Substituted acrylamides as factor Xa inhibitors: Improving bioavailability by P1 modification

Article abstract of DOI:10.1016/S0960-894X(02)00304-9

To overcome the low bioavailability of our substituted acrylamide P1 benzamidine factor Xa inhibitors reported previously, neutral and less basic groups were used to replace the benzamidine. As a result, a series of P1 aminoisoquinoline substituted acrylamide Xa inhibitors was identified to be potent, selective, and orally bioavailable. Modification of P4 moiety of these compounds further improved their pharmacokinetic properties.

Full text of DOI:10.1016/S0960-894X(02)00304-9

Bioorganic & Medicinal Chemistry Letters 12 (2002) 2043–2046
Substituted Acrylamides as Factor Xa Inhibitors:
Improving Bioavailability by P1 Modificationy
Yonghong Song,* Lane Clizbe, Chhaya Bhakta, Willy Teng, Wenhao Li,
Paul Wong, Brian Huang, Uma Sinha, Gary Park, Andrea Reed,
Robert M. Scarborough and Bing-Yan Zhu
Millennium Pharmaceuticals, Inc., 256 East Grand Ave., South San Francisco, CA 94080, USA
Received 21 January 2002; accepted 5 March 2002
Abstract—To overcome the low bioavailability of our substituted acrylamide P1 benzamidine factor Xa inhibitors reported previously,
neutral and less basic groups were used to replace the benzamidine. As a result, a series of P1 aminoisoquinoline substituted acrylamide
Xa inhibitors was identified to be potent, selective, and orally bioavailable. Modification of P4 moiety of these compounds further
improved their pharmacokinetic properties. # 2002 Elsevier Science Ltd. All rights reserved.
Factor Xa is a serine proteinase which cleaves pro-
thrombin to thrombin, leading to blood clot formation
within the blood coagulation cascade. It is the sole
enzyme responsible for activation of thrombin in the
cascade. Because of its important role in blood coagu-
lation, factor Xa has emerged as an attractive target for
development of new antithrombotic agents.2 Our
research objective is to discover and develop orally
active factor Xa inhibitors for treatment of thrombotic
disorders.
improved pharmacokinetic properties of these com-
pounds.
The SARstudy of P1 modification is shown in Table 1.
Replacement of P1 benzamidine with 3-aminophenyl and
3-hydrazinophenyl resulted in inactive compounds 2 and
3. The more basic 3-aminomethylphenyl compound 4
gave improved potency. Compounds with neutral sub-
stituted phenyl P1 (5–8) all had micromolar inhibitory
activity. Insertion of an extra carbon between the direct
phenyl–vinyl linkage (9) increased the potency slightly.
The thioamide compound 11 gave better activity as
compared to the amide 10.
In our previous communication, we have described a
series of substituted acrylamides as potent and selective
factor Xa inhibitors, as exemplified by compound 1 in
Figure 1.3 However, these compounds containing P1
benzamidine functionality suffered from low oral bio-
availability. It is generally believed that the highly basic
benzamidine group adversely effects bio-absorption of
these compounds when they are orally administered. In
order to improve their oral bioavailability, we replaced
the P1 benzamidine group with neutral and less basic
moieties. As a result, a series of potent, selective and
bioavailable factor Xa inhibitors have been discovered.
In this paper, we will discuss the structure–activity rela-
tionship (SAR) of these compounds on P1 modification
as well as P4 modification. We will also report the
As we know, Asp189 in the S1 pocket of factor Xa plays
an important role in anchoring benzamidine P1 moieties
by forming a salt bridge with the amidine group.4 To
take advantage of a dipole–charge interaction of a P1
group with the Asp189 carboxylate anion, we designed
compound 12 containing a P1 group with a significant
dipole moment due to the strong electron-withdrawing
nitro group at the para position (shown in Fig. 2). This
compound displayed enhanced activity over the des-
nitro compound 2 by more than 40-fold, even though its
activity (IC50=0.25 mM) needs to be improved further.
Previous literature indicated that 1-aminoisoquinoline
could be used as a benzamidine surrogate.5 In our series,
the aminoisoquinoline compound 13 was shown to be
quite active with an IC50 value of 0.014 mM, representing a
yFor a preliminary account of part of this work, see ref 1.
*Corresponding author. Fax: +650-244-9287; e-mail: yonghong.
song@mpi.com
0960-894X/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved.
PII: S0960-894X(02)00304-9

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Y. Song et al. / Bioorg. Med. Chem. Lett. 12 (2002) 2043–2046
Table 1. SARof P1 variation
P1
X
H
Compd
FXa
(IC50, mM)
2
>11
>11
1.3
Figure 1. Replacement of P1 benzamidine with new P1 moieties.
H
H
H
3
4
5
5.7
Figure 2. Dipole–charge interaction of P1 (12) with Asp189 in S1
pocket.
H
6
7
9.5
modest 14-fold reduction in potency as compared to
benzamidine analogue 1. However, the corresponding
‘trans’ isomer 14 (shown in Fig. 3) was 60-fold less
active than 13, indicating that the ‘cis’ geometry of P1
and P4 moieties is also highly preferred in this series. The
corresponding quinazoline compound 15 was 20-fold less
active than 13, while the diaminoquinazoline compound
16 was virtually inactive. The unsubstituted cinnamamide
17 (Fig. 3) had an IC50 of 0.078 mM, about 6-fold less
active than the methyl-fluoro analogue 13.
Br
>11
Br
8
2.9
After identification of compound 13, we carried out
SARstudy on P4 modification as shown in Table 2.
Halogen substitution at 2-position of the biphenylsulfon-
amide moiety gave compounds 18–20 with improved
potency (Ki of 0.0011–0.0016 mM) over compound 13.6
The pyridylphenyl compound 21 was equally potent as
13, while the 2-aminocarbonylbiphenyl compound 22
was much less active. Replacement of 20-aminosulfonyl
on the biphenyl moiety with cyano (23) and amino-
carbonyl (24) resulted in reduced activity. The phe-
nylpyridyl compound 25 was also less active as
compared to 13.7 Although the biphenylsulfoxide 26
was inactive, the biphenylsulfone 27 was 2-fold more
active than 13.
H
H
F
9
1.8
10
11
12
0.92
0.14
0.25
H
Compounds in this series also showed high selectivity
against other serine proteinases. For example, com-
pounds 18–20 displayed greater than 1000-fold selectiv-
ity for factor Xa versus thrombin and trypsin (Table 2).
H
H
H
13
15
16
0.014
0.27
>11
Figure 3. Compounds 14 and 17.

Y. Song et al. / Bioorg. Med. Chem. Lett. 12 (2002) 2043–2046
2045
Table 2. SARof P4 variation
with the halogen substitution on the biphenylsulfon-
amide moiety. Their bioavailability increased with
heavier halogen substitution, from hydrogen (13) to
fluorine (18), to chlorine (19). The chloro- and bromo-
substituted compounds 19 and 20 had bioavailability of
35 and 30%, respectively. They also showed greatly
reduced clearance and volume distribution compared to
1. It is worth noting that the unsubstituted cinnam-
amide 17 had oral bioavailability of 1.5% as compared
with the methyl-fluoro-substituted counterpart 13 (F,
6.8%), indicating that the methyl-fluoro substitution on
the double bond contributes positively to bioavail-
ability. In dogs, compounds 13 and 20 also showed
good oral bioavailability of 37 and 33%, respectively.
P4
Compd
Xa
IIa
(IC50, mM)
Trypsin
Xa
(Ki)
18
19
20
21
22
23
24
25
26
27
0.005
0.011
0.007
0.014
1.1
6.3
5.4
4.8
9.7 0.0016
>11
0.0011
Although compounds 18–20 are potent in vitro with Ki
of 1 nM, they showed weaker antithrombotic activity in
rabbit PT assay (6.3–10.3 mM, Table 3). Not surpris-
ingly, they were also found to be highly protein-bound
in plasma (99–99.8%). We are currently modifying these
compounds to reduce their plasma protein binding with
the goal of enhancing their antithrombotic activity.
2.4 0.0013
Syntheses of compounds of this study are exemplified in
Schemes 1 and 2. To synthesize 12, as shown in Scheme 1,
the amino group of 3-amino-6-nitroacetophenone was
protected with di-BOC by using (BOC)2O/DMAP.
Horner–Emmons reaction of the protected aceto-
phenone with triethyl 2-fluoro-2-phosphonoacetate gave
the acrylates as a mixture of cis/trans isomers in a ratio of
3:1 in favor of the desired ‘cis’ isomer. After separation,
the acrylate was subject to Weinreb amidation with the
biphenylamine to give the acrylamide, which was then
treated with trifluoroacetic acid to provide 12.
0.19
0.22
0.18
1.5
Synthesis of the aminoisoquinoline compounds 13 and
18–20 is shown in Scheme 2. Pomeranz–Fritsch iso-
quinoline synthesis starting with 3-bromobenzaldehyde
provided a mixture of 7- and 5-bromoisoquinolines in a
ratio of 6 to 4. Stille reaction of the bromide mixture
with tributyl(1-ethoxyvinyl)tin, followed by treatment
with hydrochloric acid, gave a mixture of the methyl
ketone compounds. Upon separation of the desired 7-
isomer by chromatography, it was condensed with tri-
ethyl 2-fluoro-2-phosphonoacetate ylide to give the
acrylates as a mixture of cis/trans isomers in a ratio of 3
to 1 in favor of the desired ‘cis’ isomer, which was then
separated by chromatography. Weinreb amidation of the
acrylate with the biphenylamine yielded the acrylamide.
0.007
The active aminoisoquinoline compounds 13 and 18–21
were found to have greatly improved bioavailabilities
and other pharmacokinetic properties compared to the
benzamidine analogue 1, as shown in Table 3. In rats,
compound 13 had bioavailability (F) of 6.8%, while the
amidine 1 had merely 0.4%. Interestingly, the bioavail-
ability of compounds 13, 18, and 19 were well correlated
Table 3. Pharmacokinetic data
Species
Rats
Compd
F (%)
Cl (mL/min/kg)
Vz (L/kg)
T1=2 (h)
Rabbit PT (mM)
1
17
13
18
19
20
21
0.4
1.5
6.8
13.5
35.1
30.1
13
15.4
56.4
48.7
25.3
6.7
4.3
7.4
10
3.7
0.8
0.61
2.7
3.23
1.51
2.38
1.7
1.43
1.6
6.3
9.4
10.3
4.4
19.1
1.64
Dogs
1
13
20
26.2
11.4
10.8
13.0
6.8
5.5
5.7
7.1
6.0
36.7
33.1

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Y. Song et al. / Bioorg. Med. Chem. Lett. 12 (2002) 2043–2046
J.; Woolfrey, J.; Wong, P.; Huang, B.; Tran, K.; Sinha, U.;
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Scheme 1. Synthesis of 12. Reagents: (a) (BOC)2O, DMAP, TEA,
CHCl3; (b) triethyl 2-fluoro-2-phosphonoacetate, KN(Me3Si)2, THF,
ꢀ78 ꢁC; (c) biphenylamine, AlMe3, CH2Cl2; (d) trifluoroacetic acid.
4. (a) Brandstetter, H.; Kuhne, A.; Bode, W.; Huber, R.; von
der Saal, W.; Wirthensohn, K.; Engh, R. A. J. Biol. Chem.
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H. W. Bioorg. Med. Chem. Lett. 1999, 9, 2539. (b) Rewinkel,
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219th National Meeting of the American Chemical Society,
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Scheme 2. Synthesis of 1-aminoisoquinoline compounds. Reagents:
(a) aminoacetaldehyde dimethyl acetal; (b) concd H2SO4, P2O5,
160 ꢁC; (c) tributyl(1-ethoxyvinyl)tin, Pd(Ph3P)4, toluene, reflux; (d)
H2O/HCl; (e) triethyl 2-fluoro-2-phosphonoacetate, KN(Me3Si)2,
THF, ꢀ100 ꢁC; (f) biphenylamine, AlMe3, CH2Cl2, X=H, F, Cl, Br;
(g) mCPBA, acetone; (h) TsCl/pyridine; (i) aminoethanol, CH2Cl2;
(j) trifluoroacetic acid.
The isoquinoline moiety was transformed to 1-aminoiso-
quinoline by reaction with mCPBA to give the N-oxide,
which was then treated with tosyl chloride in pyridine,
followed by reaction with aminoethanol. Removal of
t-butyl group of the aminoisoquinoline compound by
trifluoroacetic acid gave the final products.
References and Notes
1. Song, Y.; Clizbe, L.; Bhakta, C.; Teng, W.; Li, W.; Wu, Y.;
Jia, Z. J.; Zhang, P.; Wang, L.; Doughan, B.; Su, T.; Kanter,