From peptide to non-peptide. 3. Atropisomerie GPIIbIIIa antagonists containing the 3,4-dihydro-1H-1,4-benzodiazepine-2,5-dione nucleus

Article abstract of DOI:10.1021/jm960652r

The benzodiazepinedione class of non-peptidal GPIIbIIIa antagonists has been modified to allow the isolation of noninterconverting rotational isomers, or atropisomers, with the aim of examining their structure-activity relationships as compared to active

Full text of DOI:10.1021/jm960652r

J . Med. Chem. 1997, 40, 717-729
717
F r om P ep tid e to Non -P ep tid e. 3. Atr op isom er ic GP IIbIIIa An ta gon ists
Con ta in in g th e 3,4-Dih yd r o-1H-1,4-ben zod ia zep in e-2,5-d ion e Nu cleu s
Brent K. Blackburn,* Arthur Lee,* Mark Baier, Benjamin Kohl, Alan G. Olivero, Regina Matamoros,
Kirk D. Robarge, and Robert S. McDowell
Department of Bioorganic Chemistry, Genentech, Inc., 460 Pt. San Bruno Boulevard, South San Francisco, California 94080
Received September 17, 1996X
The benzodiazepinedione class of non-peptidal GPIIbIIIa antagonists has been modified to allow
the isolation of noninterconverting rotational isomers, or atropisomers, with the aim of
examining their structure-activity relationships as compared to active RGD-containing peptides
and other non-peptidal antagonists. Resolution of these antagonists was accomplished by the
introduction of a tert-butyl group at N1 and a chlorine at C9 on the 3,4-dihydro-1H-1,4-
benzodiazepine-2,5-dione nucleus and enantiospecific substitution on the â-alanine side chain
attached to N4. The relative configuration was determined by single-crystal X-ray analysis.
Further, conformational analyses using ab initio calculations were performed to assess the
conformational preferences about the â-alanine side chain. The data support a good
topographical correlation between the benzodiazepinedione class of antagonists and the “cupped”
presentation of the RGD tripeptide sequence found in the cyclic peptide G4120. The relationship
between these compounds with other peptidal and non-peptidal antagonists is discussed.
In tr od u ction
Proteins and peptides containing the tripeptide se-
quence Arg-Gly-Asp (RGD) have been shown to inhibit
the adhesive and aggregatory functions of platelets by
binding to platelet receptor GPIIbIIIa, whose natural
ligands are fibrinogen and von Willebrand factor.1,2
Fibrinogen binding to GPIIbIIIa represents the final
common event that leads to platelet aggregation regard-
F igu r e 1. Benzodiazepinedione GPIIbIIIa antagonist com-
pound 1.
less of platelet activation and, in certain circumstances,
is the primary cause of a variety of human cerebral and
cardiovascular diseases.3,4
We have reported on the design, synthesis,5 and
structural characterization6 of the RGD-containing cy-
clic peptide G4120 (cyclo-[-S(O)-Ac-Tyr-Arg-Gly-Asp-
Cys-OH]), a potent GPIIbIIIa antagonist. Based on a
1
model derived from the H NMR structure determina-
tion of G4120 and ensemble molecular dynamics simu-
lation of a series of GPIIbIIIa antagonists that included
G4120,7 a series of non-peptidal antagonists were
designed.8 These compounds utilize the benzodiaz-
epinedione nucleus (e.g., 1, Figure 1) to reproduce the
“cupped” shape of the RGD sequence observed in the
F igu r e 2. Stereoview of the 1H NMR structures of cyclo-[-
S(O)-Ac-Tyr-Arg-Gly-Asp-Cys-OH] (G4120). The RGD tripep-
tide sequence is highlighted in dark gray.
solution structure of G4120 (Figure 2).6 The neutral-
izing antibody OPG2 binds specifically to GPIIbIIIa and
features an RYD sequence in a similar conformation.9
Deviation from this topography by forcing an extended
conformation in the peptide or non-peptidal equivalent
resulted in a loss of activity.7,8,10,11 In contrast, several
investigators have reported that the RGD sequence in
potent RGD-containing cyclic peptides adopts an ex-
tended conformation as determined by 1H NMR and
X-ray crystallographic techniques.12-15 Indeed, com-
pounds designed to mimic the extended C7 conformation
of a potent RGD cyclic peptide led to the discovery of
other novel GPIIbIIIa antagonists based on the benzo-
diazepine nucleus.16
1
tional states (Figure 3).17 The H NMR spectrum of 1
showed an AB quartet for the methylene protons at
position 3 of the seven-membered ring indicating that
interconversion of the two possible rotational isomers
1
is slow on the H NMR time scale.8 It was determined
by variable temperature 1H NMR for compound 1 (D2O)
that the energy barrier between these two enantiomeric
states is 17 kcal/mol (Tc ) 343K).18 Of the two possible
ring conformations shown in Figure 3, A correlates well
with the fold and steric constraints of the cyclic peptide
G4120, whereas B does not.8 In order to assess the
differential GPIIbIIIa binding affinities of these two
isomers and attempt to provide support for the struc-
tural hypothesis that led to the design of the benzo-
diazepinedione class of GPIIbIIIa antagonists, a pair
of noninterconverting rotational isomers, or atropiso-
Benzodiazepinediones are known to exist as a mixture
of two slowly interconverting enantiomeric conforma-
* Author to whom correspondence should be addressed.
X Abstract published in Advance ACS Abstracts, February 1, 1997.
S0022-2623(96)00652-8 CCC: $14.00 © 1997 American Chemical Society

718 J ournal of Medicinal Chemistry, 1997, Vol. 40, No. 5
Blackburn et al.
odology described by Meyers was examined.25 Reaction
of the 2-oxazolinoanisole 17 with the lithium tert-
butylamide provided the N-tert-butylaniline 18 in mod-
erate yield. Unfortunately, efforts to hydrolyze the
oxazoline group resulted in the complete removal of the
tert-butyl group (Figure 5).
Preparation of the anthranilic acid 4 was accom-
plished in a two-step synthesis from p-iodofluorobenzene
(19) applying methodology previously employed by
Bridges et al. (Figure 6).26 Coupling of the enantio-
merically pure ethyl (S)-3-aminobutanoate21 to 4 fol-
lowed by acylation with bromoacetyl bromide and ring
closure afforded a diastereomeric pair of 7-iodobenzo-
diazepinediones 6c (Scheme 1). These two isomers were
separable by column chromatography but equilibrated
to a 1:1 mixture at room temperature within 24 h as
1
detected by H NMR analysis. The mixture of iodoare-
F igu r e 3. Atropisomeric conformers of the benzodiazepinedi-
one GPIIbIIIa antagonists with â-alanine rotated endo to the
aromatic ring. The guanidine surrogate has been abbreviated
to “guan”.
nes 6c were coupled with ethynylbenzamidine and
hydrolyzed to yield 7 as a mixture of diastereoisomers.
The diastereomeric pair was separated by RP-HPLC but
again equilibrated at room temperature (1H NMR).
Syntheses of the 9-chlorobenzodiazepinedione analogs
8-12 were accomplished by allowing the anilines 5b-d
to react with chlorine in acetic acid followed by the
standard sequence to form the seven-membered ring
and attachment of ethynylbenzamidine (Scheme 1).
Although the two possible diastereoisomers shown as
compound 8 could be separated by column chromatog-
1
raphy, a 1:1 mixture was detected by H NMR within
F igu r e 4. Benzodiazepinedione atropisomers.
24 h. In contrast, the diastereoisomers of the iodoarene
intermediates 6e,f could be separated by column chro-
matography to give (-)-6e, (+)-6e, (-)-6f, and (+)-6f and
elaborated individually into the desired amidino acid
derivatives 9-12, respectively. No equilibration of the
compounds 6e,f or the products 9-12 could be detected
mers,19 were prepared and evaluated for their in vitro
receptor antagonist and platelet antiaggregatory poten-
cies.
Ch em istr y
1
within 1 week at room temperature by H NMR analy-
Syn th esis. The isolation of a pair of atropisomers
has been reported for the structurally related 1,4-
benzodiazepines by incorporation of the sterically de-
manding tert-butyl substituent at N1 (Figure 4).20
Accordingly, our first attempt toward the preparation
of noninterconverting rotational isomers included the
incorporation of a tert-butyl group at the N1 position of
the benzodiazepinediones.
sis. Compounds (-)-6e and (-)-6f were converted into
the ethynylbenzonitrile adducts (S)-(-)-13 and (R)-
(-)-13 (Scheme 1), respectively, whose relative configu-
rations were assigned by X-ray crystallography (vida
infra).
Assa ys. Compounds were evaluated for their inhibi-
tory potency first in an ELISA (enzyme-linked immu-
nfluorencent solid-phase assay)-based system that mea-
sures the association of soluble GPIIbIIIa with fibrinogen
coated on a microtiter plate.5 Potent molecules were
further evaluated for inhibition of platelet aggregation
of human platelets in platelet rich plasma (PRP; 300 000
platelets/µL) stimulated with ADP (17.5 µM)5 and, on
selected compounds, with the thrombin receptor agonist
peptide (TRAP; 20 µM).27 The potency data for com-
pounds 1-3, 7-12 can be found in Table 1.
To aid the separation of the two possible enantiomeric
atropisomers, a stereogenic center on the â-alanine side
chain of 1 (at C11) was introduced to yield distinguish-
able diastereoisomers. The effect of stereogenicity at
C11 on the relative binding affinity was evaluated prior
to the introduction of the N1-tert-butyl group. Thus,
compounds 2 and 3 (R1, R2 ) Me, X ) H) were prepared
by methods shown in Scheme 1. The iodo-N-methyl-
isatoic anhydride8 was allowed to react with ethyl (R)-
or (S)-3-aminobutanoate21 followed by acylation with
bromoacetyl bromide and ring closure with base to yield
6a ,b, respectively. Incorporation of the benzamidine
moiety can be accomplished via palladium-mediated
coupling with 4-ethynylbenzamidine (15) or 4-ethynyl-
benzonitrile (16) followed by stepwise elaboration of the
nitrile into the amidine to furnish 2 and 3, as previously
described.8 Hydrolysis of the resulting amidino ester
yields the desired amidino acid adducts. Scheme 2
shows the methods used to prepare 15 and 16 from
Va r ia ble Tem p er a tu r e (VT) 1H NMR. Variable
1
temperature H NMR experiments were conducted on
compounds 1, 7, 8, and (S)-(-)-13 using a Varian 300
MHz instrument in either DMSO-d6 or tetramethylene-
1
d8 sulfone. Variable temperature H NMR experiments
on compounds 9-12 resulted in decomposition. There-
fore, to assess the barrier to ring inversion for com-
pounds substituted R1 ) Me, R2 ) But, X ) Cl, the var-
iable temperature experiments were conducted on the
nitrile ester (S)-(-)-13. The temperature of coalescence
1
1
4-bromobenzonitrile.22,23 Inspection of the H NMR of
was estimated by examination of the H NMR spectra
taken at temperatures ranging from 25 to 200 °C.
X-r a y Cr ysta llogr a p h y. Large, clear, colorless,
columnar crystals of compound (S)-(-)-13 were obtained
by slow crystallization from methylene chloride and
2 and 3 indicated two interconverting conformers in a
ratio of 3:1 (1H NMR, D2O).24
In an exploratory reaction to introduce the N1-tert-
butyl group, nucleophilic aromatic substitution meth-

Atropisomeric GPIIbIIIa Antagonists
J ournal of Medicinal Chemistry, 1997, Vol. 40, No. 5 719
Sch em e 1. Synthesis of Benzodiazepinedionesa
a
(a) DMF or CH2Cl2, Et3N, DMAP; (b) EDC, HOBT, Et3N; (c) Cl2, AcOH; (d) i. BrCH2COBr, ii. Cs2CO3, DMF or DBU, CH2Cl2 or
C6H5CH3; (e) Pd(II), Cu(I), Et3N, 15, DMF; (f) LiOH; (g) Pd(II), Cu(II), Et3N, 16, EtOAc.
Sch em e 2. Synthesis of 4-Ethynylbenzamidine and
4-Ethynylbenzonitrilea
F igu r e 6. Synthesis of N-tert-butyl-5-iodoanthranilic acid.
signed idealized locations and were included in struc-
ture factor calculations but were not refined.
Con for m a tion a l An a lysis. Relative energies of
a
rotamers about the N4-C11 and C11-C12 bonds were
calculated to ascertain whether steric interactions due
to methyl substitution at C11 would be expected to
influence the conformational profile of the â-alanine side
chain. Models of (S)-(-)-9, (R)-(-)-12, and the des-
methyl analog (R1 ) H, R2 ) But, X ) Cl) were
constructed in which the ethynylbenzamidine side chain
was replaced by a hydrogen. Approximate local minima
were obtained by systematically searching about the
C3-N4-C11-C12 and N4-C11-C12-C(carboxylate)
bonds at 10° intervals using SYBYL (Tripos Associates,
St. Louis, MO), followed by energy minimization using
MM2.28 Each of the resulting structures was further
refined by optimization at the 6-31G* 29 level using
Gaussian-94.30
(a) Pd(II), Cu(I), Et3N, trimethylsilylacetylene, EtOAc; (b) i.
H2S, pyridine, ii. MeI, iii. NH4OAc, EtOH; (c) K2CO3, MeOH.
F igu r e 5. Attempt to prepare N-tert-butylanthranilic acid.
hexanes. Colorless, platelike crystals of compound (R)-
(-)-13 were obtained by slow crystallization from hex-
anes. The structures (S)-(-)-13 (3495 unique reflec-
tions) and (R)-(-)-13 (10 636 unique reflections) were
solved by direct methods. Hydrogen atoms were as-
Resu lts a n d Discu ssion
To assess the effect of chiral substitution at C11 on
potency, compounds 2 and 3 were prepared and tested

720 J ournal of Medicinal Chemistry, 1997, Vol. 40, No. 5
Ta ble 1. Activity of Benzodiazepinedione Analogs
Blackburn et al.
In our pursuit for noninterconverting rotational iso-
mers, or atropisomers, it was postulated that the
presence of an atom ortho to the N1 group would further
increase the barrier to ring inversion. As a control, the
N1-methyl-C9-chloro analog 8 was produced to assess
the effect on potency of a chlorine atom at position 9.
As expected, the incorporation of a chlorine atom at C9
significantly increases the barrier to interconversion as
1
compared to the deschloro analogs (VT H NMR, 8 Tc
) 473 K, ∆Gq ) 23 kcal/mol, 2 and 3 Tc ) 343 K, ∆Gq
) 17 kcal/mol). However, the diastereoisomers of 8 also
equilibrated to a 1:1 mixture in 24 h at room temper-
ature after isolation by reverse-phase chromatography,
IC50 (µM)a
ELISA ADP TRAP
0.011
[R]D
entry compd
R1
R2
X
(deg)
1
2
3
4
5
6
7
8
9
1b
2
3
7
8
9
10
11
12
H
Me
H
H
H
H
NA
0.12
0.82
0.213
(R)-Me Me
(S)-Me Me
(S)-Me But
+32.6 0.060
consistent with the calculated half-life of interconversion
-37.0 0.005
0.078 0.138
298K
(t1/2
) 2.6 h).36,37 The potency data for 8 indicate
+14.2c 0.003d, 0.012e 0.092c
(S)-Me Me Cl -24.5c 0.007c
(S)-Me But Cl -85.5 0.002
(S)-Me But Cl +71.3 0.14
(R)-Me But Cl -71.1 0.018
(R)-Me But Cl +90.7 0.065
0.159c 0.313
that the effect of C9 substitution with a chlorine atom
is marginal (Table 1, entry 5). In contrast to 6c, 7, and
8, the N1-tert-butyl-9-chloro-substituted molecules 9, 10,
(-)-6e, and (+)-6e showed no signs of equilibration over
1 week at room temperature (1H NMR, RP-HPLC). The
R-substituted atropisomers 11 and 12 were similarly
prepared and also remained configurationally stable.
0.034 0.060
1.5
1.3
1.3
a
Data are presented as an average of at least n ) 3 unless
otherwise noted. The standard deviation (SD) was always (25%
of the mean for the ELISA assay and (20% for the PRP and TRAP
platelet aggregation assays. b Data for compound 1 was taken from
Upon assay, marked differences in the potencies of
the atropisomers 9-12 were observed (Table 1, entries
6-9). The relative stereochemistry of the more potent
analog (entry 6) and its diastereomer (entry 8) was
assigned by X-ray crystallography of the benzonitrile
ethyl ester analogs (S)-(-)-13 and (R)-(-)-13, respec-
tively. Attempts to obtain X-ray quality crystals of 9
or 11, or their ethyl ester, were unsuccessful.
d
ref 8. c A 1:1 mixture of diastereoisomers. A 3:1 mixture enriched
in the faster eluting diastereoisomer (n ) 1). e A 1:3 mixture
enriched in the slower eluting diastereoisomer (n ) 1).
in the protein-protein assay (ELISA) and physiologi-
cally relevant (PRP) platelet aggregation assay. The
more potent mixture of interconverting diastereoisomers
results from the (S)-â-methyl derivative 3, which is 10-
fold more potent than its enantiomer 2 (Table 1, entries
2 and 3). The absolute configuration of the more potent
C11-substituted enantiomer is in contrast to the ster-
eochemical preference observed for peptidal31 and other
non-peptidal GPIIbIIIa antagonists (Figure 7).32-35 For
example, substitution of the L-aspartic acid residue in
RGD-containing peptides with the D-enantiomer results
in reduced binding potency.31
The asymmetric unit of (S)-(-)-13 consists of a single
molecule (Figure 8A). The â-alanine side chain is
orientated exo to the benzodiazepinedione core with a
C3-N4-C11-C12 dihedral angle of 57.3°. By contrast,
the asymmetric unit of (R)-(-)-13 contains two non-
identical molecules packed in layers with interlocking
ethynylbenzonitrile side chains (Figure 8B); the layers
are separated by a molecule of hexane. The two (R)-
(-)-13 molecules differ primarily in the â-alanine side
chain conformations, having C3-C4-C11-C12 dihedral
angles of -74.3° and -66.3°, respectively. No abnormal
bond lengths or angles were observed for either com-
pound. Both (S)-(-)-13 and (R)-(-)-13 feature the same
atropisomer: the rms deviation of the benzodiazepine
cores of (S)-(-)-13 and the two molecules of (R)-(-)-13
are 0.049 and 0.072 Å, respectively. Atomic coordinates
are available as Supporting Information.
One interpretation of this apparent anomalous result
for 3, based on aqueous-phase conformational prefer-
1
ences observed by the H NMR which indicated a 3:1
ratio of the two interconverting isomers, is that asym-
metric substitution at C11 influences the ratio of
rotational isomers of the seven-membered ring such that
the (S)-methyl derivative benefits the isomer that is
productive for binding to GPIIbIIIa whereas the (R)-
methyl derivative stabilizes the isomer that is unpro-
ductive for protein binding. Alternatively, these results
may be accounted for by subtle variation in the rota-
tional preferences in the â-alanine side chain upon
substitution at C11 (vida infra).
The results of the ab initio optimizations are sum-
marized in Table 2. The optimized benzodiazepinedione
cores adopt the extreme “boat” configuration and were
virtually superimposible with the X-ray structures
of (S)-(-)-13 and (R)-(-)-13. The â-alanine side chain
of the desmethyl analog displays little conformational
preference: all six local minima (exo and endo confor-
mations of the N4-C11 bond, each with three staggered
rotamers about the C11-C12 bond) are within ∼1 kcal/
mol of each other. Both (R)- and (S)-methyl substitution
at C11 imparts a slight preference for the endo orienta-
tion about the N4-C11 bond by 1.6 kcal/mol and 1.3
kcal/mol, respectively. The energetics of the C11-C12
rotamers are significantly impacted by methyl substitu-
tion at C11, as expected for substitution of a central
atom of an sp3-sp3 bond. Interestingly, the global
minimum of the R-substituted molecule was 1.1 kcal
higher in energy than the global minimum of the
S-substituted molecule. Since the R-substituted mol-
To increase the barrier to interconversion of the two
interconverting diastereoisomers, the N1-tert-butyl de-
rivative 7 was prepared and assayed. Although the
barrier to interconversion was increased compared to 3
1
(VT H NMR, 7 Tc > 498 K, ∆Gq > 23 kcal/mol; 3 Tc )
343 K, ∆Gq ) 17 kcal/mol), the two diastereoisomers,
which could be separated by reverse-phase chromatog-
raphy, equilibrated within 24 h. Samples enriched 3:1
in the faster eluting isomer at the time of assay (ELISA)
were shown to be more potent than samples enriched
in the slower eluting diastereoisomer (Table 1, entry 4).
These data are indicative of a stereochemical atropiso-
meric preference for GPIIbIIIa binding and that the
diminished conformational freedom imposed by the N1
substituent does not limit its capacity to bind to GP-
IIbIIIa.

Atropisomeric GPIIbIIIa Antagonists
J ournal of Medicinal Chemistry, 1997, Vol. 40, No. 5 721
F igu r e 7. Stereochemical relationship of compounds 2 and 3 with RGD-containing peptides and an example of a non-peptidal
antagonist.
Ta ble 2. Relative Energies of Rotomers about the N4-C11
and C11-C12 Bonds for a Model of Compounds 9 and 12 and
Their Corresponding C11 Desmethyl Analog
dihedral angle (deg)
C3-N4- N4-C11-
relative energy
C11-C12 C12-C(O) (kcal/mol) 6-31G*
conformer
(S)-(-)-13 X-ray
(R)-(-)-13A X-ray
(R)-(-)-13B X-ray
57.3
-74.3
-66.3
-102.6
-79.8
-91.5
90.8
80.0
83.2
-115.7
-91.9
-122.9
83.9
177.0
-52.0
-50.5
61.3
-69.1
174.8
73.1
-82.1
-178.9
63.5
-70.3
157.0
74.0
-112.1
165.9
64.1
-54.7
-176.3
66.6
R1 ) H
endo
endo
endo
exo
exo
exo
0.31
1.46
0.92
0.77
0.00
1.00
0.00a
5.06
1.53
2.76
6.05
1.30
0.00a
1.15
1.23
3.52
1.61
2.30
F igu r e 8. Stereoview of the X-ray crystal structure of (A)
compound (S)-(-)-13 and (B) compound (R)-(-)-13 (conformers
A and B and hexane).
ecule is the enantiomer of the ring-inverted S-substi-
tuted analog, these data suggest that the steric effect
induced by (S)-methyl substitution at C11 should sta-
bilize the atropisomer observed in the X-ray structures.
The stereochemical disposition of the more potent
atropisomer 9 correlates with conformer A in Figure 3
and is consistent with the “cupped” shape of the RGD
sequence observed in the NMR structure of G4120. To
ideally map to the peptide conformation, the â-alanine
side chain would be oriented endo to the fused ring
system, yet the crystal structure of (S)-(-)-13 shows an
exo orientation. In both (S)-(-)-13 and (R)-(-)-13, the
â-alanine ethyl ester is tightly stacked against the
benzonitrile aromatic rings of two neighboring molecules
(Figure 9). Given that neither (R)- nor (S)-methyl
substitution at C11 appears to induce a significant steric
preference for endo vs exo orientation, it is likely that
the orientation of the â-alanine side chain observed in
the crystal structures results primarily from packing
interactions.
R1 ) (S)-CH3 endo
endo
endo
exo
exo
48.4
63.3
exo
R1 ) (R)-CH3 endo
-103.2
-59.5
-71.9
105.0
129.3
122.7
endo
endo
exo
exo
exo
-69.2
-169.1
a
The gobal minima for the (S)-Me and (R)-Me compound had
energies of -1064.9695714 hartrees and -1064.9679437 hartrees,
respectively, suggesting the (S)-substitution favors the (-) atrop-
isomer by approximately 1 kcal/mol.
potency data for 11, which is locked into the same
conformation as 9, indicates that rotational preferences
about the C11-C12 bond also play a role in reducing
the potency for the C11 R-substituted benzodiazepinedi-
one analogs.
Of the reasons proposed for the C11 (S)-methyl analog
3 displaying greater potency than its enantiomer 2, the
results of the ab inito calculations are consistent with
the (S)-methyl derivative benefiting the conformer that
is productive for binding to GPIIbIIIa. However, the
Con clu sion
Synthesis, isolation, and characterization of the two
possible atropisomers of the benzodiazepinedione class
of GPIIbIIIa antagonists has been accomplished, in

722 J ournal of Medicinal Chemistry, 1997, Vol. 40, No. 5
Blackburn et al.
as C,H,N. X-ray crystallography instrumentation at the
University of California, Berkeley, College of Chemistry X-Ray
Crystallographic Facility (CHEXRAY) consists of two Enraf-
Nonius CAD-4 diffractometers, each equipped with a nitrogen-
flow low-temperature apparatus and controlled by a microVAX
II computer. Both use Enraf-Nonius software as described in
the CAD-4 Operation Manual, Enraf-Nonius, Delft, Nov. 1977,
and updated thereafter. Calculations were performed on DEC
MicroVax computers using locally modified versions of the
Enraf-Nonius MolEN structure solution and refinement pack-
age and other programs. Heavy atom positional parameters
for compounds (S)-(-)-13 and (R)-(-)-13, and selected bond
and torsion angles, can be found in Supporting Information.
All concentrations were performed on a Bu¨chi rotary evapora-
tor.
F igu r e 9. Stereoview of the expanded unit cell for compounds
(S)-(-)-13 (light gray) and (R)-(-)-13 (dark gray) showing the
packing near the â-alanine ethyl ester moiety.
Analytical thin-layer chromatography (TLC) was conducted
on Whatman silica gel 60A M254 MK6F glass-coated plates and
visualized by UV and/or charring with 0.2% ninhydrin in
ethanol. Silica gel (SiO2) 60 (230-400 mesh, E. Merck) was
used for all preparative (flash) column chromatography puri-
fications. High-pressure liquid chromatography (HPLC, UV
detection at 214 or 254 nM) solvent gradient methods are listed
below using the syntax (method: column, solvent gradient
range, flow rate, time (%CH3CN)). Gradient protocol A:
Microsorb-Short One C18, 4.6 × 100 mm, 0-100% CH3CN/
H2O (0.1% TFA), 1.5 mL/min, 0:00 (0%), 9:00 (100%), 9:10
(100%), 11:00 (0%). B: Dynamax 83-303-C5, 4.6 × 250 mm,
0-100% CH3CN/H2O (0.1% TFA), 1.5 mL/min, 0:00 (0%), 9:00
(100%), 11:10 (100%), 12:00 (0%). C: Dynamax-60A 83-221-C
C18, 21.4 (i.d.) × 25 mm, 0-50% CH3CN/H2O (0.1% TFA), 10
mL/min, 0:00 (0%), 46:00 (50%), 67:00 (50%), 72:00 (0%). D:
Vydac C18 300 Å, 5 × 26 cm, 0-81% CH3CN/H2O (0.5% HOAc),
12 mL/min, 0:00-6:00 load, 6:00 (0%), 10:00 (18.5%), 13:00
(31.5%), 26:00 (31.5%), 50:00 (42%), 66:00 (50%), 79:00 (50%),
82:00 (81%), 84:00 (81%), 90:00 (0%). E: Vydac C18 300 Å, 5
× 26 cm, isocratic : 20% CH3CN/H2O (0.5% AcOH), 10 mL/
min. F: Vydac C18 300 Å, 5 × 26 cm, 0-50% CH3CN/H2O
(0.5% AcOH), 12 mL/min, 0:00-6:00 load, 6:00 (0%), 12:40
(10%), 26:00 (20%), 67:00 (50%), 78:00 (50%), 82:00 (81%), 84:
00 (81%), 90:00 (0%). G: Microsorb-Short One C18, 4.6 × 100
mm, 0-100% CH3CN/H2O (0.1% TFA), 1.5 mL/min, same
method as B. H: Dynamax-60A 83-221-C C18, 21.4 (i.d.) × 25
mm, 0-60% CH3CN/H2O (0.1% TFA), 10 mL/min, 0:00 (0%),
7:00 (20%), 80:00 (60%), 90:00 (80%), 97:00 (80%), 100:00 (0%).
I: Dynamax-60A 83-221-C C18, 21.4 (i.d.) × 25 mm, 0-50%
CH3CN/H2O (0.1% TFA), 10 mL/min, 0:00 (0%), 5:00 (20%),
80:00 (50%), 90:00 (80%), 97:00 (80%), 100:00 (0%). Solvents
and reagents were purchased from commercial sources and
used as received.
which compound 9 represents a conformationally rigid
and potent GPIIbIIIa antagonist. The data reported
herein supports our original structural hypothesis that
led to the design and synthesis of the benzodiazepinedi-
one class of GPIIbIIIa antagonists, derived in part from
the solution-phase structure of the cyclic peptide G4120.8
1
A structural comparison between the H NMR struc-
ture of G4120, which exhibits a bend at the Gly
methylene, and the solution-phase structures deter-
mined for other potent RGD-containing cyclic peptides,
which are extended about the Gly residue, has been
reported and indicates a striking dissimilarity between
these classes of cyclic peptide antagonists.13 Although
each of these classes of cyclic peptides were indepen-
dently used in the de novo design of potent non-peptidal
antagonists, these results highlight the difficulty in
attempting to define a single molecular pharmacophore
for GPIIbIIIa binding,38 especially considering the dy-
namic characteristics of either the purified or platelet-
bound receptor39-44 or the potential of multiple binding
sites.45-46 Furthermore, the possibility of different yet
overlapping modes of receptor binding by the diverse
set of known antagonists can not be ruled out. Further
characterization of these antagonists for their inhibitory
potential on activated or nonactivated platelets or on
the receptor is therefore warranted.47 The pharmaco-
logical response that may result from these different
classes of GPIIbIIIa antagonists also remains to be
determined.48
N-ter t-Bu tyl-5-iod oa n th r a n ilic Acid (4). (a ) To a solu-
tion of diisopropylamine (27 g, 39 mL, 0.275 mol, 1.2 equiv) in
anhydrous THF (300 mL) at -78 °C was added n-BuLi (1.8 M
in hexanes, 135 mL, 0.25 mol, 1.1 equiv). After stirring for
15 min, the LDA solution was added via cannula to a solution
of 4-fluoro-1-iodobenzene (19) (50 g, 0.225 mol, 1 equiv) in THF
(200 mL) at -78 °C. After stirring for 30 min the mixture
was rapidly transferred to a vigorously stirred slurry of dry
ice in Et2O (1.5 L). The mixture was allowed to warm to 0 °C
and then transferred to a separatory funnel. The solution was
washed twice with H2O (1 L). The aqueous layer was acidified
with concentrated HCl until pH < 1 and extracted with Et2O.
The organic layer was washed with brine (1 L), dried (MgSO4),
filtered, and concentrated in vacuo. The resulting residue was
filtered, through a silica plug with 50% EtOAc/hexanes to yield
52.21 g (87%) of 2-fluoro-5-iodobenzoic acid (20) as a white
solid: mp 147-150 °C; TLC Rf ) 0.30 (50% EtOAc/hexanes);
Exp er im en ta l Section
Gen er a l Meth od s. Melting points were determined on a
Laboratory Devices Mel-Temp II melting point apparatus and
are uncorrected. Proton spectra were recorded on a Varian
VXR-300S spectrometer or Varian Unity Inova 400 NMR
spectrometer at 293 K unless noted. Carbon NMR were
recorded on a Varian VXR-300S spectrometer at 293 K unless
noted. Samples were prepared in either CDCl3, CD3OD,
DMSO-d6, or deuterium oxide (99.9% 2H atoms) purchased
from Cambridge Isotope. Chemical shifts were measured
relative to tetramethylsilane, at 0.0 ppm, HOD, at 4.85 ppm
(1H NMR), or CDCl3 and CD3OD (13C NMR). The 1H NMR
assignments are described with the abbreviations s (singlet),
d (doublet), t (triplet), q (quartet), p (pentuplet), m (multiplet),
and b (broad), and all coupling constants are reported in hertz.
13C NMR data are given with CDCl3 or CD3OD as the internal
lock. Optical rotations were performed on a Perkin-Elmer 241
polarimeter at room temperature at the indicated wavelength;
the concentrations are reported g/100 mL. High-resolution
mass spectra were obtained on
HX110HF tandem MS/MS instrument using the positive-ion
fast-atom bombardment (FAB) technique. C, H, and
analyses were conducted by Oneida Research Services, Whites-
boro, NY. Elemental analyses observed outside (0.4% of the
calculated values are listed with the characterization data.
Elemental analyses observed within (0.4% of the calculated
can be found in the Supporting Information and are noted here
4
4
1H NMR (CDCl3) 8.32 (1H, dd, J HF ) 6.8, J HH ) 2.2, ArH
C6-H), 7.86 (1H, m, ArH C4-H), 6.95 (1H, t, 3J HH ) 8.8, 3J HF
)
10.5, ArH C3-H); 13C NMR (CDCl3) 165.5, 163.9, 160.4, 143.4,
141.0, 120.5, 119.3, 199.0, 86.4; C,H,N.
a J EOL J MS-HX110HF/
(b) To a solution of tert-butylamine (36 g, 46 mL, 0.438 mol,
2.3 equiv) in THF (400 mL) at 0 °C was added via dropping
funnel n-BuLi (1.84 M in hexanes, 227 mL, 0.42 mol, 2.2
equiv). The burgundy solution was stirred for 1h at 0 °C and
then transferred via cannula to a solution of 20 in THF (400
mL) at -78 °C. The solution was stirred at -78 °C for 20 min,
and then the reaction was quenched with 1 N HCl (500 mL).
N

Atropisomeric GPIIbIIIa Antagonists
J ournal of Medicinal Chemistry, 1997, Vol. 40, No. 5 723
After warming to room temperature, the yellow mixture was
transferred to a separatory funnel, then extracted with EtOAc
(400 mL), washed with brine (1 L), dried (MgSO4), filtered,
and concentrated in vacuo. The crude material was purified
by eluting through a silica plug with 10% acetone/CH2Cl2
yielding 19.9 g (33%) of 4 as a pale yellow solid, mp 163-167
°C dec; Rf ) 0.30 (20% EtOAc/hexanes); 1H NMR (CDCl3) 8.29
42.2, 40.0, 29.5, 20.0, 14.2; LRMS (FAB, M + H) 434.2; HRMS
(FAB) m/ z calcd for C17H26N2O3I 433.0989 found 433.0966;
C,H,N.
N-[5-Iod o-2-(ter t-bu tyla m in o)ben zoyl]-3(R)-a m in obu -
ta n oic Acid , Eth yl Ester (5d ). Compound 5d was prepared
using the method shown for 5c substituting 3(R)-aminobu-
tanoic acid, ethyl ester hydrochloride, prepared by transes-
terification of the benzyl ester21 in ethanol, for the (S)-antipode.
Purification through a plug of silica gel eluting with 10% ethyl
acetate in hexanes afforded 5d in 47% yield as a slightly tan
solid: [R ]24589 +26.6°(c ) 3.95, CHCl3); HRMS (FAB) m/ z calcd
for C17H26N2O3I 433.0989, found 433.1004.
4
3
4
(1H, d, J HH ) 2.2, ArH C6-H), 7.56 (1H, dd, J HH ) 9.0, J HH
3
) 2.2, ArH C4-H), 6.78 (1H, d, J HH ) 9.0, ArH C3-H) 1.43 (s,
9H, But); 13C NMR (CDCl3) 172.7, 149.5, 142.7, 141.1, 116.8,
112.5, 74.6, 51.5, 29.4; LRMS (FAB, M + H) 320.2; HRMS
(FAB) m/ z calcd for C11H14N1O2 320.0148, found 320.0154;
C,H,N.
1-Meth yl-4-(3(R)-bu ta n oic a cid )-7-iod o-3,4-d ih yd r o-1H-
1,4-ben zod ia zep in e-2,5-d ion e, Eth yl Ester (6a ). To a
biphasic mixture of 5a (0.269 g, 0.69 mmol, 1 equiv) in CH2-
Cl2 (15 mL) and a solution of NaHCO3 (5 equiv) in water (100
mL) at 25 °C was added bromoacetyl bromide (30 equiv). The
layers were separated, and the aqueous layer was washed with
CH2Cl2 (50 mL). The combined organics were washed with
saturated NaHCO3 (50 mL), water (50 mL), and brine (50 mL),
then dried (MgSO4), filtered, and concentrated in vacuo. The
mixture of bromoacetanilides was dissolved in dry CH2Cl2 to
which DBU (0.105 mL, 0.69 mmol, 1.0 equiv) was added
dropwise at 25 °C. After 10 min the reaction mixture was
washed with 0.1 M HCl (50 mL), water (50 mL), and brine
(50 mL), then dried (MgSO4), filtered, and concentrated in
vacuo. The crude material was purified by flash chromatog-
raphy and recrystallized from EtOAc/hexanes to yield 6a in
N-[5-Iodo-2-(m eth ylam in o)ben zoyl]-3(R)-am in obu tan o-
ic Acid , Eth yl Ester (5a ). Compound 5a was prepared using
a modified version of the procedure previously reported,8
substituting CH2Cl2 for DMF and diisopropylethylamine (DI-
PEA) for triethylamine (Et3N), in 47% yield, [R]24 +25.0° (c
589
) 0.505, CHCl3). Analytical data (1H and 13C NMR, mp, TLC,
RP-HPLC, and HRMS) were identical with those obtained for
its enantiomer 5b.
N-[5-Iodo-2-(m eth ylam in o)ben zoyl]-3(S)-Am in obu tan o-
ic Acid , Eth yl Ester (5b). To a solution of 3(S)-aminobu-
tanoic acid, ethyl ester hydrochloride (7.58 g, 45.28 mmol, 1.0
equiv) and anhydrous CH2Cl2 (175 mL) in an oven-dried 24/
40 500 mL round bottom flask equipped with a stir bar at room
temperature under an atmosphere of argon were added with
5-iodo-N-methylisatoic anhydride8 (13.9 g, 45.87 mmol, 1.01
equiv) in 3 × 4.63 g portions, Et3N (11.53 mL, 82.6 mmol, 1.8
equiv), and (dimethylamino)pyridine (0.84 g, 0.15 equiv). The
turbid solution was stirred for 13 h to give a homogeneous
purple solution. The reaction was quenched by pouring the
mixture into a Erlenmeyer flask containing ice/10% citric acid.
The layers were separated, and the aqueous layer was
extracted additionally with dichloromethane. The dichlo-
romethane layers were combined, washed once with water and
once with brine, dried (MgSO4), filtered, and concentrated.
Flash chromatography (stepped gradient elution 10% then 30%
EtOAc/hexane) of the crude dark syrup followed by drying
under high vacuum (1.0 mmHg, 16 h) afforded 5b as a tan
60% yield (0.18 g), [R]24 +2.5°(c ) 0.48, CHCl3). Analytical
589
data (1H and 13C NMR, mp, TLC, RP-HPLC, and HRMS) were
identical with those obtained for its enantiomer 6b.
1-Meth yl-4-(3(S)-bu ta n oic a cid )-7-iod o-3,4-d ih yd r o-1H-
1,4-ben zod ia zep in e-2,5-d ion e, Eth yl Ester (6b). Com-
pound 6b was prepared using the procedure previously
reported.8 The reaction was quenched by the addition of 10%
citric acid and the mixture concentrated to a residue. The
residue was dissolved in ethyl acetate/water and transferred
to a separatory funnel. The layers were separated, and the
aqueous layer extracted additionally with ethyl acetate. The
combined ethyl acetate extracts were washed once with water
and once with brine, dried (MgSO4), filtered, and concentrated
to yield crude 6b. Flash chromatography (stepped elution
gradient 50% EtOAc/hexane then EtOAc) afforded pure 6b and
mixed fractions, of which 6b was the major component. The
mixed fractions were again chromatographed (same eluting
conditions) to afford additional pure 6b as a yellow solid, a
1:1 mixture of diastereomeric rotational isomers (CDCl3): 80%
solid (66%): mp 63-64.5 °C; [R]24 -23.6° (c ) 4.6, CHCl3);
589
TLC Rf ) 0.55 (30% EtOAc/hexane); RP-HPLC (method A) tR
4
) 6.63 min; 1H NMR (CDCl3) 7.52 (1H, d, J HH ) 2.0, ArH
3
4
C6-H), 7.49 (1H, dd, J HH ) 8.7, J HH ) 2.0, ArH C4-H), 7.46
3
(1H, m, NHCH3), 6.59 (1H, bd, J HH ) 7.3, CONHCH(CH3)),
3
6.40 (1H, d, J HH ) 8.5, ArH C3-H), 4.45 (1H, m, NCH(CH3)-
3
CH2), 4.19 (2H, q, J HH ) 7.0, OCH2), 2.83 (1.5H, s, NCH3),
2.81 (1.5H, s, NCH3), 2.60 (2H, dd, 2J HH ) 5.4, 3J HH ) 1.2, CH2-
CO2), 1.29 (3H, d, 3J HH ) 6.8, NCH(CH3)CH2), 1.27 (3H, t, 3J HH
) 7.1, CO2CH2CH3); 13C NMR (CDCl3) 171.54, 167.54, 149.81,
140.87, 135.34, 117.55, 113.30, 74.03, 60.69, 42.19, 40.06,
29.49, 20.00, 14.18; LRMS (FAB) m/ z 390 (M+), 390 (100),
259.9; HRMS (FAB) m/ z calcd for C14H20N2IO3 391.0519, found
391.0500; C,H,N.
yield; mp 136-137 °C; [R]24 -2.36° (c ) 3.8, CHCl3); TLC
589
Rf ) 0.09 (50% EtOAc/hexane); RP-HPLC (method A), tR
)
5.74 min; 1H NMR (CDCl3) 8.16 (0.5H, d, 4J HH ) 2.2, ArH C6-
H), 8.11 (0.5H, d, 4J HH ) 2.2, ArH C6-H), 7.76 (1H, dd, 3J HH
)
4
3
9.0, J HH ) 2.2, ArH C8-H), 6.90 (1H, d, J HH ) 9.0, ArH C9-
H), 5.19 (0.5H, m, NCH(CH3)CH2), 5.09 (0.5H, m, NCH(CH3)-
CH2), 4.10, 4.06 (2H, 2 overlapping q’s, 3J HH ) 7.0, OCH2), 3.79
(2H, ABq, 2J HH ) 15.5, δνAB ) 8.55, C3-H), 3.32 (3H, s, NCH3),
N-[5-Iod o-2-(ter t-b u t yla m in o)b en zoyl]-3(S)-a m in obu -
ta n oic Acid , Eth yl Ester (5c). To a solution of 4 (2.38 g,
7.5 mmol, 1 equiv) in CH2Cl2 at 25 °C were added diisopro-
pylethylamine (2.25 mL, 1.75 equiv) and then BOP reagent
(3.63 g, 8.2 mmol, 1.1 equiv). To this solution was added a
mixture (2.25 g, 13.4 mmol, 1.8 equiv) of 3(S)-aminobutanoic
acid, ethyl ester hydrochloride and diisopropylamine (3.5 mL,
3 equiv) in CH2Cl2 (15 mL). The reaction mixture was stirred
for 15 min then transferred to a separatory funnel, diluted
with CH2Cl2, and washed with 1 N HCl (50 mL), saturated
NaHCO3 (50 mL), and brine (50 mL). The organic layer was
dried (MgSO4), filtered, and concentrated in vacuo. The
resulting oil was further purified by passing through a silica
plug with 10% EtOAc/hexanes as the eluting solvent to yield
2.60 g (81%) of 5c as a slightly brown solid: mp 103-104 °;
2
3
2.79 (0.5H, dd, J HH ) 16.0, J HH ) 9.0, CH2CO2), 2.50 (1.5H,
3
m, CH2CO2), 1.33 (1.5H, d, J HH ) 6.8, NCH(CH3)CH2), 1.27
(1.5H, d, 3J HH ) 6.8, NCH(CH3)CH2), 1.23 (1.5H, t, 3J HH ) 7.0,
3
OCH2CH3), 1.19 (1.5H, t, J HH ) 7.0, OCH2CH3); 13C NMR
(CDCl3) 170.36, 170.26, 169.00, 168.85, 165.42, 165.24, 140.66,
140.62, 140.51, 140.33, 139.57, 139.48, 130.63, 130.47, 122.51,
122.37, 89.21, 89.17, 60.73, 60.50, 48.31, 47.93, 46.59, 45.89,
38.92, 38.48, 34.64, 34.59, 18.31, 18.09, 14.05; LRMS (FAB)
m/ z 431.0 (M + H)+ 431.0 (100); HRMS (FAB) m/ z calcd for
C16H20N2O4I 431.0468, found 434.0452; C,H,N.
1-(ter t-Bu tyl)-4-(3(S)-bu tan oic acid)-7-iodo-3,4-dih ydr o-
1H-1,4-ben zod ia zep in e-2,5-d ion e, Eth yl Ester (6c). Com-
pound 6c was prepared using a modified version of the
procedure shown for compound 6a , substituting 1 M potassium
phosphate buffer (pH ) 7) for the water and cooling to 0 °C
for the bromoacylation step. After treatment with DBU the
dichloromethane solution was poured into a separatory funnel,
and washed twice with water, dried over anhydrous Na2SO4,
and filtered, and the solvent was removed in vacuo. The crude
reaction mixture was submitted to flash chromatography (20%
ethyl acetate in hexanes, loaded with methylene chloride) to
TLC Rf ) 0.50 (20% EtOAc/hexanes); [R]24 -26.8° (c ) 1.2,
589
CHCl3); 1H NMR (CDCl3): 7.65 (1H, bs, NH), 7.54 (1H, d, 4J HH
4
3
) 2.2, ArH C6-H), 7.43 (1H, dd, J HH ) 2.2, J HH ) 9.3, ArH),
3
6.69 (1H, d, J HH ) 9.2, ArH C3-H), 4.46 (1H, m, NCH(CH3)-
3
3
CH2), 4.17 (2H, q, J HH ) 7.1, OCH2), 2.58 (2H, d, J HH ) 5.4,
CH2CO2), 1.37 (9H, s, But), 1.29 (3H, d, 3J HH ) 6.8, NCH(CH3)-
CH2), 1.28 (3H, t, J HH ) 7.08 OCH2CH3); 13C NMR (CDCl3)
3
171.6, 167.8, 148.0, 140.1, 136.0, 118.8, 116.8, 78.0, 60.7, 50.6,
yield 6c (92%): mp 124 °C; [R]24
+36.6°(c ) 1.5, MeOH);
589

724 J ournal of Medicinal Chemistry, 1997, Vol. 40, No. 5
RP-HPLC (method A) tR ) 6.38 min; 1H NMR (CDCl3) 8.06
Blackburn et al.
hexanes) to yield 1.42 g (88%) N-[3-chloro-5-iodo-2-(tert-
butylamino)benzoyl]-3(S)-aminobutanoic acid, ethyl ester as
4
4
(0.5H, d, J HH ) 2.2, ArH), 8.03 (0.5H, d, J HH ) 2.2, ArH),
4
3
3
7.72 (1H, dd, J HH ) 2.2, J HH ) 8.4, ArH), 6.94 (1H, bd, J HH
) 8.5, ArH), 5.31 (0.5H, m, NCH(CH3)CH2), 4.99 (0.5H, m,
NCH(CH3)CH2), 4.11 (2H, dq, 3J HH ) 7.0, 7.0, OCH2), 3.66 (2H,
a colorless syrup: TLC Rf ) 0.45 (20% EtOAc/hexanes); [R]24
589
1
3
+4.2° (c ) 2.5, CHCl3); H NMR (CDCl3) 9.05 (1H, d, J HH
)
4
8.0, CONH), 8.22 (1H, d, J HH ) 2.0, ArH C6-H), 7.78 (1H, d,
3
2
m, C3-H), 2.82 (1H, dd, J HH ) 6.5, J HH ) 15.87, CH2CO2),
4J HH ) 2.0, ArH C4-H), 4.47 (1H, m, NCH(CH3)CH2), 4.13 (2H,
2.52 (1H, m, CH2CO2), 1.44 (9H, s, But), 1.25 (3H, dt, J HH
)
q, J HH ) 7.1, OCH2), 3.63 (1H, bs, NH), 2.66 (1H, dd, J HH
)
)
3
3
2
7.1, 7.1, OCH2CH3), 1.27 (3H, d, NCH(CH3)CH2); 13C NMR
(CDCl3) 171.33, 170.96, 170.81, 170.58, 170.34, 170.22, 165.42,
165.18, 138.80, 138.75, 138.657, 138.04, 137.94, 134.22, 134.02,
127.97, 91.29, 91.25, 60.74, 60.55, 59.66, 59.58, 51.08, 49.15,
49.01, 48.95, 47.06, 39.06, 38.95, 29.43, 18.62, 17.87, 14.07;
HRMS (FAB) m/ z calcd for C19H26IN2O4 473.0973, found:
473.0935; C,H,N.
15.4, J HH ) 5.1, CHHCO2), 2.47 (1H, dd, J HH ) 15.6, J HH
3
3
2
3
6.6, CHHCO2), 1.30 (3H, d, J HH ) 6.8, NCH(CH3)CH2), 1.23
(3H, t, J HH ) 7.1, OCH2CH3), 1.17 (9H, s, But); 13C NMR
3
(CDCl3) 171.2, 164.8, 139.8, 139.4, 138.4, 134.8, 133.0, 87.6,
60.5, 57.7, 42.4, 40.3, 29.5, 19.6, 14.1; LRMS (FAB, M + H)
468.2; HRMS (FAB) m/ z calcd for C17H24N2O3ICl 467.0599,
found 467.0587.
(b) To a biphasic mixture of N-[3-chloro-5-iodo-2-(tert-
butylamino)benzoyl]-3(S)-aminobutanoic acid, ethyl ester (1.35
g, 2.9 mmol, 1 equiv) in CH2Cl2 (15 mL) and saturated
NaHCO3 (100 mL) at 25 °C was added via syringe pump over
1 h bromoacetyl bromide (17.51 g, 87 mmol, 30 equiv). The
layers were separated, and the aqueous layer was washed with
CH2Cl2 (50 mL). The combined organics were washed with
saturated NaHCO3 (50 mL), water (50 mL), and brine (50 mL),
then dried (MgSO4), filtered, and concentrated in vacuo. The
crude material was purified by flash chromatography (25%
EtOAc/hexanes) to yield a mixture of bromoacetanilides. This
mixture (1.58 g, 2.7 mmol, 1 equiv) was dissolved in dry CH2-
Cl2 to which DBU (0.49 g, 0.48 mL, 3.2 mmol, 1.2 equiv) was
added dropwise at 25 °C. After 10 min the reaction mixture
was washed with 0.1 M HCl (50 mL), water (50 mL), and brine
(50 mL), then dried (MgSO4), filtered, and concentrated in
vacuo. The crude material was purified by flash chromatog-
raphy to yield a 3:2 mixture of diastereoisomers. The faster
eluting isomer (-)-6e (0.73 g) was isolated as a white solid:
1-Meth yl-4-(3(S)-bu ta n oic a cid )-9-ch lor o-7-iod o-3,4-d i-
h yd r o-1H-1,4-ben zod ia zep in e-2,5-d ion e, Eth yl Ester (6d ).
(a ) To a solution of 5b (1.06 g, 2.7 mmol) in acetic acid (5 mL)
was added dropwise a solution of chlorine in acetic acid (3
mmol, prepared by bubbling Cl2(g) into AcOH). The reaction
mixture was stirred at room temperature for 2 h. A new
product (TLC Rf ) 0.5, 30% ethyl acetate in hexanes) was
determined to be present with a small amount of unreacted
starting material. An additional 0.3 mmol of chlorine in acetic
acid was added and the reaction mixture stirred an additional
30 min. The reaction mixture was partitioned between ethyl
acetate and water and the organic layer washed once with
water. The organic layer was dried over anhydrous sodium
sulfate and filtered, and the solvent was removed in vacuo.
The product was purified by flash chromatography (30% ethyl
acetate in hexanes) to obtain 1.07 g (93%) of N-[3-chloro-5-
iodo-2-(methylamino)benzoyl]-3(S)-aminobutanoic acid, ethyl
ester: mp 92 °C; RP-HPLC (method A) tR ) 6.34 min; [R]24
589
1
4
-4.84°(MeOH, c ) 0.8); H NMR (CDCl3) 7.89 (1H, d, J HH
)
mp 160-165 °C; TLC Rf ) 0.32 (20% EtOAc/hexanes); [R]24
2.2, ArH C6-H), 7.68 (1H, d, 4J HH ) 2.2, ArH C4-H), 4.58 (1H,
589
1
4
3
-78.3° (c ) 0.75, CHCl3); H NMR (CDCl3) 7.97 (1H, d, J HH
) 2.0, ArH C6-H), 7.88 (1H, d, 4J HH ) 2.0, ArH C8-H), 4.89 (q,
m, NCH(CH3)CH2), 4.16 (2H, q, J HH ) 7.3, OCH2), 2.83 (3H,
3
3
s, NCH3), 2.60 (2H, d, J HH ) 5.1, CH2CO2), 1.33 (3H, d, J HH
3J HH ) 7.2, NCH(CH3)CH2), 4.13 (2H, q, J HH ) 7.0, OCH2),
3
3
) 6.8, NCH(CH3)CH2), 1.27 (3H, t, J HH ) 7.3, OCH2CH3);
2
2
13C NMR (CD3OD) 172.84, 169.44, 145.35, 139.53, 137.72,
126.45, 121.69, 76.84, 61.73, 49.85, 48.14, 44.50, 44.39, 41.44,
20.26, 14.60; LRMS (FAB) 427 (M + 3, 30), 426 (M + 2, 30),
425 (M + 1, 100), 424 (M+, 70); HRMS (FAB) m/ z calcd
for C14H18ClIN2O3 424.0051, found 424.0069. Anal. Calcd for
C14H18ClINO3: C, 39.60; H, 4.27; N, 6.60. Found : C, 40.06;
H, 4.46; N, 6.51.
3.69 (1H, d, J HH ) 14.7, C3-H), 3.56 (1H, d, J HH ) 14.9, C3-
H), 2.88 (1H, dd, 2J HH ) 15.5, 3J HH ) 6.5, CHHCO2), 2.60 (1H,
dd, J HH ) 15.9, J HH ) 9.0, CHHCO2), 1.42 (9H, s, But), 1.31
2
3
3
3
(3H, d, J HH ) 6.8, NCH(CH3)CH2), 1.26 (3H, t, J HH ) 7.2,
OCH2CH3); 13C NMR (CDCl3) 170.7, 170.3, 164.2, 140.4, 137.3,
137.1, 136.8, 133.8, 92.1, 62.5, 60.6, 51.8, 50.2, 38.7, 28.1, 17.8,
14.1; LRMS (FAB, M + H) 507.2; HRMS (FAB) m/ z calcd for
C19H25N2O4ICl 507.0548, found 507.0568; C,H,N. The slower
eluting diastereoisomer (+)-6e (0.45g) was isolated as a color-
(b) Compound 6d was prepared from N-[3-chloro-5-iodo-2-
(methylamino)benzoyl-3(S)-aminobutanoic acid, ethyl ester
(530 mg, 1.25 mmol) using the method described above for
compound 6c. The crude reaction mixture was submitted to
flash chromatography (10% acetone in dichloromethane) to
yield 6d in 81% yield as a 3:2 ratio of rotational isomers (1H
less syrup: TLC Rf ) 0.30 (20% EtOAc/hexanes); [R]24
589
1
4
+53.2° (c ) 0.14, CHCl3); H NMR (CDCl3) 7.87 (1H, d, J HH
4
) 2.0, ArH C6-H), 7.83 (1H, d, J HH ) 2.1, ArH C8-H), 5.23
3
(1H, m, NCH(CH3)CH2), 4.03 (2H, q, J HH ) 7.1, OCH2), 3.58
2
2
NMR): RP-HPLC (method A) tR ) 6.31 min; [R]24 -17.9° (c
(1H, d, J HH ) 15.0, C3-H), 3.50 (1H, d, J HH ) 15.0, C3-H),
2.44 (1H, dd, 2J HH ) 14.9, 3J HH ) 6.3, CHHCO2), 2.39 (1H, dd,
2J HH ) 14.9, 3J HH ) 8.8, CHHCO2), 1.35 (9H, s, But), 1.28 (3H,
d, 3J HH ) 7.0, NH(CH3)CH2), 1.17 (3H, t, 3J HH ) 6.8, OCH2CH3);
13C NMR (CDCl3) 170.5, 170.1, 164.4, 140.3, 137.1, 137.0,
136.6, 133.9, 92.1, 62.4, 60.7, 49.0, 47.3, 39.1, 28.1, 18.3, 14.0;
LRMS 507.0 (M + H); HRMS (FAB) m/ z calcd for C19H25N2O4-
ICl 507.0548, found 507.0528 (81% overall yield). The absolute
stereochemistry of the faster eluting isomer (-)-6e was as-
signed based on the X-ray crystal structure of compound (S)-
(-)-13, vida infra.
589
1
4
) 2.6, MeOH); H NMR (CDCl3) 8.08 (0.6H, d, J HH ) 2, ArH
4
4
C6-H), 8.03 (0.4H, d, J HH ) 2, ArH C6-H), 7.90 (1H, d, J HH
) 2, ArH C8-H), 5.22 (0.4 H, m, NCH(CH3)CH2), 5.10 (0.6H,
m, NCH(CH3)CH2), 4.11 (2H, dq, 3J HH ) 7, 7, OCH2), 3.78 (2H,
m, C3-H), 3.28 (3H, s, NCH3), 2.83 (0.6H, dd, 3J HH ) 9, 2J HH
)
)
3
16, CH2CO2), 2.54 (1.4H, m, CH2CO2), 1.36 (1.2H, d, J HH
6.8, NCH(CH3)CH2), 1.28 (1.8H, d, 3J HH ) 6.8, NCH(CH3)CH2),
1.24 (3H, t, 3J HH ) 7.3, OCH2CH3); 13C NMR (CD3OD) 172.10,
171.01, 166.22, 166.18, 142.92, 139.52, 139.26, 138.98, 138.76,
135.22, 135.20, 131.36, 131.29, 91.79, 91.73, 61.78, 61.54,
49.74, 49.17, 46.73, 46.68, 39.40, 38.58, 37.61, 37.45, 18.59,
18.30, 14.54, 14.51; LRMS (FAB) 467 (M + 3, 33), 466(M + 2,
20) 465 (M + 1, 100), 419 (20); HRMS (FAB) m/ z calcd for
C16H19O4NClI 465.0078, found 465.0097; C,H,N.
(+)- an d (-)-1-ter t-Bu tyl-4-(3(R)-bu tan oic acid)-9-ch lor o-
7-iod o-3,4-d ih yd r o-1H-1,4-ben zod ia zep in e-2,5-d ion e, Eth -
yl Ester [(+)-6f a n d (-)-6f]. Compounds (+)-6f and (-)-6f
were prepared using the method shown for (+)-6e and (-)-6e
substituting 5d for 5c. Compound (+)6f is the enantiomer of
compound (-)-6e and has identical spectral data (1H and 13C
NMR). The same relationship holds for (-)-6f and (+)-6e.
(a ) The crude N-[3-chloro-5-iodo-2-(tert-butylamino)benzoyl]-
3(R)-aminobutanoic acid, ethyl ester prepared in part a of the
experimental was purified by flash chromatography (15%
(+) an d (-)-1-ter t-Bu tyl-4-(3(S)-bu tan oic acid)-9-ch lor o-
7-iod o-3,4-d ih yd r o-1H-1,4-ben zod ia zep in e-2,5-d ion e, Eth -
yl Ester [(+)-6e a n d (-)-6e]. (a ) To a solution of 5c (1.50 g,
3.5 mmol, 1 equiv) in acetic acid (30 mL) at 25 °C was added
Et3N (0.70 g, 0.97 mL, 7.0 mmol, 2 equiv). To this mixture
was added a solution of Cl2 dissolved in acetic acid (3.44 mmol,
prepared by bubbling Cl2(g) into acetic acid). After stirring
for 1 h at room temperature, the mixture was concentrated in
vacuo, dissolved in EtOAc (50 mL), washed with 10% sodium
bisulfate (50 mL), water (50 mL), and brine (50 mL), then dried
(MgSO4), filtered, and concentrated in vacuo. The crude
material was purified by flash chromatography (15% EtOAc/
EtOAc/hexanes) in 76% yield as a colorless syrup: [R]24
589
-4.4° (c ) 2.8, CHCl3); HRMS (FAB) m/ z calcd for C17H25N2O3-
ICl 467.0599, found 467.0605.
(b) The crude mixture of diastereoisomers prepared in part
b from 0.9 g of N-[3-chloro-5-iodo-2-(tert-butylamino)benzoyl]-
3(R)-aminobutanoic acid, ethyl ester was purified by flash

Atropisomeric GPIIbIIIa Antagonists
J ournal of Medicinal Chemistry, 1997, Vol. 40, No. 5 725
chromatography to yield 0.44 g of the faster eluting compound
nitrogen, and heated to 50 °C (oil bath). After heating at 50
°C for 90 min, the reaction mixture was no longer homoge-
neous and TLC (25% ethyl acetate/hexane) indicated complete
consumption of the thioamide. The solvent was removed in
vacuo to give a light brown solid which was used without
further purification. The (S)-methyl thioimidate was sus-
pended in absolute ethanol (200 mL), and in an efficient fume
hood the open flask was treated with ammonium acetate (25
g, 0.325 mol, 4.1 equiv). Within minutes the solution became
dark red and homogeneous. The reaction mixture was heated
to 50 °C (oil bath) for 2.5 h, and TLC (90% CH2Cl2:8% MeOH:
2% HOAc) indicated complete comsumption of the (S)-methyl
thioimidate. A stream of nitrogen was blown over the flask
for 30 min and the remaining ethanol removed under vacuum
to a give a solid residue. The residue was triturated with
diethyl ether (4 × 75 mL), water (5 × 50 mL), and a 1:1
mixture of diethyl ether:hexane (4 × 50 mL). The solids were
transferred from the 500 mL round bottom flask to a crystal-
lizing dish and dried overnight in a vacuum dessicator (1
mmHg) to afford 18.5 g of 4-[2-(trimethylsilyl)ethynyl]benza-
midine as a tan powder (85%): mp 220-222 °C; RP-HPLC
(+)-6f as a white solid: mp 158-162 °C; [R ]24 +77.5° (c )
589
1.08, CHCl3); HRMS (FAB) m/ z calcd for C19H25N2O4ICl
507.0548, found 507.0526; C,H,N. The slower eluting com-
pound (-)-6f was a colorless syrup: 0.29g; [R ]24 -51.0° (c
589
) 1.3, CHCl3); HRMS (FAB) m/ z calcd for C19H25N2O4ICl
507.0548, found 507.0535 (75% overall yield). The relative
stereochemistry of the slower eluting isomer (-)-6f was
assigned based on the X-ray crystal structure of compound (R)-
(-)-13, vida infra.
4-[(Tr im eth ylsilyl)eth yn yl]ben zon itr ile (14). A 3-neck,
1 L round bottom flask equipped with a thermocouple probe,
condensor, and stir bar was charged with 4-bromobenzonitrile
(62 g, 0.34 mol, 1.0 equiv), Et3N (200 mL, 1.48 mol, 4.3 equiv),
and EtOAc (150 mL) immersed into a bath of water (25 °C).
The white suspension was degassed by bubbling nitrogen
through the solution for 10 min. Trimethylsilylacetylene (50
g, 0.51 mol, 1.5 equiv) was added and degassed for 4 min. Bis-
(triphenylphosphine)palladium dichloride ((Ph3P)3PdCl2; 1.2 g,
0.0017 mol, 0.005 equiv) and cuprous iodide (CuI; 0.65 g,
0.0034 mol, 0.01 equiv) were added as solids in one portion.
The golden slurry turned dark within 5 min. The reaction was
monitored to maintain an internal temperature of 50 °C, which
began to drop after 2.5 h. TLC indicated the consumption of
4-bromobenzonitrile. The reaction mixture was diluted with
ethyl acetate (400 mL) and the slurry filtered through a pad
of Celite in a sintered glass funnel (medium frit). The tan
solids were washed additionally with ethyl acetate until the
filtrate was nearly colorless. The combined filtrates were
concentrated in vacuo to yield a black, flaky solid (72 g). The
crude product was loaded as a solid onto the top of a plug of
dry silica gel (150 g) and eluted with 5% ethyl acetate/hexane
to yield 14 in two crops (one which was yellow in color and
the other which was light brown in color) which were indis-
tinguishable by TLC and melting point. The combined yield
of 14 was 96%: mp 96-98 °C; TLC Rf ) 0.45 (10% EtOAc/
hexane); RP-HPLC (method G) tR ) 8.10 min; 1H NMR (CDCl3)
7.57 (2H, d, 3J HH ) 8.55, ArH), 7.51 (2H, d, 3J HH ) 8.55, ArH),
0.24 (9H, s, Si(CH3)3); 13C NMR (CDCl3) 132.36, 131.85, 127.91,
118.34, 111.68, 102.90, 99.48, -0.33; LRMS (FAB) m/ z 200
(method G) tR ) 6.35 min; 1H NMR (DMSO-d6 + F3CCO2D
3
(10 µL)) 9.37, 9.30 (3H, 2 bs, H2NCdNH), 7.80 (2H, d, J HH
)
7.0, ArH), 7.68 (2H, d, 3J HH ) 7.0, ArH), 0.24 (9H, s, Si (CH3)3;
13C NMR (DMSO-d6 + F3CCO2D (30 µL)) 165.20, 131.99,
128.51, 128.33, 127.38, 103.62, 98.20, -0.28; LRMS (FAB) m/ z
217.1 (M + H)+, 217 (100); HRMS (FAB) m/ z calcd for
C
12H17N2Si 217.1161, found 217.1169; C,H,N.
(c) 4-[(Trimethylsilyl)ethynyl]benzamidine (21.5 g, 0.078
mol, 1.0 equiv) was suspended in methanol (150 mL) and then
treated with potassium carbonate (7.5 g, 0.054 mol, 0.7 equiv).
The slurry was stirred for 2 h at room temperature. The
solution was concentrated in vacuo, suspended in water (100
mL), and filtered through a sintered glass funnel (medium frit).
The solids were washed a second time with water (50 mL) and
dried under vacuum (1 mmHg) in a vacuum dessicator to a
constant weight to afford 13.0 g of 15 as a tan powder (90%).
Typically the 15 reagent was used as the free base without
additional purification. However, 15 could be further purified
by preparative RP-HPLC (method C), tR ) 27-32 min, to give
the trifluoroacetate salt as a white powder after lyophilization
from acetonitrile/water (0.1% TFA): mp (free base) 145-148
°C, mp (TFA salt) >370 °C; RP-HPLC (method G) tR ) 3.87
min; 1H NMR (DMSO-d6 + F3CCO2D (10 µL)) 9.36 (3H, bs,
(M + H)+, 200 (100), 184; HRMS (FAB) m/ z calcd for C12H14
NSi 200.0895, found 200.0885; C,H,N.
-
4-Eth yn ylben za m id in e (15). (a ) A 1 L round bottom flask
equipped with stir bar was charged with 14 (30.5 g, 0.15 mol),
pyridine (120 mL), and Et3N (60 mL). With efficient stirring,
hydrogen sulfide gas (stench, perform in an efficient fume
hood!!) was bubbled into the dark, homogeneous solution for
a period of approximately 5 min. The 1 L flask was stoppered
tightly with a glass 24/40 stopper and gently warmed in a
water bath (temperature of the water bath did not exceed 50
°C). The flask was charged with additional hydrogen sulfide
every 15 min for a period of 1 h. The reaction was monitored
by TLC (25% ethyl acetate/hexanes). After the last addition
of hydrogen sulfide, the reaction mixture was stirred at 50 °C
for an additional 1.5 h, monitoring by TLC (25% ethyl acetate/
hexanes), and the reaction was determined to be complete at
this time. The reaction mixture was cooled to room temper-
ature and a stream of nitrogen blown over the reaction mixture
for 45 min to remove any excess hydrogen sulfide (perform in
efficient fume hood with sash down). The dark solution was
concentrated to give a residue which was azeotroped with
toluene (2 × 20 mL) to remove the remaining pyridine. The
residue was suspended in ethyl acetate (100 mL), adsorbed
onto 70 g of silica gel, and concentrated in vacuo to a dry
powder. The powder was loaded onto 500 g of silica gel and
eluted with 25% ethyl acetate/hexane. Removal of the ethyl
acetate/hexane and drying under vacuum gave 26 g (73%)
of 4-[2-(trimethylsilyl)ethynyl]benz(thio)amide as a yellow
powder: TLC Rf ) 0.25 (25% EtOAc/hexane); RP-HPLC assay
3
3
H2NCdNH), 7.81 (2H, d, J HH ) 8.0, ArH), 7.70 (2H, d, J HH
) 8.0, ArH), 4.51 (1H, s, CCH); 13C NMR (DMSO-d6
+
F3CCO2D (30 µL)) 164.91, 132.07, 129.95, 128.23, 126.30,
83.99, 82.49; LRMS (FAB) m/ z 145 (M + H)+, 145 (100);
HRMS (FAB) m/ z calcd for C9H9N2, 145.0765, found 145.0768;
C,H,N.
4-Eth yn ylben zon itr ile (16). Compound 14 was desily-
lated with potassium carbonate in methanol.23 The reaction
mixture was stirred at room temperature for 16 h, and TLC
(10% EtOAc/hexane) revealed that 14 had been completely
consumed. The methanolic solution was concentrated to a
residue, dissolved in water and ethyl acetate, and transferred
to a separatory funnel, and the layers were separated. The
aqueous layer was extracted additionally with ethyl acetate;
the ethyl acetate layers were combined, washed with saturated
NaCl, dried (MgSO4), filtered, and concentrated to a residue.
Flash chromatography (10% EtOAc/hexane) afforded 16 as a
white solid (80%): mp 154-156 °C; TLC Rf ) 0.34 (10% EtOAc/
hexane); RP-HPLC (method B) tR ) 6.05 min; 1H NMR (CDCl3)
3
3
7.63 (2H, d, J HH ) 8.3, Ar-H), 7.58 (2H, d, J HH ) 8.3, Ar-H),
3.31 (1H, s, CCH); 13C NMR (CDCl3) 132.61, 131.97, 126.93,
118.20, 112.27, 94.44, 91.70; LRMS (FAB) m/ z 127.0 (M + H)+;
C,H,N.
1
(method G) tR ) 7.59 min; H NMR (DMSO-d6) 9.92 (1H, bs,
1-ter t-Bu tyl-4-(3(S)-bu ta n oic a cid )-7-[(4-cya n op h en yl)-
et h yn yl]-9-ch lor o-3,4-d ih yd r o-1H -1,4-b en zod ia zep in e-
2,5-d ion e, Eth yl Ester [(S)-(-)-13]. A solution of (-)-6e
(0.30 g, 0.6 mmol, 1 equiv) and 16 (0.15 g, 1.2 mmol, 2 equiv)
in EtOAc (15 mL) was degassed and the reaction vessel purged
with Ar at 25 °C. A catalytic amount of (PPh3)2PdCl2 (4.2 mg)
and CuI (2.3 mg) followed by Et3N (300 mg, 410 µL, 5 equiv)
were added sequentially, degassing with Ar after the addition
of each reagent. The mixture was stirred for 2 h, and the
3
HNdCSH), 9.51 (1H, bs, HNdCSH), 7.86 (2H, d, J HH ) 8.0,
3
ArH), 7.46 (2H, d, J HH) 8.0, ArH), 0.21 (9H, s, Si(CH3)3);
LRMS (FAB) m/ z 234 (M + H)+, 234 (100), 217, 200, 184.
(b) A 24/40 500 mL round bottom flask equipped with a
stirring bar was charged with 4-[2-(trimethylsilyl)ethynyl]-
benz(thio)amide (18.4 g, 0.079 mol, 1.0 equiv), acetonitrile (100
mL), and methyl iodide (22.7 g, 9.9 mL, 0.16 mol, 2.0 equiv).
The flask was equipped with
a condensor, flushed with

726 J ournal of Medicinal Chemistry, 1997, Vol. 40, No. 5
Blackburn et al.
solvent was removed in vacuo. The crude product was purified
by flash chromatography over two silica gel columns sequen-
tially (30% EtOAc/hexanes), to yield (S)-(-)-13 (0.28 g, 92%)
1-Meth yl-4-(3(S)-bu ta n oic a cid )-7-[(4-a m id in op h en yl)-
eth yn yl]-3,4-dih ydr o-1H-1,4-ben zodiazepin e-2,5-dion e (3).
(a ) 1-Methyl-4-(3(S)-butanoic acid)-7-[(4-amidinophenyl)ethy-
nyl-3,4-dihydro-1H-1,4-benzodiazepine-2,5-dione, ethyl ester:
RP-HPLC (method D), lyophilization from H2O/CH3CN with
0.5% HOAc yielded the ethyl ester as a light yellow powder
(ca. a 3:2 mixture of rotational isomers of the seven-membered
as a slightly tan solid: mp 150-152 °C; TLC Rf ) 0.73 (50%
1
EtOAc/hexanes); [R]24 -133.6° (c ) 0.63, CHCl3); H NMR
589
4
4
(CDCl3) 7.85 (1H, d, J HH ) 2.0, ArH C6-H), 7.71 (1H, d, J HH
3
) 2.5, ArH C8-H), 7.67 (2H, d, J HH ) 8.2, ArH), 7.60 (2H, d,
3J HH ) 8.9, ArH), 4.92 (1H, m, NCH(CH3)CH2), 4.14 (2H, q,
ring, CD3OD) in 61% yield; mp 228-230 °C; [R]24 -52.6° (c
589
3J HH ) 7.1, OCH2), 3.72 (1H, d, J HH ) 14.5, C3-H), 3.59 (1H,
2
) 0.56, CH3OH); TLC Rf ) 0.96 (90% CH2Cl2, 8% CH3OH, 2%
2
2
3
d, J HH ) 15.3, C3-H), 2.91 (1H, dd, J HH ) 16.1, J HH ) 6.1,
AcOH); RP-HPLC (method D) tR 50-59 min, (method A) tR
)
2
3
4
) 5.62 min; 1H NMR (CD3OD) 7.97 (0.5H, d, J HH ) 2.0, ArH
CHHCO2), 2.62 (1H, dd, J HH ) 15.8, J HH ) 8.7, CHHCO2),
1.44 (9H, s, But), 1.33 (3H, d, 3J HH ) 7.0, NCH(CH3)CH2), 1.26
C6-H), 7.90 (0.5H, d, 4J HH ) 2.0, ArH C6-H), 7.82 (2H, d, 3J HH
(3H, t, J HH ) 7.0, OCH2CH3); 13C NMR (CDCl3) 170.8, 170.4,
3
3
) 8.54, ArH), 7.76 (3H, m, J HH ) 7.6, ArH C8-H, C6H4CC),
3
3
164.9, 137.8, 136.3, 134.7, 133.3, 132.2, 131.3, 126.9, 123.0,
118.2, 113.6, 112.4, 90.5, 90.2, 62.8, 60.6, 52.0, 50.3, 38.8, 28.1,
17.8, 14.2; LRMS (FAB, M + H) 506.2; HRMS (FAB) m/ z calcd
for C28H29N3O4Cl 506.1847, found 506.1871; C,H,N. X-ray
quality crystals of (S)-(-)-13 were obtained by slow evapora-
tion from 10% CH2Cl2/hexanes.
7.45 (0.5H, d, J HH ) 8.5, ArH C9-H), 7.44 (0.5H, d, J HH
)
8.5, ArH C9-H), 5.15 (1H, m, NCH(CH3)CH2), 4.10, 4.05 (2H,
3
2 overlapping q’s, J HH ) 7.0, OCH2), 3.91 (2H, 2 overlapping
2
2
ABq’s, J HH ) 18.3, δνAB ) 10.3, J HH ) 12.2, δνAB ) 16.5, C3-
H), 3.39 (1.2H, s, NCH3), 3.37 (1.8 H, s, NCH3), 2.80 (0.5H,
dd, 2J HH ) 16.4, 3J HH ) 9.8, CH2CO2), 2.61 (1.5H, m, CH2CO2),
1.33 (1.2 H, d, 3J HH ) 7.0, NCH(CH3)CH2), 1.27 (1.8 H, d, 3J HH
1-ter t-Bu tyl-4-(3(R)-bu ta n oic a cid )-7-[(4-cya n op h en yl)-
eth yn yl-9-ch lor o-3,4-d ih yd r o-1H-1,4-ben zod ia zep in e-2,5-
d ion e, Eth yl Ester [(R)-(-)-13]. Compound (R)-(-)-13 was
prepared using the method described for (S)-(-)-13 substitut-
ing (-)-6f for (-)-6e: 89% yield, slightly tan solid; mp 150-
3
) 7.0, NCH(CH3)CH2), 1.23 (1.2H, t, J HH ) 7.0, OCH2CH3),
1.19 (1.8H, t, 3J HH ) 7.0, OCH2CH3); 13C NMR (CD3OD) 172.34,
172.25, 171.21, 171.05, 168.21, 167.87, 142.81, 136.29, 135.11,
134.87, 133.31, 130.22, 130.14, 129.85, 129.42, 129.26, 124.49,
123.18, 123.06, 120.79, 92.23, 92.15, 89.61, 61.89, 61.69, 46.86,
38.94, 35.19, 18.65, 18.20, 14.47; LRMS (FAB) m/ z 447.2 (M
+ H)+, 447.2 (100); HRMS (FAB) m/ z calcd for C25H27N4O4
447.2032, found 447.2011. Anal. Calcd for C29H35F3N4O7 (1.0
TFA): C, 57.86; H, 4.86; N, 10.0. Found: C, 57.65; H, 5.58;
N, 10.03.
(b) Crude 3, a yellow powder, was dissolved in a mixture of
2.5 H2O/1.0 CH3CN/0.05 TFA, filtered through a pipet contain-
ing a cotton plug, and purified by preparative RP-HPLC
(method F), tR ) 63-67 min, to afford 3 (acetate salt) as a light
yellow powder (ca. 3:2 mixture of rotational isomers, CD3OD)
after lyophilization from H2O/CH3CN with 0.5% HOAc in 86%
yield: RP-HPLC (method A) tR ) 4.85 min; 1H NMR (CD3OD)
152 °C; Rf ) 0.71 (50% EtOAc/hexanes); [R ]24 -96.3° (c )
589
1
4
0.89, CHCl3); H NMR (CDCl3) 7.79 (1H, d, J HH ) 1.9, ArH
4
3
C6-H), 7.70 (1H, d, J HH ) 2.1, ArH C8-H), 7.67 (2H, d, J HH
3
) 8.5, ArH), 7.60 (2H, d, J HH ) 8.5, ArH), 5.31 (1H, m, 1H,
3
NCH(CH3)CH2), 4.09 (2H, q, J HH ) 7.6, OCH2), 3.65 (1H, d,
2J HH ) 14.2, C3-H), 3.57 (1H, d, J HH ) 15.2, C3-H), 2.54 (1H,
2
2
3
2
dd, J HH ) 14.2, J HH ) 5.6, CHHCO2), 2.42 (1H, dd, J HH
)
15.2, 3J HH ) 8.4, CHHCO2), 1.43 (9H, s, But), 1.34 (3H, d, 3J HH
) 6.9, NCH(CH3)CH2), 1.22 (3H, t, 3J HH ) 7.5, OCH2CH3); 13
C
NMR (CDCl3) 170.6, 170.2, 165.2, 137.6, 136.1, 134.6, 133.3,
132.2, 132.1, 131.1, 126.9, 123.0, 118.2, 112.3, 90.4, 90.2, 62.7,
60.7, 49.0, 47.4, 39.1, 28.1, 18.3, 14.1; LRMS (FAB, M + H)
506.4; HRMS (FAB) m/ z calcd for C28H29N3O4Cl 506.1847
found 506.1859. Anal. Calcd for C34H43N3O4Cl (0.5 hex-
anes): C, 68.04; H, 6.52; N, 7.56. Found: C, 63.88; H, 6.26;
N, 6.99. X-ray quality crystals of (R)-(-)-13 were obtained by
dissolution, filtration, and slow evaporation from hexanes.
Gen er a l P r oced u r e for th e P r ep a r a tion of Am id in o
Acid s 2, 3, a n d 7-12. (a ) The iodoarene (1.0 equiv), 15 (1.8
equiv), dimethylformamide, and 5 equiv of Et3N (or diisopro-
pylethylamine for compounds 7, 8) were combined and deoxy-
genated. CuI (0.1 equiv) and (Ph3P)2PdCl2 (0.05 equiv) were
added and placed under nitrogen. The reaction was allowed
to stir at 50-60 °C (or at room temperature for compounds 7,
8) monitoring by RP-HPLC. After cooling to room tempera-
ture, the solution was concentrated in vacuo. The crude
amidino esters of compounds 7 and 8 were purified by
preparative RP-HPLC, and the amidino esters of compounds
2, 3, and 9-12 were purified first by flash chromatography
using 10% CH3OH/0.1% AcOH/CH2Cl2 as the eluting solvent
(compounds 2, 9-12) or 8% CH3OH/2% AcOH/CH2Cl2, for
compound 3, and then by preparative RP-HPLC.
4
4
7.97 (0.33H, d, J HH ) 2.0, ArH C6-H), 7.89 (0.67H, d, J HH
)
3
2.0, ArH C6-H), 7.82 (1H, d, J HH ) 5.4, ArH), 7.79 (1H, d,
3J HH ) 5.4, ArH), 7.76 (1H, d, J HH ) 8.3, ArH), 7.72 (1H, dd,
3
4J HH ) 2.0, J HH ) 8.3, ArH C8-H), 7.59 (1H, d, J HH ) 8.3,
3
3
3
ArH), 7.43 (1H, d, J HH ) 8.3, ArH C9-H), 5.32 (0.6H, m,
NCH(CH3)CH2), 5.07 (0.4H, m, NCH(CH3)CH2), 3.92 (2H, ABq,
2J HH ) 15.0, δνAB ) 18.7, C3-H), 3.39 (1.80H, s, NCH3), 3.37
2
3
(1.20H, s, NCH3), 2.77 (0.20H, dd, J HH ) 16.5, J HH ) 9.2,
3
CH2CO2), 2.50 (1.8H, m, CH2CO2), 1.32 (1.2H, d, J HH ) 7.0,
NCH(CH3)CH2), 1.29 (1.8H, d, 3J HH ) 7.0, NCH(CH3)CH2); 13
C
NMR (CD3OD) 174.16, 174.05, 171.22 ,171.16, 168.18, 167.82,
142.81, 142.51, 136.24, 136.17, 135.04, 134.92, 133.26, 130.22,
130.19, 129.88, 129.23, 123.13, 122.93, 120.78, 120.74, 92.21,
89.56, 39.23, 38.85, 35.19, 35.02, 18.55, 18.11; LRMS (FAB)
m/ z 419.17 (M + H)+ 419.1(100); HRMS (FAB) m/ z calcd for
C23H23N4O4 419.1719, found 419.1719.
An analytical sample was prepared by dissolving a portion
of the acetate salt (100 mg) in 10 mL of 20% CH3CN/H2O
containing 1.0 mL of TFA and lyophilized. To remove any
excess trifluoroacetic acid, the lyophilized powder was dis-
solved in 10 mL of 20% CH3CN/H2O and lyophilized a second
time to yield the more soluble trifluoroacetate salt of 3 as a
55/45 mixture of diastereomeric rotational isomers (1H NMR,
(b) The amidino ethyl esters were hydrolyzed with 1 N
LiOH (3 equiv for compounds 2, 3, 7, 8; 5 equiv for compounds
9-12) in a 3:2:1 solution of THF/H2O/MeOH at 0 °C during
the addition of LiOH (compounds 2, 3, 7, 8) or a 1:1 solution
of THF/H2O at room temperature (compounds 9-12) monitor-
ing by RP-HPLC. The reaction may be quenched with 4 N
HCl in dioxane (compounds 2, 3) prior to concentration in
vacuo and purification by RP-HPLC.
CD3OD): [R]24
-34.1° (c ) 0.57, CH3OH); 1H NMR (CD3-
589
4
OD) 7.99 (0.55H, d, J HH ) 2.0, ArH C6-H), 7.95 (0.45H, d,
4J HH ) 2.0, ArH C6-H),7.83 (2H, d, J HH ) 8.60, ArH), 7.77
3
(3H, dd overlapping with a d, 4J HH ) 2.0, 3J HH ) 8.1, ArH C8-
1-Meth yl-4-(3(R)-bu ta n oic a cid )-7-[(4-a m id in op h en yl)-
eth yn yl]-3,4-dih ydr o-1H-1,4-ben zodiazepin e-2,5-dion e (2).
(a ) 1-Methyl-4-(3(R)-butanoic acid)-7-[(4-amidinophenyl)ethy-
nyl]-3,4-dihydro-1H-1,4-benzodiazepine-2,5-dione, ethyl es-
ter: RP-HPLC (method F) followed by recrystallization from
3
3
H, J HH ) 8.1, ArH), 7.46 (0.45H, d, J HH ) 8.61, ArH C9-H),
7.45 (0.55H, d, 3J HH ) 8.61, ArH C9-H), 5.14 (1H, m, NCH(CH3)-
CH2), 3.94 (2H, 2 overlapping ABq’s, 2J HH ) 15.4, δνAB ) 18.9,
2J HH 15.4, δνAB 16.7, C3-H), 3.41 (1.35H, s, NCH3), 3.38
)
)
(1.65H, s, NCH3), 2.81 (0.6H, dd, 2J HH ) 16.5, 3J HH ) 9.0, CH2-
CO2), 2.60 (1.4H, m, CH2CO2), 1.35 (1.35H, d, 3J HH ) 7.0, NCH-
(CH3)CH2), 1.30 (1.65H, d, 3J HH ) 7.0, NCH(CH3)CH2); C,H,N.
EtOH gave the amidino ester in 65% yield, [R]24 +53.3° (c
589
) 0.57, CH3OH). Analytical data (13C and 1H NMR) were
identical with its enantiomer 1-methyl-4-(3(S)-butanoic acid)-
7-[(4-amidinophenyl)ethynyl]-3,4-dihydro-1H-1,4-benzodiazepine-
2,5-dione, ethyl ester.
1-ter t-Bu tyl-4-(3(S)-bu ta n oic a cid )-7-[(4-a m id in op h e-
n yl)et h yn yl]-3,4,d ih yd r o-1H -1,4-b en zod ia zep in e-2,5-d i-
on e (7). (a ) 1-tert-Butyl-4-(3(S)-butanoic acid)-7-[(4-amidi-
nophenyl)ethynyl]-3,4,dihydro-1H-1,4-benzodiazepine-2,5-
dione, ethyl ester was obtained in 33% yield after purification
by RP-HPLC (method H) as a white solid: mp ) 216-220 °C;
(b) RP-HPLC (method F) purification followed by recrys-
tallization from EtOH gave 2 in 41% yield, [R]24 +32.6° (c
589
) 0.95, CH3OH). Analytical data (13C and 1H NMR) were
identical with its enantiomer 3.

Atropisomeric GPIIbIIIa Antagonists
J ournal of Medicinal Chemistry, 1997, Vol. 40, No. 5 727
[R]24 +27.6° (c ) 1.5, CH3OH); RP-HPLC (method A) tR
)
ethynyl]-9-chloro-3,4-dihydro-1H-1,4-benzodiazepine-2,5-di-
one, ethyl ester (79%) as a white solid after lyophilization from
20% CH3CN/H2O: [R]24589 -87.4° (c ) 0.42, CH3OH); RP-HPLC
(method A) tR ) 6.24 min; 1H NMR (CD3OD) 7.89 (1H, d, 4J HH
589
5.73 min; 1H NMR (CD3OD) 7.82 (2H, d, 3J HH ) 8.8, ArH), 7.76
3
4
(3H, m, ArH C6-H, C6H4CC), 7.70 (1H, dd, J HH ) 8.3, J HH
)
2.0, ArH C8-H), 7.43 (1H, d, 3J HH ) 8.3, ArH C9-H), 5.24 (1H,
3
3
m, NCH(CH3)CH2), 4.10 (2H, q, J HH ) 7.2, OCH2), 3.72 (2H,
) 1.9, ArH C6-H), 7.85 (2H, d, J HH ) 8.6, ArH), 7.80 (2H, d,
m, C3-H), 2.5-2.85 (2H, m, CH2CO2), 1.46 (9H, s, But), 1.31
3J HH ) 8.7, ArH), 7.79 (1H, d, 4J ) HH1.9, ArH C8-H), 4.94
3
3
3
3
(3H, d, J HH ) 7.1, NCH(CH3)CH2), 1.21(3H, t, J HH ) 7.2,
OCH2CH3); 13C NMR (CD3OD) 173.27, 172.90, 172.26, 168.44,
168.22, 167.87, 140.79, 140.66, 134.51, 133.94, 133.85, 133.35,
132.95, 129.71, 129.58, 129.22, 128.74, 122.60, 122.55, 91.96,
91.90, 90.17, 61.88, 61.75, 61.14, 61.02, 51.47, 50.19, 39.52,
29.76, 18.89, 18.12, 14.47; LRMS (FAB) 489 (M + 1, 100), 433
(80); HRMS (FAB) m/ z calcd for C28H33N4O4 489.2502, found
489.2481; C,H,N.
(1H, q, J HH ) 6.7, NCH(CH3)CH2), 4.11 (2H, q, J HH ) 7.6,
2 2
OCH2), 3.82 (1H, d, J HH ) 15.1, C3-H), 3.66 (1H, d, J HH
13.8, C3-H), 2.86 (1H, dd, J HH ) 15.1, J HH ) 6.3, CHHCO2),
)
2
3
2
3
2.64 (1H, dd, J HH ) 15.1, J HH ) 8.8, CHHCO2), 1.43 (9H, s,
But), 1.29 (3H, d, 3J HH ) 7.2, NCH(CH3)CH2), 1.25 (3H, t, 3J HH
) 7.2, OCH2CH3); 13C NMR (CD3OD) 172.4, 172.3, 167.8, 167.2,
139.1, 137.6, 136.2, 134.9, 133.5, 132.0, 129.9, 129.3, 129.2,
124.6, 91.5, 90.5, 63.7, 61.8, 52.4, 51.4, 39.5, 28.6, 18.0, 14.5;
LRMS (FAB, M + H) 523.2; HRMS (FAB) m/ z calcd for
C28H32N4O4Cl 523.2112, found 523.2094. Anal. Calcd for
C30H34ClF3N4O7 (1.0 TFA, 1.0 H2O): C, 55.01; H, 5.23; N, 8.55.
Found C, 55.37; H, 5.83; N, 8.58.
(b) RP-HPLC purification (method I) yielded 7 (57%) as a
white solid: mp 240 °C dec; [R]24 -14.2° (c ) 0.4, CH3OH);
589
1
RP-HPLC (method A) tR ) 5.23, 5.35 min; H NMR (CD3OD)
3
3
7.84 (1H, d, J HH ) 8 ArH), 7.83 (1H, d, J HH ) 5 ArH), 7.78
(1H, d, 3J HH ) 5 ArH), 7.74 (1H, d, 3J HH ) 8 ArH), 7.68 (0.5H,
(b) RP-HPLC purification (method F) yielded 9 (75%) after
3
4
3
dd, J HH ) 8.3, J HH ) 2.0, ArH C8-H), 7.65 (0.5H, dd, J HH
)
lyophylization from 20% CH3CN/H2O; [R]24 -88.5° (c ) 0.3,
589
4
8.3, J HH ) 2.0, ArH C8-H), 7.60 (0.5H, bs, ArH C6-H), 7.57
CH3OH); RP-HPLC (method A) tR ) 5.65 min; 1H NMR (CD3-
3
(0.5H, bs, ArH C6-H), 7.43 (0.5H, d, J HH ) 8.3, ArH C9-H),
OD) 7.89 (d, 1H, 4J HH ) 2.2, 1H, ArH C6-H), 7.84 (2H, d, 3J HH
3
7.42 (0.5H, d, J HH ) 8.3, ArH C9-H), 5.40 (1H, m, NCH-
) 8.5, ArH), 7.79 (2H, d, 3J HH ) 8.1, ArH), 7.79 (1H, d, 4J HH
)
(CH3)CH2), 3.76 (2H, m, C3-H), 2.48 (2H, m, CH2CO2), 1.96
2.0, ArH C8-H), 4.92 (1H, m, NCH(CH3)CH2), 3.82 (1H, d, 2J HH
(3H, s, CH3CO2H), 1.47 (9H, s, But), 1.30 (3H, d, J HH ) 6.6,
) 15.2, C3-H), 3.66 (1H, d, J HH ) 15.1, C3-H), 2.85 (1H, dd,
3
2
NCH(CH3)CH2); 13C NMR (CD3OD) 173.36, 173.07, 168.48,
168.24, 167.80, 140.84, 140.58, 134.36, 134.08, 133.91, 133.35,
133.00, 129.76, 129.67, 129.51, 129.46, 129.26, 129.22, 128.64,
122.54, 122.50, 92.02, 90.03, 61.15, 61.00, 51.67, 50.80, 29.75,
18.97, 18.08; LRMS (FAB) 460 (M + 1, 90), 405 (100), 319 (15);
HRMS (FAB) m/ z calcd for C26H29N4O4 461.2189, found
461.2190; C,H,N.
2J HH ) 16.4, J HH ) 6.6, CHHCO2), 2.62 (1H, dd, J HH ) 16.1,
3
3
2
3J HH ) 8.1, CHHCO2), 1.43 (9H, s, But), 1.30 (3H, d, J HH
)
7.2, NCH(CH3)CH2); 13C NMR (CD3OD) 174.2, 172.5, 167.9,
167.2, 139.1, 137.6, 136.2, 134.8, 133.5, 131.9, 129.8, 129.3,
129.2, 124.6, 91.5, 90.5, 63.8, 52.0, 51.7, 39.5, 28.6, 18.0; LRMS
(FAB, M + H) 495.2; HRMS (FAB) m/ z calcd for C26H28N4O4-
Cl 495.1799, found 495.1794. Anal. Calcd for C28H32ClF3N4O8
(1.0 TFA, 2.0 H2O): C, 52.14; H, 5.00; N, 8.69. Found C, 52.33;
H, 5.44; N, 8.71.
1-Meth yl-4-(3(S)-bu ta n oic a cid )-7-[(4-a m id in op h en yl)-
et h yn yl]-9-ch lor o-3,4-d ih yd r o-1H -1,4-b en zod ia zep in e-
2,5-d ion e (8). (a ) RP-HPLC purification (method H) yielded
1-methyl-4-(3(S)-butanoic acid)-7-[(4-amidinophenyl)ethynyl]-
9-chloro-3,4-dihydro-1H-1,4-benzodiazepine-2,5-dione, ethyl es-
1-ter t-Bu tyl-4-(3(S)-bu ta n oa te)-7-[(4-a m id in op h en yl)-
et h yn yl]-9-ch lor o-3,4-d ih yd r o-1H -1,4-b en zod ia zep in e-
2,5-d ion e (10). (a ) RP-HPLC purification (method F) yielded
(+)-1-tert-butyl-4-(3(S)-butanoic acid)-7-[(4-amidinophenyl)-
ethynyl]-9-chloro-3,4-dihydro-1H-1,4-benzodiazepine-2,5-di-
one, ethyl ester (74%) as a white solid after lyophilization from
20% CH3CN/H2O: [R]24589 +62.5° (c ) 0.24, CH3OH); RP-HPLC
(method A) tR ) 6.19 min; 1H NMR (CD3OD) 7.89 (1H, d, 4J HH
ter (58%) as a white solid: mp ) 216 °C; RP-HPLC (method
1
A) tR ) 5.73 min; [R]24 +11.8° (c ) 0.7, CH3OH); H NMR
589
4
4
(CD3OD) 7.91 (1H, d, J HH ) 2, ArH), 7.90 (1H, d, J HH ) 2,
3
3
ArH), 7.84 (2H, d, J HH ) 8.8, ArH), 7.81 (2H, d, J HH ) 8.8,
ArH), 5.16 (1H, m, NCH(CH3)CH2), 4.09 (2H, m, OCH2), 3.97
(0.5H, d, 2J HH ) 15.4, C3-H), 3.91 (1H, s, C3-H), 3.85 (0.5H, d,
3
) 1.9, ArH C6-H), 7.85 (2H, d, J HH ) 8.6, ArH), 7.79 (2H, d,
2J HH ) 15.4, C3-H), 3.31 (3H, s, NCH3), 2.84 (0.5H, dd, 3J HH
)
3J HH ) 8.8, ArH), 7.73 (1H, d, J HH ) 2.0, ArH C8-H), 5.23
4
10, 2J HH ) 16.6, CH2CO2), 2.64 (0.5H, s, CH2CO2), 2.61 (0.5H,
s, CH2CO2), 2.59 (0.5H, dd, 3J HH ) 4.6, 2J HH ) 16.6, CH2CO2),
1.34 (1.5 H, d, 3J HH ) 6.8, NCH(CH3)CH2), 1.27 (1.5H, d, 3J HH
) 6.8, NCH(CH3)CH2), 1.24 (1.5H, t, 3J HH ) 7, OCH2CH3), 1.22
(1.5H, 3J HH ) 7, OCH2CH3); 13C NMR (CD3OD) 172.45, 171.28,
167.73, 167.19, 139.99, 139.71, 137.40, 134.29, 133.49, 133.27,
132.98, 130.99, 130.93, 129.67, 129.30, 123.61, 123.54, 91.31,
91.11, 90.63, 90.53, 61.99, 61.77, 46.71, 39.41, 38..59, 37.78,
37.58, 18.60, 18.29, 14.50; LRMS (FAB) 483 (M + 3, 33), 482
(M + 2, 30), 481 (M + 1, 100); HRMS (FAB) m/ z calcd for
C25H26O4N4Cl 481.1642, found 481.1654; C,H,N.
(1H, m, NCH(CH3)CH2), 4.07 (2H, q, J HH ) 7.5, OCH2), 3.70
3
(2H, s, C3-H), 2.56 (2H, m, CH2CO2), 1.43 (9H, s, But), 1.32
3
3
(3H, d, J HH ) 7.0, NCH(CH3)CH2), 1.20 (3H, t, J HH ) 7.4,
OCH2CH3); 13C NMR (CD3OD) 172.6, 172.2, 167.8, 167.6,
139.0, 137.6, 136.2, 135.0, 133.5, 131.7, 129.9, 129.3, 129.2,
124.7, 91.5, 90.5, 63.7, 61.9, 39.6, 28.6, 18.6, 14.5 (2 peaks
under CD3OD); LRMS (FAB, M + H) 523.2; HRMS (FAB) m/ z
calcd for C28H32N4O4Cl 523.2112, found 523.2101; C,H,N.
(b) RP-HPLC purification (method F) yielded 10 in 70%
yield after lyophilization from 20% CH3CN/H2O: [R]24589 +71.3°
1
(c ) 0.23, CH3OH); RP-HPLC (method A) tR ) 5.75 min; H
4
(b) RP-HPLC purification (method I) yielded 8 (72%) as a
white solid: mp 206 °C; RP-HPLC (method A) tR ) 5.08, 5.17
NMR (CD3OD) 7.89 (1H, d, J HH ) 1.9, ArH C6-H), 7.85 (2H,
d, 3J HH ) 8.6, ArH), 7.79 (2H, d, 3J HH ) 8.6, ArH), 7.76 (1H, d,
4J HH ) 1.9, ArH C8-H), 5.24 (1H, m, 3J HH ) 7.6, NCH(CH3)CH2),
3.70 (2H, s, C3-H), 2.55 (2H, m, CH2CO2), 1.45 (9H, s, But),
min; [R]24 -24.5° (c ) 0.6, CH3OH); 1H NMR (CD3OD) 7.90
589
(1H, s, ArH), 7.81 (5H, m, ArH), 5.16 (1H, m, NCH(CH3)CH2),
2
3
3.97 (0.5H, d, J HH ) 15.2, C3-H), 3.91 (1H, s, C3-H), 3.85
1.33 (3H, d, J HH ) 7.2, NCH(CH3)CH2); 13C NMR (CD3OD)
2
(0.5H, d, J HH ) 15.2, C3-H), 3.32 (3H, s, NCH3), 2.84 (0.5H,
174.1, 172.7, 167.9, 167.6, 138.9, 137.7, 136.1, 134.9, 133.5,
131.8, 129.9, 129.3, 129.2, 124.7, 91.4, 90.6, 63.7, 39.4, 28.6,
18.5 (2 peaks under CD3OD); LRMS (FAB, M + H) 495.2;
HRMS (FAB) m/ z calcd for C26H28N4O4Cl 495.1799, found
495.1801; C,H,N.
3
2
dd, J HH ) 11.3, J HH ) 16.9, CH2CO2), 2.56 (1H, s, CH2CO2),
3
2
2.59 (0.5H, dd, J HH ) 4.6, J HH ) 16.9, CH2CO2), 1.34 (1.5 H,
d, J ) 6.8, NCH(CH3)CH2), 1.27 (1.5H, d, J HH ) 6.8, NCH-
3
(CH3)CH2); 13C NMR (CD3OD) 174.09, 171.35, 171.24, 167.84,
167.18, 140.14, 139.76, 137.35, 137.28, 134.59, 134.45, 133.48,
133.33, 133.14, 131.02, 130.85, 129.79, 129.32, 123.60, 123.52,
91.03, 91.01, 90.69, 90.65, 47.09, 46.84, 39.25, 38.58, 37.74,
37.50, 18.51, 18.23; LRMS (FAB) 455 (M + 3, 33), (M + 2, 20),
453 (M + 1, 100); HRMS (FAB) m/ z calcd for C23H22ClN4O4
453.1329, found 453.1344. Anal. Calcd for C25H26ClF3N4O8
(1.0 TFA, 2.0 H2O): C, 49.80; H, 4.35; N, 9.29. Found: C,
49.97; H, 5.30; N, 10.52.
1-ter t-Bu tyl-4-(3(R)-bu ta n oa te)-7-[(4-a m id in op h en yl)-
et h yn yl]-9-ch lor o-3,4-d ih yd r o-1H -1,4-b en zod ia zep in e-
2,5-d ion e (11). (a ) RP-HPLC purification (method F) yielded
(-)-1-tert-butyl-4-(3(R)-butanoate)-7-[(4-amidinophenyl)ethy-
nyl]-9-chloro-3,4-dihydro-1H-1,4-benzodiazepine-2,5-dione, eth-
yl ester (64%) as a white solid after lyophilization from 20%
CH3CN/H2O: [R ]24
-58.2° (c ) 0.17, CH3OH); RP-HPLC
589
(method A) tR ) 6.21 min; 1H NMR (CD3OD) 7.90 (1H, d, 4J HH
3
1-ter t-Bu tyl-4-(3(S)-bu ta n oa te)-7-[(4-a m id in op h en yl)-
et h yn yl]-9-ch lor o-3,4-d ih yd r o-1H -1,4-b en zod ia zep in e-
2,5-d ion e (9). (a ) RP-HPLC purification (method F) yielded
(-)-1-tert-butyl-4-(3(S)-butanoic acid)-7-[(4-amidinophenyl)-
) 1.9, ArH C6-H), 7.86 (2H, d, J HH ) 8.6, ArH), 7.80 (2H, d,
3J HH ) 8.3, ArH), 7.74 (1H, d, J HH ) 1.8, ArH C8-H), 5.24
4
3
(1H, m, NCH(CH3)CH2), 4.08 (2H q, J HH ) 7.4, OCH2), 3.72
(2H, s, C3-H), 2.57 (2H, m, CH2CO2), 1.44 (9H, s, But), 1.32

728 J ournal of Medicinal Chemistry, 1997, Vol. 40, No. 5
Blackburn et al.
3
3
(3H, d, J HH ) 7.0, NCH(CH3)CH2), 1.20 (3H, t, J HH ) 6.9,
OCH2CH3); 13C NMR (CD3OD) 172.6, 172.2, 167.8, 167.5,
138.9, 137.6, 136.2, 135.0, 133.5, 131.7, 129.9, 129.3, 129.2,
124.7, 91.5, 90.5, 63.7, 61.8, 39.5, 28.6, 18.6, 14.5 (2 peaks
under CD3OD); LRMS (FAB, M + H) 523.4; HRMS (FAB) m/ z
calcd for C28H32N4O4Cl 523.2112, found 523.2126; C,H,N.
(b) RP-HPLC purification (method F) yielded 11 (71%) after
lyophilization from 20% CH3CN/H2O: [R ]24589 -71.1° (c ) 0.46,
CH3OH); RP-HPLC (method A) tR ) 5.73 min; 1H NMR (CD3-
Ack n ow led gm en t. We are grateful to Mr. Sheldon
Mullins of the Bioorganic Chemistry Department for
1
conducting the variable temperature H NMR experi-
ments, to Ms. Sherry Bullens of the Cardiovascular
Department for conducting the platelet aggregation
assays, to Ms. Andrea Hebert of the Bioanalytical
Technology Department for conducting the ELISA, to
Dr. Charles Eigenbrot of the Protein Engineering
Department for his assistance in developing suitable
X-ray quality crystals, and to Drs. J ames Marsters and
Kevin J udice of the Biooorganic Department for their
insight and enlightening discussion, all of Genentech.
We would also like to acknowledge Dr. Fred Hollander
of the Department of Chemistry, University of Califor-
nia, Berkeley, for solving the X-ray crystal structure of
compounds (S)-(-)-13 and (R)-(-)-13.
4
3
OD) 7.89 (1H, d, J HH ) 1.9, ArH C6-H), 7.86 (2H, d, J HH
)
)
3
4
8.1, ArH), 7.79 (2H, d, J HH ) 8.7, ArH), 7.76 (1H, d, J HH
2.0, ArH C8-H), 5.25 (1H, m, NCH(CH3)CH2), 3.84 (1H, d, 2J HH
2
) 15.7, C3-H), 3.67 (1H, d, J HH ) 15.2Hz, C3-H), 2.85 (1H,
dd, J HH ) 15.1, J HH ) 6.3, CHHCO2), 2.51 (1H, dd, J HH
2
3
2
)
15.5, 3J HH ) 8.2, CHHCO2), 1.41 (9H, s, But), 1.32 (3H, d, 3J HH
) 6.9, NCH(CH3)CH2); 13C NMR (CD3OD) 174.0, 172.7, 167.8,
167.6, 138.9, 137.7, 136.1, 134.9, 133.5, 131.8, 129.9, 129.3,
129.2, 124.7, 91.4, 90.5, 63.7, 39.4, 28.6, 18.5 (2 peaks under
CD3OD); LRMS 495.2 (M + H); HRMS (FAB) m/ z calcd for
C26H28N4O4Cl 495.1799, found 495.1779. Anal. Calcd for
C28H33ClF3N4O8.5 (1.0 TFA, 1.5 H2O): C, 52.88; H, 4.91; N,
8.81. Found C, 52.84; H, 4.41; N, 8.63.
Su p p or tin g In for m a tion Ava ila ble: Listing of elemental
analyses on selected comounds and atomic coordinates and
selected bond angles for the X-ray crystal structures (R)-(-)-
13 and (S)-(-)-13 (11 pages). See any current masthead page
for ordering information.
1-ter t-Bu tyl-4-(3(R)-bu ta n oic a cid )-7-[(4-a m id in op h e-
n yl)eth yn yl]-9-ch lor o-3,4-dih ydr o-1H-1,4-ben zodiazepin e-
2,5-d ion e (12). (a ) RP-HPLC purification (method C) yielded
(+)-1-tert-butyl-4-(3(R)-butanoic acid)-7-[(4-amidinophenyl)-
ethynyl]-9-chloro-3,4-dihydro-1H-1,4-benzodiazepine-2,5-di-
one, ethyl ester (79%) as a white solid after lyophilization from
Refer en ces
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Peptide to Non-peptide. 2. The de novo Design of Potent,
20% CH3CN/H2O: [R ]24
+95.2° (c ) 0.25, CH3OH); RP-
589
HPLC (method A) tR ) 6.25 min; 1H NMR (CD3OD) 7.90 (1H,
4
3
d, J HH ) 1.9, ArH C6-H), 7.86 (2H, d, J HH ) 7.4, ArH), 7.80
3
4
(2H, d, J HH ) 8.7, ArH), 7.80 (1H, d, J HH ) 1.9, ArH C8-H),
3
3
4.95 (1H, m, J HH ) 7.0, NCH(CH3)CH2), 4.13 (2H, q, J HH
)
2
2
7.2, OCH2), 3.83 (1H, d, J HH ) 14.1 C3-H), 3.66 (1H, d, J HH
) 14.1, C3-H), 2.87 (1H, dd, 2J HH ) 16.0, 3J HH ) 6.9, CHHCO2),
2
3
2.64 (1H, dd, J HH ) 16.1, J HH ) 8.0, CHHCO2), 1.44 (9H, s,
But), 1.32 (3H, d, 3J HH ) 7.0, NCH(CH3)CH2), 1.20 (3H, t, 3J HH
) 7.0, 3H, OCH2CH3); 13C NMR (CD3OD) 172.4, 172.3, 167.8,
167.2, 139.1, 137.6, 136.2, 134.9, 133.5, 132.0, 129.9, 129.3,
129.3, 124.7, 91.5, 90.5, 63.7, 61.8, 52.4, 51.4, 39.5, 28.6, 18.1,
14.5; LRMS (FAB, M + H) 523.4; HRMS (FAB) m/ z calcd for
C28H32N4O4Cl 523.2112, found 523.2093; C,H,N.
(b) RP-HPLC purification (method F) yielded 12 (87%) after
lyophilization from 20% CH3CN/H2O + 0.1% TFA: [R ]24
589
+90.7° (c ) 0.37, CH3OH); RP-HPLC (method A) tR ) 5.64 min;
1H NMR (CD3OD) 7.89 (1H, d, J HH ) 2.0, ArH C6-H), 7.86
4
3
3
(2H, d, J HH ) 8.6, ArH), 7.80 (2H, d, J HH ) 8.8, ArH), 7.80
4
(1H, d, J HH ) 2.0, ArH C8-H), 4.93 (1H, m, NCH(CH3)CH2),
2
2
3.84 (1H, d, J HH ) 15.5, C3-H), 3.67 (1H,d, J HH ) 15.5, C3-
H), 2.85 (1H, dd, 2J HH ) 16.1, 3J HH ) 6.7, CHHCO2), 2.62 (1H,
dd, J HH ) 16.1, J HH ) 7.9, CHHCO2), 1.44 (9H, s, But), 1.31
2
3
3
(3H, d, J HH ) 7.0, NCH(CH3)CH2); 13C NMR (CD3OD) 174.1,
172.4, 167.8, 167.2, 139.1, 137.6, 136.2, 134.8, 133.5, 132.0,
129.9, 129.3, 129.2, 124.6, 91.4, 90.5, 63.7, 52.5, 51.6, 39.4, 28.6,
18.0; LRMS (FAB, M + H) 495.2; HRMS (FAB) m/ z calcd for
C26H28N4O4Cl 495.1799, found 495.1812. Anal. Calcd for
C28H32ClF3N4O8 (1.0 TFA, 2.0 H2O): C, 52.14; H, 5.00; N, 8.69.
Found C, 51.93; H, 5.63; N, 8.43.
Nonpeptidal Inhibitors of Platelet Aggregation Based on
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Cr ysta llogr a p h ic Da ta a n d Da ta Collection P a r a m -
eter s for (S)-(-)-13. Large, columnar crystals of (S)-(-)-13
were obtained by slow crystallization from CH2Cl2/hexanes.
Cr ysta l p a r a m eter s:
C28H28N3O4Cl, M ) 506.0; a )
9.2135(16) Å, b ) 10.5830(20) Å, c ) 13.7750(23) Å; R ) 90.0°,
â ) 94.122(14)°, γ ) 90.0°; V ) 1339.7(7) Å3, Z ) 2, Dcalc
)
1.25 g cm-3, space group P21, crystal dimensions 0.26 × 0.40
× 0.45 mm; number of reflections collected 3760, unique
reflections 3495.
Cr ysta llogr a p h ic Da ta a n d Da ta Collection P a r a m -
eter s for (R)-(-)-13. A colorless platelike crystal of (R)-(-)-
13 was prepared by slow recrystallization hexanes.
Cr ysta l p a r a m eter s: ClO4N3C31H35, M ) 549.09; a )
10.2189(1) Å, b ) 13.2252(2) Å, c ) 43.4972(5) Å; V ) 5878.5-
(1) Å3, Z ) 8, Dcalc ) 1.241 g cm-3, space group P212121 (No.
19), crystal dimensions ) 0.08 × 0.31 × 0.45 mm; number of
reflections used for unit cell determination (2θ range) ) 999
(3.0-45.0°), number of reflections collected 28 614, unique
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