incorporation of geminal and spirocyclic substituted azepinones in mercaptoacyl dipeptides

Article abstract of DOI:10.1021/jm980542f

A series of 7-(di)alkyl and spirocyclic substituted azepinones were generated and incorporated as conformationally restricted dipeptide surrogates in mercaptoacyl dipeptides. Clear structure-activity relationships with respect to both angiotensin-converti

Full text of DOI:10.1021/jm980542f

J . Med. Chem. 1999, 42, 305-311
305
Va sop ep tid a se In h ibitor s: In cor p or a tion of Gem in a l a n d Sp ir ocyclic
Su bstitu ted Azep in on es in Mer ca p toa cyl Dip ep tid es
J effrey A. Robl,* Richard Sulsky, Ellen Sieber-McMaster, Denis E. Ryono, Maria P. Cimarusti,
Ligaya M. Simpkins, Donald S. Karanewsky, Sam Chao, Magdi M. Asaad, Andrea A. Seymour, Maxine Fox,
Patricia L. Smith, and Nick C. Trippodo
The Bristol-Myers Squibb Pharmaceutical Research Institute, P.O. Box 5400, Princeton, New J ersey 08543-5400
Received September 28, 1998
A series of 7-(di)alkyl and spirocyclic substituted azepinones were generated and incorporated
as conformationally restricted dipeptide surrogates in mercaptoacyl dipeptides. Clear structure-
activity relationships with respect to both angiotensin-converting enzyme (ACE) and neutral
endopeptidase (NEP) activity in vitro were observed. The best in this series, compound 1g, a
geminally dimethylated C-7-substituted azepinone, demonstrated excellent blood pressure
lowering in animal models. Compound 1g (BMS-189921) is characterized by a good duration
of activity and excellent oral efficacy in models relevant to ACE or NEP inhibition, and its
activity is comparable to that of the clinically efficacious agent omapatrilat. Consequently this
inhibitor has been advanced clinically for the treatment of hypertension and congestive heart
failure.
Ch a r t 1
In tr od u ction
Angiotensin-converting enzyme (ACE) and neutral
endopeptidase (NEP) are zinc metalloproteases respon-
sible for angiotensin II (AII) formation and atrial
natriuretic peptide (ANP) degradation, respectively. AII
serves to raise blood pressure by both vasoconstriction
and release of aldosterone. In contrast ANP, a peptidic
hormone secreted by the heart in response to atrial
distention, promotes the generation of cGMP via gua-
nylate cyclase activation, which in turn causes vasodi-
latation, natriuresis, diuresis, and possibly inhibition
of aldosterone formation. Because of the functionally
opposed hormonal actions of AII and ANP, coinhibition
of ACE and NEP has the potential to act synergistically
to lower vascular resistance and inhibit activation of the
renin-angiotensin-aldosterone system. Additionally,
simultaneous inhibition of ACE and NEP may be
effective in potentiating other vasoactive endogenous
peptides such as bradykinin, a peptide which has been
shown to be important in cardiovascular protection.1
Hence, to fully represent the scope of ACE/NEP inhibi-
tors in vivo, we have termed this class of compounds as
vasopeptidase inhibitors (VPIs).
both ACE and NEP and to exhibit a prolonged duration
of activity in animal models. As demonstrated in previ-
ous studies,6 the ability of these compounds to perform
in vivo is subject to many factors, one of which is the
nature of the dipeptide mimetic framework.
Although omapatrilat continues to distinguish itself
from other classes of established antihypertensive drugs,
it was felt desirable to advance other potential agents
with modified biological properties into the clinic. Our
interest in the monocyclic based azepinone series in part
was derived from the observation that appropriate
substitution on the lactam ring could confer better in
vitro potency and enhanced pharmacodyamic activity7
(compare C-7 methyl-substituted lactam 1b with its
unsubstituted counterpart 1a , Chart 1). Compound 1b
was significantly more potent against NEP and ACE
in vitro and exhibited a more robust response and
greater duration of activity in a functional assay of in
vivo ACE inhibition (AI pressor assay). Noting the effect
of this modification and suspecting that metabolism at
the C-7 position of the lactam ring could be limiting
efficacy in vivo, we generated a series of C-7 geminally
and spirocyclic substituted lactams, generically repre-
A number of pharmaceutical groups have engaged in
developing single agents that act as an inhibitor to both
enzymes. Several review articles have highlighted ad-
vances in this field.2 In recent reports,3,4 we described
the design, synthesis, in vitro characterization, and in
vivo pharmacology of a series of conformationally re-
stricted mercaptoacetyls possessing a core bicyclic aze-
pinone framework. From this series, BMS-186716 (oma-
patrilat) was selected for clinical development and is
currently in phase III clinical trials for hypertension.
Preliminary data in humans has demonstrated that
omapatrilat is a well-tolerated and highly effective oral
antihypertensive agent with a once daily duration of
activity.5 Preclinically, omapatrilat was only one of a
few compounds to exhibit good in vitro potency against
10.1021/jm980542f CCC: $18.00 © 1999 American Chemical Society
Published on Web 01/05/1999

306 J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 2
Robl et al.
Sch em e 1a
forcing conditions afforded a mixture of unreacted and
N-alkylated products which were difficult to separate.8
To circumvent this problem, a trityl group was utilized
as the primary amine-protecting group, leading exclu-
sively to the formation of the desired lactam alkylation
product. Thus, treatment of 8 with a 5-fold excess of
LiN(TMS)2 and ethyl bromoacetate afforded a crude
alkylation mixture. Amine 9 could be isolated in nearly
pure form after trityl deprotection and acid-base ex-
traction. EDAC-mediated coupling of amine 9 with (S)-
2-(acetylthio)benzenepropanoic acid afforded the cou-
plingproduct with little or noracemization. Saponification
under anaerobic conditions thus afforded 1g. Utilizing
similar coupling/deprotection procedures, compounds
1a -f were also prepared.
Discu ssion
Table 1 lists in vitro data and ED50 AI pressor
responses (intravenous administration in rats) for com-
pounds 1a -g as well as for omapatrilat. All of the
compounds were effective inhibitors against ACE with
IC50’s ranging from 6 to 29 nM. As a general trend, the
C-7 alkyl-substituted azepinones appeared less active
versus NEP than ACE in vitro, with a greater disparity
between ACE and NEP potency observed in the C-7
spirocyclic analogues. These structure-activity relation-
ships outline the subtle yet distinct structural require-
ment necessary for effective inhibition of both enzymes.
Spirocyclopropane 1d and dimethyl lactam 1g differ
structurally by only two hydrogen atoms and a single
bond, yet they display equivalent in vitro ACE activity
but a 6-fold difference with respect to NEP. The reason
for this disparity is unclear, but the data suggests that
the geminal dimethyl groups in 1g may be bisecting a
critical residue in the P1 pocket of NEP that cannot be
avoided by the spirocyclic compounds due to increased
steric bulk and covalent bonding between the R1 and
R2 substituents. The observation that ACE activity is
marginally affected by these changes argues against
major conformational differences among the spirocyclic
and nonspirocyclic substituted azepinones. Despite its
apparent modest IC50 values, Lineweaver-Burk analy-
sis of 1g against rabbit lung ACE and rat kidney NEP
indicate that it is a linear competitive inhibitor of these
enzymes with inhibitor constants (Ki) of 5.3 and 16 nM,
respectively. These values compare favorably with the
current clinical compound omapatrilat (ACE Ki ) 6.0
nM, NEP Ki ) 8.9 nM).
The nature of the substitution at the C-7 position had
a pronounced effect on in vivo activity as well.7 Both
the monomethyl (1b) and dimethyl (1g) azepinones were
approximately 8-fold more potent than their unsubsti-
tuted analogue 1a in the acute AI pressor response
assay (Table 1). Despite similar ED50’s, 1g also exhibited
a greater duration of activity (data not shown) in this
assay, suggesting this compound may have a better
pharmacodynamic profile and be suitable for once daily
dosing. Importantly, compound 1g distinguished itself
from other compounds in this class with its high level
of oral efficacy (ED50 ) 0.6 µmol/kg, po) in the AI pressor
assay (Figure 1) and exhibited a more robust response
as compared to either compound 1b or the clinically
efficacious, once-a-day, selective ACE inhibitor fosino-
pril. Based on its in vitro activity and performance in
a
(a) BnBr, Cs2CO3, DMF, 95%; (b) Swern oxidation; (c) Me3Al
in hexanes, CH2Cl2, 91% (2 steps); (d) Swern oxidation, 97%; (e)
MeTiCl3, Et2O, 0 °C, 87%; (f) TMSN3, BF3‚OEt2, CH2Cl2, rt 5 days,
81%; (g) H2, Pd/C, DMF, then EDAC, HOAt, 88%; (h) H2N-
NH2‚H2O, MeOH; (i) Ph3CCl, TEA, CH2Cl2, 96% (2 steps); (j) xs
LiN(TMS)2, xs BrCH2CO2Et, THF; (k) TFA, CH2Cl2, 85% (2 steps);
(l) (S)-AcSCH(CH2Ph)CO2H, EDAC, CH2Cl2; (m) NaOH, H2O,
MeOH, then H3O+, 95% (2 steps).
sented by the structure 1, and determined their effect
on NEP and ACE inhibition.
Ch em istr y
We have previously reported biological and chemical
information on vasopeptidase inhibitors 1a -c.7 Chemi-
cal methods for the generation of the requisite azepi-
nones in 1d -g have been outlined as well by selective
(1d ) and nonstereoselective (1e-g) routes.8 The potent
activity observed with 1g (BMS-189921) in our assays
prompted the development of a homochiral synthesis of
this compound which is outlined in Scheme 1. Benzyl-
ation of (S)-6-hydroxy-2-phthalimidohexanoic acid (2)3
followed by Swern oxidation of the alcohol functionality
and methyl addition9 with Me3Al afforded 4 in good
yield as a 1:1 mixture of diastereomers. Swern oxidation
provided the intermediate ketone. Treatment of the
ketone with Me3Al failed to provide the desired tertiary
alcohol, and addition of more conventional agents
(MeMgCl, MeLi) led to the destruction of the phthalimdo
protecting group. In contrast, reaction with methyl-
titanium trichloride,10 generated in situ by the addition
of MeLi to TiCl4, afforded tertiary alcohol 5 in reason-
able overall yield. Treatment of 5 with TMSN3 and BF3‚
OEt2 rapidly formed a mixture of azide 6 and the related
olefin elimination product,11 which slowly underwent
conversion to the desired azide over several days.
Palladium-catalyzed hydrogenation of 6 effected both
reduction of the azide to the amine and hydrogenolysis
of the benzyl ester. EDAC-mediated cyclization of the
intermediate amino acid gave azepinone 7 in good
overall yield. We have demonstrated that C-7 monoalkyl-
substituted lactams related to 7 can be cleanly and
quickly alkylated at the lactam nitrogen under near
stoichiometric conditions.12 In contrast, the steric en-
vironment of geminally substituted azepinones severely
retards this desired transformation. For example, alky-
lation of the racemic Boc-protected azepinone of 8 under

Vasopeptidase Inhibitors
J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 2 307
Ta ble 1. Inhibition of ACE and NEP in Vitro and AI Pressor Responses for Compounds 1a -g
IC50 (nM)
d
AI pressor ED50
(µmol/kg, iv)
no.
R1
R2
formulaa
17H22N2O4S
ACEb
NEPc
omapatrilat
5
22
8.2
16
9.6
29
6
8
82
49
149
377
641
426
63
0.07
0.84
0.11
ND
ND
ND
ND
0.1
1a
1b
1c
1d
1ee
1fe
1g
H
H
Me
H
Me
H
C
C
C
18H24N2O4S
18H24N2O4S‚0.31H2O
-(CH2)2-
-(CH2)3-
-(CH2)4-
C19H24N2O4S‚0.5H2O
C20H26N2O4S‚0.33toluene
C21H28N2O4S‚0.8EtOAcf
Me
Me
C
19H26N2O4S
12
a
All spectral data were consistent with the assigned structures. All compounds were analyzed for C, H, N, and S for the formula
b
shown. Compounds were assayed against angiotensin-converting enzyme isolated from rabbit lung extract using hippuryl-L-histidyl-L-
leucine (HHL) as the substrate. c Compounds were assayed against purified rat kidney neutral endopeptidase using a fluorometric assay
d
with dansyl-Gly-Phe-Arg as the substrate. Represents dose required for 50% inhibition of the AI pressor response in normotensive rats.
e Compounds 1e and 1f were prepared as a 1:1 mixture of diastereomers from the racemic lactam. f Anal. (C21H26N2O4S‚0.8EtOAc) C, H,
N; S: calcd, 61.96; found, 60.61.
a progressive fall in 24-h averaged MAP during the first
5-6 days of dosing (Figure 2A). At the end of 9 days,
24-h MAP decreased by approximately 30 mmHg in the
drug-treated group. The changes in MAP averaged over
2-h periods during the ninth day of study are depicted
in Figure 2B. Starting at 3 h after administration of 1g,
MAP decreased by approximately 40 mmHg and in-
creased slightly over the next 20 h. At completion of the
study, MAP was clearly lower in the drug-treated as
compared to the vehicle-treated group, indicating that
the duration of antihypertensive activity was at least
23 h. The activity of 1g was comparable to, if not slightly
greater than, that of omapatrilat under the same
conditions.
In vivo inhibition of NEP for 1g was demonstrated
in 1-kidney DOCA salt hypertensive rats, a sodium-
dependent model of hypertension that is responsive to
NEP inhibitors but refractory to selective ACE inhibi-
tors. In this assay, compound 1g was administered
orally at 100 µmol/kg for 4 consecutive days and systolic
blood pressure (SBP) was measured by tail-cuff 4 h after
each dose (Figure 3). Compound 1g demonstrated a
F igu r e 1. Inhibition of the MAP response to AI (iv adminis-
tration) in conscious rats after oral (po) administration of
rapid onset of action, lowering SBP by approximately
60 mmHg over the duration of the study. Qualitatively,
the results were similar to those in a separate study3
performed with omapatrilat, which gave ≈45 mmHg
SBP lowering but a slower onset of action.
fosinopril, compound 1g, or compound 1b was determined
according to procedures previously described.13 Conscious
animals (n ) 4/group), instrumented with implanted arterial
and venous catheters at least 2 weeks prior to study, were
prepared for direct recording of aterial blood pressure using a
pressure transducer. Changes in MAP in response to iv
injections of AI (310 ng/kg) were obtained before (control) and
at intervals after the administration of fosinopril, compound
1g, or compound 1b. The percent change (mean ( SE) from
the control response (percent inhibition) was determined for
each response after drug or vehicle administration.
To ascertain the pharmacodynamics of 1g in a non-
rodent animal model, conscious cynomologus monkeys
were dosed with compound (50 µmol/kg, po) once daily
and the AI pressor response was measured at 24 h after
each dose (Figure 4A). Inhibition of NEP activity was
assessed in these monkeys by measuring the urinary
ANP response to iv injection of human ANP 24 h after
the second and fourth doses (Figure 4B). The results
indicate that 1g inhibits ACE and renal NEP activities
in vivo for at least 24 h and that inhibition of both
enzymes is sustained during 4 days of repeat dosing in
conscious monkeys.
the AI pressor assay, 1g was selected for further
evaluation in other relevant animal models.13
The spontaneously hypertensive rat (SHR) is a model
widely used for essential hypertension and generally has
normal plasma renin activity in the sodium replete
state. The antihypertensive effects of 1g and omapat-
rilat at 100 µmol/kg, once daily, were determined in
unrestrained SHR by telemetry. This method allows
measurements of mean arterial pressure (MAP) in a
relatively undisturbed manner. Compound 1g elicited
The overall in vitro and in vivo pharmacology of 1g
is consistent with potent inhibition of both ACE and
NEP, and like omapatrilat, 1g is characterized by a good

308 J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 2
Robl et al.
F igu r e 3. Effect on systolic blood pressure upon oral admin-
istration once daily of vehicle (5% NaHCO3) or compound 1g
in 1-K DOCA salt hypertensive rats. Systolic blood pressure
was measured 4 h after each dose by the tail-cuff method after
conditioning rats to the procedure for 3 consecutive days prior.
Dosing was initiated on day 1.
reagents used were of commercial quality and were obtained
from Aldrich Chemical Co. or Sigma Chemical Co. Melting
points were obtained on a Hoover Uni-melt melting point
apparatus and are uncorrected. Infrared spectra were recorded
on a Mattson Sirius 100-FTIR spectrophotometer. 1H (400
MHz) and 13C (100 MHz) NMR spectra were recorded on a
J EOL GSX400 spectrometer using Me4Si as an internal
standard. Optical rotations were measured in a 1-dm cell on
a Perkin-Elmer 241 polarimeter, and c is expressed in g/100
mL. All flash chromatographic separations were performed
using E. Merck silica gel (60, particle size 0.040-0.063 mm).
Reactions were monitored by TLC using 0.25-mm E. Merck
silica gel plates (60 F254) and were visualized with UV light or
5% phosphomolybdic acid in 95% EtOH. Omapatrilat (BMS-
186716) and fosinopril were synthesized at The Bristol-Myers
Squibb Pharmaceutical Research Institute (Princeton, NJ ).
(S)-2-P h th a lim id o-6-h yd r oxyh exa n oic Acid , P h en yl-
m eth yl Ester (3). A slurry of Cs2CO3 (3.82 g, 11.7 mmol) and
(S)-2-phthalimido-6-hydroxyhexanoic acid (2; 6.000 g, 21.6
mmol) in DMF (60 mL) was treated with benzyl bromide (3.30
mL, 4.75 g, 27.7 mmol). After stirring at room temperature
for 2 h, the mixture was partitioned between EtOAc and H2O.
The organic extract was washed twice with H2O and brine,
then dried (Na2SO4), filtered, and concentrated in vacuo to give
an oil. The oil was flash-chromatographed (6:4 EtOAc:hexanes
as eluant) to give essentially pure 3 as a solid. Recrystallization
from EtOAc:hexane gave 7.57 g (95%) of analytically pure
compound 3: TLC Rf 0.43 (75:25 EtOAc:hexanes); mp 106-
F igu r e 2. Changes in MAP in conscious unrestrained SHR
after once daily oral administration of vehicle (5% NaHCO3,
n ) 10), omapatrilat (n ) 9), or compound 1g (n ) 9) as
measured by telemetry. Mean arterial pressures before ad-
ministration of agents were (mean ( SE): 130 ( 4, 138 ( 5,
and 145 ( 2 mmHg in the vehicle, omapatrilat, and compound
1g groups, respectively. (A) Changes in MAP averaged over a
24-h period for 9 days of dosing. (B) Changes in MAP averaged
over 2-h periods during the ninth day of the study.
duration of action consistent with once daily oral dosing.
Both compound 1g and omapatrilat display favorable
similarities in their preclinical pharmacological profiles,
although preliminary pharmacological data suggest that
1g may have a somewhat greater effect on NEP inhibi-
tion in vivo. Additional preclinical and clinical studies
are warranted to ascertain a better differentiation
among these compounds. Compound 1g (BMS-189921)
was selected for further development and is currently
in phase II clinical trials for the treatment of hyperten-
sion and congestive heart failure, where early data from
these trials confirm a favorable safety and efficacy
profile with this inhibitor.
1
108.5 °C; [R]D -27.5° (c 1.5, MeOH); H NMR (CDCl3) δ 1.50
(m, 4H), 2.32 (m, 2H), 3.62 (m, 2H), 4.91 (dd, 1H), 5.22 (d, 2H),
7.31 (m, 5H), 7.77 (m, 2H), 7.86 (m, 2H); 13C NMR (CDCl3) δ
22.62, 28.46, 31.91, 52.32, 62.32, 67.46, 123.55, 128.06, 128.31,
128.53, 131.77, 134.23, 135.28, 167.76, 169.25.
(2S)-2-P h th a lim id o-6-h yd r oxyh ep ta n oic Acid , P h en yl-
m eth yl Ester (4). A -78 °C solution of oxalyl chloride (3.0
mL, 4.36 g, 34.4 mmol) in CH2Cl2 (100 mL) was treated
dropwise with a solution of dry DMSO (4.8 mL, 5.28 g, 67.6
mmol) in CH2Cl2 (2.0 mL). After 10 min, a solution of alcohol
3 (10.365 g, 28.2 mmol) in CH2Cl2 (20 mL) was added over a
7-min period. After an additional 15 min, dry TEA (17 mL)
was added, and the mixture was stirred at -78 °C for 5 min
and then let gradually warm to 0 °C. The mixture was
partitioned between Et2O and H2O. The organic layer was
washed with 1 N HCl and brine, dried (Na2SO4), filtered, and
concentrated in vacuo to give the desired intermediate alde-
hyde as an oil: TLC Rf 0.56 (6:4 EtOAc:hexanes); 1H NMR
Exp er im en ta l Section
All reactions were carried out under a static atmosphere of
argon and stirred magnetically unless otherwise noted. All

Vasopeptidase Inhibitors
J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 2 309
colorless oil. Flash chromatography (6:4 EtOAc:hexanes as
eluant) afforded pure alcohol 4 (9.836 g, 91% from 3) as a
colorless oil (1:1 mixture of diastereomers): TLC Rf 0.42 (6:4
EtOAc:hexanes); 1H NMR (CDCl3) δ 1.12 (d, 3H), 1.43 (m, 4H),
3.73 (m, 2H), 4.90 (dd, 1H), 5.19 (d, 2H), 7.30 (m, 5H), 7.76
(m, 2H), 7.86 (m, 2H); 13C NMR (CDCl3) δ 22.5, 23.40, 28.47,
28.59, 38.20, 38.34, 52.20.67.35, 67.51, 123.43, 127.94, 128.19,
128.41, 131.65, 134.11, 135.16, 167.62, 167.67, 169.13.
(S)-2-P h th a lim id o-6-m eth yl-6-h yd r oxyh ep ta n oic Acid ,
P h en ylm eth yl Ester (5). A -78 °C solution of oxalyl chloride
(1.52 mL, 2.21 g, 17.4 mmol) in CH2Cl2 (120 mL) was treated
dropwise with a solution of dry DMSO (2.50 mL, 2.75 g, 35.2
mmol) in CH2Cl2 (2.0 mL). After 10 min, a solution of alcohol
4 (5.078 g, 13.3 mmol) in CH2Cl2 (30 mL) was added. After an
additional 15 min, dry TEA (10 mL) was added, and the
mixture was stirred at -78 °C for 5 min and then let gradually
warm to 0 °C. The mixture was partitioned between Et2O and
1 N aqueous HCl. The aqueous layer was back-extracted with
Et2O, and the pooled organic extracts were washed with brine,
dried (Na2SO4), filtered, and concentrated in vacuo. Flash
chromatography (1:1 EtOAc:hexanes as eluant) afforded the
intermediate ketone (4.89 g, 97%) as a colorless oil: TLC Rf
0.32 (1:1 EtOAc:hexanes); [R]D -10.7° (c 0.9, CHCl3); 1H NMR
(CDCl3) δ 1.60 (m, 2H), 2.10 (s, 3H), 2.26 (m, 2H), 2.47 (m,
2H), 4.90 (dd, 1H), 5.19 (d, 2H), 7.30 (m, 5H), 7.74 (m, 2H),
7.84 (m, 2H); 13C NMR (CDCl3) δ 20.15, 27.93, 29.84, 42.47,
51.89, 67.40, 123.46, 127.97, 128.23, 128.43, 131,61, 134.17,
135.10, 167.57, 168.93, 207.80.
Neat TiCl4 (2.48 mL, 4.28 g, 22.5 mmol) was added dropwise
to dry Et2O (150 mL) at -78 °C, resulting in a bright-yellow
suspension. Addition of MeLi (1.4 M in Et2O, 16.1 mL, 22.5
mmol) over a 5-min period afforded a dark-brown nonhomo-
geneous mixture. Gradual warming to -35 °C resulted in a
deep-brown-purple near-homogeneous solution. The interme-
diate ketone (5.68 g, 15.0 mmol) in Et2O (30 mL) was added
dropwise to the above solution, affording a gummy intractable
reaction mixture. The reaction was warmed to 0 °C and
occasionally agitated with a spatula in order to augment
magnetic stirring. After 4 h at 0 °C, the mixture was quenched
with saturated NH4Cl, diluted with H2O, and extracted with
EtOAc. The organic layer was washed with H2O and brine,
dried (Na2SO4), filtered, and concentrated in vacuo. The
residue was flash-chromatographed (1:1 EtOAc:hexanes as
eluant) to afford compound 5 (5.17 g, 87%) as an oil: TLC Rf
F igu r e 4. (A) Inhibition of the MAP response to AI in
conscious cynomologus monkeys after oral administration once
daily with vehicle (agar) or compound 1g (50 µmol/kg) and
measured 24 h after each dose. Changes in MAP in response
to iv injections of AI (310 ng/kg) were obtained before (control)
and at intervals after the administration of vehicle or com-
pound 1g. The percent change (mean ( SE) from the control
response (percent inhibition) was determined for each response
after drug or vehicle administration. (B) Potentiation of
urinary ANP response to iv injections of 1 nmol/kg human ANP
99-126 in conscious cynomologus monkeys treated once daily
with vehicle (agar) or compound 1g (50 µmol/kg) and measured
24 h after each dose. Changes in ANP excretion were obtained
before (control) and at intervals after the administration of
vehicle or compound 1g. The percent change (mean ( SE) from
the control response (percent inhibition) was determined for
each response after drug or vehicle administration.
1
0.25 (1:1 EtOAc:hexanes); [R]D -3.4° (c 0.7, CHCl3); H NMR
(CDCl3) δ 1.14 (s, 6H), 1.45 (m, 4H), 2.30 (m, 2H), 4.90 (dd,
1H), 5.19 (d, 2H), 7.30 (m, 5H), 7.74 (m, 2H), 7.86 (m, 2H); 13
C
NMR (CDCl3) δ 20.88, 29.00, 29.17, 42.78, 52.13, 67.35, 70.47,
123.44, 127.95, 128.19, 128.41, 131.66, 134.11, 167.66, 169.14.
The above reactions were also executed in greater scale (0.4
mol) with no discernible difference in yield.
(S)-2-P h t h a lim id o-6-m et h yl-6-a zid oh ep t a n oic Acid ,
P h en ylm eth yl Ester (6). A solution of alcohol 5 (144.3 g,
364.9 mmol) and azidotrimethylsilane (63.06 g, 547.3 mmol)
in dry CH2Cl2 (2.2 L) at room temperature under argon was
treated with neat BF3‚OEt2 (67.32 g, 474.4 mmol). After
stirring for 5 days, the resulting solution was quenched with
water (1.5 L). The organic layer was separated, washed with
saturated NaHCO3, water, and brine, then dried (MgSO4), and
concentrated in vacuo. The residue was flash-chromatographed
(1:3 EtOAc:hexane as eluant) to afford azide 6 (124.9 g, 81%)
as a light-yellow oil: TLC Rf 0.35 (35:65 EtOAc:hexanes); [R]D
-9.2° (c 0.6, CHCl3); 1H NMR (CDCl3) δ 1.20 (s, 6H), 1.45 (m,
4H), 2.30 (m, 2H), 4.90 (dd, 1H), 5.19 (d, 2H), 7.30 (m, 5H),
7.74 (m, 2H), 7.86 (m, 2H), 13C NMR (CDCl3) δ 20.97, 25.67,
25.92, 28.80, 40.53, 52.02, 61.16, 67.40, 123.47, 127.97, 128.23,
128.43, 131.66, 134.14, 135.12, 167.60, 169.01.
(S)-Hexa h yd r o-6-p h th a lim id o-2,2-d im eth yl-2H-a zep in -
7-on e (7). A solution of azide 6 (124.8 g, 296.8 mmol) and 10%
Pd/C (32 g) in dry DMF (2.0 L) was hydrogenated (balloon)
for 24 h. After completion of the reaction, argon was bubbled
through the mixture to remove excess hydrogen, and methyl
sulfide (2.6 mL) was added to poison the palladium catalyst.
To this solution was added 1-hydroxybenzotriazole hydrate
(CDCl3) δ 1.66 (m, 2H), 2.40 (m, 4H), 4.90 (dd, 1H), 5.18 (d,
2H), 7.35 (m, 5H), 7.74 (m, 2H), 7.86 (m, 2H), 9.72 (s, 1H); 13
C
NMR (CDCl3) δ 18.66, 27.99, 42.87, 51.83, 67.47, 123.50,
128.00,128.26, 128.44, 131.58, 134.21, 135.04, 167.55, 168.80,
201.31.
The crude aldehyde was redissolved in dry CH2Cl2 (170 mL),
chilled to 0 °C, and then treated dropwise with Me3Al (2.0 M
in hexanes, 20.0 mL).9 After 20 min, additional Me3Al solution
(5.0 mL) was added, and stirring was continued for 10 min.
The mixture was cautiously quenched by the addition of
saturated NH4Cl and then partitioned between Et2O and H2O.
The aqueous layer was back-extracted with EtOAc, and the
pooled organic extracts were washed with brine, dried (Na2-
SO4), filtered, and concentrated in vacuo to give a near-

310 J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 2
Robl et al.
(HOBT; 46.74 g, 346 mmol) followed by ethyl-3-(3-dimethyl-
amino)propylcarbodiimide hydrochloride salt (EDAC; 68.74 g,
360 mmol). After stirring at room temperature under argon
for 3.5 h, the reaction was diluted with EtOAc (2 L) and filtered
through a pad of Celite. The filtrate was washed in succession
with 0.5 N aqueous HCl, saturated NaHCO3, and brine, then
dried (MgSO4), and concentrated in vacuo to give a gum.
Trituration with 2:1 Et2O:hexanes afforded pure lactam 7 (74.5
g, 88%) as a white solid: TLC Rf 0.35 (3:7 EtOAc:hexanes);
EtOAc (3 × 1.2 L). The EtOAc extracts were combined, washed
with water, saturated NaHCO3, and brine, then dried (Na2-
SO4), and concentrated in vacuo. Flash chromatography (1.6
kg of SiO2, 35:65 EtOAc:hexanes as eluant) afforded the
penultimate coupled intermediate (54.5 g, 92%) as a gum: TLC
1
Rf 0.20 (4:6 EtOAc:hexanes); H NMR (CDCl3) δ 1.28 (t, 3H),
1.35 (s, 3H), 1.43 (s, 3H), 1.46 (m, 1H), 1.92 (m, 4H), 2.13 (m,
1H), 3.01 (dd, 1H), 3.30 (dd, 3H), 4.00 (d, 1H), 4.22 (q, 2H),
4.28 (d, 1H), 4.32 (d, 2H), 4.74 (m, 1H), 7.24 (s, 5H), 7.40 (m,
1H); 13C NMR (CDCl3) δ 14.03, 20.00, 27.78, 29.65, 30.26,
30.57, 36.75, 39.85, 46.67, 48.15, 52.14, 58.90, 60.98, 126.66,
128.25, 129.12, 137.51, 168.84, 170.04, 172.38, 178.00.
1
mp 193-194 °C; [R]D +58.5° (c 1.2, CHCl3); H NMR (CDCl3)
δ 1.30 (s, 3H), 1.45 (s, 3H), 1.74 (m, 2H), 1.96 (m, 3H), 2.74
(m, 1H), 4.98 (d, 1H), 6.00 (s, 1H), 7.20 (m, 2H), 7.85 (m, 2H);
13C NMR (CDCl3) δ 23.89, 26.65, 29.58, 33.32, 40.68, 52.69,
54.51, 123.34, 123.15, 133.87, 168.06, 171.03. Anal. Calcd for
A chilled (0 °C, ice bath) solution of the above coupling
product (54.5 g, 121.5 mmol) in CH3OH (400 mL, oxygen
purged via argon bubbling) was treated dropwise with a
solution of 1.0 N NaOH (688 mL, previously sparged with
argon). After addition was complete, the ice bath was removed,
and the reaction was stirred for an additional 5.5 h. The
mixture was continuously purged with argon during the
reaction sequence. The resulting solution was carefully acidi-
fied to pH 2 with 6.0 N HCl and extracted with EtOAc (3 × 1
L). The EtOAc extracts were combined, washed with brine,
dried (Na2SO4), and concentrated in vacuo to give a foam.
Trituration with 1:1 Et2O:hexane afforded a white solid which
was filtered, washed with water and Et2O, and dried under
high vacuum to afford 1g (BMS-189921; 43.6 g, 95%): TLC Rf
0.61 (2:98 HOAc:EtOAc); [R]D -18.9° (c 0.38, CHCl3); mp 173-
C
16H18N2O3: C, 67.12; H, 6.34; N, 9.78. Found: C, 66.83; H,
6.31; N, 9.74.
(S)-Hexa h yd r o-7,7-d im eth yl-3-[(tr ip h en ylm eth yl)a m i-
n o]-2H-a zep in -2-on e (8). A solution of lactam 7 (74.5 g, 260.2
mmol) in CH3OH (900 mL) and CH2Cl2 (250 mL) at room
temperature under argon was treated with hydrazine mono-
hydrate (18.24 g, 364.3 mmol). After 48 h, the precipitate was
removed by filtration, and the filtrate was concentrated in
vacuo to give a solid (≈41 g). The solid was dissolved in CH2-
Cl2 (2 L) and subsequently treated with triethylamine (50 mL)
and triphenylmethyl chloride (83.41 g) at room temperature.
After stirring for 1.5 h, the resulting slurry was diluted with
EtOAc, washed with water and brine, dried (MgSO4), and
concentrated in vacuo to give a gum. Trituration with Et2O:
pentane afforded compound 8 (100.1 g, 96%) as a white solid:
1
177 °C; H NMR (CDCl3) δ 1.39 (t, 3H), 1.43 (s, 3H), 1.53 (m,
1H), 1.96 (m, 6H), 3.04 (dd, 1H), 3.25 (dd, 1H), 3.58 (m, 1H),
4.02 (d, 1H), 4.32 (d, 1H), 4.79 (m, 2H), 7.24 (m, 5H), 7.68 (m,
2H); 13C NMR (CDCl3) δ 20.04, 27.83, 29.57, 30,50,39.66, 41.14,
44.53, 46.65, 52.05, 59.07, 126.78, 128.27, 129.32, 137.43,
171.06, 172.88, 174.14. Anal. Calcd for C19H26N2O4S: C, 60.30;
H, 6.92; N, 7.40; S, 8.47. Found: C, 60.16; H, 7.06; N, 7.06; S,
8.10.
1
TLC Rf 0.53 (6:4 EtOAc:hexanes); H NMR (CDCl3) δ 1.00 (s,
3H), 1.10 (s, 3H), 1.46 (m, 6H), 3.36 (m, 1H), 4.03 (m, 1H),
5.20 (d, 1H), 6.00 (s, 1H), 7.20 (m, 2H), 7.85 (m, 2H); 13C NMR
(CDCl3) δ 22.86, 25.81, 33.50, 34.23, 40.16, 51.97, 55.60, 71.89,
126.22, 127.61,128.96, 146.48, 176.71.
(S)-6-Am in oh exa h yd r o-2,2-d im eth yl-7-oxo-1H-a zep in e-
1-a cetic Acid Eth yl Ester (9). To a well-stirred solution of
lactam 8 (50 g, 125 mmol) in dry THF (1.02 L) at room
temperature was added simultaneously and at the same rate
a solution of lithium bis(trimethylsilyl)amide (1.0 M solution
in THF, 627.3 mL, 627.3 mmol) and ethyl bromoacetate (104.8
g, 627.3 mmol) in THF (523 mL) over a 1-h period. After
stirring for 30 h, the reaction was quenched with saturated
NH4Cl (1.0 L) and extracted with EtOAc (3 × 700 mL). The
EtOAc extracts were combined, washed with saturated NaH-
CO3 and brine, dried (MgSO4), and concentrated in vacuo to
afford a black oil. The experiment was repeated on the same
scale to give a similar result. The combined oils were flash-
chromatographed (1:4 EtOAc:hexanes as eluant) to give the
impure alkylated lactam as a light-yellow oil. The oil was
dissolved in dry CH2Cl2 (2 L) and treated with trifluoroacetic
acid (78 mL) at room temperature. After 1 h the solvent was
removed by rotary evaporation, and the residue was dissolved
in 1.0 N aqueous HCl (400 mL) and washed with Et2O (2 ×
400 mL, discarded). The aqueous layer was carefully neutral-
ized to pH 7-8 with solid NaHCO3 (foaming!!) and extracted
with CH2Cl2 (3 × 1.2 L). The CH2Cl2 extracts were combined,
dried (Na2SO4), and concentrated in vacuo to afford pure amine
9 (51.5 g, 85%) as a light-brown oil: TLC Rf 0.30 (8:1:1 CH2-
Cl2:CH3OH:AcOH); 1H NMR (CDCl3) δ 1.28 (t, 3H), 1.36 (s,
3H), 1.38 (s, 3H) 1.60 (m, 1H), 1.90 (m, 5H), 3.75 (m, 1H), 4.00
(d, 1H), 4.22 (q, 2H), 4.28 (d, 2H); 13C NMR (CDCl3) δ 14.00,
20.06, 28.19, 30.07, 32.29, 39.98, 46.87, 53.20, 58.38, 60.73,
170.35, 177.06.
Ack n ow led gm en t. We gratefully acknowledge Dr.
Edward W. Petrillo and Dr. J ames Powell for their
contributions to this project.
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