Novel Agents Combining Platelet Activating Factor (PAF) Receptor Antagonist with Thromboxane Synthase Inhibitor (TxSI)

Article abstract of DOI:10.1016/S0960-894X(02)00005-7

Compounds 1 or 2 which possess dual-acting PAF antagonist/TxSI in a previous paper were modified and evaluated for the dual-acting activity. It was found that several compounds were potent dual-acting PAF antagonist/TxSI in and ex vivo. 6-(2-Chlorophenyl)-3-[4-[(E/Z)-6-ethoxycarbonyl-1-(3-pyridyl)-1- hexenyl]phenylmethyl]-8,11-dimethyl-2,3,4,5-tetrahydro-8H-pyrido[4′, 3′: 4,5]thieno[3,2-f][1,2,4]triazolo[4,3-a][1,4]diazepine (12) is excellent orally dual-acting PAF antagonist/TxSI.

Full text of DOI:10.1016/S0960-894X(02)00005-7

Bioorganic & Medicinal Chemistry Letters 12 (2002) 771–774
Novel Agents Combining Platelet Activating
Factor (PAF) Receptor Antagonist with
Thromboxane Synthase Inhibitor (TxSI)
Masakazu Fujita,* Taketsugu Seki, Haruaki Inada, Kazuhiro Shimizu,
Akane Takahama and Tetsuro Sano
Omiya Research Laboratory, Nikken Chemicals Co., Ltd., 1-346, Kitabukuro-cho, Saitama-shi, Saitama 330-0835, Japan
Received 15 November 2001; accepted 17 December 2001
Abstract—Compounds 1 or 2 which possess dual-acting PAF antagonist/TxSI in a previous paper were modified and evaluated for the
dual-acting activity. It was found that several compounds were potent dual-acting PAF antagonist/TxSI in and ex vivo. 6-(2-Chloro-
phenyl)-3-[4-[(E/Z)-6-ethoxycarbonyl-1-(3-pyridyl)-1-hexenyl]phenylmethyl]-8,11-dimethyl-2,3,4,5-tetrahydro-8H-pyrido[40,30: 4,5]-
thieno[3,2-f][1,2,4]triazolo[4,3-a][1,4]diazepine (12) is excellent orally dual-acting PAF antagonist/TxSI. # 2002 Elsevier Science
Ltd. All rights reserved.
Platelet activating factor (PAF) is a mediator of
inflammation and plays important roles in the pathol-
ogy of ischemia/thrombosis,1 septic shock,2 asthma.3
Thromboxane A2 (TxA2) is a potent vasoconstrictor
and platelet aggregating agent, may make an important
contribution to the pathogenesis of various circulatory
and certain renal disorders.4ꢀ7 Therefore, it has been
proposed that novel agents combining PAF antagonist
and TxA2 synthase inhibitor (TxSI) would be more
beneficial than either agent alone in the treatment of
these disorders. To avoid the complications associated
with administration of two separate drugs we have
engaged in a program to synthesize agents that pos-
sess both the above biological activities in the same
molecule.
synthetic sequence previously reported by us.8 All com-
pounds except for 3, 7 and 8 in Table 1, and compound
10 in Table 2 were provided by coupling or condensa-
tion of the diazepines10 and the mesylated esters shown
in Scheme 1. As shown in Scheme 1, in the case of
hydroxyethyl group, the mesylation gave the corre-
sponding ethylene in high yield without the desired
mesylate. On the other hand, the mesylated products
were easily chlorinated by treatment with brine. Fur-
thermore, interestingly, it appeared that the syntheses of
compounds 4 and 5 were accompanied with producing
the carbamates.11 Compound 9 was given using the
N-bromoacetyl diazepine. Compound 3 was afforded by
similar previous methodology using phthalic anhydride.
In a previous paper we have described a series of (E/Z)-
5-[phenyl(3-pyridyl)methyleneaminooxy]pentanoic acid
derivatives represented by 1 or 2, which possess dual-
acting PAF antagonist/TxSI has been generated by the
approach of linking the known PAF antagonists and
TxSIs, that is, the structural hybridization (Fig. 1).8
The synthesis of these and related compounds9 star-
ted from the substituted bromobenzene and utilized
*Corresponding author. Tel.: +81-48-641-2334; fax: +81-48-641-
5749; e-mail: souyaku@jade.dti.ne.jp
Figure 1.
0960-894X/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved.
PII: S0960-894X(02)00005-7

772
M. Fujita et al. / Bioorg. Med. Chem. Lett. 12 (2002) 771–774
Compounds 7 and 8 were prepared from the diazepines
bearing the corresponding ketones synthesized by Wit-
tig olefination, catalytic hydrogenation, and so on of 3-
bromobenzaldehyde as shown in Scheme 2. Compounds
11 and 12 in Table 3 were obtained using the corre-
sponding esters by Wittig olefination and esterification
as shown in Scheme 3. Compounds 14–17 in Table 4
were prepared using the corresponding 5-bromoval-
erates or amide as shown in Scheme 4.
Our final goal was to develop a dual-acting agent which
possesses excellent in and ex vivo activities as a clinically
useful drug. According to our previous results, com-
pounds 1 and 2 proved to show potent PAF antagonist
activity in orally dosed mouse in vivo test. Therefore,
based on this information, chemical modifications of
compounds 1 and 2 were started. We initially investi-
gated in vitro SAR concerning the appropriate positions
and length for linking the diazepine to the ethyl ester
(Table 1). All compounds except for 3 with a substituent
at the 2-position of phenyl group showed similar results
in both PAF antagonist and TxSI activity. From this
result, it was clear that 2-substitution was not desirable.
On the other hand, from these results, compounds 1–9
indicated more potent PAF antagonist activity than
Table 1. In vitro PAF antagonist and TxA2 synthase inhibitory
activities of compounds 1–9, 18 and 19
Compd
A
Postn E/Za
IC50 (mM)
PAF TxA2
antagonistb synthasec
3
1
2
4
5
6
7
8
CO
CO
CO
CH2
2
3
4
3
4
4
3
3
4
2:3
2:3
2:3
2:3
2:3
2:3
2:3
2:3
2:3
0.200
0.060
0.100
0.047
0.046
0.085
0.039
0.054
0.060
0.245
NTe
>1.000
0.065
0.072
0.059
0.080
0.069
0.041
0.021
0.058
>1.000
0.001
>1.000
NT
CH2
Table 2. In vitro PAF antagonist and TxA2 synthase inhibitory
activities of compounds 4 and 10
COCH2
CO(CH2)3
(CH2)4
COCH2OCH2
9
18d
19d
2:3
(ꢁ)-E6123f
UK74505g
Ozagrel
Isbogrelh
0.036
0.029
NT
0.024
0.0009
NT
aDetermined by 1H NMR spectra.
Compd
R1
E/Z
IC50 (mM)
bInhibition of the PAF-induced platelet aggregation in rabbit platelet
rich plasma (PRP). This was performed according to the method of
PAF antagonista
TxA2 synthaseb
Terashita et al. with slight modification.13
cInhibition of TxB2 production by incubating prostaglandin
H2(PGH2) with human platelet microsomes. This was performed
4
10
Me
H
2:3
2:3
0.047
0.200
0.059
0.065
according to the method of Terashita et al. with slight modification.12
dSee Fig. 1.
eNT=not tested.
fSee ref 10.
gSee ref 14.
hSee ref 15.
aInhibition of the PAF-induced platelet aggregation in rabbit platelet
rich plasma (PRP). This was performed according to the method of
Terashita et al. with slight modification.13
bInhibition of TxB2 production by incubating prostaglandin
H2(PGH2) with human platelet microsomes. This was performed
according to the method of Terashita et al. with slight modification.12
Scheme 1. Reagents and conditions: (a) (n=1) KMnO4, 90% aq acetone, 54–65%; (n=2) Jones reagent, ꢀ20 ꢂC, 39%; (b) MsCl, Et3N , CHCl2; (c)
2
brine, CHCl3, 77% quant.

M. Fujita et al. / Bioorg. Med. Chem. Lett. 12 (2002) 771–774
773
compound 18 without having N-substitution, but
weaker TxSI activity than compound 19 without the
substitution of phenyl moiety.
Tables 3 and 4 summarize the in vitro activity for the
modified esters. Changing oxime moiety to methine
moiety makes little difference to activity. However, the
modification of ethyl group of ester affected activities.
Namely, replacement of ethoxy moiety with other sub-
stitutions showed weaker PAF antagonist activity, in
particular, hydroxyl was remarkable. On the contrary,
only hydroxyl displayed more potent TxSI activity.
Next, we modified a part of the diazepine and the ester,
respectively. We considered that a balance of both
activities was not kept by a large modification, since the
diazepine and the ester have already been optimized,
respectively. Thus, replacement of methyl with hydro-
gen atom indicated weaker PAF antagonist activity,
while TxSI activity was retained (Table 2).
Table 5 summarizes in vivo PAF antagonist and ex vivo
TxA2 synthase inhibitory activities. All of compounds
Scheme 3. Reagents and conditions: (a) BrꢀPh3P+(CH2)5COOH,
NaH, tBuOH, 56–87%; (b) conc.H2SO4, EtOH, 91%.
Scheme 2. Reagents and conditions: (a) BrꢀPh3P+(CH2)2COOH,
KOtBu, THF; (b) SOCl2, EtOH, quant. (2 steps); (c) LAH, THF,
75%; (d) TBDPSiCl, imidazole, DMF, quant.; (e) nicotinaldehyde,
nBuLi, THF, ꢀ78 ꢂC, 62%; (f) H2, 10%Pd-C, AcOH, MeOH, 65%;
(g) MnO2, CH2Cl2, reflux, 86%; (h) TBAF, THF, quant; (i) MsCl,
Scheme 4. Reagents and conditions: (a) alcohols or amine, pyridine–
CH2Cl2.
Et3N , CHCl2, quant; (j) KMnO4, H2O, 60 ꢂC, 55%.
2
Table 4. In vitro PAF antagonist and TxA2 synthase inhibitory
activities of compounds 2 and 13–17
Table 3. In vitro PAF antagonist and TxA2 synthase inhibitory
activities of compounds 4, 5, 11 and 12
Compd
R2
E/Za
IC50 (mM)
PAF TxA2
antagonistb synthasec
Compd
X
Position
E/Za
IC50 (mM)
PAF
antagonistb
TxA2
synthasec
4
OEt
OH
2:3
2:3
2:3
2:3
2:3
2:3
0.047
0.980
0.081
0.098
0.071
0.065
0.059
0.024
0.151
0.465
0.540
>1.000
4
5
11
12
NO
NO
CH
CH
3
4
3
4
2:3
2:3
1:1
1:2
0.047
0.046
0.039
0.032
0.059
0.080
0.068
0.072
13
14
15
16
17
O(CH2)2-4-Morpholinyl
OCH2Ph
NH(CH2)2Me
O(CH2)3-3-Pyridyl
aDetermined by 1H NMR spectra.
bInhibition of the PAF-induced platelet aggregation in rabbit platelet
rich plasma (PRP). This was performed according to the method of
Terashita et al. with slight modification.13
aDetermined by 1H NMR spectra.
bInhibition of the PAF-induced platelet aggregation in rabbit platelet
rich plasma (PRP). This was performed according to the method of
Terashita et al. with slight modification.13
cInhibition of TxB2 production by incubating prostaglandin
H2(PGH2) with human platelet microsomes. This was performed
according to the method of Terashita et al. with slight modifica-
tion.12
cInhibition of TxB2 production by incubating prostaglandin
H2(PGH2) with human platelet microsomes. This was performed
according to the method of Terashita et al. with slight modification.12

774
M. Fujita et al. / Bioorg. Med. Chem. Lett. 12 (2002) 771–774
methodology as after intravenous administration. As
the results, compound 12 showed 1.6 and 5.2 mg/kg in
both PAF antagonist and TxSI activity, respectively.
Table 5. In vivo PAF antagonist and ex vivo TxA2 synthase inhibi-
tory activities of compounds 1–19
Compd
ED50 (mg/kg iv)
ED50 (mg/kg po)
In conclusion, we have found that several compounds
indicate good dual PAF antagonist/TxSI activity by
intravenous dosing, and that a compound (12) indicate
excellent dual activity by oral dosing. These compounds
appeared to be not parted in the diazepine and the ester
in vivo. Further progress in this work will be the subject
of future reports.
PAF
antagonista
TxA2
synthaseb
PAF
antagonista
TxA2
synthaseb
3
1
2
4
5
6
7
8
9
10
11
12
13
14
15
16
2.4
0.47
0.2
0.2
1.35
4.2
1.05
0.38
4.2
>1.0
>1.0
>1.0
0.1
>10.0
2.3
0.5
NTc
NT
NT
>10.0
>10.0
>10.0
>10.0
>10.0
>10.0
>10.0
>10.0
1.6
>10.0
>10.0
>10.0
>10.0
>10.0
NT
>10.0
>10.0
NT
NT
6.9
1.0
>1.0
>1.0
0.53
>1.0
0.1
0.71
1.0
1.0
0.77
>1.0
>1.0
>1.0
NT
0.01
NT
NT
NT
References and Notes
0.8
>10.0
3.2
5.2
10.0
8.9
NT
NT
NT
NT
>0.1
NT
NT
0.1
0.05
0.60
0.55
0.47
0.54
0.54
0.54
0.54
>5.0
NT
0.02
0.1
NT
NT
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18
19
NT
0.025
1.55
NT
NT
(ꢁ)-E6123
UK74505
Ozagrel
Isbogrel
0.02
0.01
aActivity in vivo was demonstrated by the ability to protect mice from
the lethal effects of an injection of PAF. The ED50 values represent the
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bInhibition of serum TxB2 production in the rats. This was performed
according to the method of Terashita et al. with slight modification.12
cNT=not tested.
1–19 were tested in and ex vivo after intravenous
administration. PAF antagonist activity was assessed in
the mouse, using a PAF-induced death assay.14 As the
results, the ED50 values for all compounds except for 18
and 19 were in the range 0.2–4.2 mg/kg. On the other
hand, TxSI activity was assessed by ex vivo inhibition of
serum TxB2 production in the rat.12 As the results, the
ED50 values for compounds 4–14 except for 6, 7 and 9
were in the range 0.1–1.0 mg/kg, and compound 19 was
0.01 mg/kg.
Furthermore, these representative compounds were tes-
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kawa, K. J. Med. Chem. 1985, 28, 287.