Orally active factor Xa inhibitors: Investigation of a novel series of 3-amidinophenylsulfonamide derivatives using an amidoxime prodrug strategy

Article abstract of DOI:10.1016/j.bmcl.2008.07.009

A series of novel and potent 3-amidinophenylsulfonamide derivatives of factor Xa inhibitors were designed and synthesized using an amidoxime prodrug strategy. We focused on systemic clearance of parent compounds in rats, and performed in vivo pharmacokinetic screening. Incorporation of a carboxymethoxy group markedly improved systemic clearance (compound 43), and the related amidoxime 44 showed sufficient prodrug conversion. Compound 45, the double prodrug of 43, exhibited practicable bioavailability after oral administration in rats. Among the various compounds under investigation, KFA-1982 was selected for clinical development.

Full text of DOI:10.1016/j.bmcl.2008.07.009

Bioorganic & Medicinal Chemistry Letters 18 (2008) 4682–4687
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Orally active factor Xa inhibitors: Investigation of a novel series of 3-amidi-
nophenylsulfonamide derivatives using an amidoxime prodrug strategy
a
a
a
a
Masahiko Uchida a, , Kosuke Okazaki , Harunobu Mukaiyama , Hidetoshi Isawa , Hiroaki Kobayashi ,
Hiroaki Shiohara a, Hideyuki Muranaka a, Yuichiro Kai a, Norihiko Kikuchi a, Hideki Takeuchi a,
Kenji Yokoyama a, Eiichi Tsuji a, Tomonaga Ozawa a, Yuji Hoyano a, Takashi Koizumi a, Keiko Misawa a,
Kiyoto Hara a, Shigeru Nakano a, Yasuoki Murakami b, Hiroaki Okuno c
*
a Research and Development Division, Kissei Pharmaceutical Co., Ltd, 4365-1 Hotaka-Kashiwabara, Azumino-City, Nagano 399-8304, Japan
b Faculty of Pharmacy, Chiba Institute of Science, 3 Shiomi-cho, Choshi, Chiba 288-0025, Japan
c School of Pharmaceutical Science, Toho University, 2-2-1 Miyama, Funabashi, Chiba 274-8510, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of novel and potent 3-amidinophenylsulfonamide derivatives of factor Xa inhibitors were
designed and synthesized using an amidoxime prodrug strategy. We focused on systemic clearance of
parent compounds in rats, and performed in vivo pharmacokinetic screening. Incorporation of a carboxy-
methoxy group markedly improved systemic clearance (compound 43), and the related amidoxime 44
showed sufficient prodrug conversion. Compound 45, the double prodrug of 43, exhibited practicable bio-
availability after oral administration in rats. Among the various compounds under investigation, KFA-
1982 was selected for clinical development.
Received 13 March 2008
Revised 10 June 2008
Accepted 3 July 2008
Available online 9 July 2008
Keywords:
Anticoagulant
Serine protease inhibitor
Factor Xa
Ó 2008 Elsevier Ltd. All rights reserved.
Amidoxime
Prodrug
Thromboembolic diseases such as deep vein thrombosis, pul-
monary embolism, myocardial infarction, and thromboembolic
stroke are major causes of morbidity and mortality in developed
countries.1 Currently available anticoagulants such as warfarin,
heparin, and low-molecular-weight heparins are widely used for
the treatment and prevention of thromboembolic diseases; how-
ever, these anticoagulants have many therapeutic limitations.
Therefore, orally active anticoagulant drugs are attractive thera-
peutic targets.2
CO2H
HN
H2N
NH
Me
N
O
1: DX-9065a
H
N
HN
H2N
N
O
N
NH
Activated blood coagulation factor X (fXa) is a trypsin-like ser-
ine protease. It resides at the juncture of the intrinsic and extrinsic
pathways in the blood coagulation cascade, and plays a critical role
in thrombus formation.3 Since the 1990s, a number of small-mol-
ecule fXa inhibitors, including DX-9065a (Fig. 1, compound 1),
have been reported as promising anticoagulant drugs.2,4 More re-
cently, several orally active small-molecule fXa inhibitors such as
rivaroxaban and apixaban are in late-stage clinical trials.5,6 These
reports have prompted us to disclose our efforts for the discovery
of novel fXa inhibitors. In this paper, we describe the discovery
O
CO2H
Me
2: KFA-1411
Figure 1. Structures of bisamidine fXa inhibitors.
and optimization of novel sulfonamide derivatives as orally active
fXa inhibitors.
Initial research in our laboratory focused on bis-amidine com-
pounds. We have already reported a potent and selective fXa inhib-
itor, KFA-1411 (Fig. 1, compound 2), that exhibits effective
anticoagulant activity in an animal hemodialysis model.7 Unfortu-
nately, however, 2 showed marginal oral anticoagulant activity,
probably because of its high polarity due to the presence of two
amidino groups and one carboxyl group.
* Corresponding author at present address: Strategic Product Planning, Kissei
Pharmaceutical Co., Ltd., 19-48, Yoshino, Matsumoto-City, Nagano 399-8710, Japan.
Tel.: +81 (0) 263 25 9522; fax: +81 (0)263 25 9515.
E-mail address: masahiko_uchida@pharm.kissei.co.jp (M. Uchida).
0960-894X/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2008.07.009

M. Uchida et al. / Bioorg. Med. Chem. Lett. 18 (2008) 4682–4687
4683
non-polar substituents and explored various linkers; these efforts
led to the discovery of compounds of a novel 3-amidinophenylsulf-
onamide series.
CO2Et
O
O
Me
N
N
H
N
N
O
General synthetic routes of the 3-amidinophenylsulfonamide
series are outlined in Scheme 1. The phenylsulfonylchlorides I
were coupled with appropriate phenethylamines VII to give the
sulfonamides II. The N-substituted sulfonamides III were prepared
by alkylation of the sulfonamides II in the presence of K2CO3. Con-
version of the 2-methoxyphenylsulfonamides II and III to the cor-
responding 2-hydroxy derivatives IV was accomplished by heating
with LiCl in DMF. Treatment of the benzonitriles II and IV with eth-
anolic HCl followed by ammonium acetate or hydroxylammonium
acetate gave the corresponding amidines or amidoximes (35–37
and V). The carboxylic acids 40, 41, 43, 44, and 46–49 were pre-
pared from the corresponding esters of V by hydrolysis under
acidic or basic conditions. The carboxylic acid 48 was heated with
n-butanolic HCl to give the n-butyl ester 50.
The phenethylamines 8, 12, 14, 18, and 21 were prepared as
shown in Scheme 2. The phenol 5 was acylated by Friedel–
Crafts-type reaction with N-cyanomethyl-2,2,2-trifluoroacetamide
to give the aminoacetophenone derivative 6. Reduction of the ke-
tone with triethylsilane in TFA followed by alkylation of the pheno-
lic hydroxy group with ethyl bromoacetate gave compound 7.
Hydrolysis of the protecting group of 7 followed by treatment with
ethanolic HCl gave the phenethylamine 8. The 2-nitrotoluene 9
was successively treated with (CO2Et)2/NaOEt, aqueous NaOH,
and hydroxylamine to give oxime 10. The oxime 10 was converted
to the nitrile 11 in the presence of acetic anhydride, and then
hydrogenated with BH3 to give the 2-nitrophenethylamine 12.
The anilide 14 was prepared from 12 via conventional synthesis.
Boc protection of the amino group of 12 followed by reduction of
the nitro group to give 13, which was acylated with ethyl oxalyl
chloride and then treated with ethanolic HCl to give 14. Catalytic
hydrogenation of 7-hydroxychromen-2-one (15) followed by
masking of phenol as a benzyl ether gave the chroman-2-one 16,
which was treated with ammonia followed by alkylation of pheno-
lic hydroxy group with chloromethyl methyl ether to give the phe-
HO
HO
NH2
NH2
3: sibrafiban
O
O
H
N
CO2Et
N
H
N
4: ximelagatran
Figure 2. Structures of amidoxime prodrugs.
Amidoximes have been well known as prodrugs of amidine-con-
taining drugs,8 including sibrafiban and ximelagatran (Fig. 2).9–12
These efforts convinced us that the amidoxime prodrug strategy,
at least for mono-amidine derivatives, could be one of the most
promising approaches for the development of orally active fXa
inhibitors.
Results based on docking studies of our compounds with fXa
suggested that the interaction of the 3-amidinophenyl moiety (A)
with Asp189 in the S1 pocket, and the rigid phenylene moiety
(B) toward the hydrophobic S4 pocket, may play critical roles in
inhibitor-protein binding (Fig. 3). We initially sought to replace
the acetimidoyl moiety at the P4 position in the S4 pocket by
Asp189
Phe175
B
O
S4 pocket
H
−
O
NH
+
H
Linker
P4
N
A
H
Trp215
S1 pocket
Tyr99
O
Ser195
Figure 3. Schematic of essential interactions between inhibitor and fXa.
Z
X
H
S
H2N
X
X
S
Z
N
O
H
N
HN
VII
e, f
Y
O
NC
NC
SO2Cl
NC
Me
Me
a or
NH2
O
O
b (for Y = OH)
Y
I
II
35: X = H
36: X = Cl
37: X = OMe
c
X = OMe
d
OMe
R
OH
N
O
R
Z
d
for W = H: e, f
S
N
O
Me
Me
NC
S
for W = OH: e, g
O
O
Y
III
IV
40: W = H, R = CO2H, Y = i-Pr, Z = H
41: W = OH, R = CO2H, Y = i-Pr, Z = H
OH
R
Z
h or i
N
O
N
43: W = H, R = H, Y = i-Pr, Z = OCH2CO2H
44: W = OH, R = H, Y = i-Pr, Z = OCH2CO2H
46: W = H, R = H, Y = i-Pr, Z = NHCH2CO2H
47: W = H, R = H, Y = i-Pr, Z = NHCOCO2H
48: W = H, R = H, Y = 2-MeSO2Ph, Z = OCH2CO2H
49: W = H, R = H, Y = 2-MeSO2Ph, Z = NHCH2CO2H
S
W
O
NH2
Y
V
32: W = H, R = H, Y = i-Pr, Z = H
33: W = H, R = H, Y = Oi-Pr, Z = H
34: W = H, R = H, Y = t-Bu, Z = H
38: W = H, R = Me, Y = i-Pr, Z = H
39: W = OH, R = H, Y = i-Pr, Z = H
j
50: W = H, R = H, Y = 2-MeSO2Ph, Z = OCH2CO2n-Bu
42: W = OH, R = CO2Et, Y = i-Pr, Z = H
45: W = OH, R = H, Y = i-Pr, Z = OCH2CO2Et
Scheme 1. General synthetic routes of 3-amidinophenylsulfonamide derivatives. Reagents and conditions: (a) Et3N or K2CO3, THF, H2O, rt; (b) NaHCO3, THF, H2O, rt; (c)
BrCH2CO2Et or MeI, K2CO3, DMF, rt; (d) LiCl, DMF, 140 °C; (e) HCl (gas), EtOH, rt; (f) NH4OAc, EtOH, rt; (g) NH2OHÁHOAc, EtOH, rt; (h) 1 N HCl, CH3CN, 60 °C; (i) 2 N NaOH,
EtOH or CH3CN, 0 °C to rt; (j) HCl (gas), n-BuOH, 100 °C.

4684
M. Uchida et al. / Bioorg. Med. Chem. Lett. 18 (2008) 4682–4687
O
·HCl
NH2
NHCOCF3
NHCOCF3
CO2Et
a
b, c
d, e
Me
Me
Me
Me
Me
OH
Me
OH
O
CO2Et
O
Me
Me
Me
Me
Me
Me
5
6
7
8
NO2
O
NO2
CN
NO2
NO2
NH2
OH
f, g
h
i
NOH
Me
Me
Me
Me
Me
9
10
11
12
NHCOCO2Et
NH2
NH2
NHBoc
·HCl
j, k
l, m
Me
Me
Me
Me
13
14
CONH2
OMe
NH2
o, p
q, r
s, t, u
HO
Br
O
15
O
BnO
O
O
BnO
O
17
HO
O
18
OMe
16
NHCOCF3
NO2
NH2
NO2
NH2
v, w
x
Br
Br
19
20
21
Scheme 2. Preparation of phenethylamines. Reagents and conditions: (a) CF3CONHCH2CN, BCl3, AlCl3, CH2Cl2, rt; (b) Et3SiH, TFA, rt; (c) BrCH2CO2Et, K2CO3, DMF, rt; (d)
K2CO3, H2O, MeOH, rt; (e) HCl, EtOH, rt; (f) (CO2Et)2, NaOEt, THF, reflux, then NaOH aq. 60 °C; (g) NH2OHÁHCl, pyridine, EtOH, 70 °C; (h) Ac2O, AcOH, 50 °C; (i) BH3-THF, THF, rt;
(j) Boc2O, THF, rt; (k) H2, Pd-C (10%), EtOH, rt; (l) ClCOCO2Et, pyridine, CH2Cl2, rt; (m) HCl (gas), EtOH, rt; (o) H2, Pd-C (10%), THF, EtOH, 65 °C; (p) BnCl, K2CO3, DMF, rt; (q) NH3
aq, THF, rt; (r) NaH, DMF, 50 °C, then CH3OCH2Cl, rt; (s) NBS, DBU, MeOH, 65 °C, (t) KOH aq., EtOH, reflux; (u) H2, Pd-C (10%), EtOH, rt; (v) TFAA, Et3N, CH2Cl2, rt; (w) NO2BF4,
CH3CN, rt; (x) NaOH aq., MeOH, 50 °C.
nylpropionamide 17. Conversion of the amide 17 into the amine 18
was performed by the Hoffmann rearrangement followed by treat-
ment with KOH and deprotection of the benzyl group. Protection of
amino group of 4-bromophenetylamine 19 by trifluoroacetylation
followed by treatment with nitronium tetrafluoroborate gave
o-nitrophenethylamine 20, and then the trifluoroacetyl group was
removed by hydrolysis to give 4-bromo-2-nitrophenetylamine 21.
The synthetic route of compounds 24 and 25, which have an
ethoxycarbonylmethylamino group, and compounds 26 and 31,
which have a biphenyl moiety, are shown in Scheme 3. Compounds
24 and 25 were prepared from the corresponding nitro derivatives
22 and 23 by reduction followed by alkylation with ethyl
bromoacetate, respectively. The phenol 27 was treated with tri-
fluoromethanesulfonic anhydride in the presence of 4-dimethyl-
aminopyridine to give the triflate 28. The biphenyl compounds
26 and 29 were synthesized from 24 and 28, respectively, using
the Suzuki coupling reaction. Oxidation of the methylthio group
of compound 29 resulted in the methanesulfonyl derivative 30.
OMe
OMe
NO2
HN CO2Et
Y
H
H
a, b
24: Y = Br
25: Y = i-Pr
26: Y = 2-MeSO2Ph
N
O
N
c
NC
NC
S
NC
S
O
O
O
O
Y
22: Y = Br
23: Y = i-Pr
OMe
H
OMe
H
OMe
O
OMe
SMe
O
OMe
OH
O
OMe
H
N
d
e
N
S
N
S
NC
NC
S
O
O
O
O
O
28
OTf
27
29
OMe
OMe
O
OMe
SO2Me
O
CO2Et
SO2Me
H
N
H
N
f
g, h
NC
S
NC
S
O
O
O
O
30
31
Scheme 3. Reagents and conditions: (a) Zn, HCl (conc.), AcOH, THF, rt; (b) BrCH2CO2Et, i-Pr2NEt, DMF, 55 °C; (c) (i) bis(pinacolato)diboron, Pd(dppf)Cl2, dppf, KOAc, dioxane,
80 °C; (ii) 2-BrPhSO2Me, Pd(dppf)Cl2, K3PO4, dioxane, 80 °C; (d) (CF3SO2)2O, DMAP, CH2Cl2, 0 °C; (e) 2-MeSPhB(OH)2, Pd(PPh3)4, (n-Bu)4NBr, Na2CO3, H2O, toluene, 85 °C; (f)
OxoneÒ, NaHCO3, acetone, H2O, water cooling; (g) HCl (conc.), i-PrOH, THF, 50 °C; (h) BrCH2CO2Et, i-Pr2NEt, DMF, 50 °C.

M. Uchida et al. / Bioorg. Med. Chem. Lett. 18 (2008) 4682–4687
4685
Deprotection of the methoxymethyl ether group of compound 30
followed by alkylation with ethyl bromoacetate gave compound
31.
fXa-specific effect of the hydroxy group is probably due to the
interaction with the characteristic residue in fXa (e.g., Tyr99).
A rat pharmacokinetic study for the mono-amidine compound
32 showed low bioavailability (Table 2). The related prodrug of ami-
doxime 39 showed good oral absorption (F = 29%), but the prodrug
conversion to parent 32 was negligible. These results suggested that
low bioavailability of the parent 32 after oral administration of the
prodrug 39 may be due to relatively high systemic clearance of 32
and 39 compared with the prodrug conversion rate of 39 to 32. Pre-
vious literature suggested that the nature of the parent depends sig-
nificantly on the substituent incorporated.11,12 Successful
approaches using amidoxime prodrugs such as sibrafiban (3) and
ximelagatran (4) have been reported;9,10,12 these prodrugs have a
carboxyl moiety in their parent compounds. We therefore explored
the incorporation of a carboxyl group at the position that allows
Table 1 shows the anti-fXa, anti-thrombin, and anti-trypsin
activities of compounds 1, 2, and 32–38. The 3-amidinophenylsul-
fonamide with an isopropyl group substituted at the P4 position
(32) showed potent anti-fXa activity and good selectivity against
thrombin and trypsin. Replacement of the isopropyl group with
an isopropoxy group reduced the activities of both anti-fXa and
anti-trypsin (33 vs 32). Upon replacement with a more bulky sub-
stituent, a tert-butyl group, the anti-fXa activity was retained (34
vs 32). Incorporation of a methyl group at the sulfonamide nitro-
gen was tolerable (38). Elimination or replacement of the hydroxy
group resulted in a significant decrease in the anti-fXa activity and
loss of selectivity over trypsin (35–37). We considered that this
Table 1
Inhibitory activity of compounds 1, 2, and 32–38 against human fXa, thrombin, and
trypsin
X
R
N
O
HN
H2N
S
O
Y
Entry
X
R
Y
Kia (nM)
fXa
Thrombin
Trypsin
1
2
(DX-9065a)
(KFA-1411)
H
H
H
H
H
H
41b
1.73
29
100
27
> 2,000,000b
26,000
620b
6170
800
(1700)
NT
(9700)
4000
NT
32
33
34
35
36
37
38
OH
OH
OH
H
Cl
OMe
OH
i-Pr
Oi-Pr
t-Bu
i-Pr
i-Pr
i-Pr
i-Pr
> 10À5
> 10À5
NT
M
M
2100c
3000
14,000
59
> 10À5
NT
M
NT
NT
Me
770
a
Ki values were measured as described in reference 7a (n P 2). Data in paren-
Figure 4. Binding model of compound 32 bound to fXa. The protein surface is
colored light green; tolerable substitution points are indicated by yellow arrows.
Water molecules in the crystal structure have been removed for clarity. Coordinates
of fXa can be obtained from the Protein Data Bank (PDB entry: 1FJS).
theses represent IC50 values.
b
Ref. 4a.
c
Ki value calculated according to the Cheng–Prusoff equation: Ki = IC50/(1 + [S]/Km).15
Table 2
Factor Xa inhibitory activities, anticoagulant activities, and PK parameters for compounds 2, 32, and 39–45
OH
R
Z
N
N
H2N
S
W
O
O
Me
Me
PT2c
(l
M)
Cltot (mL/min)
Prodrug conversione (%)
Ff (%)
d
Entry
W
R
Z
fXa Kia (nM)
2
32
39
40
41
42
43
44
45
(KFA-1411)
H
H
CH2CO2H
CH2CO2H
CH2CO2Et
H
H
H
1.7
0.84
2.6
NT
1.4
NT
NT
7.2
NT
NT
23
27
27
8.1
13
NT
1.7
7.5
NT
—
—
1
—
16
NT
—
57
NT
0.9
3.7
H
OH
H
OH
OH
H
OH
OH
H
H
H
H
29
7300b
14
6.6 (29g)
NT
7000b
3700b
51
NT
H
< 1 (7.0h)
NT
OCH2CO2H
OCH2CO2H
OCH2CO2Et
> 10À5
3500b
M
9.2 (2.5i)
13 (4.0i)
a
Against human fXa: Ki values were measured as described in Ref. 7a (n P 2).
b
c
Ki value calculated according to the Cheng–Prusoff equation: Ki = IC50/(1 + [S]/Km).15
Human prothrombin time: plasma concentration required to double clotting time.
Total body clearance after iv administration in rats (n P 2).
d
e
Prodrug conversion was calculated by the dose-normalized AUC of the parent after intravenous administration of prodrug by the AUC of the parent after intravenous
administration of parent in rats.
f
Bioavailability (F%) was calculated by the dose-normalized AUC of the parent after oral administration of prodrug or parent by the AUC of the parent after intravenous
administration of parent in rats.
g
Bioavailability of the unchanged prodrug 39.
Bioavailability of compound 41, the unchanged amidoxime.
Bioavailability of compound 44, the unchanged amidoxime.
h
i

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M. Uchida et al. / Bioorg. Med. Chem. Lett. 18 (2008) 4682–4687
extension without enzyme interaction. The binding model of com-
pound 32 bound to fXa is shown in Figure 4. Incorporation of the
substituent at the sulfonamide nitrogen (demonstrated above 38)
and the proximal position of the phenylene ring (indicated by ar-
rows) were considered tolerable.
OH
O
CO2Q
SO2Me
H
N
O
N
H2N
X
S
O
We focused on the systemic clearance of parent compounds;
therefore, in vivo pharmacokinetic screening in the rat was carried
out. Incorporation of a carboxymethyl group at the sulfonamide
nitrogen (40) resulted in a twofold improvement in anti-fXa activ-
ity compared with 32. Systemic clearance was also improved (re-
duced from 27 to 8.1 mL/min), but the prodrug conversion of the
related amidoxime 41 was not sufficient. In contrast, introduction
of a carboxymethoxy group at the proximal position of the pheny-
lene ring (43) greatly improved systemic clearance, although anti-
fXa activity was inconsiderably diminished compared with 32 (less
than twofold). The related amidoxime 44 showed sufficient pro-
drug conversion. Compound 45, a double prodrug of 43, exhibited
practicable bioavailability after oral administration in rats.
X = H, Q = H
Free form 48
X = OH, Q = n-Bu
Free form 50
HCl salt
KFA-1829
HCl salt
KFA-1982
In vitro activities
Bioavailability
Mouse: 15%
Rabbit: 23%
Dog: 4.9%
Cynomolgus monkey: 11%
Anti-fXa Ki = 5.00 nM
Anti-thrombin Ki = 57800 nM
Anti-trypsin Ki = 1170 nM
PT2 = 1.01 μM
Figure 6. Structures and profiles of KFA-1982 and KFA-1829.
Figure 5 demonstrates evaluation of the preventive effects of
the double prodrug 45 and low-molecular-weight heparin, dalte-
parin, on an in vivo thrombosis model in mice. Compound 45
exhibited encouraging oral antithrombotic activity in a dose-
dependent manner, with an ED50 value of 15.8 mg/kg. Bioavailabil-
ity of the parent 43 after oral administration of the double prodrug
45 (30 mg/kg) in mice was 38%.
100
80
60
40
20
0
We were concerned that compound 43, the parent of compound
45, would not have sufficient anti-fXa and anticoagulation activi-
ties for further development. Therefore, we carried out further
optimization of the parent compounds (Table 3). Replacement of
the carboxymethoxy group of 43 with the carboxymethylamino
group (46) exhibited similar anti-fXa activity and increased sys-
temic clearance by less than twofold. The oxalylamino analogue
47 showed a fivefold increase in anti-fXa activity, but unfortu-
nately, the systemic clearance was also increased. Improvement
in anti-fXa activity was realized by incorporation of the ortho-
substituted phenyl group at P4 position, which had been known
as the optimal scaffold for the S4 pocket.13 Replacement of the iso-
propyl group by the 2-methanesulfonylphenyl group markedly in-
creased anti-fXa activities (48, 49). As in the case of compounds 43
and 46, equivalent efficacy was seen in the carboxymethoxy deriv-
ative 48 and the carboxymethylamino derivative 49, but the sys-
temic clearance of 48 was threefold better than that of 49.
Compound 48 exhibited high selectivity for fXa over thrombin
and trypsin, and good anticoagulant activity in plasma (Fig. 6).
An amidoxime/n-butyl ester double prodrug 50 demonstrated suf-
ficient oral bioavailability in several animal species including pri-
mates.14 On the basis of the oral bioavailability, and the in vitro
potency and selectivity of its parent form (48), KFA-1982, a hydro-
chloride salt of 50, was selected for clinical development.
a
a
V
3
10
30
100
V
100
300
1000
Dalteparin (IU/kg s.c.)
ED50 = 338 IU/kg
Compound 45 (mg/kg p.o.)
ED50 = 15.8 mg/kg
Figure 5. Preventive effects of compound 45 and dalteparin on thromboplastin-
induced lethal thromboembolism in mice. Agents were administrated orally
(compound 45, suspended in 0.5% methyl cellulose) or subcutaneously (dalteparin
sodium, diluted in 5 mL/kg saline) 30 min prior to thromboplastin injection (n = 9–
10). Lethality (%) was calculated from the number of mice survived. aVehicle.
Table 3
Factor Xa inhibitory activities and Cltot for compounds 43 and 46–49
OH
Acknowledgments
Z
H
N
HN
H2N
S
O
O
We thank Dr. Makio Kitazawa, Dr. Toshiki Honma, and Dr.
Yoshihiro Terao for their valuable advice and useful discussions
during this study.
Y
c
Entry
Z
Y
fXaKia (nM)
Cltot (mL/min)
43
46
47
OCH2CO2H
NHCH2CO2H
NHCOCO2H
i-Pr
i-Pr
i-Pr
51
1.7
3.2
20
62b
9.7b
References
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SO2Me
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5.0
7.5
25
49
NHCH2CO2H
5.7b
a
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