New oxadiazole derivatives showing partly antiplatelet, antithrombotic and serotonin antagonistic properties

Article abstract of DOI:10.1002/ardp.200400927

Ten new 1,2,4-oxadiazole- and six new 1,3,4-oxadiazole-carboxamides containing different lipophilic moieties (i.e. 4-biphenyl-, 1-naphthyl, phenylpropyl- and n-hexyl substituents) and additional basic groups which are mainly alkyl- and dialkylaminoalkyl residues have been synthesized and tested for antiplatelet effects in vitro (Born-test) and antithrombotic properties in vivo (laser thrombosis model). If the platelet aggregation was induced by collagen, the inhibitory effects (IC50) were between 58 μM and 300 μM. Using serotonin (5-HT) as an inducer, compound 6a (N-(3-dimethylaminopropyl-5- (biphenyl-4-yl)-1,3,4-oxadiazole-2-carboxamide) had an IC50 = 1 μM (12e: (N-3-Dimethylaminopropyl)-3-(1-naphthyl)-1,2,4-oxadiazole-5-carboxamide, 6.7 μM). In an in vitro rat tail artery assay 6a and 12e behaved as a competitive 5-HT2A receptor antagonist (6a: pKB = 6.86 ± 0.04; 12e: pKB = 6.66 ± 0.05). The antithrombotic effects of some compounds were small but significant (7-10% inhibition of thrombus formation).

Full text of DOI:10.1002/ardp.200400927

78
DOI 10.1002/ardp.200400927
Arch. Pharm. Chem. Life Sci. 2005, 338, 78−86
New Oxadiazole Derivatives Showing partly Anti-
platelet, Antithrombotic and Serotonin Antagonistic
Properties*
Katrin Bethge, Heinz H. Pertz, and Klaus Rehse
Institut für Pharmazie, Freie Universität Berlin, Berlin, Germany
Ten new 1,2,4-oxadiazole- and six new 1,3,4-oxadiazole-carboxamides containing different lipophilic
moieties (i.e. 4-biphenyl-, 1-naphthyl, phenylpropyl- and n-hexyl substituents) and additional basic
groups which are mainly alkyl- and dialkylaminoalkyl residues have been synthesized and tested for
antiplatelet effects in vitro (Born-test) and antithrombotic properties in vivo (laser thrombosis model).
If the platelet aggregation was induced by collagen, the inhibitory effects (IC50) were between 58 μM
and 300 μM. Using serotonin (5-HT) as an inducer, compound 6a (N-(3-dimethylaminopropyl-5-
(biphenyl-4-yl)-1,3,4-oxadiazole-2-carboxamide) had an IC50 ϭ 1 μM (12e: (N-3-Dimethylaminopro-
pyl)-3-(1-naphthyl)-1,2,4-oxadiazole-5-carboxamide, 6.7 μM). In an in vitro rat tail artery assay 6a and
12e behaved as a competitive 5-HT2A receptor antagonist (6a: pKB ϭ 6.86 0.04; 12e: pKB ϭ 6.66
0.05). The antithrombotic effects of some compounds were small but significant (7Ϫ10% inhibition
of thrombus formation).
Keywords: Oxadiazole derivatives; Antiaggregatory properties; 5 HT2A-Antagonists
Received: July 16, 2004; Accepted: January 6, 2005 [FP927]
Introduction
creased the pharmacological effects in vitro and in vivo we
wonder whether this is also true for non condensed hetero-
cycles such as oxadiazoles.
An important discovery for the development of new drugs
against cardiovascular diseases was the identification of the
endothelium-derived relaxing factor (EDRF) [1] as nitric
oxide (NO) or a labile NO-separating compound [2]. NO
acts as a vasodilating agent and decreases the aggregation
and adhesion of platelets. By activation of the intracellular
located soluble guanylyl cyclase (sGC) NO causes an in-
crease in the concentration of cyclic guanosine monophos-
phate (cGMP). The reference compound 3-(5-hydroxy-
methyl-2 furyl)-1 phenylmethyl-benzo[c]pyrazole (YC 1) di-
rectly activates the enzymes sGC [3] in a NO-independent
manner whereupon the level of cGMP increases.
Chemistry
1,3,4-Oxadiazole-2-carboxamides 6 were prepared accord-
ing to Figure 2. The synthesis of oxalic acid ethyl ester hy-
drazide 3 from hydrazine hydrate 1 and oxalic acid diethyl
Simultaneously, YC 1 inhibits several isoforms of phospho-
diesterases (PDE) [4]. These enzymes catalyze the decompo-
sition of cGMP by hydrolysis.
The aim of the present study was to synthesize new com-
pounds with antiaggregatory and antithrombotic activity by
stimulating the sGC and inhibiting those types of phospho-
diesterases which are found in blood platelets (see Figure 1).
Based on the findings of Straub et al. [5] who showed that
the introduction of basic moieties in analogues of YC 1 in-
Figure 1. 1,2,4-Oxadiazoles and 1,3,4-oxadiazoles derived
from YC-1.
Correspondence: Klaus Rehse, Institut für Pharmazie, Freie
Universität Berlin, Königin-Luise-Str. 2ϩ4, D-14195 Berlin,
Germany. Phone: ϩ49 30 838-53290, Fax: ϩ49 30 838-53251,
rehiwer@zedat.fu-berlin.de
* Part of the PhD thesis Katrin Bethge, FU Berlin, 2002.
© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Arch. Pharm. Chem. Life Sci. 2005, 338, 78−86
New Oxadiazole Derivatives
79
Results and discussion
Inhibition of blood platelet aggregation in
vitro (Born-test)
The platelet aggregation experiments were carried out as
described by Born [12] and Seuter [13]. In brief, platelet
rich plasma (PRP) was prepared from freshly drawn citrated
human blood by mild centrifugation. The platelet aggre-
gation was normally induced by collagen. The time-depen-
dent increase in light transmission was recorded in an
APACT aggregometer (control).
The PRP was incubated with different concentrations of the
test compound. The influence of collagen on the light trans-
mission was recorded again. The concentration which in-
hibited the platelet aggregation half-maximally (IC50) was
determined graphically from the percentage of inhibition at
various concentrations (lg c) of the test compound. The re-
sults are summarized in Table 1.
Figure 2. Synthesis of 1,3,4-oxadiazole-2-carboxamides 6
from hydrazine 1 and oxalic acid diethyl ester 2.
The table contains 1,3,4-oxadiazoles (6a؊j) and 1,2,4-oxa-
diazoles (12a؊f). In the row of the type 6 compounds the
lipophilic biphenyl rest R1 which already had proven to be
very suitable for antiplatelet activities [9, 10] was held con-
stant (6a؊g, 6j) and R2 was varied. Especially substituents
with a basic moiety (pKB ~5) were chosen according to for-
mer experiences with ether heterocycles [9, 10]. The excep-
tion is 6f with neutral R2 (i.e. ϪCH2OH) which gave not
unexpectedly an inactive compound. The other rests are sec-
ondary (6d, 6e, 6g) or tertiary (6a, 6b, 6c, 6j) amines which
all exhibit antiaggregatory activity when the aggregation is
induced by collagen. Comparison of 6a and 6e shows only
a small difference between secondary and tertiary amines
(IC50 65 vs. 84 μM). Dimethylamino- and diethylamino
functions give comparable results (IC50 6a ϭ 65 vs. 6c ϭ
93 μM). A shorter chain length in R2 is not favorable (IC50
6a ϭ 65 vs. 6b ϭ 170 μM). A hydroxy group at the end of
R2 similar to YC 1 (see 6d) is neither essential nor favorable.
Figure 3. Synthesis of 1,2,4-oxadiazole-5-carboxamides 12
from the nitriles 7 and hydroxylamine.
Cyclic amines like 1-methylpyrrolidine-2-yl (see 6j, IC50
ϭ
´
ester 2 which was first described by Stolle [6]. The acylation
86 μM) are acceptable. The best R2 i.e. dimethylaminome-
thyl (6a) was chosen for comparison with other R1 rests (6a
vs. 6h or 6i). Small activity (6h, IC50 ϭ 230 μM, R1 ϭ hexyl)
or total lack of activity (6i IC50 >300 μM, R1 ϭ 3-phe-
nylpropyl) is observed.
with acid chlorides to N’-acyloxalic acid ethyl ester hydra-
zide 4 was carried out in dry tertahydrofuran [7]. Heating
with POCl3 led to the 1,3,4 oxadiazole-2-carboxylicacid-
ethylesters 5. The final step to the resulting 1,3,4 oxadiazole-
2-carboxamides 6 was the reaction with various amines.
The type 12 1,2,4-oxadiazole derivatives show a pattern of
activities very similar to the type 6 compounds e.g. IC50
6a ϭ 65 vs. 12a ϭ 84 μM, 6b ϭ 170 vs. 12b ϭ 125 μM,
6d ϭ 160 vs. 12d ϭ 105 μM and 12f ϭ 58 vs. 6e ϭ 84 M.
Concerning R1 a naphthyl substituent is nearly equipotent
to a biphenyl rest (see 12a vs. 12e). The most active 12f
(IC50 ϭ 58 μM) is comparable to 6e (IC50 ϭ 84 μM).
The isomeric 1,2,4-oxadiazoles were prepared as according
to Figure 3. Two equivalents of hydroxyl amine were added
to the nitrile in order to get the carboxamidoximes 8
(Knudsen [8]). The second step was the reaction with oxalic
acid ethyl ester chloride 9 according to the procedure of
Palazzo [11]. Some compounds of type 10 cyclized spon-
taneously by elimination of water. Other compounds were
boiled in toluene for 2 h in order to obtain the 1,2,4-oxadi-
azole-5-carboxylicacidethylesters 11. Subsequent reaction
with amines led to a number of 1,2,4-oxadiazole-5 carbox-
amides 12.
To get more information on the mechanism of the antiplate-
let activity three 1,3,4-oxadiazoles (6a, 6d, 6e) and two
1,2,4-oxadiazoles (12e, 12f) were selected for an investi-
gation in the Born-test using other inducers than collagen
© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

80
Rehse et al.
Arch. Pharm. Chem. Life Sci. 2005, 338, 78−86
Table 1. The in vitro antiplatelet properties of oxadiazoles. In the Born-test the relative standard deviation is <10% see asa.
The other assay were run in duplicate.
Compound
R1
R2
Born test IC50 [μM]
6a
6b
4-Biphenyl-
4-Biphenyl-
4-Biphenyl-
4-Biphenyl-
4-Biphenyl-
4-Biphenyl-
4-Biphenyl-
C6H13-
Phenyl-(CH2)3-
4-Biphenyl-
4-Biphenyl-
4-Biphenyl-
4-Biphenyl-
4-Biphenyl-
1-Naphthyl-
4-Biphenyl-
Ϫ
-CH2-N(CH3)2
-N(CH3)2
-CH2-N(CH2-CH3)2
-CH2-NH(CH2)2OH
-CH2-NHCH3·HCl
-CH2-OH
-NH(CH2)2OH
-CH2-N(CH3)2
-CH2-N(CH3)2
1-Methylpyrrolidine-2-yl-
-CH2-N(CH3)2
-N(CH3)2
-CH2-N(CH2-CH3)2
-CH2-NH(CH2)2OH
-CH2-N(CH3)2
-CH2-NHCH3·HCl
Ϫ
65
170
93
160
84
>300
270
230
>300
86
6c
6d
6e
6f
6g
6h
6i
6j
12a
12b
12c
12d
12e
12f
asa
84
215
190
105
93
58
175 20
Table 2. IC50 values for 1,2,4- and 1,3,4-oxadiazole-carboxamides using different inducers of aggregation in the Born test. The
relative standard deviation is <10%.
IC50 of the test compounds [μM]
Inducer of aggregation
Collagen
ADP
5-HT
Adrenaline
PAF
6a
65
118
1.0
110
28
6d
160
60
110
215
52
6e
84
53
75
> 300
120
12e
93
105
6.7
217
28
12f
58
63
27
160
150
for the platelet aggregation. The criterium for selection was
the ability to inhibit the aggregation by collagen. For com-
parison one compound (6d) with small activity was in-
cluded.
Inhibition of thrombus formation in vivo
(laser-thrombosis model)
In order to examine the inhibition of thrombosis of our
oxadiazoles we used an in vivo thrombosis model [14]. In
brief, the formation of thrombi in mesenteric vessels of rats
was induced by the beam of an argon laser via a microscope
(35 mW, 50 ms). The number of exposures (“shots”) neces-
sary to form a thrombus of defined size was counted. From
the average shot number the percentage of inhibition of
thrombosis was calculated.
Table 2 shows the results of the Born test with other in-
ducers of the platelet aggregation. The IC50 values of stand-
ard drugs were: WEB 2086 (apafant) 2 μM; phentolamine
mesylate 3 μM; NECA, 5Ј-N-ethylcarboxamidoadenosine
2 μM; imipramine hydrochloride 5 μM.
It is evident that the platelet aggregation induced by sero-
tonin can be inhibited by rather small concentrations of
some compounds. The best effects were observed with com-
pounds 12e (IC50 ~7 μM) and 6a (IC50 ~1 μM). The induc-
tion by ADP, adrenaline and PAF is inhibited in the same
order of magnitude as by collagen. Therefore, it is suggested
that the mechanism of action at least in 6a and 12e is
associated with 5-HT.
All compounds of Table 1 were tested but only 6b, 6d, 6e
showed small antithrombotic effects. The effect of 12d has
to be regarded as marginal (see Table 3). The common
structural feature obviously is a 4-biphenyl rest as R1 and a
basic moiety with pKB ~5 in R2. However several of other
compounds of Table 1 do fulfill these structural require-
ments without showing antithrombotic activity. Therefore
© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Arch. Pharm. Chem. Life Sci. 2005, 338, 78−86
New Oxadiazole Derivatives
81
Table 3. Antithrombotic effects of oxadiazoles 2 h after p.o. administration of 60 mg/kg of the test compound to rats. Statistics:
Wilcoxon Man Whitney U test, n.s.Ϫnot significant.
Compound
Inhibition of thrombus formation in
arterioles
R1
R2
venules
sx
IC50
μmol/L
%
p Յ
%
sx
p Յ
6b
6d
4-Biphenyl-
4-Biphenyl-
4-Biphenyl-
4-Biphenyl-
Ϫ
-N(CH3)2
-CH2-NH(CH2)2OH
-CH2-NHCH3 · HCl
-CH2-NH(CH2)2OH
Ϫ
2
0
4
0
20
1
2
1
1
5
n.s.
n.s.
0.02
n.s.
7
7
10
1
1
1
1
0.01
0.01
0.002
0.1
170
160
84
105
175
6e
12d
asa
4
0.002
48 10
0,002
concise structure activity relationships cannot be drawn.
Comparison of 6d with 12d which only differ in the oxadi-
zole part shows a slight advantage for the 1,3,4-oxadiazole
structure. Derivative 6e had the highest antithrombotic ef-
fect in this model.
to the right in a parallel manner (Figure 4). The Schild
analysis [19] gave a pKB value of 6.86 0.03 (n ϭ 12). The
slope of the Schild plot was 0.90 0.05 and not significantly
different from unity (p <0.05) [20]. Compound 12e showed
a nearly identical behavior. The pKB value is 6.66 0.06.
The slope of the Schild is plot 1.06 0.08 and as well not
significantly different from unity (p <0.05). In this model
Activation of sGC
Compounds 6a, 6d, 6e, 12e and 12f were tested by the
method of Hoenicka et al. [15] in a heme-containing sGC-
assay [14] in the presence of Mg2ϩ ions towards their ability
to stimulate sGC (Institute of Cardiovascular Research,
Bayer AG, Wuppertal).
There was no increase of the basal activity of sGC measured
with any of the compounds tested. Even the addition of
DEA/NO (N,N-dimethylamino-diazenolat-2-oxide) did not
show an additional effect as described for YC-1 and the
reference substance BAY 41-8543, respectively [16, 17].
Inhibition of phosphodiesterases
In order to examine the effect towards several isoforms of
phosphodiesterases, compounds 6a, 6d, 6e, 12e and 12f were
tested for their inhibitory activity in different cGMP-SPA
[15] and cAMP-SPA tests (Amersham Biosciences) at the
Institute of Cardiovascular Research, Bayer AG, Wupper-
tal.
No inhibition was observed (IC50 >100 μM) against PDE
1, 2, 3, 4, 5, or 9 for any of the oxadiazole derivatives tested.
Antagonism at the 5-HT2A-receptor
Since 5-HT2A receptors are involved in 5-HT-induced plate-
let aggregation, we tested the inhibition of the compounds
6a and 12e against the contractile effect of 5-HT in the iso-
lated rat tail artery [18] which is a tissue that is endowed
with 5-HT2A receptors. Details about experimental pro-
cedure are given in reference [18]. Compound 6a concen-
tration-dependently antagonized the contractile response to
5-HT. Concentration-response curves to 5-HT were shifted
Figure 4. Antagonism of 5-HT-induced contraction by 6a in
rat tail artery. The upper panel represents cumulative concen-
tration-response curves to 5-HT in the absence and presence
of 6a. The data are mean SEM from 4 experiments each.
The lower panel represents the Schild regression analysis.
© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

82
Rehse et al.
Arch. Pharm. Chem. Life Sci. 2005, 338, 78−86
Oxalic acid ethyl ester- N2-hexylcarbonylhydrazide (4b)
the standard drug ketanserin showed a pKB ϭ 9.55 0.02.
Sarpogrelate gave a pKB ϭ 8.46 0.04. We conclude that
6a and 12e act as a competitive antagonist of 5-HT at the
5-HT2A receptor of rat tail artery. In summary, the results
indicate that the effects of compound 6a and 12e in the
Born test are related to a competitive antagonism against 5-
HT at the 5-HT2A receptor.
From 1.5 g (10 mmol) hexane-carboxylic acid chloride. Powder, mp.
52°C, yield 0.3 g (13%). Anal. C11H20N2O4 (244.2). 1H-NMR / 400
MHz ([D6]DMSO): δ (ppm) ϭ 0.85Ϫ0.88 (m, 3H, CH3-(CH2)5),
1.19Ϫ1.32 (m, 9H, CH3-CH2O and (CH2)3-CH3), 1.47Ϫ1.53 (m,
2H, CH2-(CH2)3CH3), 2.13 (t, J ϭ 7.3 Hz, 2H, CH2CϭO), 4.26 (q,
J ϭ 7.1 Hz, 2H, OCH2), 9.91 (s, 1H, NH-(CϭO)CH2, D2O ex-
change), 10.66 (s, 1H, NH-(CϭO)CϭO, D2O exchange). MS (EI,
100°C): m/z (%) ϭ 244 (2) [Mϩ•], 171 (13), 132 (18), 113 (81)
[C7H13Oϩ], 85 (30), 57 (15), 55 (12), 43 (100) [C3H7ϩ], 41 (19).
Oxalic acid ethyl ester-N2-(3-phenylpropyl)-carbonylhydrazide (4c)
Experimental
From 16.4 g (0.1 mol) 4-phenylbutyricacid. Powder, mp. 51°C, yield
7.6 g (27%). Anal. C14H18N2O4 (278.2). 1H-NMR / 400 MHz
([D6]DMSO): δ (ppm) ϭ 1.28 (t, J ϭ 7.0 Hz, 3H, CH3), 1.77Ϫ1.84
(m, 2H, CH2-CH2Ph), 2.21 (t, J ϭ 7.5 Hz, 2H, CH2CϭO), 2.60 (t,
J ϭ 7.5 Hz, 2H, CH2-Ph), 4.26 (q, J ϭ 7.1 Hz, 2H, CH2-CH3),
7.16Ϫ7.30 (m, 5H, Ph), 9.96 (s, 1H, NH-(CϭO)CH2, D2O ex-
change), 10.69 (s, 1H, NH-(CϭO)CϭO, D2O exchange). MS (EI,
110°C): m/z (%) ϭ 278 (6) [Mϩ•], 220 (15), 174 (43), 147 (77), 132
(22), 129 (13), 105 (10), 104 (25), 91 (100) [C7H7ϩ], 74 (25), 65 (11),
41 (13), 32 (14).
Chemistry
Mp. (uncorr.), Linström. Elemental analysis: Elementar Vario EL.
IR: Perkin Elmer 1420 Ratio Recording IR-Spectrophotometer and
ATI Mattson Genesis Serie FTIR. NMR: Bruker Avance/DPX 400.
EI-MS: CH-7A-Varian MAT (70 eV). The synthesis of 3 [6] and 8b
[19] already has been reported. All other compounds were prepared
for the first time.
´
Synthesis of oxalic acid ethyl ester hydrazide 3 (method of Stolle
[6])
General procedure for the cyclization of the ester acylhydrazides 4 to
1,3,4-oxadiazole-2-carboxylic acid ethyl esters 5 (method from Dost
et al. [7] modified)
To 16.6 g oxalic acid ethyl ester (0.11 mol) dissolved in 6 mL ethanol
was dropped slowly the equivalent amount of hydrazine hydrate
(5.7 g) in ethanol at a temperature of -10 to -15°C. Subsequently,
the solvent was removed in vacuo at temperatures below 25°C.
0.02 mol of the corresponding oxalicacidethylester-N2-acylhydra-
zide were stirred with 30 mL POCl3 for 5 h at 65°C. The excess of
POCl3 was removed in vacuo (2000 Pa) at temperatures below 40°C.
The residue was poured carefully on ice. The mixture was adjusted
to pH ϭ 6.5Ϫ7.0 with 10% NaOH and extracted with ether several
times. The combined amounts of ether were dried and the solvent
was removed in vacuo. The final purification was performed by
recrystallization in the solvent stated or by column chromatogra-
phy.
Powder, mp. 71°C (ethanol), yield 13 g (87%). Anal. C4H8N2O3
1
(132.2). H-NMR / 400 MHz ([D6]DMSO): δ (ppm) ϭ 1.25 (t, J ϭ
7.1 Hz, 3H, CH3), 4.21 (q, J ϭ 7.1 Hz, 2H, CH2), 9.92 (s, 2H, NH2,
D2O exchange), 10.21 (s, 1H, NH, D2O exchange). MS (EI, 80°C):
m/z (%) ϭ 132 (29) [Mϩ•], 104 (65) [Mϩ•-C2H4], 76 (15), 59 (41),
58 (68), 45 (43), 43 (10), 32 (51), 31 (100) [N2H3ϩ], 30 (23).
5-(Biphenyl-4-yl)-1,3,4-oxadiazole-2-carboxylic acid ethyl ester (5a)
General procedure for the synthesis of N2-acyloxalic acid ethyl ester
hydrazides (4) (method of Dost et al. [7] slightly modified)
From 5.9 g (0.02 mol) 4a. Crystals, mp. 102°C (ether), yield 4.7 g
(84%). Anal. C17H14N2O3 (294.3). IR (KBr): ν ϭ 1740 cmϪ1 (Cϭ
O); 1610 (CϭN); 1570 1H-NMR / 400 MHz ([D6]DMSO): δ
(ppm) ϭ 1.39 (t, J ϭ 7.1 Hz, 3H, CH3), 4.47 (q, J ϭ 7.1 Hz, 2H,
CH2), 7.44Ϫ7.47 (m, 1H, biph 4Ј-H), 7.52Ϫ7.55 (m, 2H, biph 3Ј-
H, 5Ј-H), 7.79 (d, J ϭ 7.4 Hz, 2H, biph 2Ј-H, 6Ј-H), 7.96 (d, J ϭ
8.4 Hz, 2H, biph 2-H, 6-H), 8.16 (d, J ϭ 8.3 Hz, 2H, biph 3-H, 5-
H). MS (EI, 120°C): m/z (%) ϭ 295 (16), 294 (88) [Mϩ•], 221 (36)
[Mϩ-C3H5O2], 181 (41), 180 (16), 179 (100), 153 (15), 152 (20).
Dry oxalic acid ethyl ester hydrazide 3 (0.1 mol) was suspended in
25 mL of dry tetrahydrofuran and mixed with 0.1 mol NaHCO3.
Then 0.1 mol acid chloride was dropped into the suspension within
30 min at a temperature of 45°C. The acid chlorides were obtained
from the corresponding acids by boiling with freshly distilled thionyl
chloride followed by fractionated distillation. The suspension was
stirred for 12 h at 45Ϫ50°C. The access of water was carefully
avoided. Then the mixture was filtered and the solvent removed in
vacuo. The products were recrystallized from ether. It was not pos-
sible to obtain the compounds analytically pure because of their
insolubility in organic solvents and their tendency to decompose or
to undergo cyclization during heating.
5-Hexyl-1,3,4-oxadiazole-2-carboxylic acid ethyl ester (5b)
From 4.9 g (0.02 mol) 4b. Oil, Eluent chloroform, yield 3.1 g (68%).
Anal. C11H18N2O3 (226.3). IR (film): ν ϭ 1749 cmϪ1 (CϭO); 1556
(CϭN). 1H-NMR / 400 MHz ([D6]DMSO): δ (ppm) ϭ 0.86 (t, J ϭ
7.0 Hz, 3H, CH3-(CH2)5), 1.26Ϫ1.29 (m, 6H, (CH2)3-CH3), 1.33 (t,
J ϭ 7.1 Hz, 3H, CH3-CH2O), 1.68Ϫ1.74 (m, 2H, CH2-CH2Ox),
2.94 (t, J ϭ 7.5 Hz, 2H, CH2Ox), 4.41 (q, J ϭ 7.1 Hz, 2H, OCH2-
CH3). MS (EI, 80°C): m/z (%) ϭ 226 (2) [Mϩ•], 197 (10), 183 (20),
169 (44), 156 (100) [Mϩ-C5H10], 153 (32) [Mϩ-C3H5O2], 128 (17),
113 (20), 69 (13), 55 (18), 43 (48) [C3H7ϩ], 41 (36).
Oxalic acid ethyl ester-N2-biphenyl-4-yl-carbonylhydrazide (4a)
From 6.0 g (0.03 mol) 4-biphenyl-carboxylic acid chloride. Powder,
mp. 108°C, yield 5.9 g (41%). Anal. C17H16N2O4 (312.2). 1H-
NMR / 400 MHz ([D6]DMSO): δ (ppm) ϭ 1.32 (t, J ϭ 7.2 Hz, 3H,
CH3), 4.31 (q, J ϭ 7.2 Hz, 2H, CH2-CH3), 7.43 (t, J ϭ 7.2 Hz, 1H,
biph 4Ј-H), 7.41Ϫ7.44 (m, 2H, biph 3Ј-H, 5Ј-H), 7.75 (d, J ϭ 7.8
Hz, 2H, biph 2Ј-H, 6Ј-H), 7.83 (d, J ϭ 8.1 Hz, 2H, biph 2-H, 6-H),
7.98 (d, J ϭ 8.2 Hz, 2H, biph 3-H, 5-H), 10.63 (s, 1H, NH-
(CϭO)Ph, D2O exchange), 10.95 (s, 1H, NH-(CϭO)CϭO, D2O ex-
change). MS (EI, 130°C): m/z (%) ϭ 312 (3) [Mϩ•], 182 (14), 181
(100), 153 (16), 152 (23).
5-(3-Phenylpropyl)-1,3,4-oxadiazole-2-carboxylic acid ethyl ester
(5c)
From 8.1 g (0.03 mol) 4c. Oil, Eluent dichloromethane/methanol
(99:1), yield 1.0 g (13%). Anal. C14H16N2O3 (260.3). IR (film): ν ϭ
© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Arch. Pharm. Chem. Life Sci. 2005, 338, 78−86
1747 cmϪ1 (CϭO); 1553 (CϭN). 1H-NMR
New Oxadiazole Derivatives
83
/
400 MHz
N-(3-Diethylaminopropyl)-5-(biphenyl-4-yl)-1,3,4-oxadiazole-2-
([D6]DMSO): δ (ppm) ϭ 1.33 (t, J ϭ 7.1 Hz, 3H, CH3-CH2O),
1.99Ϫ2.07 (m, 2H, CH2-CH2Ph), 2.68 (t, J ϭ 7.6 Hz, 2H, CH2Ph),
2.94 (t, J ϭ 7.4 Hz, 2H, CH2Ox), 4.41 (q, J ϭ 7.1 Hz, 2H, OCH2-
CH3), 7.17Ϫ7.31 (m, 5H, Ph). MS (EI, 90°C): m/z (%) ϭ 260 (4)
[Mϩ•], 156 (100) [Mϩ-C8H8], 128 (20), 91 (19) [C7H7ϩ].
carboxamide (6c)
From 530 mg (1.8 mmol) 5a (method C). Crystals, mp. 70.5°C
(methanol), yield 290 mg (35%). Anal. C22H26N4O2 (378.5). IR
(KBr): ν ϭ 1687 cmϪ1 (CϭO); 1611 (CϭN). 1H-NMR/400 MHz
([D6]DMSO): δ (ppm) ϭ 0.97 (t, J ϭ 7.1 Hz, 6H, 2x CH3),
1.65Ϫ1.72 (m, 2H, CH2-CH2N), 2.44Ϫ2.48 (m, 6H, 3 x CH2N),
3.36 (after D2O exchange t, J ϭ 6.9 Hz, 2H, CH2-NHCO), 7.45 (t,
J ϭ 7.3 Hz, 1H, biph 4Ј-H), 7.51Ϫ7.55 (m, 2H, biph 3Ј-H, 5Ј-H),
7.79 (d, J ϭ 7.7 Hz, 2H, biph 2Ј-H, 6Ј-H), 7.96 (d, J ϭ 8.4 Hz, 2H,
biph 2-H, 6-H), 8.16 (d, J ϭ 8.4 Hz, 2H, biph 3-H, 5-H), 9.48 (t,
J ϭ5.4 Hz, 1H, NH, D2O exchange.). MS (EI, 90°C): m/z (%) ϭ
378 (3) [Mϩ•], 86 (100) [C5H12Nϩ], 72 (15) [C4H10Nϩ].
General procedure for the synthesis of the 1,3,4-oxadiazole-2-carbox-
amides 6 (method from Dost et al. [7] modified)
Method A: 0.02 mol of the corresponding ester were dissolved in 50
mL methanol or ethanol, mixed with 0.02 mol of the amine and
refluxed for 5 min. After cooling, solid crystals were isolated.
Further product was obtained by concentrating the solution. The
final cleaning was achieved by recrystallization from methanol/
water.
N-[3-(2-Hydroxyethylamino)-propyl]-5-(biphenyl-4-yl)-1,3,4-oxa-
diazole-2-carboxamide (6d)
Method B: One equivalent of the corresponding ester was dissolved
in dichloromethane and mixed with 1.5 equivalents of the amine.
The solution was heated under reflux for 30 min. The solvent was
removed in vacuo and the residue recrystallized from methanol.
From 540 mg (1.8 mmol) 5a (method C). Powder, mp. 135°C (meth-
anol), yield 430 mg (63%). Anal. C20H22N4O3 (366.4). IR (KBr):
ν
ϭ
1688 cmϪ1 (CϭO); 1611 (CϭN). 1H-NMR/400 MHz
([D6]DMSO): δ (ppm) ϭ 1.66Ϫ1.73 (m, 2H, CH2-CH2-CH2),
2.56Ϫ2.62 (m, 4H, CH2-NH-CH2), 3.35Ϫ3.38 (m, after D2O ex-
change t, J ϭ 6.8 Hz, 2H, CH2-NHCO), 3.45 (“q”, J ϭ 5.5 Hz, 2H,
CH2-OH), 4.44 (t, J ϭ 5.3 Hz, 1H, OH, D2O exchange), 7.43Ϫ7.47
(m, 1H, biph 4Ј-H), 7.51-7.55 (m, 2H, biph 3Ј-H, 5Ј-H), 7.78Ϫ7.80
(m, 2H, biph 2Ј-H, 6Ј-H), 7.95 (d, J ϭ 8.4 Hz, 2H, biph 2-H, 6-H),
8.17 (d, J ϭ 8.3 Hz, 2H, biph 3-H, 5-H), 9.46 (br. s, 1H, NHCO,
D2O exchange). MS (EI, 180°C): m/z (%) ϭ 366 (3) [Mϩ•], 336
(25), 335 (100) [Mϩ•-CH3O], 306 (17) [Mϩ•-C2H6NO], 223 (34), 181
(23), 179 (33), 153 (10), 152 (12), 113 (18), 74 (12) [C3H8NOϩ], 56
(13), 44 (26).
Method C: One equivalent of the corresponding ester was dissolved
in dichloromethane. Two equivalents of the amine were dropped
into the solution. After stirring and carefully avoiding the access of
oxygen for 1Ϫ2 wk at room temperature the solvent was removed
in vacuo. The residue was dissolved again in dichloromethane,
washed with water until neutral reaction was reached, and then
mixed three times with 0.1 N-HCl. The combined volumes of hydro-
chloric acid were mixed with a saturated solution of Na2CO3 until
basic reaction occurred. Subsequently, the solution was extracted
with dichloromethane. After drying the solution with Na2SO4 the
solvent was removed in vacuo. A final cleaning step was achieved
by column chromatography or recrystallisation.
N-(3-Methylaminopropyl)-5-(biphenyl-4-yl)-1,3,4-oxadiazole-2-
carboxamide hydrochloride (6e)
N-(3-Dimethylaminopropyl)-5-(biphenyl-4-yl)-1,3,4-oxadiazole-2-
carboxamide (6a)
From 580 mg (2.0 mmol) 5a (method B). Crystals, mp. 198°C
(methanol/HCl), yield 290 mg (39%). Anal. C19H21ClN4O2 (372.8).
1
IR (KBr): ν ϭ 2441 cmϪ1 (NH2ϩ), 1693 (CϭO); 1612 (CϭN). H-
From 840 mg (2.9 mmol) 5a (method C). Powder, mp. 104°C
NMR / 400 MHz ([D6]DMSO): δ (ppm) ϭ 1.86Ϫ1.93 (m, 2H, CH2-
CH2N), 2.56 (t, J ϭ 5.4 Hz, 3H, CH3N), 2.92Ϫ2.99 (m, 2H,
CH2Nϩ), 3.40-3.46 (m, 2H, CH2-NHCO), 7.44Ϫ7.48 (m, 1H, biph
4Ј-H), 7.52Ϫ7.56 (m, 2H, biph 3Ј-H, 5Ј-H), 7.79Ϫ7.81 (m, 2H, biph
2Ј-H, 6Ј-H), 7.97 (d, J ϭ 8.4 Hz, 2H, biph 2-H, 6-H), 8.17Ϫ8.19
(m, 2H, biph 3-H, 5-H), 8.63 (br. s, 2H, NH2ϩ, D2O exchange),
9.51 (t, J ϭ 5.9 Hz, 1H, NHCO). MS (EI, 80°C): m/z (%) ϭ 336
(4) [Mϩ• base], 236 (11), 181 (10), 179 (19), 71 (30), 70 (19), 58 (18)
[C3H8Nϩ], 44 (100) [C2H6Nϩ], 36 (15), 28 (15).
(ether), yield 620 mg (62%). Anal. C20H22N4O2 (350.4). IR (KBr):
ν
ϭ
1691 cmϪ1 (CϭO); 1613 (CϭN). 1H-NMR/400 MHz
([D6]DMSO): δ (ppm) ϭ 1.66Ϫ1.73 (m, 2H, CH2-CH2N), 2.15 (s,
6H, (CH3)2N), 2.28 (t, J ϭ 7.0 Hz, 2H, CH2-N(CH3)2), 3.32 (after
D2O exchange t, J ϭ7.1 Hz, 2H, CH2-NHCO), 7.45 (t, J ϭ 7.3 Hz,
1H, biph 4Ј-H), 7.51Ϫ7.55 (m, 2H, biph 3Ј-H, 5Ј-H), 7.78Ϫ7.81 (m,
2H, biph 2Ј-H, 6Ј-H), 7.96 (d, J ϭ 8.4 Hz, 2H, biph 2-H, 6-H), 8.16
(d, J ϭ 8.4 Hz, 2H, biph 3-H, 5-H), 9.42 (t, J ϭ5.7 Hz, 1H, NH,
D2O exchange). MS (EI, 100°C): m/z (%) ϭ 308 (<1) [Mϩ•], 58
(100) [C3H8Nϩ].
N-(3-Hydroxypropyl)-5-(biphenyl-4-yl)-1,3,4-oxadiazole-2-carbox-
amide (6f)
N-(2-Dimethylaminoethyl)-5-(biphenyl-4-yl)-1,3,4-oxadiazole-2-
carboxamide (6b)
From 910 mg (3.1 mmol) 5a (method A). Powder, mp. 166°C (etha-
nol), yield 570 mg (57%). Anal. C18H17N3O3 (323.4). IR (KBr): ν ϭ
From 730 mg (2.5 mmol) 5a (method C). Powder, mp. 110°C (meth-
1687 cmϪ1 (CϭO); 1612 (CϭN). 1H-NMR
/
400 MHz
anol), yield 340 mg (42%). Anal. C19H20N4O2 (336.4). IR (KBr):
([D6]DMSO): δ (ppm) ϭ 1.69Ϫ1.76 (m, 2H, CH2-CH2OH),
ν
ϭ
1698 cmϪ1 (CϭO); 1613 (CϭN). 1H-NMR/400 MHz
3.35Ϫ3.40 (m, 2H, CH2-NHCO), 3.47-3.51 (m, 2H, CH2-OH), 4.53
(t, J ϭ 5.1 Hz, 1H, OH, D2O exchange), 7.45 (t, J ϭ 7.3 Hz, 1H,
biph 4Ј-H), 7.51-7.55 (m, 2H, biph 3Ј-H, 5Ј-H), 7.79 (d, J ϭ 7.7 Hz,
2H, biph 2Ј-H, 6Ј-H), 7.96 (d, J ϭ 8.4 Hz, 2H, biph 2-H, 6-H), 8.17
(d, J ϭ 8.3 Hz, 2H, biph 3-H, 5-H), 9.31 (t, J ϭ 5.7 Hz, 1H, NH).
MS (EI, 140°C): m/z (%) ϭ 323 (44) [Mϩ•], 294 (11), 239 (13), 224
(13), 23 (18), 181 (38), 180 (31), 179 (100), 153 (17), 152 (22) 151
(11), 74 (49), 56 (17), 44 (10), 31 (19).
([D6]DMSO): δ (ppm) ϭ 2.19 (s, 6H, (CH3)2N), 2.44 (t, J ϭ 6.7 Hz,
2H, CH2-N(CH3)2), 3.38Ϫ3.44 (m, 2H, CH2-NHCO), 7.43Ϫ7.47
(m, 1H, biph 4Ј-H), 7.51Ϫ7.55 (m, 2H, biph 3Ј-H, 5Ј-H), 7.79 (d,
J ϭ 7.4 Hz, 2H, biph 2Ј-H, 6Ј-H), 7.96 (d, J ϭ 8.4 Hz, 2H, biph 2-
H, 6-H), 8.17 (d, J ϭ 8.3 Hz, 2H, biph 3-H, 5-H), 9.18Ϫ9.19 (m,
1H, NH, D2O exchange.). MS (EI, 110°C): m/z (%) ϭ 336 (<1)
[Mϩ•], 58 (100) [C3H8Nϩ].
© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

84
Rehse et al.
Arch. Pharm. Chem. Life Sci. 2005, 338, 78−86
N-[2-(2-Hydroxyethylamino)-ethyl]-5-(biphenyl-4-yl)-1,3,4-oxa-
diazole-2-carboxamide (6g)
than 35°C. Then 1 N HCl was added. In order to remove rests of
the nitrile the solution was washed with ether or ethylacetate. Now
a saturated solution of Na2CO3 was added until a pH-value of 7Ϫ8
is reached. The mixture was extracted with ether, dried and the sol-
vent removed in vacuo.
From 800 mg (2.7 mmol) 5a (method C). Crystals, mp. 157°C
(methanol), yield 570 mg (60%). Anal. C19H20N4O3 (352.4). IR
1
(KBr): ν ϭ 1688 cmϪ1 (CϭO); 1611 (CϭN). H-NMR / 400 MHz
([D6]DMSO): δ (ppm) ϭ 2.61 (t, J ϭ 5.8 Hz, 2H, CH2-CH2OH),
2.74 (t, J ϭ 6.5 Hz, 2H, CH2-CH2NHCO), 3.39 (t, J ϭ 6.4 Hz, 2H,
CH2-NHCO), 3.45 (br. s, 2H, CH2-OH), 4.45 (br. s, 1H, OH, D2O
exchange), 7.43Ϫ7.47 (m, 1H, biph 4Ј-H), 7.51Ϫ7.55 (m, 2H, biph
3Ј-H, 5Ј-H), 7.76Ϫ7.80 (m, 2H, biph 2Ј-H, 6Ј-H), 7.94Ϫ7.97 (m,
2H, biph 2-H, 6-H), 8.16Ϫ8.18 (m, 2H, biph 3-H, 5-H), 9.25 (br. s,
1H, NHCO, D2O exchange). MS (EI, 150°C): m/z (%) ϭ 352 (<1)
[Mϩ•], 303 (13), 221 (21), 181 (54), 179 (27), 153 (14), 152 (18), 87
(11), 74 (100) [C3H8NOϩ], 56 (33), 30 (12).
4-Biphenyl-1-carboxamidoxime (8a)
From 17.9 g (0.10 mol) 4-biphenyl-1-carbonitrile, extracted with
ethylacetate. Crystals (ethylacetate/petroleum ether), mp. 165°C,
yield 8 g (38%). Anal. C13H12N2O (212.3). IR (KBr): ν ϭ 1643
cmϪ1 (CϭN). 1H-NMR/400 MHz ([D6]DMSO): δ (ppm) ϭ 5.84 (s,
2H, NH2, D2O exchange), 7.38 (t, J ϭ 7.4 Hz, 1H, Biph 4Ј-H),
7.45-7.49 (m, 2H, biph 3Ј-H, 5Ј-H), 7.67Ϫ7.71 (m, 4H, biph 2-H-,
6-H, 2Ј-H, 6Ј-H), 7.77 (d, J ϭ 8.4 Hz, 2H, biph 3-H, 5-H), 9.67 (s,
1H, OH, D2O exchange). MS (EI, 40°C): m/z (%) ϭ 213 (15), 212
(100) [Mϩ•], 196 (18), 195 (96) [Mϩ•-OH• respectively NH3], 180
(37) [Mϩ•-H2NO•], 179 (17), 166 (15), 153 (14), 152 (35), 151 (13),
97 (10), 76 (11).
N-(3-Dimethylaminopropyl)-5-hexyl-1,3,4-oxadiazole-2-carbox-
amide (6h)
From 810 mg (3.5 mmol) 5b (method B). Powder, mp. 34°C (eluent:
dichloromethane/methanol 10:1), yield 890 mg (90%). Anal.
14H26N4O2 (282.4). IR (KBr): ν ϭ 1690 cmϪ1 (CϭO); 1562 (Cϭ
1-Naphthaline-carboxamidoxime (8b)
C
1
N). H-NMR / 400 MHz ([D6]DMSO): δ (ppm) ϭ 0.86 (t, J ϭ 6.7
Hz, 3H, CH3), 1.28Ϫ1.36 (m, 6H, (CH2)3CH3), 1.61Ϫ1.75 (m, 4H,
CH2-CH2N u. CH2-CH2Ox), 2.13 (s, 6H, (CH3)2N), 2.25 (t, J ϭ
6.7 Hz, 2H, CH2-N(CH3)2), 2.91 (t, J ϭ 7.5 Hz, 2H, CH2Ox),
3.25Ϫ3.29 (m, after D2O exchange t, J ϭ7.0 Hz, 2H, CH2-NHCO),
9.26Ϫ9.29 (m, 1H, NH, D2O exchange). MS (EI, 40°C): m/z (%) ϭ
282 (<1) [Mϩ•], 58 (100) [C3H8Nϩ].
From 15.3 g (0.10 mol) 1-naphthaline-carbonitrile. Crystals (ether),
mp. 146°C ([21] 148-149°C), yield 5.6 g (30%). Anal. C11H10N2O
(186.1). IR (KBr): ν ϭ 1653 cmϪ1 (CϭN). 1H-NMR / 400 MHz
([D6]DMSO): δ (ppm) ϭ 5.96 (s, 2H, NH2, D2O exchange),
7.50Ϫ8.32 (m, 7H, naphth), 9.55 (s, 1H, OH, D2O exchange). MS
(EI, 35°C): m/z (%) ϭ 186 (76) [Mϩ•], 170 (16), 169 (100) [Mϩ•
-
OH• respectively NH3], 168 (17), 155 (13), 154 (58) [Mϩ•-H2NO•],
153 (23), 141 (11), 140 (14), 128 (13), 127 (48), 126 (20), 114 (11),
84 (10), 77 (21), 63 (11), 32 (66).
N-(3-Dimethylaminopropyl)-5-(3-phenylpropyl)-1,3,4-oxadiazole-2-
carboxamide (6i)
From 520 mg (2.0 mmol) 5c (method C). Crystals, mp. 47.5°C
(methanol), yield 490 mg (78%). Anal. C17H24N4O2 (316.4). IR
(KBr): ν ϭ 1689 cmϪ1 (CϭO); 1561 (CϭN). 1H-NMR / 400 MHz
([D6]DMSO): δ (ppm) ϭ 1.61Ϫ1.66 (m, 2H, CH2-CH2N), 2.00-2.07
(m, 2H, CH2-CH2Ph), 2.12 (s, 6H, (CH3)2N), 2.24 (t, J ϭ 7.0 Hz,
2H, CH2-N(CH3)2), 2.66Ϫ2.70 (m, 2H, CH2-Ph), 2.92 (t, J ϭ 7.5
Hz, 2H, CH2Ox), 3.25Ϫ3.28 (m, after D2O exchange t, J ϭ7.0 Hz,
2H, CH2-NHCO), 7.17Ϫ7.31 (m, 5H, Ph), 9.24Ϫ9.25 (m, 1H, NH,
D2O exchange). MS (EI, 100°C): m/z (%) ϭ 316 (2) [Mϩ•], 58
(100) [C3H8Nϩ].
Synthesis of O-ethyloxalyl-carboxamidoxime 10 (procedure of Pal-
azzo [9] modified)
The carboxamidoxime (0.01 mol) was dissolved in anhydrous ace-
tone and mixed with equivalent amounts of K2CO3. A solution of
oxalic acid ethyl ester chloride (0.01 mol) in 5 mL of acetone was
added dropwise while cooling with ice and stirring for 30 min. After
stirring for 2 h at room temperature the solvent was removed in
vacuo. The product was dissolved in dichloromethane, washed with
water and 0.1 N HCl and dried with Na2SO4. The solvent was re-
moved in vacuo. The product was recrystallized from ether/petro-
leum ether.
N-[2-(1-Methylpyrrolidin-2-yl)-ethyl]-5-(biphenyl-4-yl)-1,3,4-oxa-
diazole-2-carboxamide (6j)
O-Ethyloxalyl-biphenyl-4-yl-carboxamidoxime (10a)
From 520 mg (1.8 mmol) 5a (method C). Crystals, mp. 126°C
From 5 g (23.6 mmol) 8a. Powder, mp. 112°C (dichloromethane),
yield 4.8 g (65%). Anal. C17H16N2O4 (312.4). IR (KBr): ν ϭ 1766
cmϪ1 (CϭO); 1746 (CϭO); 1633 (CϭN). 1H-NMR / 400 MHz
([D6]DMSO): δ (ppm) ϭ 1.31 (t, J ϭ 7.2 Hz, 3H, CH3), 4.32 (q,
J ϭ 7.1 Hz, 2H, CH2CH3), 7.13 (br. s, 2H, NH2, D2O exchange),
7.41 (t, J ϭ 7.3 Hz, 1H, biph 4Ј-H), 7.48Ϫ7.52 (m, 2H, biph 3Ј-H,
5Ј-H), 7.72Ϫ7.74 (m, 2H, biph 2Ј-H, 6Ј-H), 7.77Ϫ7.82 (m, 4H, biph
2-H, 6-H, 3-H, 5-H). MS (EI, 100°C): m/z (%) ϭ 312 (<1) [Mϩ•],
295 (20), 294 (100) [Mϩ•-H2O], 195 (16), 181 (18), 154 (10).
(methanol), yield 430 mg (65%). Anal. C22H24N4O2 (376.5). IR
(KBr): ν ϭ 1687 cmϪ1 (CϭO); 1611 (CϭN). H-NMR / 400 MHz
1
([D6]DMSO): δ (ppm) ϭ 1.43-1.53 (m, 2H, CH2pyrr), 1.60Ϫ1.65
(m, 2H, pyrr-CH2), 1.86Ϫ1.97 (m, 2H, pyrr-CH2), 2.02Ϫ2.12 (m,
2H, pyrr-CH2), 2.22 (s, 3H, CH3N), 2.92Ϫ2.99 (m, 1H, pyrr 2-H),
3.34Ϫ3.37 (m, 2H, CH2-NH), 7.43Ϫ7.47 (m, 1H, biph 4Ј-H),
7.51Ϫ7.55 (m, 2H, biph 3Ј-H, 5Ј-H), 7.78Ϫ7.80 (m, 2H, biph 2Ј-H,
6Ј-H), 7.96 (d, J ϭ 8.4 Hz, 2H, biph 2-H, 6-H), 8.16 (d, J ϭ 8.4
Hz, biph 3-H, 5-H), 9.44 (t, J ϭ 5.7 Hz, 1H, NH, D2O exchange).
MS (EI, 160°C): m/z (%) ϭ 376 (3) [Mϩ•], 84 (100) [Pyrrϩ].
O-Ethyloxalyl-1-naphthyl-carboxamidoxime (10b)
Synthesis of the carboxamidoximes 8 (procedure from Knudsen [8]
modified)
Ether was used for the final extraction. From 5 g (26.9 mmol) 8b.
Crystals, mp. 75°C, yield 2.4 g (31%). Anal. C15H14N2O4 (286.3).
1
13.9 g hydroxylamine hydrochloride (0.2 mol) and 10.6 g Na2CO3
(0.1 mol) were dissolved in 50 mL of water. The mixture was added
to the corresponding nitrile (0.1 mol) in 50 mL ethanol. After stir-
ring for 64 h at a temperature of 30 to 40°C the mixture was filtered
off. The filtrate was concentrated in vacuo at a temperature of less
IR (KBr): ν ϭ 1772 cmϪ1 (CϭO); 1743 (CϭO); 1627 (CϭN). H-
NMR / 400 MHz ([D6]DMSO): δ (ppm) ϭ 1.30 (t, J ϭ 7.1 Hz, 3H,
CH3), 4.30 (q, J ϭ 7.1 Hz, 2H, CH2CH3), 7.29 (br. s, 2H, NH2,
D2O exchange), 7.57Ϫ8.25 (m, 7H, naphth). MS (EI, 80°C): m/z
(%) ϭ 286 (<1) [Mϩ•], 269 (18), 268 (100) [Mϩ•-H2O], 195 (37),
© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Arch. Pharm. Chem. Life Sci. 2005, 338, 78−86
New Oxadiazole Derivatives
85
169 (14), 168 (35), 153 (27), 140 (18), 127 (23) [C10H7ϩ], 126 (13),
31 (12), 29 (45) [C2H5ϩ].
N-(3-Diethylaminopropyl)-3-(biphenyl-4-yl)-1,2,4-oxadiazole-5-
carboxamide (12c)
From 520 mg (1.8 mmol) 11a (method C). Oil, yield 270 mg (41%).
Anal. C22H26N4O2 (378.5). IR (film): ν ϭ 1697 cmϪ1 (CϭO); 1575
(CϭN). 1H-NMR / 400 MHz ([D6]DMSO): δ (ppm) ϭ 0.98 (t, J ϭ
7.1 Hz, 6H, 2 x CH3), 1.66Ϫ1.73 (m, 2H, CH2-CH2N), 2.46-2.48
(m, 6H, 3 x CH2N), 3.38 (after D2O exchange br. s, 2H, 2H, CH2-
NH), 7.42Ϫ7.46 (m, 1H, biph 4Ј-H), 7.50Ϫ7.54 (m, 2H, biph 3Ј-H,
5Ј-H), 7.76Ϫ7.79 (m, 2H, biph 2Ј-H, 6Ј-H), 7.92Ϫ7.94 (m, 2H, biph
2-H, 6-H), 8.13Ϫ8.15 (m, 2H, biph 3-H, 5-H), 9.71 (s, 1H, NH,
D2O exchange). MS (EI, 90°C): m/z (%) ϭ 378 (4) [Mϩ•], 86
(100) [C5H12Nϩ].
Synthesis of the 1,2,4-oxadiazole-5-carboxylic acid ethyl ester 11
The O-ethyloxalyl-carboxamidoxime was refluxed in toluene for 2
h with separation of the water formed. After having removed the
solvent in vacuo there was a final recrystallization in the solvent
stated.
3-(Biphenyl-4-yl)-1,2,4-oxadiazole-5-carboxylic acid ethyl ester
(11a)
From 3.5 g (11.2 mmol) 10a. Powder, mp. 74°C (ether/petroleum
ether), yield 2.1 g (65%). Anal. C17H14N2O3 (294.3). IR (KBr): ν ϭ
1749 cmϪ1 (CϭO); 1611 (CϭN). 1H-NMR/400 MHz ([D6]DMSO):
δ (ppm) ϭ 1.39 (t, J ϭ 7.1 Hz, 3H, CH3), 4.48 (q, J ϭ 7.1 Hz, 2H,
OCH2CH3), 7.43Ϫ7.48 (m, 1H, biph 4Ј-H), 7.51Ϫ7.55 (m, 2H, biph
3Ј-H, 5Ј-H), 7.78 (d, J ϭ 7.8 Hz, 2H, biph 2Ј-H, 6Ј-H), 7.92 (d, J ϭ
8.3 Hz, 2H, biph 2-H, 6-H), 8.15 (d, J ϭ 8.2 Hz, 2H, aromat. 3-H,
5-H). MS (EI, 110°C): m/z (%) ϭ 295 (20), 294 (100) [Mϩ•], 195
(12), 179 (12).
N-[3-(2-Hydroxyethylamino)-propyl]-3-(biphenyl-4-yl)-1,2,4-oxa-
diazole-5-carboxamide (12d)
From 540 mg (1.8 mmol) 11a (method C). Crystals, mp. 114°C
(ethylacetate), yield 370 mg (56%). Anal. C20H22N4O3 (366.4). IR
1
(KBr): ν ϭ 1683 cmϪ1 (CϭO); 1577 (CϭN). H-NMR / 400 MHz
([D6]DMSO): δ (ppm) ϭ 1.66Ϫ1.73 (m, 2H, CH2-CH2-CH2),
2.57Ϫ2.63 (m, 4H, CH2-NH-CH2), 3.39 (after D2O exchange t, J ϭ
6.9 Hz, 2H, CH2-NHCO), 3.47 (“q”, J ϭ 5.4 Hz, 2H, CH2-OH,
after D2O exchange t, J ϭ 5.8 Hz), 4.46 (t, J ϭ 5.2 Hz, 1H, OH,
D2O exchange), 7.44 (t, J ϭ 7.3 Hz, 1H, biph 4Ј-H), 7.51Ϫ7.54 (m,
2H, biph 3Ј-H, 5Ј-H), 7.77 (d, J ϭ 7.6 Hz, 2H, biph 2Ј-H, 6Ј-H),
7.92 (d, J ϭ 8.4 Hz, 2H, biph 2-H, 6-H), 8.15 (d, J ϭ 8.3 Hz, 2H,
biph 3-H, 5-H), 9.50 (br. s, 1H, NHCO, D2O exchange). MS (EI,
3-(1-Naphthyl)-1,2,4-oxadiazole-5-carboxylic acid ethyl ester (11b)
From 2.4 g (8.4 mmol) 10b. Slightly violet powder, mp. 45°C (ether/
petroleum ether), yield 2.0 g (89%). Anal. C15H12N2O3 (268.3). IR
1
(KBr): ν ϭ 1748 cmϪ1 (CϭO); 1577 (CϭN). H-NMR / 400 MHz
80°C): m/z (%) ϭ 366 (<1) [Mϩ•], 336 (22); 335 (100) [Mϩ•
-
([D6]DMSO): δ (ppm) ϭ 1.40 (t, J ϭ 7.1 Hz, 3H, CH3), 4.50 (q,
J ϭ 7.1 Hz, 2H, OCH2CH3), 7.66Ϫ8.77 (m, 7H, naphth). MS (EI,
45°C): m/z (%) ϭ 268 (25) [Mϩ•], 195 (11), 168 (11), 154 (14), 153
(100) [C11H7Nϩ], 127 (13), 126 (20), 63 (11), 57 (11).
CH2OH], 222 (24), 195 (13), 180 (15), 179 (71), 178 (13), 153 (10),
152 (13), 140 (12), 113 (40), 76 (10), 74 (32) [C3H8NOϩ], 70 (15),
56 (24), 44 (48) [C2H4Oϩ], 43 (13), 42 (10), 41 (10), 30 (18), 28 (16).
N-(3-Dimethylaminopropyl)-3-(1-naphthyl)-1,2,4-oxadiazole-5-
General procedure of the synthesis of 1,2,4-oxadiazole-5-carbox-
carboxamide (12e)
amides 12
From 550 mg (2.1 mmol) 11b (method C). Brown oil, yield 406 mg
(61%). Anal. C18H20N4O2 (324.4). IR (film): ν ϭ 1691 cmϪ1 (Cϭ
O); 1574 (CϭN). 1H-NMR / 400 MHz ([D6]DMSO): δ (ppm) ϭ
1.68Ϫ1.75 (m, 2H, CH2-CH2N), 2.16 (s, 6H, (CH3)2N), 2.30 (t, J ϭ
6.9 Hz, 2H, CH2-N(CH3)2), 3.34Ϫ3.40 (m, 2H, CH2-NH),
7.67Ϫ8.78 (m, 7H, naphth), 9.60 (br. s, 1H, NH, D2O exchange).
MS (EI, 130°C): m/z (%) ϭ 324 (4) [Mϩ•], 58 (100) [C3H8Nϩ].
The same procedure as described for the synthesis of the 1,3,4-oxa-
diazole-2-carboxamides 6 was used.
N-(3-Dimethylaminopropyl)-3-(biphenyl-4-yl)-1,2,4-oxadiazole-5-
carboxamide (12a)
From 560 mg (1.9 mmol) 10a (method C). Powder, mp. 79°C (di-
chloromethane), yield 450 mg (68%). Anal. C20H22N4O2 (350.4).
IR (KBr): ν ϭ 1697 cmϪ1 (CϭO); 1574 (CϭN). 1H-NMR / 400
MHz ([D6]DMSO): δ (ppm) ϭ 1.67-1.74 (m, 2H, CH2-CH2N), 2.18
(s, 6H, (CH3)2N), 2.32 (t, J ϭ 6.9 Hz, 2H, CH2-N(CH3)2), 3.36
(after D2O exchange t, J ϭ 7.0 Hz, 2H, CH2-NH), 7.42-7.46 (m,
1H, biph 4Ј-H), 7.51-7.54 (m, 2H, biph 3Ј-H, 5Ј-H), 7.77-7.79 (m,
2H, biph 2Ј-H, 6Ј-H), 7.92-7.94 (m, 2H, biph 2-H, 6-H), 8.14-8.16
(m, 2H, biph 3-H, 5-H), 9.61 (t, J ϭ5.7 Hz, 1H, NH, D2O ex-
change). MS (EI, 90°C): m/z (%) ϭ 350 (3) [Mϩ•], 212 (14), 195
(12), 179 (10), 58 (100) [C3H8Nϩ], 32 (12), 28 (50).
N-(3-Methylaminopropyl)-3-(biphenyl-4-yl)-1,2,4-oxadiazole-5-
carboxamide hydrochloride (12f)
From 580 mg (2.0 mg) 11a (method B). Crystals, mp. 209°C (meth-
anol/few HClkonz), yield 500 mg (68%). Anal. C19H21ClN4O2
(372.9). IR (KBr): ν ϭ 1683 cmϪ1 (CϭO); 1577 (CϭN). 1H-NMR/
400 MHz ([D6]DMSO): δ (ppm) ϭ 1.88Ϫ1.95 (m, 2H, CH2-CH2N),
2.54Ϫ2.56 (m, 3H, CH3), 2.96 (br. s, 2H, CH2-NH2CH3), 3.39-3.43
(m, 2H, CH2-NHCO), 7.43Ϫ7.46 (m, 1H, biph 4Ј-H), 7.51Ϫ7.55
(m, 2H, biph 3Ј-H, 5Ј-H), 7.77Ϫ7.79 (m, 2H, biph 2Ј-H, 6Ј-H),
7.93Ϫ7.95 (m, 2H, biph 2-H, 6-H), 8.15Ϫ8.17 (m, 2H, biph 3-H, 5-
H), 8.73 (br. s, 2H, NH2, D2O exchange), 9.61 (t, J ϭ 5.8 Hz, 1H,
NHCϭO, D2O exchange). MS (EI, 140°C): m/z (%) ϭ 336 (<1)
[Mϩ• der Base], 180 (10), 179 (42), 152 (13), 85 (19), 70 (16), 57
(12), 44 (100) [C2H6Nϩ], 43 (11), 28 (28).
N-(2-Dimethylaminoethyl)-3-(biphenyl-4-yl)-1,2,4-oxadiazole-5-
carboxamide (12b)
From 580 mg (2.0 mmol) 11a (method A). Shining crystals, mp.
97°C (methanol), yield 244 mg (37%). Anal. C19H20N4O2 (336.4).
IR (KBr): ν ϭ 1695 cmϪ1 (CϭO); 1578 (CϭN). 1H-NMR / 400
MHz (CDCl3): δ (ppm) ϭ 2.75 (s, 6H, (CH3)2N), 3.12 (s, 2H, CH2-
N(CH3)2), 3.89Ϫ3.90 (m, 2H, CH2-NHCO), 7.38Ϫ7.42 (m, 1H,
biph 4Ј-H), 7.45Ϫ7.49 (m, 2H, biph 3Ј-H, 5Ј-H), 7.63Ϫ7.65 (m, 2H,
biph 2Ј-H, 6Ј-H), 7.71Ϫ7.73 (m, 2H, biph 2-H, 6-H), 8.20Ϫ8.22 (m,
2H, biph 3-H, 5-H), 8.81 (br. s, 1H, NH, D2O exchange.). MS (EI,
110°C): m/z (%) ϭ 336 (1) [Mϩ•], 58 (100) [C3H8Nϩ].
Biology
Born test
Preparation of the blood plasmas
Freshly drawn venous human citrated blood (1 pt sodium citrate
solution 3, 13%, Fa. Eifelfango, Neuenahr, 9 pts blood) from
© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

86
Rehse et al.
Arch. Pharm. Chem. Life Sci. 2005, 338, 78−86
healthy subjects who had not taken acetylsalicylic acid or other
drugs with antiplatelet activity for 10 days was centrifuged (Micro
20, A. Hettich GmbH, Tutlingen) with 100g (800 rpm) for platelet
rich plasma (PRP) or 2000g (Biofuge A, Haereus, 12 500 rpm) for
platelet poor plasma (PPP).
NECA 1.0; adrenaline 0.1Ϫ1.0/phentolaminemesylate 2.0; PAF
0.25Ϫ1.0/apafant (WEB 2086) 0.6; serotonin 0.1Ϫ2.0 / imipramine
2.0.
Acknowledgments
Platelet aggregation procedures [12, 13]
We are indebted to Mrs. Nora Reitner and Mrs. Heike
Scheffler for the skilful performance of the biological tests.
We thank Dr. H.-P. Stasch and Dr. E. Bischoff for the s-GC
and PDE tests.
Platelet aggregation induced by collagen
At first the concentration of collagen fibrils which induce maximum
aggregation of the platelets is determined. To 200 μL of PRP
20 μL of hepes buffer i.e. 2-[4-(2-Hydroxyethyl)-piperazin-1-yl]-eth-
ane-sulfonic acid 0.001 M (ϭ 238.3 mg/L) Fa. Sigma (without test
compound) are added and the mixture incubated 4 min at 37.4°C.
Now the cuvette is put in the channel of the APACT aggregometer
(Automated Platelet Aggregation and Coagulation Tracer, Bio-
chemica GmbH, D-65558 Flacht) with software APACT pro-
fessional version 1.1.
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While automatically stirred by a small magnet 20 μL of the aggre-
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Platelet aggregation with other inducers
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© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim