Non-peptide glycoprotein IIb/IIIa antagonists. 11. Design and in vivo evaluation of 3,4-dihydro-1(1H)-isoquinolinone-based antagonists and ethyl ester prodrugs

Article abstract of DOI:10.1021/jm9604787

The structure-activity relationship of a series of orally active glycoprotein IIb/IIIa antagonists containing a nitrogen heterocycle grafted onto a 3,4-dihydro-1(1H)-isoquinolinone core is described. These compounds are structurally novel analogs of the p

Full text of DOI:10.1021/jm9604787

J . Med. Chem. 1996, 39, 4583-4591
4583
Non -P ep tid e Glycop r otein IIb/IIIa An ta gon ists. 11. Design a n d in Vivo
Eva lu a tion of 3,4-Dih yd r o-1(1H)-isoqu in olin on e-Ba sed An ta gon ists a n d Eth yl
Ester P r od r u gs
J ohn H. Hutchinson,*,† J acquelynn J . Cook,‡ Karen M. Brashear,† Michael J . Breslin,† J oan D. Glass,‡
Robert J . Gould,‡ Wasyl Halczenko,† Marie A. Holahan,‡ Robert J . Lynch,‡ Gary R. Sitko,‡
Maria T. Stranieri,‡ and George D. Hartman†
Merck Research Laboratories, P.O. Box 4, West Point, Pennsylvania 19486
Received J uly 3, 1996X
The structure-activity relationship of a series of orally active glycoprotein IIb/IIIa antagonists
containing a nitrogen heterocycle grafted onto a 3,4-dihydro-1(1H)-isoquinolinone core is
described. These compounds are structurally novel analogs of the progenitor compound 1 (L-
734,217, [[3(R)-[2-(piperidin-4-yl)ethyl]-2-oxopiperidinyl]acetyl]-3(R)-methyl-â-alanine) in which
the lactam chiral center has been removed. The 4-piperazinyl- and 4-piperidinyl-substituted
3,4-dihydro-1(1H)-isoquinolinones were found to be optimal for in vitro potency. In addition,
substitution at the 3-position of the â-amino acid enhanced potency with the 3-pyridyl and
3-ethynyl analogs being the most potent prepared. Attempts to improve the in vivo profile of
these compounds focused on modification of the physical properties. Ester prodrugs were
prepared to increase the lipophilicity and remove the zwitterionic nature of the antagonists.
The prodrug approach, coupled with the arylpiperazine terminus (pKa ) ∼9.0), afforded
moderately basic and relatively nonpolar compounds. The acid N-[[7-(piperazin-1-yl)-3,4-
dihydro-1(1H)-oxoisoquinolin-2-yl]acetyl]-3(S)-ethynyl-â-alanine, 6d (L-767,679), is a potent
fibrinogen receptor antagonist able to inhibit the ADP-induced aggregation of human gel-filtered
platelets with an IC50 of 12 nM. Although 6d is orally active based on the results of an ex vivo
dog assay at 0.3 mg/kg, the ethyl ester prodrug of this compound, 19 (L-767,685), is better
absorbed at this dose than 6d . Upon oral dosing, the ester 19 is converted to 6d in vivo in dog
with an estimated oral systemic availability of >17% (0-8 h, AUC19po/AUC6d iv). In addition,
studies in monkey at an oral dose of 1 mg/kg show that 19 affects the complete inhibition of
the ex vivo platelet aggregation in response to ADP between 2 and 8 h postdose with the level
of inhibition remaining at 40% at 12 h postdose. This level of activity was superior to that
observed for 6d and 1 at the same dose. Using ex vivo ADP-induced aggregation data from
rhesus monkey (n ) 2, 0-8 h using the AUC19po/AUC6d iv), the estimated systemic oral
availability of 6d when dosed as 19 is 32%.
In tr od u ction
subunit arginine-glycine-aspartic acid (RGD). Thus
small molecule mimetics of RGD (which are capable of
antagonizing the GP IIb/IIIa receptor) should prevent
the fibrinogen-mediated cross-linking of platelets. In-
deed, a GP IIb/IIIa specific antibody5 has been shown
to be clinically effective in this regard,6 and currently a
number of RGD mimetics are also undergoing clinical
evaluation.7-16
Recently, we have described the design and synthesis
of novel, low molecular weight, and orally active fibrino-
gen receptor antagonists.10 From this work, the lactam
1 (L-734,217) was selected for further evaluation in
clinical trials. Utilizing this compound as a starting
point, we have continued to focus on the preparation of
structurally simple antagonists which display good oral
bioavailability. In this paper, we will present the
structure-activity relationships (SAR) and in vivo
evaluation of a novel series of antagonists employing
an achiral bicyclic core. From this study, the 3,4-
dihydro-1(1H)-isoquinolinone (benzolactam) acid 6d , as
the ethyl ester prodrug 19, was found to be orally active
in both dog and monkey at doses lower than that
required for 1 to produce a similar response.
The hemostatic system is designed to maintain fluid
blood flow under normal physiological conditions while
being capable of reacting rapidly to form a clot to seal
sites of vascular damage. When vascular injury occurs,
subendothelial adhesion proteins such as collagen and
von Willebrand factor are exposed leading to subsequent
platelet adherence and activation. Activated platelets
secrete agonists such as ADP, serotonin, and throm-
boxane A2 which promote further activation of platelets.
The symmetrical protein fibrinogen bridges platelets to
form the hemostatic plug.1 This process may also occur
when an atherosclerotic plaque is ruptured, and the
resulting thrombus can lead to heart attacks, strokes,
and angina.2 Thus, a method to inhibit the formation
of a thrombus would have wide clinical significance.3
The binding of fibrinogen to platelet glycoprotein (GP)
IIb/IIIa is the final obligatory step in the platelet
aggregation cascade and is independent of the numerous
activation mechanisms. For this reason, it has been
identified as an attractive target for the development
of novel antithrombotics.4 It has been shown that a
recognition sequence present in fibrinogen involves the
Ch em istr y
* Author to whom correspondence should be addressed.
† Department of Medicinal Chemistry.
The chemistry for the construction of the benzolactam
core and the subsequent elaboration to the target
compounds is shown in Scheme 1. Alternative hetero-
‡ Department of Pharmacology.
X Abstract published in Advance ACS Abstracts, October 1, 1996.
S0022-2623(96)00478-5 CCC: $12.00 © 1996 American Chemical Society

4584 J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 23
Hutchinson et al.
Ta ble 1
inhibition of
aggregationa
IC50 (nM)
compd
X
Y
R1
R2
1
32
140
30
16
12
13
18
630
140
15
6a
6b
6c
6d
6e
6f
6g
6h
6i
H
H
H
H
H
H
H
H
F
H
H
H
H
H
H
H
H
H
H
H
Me
H
H
H
H
H
H
Ph(CH2)2
CtCH
3-pyridyl
3-pyridyl N-oxide
H
cyclic core structures were synthesized according to the
routes given in Schemes 2-5. For all the antagonists,
standard methodologies were used for the preparation
of substituted â-alanines.17
NH2
NHSO2Ph
H
H
H
H
CtCH
CtCH
6j
6k
Cl
H
19
35
The synthesis of the key intermediate benzolactam
3a commences with 2a and employs previously de-
scribed chemistry.18 The piperazine was then installed
using bis(chloroethyl)amine hydrochloride in n-butanol/
H2O with 1 N NaOH, the product was protected as the
Boc derivative (52% for two steps), and subsequent
alkylation with ethyl bromoacetate yielded 4a in 85%
yield. In a similar fashion, 4b was prepared from 2b.
Chlorination of 4a using N-chlorosuccinimide in THF
yielded a 3:1 mixture of the 8-chloro (5b) to 6-chloro (5a )
products which were separable by silica gel chromatog-
raphy and identified by NMR. Finally, hydrolysis of
either 4 or 5 followed by a peptide coupling with the
appropriate â-alanine derivative,19 deprotection, and
HPLC purification then gave 6a -k (see Table 1).
Compound 8a , containing a morpholine terminus, was
derived from 3a by condensation with bis(bromoethyl)
ether in DMF followed by alkylation with tert-butyl
bromoacetate. Alternatively, transformation of the
amine of 3a to the iodide, alkylation with ethyl bro-
moacetate, and then a palladium-catalyzed conversion
of iodine to tributyltin yielded the aryltin intermediate
7. The remaining compounds (8b-d ) were obtained via
cross-coupling reactions of 7 with either 4-iodoimida-
zole20 (to give 8b) or 4-bromopyridine (to give 8c).
Catalytic reduction of 8c and protection yielded the
piperidine analog 8d . Standard chemical transforma-
tions, as before, allowed the conversion of 8a -d to 9a -
d , and the compounds prepared in this manner are
listed in Table 2.
A series of analogs with variations in the bicyclic
heterocyclic nucleus were also synthesized, and the key
steps are outlined as follows. Scheme 2 shows the
preparation of the dehydrobenzolactam analog 11a via
10. Dehydrogenation of the benzolactam 4a was
achieved using 10% Pd on carbon in cyclohexene/ethanol
to give 10 in 95% yield.
For the tetrahydroisoquinoline analog 11b (Scheme
3), the direct reduction of various advanced benzolactam
intermediates was unsuccessful, so the tetrahydroiso-
quinoline core was constructed first. Thus, the trifluo-
roacetamide 12 was reacted with paraformaldehyde in
HOAc and H2SO4 to give (after hydrolysis of the
trifluoroacetamide) a 75% yield of the desired tetrahy-
droisoquinoline.21 This was alkylated with ethyl bro-
moacetate in Et3N/CH2Cl2 and the nitro group reduced
catalytically to produce 13 in near-quantitative yield.
Cl CtCH
a
In vitro inhibition of human gel-filtered platelets using ADP
agonist. See the Experimental Section for details.
Ta ble 2
a
a
In vitro inhibition of human gel-filtered platelets using ADP
agonist. See the Experimental Section for details.
The preparation of the quinazolinone 11c commences
with chloronitrobenzoic acid 14 (Scheme 4) which was
fused with piperazine hydrochloride to install the pip-
erazine group. Protection with Boc anhydride and
coupling with ethylglycine afforded 15 which was re-
duced and ring closed to yield the core quinazolinone
16.
Finally, Scheme 5 outlines the preparation of the
quinazolinedione 11d . In this case, the quinazolinedi-
one ring was constructed by first coupling 17 with ethyl-
glycine and then cyclization with carbonyldiimidazole.
Reduction of the nitro group then yielded 18 which was
elaborated (piperazine formation and peptide coupling)
as before to give the target compound.
Resu lts a n d Discu ssion
The compounds described were evaluated in a platelet
aggregation assay to assess the ability to inhibit ADP-
induced aggregation of human gel-filtered platelets
(GFPs). The results are given as IC50s (concentration
required for 50% inhibition) and shown in Tables 1-3.

Non-Peptide GP IIb/ IIIa Antagonists
J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 23 4585
Sch em e 1a
a
Reagents: (i) EtOCOCl, Et3N, THF; (ii) PPA, 150 °C; (iii) KNO3, H2SO4; (iv) 10% Pd-C, H2, MeOH; (v) HN(CH2CH2Cl)2‚HCl, n-BuOH,
110 °C; (vi) (Boc)2O, K2CO3, THF, H2O; (vii) NaHMDS, THF, BrCH2CO2Et; (viii) NCS, THF; (ix) 1 N LiOH, MeOH; (x) â-alanine ester,
EDC, HOBT, Et3N, DMF; (xi) HCl(g), EtOAc; (xii) NaNO2, H2O, 3 N HCl, KI; (xiii) (n-Bu3Sn)2, (PPh3)4Pd, 1,4-dioxane, 80 °C; (xiv)
haloheteroaryl, (PPh3)4Pd, DMF, 120 °C; (xv) trityl chloride, Et3N, DMF; (xvi) O(CH2CH2Br)2, DIPEA, DMF, 100 °C; (xvii) NaHMDS,
THF, BrCH2CO2tBu;
Sch em e 2a
Sch em e 3a
a
Reagents: (i) HOAc, H2SO4, (CH2O)x; (ii) 1 N LiOH, MeOH,
THF; (iii) BrCH2CO2Et, Et3N, CH2Cl2; (iv) 10% Pd-C, H2, EtOH.
a
Reagents: (i) 10% Pd-C, EtOH, cyclohexane, 75 °C.
could be harnessed to boost the oral performance of
these compounds (vide infra).
Our initial attempt to constrain the piperidine side
chain of 1 by incorporation of a benzene ring resulted
in the achiral analog 6a which had an IC50 of 140 nM.
Installation of a 3(R)-methyl group (6b), to provide the
conformational bias present in 1, improved the potency
further to 30 nM. That 6b and 1 were equipotent was
a gratifying result as this achieved our initial goal of
simplifying the molecule by removing a chiral center.
In addition, this modification yielded a compound in
which the basicity of the N-terminus is considerably
reduced compared to that of 1. The pKa of the piperidine
is ∼11, while the aryl piperazine is about 2 log units
lower at ∼9.22 It was hoped that this reduced basicity
Several other 3-substituted â-alanine analogs were
prepared for testing since substitution at this site has
been shown to significantly enhance potency. Thus,
incorporation of a phenethyl moiety afforded 6c (16 nM)
which is about 2-fold more potent than 6b . The
â-acetylene derivative 6d and the â-3-pyridyl derivative
6e were found to be equipotent in the platelet aggrega-
tion assay at 12 and 13 nM, respectively. The excellent
potency-enhancing effect achieved with these two sub-
stituents was originally discovered by workers at Mon-
santo-Searle11,19c culminating in the discovery of xe-
milofiban which is a prodrug in phase III clinical trials
as an oral agent.11 In fact, 6d ,e represent the most

4586 J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 23
Hutchinson et al.
Sch em e 4a
Ta ble 3
a
a
Reagents: (i) piperazine, 110 °C, neat; (ii) 1 N NaOH, (Boc)2O,
1,4-dioxane; (iii) H2NCH2CO2Et‚HCl, EDC, HOBT, NMM, DMF;
(iv) 10% Pd-C, H2, EtOH; (v) HC(OEt)3, reflux.
Sch em e 5a
a
In vitro inhibition of human gel-filtered platelets using ADP
agonist. See the Experimental Section for details.
using the 3-alkynyl-â-alanine C-terminus. The 6-F (6i)
and 6-Cl (6j) derivatives are equipotent to the parent
compound 6d . In contrast, the 8-Cl analog 6k is 3 times
less potent than 6d (IC50 ) 35 compared to 12 nM) at
inhibiting the aggregation of GFPs. Presumably, the
presence of the chlorine at C-8 causes the piperazine to
adopt a less favorable conformation or interferes (steri-
cally or electronically) with an interaction between the
lactam amide and the receptor.
Examination of a series of heterocycles at the N-
terminus (Table 2) shows clearly the requirement for a
basic nitrogen to obtain very potent inhibitors. The
morpholine analog 9a , wherein the oxygen atom re-
places the piperazine nitrogen, is inactive at 300 µM.
Moderately basic heterocycles such as imidazole (9b)
and pyridine (9c) have modest potency in the platelet
aggregation assay, whereas the highly basic piperidine
9d is roughly equipotent to that of the corresponding
piperazine 6d .
Replacement of the benzolactam core with alternative
bicyclic heterocycles (as shown in Table 3) was also
investigated. Dehydrogenation of the lactam ring af-
forded 11a which has an IC50 ) 81 nM and is ap-
proximately 4-fold less potent than the parent com-
pound 6d . The detrimental effect of removing the
carbonyl group of 6d is demonstrated with the amine
11b. In this case, 11b is significantly less potent (IC50
) 320 nM) than 6d , and this may reflect the altered
conformation of the side chain or, perhaps, the fact that
a basic site in the center of the molecule gives rise
to unfavorable ionic interactions. Interestingly, the
quinazolinone 11c is also a relatively poor fibrinogen
receptor antagonist, whereas the close analog quinazo-
linedione 11d is some 10 times more potent (IC50s of
330 and 27 nM, respectively). Calculations show that
a
Reagents: (i) H2NCH2CO2Et‚HCl, EDC, HOBT, NMM, DMF;
(ii) CDI, THF, reflux; (iii) 10% Pd-C, H2, EtOH.
potent compounds prepared in this series to date.
Interestingly, the pyridine N-oxide 6f is also very potent
(IC50 ) 18 nM) indicating that the receptor will tolerate
both lipophilic (e.g., phenethyl) and very polar substit-
uents at this position.
In previous publications, we reported on a novel series
of fibrinogen receptor antagonists which employ a
sulfonamide R to the C-terminus acid.9a,23 The sulfona-
mide appears to bind noncovalently to the GP IIb/IIIa
receptor at an exosite and confers, in certain cases, a
considerable enhancement in potency. It was, therefore,
of interest to see if this effect could be utilized in the
benzolactam series. Accordingly, the sulfonamide 6h
and the corresponding amine 6g were prepared. As can
be seen by comparison of the unsubstituted analog 6a
with the amine 6g (140 versus 630 nM), the presence
of an R-amino group has a detrimental effect on potency.
Addition of the sulfonamide functionality to give 6h
gives an antagonist of modest potency (IC50 ) 140 nM).
Unfortunately, this is considerably less potent than the
3-substituted â-alanine analogs described herein, and
clearly the sulfonamide group is not a general solution
to the problem of potency enhancement for fibrinogen
receptor antagonists.
Substitution of the aromatic ring with F or Cl was
undertaken to deactivate this electron rich system and
to probe the steric effects between the heteroatom and
the piperazine ring. These compounds were all made

Non-Peptide GP IIb/ IIIa Antagonists
J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 23 4587
there is little difference in the electronic character of
the lactam carbonyl present in compounds 6d and 11a -
d ; therefore, the observed differences in relative poten-
cies may reflect subtle differences in the conformations
of the side chains. Nevertheless, the results of the SAR
studies presented show that the benzolactam core in
conjunction with a 3-substituted â-alanine and a pip-
erazine or piperidine N-terminus yields compounds that
are superior in potency to the lactam 1. In addition,
the asymmetric center present in the lactam of 1 has
been removed and the N-terminus side chain con-
strained by appending an aromatic ring. This has the
additional effect of reducing the basicity of the N-
heterocycle, especially in the case of the arylpiperazine
22
which is approximately 2-3 log units lower in pKa
than the piperidine of lactam 1.
The oral profile of the more potent inhibitors de-
scribed herein (deemed as those with an IC50 < 30 nM,
i.e., 6b -e,i,j, 9d , and 11d ) was assessed in dogs by
measuring the inhibition of the extent of ex vivo ADP-
induced aggregation of platelet rich plasma as a function
of time. Compounds were screened with an oral dose
of either 0.3, 0.5, or 1 mg/kg (n ) 2-5), and selected
compounds were also evaluated as the corresponding
ethyl ester prodrug. The results are displayed in Table
4. All of the parent acids showed good peak activity
(maximum inhibition >80%), with the exception of 6c
and 11d which are essentially inactive at this dose. The
time to reach peak inhibition of aggregation (Tmax) was
also fairly constant, with all compounds achieving a Tmax
between 1 and 3 h. Unfortunately, the duration of
activity was less than desired as, in all cases, the
inhibitory effects returned to base line within 6-8 h.
We next examined the effect of ester prodrugs of
several of these compounds to see if this would lead to
increased absorption and a prolonged duration of action.
Indeed, there are several fibrinogen receptor antagonist
prodrugs that show enhanced absorption and/or dura-
tion which are currently under clinical investiga-
tion.11,13,14a,15 By masking the carboxylate functionality
as an ester, the zwitterionic character is removed and
the polarity of the molecule is therefore attenuated.
Both of these factors may aid absorption. In addition,
for those compounds containing an arylpiperazine moi-
ety, it was postulated that an ester prodrug may be
better absorbed due to the relatively low basicity of the
piperazine.
F igu r e 1. Effect of drug on ex vivo platelet aggregation
response to ADP agonist expressed as percent inhibition over
time (h) in conscious dogs. Drug was administered as follows:
0.3 mg/kg po (n ) 5) for (- -) 1, (O) 6d , and (b) 19; 0.01 mg/
kg iv bolus (n ) 3) for (4) 6d .
Ta ble 4. Effect of Compound on Inhibition of the Extent of ex
Vivo ADP-Induced Aggregation in Canine Platelet Rich Plasma
free acid
ethyl ester prodrug
max
max
po dose inhibition Tmax
po dose inhibition Tmax
compd (mg/kg)
(%)
(h) compd (mg/kg)
(%)
(h)
6b
6c
6d
6e
6i
6j
9d
11d
0.5
0.5
0.3
0.5
0.5
0.5
0.3
0.5
100
20
80
100
95
80
1
0.5
1.5-3
1-4
1-3
1-1.5
1-4
19
20
21
0.5
0.5
0.3
100
75
100
2.5-8
2.5
7-8
100
0
22
23
0.3
1.0
40
0
4
(esters of 6d ,i, respectively) showed excellent activity.
In particular, dogs dosed at 0.5 mg/kg with 19 were
completely inhibited from 2.5 h until the end of the 8 h
experimental period. The 6-F analog 21 also showed
complete inhibition at 8 h using the same dose, but in
this case, the time to peak activity was longer (7 h).
Interestingly, 22, the ethyl ester of piperidine analog
9d , showed poor activity when dosed orally at 0.3 mg/
kg. The contrast in behavior between the ethyl esters
19 and 22 perhaps reflects a difference in the absorption
of the two compounds. This may be related to the
increased polarity and basicity of the arylpiperidine of
22 (log P ) -1.54 in comparison to the arylpiperazine
of 19, log P ) -0.85) which diminishes the ability of 22
to cross the intestinal wall.
Due to the excellent activity of 6d when dosed orally
as the ethyl ester prodrug 19 at 0.5 mg/kg, we decided
to evaluate this compound in depth and demonstrate
that it has potential for b.i.d. dosing in two species (dog
and monkey) at a lower dose than that required for 1.
Figure 1 shows the effects in dog on ex vivo platelet
aggregation in response to ADP for 1, 6d , and 19. When
6d was administered orally at 0.3 mg/kg (n ) 5), the
inhibition of ADP-stimulated platelet aggregation peaked
at 85% from 1 to 1.5 h and fell rapidly back to base line
levels by 8 h. However, when 19 was administered
orally at the same dose (n ) 5), the degree of inhibition
Of the original compounds investigated, the ethyl
esters of 6d ,e,i, 9d , and 11d were prepared. In all
cases, the esters prepared had an IC50 of >1 µM in the
platelet aggregation assay. In addition, the log P24 of
the parent acids were approximately 2-3 orders of
magnitude lower than that of the corresponding ethyl
ester. For example, the acid 6d , with a log P of less
than -3.3, is considerably more polar than the ethyl
ester prodrug 19, log P of -0.85. To examine the effect
of the ester prodrug in vivo, the prodrugs were dosed
orally in dogs, and the results are included in Table 4.
As with the quinazolinedione acid 11d , the ethyl ester
23 showed no ex vivo activity despite the relatively high
dose of 1 mg/kg. Of the arylpiperazine-containing
compounds (6d ,e,i), the â-pyridyl analog 20 (ester of 6e)
was disappointing as the activity was less than that
observed for the free acid when given at the same dose.
In contrast, both the â-acetylene derivatives 19 and 21

4588 J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 23
Hutchinson et al.
In conclusion, we have discovered a novel series of
orally active fibrinogen receptor antagonists containing
a piperazine grafted onto a benzolactam core. These
compounds are structural analogs of the progenitor
compound lactam 1 which embody only one chiral
center. Substitution at the 3-position of the â-amino
acid enhanced potency with the 3-pyridyl (6e) and
3-ethynyl (6d ) congeners being the most potent pre-
pared. Attempts to improve the in vivo profile of these
compounds focused on modification of the physical
properties. Ester prodrugs were prepared to increase
the lipophilicity and remove the zwitterionic nature of
the antagonists. This, coupled with the arylpiperazine
terminus (pKa ) ∼9.0), afforded moderately basic and
relatively nonpolar compounds. Thus, although the acid
6d is orally active in the inhibition of ex vivo aggregation
in the dog and monkey, the ethyl ester prodrug of this
compound (19) appears better absorbed in both species
and is converted to 6d in vivo. The estimated oral
systemic availability of 6d (when dosed as 19) is >17%
in dog and 32% in rhesus monkey. In addition, in both
dog and rhesus monkey the ester 19 appears suitable
for b.i.d. administration, and it has been demonstrated
to be more efficacious in these species than 1 at the
same dose.
F igu r e 2. Effect of drug on ex vivo platelet aggregation
response to ADP agonist expressed as percent inhibition over
time (h) in conscious rhesus monkeys. Drug was administered
as follows: 1.0 mg/kg po for (- -) 1 (n ) 2), (O) 6d (n ) 3),
and (b) 19 (n ) 2).
was equal to or greater than 75% from 4 to 8 h. In
contrast, 1 did not perform as well reaching a maximum
inhibition of 55% at 2 h with the effect lost at 6 h. For
an estimate of the systemic oral availability of 19, the
acid 6d was given at 0.01 mg/kg iv (n ) 3). Maximum
inhibition was observed at the first time point (100%
inhibition at 5 min), and by 2 h the level of inhibition
had returned to base line. From the AUC data, the
systemic oral availability (0-8 h) of 6d is 13% and,
when dosed orally as the ethyl ester prodrug 19, is
increased to at least 17%. This is a grossly underesti-
mated value since, at the end of the study at 8 h, the
level of inhibition for 19 is still 80%. In fact, in a
separate experiment in which two dogs were dosed
orally with 19 (same dose, 0.3 mg/kg) and monitored
over 12 h, the profile was similar to that shown in
Figure 1 and the level of inhibition at 10 and12 h was
64% and 51%, respectively. Thus it appears that 19 is
suitable for b.i.d. dosing in dog.
Exp er im en ta l Section
In Vitr o In h ibition of Gel-F ilter ed P la telets Assa y.
Human blood was collected into 0.1 vol of acid citrate/dextrose,
and platelets were isolated by differential centrifugation
followed by gel filtration on Sepharose 2B in divalent ion-free
Tyrode’s buffer (pH 7.4) containing 2% bovine serum albumin.
Platelet aggregation was measured at 37 °C in a Chronolog
aggregometer. The reaction mixture contained gel-filtered
human platelets (2 × 108/mL), fibrinogen (100 µg/mL), Ca2+
(1 mM), and the compound to be tested. The aggregation was
initiated by adding 10 µM ADP 1 min after the other
components were added. The reaction was then allowed to
proceed for at least 2 min. The extent of inhibition of
aggregation is expressed as the percentage of the rate of
aggregation observed in the absence of inhibitor. The IC50 is
the dose of a particular compound inhibiting aggregation by
50% relative to a control lacking the compound.
Exp er im en ta l P r otocol for in Vivo Stu d ies. Conscious,
purpose-bred mongrel dogs of either sex (8-12 kg) were
administered test compounds as an intravenous bolus (vehicle
) saline) or orally by gastric lavage (vehicle ) water). During
these studies the dogs rested comfortably in nylon slings. At
specified time points, 5 mL blood samples were drawn from
either saphenous or cephalic veins (0.38% sodium citrate, final
concentration) for the measurement of ex vivo platelet ag-
gregation responses to ADP and for whole blood platelet
counts.25 Blood samples were obtained before compound
administration (base line) and at 1, 5, 15, 30, 45, 60, 75, 90,
120, and 180 min after dosing for the iv studies and at 20, 40,
70, 90, 150, 200, 250, 300, 350, and 480 min after dosing for
the oral studies in dogs. Compounds were also administered
orally by nasogastric lavage (vehicle ) water) to conscious
rhesus monkeys (5-7 kg) which were placed in primate
restraint chairs. Blood samples (3 mL) were obtained before
compound administration (base line) and at 30, 60, 120, 180,
240, 300, 360, 480, 600, and 720 min after dosing.
Mea su r em en t of ex Vivo P la telet Aggr ega tion . Platelet
rich plasma (PRP) was prepared by centrifugation of whole
blood at 150g for 5 min, and the platelet concentration was
adjusted to 2 × 108 platelets/mL with time-matched platelet
poor plasma (PPP). PRP (300 µL, 2 × 108 platelets/mL) was
incubated at 37 °C for 3 min prior to the addition of agonist.
Platelet aggregation was measured by the change in light
transmittance (PPP represents 100%) under stirring conditions
(1100 rpm) at 37 °C in a Biodata platelet aggregation profiler,
A similar study was performed in rhesus monkey
comparing 1, 6d , and 19 at an oral dose of 1 mg/kg
during a 12 h protocol. The effects on ex vivo platelet
aggregation in response to ADP are shown in Figure 2.
At this dose, 6d achieved a maximum inhibition of 65-
70% between 2 and 6 h falling below 30% inhibition at
10 h. In contrast, the prodrug 19 showed full inhibition
of aggregation between 2 and 8 h, declining to 40%
inhibition by 12 h after dosing. This result with a single
dose suggests that 19 may be suitable for b.i.d. dosing
in primates. The lactam 1 did not perform as well as
19, since the peak activity of 1 occurred between 1 and
5 h and the level of inhibition dropped below 40% at 8
h. In a separate 8 h study (data not shown) in rhesus
monkey (n ) 2, cross-over using 0.25 mg/kg iv 6d and
1.25 mg/kg po 19), the systemic oral availability (using
the AUC19po/AUC6div of the inhibition of ADP-stimulated
platelet aggregation) was estimated to be 32%. Thus,
the ethyl ester 19 is well absorbed and converted in vivo
to the acid 6d in both dog and rhesus monkey.

Non-Peptide GP IIb/ IIIa Antagonists
J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 23 4589
Ta ble 5. Analytical Data
3.6 (6H, m), 6.15 (1H, br s), 7.02 (1H, dd, J ) 8.3, 2.7 Hz),
7.13 (1H, d, J ) 8.3 Hz), 7.62 (1H, d, J ) 2.7 Hz).
compd
formula
analysisa
A solution of this isoquinolinone (2.37 g, 7.16 mmol) in THF
(30 mL) at -78 °C under argon was treated with NaHMDS (1
M solution in THF; 7.88 mL, 7.88 mmol), and the temperature
was allowed to rise to -50 °C over 30 min. The solution was
cooled back to -78 °C, and ethyl bromoacetate (1.19 mL, 10.7
mmol) was added in one lot. After stirring at ambient
temperature for 3 h, the mixture was poured into EtOAc,
extracted with 1 N HCl, washed with brine (twice), dried
(MgSO4), and evaporated to give an oil. Column chromatog-
raphy (hexane/EtOAc, 1:1 and then 1:2) gave 4a as a solid (3.0
g, quantitative). 1H NMR (CDCl3): δ 1.29 (3H, t, J ) 7.1 Hz),
2.98 (2H, t, J ) 6.6 Hz), 3.15 (4H, m), 3.6 (6H, m), 4.21 (2H,
q, J ) 7.1 Hz), 4.33 (2H, s), 7.0 (1H, dd, J ) 8.3, 2.4 Hz), 7.10
(1H, d, J ) 8.3 Hz), 7.64 (1H, d, J ) 2.4 Hz).
6a
6b
6c
6d
6e
6f
6g
6h
6i
6j
6k
9a
C18H24N4O4‚0.9H2O‚1.65TFA
C, H, N
C, H, N
C, H, N
C, H, N
C, H, N
C, H, N
C, H, N
C, H, N
C, H, N.
C, H, N
C, H, N
b
C, H, N
C, H, N
C, H, N
C, H, N
C, H, N
C, H, N
C, H, N
C, H, N
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
19H26N4O4‚1.7H2O‚1.45TFA
26H32N4O4‚1.0H2O‚2.1TFA
20H24N4O4‚0.25H2O‚1.55TFA
23H27N5O4‚2.0H2O‚2.65TFA
23H27N5O5‚0.9H2O‚2.4TFA
18H25N5O4‚2.05H2O‚2.05TFA
24H29N5O6S‚1.0H2O‚1.8TFA
20H23N4O4F‚0.4H2O‚1.35TFA
20H23N4O4Cl‚1.25H2O‚1.75TFA
20H23N4O4Cl‚0.15H2O‚1.45TFA
23H27N4O5
22H21N5O4‚1.2H2O‚1.65TFA
21H19N3O4‚0.25H2O‚1.2TFA
21H25N3O4‚0.8H2O‚1.35TFA
20H22N4O4‚0.6CH3CN‚2.0TFA
20H26N4O3‚3TFA
9b
9c
9d
11a
11b
11c
11d
19
Eth yl 6-Ch lor o-7-(4-N-Boc-p ip er a zin -1-yl)-3,4-d ih yd r o-
1(1H)-isoqu in olin on e-2-a ceta te (5a ) a n d Eth yl 6-Ch lor o-
7-(4-N-Boc-p ip er a zin -1-yl)-3,4-d ih yd r o-1(1H)-isoqu in oli-
n on e-2-a ceta te (5b). To a solution of 4a (250 mg, 0.61 mmol)
in THF (11 mL) was added NCS (114 mg, 0.85 mmol), and
the reaction mixture was then stirred for 48 h. The solvent
was removed and the residue chromatographed (silica gel;
hexane/EtOAc, 3:2) to give the first eluted compound 5a (30
mg). 1H NMR (CDCl3): δ 1.27 (3H, t), 1.46 (9H, s), 3.0 (6H,
m), 3.5-3.7 (6H, m), 4.23 (2H, q), 4.33 (2H, s), 7.24 (1H, s),
7.75 (1H, s). This was followed by the slower eluting compound
5b (100 mg). 1H NMR (CDCl3): δ 1.27 (3H, t), 1.50 (9H, s),
3.0 (6H, m), 3.6 (6H, m), 4.23 (2H, q), 4.35 (2H, s), 7.1 (2H, s).
Eth yl 7-(Tr ibu tylsta n yl)-3,4-d ih yd r o-1(1H)-isoqu in o-
lin on e-2-a ceta te (7). To a solution of 7-iodo-3,4-dihydro-
1(1H)-isoquinolinone (7.03 g, 25.7 mmol) in THF (125 mL) at
-78 °C under argon was added NaHMDS (1 M in hexane; 28.3
mL, 28.3 mmol). The solution was warmed to -30 °C over 30
min and then cooled back to -78 °C and ethyl bromoacetate
(4.27 mL, 38.6 mmol) added. After warming to room temper-
ature, the mixture was stirred for 1 h and then partitioned
between EtOAc and 10% citric acid solution. The organic
extracts were washed with brine, dried, and evaporated to give
an orange oil (11.6 g). Column chromatography (silica gel;
hexane/EtOAc, 1:1) yielded ethyl 7-iodo-3,4-dihydro-1(1H)-
isoquinolinone-2-acetate as a solid (9.8 g, quantitative).
The iodide (5 g, 13.9 mol), hexabutylditin (14 mL, 17.9
mmol), and tetrakis(triphenylphosphine)palladium(0) (805 mg,
0.7 mmol) were stirred in 1,4-dioxane (75 mL) at 80 °C for 16
h. After cooling, the solvent was removed and the residue
purified on silica gel eluting with hexane/EtOAc (4:1) to give
7 as an oil (4.36 g, 60%). 1H NMR (CDCl3): δ 1.27 (3H, t),
1.03 (13H, m), 1.45 (17H, m), 3.05 (2H, t), 3.67 (2H, t), 4.22
(2H, q), 4.33 (2H, s), 7.14 (1H, d), 7.53 (1H, d), 8.19 (1H, s).
ter t-Bu tyl 7-(4-N-Mor p h olin yl)-3,4-d ih yd r o-1(1H)-iso-
qu in olin on e-2-a ceta te (8a ). A solution of 3a (391 mg, 2.41
mmol), diisopropylethylamine (1.26 mL, 7.2 mmol), and bis-
(2-bromoethyl) ether (363 µL, 2.9 mmol) in DMF (15 mL) was
heated at 100 °C for 16 h. The cooled solution was diluted
with EtOAc, washed with saturated NaHCO3 and then brine,
dried, and concentrated. Chromatography of the residue (silica
gel; 5% EtOH in EtOAc) afforded 7-(4-N-morpholinyl)-3,4-
dihydro-1(1H)-isoquinolinone as a solid (402 mg, 72%).
This isoquinolinone was alkylated with tert-butyl bromoac-
etate using the conditions for 4a to yield (after chromatogra-
phy) 8a as a solid (82%). 1H NMR (CDCl3): δ 1.48 (9H, s),
2.95 (2H, t), 3.18 (4H, m), 3.61 (2H, t), 3.86 (4H, m), 4.24 (2H,
s), 7.00 (1H, dd), 7.10 (1H, d), 7.63 (1H, d).
19H21N5O4‚0.5H2O‚2TFA
19H21N5O5‚1.45TFA
22H28N4O4‚2.65HCl
a
All compounds (except 9a ) characterized by analysis, mass
spectra, and H NMR. Exact mass and H NMR obtained for this
compound.
1
b
1
Model PAP-4. Aggregation in dog PRP was initiated by the
addition of 10 µM ADP + 1 µM epinephrine; epinephrine is
used to enhance the aggregation response of canine platelets
to other agonists. Aggregation in monkey PRP was initiated
by the addition of 20 µM ADP. The extent of aggregation was
reported as the peak percent of aggregation achieved based
on a maximum of 100% (standardized with PPP). The effect
of compound treatment on the extent and rate of aggregation
is expressed as the percent inhibition using the base line,
pretreatment aggregation response as 100%.
Ch em istr y. Proton nuclear magnetic resonance spectra
were obtained on a Varian 300 spectrometer, and proton
chemical shifts are relative to tetramethylsilane (TMS) as
internal standard. Elemental analyses and high-resolution
mass spectra were provided by the Analytical Department and
the Mass Spectroscopy Department of Merck, West Point, PA.
Where elemental analyses are reported only by symbols of the
elements, results are within 0.4% of the theoretical values.
All reactions were carried out under an argon atmosphere, and
all worked-up reaction solutions were dried using MgSO4.
Final compounds were purified by reverse phase HPLC
eluting with a gradient of acetonitrile/water containing 0.1%
TFA. Excess acetonitrile was removed in vacuo, and the
resulting solution was frozen and lyophilized to afford the TFA
salt of the desired compound as an amorphous powder.
The physical data for the final compounds (prepared as
described for compounds 6d /19 using the appropriate â-alanine
derivatives and standard peptide reactions17,19) are give in
Table 5.
Eth yl 7-(4-N-Boc-p ip er a zin -1-yl)-3,4-d ih yd r o-1(1H)-iso-
qu in olin on e-2-a ceta te (4a ). A solution of 3a 18 (5.0 g, 30.8
mmol) and bis(2-chloroethyl)amine hydrochloride (6.3 g, 33.9
mmol) in n-butanol (250 mL) was stirred at 110 °C for 3 days.
The precipitate was removed by filtration to provide the
starting amine as the HCl salt (3.6 g). Evaporation of the
n-butanol under reduced pressure afforded a dark oil which
was purified by column chromatography (silica gel; EtOH/H2O/
NH4OH, 10:0.5:0.5) to give 7-(piperazin-1-yl)-3,4-dihydro-1(1H)-
isoquinolinone (2.22 g). 1H NMR (CD3OD): δ 2.86 (2H, t), 3.10
(4H, m), 3.22 (4H, m), 3.44 (2H, t), 7.18 (2H, m), 7.55 (1H, m).
This piperazine (2.22 g, 9.61 mmol), (Boc)2O (2.30 g, 10.6
mmol), and K2CO3 (1.33 g, 9.61 mmol) were stirred in THF
(20 mL) and H2O (20 mL) for 24 h. The solution was poured
into water, extracted with EtOAc (3×), washed with water and
then brine, dried (MgSO4), and evaporated. Chromatography
of the residue (EtOAc) gave a yellow solid which was swished
with ether to afford 7-(4-N-Boc-piperazin-1-yl)-3,4-dihydro-
1(1H)-isoquinolinone as a white solid (2.0 g, 63%). 1H NMR
(CDCl3): δ 1.49 (9H, s), 2.92 (2H, t, J ) 6.6 Hz), 3.19 (4H, m),
Eth yl 7-(4-P yr id yl)-3,4-d ih yd r o-1(1H)-isoqu in olin on e-
2-a ceta te (8c). A solution of 7 (4.36 g, 8.35 mol), 4-bromopy-
ridine (1.79 g, 9.19 mmol), and tetrakis(triphenylphosphine)-
palladium(0) (965 mg, 0.84 mmol) in DMF (40 mL) purged with
argon was stirred at 120 °C for 16 h. The solution was poured
into saturated NaHCO3 and EtOAc, extracted with EtOAc,
washed with brine, dried, and evaporated to give a brown oil.
Chromatography (silica gel; EtOAc and then 5% MeOH in
EtOAc) gave 8c as a pale yellow oil (1.55 g, 60%). 1H NMR
(CD3OD): δ 1.28 (3H, t), 3.18 (2H, t), 3.75 (2H, t), 4.21 (2H,
q), 4.38 (2H, s), 7.48 (1H, d), 7.77 (2H, d), 7.92 (1H, d), 8.33
(1H, s), 8.60 (2H, d).

4590 J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 23
Hutchinson et al.
Eth yl 7-(4-N-Boc-p ip er id in -1-yl)-3,4-d ih yd r o-1(1H)-iso-
qu in olin on e-2-a ceta te (8d ). The pyridine 8b was hydroge-
nated in EtOH (100 mL) with HOAc (20 mL) using 10% Pd-C
(200 mg added after each 24 h; 800 mg total) at 64 psi for 5
days. The mixture was filtered through Celite, the solvent
removed and the crude product protected using (Boc)2O, K2-
CO3 in THF/water (cf. preparation of 4a ). Chromatography
(silica gel; hexane/EtOAc, 1:1) gave 8d as a colorless oil (20%
for two steps).
Eth yl 7-(1-Tr ityl-4-im id a zolyl)-3,4-d ih yd r o-1(1H)-iso-
qu in olin on e-2-a ceta te (8b). This compound was prepared
as for 8c but using 4-iodoimidazole. The product was then
protected using trityl chloride in Et3N/DMF to yield 8b. 1H
NMR (CDCl3): δ 1.28 (3H, t), 3.05 (2H, t), 3.65 (2H, t), 4.31
(2H, s), 4.40 (2H, q), 7.19 (6H, m), 7.34 (9H, s), 7.47 (2H, m),
7.66 (1H, m), 8.05 (1H, d), 8.18 (1H, s).
N-[[7-(P ip er a zin -1-yl)-3,4-d ih yd r o-1(1H)-oxoisoqu in o-
lin -2-yl]a cetyl]-3(S)-eth yn yl-â-a la n in e Eth yl Ester Hy-
d r och lor id e (19). The ethyl ester 4a (2.9 g, 6.95 mmol), 1 N
LiOH (20.9 mL, 20.9 mmol), and MeOH (50 mL) were stirred
for 16 h at room temperature. The solvent was removed; the
residue was taken up in EtOAc and washed with 1 N HCl.
Repeated extraction of the aqueous phase followed by washing
of the combined organic layers with brine (5 mL), drying
(MgSO4), and evaporation gave 7-(4-N-Boc-piperazin-1-yl)-3,4-
dihydro-1(1H)-isoquinolinone-2-acetic acid as a solid (2.5 g,
92%). 1H NMR (CD3OD): δ 1.48 (9H, s), 2.99 (2H, t), 3.20
(4H, m), 3.62 (6H, m), 4.31 (2H, s), 7.22 (2H, s), 7.60 (1H, s).
To a solution of this acid (150 mg, 0.39 mmol), HOBT (63
mg, 0.46 mmol), and EDC (111 mg, 0.58 mmol) were added
3(S)-ethynyl-â-alanine ethyl ester hydrochloride (82 mg, 0.46
mmol) and Et3N (80.7 mL, 0.58 mmol). The mixture was
stirred at room temperature under argon for 16 h and then
partitioned between EtOAc and 10% citric acid. The aqueous
phase was extracted with EtOAc (×3), and the combined
organic layers were then washed with saturated aqueous
NaHCO3 followed by brine. Removal of the dried (MgSO4)
solvent afforded a yellow oil which was purified by column
chromatography (silica gel; hexane/EtOAc, 1:1) to give N-[[7-
(4-N-Boc-piperazin-1-yl)-3,4-dihydro-1(1H)-oxoisoquinolin-2-yl]-
acetyl]-3(S)-ethynyl-â-alanine ethyl ester as an oil.
HCl(g) was bubbled through a solution of the Boc-piperidine
(176 mg, 0.37 mmol) in 50 mL of EtOAc for 5 min. The solvent
was removed in vacuo to leave 19 as the HCl salt. 1H NMR
(CD3OD): δ 1.25 (3H, t, J ) 7.1 Hz), 2.75 (3H, m), 2.99 (2H, t,
J ) 6.4 Hz), 3.4 (8H, m), 3.64 (2H, t, J ) 6.4 Hz), 4.14 (2H, q,
J ) 7.1 Hz), 4.24 (2H, s), 5.06 (1H, dd, J ) 7.2, 2.4 Hz), 7.22
(2H, m), 7.55 (1H, d, J ) 2.2 Hz).
N-[[7-(P ip er a zin -1-yl)-3,4-d ih yd r o-1(1H)-oxoisoqu in o-
lin -2-yl]acetyl]-3(S)-eth yn yl-â-alan in e Tr iflu or oacetic Acid
Sa lt (6d ). The ester 19 (70 mg, 0.16 mmol) was stirred in 10
mL of MeOH and 0.65 mL of 1 N LiOH for 16 h, and then 1 N
HCl was added to give pH ) 4. After removal of the solvent,
the residue was purified by reverse phase HPLC (C18 column,
H2O/CH3CN with 0.1% TFA as gradient) to give 6d as the TFA
salt. 1H NMR (CD3OD): δ 2.72 (3H, m), 2.99 (2H, t, J ) 6.6
Hz), 3.4 (8H, m), 3.64 (2H, t, J ) 6.6 Hz), 4.25 (2H, s), 5.05
(1H, m), 7.22 (2H, m), 7.55 (1H, d, J ) 2.4 Hz), 8.62 (1H, d, J
) 8.1 Hz).
evaporated to give an oil (10.2 g). Chromatography on silica
gel eluting with hexane/EtOAc (2:1) gave the tetrahydroiso-
quinoline (8.9 g, 81%).
This tetrahydroisoquinoline (750 mg, 2.7 mmol) was treated
with 1 N LiOH (5.5 mL, 5.5 mmol), MeOH (8 mL), and THF
(2 mL) for 1 h. The solution was poured into water, extracted
with EtOAc, washed with brine, dried, and evaporated to give
a solid (487 mg, 92%).
The tetrahydroisoquinoline (440 mg, 2.47 mmol), ethyl
bromoacetate (0.29 mL, 2.6 mmol), and Et3N (0.41 mL, 3.0
mmol) were stirred in CH2Cl2 (10 mL) for 16 h. After removal
of the solvent, the residue was taken up in saturated NaHCO3,
extracted with EtOAc, washed with brine, dried, and evapo-
rated. Chromatography (silica gel; EtOAc) yielded a yellow
oil (627 mg, 96%).
To a solution of the nitrotetrahydroisoquinoline (627 mg,
2.38 mmol) in EtOH (30 mL) previously degassed with argon
was added 10% Pd-C (60 mg), and then the mixture was
placed under an atmosphere of H2 (balloon) for 3 h. The
mixture was filtered through Celite, and the solvent was
removed to give 13 as an oil (526 mg, 95%). 1H NMR
(CDCl3): δ 1.29 (3H, t), 2.73 (4H, m), 3.38 (2H, s), 3.72 (2H,
s), 4.22 (2H, q), 6.35 (1H, d), 6.52 (1H, dd), 6.89 (1H, d).
N -[1-Nit r o-4-(N -Boc-p ip e r a zin -1-yl)-2-b e n zoyl]gly-
cin e Eth yl Ester (15). Piperazine (4.65 g, 54 mmol) and
4-chloro-1-nitrobenzoic acid (14) (2.26 g, 11.2 mmol) were
heated neat at 110 °C (oil bath temperature) for 2 h. After
cooling, the residue was stirred in 10% aqueous KHSO4 (pH
∼ 4-5) for 15 min and the yellow-orange solid then collected
by filtration (2.8 g).
This piperazine (2.8 g, 11 mmol) was dissolved in 1 N NaOH
(50 mL) and 1,4-dioxane (100 mL) at 0 °C, and to this solution
was added Boc-anhydride (4.0 g, 18 mmol). After stirring for
16 h, the mixture was concentrated in vacuo; the residue was
taken up in H2O (100 mL), filtered, and then acidified to pH
∼ 3-4 with 10% aqueous KHSO4. The precipitate was
collected by filtration, dissolved in EtOAc, washed with 10%
aqueous KHSO4 and then brine, dried, and evaporated to yield
a yellow solid (2.95 g).
To a solution of the acid (2.81 g, 8 mmol), glycine ethyl ester
hydrochloride (1.12 g, 8 mmol), and HOBT (1.19 g, 8.8 mmol)
in DMF were added NMM (1.76 mL, 11.6 mmol) and EDC
(1.84 g, 9.6 mmol). After stirring for 16 h, the DMF was
removed in vacuo and the residue partitioned between H2O
and EtOAc. The organic extracts were washed with 10%
aqueous KHSO4, brine, saturated NaHCO3, and then brine,
dried, and concentrated in vacuo to give a yellow solid.
Column chromatography (silica gel; hexane/EtOAc, 2:3) af-
forded 15 as a yellow solid (3.1 g). 1H NMR (CDCl3): δ 1.25-
1.35 (3H, t), 1.48 (9H, s), 3.34-3.5 (4H, m), 3.6 (4H, m), 4.19-
4.32 (4H, m), 6.23-6.35 (1H, m), 6.75-6.86 (2H, m), 8.1 (1H,
d).
Eth yl 6-(N-Boc-p ip er a zin -1-yl)-4(3H)-qu in a zolin on e-3-
a ceta te (16). To a solution of 15 (3.0 g, 11.2 mmol) in EtOH
(150 mL) previously degassed with argon was added 10%
Pd-C (0.35 g), and then the mixture was placed under an
atmosphere of H2 (balloon) for 3 h. The mixture was filtered
through Celite and the solvent removed to give a yellow-brown
foam (2.8 g).
Eth yl 7-(4-N-Boc-p ip er a zin -1-yl)-1(1H)-isoqu in olin on e-
2-a ceta te (10). A solution of 4a (329 mg, 1 mmol) in EtOH
(5 mL) and cyclohexene (5 mL) was treated with 300 mg of
10% Pd-C and heated to 75 °C for 48 h. The mixture was
cooled and filtered through Celite (washing with copious
amounts of EtOH) and the solvent removed to give 10 (311
mg, 95%) as a foam. 1H NMR (CDCl3): δ 1.26 (3H, t), 1.47
(9H, s), 3.24 (4H, m), 3.6 (4H, m), 4.25 (2H, q), 4.70 (2H, s),
6.47 (2H, d), 6.88 (2H, d),7.33 (1H, dd), 7.43 (1H, d), 7.81 (1H,
d).
E t h yl 7-Am in o-1,2,3,4-t et r a h yd r oisoq u in olin e-2-a c-
eta te (13). To a solution of 12 (10.5 g, 40.1 mmol) in 20 mL
of HOAc was added a cooled, premixed solution of 120 mL of
H2SO4 and 60 mL of HOAc followed by paraformaldehyde (1.44
g, 48.1 mmol). The mixture was stirred for 16 h, poured into
ice, and extracted three times with EtOAc. After washing with
water and then brine, the organic layer was dried and
The aniline (1.4 g, 3.4 mmol) and triethyl orthoformate (15
mL) were heated at reflux for 16 h. After cooling, the excess
solvent was removed in vacuo and the residue taken up in
EtOAc, washed with H2O, dried, and evaporated to give an
oil. Chromatography on silica gel (hexane/EtOAc, 1:4) afforded
16 as a pale yellow solid (0.65 g). 1H NMR (CDCl3): δ 1.25-
1.35 (3H, t), 1.49 (9H, s), 3.2-3.32 (4H, m), 3.54-3.66 (4H,
m), 4.21-4.32 (2H, q), 4.69 (2H, s), 7.42 (1H, dd), 7.6-7.68
(2H, m), 7.85 (1H, s).
Eth yl 6-Am in o-2,4(1H,3H)-qu in a zolin ed ion e-3-a ceta te
(18). 4-Amino-1-nitrobenzoic acid (17) (5.46 g, 30 mmol) was
coupled with ethylglycine hydrochloride using the procedure
described for 15. After workup, a solid was obtained which
was triturated with ether and filtered to give a yellow solid
(6.62 g).
A solution of the aniline (1.34 g, 5 mmol) and CDI (0.97 g,
6 mmol) in THF (25 mL) was heated at reflux for 27 h. The

Non-Peptide GP IIb/ IIIa Antagonists
J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 23 4591
Thoolen, M. J .; Reilly, T. M.; DeGrado, W. F.; Olsen, R. E.;
Wexler, R. R. Synthesis and Pharmacology of Orally Active,
Isoxazoline Glycoprotein IIb-IIIa Receptor Antagonists. 211th
ACS Meeting, March 1996; Med132 (abstr). (b) Zhang, L.-h.;
Anzalone, L.; Ma, P.; Kauffman, G. S.; Storace, L.; Ward, R. The
Chiral Specific Synthesis of DMP 754, a Platelet GP IIb/IIIa
Antagonist. Tetrahedron Lett. 1996, 37, 4455-4458.
solvent was removed, and the residue was chromatographed
(silica gel; hexane/EtOAc, 2:3) to yield the quinazolinedione
(0.94 g) as a pale yellow solid.
The nitroquinazolinedione was reduced using H2 and 10%
Pd-C in EtOH. After filtration and removal of the solvent,
the residue was chromatographed (silica gel; 2.5% MeOH in
CHCl3) to give 18 as a pale yellow solid (0.41 g). 1H NMR
(CD3OD): δ 1.2-1.35 (3H, t), 4.14-4.3 (2H, q), 4.72 (2H, s),
6.99 (1H, d), 7.1 (1H, dd), 7.30 (1H, d).
(14) (a) Weller, T.; Alig, L.; Beresini, M.; Blackburn, B.; Bunting, S.;
Hadvary, P.; Muller, M. H.; Knopp, D.; Levet-Trafit, B.; Lipari,
M. T.; Modi, N. B.; Muller, M.; Refino, C. J .; Schmitt, M.;
Schonholzer, P.; Weiss, S.; Steiner, B. Orally Active Fibrinogen
Receptor Antagonists. 2. Amidoximes as Prodrugs of Amidines.
J . Med. Chem. 1996, 39, 3139-3147. (b) Theroux, P.; Kouz, S.;
Knudtson, M. L.; Kells, C.; Nasmith, J .; Roy, L.; Ave, S. D.;
Steiner, B.; Xiao, Z.; Rapold, H. J . A Randomized Double-Blind
Controlled Trial With the Non-Peptidic Platelet GPIIb/IIIa
Antagonist Ro 44-9883 in Unstable Angina. Circulation 1994,
90, I-232 (abstr).
Ack n ow led gm en t. We thank Dr. G. Smith and the
Analytical Department, Dr. K. Holloway, Dr. H. Ramjit,
A. Coddington, and J . Perkins for their help and advice.
Su p p or tin g In for m a tion Ava ila ble: NMR data for final
compounds (2 pages). Ordering information is given on any
current masthead page.
(15) Himmelsbach, F.; Austel, V.; Guth, B.; Linz, G.; Muller, T. H.;
Pieper, H.; Seewaldt-Becker, E.; Weisenberger, H. Design of
Highly Potent Nonpeptidic Fibrinogen Receptor Antagonists.
Eur. J . Med. Chem. 1995, 30, 243s-254s.
Refer en ces
(1) Colman, R. W.; Marder, V. J .; Salzman, E. W.; Hirsch, J .
Hemostasis and Thrombosis: Basic Principles and Clinical
Practices; Lippincott Publishers: Philadelphia, PA, 1994.
(2) Fitzgerald, D. J .; Roy, L.; Catella, F.; Fitzgerald, G. A. Platelet
Activation in Unstable Coronory Disease. N. Engl. J . Med. 1986,
315, 983-989.
(16) Miller, W. H.; Ku, T. W.; Ali, F. E.; Bondinell, W. E.; Calvo, R.
R.; Davis, L. D.; Erhard, K. F.; Hall, L. B.; Huffman, W. F.;
Keenan, R. M.; Kwon, C.; Newlander, K. A.; Ross, S. T.;
Samanen, J . M.; Takata, D. T.; Yuan, C.-K. Enantiospecific
Synthesis of SB 214857, a potent, Orally Active, Nonpeptide
Fibrinogen Receptor Antagonists. Tetrahedron Lett. 1995, 36,
9433-9436.
(17) For the synthesis of â-alanines, see: (a) Cole, D. C. Recent
Stereoselective Synthetic Approaches to â-Amino Acids. Tetra-
hedron 1994, 50, 9517-9582. (b) J uaristi, E.; Quintana, D.;
Escalante, J . Enantioselective Synthesis of â-Amino Acids.
Aldrichim. Acta 1994, 27, 3.
(18) (a) Girard, Y.; Atkinson, J . G.; Belanger, P. C.; Fuentes, J . J .;
Rokash, J .; Rooney, C. S.; Remy, D. C.; Hunt, C. A. Synthesis,
Chemistry, and Photochemical Substitutions of 6,11-Dihydro-
5H-pyrrolo[2,1-b][3]benzazepin-11-ones. J . Org. Chem. 1983, 48,
3220-3234. (b) Samanen, J . Patent WO 94/29273, Dec. 22, 1994.
(19) Specific â-alanines. (a) 3-Methyl, see ref 10. (b) 3-Ethynyl, see
ref 11. (c) 3-Pyrid-3-yl, see Rico, J . G.; Lindmark, R. J .; Rogers,
T. E.; Bovy, P. R. A highly Stereoselective Michael Addition to
an R,â-Unsaturated Ester as the Crucial Step in the Synthesis
of a Novel â-Amino Acid-Containing Fibrinogen Receptor An-
tagonist. J . Org. Chem. 1993, 58, 7948-7951. (d) 2-Amino and
2-tosylamino, see Xue, C.-B.; Rafalski, M.; Roderick, J .; Eyer-
mann, C. J .; Mousa, S.; Olsen, R. E.; DeGrado, W. F. Design
and Synthesis and in Vitro Activities of a Series of Benzimida-
zole/Benzoxazole Glycoprotein IIb/IIIa Inhibitors. Bioorg. Med.
Chem. Lett. 1996, 6, 339-344.
(20) (a) Kirk, K. L. 4-Lithio-1-tritylimidazole as a Synthetic Inter-
mediate. Synthesis of Imidazole-4-carboxaldehyde. J . Heterocycl.
Chem. 1985, 22, 57-59. (b) Iddon, B.; Lim, B. L. Metal-Halogen
Exchange Reactions of Mono- and Polyhalogenimidazoles, J .
Chem. Soc., Perkin Trans. 1 1983, 735-739.
(21) Stokker, G. E. Preparation of 1,2,3,4-Tetrahydroisoquinolines
Lacking Electron Donating Groups - An Intramolecular Cycliza-
tion Complementary to the Pictet-Spengler Reaction. Tetrahe-
dron Lett. 1996, 37, 5453-5456.
(22) Compounds 1 and 6d had measured pKa values of 11.2 and 8.7,
respectively.
(23) Egbertson, M. S.; Chang, C. T.-C.; Duggan, M. E.; Gould, R. J .;
Halczenko, W.; Hartman, G. D.; Laswell, W. L.; Lynch, J . J .;
Lynch, R. J .; Manno, P. D.; Naylor, A. M.; Prugh, J . D.; Ramjit,
D. R.; Sitko, G. R.; Smith, R. S.; Turchi, L. M.; Zhang, G. Non-
Peptide Fibrinogen Receptor Antagonists. 2. Optimization of a
Tyrosine Template as a Mimic for Arg-Gly-Asp. J . Med. Chem.
1994, 37, 2537-2551.
(24) log P data were measured using 1-octanol/phosphate buffer, pH
7.4, system.
(25) The intravenous and oral administration of these compounds
to dogs and monkeys in the in vivo studies described did not
result in any significant change in circulating whole blood
platelet count.
(3) Schror, K. Antiplatelet Drugs a Comparative Review. Drugs
1995, 50 (1), 7-28.
(4) Lefkovits, J .; Plow, E. F.; Topol, E. J . Platelet Glycoprotein IIb/
IIIa Receptors in Cardiovascular Medicine. N. Engl. J . Med.
1995, 332, 1553-1559.
(5) Robinson, C. Abciximab. Drugs Future 1995, 20, 457-463.
(6) The EPIC Investigators. Use of a Monoclonal Antibody Directed
Against the Platelet Glycoprotein IIb/IIIa Receptor in High-Risk
Coronary Angioplasty. N. Engl. J . Med. 1994, 330, 956.
(7) Raddatz, P.; Gante, J . Recent Developments in Gylcoprotein IIb/
IIIa Antagonists. Expert Opin. Ther. Pat. 1995, 5 (11), 1163-
1183.
(8) Ojima, I.; Chakravarty, S.; Dong, Q. Antithrombotic Agents:
From RGD to Peptide Mimetics, Bioorg. Med. Chem. 1995, 3,
337-360.
(9) (a) Hartman, G. D.; Egbertson, M. S.; Halczenko, W.; Laswell,
W. L.; Duggan, M. E.; Smith, R. L.; Naylor, A. M.; Manno, P.
D.; Lynch, R. J .; Zhang, G.; Chang, C. T.-C.; Gould, R. J . Non-
Peptide Fibrinogen Receptor Antagonists 1. Discovery and
Design of Exosite Inhibitors. J . Med. Chem. 1992, 35, 4640-
4642. (b) Peerlinck, K.; De Lepeleire, I.; Goldberg, M.; Farrell,
D.; Barrett, J .; Hand, E.; Panebianco, D.; Deckmyn, H.; Ver-
mylen, J .; Arnout, J . MK-383 (L-700,462), a Selective Nonpeptide
Platelet Glycoprotein IIb/IIIa Antagonist, Is Active in Man.
Circulation 1993, 88 (1), 1512-1517.
(10) Duggan, M. E.; Naylor-Olsen, A. M.; Perkins, J . J .; Anderson,
P. S.; Chang, C. T.-C.; Cook, J . J .; Gould, R. J .; Ihle, N. C.;
Hartman, G. D.; Lynch, J . J .; Lynch, R. J .; Manno, P. D.;
Schaffer, L. W.; Smith, R. L. Non-Peptide Fibrinogen Receptor
Antagonists. 7. Design and Synthesis of a Potent, Orally Active
Fibrinogen Receptor Antagonist. J . Med. Chem. 1995, 38, 3332-
3341.
(11) Zablocki, J . A.; Rico, J . G.; Garland, R. B.; Rogers, T. E.;
Williams, K.; Schretzman, L. A.; Shashidhar, A. R.; Bovy, P. R.;
Tjoeng, F. S.; Lindmark, R. J .; Toth, M.V.; Zupec, M. E.;
McMackins, D. E.; Adams, S. P.; Miyano, M.; Markos, C. S.;
Milton, M. N.; Paulson, S.; Herin, M.; J acqmin, P.; Nicholson,
N. S.; Panzer-Knodle, S. G.; Haas, N. F.; Page, J . D.; Szalony, J .
A.; Taite, B. B.; Salyers, A. K.; King, L. W.; Campion, J . G.;
Feigen, L. P. Potent in Vitro and in Vivo Inhibitors of Platelet
Aggregation Based Upon the Arg-Gly-Asp Sequence of Fibrino-
gen. (Aminobenzamidino)succinyl (ABAS) Series of Orally Active
Fibrinogen Receptor Antagonists. J . Med. Chem. 1995, 38,
2378-2394.
(12) Scarborough, R. M.; Naughton, M. A.; Teng, W.; Rose, J . W.;
Phillips, D. R.; Nannizzi, L.; Arfsten, A.; Campbell, A. M.; Charo,
I. F. Design of Potent and Specific Integrin Antagonists. J . Biol.
Chem. 1993, 268, 1066-1073.
(13) (a) Xue, C.-B.; Wityak, J .; Sielecki, T. M.; Cain, G. A.; Liu, J .;
Bostrom, L. L.; DiMeo, S. V.; Higley, C. A.; Lalka, G. K.; Tobin,
A. E.; Frietze, W. E.; Emmett, G.; Mousa, S. A.; Sze, J . Y.;
J M9604787