Synthesis of new 3-pyridinecarboxylates of potential vasodilation properties

Article abstract of DOI:10.1016/j.ejmech.2007.11.025

2-(Alicyclic-amino)-4,6-diaryl-3-pyridinecarboxylates 5a-d were prepared via aromatic nucleophilic substitution reaction of secondary amines (piperidine or morpholine) with 2-bromo-3-pyridinecarboxylate derivatives 3a,b. The latters were obtained through

Full text of DOI:10.1016/j.ejmech.2007.11.025

Available online at www.sciencedirect.com
European Journal of Medicinal Chemistry 43 (2008) 1818e1827
http://www.elsevier.com/locate/ejmech
Original article
Synthesis of new 3-pyridinecarboxylates
of potential vasodilation properties
a
b
c
a
Adel S. Girgis a, , Nawal Mishriky , Ahmad M. Farag , Wafaa I. El-Eraky , Hanaa Farag
*
a Pesticide Chemistry Department, National Research Centre, El-Behoos Street, Dokki, 12622 Cairo, Egypt
b Chemistry Department, Faculty of Science, Cairo University, 12613 Giza, Egypt
c Pharmacology Department, National Research Centre, Dokki, 12622 Cairo, Egypt
Received 28 June 2007; received in revised form 9 November 2007; accepted 22 November 2007
Available online 8 December 2007
Abstract
2-(Alicyclic-amino)-4,6-diaryl-3-pyridinecarboxylates 5aed were prepared via aromatic nucleophilic substitution reaction of secondary
amines (piperidine or morpholine) with 2-bromo-3-pyridinecarboxylate derivatives 3a,b. The latters were obtained through bromination of 3-
aryl-4-benzoyl-2-cyanobutyrates 2a and 2b, which were obtained from the base promoted addition of ethyl cyanoacetate to 2-propen-1-ones
1a and 1b, with bromine in glacial acetic acid. Reaction of 3 with piperazine hexahydrate in 2:1 molar ratio afforded 1,4-bis[(ethyl 4,6-dia-
ryl-3-pyridinecarboxylate)-2-yl]piperazines 6a,b. Reaction of 3 with anilines in refluxing pyridine unexpectedly gave 2-(aryl-amino)-3-pyridi-
necarboxylates 8aeg and 2-amino-3-pyridinecarboxylates 9a and 9b. Vasodilation activity screening for the synthesized pyridinecarboxylates
using isolated thoracic aortic rings’ standard method of rats shows considerable properties. Compounds 5b, 5c, 6b and 8g reveal remarkable
vasodilation potency (IC50, concentrations necessary for 50% reduction of maximal norepinephrine hydrochloride induced contracture)
0.175, 0.146, 0.229 and 0.233 mM, respectively.
Ó 2007 Elsevier Masson SAS. All rights reserved.
Keywords: 3-Pyridinecarboxylates; 2-Propen-1-ones; Aromatic nucleophilic substitution; Vasodilation
1. Introduction
pharmacological properties of nicotinate esters as antihyperli-
pidemic [2] and cholesteryl ester transfer protein inhibitors
[3]. Pharmacological compositions containing nicotinate es-
ters have also been reported as stimulating hair growth due to
their blood circulation promoter properties [4].
In the present work, it is intended to investigate synthesis of
novel ethyl nicotinate derivatives, especially those substituted
with fluorophenyl residue adopting easily accessible starting
materials and facile synthetic approaches. The interest for con-
struction of fluorine-containing compounds is originated due
to their unique properties such as high thermal stability and
lipophilicity [5]. This investigation is considered a continuation
of our previous work directed towards preparation of pharma-
cologically active agents [6e10]. So, the vasodilation proper-
ties of the prepared compounds will be screened in an attempt
to determine a new heterocyclic agent which could be useful
as a hint in a drug discovery program.
3-Pyridinecarboxylate derivatives have occupied a unique
place in the field of medicinal chemistry. They have a wide
range of pharmacological applications. For example, cicloni-
cate ‘‘3-pyridinecarboxylic acid 3,3,5-trimethylcyclohexyl
ester’’, nicametate ‘‘3-pyridinecarboxylic acid 2-(dimethyla-
mino)ethyl ester’’, hepronicate ‘‘3-pyridinecarboxylic acid
2-hexyl-2-[[(3-pyridinylcarbonyl)oxy]methyl]-1,3-propanediyl
ester’’ and inositol niacinate ‘‘myo-inositol hexa-3-pyridinecar-
boxylate’’ are well known vasodilating drugs [1] (Scheme 1).
In addition, many research articles reported about the
* Corresponding author. Tel.: þ20 202 22352405; fax: þ20 202 33370931.
E-mail address: girgisas10@yahoo.com (A.S. Girgis).
0223-5234/$ - see front matter Ó 2007 Elsevier Masson SAS. All rights reserved.
doi:10.1016/j.ejmech.2007.11.025

A.S. Girgis et al. / European Journal of Medicinal Chemistry 43 (2008) 1818e1827
1819
H3C
H
CH3
CH3
CH3
O
O
CH3
N
O
H
O
N
N
Ciclonicate
Nicametate
H3C
N
N
O
N
N
O
O
O
N
O
O
O
O
O
O
O
O
O
O
N
O
O
N
O
O
N
N
Hepronicate
Inositol niacinate
Scheme 1.
2. Results and discussion
However, only one carbonyl stretching vibration band is ob-
served at n ¼ 1719 cmꢀ1 corresponding to the stretching vibra-
tion of ester residue. 1H NMR spectra of 3a,b exhibit the ethyl
ester group in addition, to the characteristic pyridinyl H-5 as
a singlet signal at d ¼ 7.67e7.69. Mass spectra (EI) of 3a,b
show (M þ 1) fragmentation peaks with recognizable relative
intensity values, beside the naturally isotopic abundance peaks
due to the bromine atom, which add a conclusive evidence to
the achieved structures (Scheme 2).
2.1. Chemistry
Reaction of 1,3-diaryl-2-propen-1-ones 1a,b with ethyl
cyanoacetate in refluxing ethanol in the presence of piperidine
as a basic catalyst afforded ethyl 3-aryl-4-benzoyl-2-cyanobu-
tyrates 2a,b in good yields. The structure of 2 was established
1
through spectroscopic (IR, H NMR) and elemental analyses
data. The IR spectra of 2a,b reveal the presence of two car-
bonyl functions at n ¼ 1729, 1691e1690 cmꢀ1 assignable to
the stretching vibrations of ester and ketonic residues, respec-
tively. A nitrile stretching vibration band is also recognized at
n ¼ 2250e2249 cmꢀ1 confirming isolation of the open-chain
Reaction of 2-bromo-3-pyridinecarboxylates 3a,b with
secondary amines (piperidine or morpholine) 4a,b in refluxing
tetrahydrofuran led to aromatic nucleophilic substitution giv-
ing 2-(alicyclic-amino)-3-pyridinecarboxylates 5aed, whose
1
structures were deduced through spectroscopic (IR, H NMR,
1
Michael adduct product. H NMR spectra of 2a,b exhibit the
MS) and elemental analyses data. 1H NMR spectra of 5aed re-
veal the alicyclic-amino function (piperidinyl as multiplet sig-
nals at d ¼ 1.66e1.73, 3.45e3.49 and morpholinyl as triplet
signals at d ¼ 3.50e3.51, 3.84e3.86) beside the ethyl ester sig-
nals (triplet at d ¼ 1.04e1.07 and quartet at d ¼ 4.07e4.09 cor-
responding to the methyl and methylene protons, respectively).
Meanwhile, reaction of 3a,b with piperazine hexahydrate in
refluxing pyridine in 2:1 molar ratio afforded the correspond-
ing 1,4-bis[(ethyl 4,6-diaryl-3-pyridinecarboxylate)-2-yl]pi-
perazines 6a,b. 1H NMR spectra of 6 exhibit the four
ethyl ester beside the methylene protons of H2C-4 as two
sets of double doublet signals ‘‘at d ¼ 3.48e3.51, 3.69e
3.70’’ due to the mutual coupling with each other
(J ¼ 18.2e18.3 Hz) and in turn with the vicinal methine pro-
ton HC-3 (J ¼ 5.1e5.5, 8.6e9.3 Hz). The methine proton of
HC-2 appears as a doublet signal (d ¼ 4.33, J ¼ 5.4 Hz). How-
ever, the methine proton of HC-3 appears as a multiplet signal
hidden under the quartet of methylene protons of ethyl ester
group. Single crystal X-ray diffraction of 2a adds a good
support for the established structure (Fig. 1).
piperazinyl methylene protons as
a singlet signal at
Bromination of 2a,b with bromine in glacial acetic acid at
60e70 ꢁC afforded directly ethyl 2-bromo-4,6-diaryl-3-pyridi-
necarboxylates 3a,b in good yields. The structure of 3 was in-
ferred from IR, H NMR, MS and elemental analyses data.
The IR spectra of 3 lack any band assignable for nitrile func-
tion confirming its involvement in the cyclization process.
d ¼ 3.69e3.72.
However, reaction of 3a,b with primary aromatic amines
7aed in refluxing pyridine gave 2-(aryl-amino)-3-pyridinecar-
boxylates 8aeg beside the unexpected 2-(unsubstituted
amino)-3-pyridinecarboxylates 9a,b (Scheme 3). Formation
of 9 during the mentioned reaction seems similar to what
1

1820
A.S. Girgis et al. / European Journal of Medicinal Chemistry 43 (2008) 1818e1827
H
H
O
R
Ph
NCCH2CO2Et
R
Ph
EtOH, piperidine
O
NC
CO2Et
(1)
(2)
Br2, AcOH
(60-70°C)
R
N
CO2Et
Br
Ph
(3)
1a,2a,3a, R = 4-FC6H4
1b,2b,3b, R = 4-H3CC6H4
Fig. 1. ORTEP projection of single crystal X-ray diffraction of 2a. Selected
intramolecular bond lengths (A) and bond angles (ꢁ) of 2a.
˚
Scheme 2.
O(1)eC(9) ¼ 1.220(2),
O(3)eC(7) ¼ 1.207(2),
C(5)eC(10) ¼ 1.5559,
O(2)eC(7) ¼ 1.328(2),
F(4)eC(17) ¼ 1.365(2),
C(5)eC(13) ¼ 1.5326,
O(2)eC(20) ¼ 1.470(2),
C(5)eC(8) ¼ 1.512(2),
C(6)eC(9) ¼ 1.489(2),
thoracic aortic rings of male Wister rats pre-contracted with
norepinephrine hydrochloride according to the standard
known procedure [8,13,14]. From the observed data (Table 1,
Figs. 2 and 3), it has been noticed that all the tested com-
pounds show considerable vasodilation properties. Compound
5c reveals the best vasodilation potency effect (IC50, concen-
tration necessary for 50% reduction of maximal norepineph-
rine hydrochloride induced contracture) among the whole
tested compounds (IC50 ¼ 0.146 mM). In addition, few
synthesized compounds especially 5b, 6b and 8g show
remarkable vasodilation potency (IC50 ¼ 0.175, 0.229 and
0.233 mM, respectively).
Structureeactivity relationship based on the observed
results indicated that, substitution of pyridinecarboxylate nu-
cleus with alicyclic-amino function (piperidinyl, morpholinyl
or piperazinyl) at the 2-position enhances the vasodilation
properties (IC50 of 5a, 5b, 5c, 5d and 6b is 0.346, 0.175,
0.146, 0.340 and 0.229 mM, respectively) than the case of
using either phenyl- or 4-chlorophenylamino residue (IC50 of
8a, 8b and 8c is 0.367, 0.715 and 0.266 mM, respectively).
In addition, substitution of the phenylamino group with an
electron-donating function (e.g. methoxy residue) (IC50 of 8f
and 8g is 0.254 and 0.233 mM, respectively) enhances the
observed vasodilation effects than the case of using electron-
withdrawing function (e.g. chloro residue) (IC50 of 8b and
8c is 0.715 and 0.266 mM, respectively). However, there is
no precise rule could be attained, through the observed data,
governing the type of substitution of the phenyl group (either
fluoro or methyl function) attached to the 4-position of 3-pyr-
idinecarboxylates in affecting the total observed vasodilation
properties.
C(6)eC(14) ¼ 1.391(3), C(6)eC(19) ¼ 1.374(3), C(7)eC(10) ¼ 1.514(3),
C(8)eC(12) ¼ 1.381(3), C(8)eC(22) ¼ 1.373(3), C(9)eC(13) ¼ 1.509(3),
C(10)eC(16) ¼ 1.473(3), N(11)eC(16) ¼ 1.145(2), C(12)eC(18) ¼ 1.380(3),
C(14)eC(15) ¼ 1.378(3), C(15)eC(21) ¼ 1.356(3), C(17)eC(18) ¼ 1.351(3),
C(17)eC(24) ¼ 1.352(3), C(19)eC(25) ¼ 1.385(3), C(20)eC(23) ¼ 1.469(3),
C(21)eC(25) ¼ 1.358(3), C(22)eC(24) ¼ 1.366(3), C(5)eH(5) ¼ 0.9600(15),
C(10)eH(10) ¼ 0.91(2), C(7)eO(2)eC(20) ¼ 114.6(2), C(9)eC(6)eC(14) ¼
123.2(2),
C(9)eC(6)eC(19) ¼ 119.4(2),
C(14)eC(6)eC(19) ¼ 117.4(2),
O(2)eC(7)eO(3) ¼ 124.1(2), O(2)eC(7)eC(10) ¼ 111.8(2), O(3)eC(7)e
C(10) ¼ 124.1(2),
C(5)eC(8)eC(12) ¼ 120.2(2),
C(5)eC(8)eC(22) ¼
122.1(2), C(12)eC(8)eC(22) ¼ 117.6(2), O(1)eC(9)eC(6) ¼ 121.1(2), O(1)e
C(9)eC(13) ¼ 121.1(2), C(6)eC(9)eC(13) ¼ 117.8(2), C(7)eC(10)eC(16) ¼
108.3(2), C(8)eC(12)eC(18) ¼ 121.0(2), C(6)eC(14)eC(15) ¼ 121.3(2),
C(14)eC(15)eC(21) ¼ 119.8(2),
C(10)eC(16)eN(11) ¼ 179.7(2),
F(4)e
C(17)eC(18) ¼ 118.9(2),
F(4)eC(17)eC(24) ¼ 119.3(2),
C(18)eC(17)e
C(24) ¼ 121.9(2), C(12)eC(18)eC(17) ¼ 118.9(2), C(6)eC(19)eC(25) ¼ 120.9(2),
O(2)eC(20)eC(23) ¼ 108.0(2), C(15)eC(21)eC(25) ¼ 120.3(2), C(8)eC(22)e
C(24) ¼ 121.8(2),
C(17)eC(24)eC(22) ¼ 118.9(2),
C(19)eC(25)eC(21) ¼
120.2(2), C(8)eC(5)eH(5) ¼ 108.23(14), C(7)eC(10)eH(10) ¼ 109.9(11), C(16)e
C(10)eH(10) ¼ 109.0(11).
was previously reported about the formation of 2-amino-3-
pyridine derivatives through either reaction of 2-bromonicoti-
nonitriles or 2-bromonicotinate ester analogues with a-amino
acid esters in refluxing pyridine [8,11]. It was assumed in
the latter reaction that, the mechanistic pathway proceeded
analogously to the famous ninhydrin reaction with a-amino
acids [12]. Where, the amino acids isomerize to the corre-
sponding imino acid forms under the effect of applied reaction
conditions. Then, upon hydrolysis, due to unavoidable
moisture, ammonia liberates which in turn interacts with
2-bromopyridines yielding the 2-amino derivatives. Similar
observation was recently reported about the formation of 2-
aminonicotinamides during the reaction of 2-bromonicotina-
mides with primary aromatic amines in refluxing pyridine [7].
3. Experimental
2.2. Vasodilation activity
Melting points are uncorrected and recorded on an Electro-
thermal 9100 digital melting point apparatus. IR spectra (KBr)
were recorded on a Nexus 670 FT-IR spectrophotometer.
Vasodilation activity screening for the synthesized pyridi-
necarboxylates was investigated in vitro using isolated

A.S. Girgis et al. / European Journal of Medicinal Chemistry 43 (2008) 1818e1827
1821
R
HN
THF
X
(4)
CO2Et
N
Ph
N
X
(5)
R
R
N
CO2Et
N
NH 6H2O
HN
pyridine
EtO2C
N
(3)
Ph
N
Ph
(6)
R
R
CO2Et
NHR'
(7)
R'NH2
CO2Et
+
pyridine
Ph
N
Ph
N
NH2
(9)
(8)
4a, X = CH2
4b, X = O
8a, R = 4-FC6H4, R' = Ph
8b, R = 4-FC6H4, R' = 4-ClC6H4
8c, R = 4-H3CC6H4, R' = 4-ClC6H4
8d, R = 4-FC6H4, R' = 4-H3CC6H4
8e, R = R' = 4-H3CC6H4
8f, R = 4-FC6H4, R' = 4-H3COC6H4
8g, R = 4-H3CC6H4, R' = 4-H3COC6H4
5a, R = 4-FC6H4, X = CH2
5b, R = 4-H3CC6H4, X = CH2
5c, R = 4-FC6H4, X = O
5d, R = 4-H3CC6H4, X = O
6a, 9a, R = 4-FC6H4
6b, 9b, R = 4-H3CC6H4
7a, R' = Ph
7b, R' = 4-ClC6H4
7c, R' = 4-H3CC6H4
7d, R' = 4-H3COC6H4
Scheme 3.
H NMR spectra were recorded on Varian GEMINI 200 MHz
and MERCURY 300 MHz spectrometers in CDCl3. Mass
spectra were recorded on Shimadzu GCMS-QP 1000 EX
and Finnigan SSQ 7000 spectrometers (EI, 70 eV). The start-
ing compounds 1a,b [15,16] were prepared according to the
previously reported procedures.
nmax/cmꢀ1 2249 (C^N), 1729 (C]O ester), 1690 (C]O ke-
tone), 1597, 1580 (C]C). H NMR: d 1.12 (t, 3H, CH3CH2,
1
J ¼ 7.1 Hz), 3.48 (dd, 1H, upfield H of CH2CO, J ¼ 5.5,
18.2 Hz), 3.70 (dd, 1H, downfield H of CH2CO, J ¼ 8.6,
18.2 Hz), 4.00e4.20 (m, 3H, OCH2CH3 þ CHCH2CO), 4.33
(d, 1H, CHCHCH2, J ¼ 5.4 Hz), 6.95e8.00 (m, 9H, arom.
H). Anal. Calcd for C20H18FNO3 (339.35): C, 70.78; H,
5.35; N, 4.13. Found: C, 70.91; H, 5.45; N, 4.12.
3.1. Synthesis of ethyl 3-aryl-4-benzoyl-2-
cyanobutyrates 2a,b
3.1.2. Ethyl 4-benzoyl-2-cyano-3-(4-methylphenyl)
butyrate (2b)
A mixture of 1a,b (10 mmol) and ethyl cyanoacetate
(11 mmol) in absolute ethanol (20 ml) containing piperidine
(3e5 drops) was boiled under reflux for the appropriate
time. The separated solid upon cooling the reaction mixture
(4 ꢁC) was collected and crystallized from a suitable solvent
affording 2a,b.
Colourless crystals from methanol, mp 84e86 ꢁC, yield
84%. IR: nmax/cmꢀ1 2250 (C^N), 1729 (C]O ester), 1691
1
(C]O ketone), 1596, 1579 (C]C). H NMR: d 1.14 (t, 3H,
CH3CH2, J ¼ 7.2 Hz), 2.33 (s, 3H, ArCH3), 3.51 (dd, 1H,
upfield H of CH2CO, J ¼ 5.1, 18.3 Hz), 3.69 (dd, 1H, down-
field H of CH2CO, J ¼ 9.3, 18.3 Hz), 4.07e4.15 (m, 3H,
OCH2CH3 þ CHCH2CO), 4.33 (d, 1H, CHCHCH2,
J ¼ 5.4 Hz), 7.13e7.98 (m, 9H, arom. H). Anal. Calcd for
C21H21NO3 (335.39): C, 75.20; H, 6.31; N, 4.18. Found: C,
75.02; H, 6.18; N, 4.02.
3.1.1. Ethyl 4-benzoyl-2-cyano-3-(4-fluorophenyl)
butyrate (2a)
Colourless crystals from benzeneelight petroleum (60e
80 ꢁC) mixture as 1:2 v/v, mp 86e88 ꢁC, yield 77%. IR:

1822
A.S. Girgis et al. / European Journal of Medicinal Chemistry 43 (2008) 1818e1827
Table 1
Concentration of compounds necessary to reduce maximal norepinephrine-in-
duced contracture by 50% (IC50) in thoracic rat aorta
3.3. Reaction of 3 with 4
A mixture of 3a,b (2.5 mmol) and the corresponding 4a,b
(5 mmol) in tetrahydrofuran (20 ml) was boiled under reflux
for the appropriate time. The clear reaction mixture was
evaporated till dryness under reduced pressure. The sepa-
rated solid, upon triturating the remaining residual material
with methanol (5 ml), was collected and crystallized from
light petroleum (60e80 ꢁC) affording 5aed as colourless
crystals.
Compound
Potency (IC50
mM
)
mg/l
5a
5b
5c
5d
6b
8a
8b
8c
8f
0.346
0.175
0.146
0.340
0.229
0.367
0.715
0.266
0.254
0.233
0.335
0.327
139.9
70.1
59.3
136.8
164.2
151.4
319.5
117.8
112.4
102.2
112.7
108.7
3.3.1. Ethyl 4-(4-fluorophenyl)-6-phenyl-2-(1-piperidinyl)-
3-pyridinecarboxylate (5a)
8g
9a
9b
Reaction time 20 h, mp 104e106 ꢁC, yield 89%. IR:
nmax/cmꢀ1 1716 (C]O), 1606, 1545 (C]N, C]C). 1H
NMR: d 1.05 (t, 3H, CH3CH2, J ¼ 7.2 Hz), 1.68e1.72 (m,
6H, piperidinyl 3CH2), 3.46e3.49 (m, 4H, piperidinyl
2NCH2), 4.07 (q, 2H, OCH2CH3, J ¼ 7.2 Hz), 7.07e8.05
(m, 10H, 9 arom. H þ pyridinyl H-5). MS: m/z (%) 404 (M,
42), 375 (100), 359 (9), 331 (27), 248 (44). Anal. Calcd for
C25H25FN2O2 (404.47): C, 74.23; H, 6.23; N, 6.93. Found:
C, 74.37; H, 6.29; N, 7.12.
3.2. Synthesis of ethyl 2-bromo-4,6-diaryl-3-
pyridinecarboxylates 3a,b
To a solution of 2a,b (5 mmol) in glacial acetic acid (10 ml)
warmed at 60e70 ꢁC, a solution of bromine (5.5 mmol) in gla-
cial acetic acid (5 ml) was added dropwise while stirring at
such a rate maintaining the same adjusted temperature within
a period of 10 min. After complete addition, the reaction was
kept at the same temperature for 3 h. Then, stored at room
temperature overnight and poured into water (200 ml). The
separated solid was collected, washed with water and crystal-
lized from a suitable solvent giving 3a,b.
3.3.2. Ethyl 4-(4-methylphenyl)-6-phenyl-2-(1-piperidinyl)-
3-pyridinecarboxylate (5b)
Reaction time 24 h, mp 93e95 ꢁC, yield 80%. IR:
nmax/cmꢀ1 1717 (C]O), 1585, 1543 (C]N, C]C). 1H
NMR: d 1.07 (t, 3H, CH3CH2, J ¼ 7.2 Hz), 1.66e1.73 (m,
6H, piperidinyl 3CH2), 2.42 (s, 3H, ArCH3), 3.45e3.49 (m,
4H, piperidinyl 2NCH2), 4.09 (q, 2H, OCH2CH3, J ¼ 7.2 Hz),
7.21e8.07 (m, 10H, 9 arom. H þ pyridinyl H-5). MS: m/z (%)
400 (M, 52), 371 (100), 355 (11), 327 (21), 244 (13). Anal.
Calcd for C26H28N2O2 (400.50): C, 77.97; H, 7.05; N, 7.00.
Found: C, 78.06; H, 7.13; N, 7.11.
3.2.1. Ethyl 2-bromo-4-(4-fluorophenyl)-6-
phenyl-3-pyridinecarboxylate (3a)
Colourless crystals from ethanol, mp 151e153 ꢁC, yield
75%. IR: nmax/cmꢀ1 1719 (C]O), 1605, 1525 (C]N,
3.3.3. Ethyl 4-(4-fluorophenyl)-2-(4-morpholinyl)-6-phenyl-
3-pyridinecarboxylate (5c)
1
C]C). H NMR: d 1.2 (t, 3H, CH3CH2, J ¼ 7.6 Hz), 4.25
(q, 2H, OCH2CH3, J ¼ 7.6 Hz), 7.10e7.50 (m, 7H, arom.
H), 7.67 (s, 1H, pyridinyl H-5), 8.00e8.10 (m, 2H, arom.
H). MS: m/z (%) 402 [(M þ 3), 59], 401 [(M þ 2), 60], 400
[(M þ 1), 66], 399 (M, 59), 370 (13), 354 (78), 326 (5), 320
(4). Anal. Calcd for C20H15BrFNO2 (400.24): C, 60.01; H,
3.78; N, 3.50. Found: C, 60.22; H, 3.70; N, 3.47.
Reaction time 20 h, mp 134e136 ꢁC, yield 79%. IR:
nmax/cmꢀ1 1716 (C]O), 1606, 1544 (C]N, C]C). 1H
NMR: d 1.04 (t, 3H, CH3CH2, J ¼ 7.2 Hz), 3.50 (t, 4H, mor-
pholinyl 2NCH2, J ¼ 4.5 Hz), 3.84 (t, 4H, morpholinyl
2OCH2, J ¼ 4.5 Hz), 4.07 (q, 2H, OCH2CH3, J ¼ 7.2 Hz),
7.09e8.05 (m, 10H, 9 arom. H þ pyridinyl H-5). MS: m/z
(%) 406 (M, 93), 377 (83), 361 (51), 333 (88), 248 (100).
Anal. Calcd for C24H23FN2O3 (406.44): C, 70.92; H, 5.70;
N, 6.89. Found: C, 70.72; H, 5.59; N, 7.03.
3.2.2. Ethyl 2-bromo-4-(4-methylphenyl)-6-
phenyl-3-pyridinecarboxylate (3b)
Colourless crystals from light petroleum (40e60 ꢁC), mp
126e128 ꢁC, yield 81%. IR: nmax/cmꢀ1 1719 (C]O), 1559,
1523 (C]N, C]C). 1H NMR: d 1.19 (t, 3H, CH3CH2,
J ¼ 7.2 Hz), 2.43 (s, 3H, ArCH3), 4.26 (q, 2H, OCH2CH3,
J ¼ 7.2 Hz), 7.26e7.50 (m, 7H, arom. H), 7.69 (s, 1H, pyri-
dinyl H-5), 8.02e8.05 (m, 2H, arom. H). MS: m/z (%) 398
[(M þ 3), 19], 397 [(M þ 2), 87], 396 [(M þ 1), 21], 395 (M,
84), 366 (12), 350 (99), 322 (0.9), 316 (3). Anal. Calcd for
C21H18BrNO2 (396.27): C, 63.65; H, 4.58; N, 3.53. Found:
C, 63.79; H, 4.68; N, 3.46.
3.3.4. Ethyl 4-(4-methylphenyl)-2-(4-morpholinyl)-6-
phenyl-3-pyridinecarboxylate (5d)
Reaction time 24 h, mp 103e105 ꢁC, yield 80%. IR:
nmax/cmꢀ1 1720 (C]O), 1585, 1541 (C]N, C]C). 1H
NMR: d 1.05 (t, 3H, CH3CH2, J ¼ 7.2 Hz), 2.42 (s, 3H,
ArCH3), 3.51 (t, 4H, morpholinyl 2NCH2, J ¼ 4.5 Hz), 3.86
(t, 4H, morpholinyl 2OCH2, J ¼ 4.5 Hz), 4.09 (q, 2H,
OCH2CH3, J ¼ 7.2 Hz), 7.25e8.07 (m, 10H,
9 arom.
H þ pyridinyl H-5). MS: m/z (%) 402 (M, 100), 373 (76),

A.S. Girgis et al. / European Journal of Medicinal Chemistry 43 (2008) 1818e1827
1823
100
90
80
70
60
50
40
30
20
10
0
Compound 5a
Compound 5b
100
90
80
70
60
50
40
30
20
10
0
0
0.1
0.2
0.3
0.4
-10
-20
-30
-40
0
0.1
0.2
0.3
0.4
Concentration (mM)
0.5
0.6
0.7
0.8
-10
-20
-30
Concentration (mM)
Compound 5c
Compound 5d
100
90
80
70
60
50
40
30
20
10
0
110
100
90
80
70
60
50
40
30
20
10
0
-10 0
-20
0.1
0.2
0.3
0.4
0
0.1
0.2
0.3
Concentration (mM)
0.4
0.5
-30
-10
Concentration (mM)
Compound 6b
Compound 8a
100
90
80
70
60
50
30
40
20
0
100
90
80
70
60
50
40
30
20
10
0
10
-10
-20
-30
-40
0
0.1
0.2
0.3
0.4
0.5
0.6
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
-10
-20
Concentration (mM)
Concentration (mM)
Fig. 2. Effect of tested compounds on contracture induced by norepinephrine hydrochloride in thoracic rat aortic rings.
357 (53), 329 (74), 244 (31). Anal. Calcd for C25H26N2O3
(402.48): C, 74.60; H, 6.51; N, 6.96. Found: C, 74.52; H,
6.44; N, 6.80.
(60e80 ꢁC) as 3:1 v/v for elution, giving 6a,b as colourless
crystals.
3.4.1. 1,4-Bis[[ethyl 4-(4-fluorophenyl)-6-phenyl-3-
pyridinecarboxylate]-2-yl]piperazine (6a)
3.4. Reaction of 3 with piperazine hexahydrate
Reaction time 25 h, mp 246e248 ꢁC, yield 41%. IR:
nmax/cmꢀ1 1716 (C]O), 1575, 1544 (C]N, C]C). 1H
NMR: d 1.08 (t, 6H, 2CH3CH2, J ¼ 7.2 Hz), 3.69 (s, 8H, piper-
azinyl 4NCH2), 4.11 (q, 4H, 2OCH2CH3, J ¼ 7.2 Hz), 7.10e
8.08 (m, 20H, 18 arom. H þ 2 pyridinyl H-5). MS: m/z (%)
723 [(M-1), 0.8], 679 (2), 651 (2), 387 (100), 360 (29), 332
(4), 302 (71). Anal. Calcd for C44H38F2N4O4 (724.77): C,
72.91; H, 5.28; N, 7.73. Found: C, 73.02; H, 5.38; N, 7.53.
A mixture of 3a,b (5 mmol) and piperazine hexahydrate
(2.5 mmol) in pyridine (20 ml) was boiled under reflux for
the appropriate time. The separated solid upon pouring the
reaction mixture in ice-cold water (200 ml) acidified with
dil. HCl (5%), was collected, washed with water and purified
on silica gel TLC (F254) using chloroformelight petroleum

1824
A.S. Girgis et al. / European Journal of Medicinal Chemistry 43 (2008) 1818e1827
Compound 8b
Compound 8c
100
90
100
90
80
70
60
50
40
30
20
10
0
80
70
60
50
40
30
20
10
0
0.3
0.2
-10 0
-20
-30
-40
0.1
0.4
0.6
0
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2
Concentration (mM)
Concentration (mM)
Compound 8g
Compound 8f
100
90
80
70
60
50
40
30
20
10
0
100
90
80
70
60
50
40
30
20
10
0
0.3
0
0.1
0.2
0.4
0.5
-20
-10
-30
-40
0
0.1
0.2
0.3
Concentration (mM)
0.4
0.5
-10
Concentration (mM)
Compound 9b
Compound 9a
100
90
80
70
60
50
30
40
20
10
0
100
90
80
70
60
50
30
40
20
10
0
0
0.1
0.2
0.3
0.4
0.5
0.6
-10
-20
0
0.1
0.2
0.3
0.4
Concentration (mM)
0.5
0.6
-10
-20
Concentration (mM)
Fig. 2. (continued).
3.4.2. 1,4-Bis[[ethyl 4-(4-methylphenyl)-6-phenyl-3-
the appropriate time. The separated solid, upon pouring the re-
action mixture into ice-cold water (200 ml) acidified with dil.
HCl (5%), was collected, washed with water and purified on
silica gel TLC (F254) affording 8aeg and 9a,b.
pyridinecarboxylate]-2-yl]piperazine (6b)
Reaction time 30 h, mp 224e225 ꢁC, yield 45%. IR: nmax
/
cmꢀ1 1724 (C]O), 1577, 1542 (C]N, C]C). H NMR:
d 1.08 (t, 6H, 2CH3CH2, J ¼ 7.5 Hz), 2.43 (s, 6H, 2 ArCH3),
3.72 (s, 8H, piperazinyl 4NCH2), 4.13 (q, 4H, 2OCH2CH3,
J ¼ 7.2 Hz), 7.24e8.08 (m, 20H, 18 arom. H þ 2 pyridinyl
H-5). MS: m/z (%) 715 [(M-1), 0.7], 671 (3), 643 (3), 383
(100), 356 (30), 328 (4), 298 (67). Anal. Calcd for
C46H44N4O4 (716.84): C, 77.07; H, 6.19; N, 7.82. Found: C,
77.25; H, 6.32; N, 7.89.
1
3.5.1. Ethyl 4-(4-fluorophenyl)-6-phenyl-2-(phenylamino)-
3-pyridinecarboxylate (8a)
Reaction time 45 h, pale yellow crystals purified by silica
gel TLC (F254) using chloroformelight petroleum (60e
80 ꢁC) mixture as 2:3 v/v for elution, mp 92e94 ꢁC, yield
39%. IR: nmax/cmꢀ1 3303 (NH), 1674 (C]O), 1601, 1578
3.5. Reaction of 3 with 7
(C]N, C]C). 1H NMR:
d 0.92 (t, 3H, CH3CH2,
J ¼ 7.2 Hz), 4.08 (q, 2H, OCH2CH3, J ¼ 7.2 Hz), 7.13e8.18
(m, 15H, 14 arom. H þ pyridinyl H-5), 9.68 (s, 1H, NH).
MS: m/z (%) 412 (M, 100), 367 (7), 366 (16), 339 (15), 338
A mixture of 3a,b (5 mmol) and the corresponding 7aed
(10 mmol) in pyridine (20 ml) was boiled under reflux for

A.S. Girgis et al. / European Journal of Medicinal Chemistry 43 (2008) 1818e1827
1825
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
5a
5b
5c
5d
6b
8a
8b
Tested Compounds
8c
8f
8g
9a
9b
Fig. 3. Potency (IC50, mM) of the tested compounds on contracture induced by norepinephrine hydrochloride in thoracic rat aortic rings.
(18), 335 (2). Anal. Calcd for C26H21FN2O2 (412.45): C,
75.71; H, 5.13; N, 6.79. Found: C, 75.52; H, 5.02; N, 6.85.
C27H23FN2O2 (426.47): C, 76.04; H, 5.44; N, 6.57. Found:
C, 75.92; H, 5.36; N, 6.61.
3.5.2. Ethyl 2-[(4-chlorophenyl)amino]-4-(4-fluorophenyl)-
6-phenyl-3-pyridinecarboxylate (8b)
3.5.5. Ethyl 4-(4-methylphenyl)-2-[(4-methylphenyl)amino]-
6-phenyl-3-pyridinecarboxylate (8e)
Reaction time 60 h, yellow crystals purified by silica gel
TLC (F254) using chloroformelight petroleum (60e80 ꢁC)
mixture as 2:3 v/v for elution, mp 144e146 ꢁC, yield 20%.
IR: nmax/cmꢀ1 3261 (NH), 1682 (C]O), 1615, 1573 (C]N,
Reaction time 45 h, pale yellow crystals purified by silica
gel TLC (F254) using chloroformelight petroleum (60e
80 ꢁC) mixture as 1:1 v/v for elution, mp 97e99 ꢁC, yield
40%. IR: nmax/cmꢀ1 3345 (NH), 1677 (C]O), 1597, 1576
1
(C]N, C]C). 1H NMR:
d 0.70 (t, 3H, CH3CH2,
C]C). H NMR: d 0.83 (t, 3H, CH3CH2, J ¼ 7.2 Hz), 3.99
(q, 2H, OCH2CH3, J ¼ 7.2 Hz), 7.10e8.07 (m, 14H, 13
arom. H þ pyridinyl H-5), 9.68 (s, 1H, NH). MS: m/z (%)
448 [(M þ 2), 29], 446 (M, 100), 401 (20), 400 (47), 373
(18), 372 (11), 335 (5). Anal. Calcd for C26H20ClFN2O2
(446.89): C, 69.87; H, 4.51; N, 6.27. Found: C, 69.81; H,
4.44; N, 6.11.
J ¼ 7.2 Hz), 2.27 (s, 3H, ArCH3), 2.34 (s, 3H, ArCH3), 3.87
(q, 2H, OCH2CH3, J ¼ 7.2 Hz), 7.07e8.01 (m, 14H, 13
arom. H þ pyridinyl H-5), 9.38 (br s, 1H, NH). MS: m/z (%)
422 (M, 45), 421 (94), 377 (64), 376 (78), 349 (60), 348
(83), 331 (18). Anal. Calcd for C28H26N2O2 (422.51): C,
79.59; H, 6.20; N, 6.63. Found: C, 79.68; H, 6.29; N, 6.74.
3.5.3. Ethyl 2-[(4-chlorophenyl)amino]-4-(4-methylphenyl)-
6-phenyl-3-pyridinecarboxylate (8c)
3.5.6. Ethyl 4-(4-fluorophenyl)-2-[(4-methoxyphenyl)
amino]-6-phenyl-3-pyridinecarboxylate (8f)
Reaction time 60 h, pale yellow crystals purified by silica
gel TLC (F254) using chloroformelight petroleum (60e
80 ꢁC) mixture as 1:2 v/v for elution, mp 122e124 ꢁC, yield
23%. IR: nmax/cmꢀ1 3246 (NH), 1681 (C]O), 1617, 1574
Reaction time 40 h, yellow crystals purified by silica gel
TLC (F254) using ethyl acetateen-hexane mixture as 1:9 v/v
for elution, mp 129e131 ꢁC, yield 50%. IR: nmax/cmꢀ1 3275
1
(C]N, C]C). 1H NMR:
d 0.80 (t, 3H, CH3CH2,
(NH), 1683 (C]O), 1618, 1581 (C]N, C]C). H NMR:
d 0.83 (t, 3H, CH3CH2, J ¼ 7.2 Hz), 3.84 (s, 3H, OCH3),
3.97 (q, 2H, OCH2CH3, J ¼ 6.9 Hz), 6.92e8.07 (m, 14H, 13
arom. H þ pyridinyl H-5), 9.55 (br s, 1H, NH). MS: m/z (%)
442 (M, 100), 397 (14), 396 (41), 369 (5), 368 (6), 335 (2).
Anal. Calcd for C27H23FN2O3 (442.47): C, 73.29; H, 5.24;
N, 6.33. Found: C, 73.45; H, 5.31; N, 6.23.
J ¼ 7.2 Hz), 2.44 (s, 3H, ArCH3), 3.98 (q, 2H, OCH2CH3,
J ¼ 7.2 Hz), 7.21e8.08 (m, 14H, 13 arom. H þ pyridinyl H-
5), 9.60 (s, 1H, NH). MS: m/z (%) 444 [(M þ 2), 44], 442
(M, 100), 397 (22), 396 (67), 369 (17), 368 (10), 331 (5).
Anal. Calcd for C27H23ClN2O2 (442.92): C, 73.21; H, 5.23;
N, 6.33. Found: C, 73.05; H, 5.14; N, 6.19.
3.5.4. Ethyl 4-(4-fluorophenyl)-2-[(4-methylphenyl)amino]-
6-phenyl-3-pyridinecarboxylate (8d)
3.5.7. Ethyl 2-[(4-methoxyphenyl)amino]-4-
(4-methylphenyl)-6-phenyl-3-pyridinecarboxylate (8g)
Reaction time 40 h, pale yellow crystals purified by silica
gel TLC (F254) using chloroformelight petroleum (60e
80 ꢁC) mixture as 1:2 v/v for elution, mp 88e90 ꢁC, yield
55%. IR: nmax/cmꢀ1 3335 (NH), 1681 (C]O), 1596, 1578
Reaction time 45 h, pale yellow crystals purified by silica
gel TLC (F254) using chloroformelight petroleum (60e
80 ꢁC) mixture as 2:3 v/v for elution, mp 103e105 ꢁC, yield
40%. IR: nmax/cmꢀ1 3313 (NH), 1681 (C]O), 1614, 1576
(C]N, C]C). 1H NMR:
d
0.83 (t, 3H, CH3CH2,
(C]N, C]C). 1H NMR:
d 0.81 (t, 3H, CH3CH2,
J ¼ 7.2 Hz), 2.36 (s, 3H, ArCH3), 3.98 (q, 2H, OCH2CH3,
J ¼ 7.2 Hz), 7.09e8.09 (m, 14H, 13 arom. H þ pyridinyl H-5),
9.57 (s, 1H, NH). MS: m/z (%) 426 (M, 100), 381 (12), 380
(36), 353 (16), 352 (19), 335 (2). Anal. Calcd for
J ¼ 7.2 Hz), 2.44 (s, 3H, ArCH3), 3.86 (s, 3H, OCH3), 3.98
(q, 2H, OCH2CH3, J ¼ 7.2 Hz), 6.94e8.09 (m, 14H, 13
arom. H þ pyridinyl H-5), 9.40 (br s, 1H, NH). MS: m/z (%)
438 (M, 100), 393 (78), 392 (10), 365 (26), 364 (34), 331

1826
A.S. Girgis et al. / European Journal of Medicinal Chemistry 43 (2008) 1818e1827
(6). Anal. Calcd for C28H26N2O3 (438.51): C, 76.69; H, 5.98;
N, 6.39. Found: C, 76.82; H, 6.06; N, 6.48.
[8,13,14] by testing the effects of the synthesized pyridinecar-
boxylate derivatives on isolated thoracic aortic rings of male
Wister rats (250e350 g). After light ether anaesthesia, the
rats were sacrificed by cervical dislocation and bleeding.
The aortae were immediately excised, freed of extraneous tis-
sues and prepared for isometric tension recording. Aorta was
cut in 2e3 mm ring and placed in a vertical chamber filled
with modified KrebseHenseleit solution composed of (in
mM): NaCl, 118.0; KCl, 4.7; NaHCO3, 25.0; CaCl2, 1.8;
NaH2PO4, 1.2; MgSO4, 1.2; glucose, 11.0 and oxygenated
with carbogen gas (95% O2/5% CO2) at 37 ꢂ 0.5 ꢁC. Each
aorta ring was mounted between two hooks in which one
was attached to a force transducer (AD Instruments, model
MLT0201/D) connected with an organ bath (LETICA, Organ
Bath LE01.086). The transducer signals were displayed and
stored on a computer for further analysis using AD Instru-
ments PowerLab software.
Preparations were stabilized under 2 g resting tension dur-
ing 2 h and then the contractile response to norepinephrine hy-
drochloride (3 ꢃ 10ꢀ7 to 3 ꢃ 10ꢀ3 M) was measured before
and after exposure to increasing concentrations of the tested
synthesized compounds. The tested compounds were dis-
solved in dimethylsulfoxide (DMSO) as stock solution
(50 mg/ml). Removal of functional endothelium was achieved
by acetylcholine-induced relaxation test of pre-contracted
aorta (relaxation < 10%). Control experiments were per-
formed in the presence of DMSO alone, at the same concen-
trations at those used with the derivatives tested, which
demonstrated that the solvent did not affect the contractile
response of isolated aorta.
3.5.8. Ethyl 2-amino-4-(4-fluorophenyl)-6-
phenyl-3-pyridinecarboxylate (9a)
Colourless crystals, mp 169e171 ꢁC, yield 36, 48, 30 and
18% ‘‘during preparation of 8a, 8b, 8d and 8f, respectively’’.
IR: nmax/cmꢀ1 3448, 3280, 3169 (NH2), 1681 (C]O), 1615,
1570 (C]N, C]C). 1H NMR: d 0.84 (t, 3H, CH3CH2,
J ¼ 7.2 Hz), 3.98 (q, 2H, OCH2CH3, J ¼ 7.2 Hz), 6.26 (s,
2H, NH2), 6.99 (s, 1H, pyridinyl H-5), 7.07e8.01 (m, 9H,
arom. H). MS: m/z (%) 336 (M, 100), 291 (29), 263 (25).
Anal. Calcd for C20H17FN2O2 (336.36): C, 71.41; H, 5.10;
N, 8.33. Found: C, 71.56; H, 5.21; N, 8.27.
3.5.9. Ethyl 2-amino-4-(4-methylphenyl)-6-
phenyl-3-pyridinecarboxylate (9b)
Colourless crystals, mp 119e121 ꢁC, yield 54, 24 and 15%
‘‘during preparation of 8c, 8e and 8g, respectively’’. IR: nmax
cmꢀ1 3437, 3277, 3172 (NH2), 1679 (C]O), 1619, 1567
(C]N, C]C). 1H NMR:
0.82 (t, 3H, CH3CH2,
/
d
J ¼ 7.2 Hz), 2.43 (s, 3H, ArCH3), 3.99 (q, 2H, OCH2CH3,
J ¼ 7.2 Hz), 6.23 (s, 2H, NH2), 7.05 (s, 1H, pyridinyl H-5),
7.23e8.03 (m, 9H, arom. H). MS: m/z (%) 332 (M, 100),
287 (30), 259 (73). Anal. Calcd for C21H20N2O2 (332.39):
C, 75.88; H, 6.07; N, 8.43. Found: C, 75.83; H, 6.03; N, 8.26.
3.6. Single crystal X-ray crystallographic data of 2a
For X-ray crystallographic studies, compound 2a was
recrystallized as prismatic colourless crystals from benzenee
light petroleum (60e80 ꢁC) mixture as 1:2 v/v. The crystallo-
graphic data were collected at T ¼ 298 K on a Kappa CCD
Enraf Nonius FR 590 diffractometer using a graphite mono-
Acknowledgment
This work is sponsored by the U.S.eEgypt Science and
Technology Joint Fund under Project No. MAN10-007-002.
˚
chromator with Mo Ka radiation (l ¼ 0.71073 A). The crystal
structure was determined by SIR92 [17] and refined by maXus
[18] (Bruker Nonius, Delft and MacScience, Japan). Chemical
formula C20H18FNO3, Mr ¼ 339.366, monoclinic, crystallizes
in space group P21/c, cell lengths ‘‘a ¼ 9.6989(4),
References
˚
b ¼ 19.8809(8), c ¼ 9.3483(3) A’’, cell angles ‘‘a ¼ 90.00,
[1] M.J. O’Neil, A. Smith, P.E. Heckelman, J.R. Obenchain Jr.,
J.A.R. Gallipeau, M.A. D’Arecca, S. Budavari, The Merck Index, An
Encyclopedia of Chemicals, Drugs and Biologicals, 13th ed. Merck
Research Laboratories Division of Merck & Co., Whitehouse Station,
NJ, USA, 2001, p. 393, 831, 894 and 1164.
3
b ¼ 98.070(2), g ¼ 90.00ꢁ’’, V ¼ 1784.72(12) A , Z ¼ 4,
˚
Dc ¼ 1.263 mg/m3, q values 2.910e26.022ꢁ, absorption coeffi-
cient m (Mo Ka) ¼ 0.09 mmꢀ1, F(000) ¼ 712. The unique
reflections measured 4234 of which 1346 reflections with
threshold expression I > 3s(I ) were used in the structural
analysis. Convergence for 265 variable parameters by least-
squares refinement on F2 with w ¼ 1/[s2(Fo2) þ 0.10000Fo2].
The final agreement factors were R ¼ 0.039 and wR ¼ 0.070
with a goodness-of-fit of 1.435. Full crystallographic details,
excluding structure factors, have been deposited at Cambridge
Crystallographic Data Centre (CCDC) as supplementary pub-
lication number CCDC 222213.
[2] Z. Zhao (Lunan Pharmaceutical Co., Ltd., Peop. Rep. China). Faming
Zhuanli Shenqing Gongkai Shuomingshu CN 1,457,786 (Cl. A61K31/
505), 26 Nov. 2003; Chem. Abstr. 142 (2005) 379358.
[3] L.F. Lee, K.C. Glenn, D.T. Connolly, D.G. Corley, D.L. Flynn, A. Hamme,
S.G. Hegde, M.A. Melton, R.J. Schilling, J.A. Sikorski, N.N. Wall, J.A.
Zablocki (G.D. Searle & Co., USA). PCT Int. Appl. WO 99 41.237 (Cl.
CO7D213/80), 19 Aug. 1999; Chem. Abstr. 131 (1999) 157711.
[4] T. Omori, S. Takeda, Y. Tsuji, H. Kanokogi (Shiseido Co., Ltd., Japan).
Jpn. Kokai Tokkyo Koho JP 2005 206,475 (Cl. A61K7/06), 4 Aug. 2005;
Chem. Abstr. 143 (2005) 179114.
[5] T. Haga, K. Fujikawa, T. Koyanagi, T. Nakajima, K. Hayashi, Heterocy-
cles 22 (1984) 117.
3.7. Vasodilation activity screening
[6] F.F. Barsoum, H.M. Hosni, A.S. Girgis, Bioorg. Med. Chem. 14 (2006)
3929e3937.
The vasodilation activity screening procedures were car-
ried out according to the standard reported techniques
[7] A.S. Girgis, H.M. Hosni, F.F. Barsoum, Bioorg. Med. Chem. 14 (2006)
4466e4476.

A.S. Girgis et al. / European Journal of Medicinal Chemistry 43 (2008) 1818e1827
1827
[8] A.S. Girgis, A. Kalmouch, M. Ellithey, Bioorg. Med. Chem. 14 (2006)
8488e8494.
[14] A.G. Silva, G. Zapata-Sudo, A.E. Kummerle, C.A.M. Fraga,
E.J. Barreiro, R.T. Sudo, Bioorg. Med. Chem. 13 (2005)
3431e3437.
[9] A.S. Girgis, M. Ellithey, Bioorg. Med. Chem. 14 (2006) 8527e8532.
[10] A.S. Girgis, N. Mishriky, M. Ellithey, H.M. Hosni, H. Farag, Bioorg.
Med. Chem. 15 (2007) 2403e2413.
[11] A.S. Girgis, A. Kalmouch, H.M. Hosni, Amino Acids 26 (2004)
139e146.
[15] S. Toma, Collect. Czech. Chem. Commun. 34 (1969) 2771e2781.
[16] H.H. Szmant, A.J. Basso, J. Am. Chem. Soc. 74 (1952) 4397e4400.
[17] A. Altomare, G. Cascarano, C. Giacovazzo, A. Guagliardi, M.C. Burla,
G. Polidori, M. Camalli, J. Appl. Cryst. 27 (1994) 435.
[12] J.P. Greenstein, M. Winitz, in: , Chemistry of the Amino Acids, vol. 2,
John Wiley and Sons Inc., New York, 1961 p. 1301.
[13] J.M. Raimundo, R.T. Sudo, L.B. Pontes, F. Antunes, M.M. Trachez,
G. Zapata-Sudo, Eur. J. Pharmacol. 530 (2006) 117e123.
[18] S. Mackay, C.J. Gilmore, C. Edwards, N. Stewart, K. Shankland, maXus
Computer Program for the Solution and Refinement of Crystal
Structures, Bruker Nonius/MacScience/The University of Glasgow, The
Netherlands/Japan, 1999.