Design and synthesis of methyl 2-methyl-7,7-dihalo-5-phenyl-2-azabicyclo[4. 1.0]hept-3-ene-4-carboxylates with calcium channel antagonist activity

Article abstract of DOI:10.1016/j.bmc.2004.03.063

A group of methyl 2-methyl-7,7-dihalo-5-(substituted-phenyl)-2- azabicyclo[4.1.0]hept-3-ene-4-carboxylates were prepared by reaction of dihalocarbenes (:CX₂, X=Br, Cl) with methyl 1-methyl-4-(substituted- phenyl)-1,4-dihydropyridine-3-carboxyla

Full text of DOI:10.1016/j.bmc.2004.03.063

Bioorganic & Medicinal Chemistry 12 (2004) 3215–3220
Design and synthesis of methyl 2-methyl-7,7-dihalo-5-phenyl-2-
azabicyclo[4.1.0]hept-3-ene-4-carboxylates with calcium channel
antagonist activity
Javid S. Mojarrad,a,b Ramin Miria,c and Edward E. Knausa,*
aFaculty of Pharmacy and Pharmaceutical Sciences, University of Alberta, Edmonton, Alberta, Canada T6G 2N8
bSchool of Pharmacy, Tabriz University of Medical Sciences and Health Sciences, Tabriz, PO Box 51664, Iran
cFaculty of Pharmacy, Shiraz University of Medical Sciences, Shiraz, PO Box 71345-1149, Iran
Received 8 March 2004; revised 29 March 2004; accepted 30 March 2004
Available online 10 May 2004
Abstract—A group of methyl 2-methyl-7,7-dihalo-5-(substituted-phenyl)-2-azabicyclo[4.1.0]hept-3-ene-4-carboxylates were pre-
pared by reaction of dihalocarbenes (:CX2, X ¼ Br, Cl) with methyl 1-methyl-4-(substituted-phenyl)-1,4-dihydropyridine-3-carb-
oxylates. In vitro calcium channel antagonist activities were determined using a guinea pig ileum longitudinal smooth muscle assay.
The title compounds exhibited weaker CC antagonist activity (10ꢀ5–10ꢀ6 M range) than the reference drug nifedipine (1.4 · 10ꢀ8 M).
Structure–activity relationship studies showed that the position of a nitro substituent on the C-5 phenyl ring where the relative
potency order was ortho > meta > para, and the size and/or electronegativity of the C-7 geminal-dihalo substituents (Br > Cl), were
determinants of calcium channel antagonist activity. This class of compounds did not exhibit any inotropic effect on guinea pig left
atria. A dihalocyclopropyl moiety is a potential bioisostere for the 2-methyl-3-methoxycarbonylvinyl moiety present in the calcium
channel antagonist nifedipine.
ꢀ 2004 Elsevier Ltd. All rights reserved.
1. Introduction
substituents is relieved most notably by puckering of the
1,4-DHP ring and distortion of the bond angles about
C-4 with the most potent compounds showing the
smallest degree of ring distortion from planarity.3;13 It
has been suggested that synperiplanar (sp) carbonyl
groups may be a common feature of DHP calcium
channel antagonists, and that an antiperiplanar (ap)
carbonyl group, such as the lactone group in the rigid
CGP 28 392 (2) may be a requirement for calcium
channel agonist activity.14 Molecular orbital (MOPAC)
conformational calculations suggested that both car-
bonyl groups in calcium channel antagonists are pref-
erentially oriented in a plane that intersects the DHP
ring with an angle between 30ꢁ and 60ꢁ. In contrast, the
nitro group of the calcium channel agonist Bay K 8644
(3) is oriented in the plane of the DHP ring.16 Differ-
ences in the molecular electrostatic potentials between
calcium channel antagonist and agonist structures, with
respect to binding at the C-3 and C-5 regions, may
provide a mechanism by which the receptor distin-
guishes between agonist and antagonist ligands.
Accordingly, antagonists show a positive potential in
this region when a C-3 ester group is present, whereas
calcium channel activators are reported to have a strong
negative potential in the region adjacent to the C-3 nitro
The design of 1,4-dihydropyridine (1,4-DHP) calcium
channel modulators related to the first-generation cal-
cium channel antagonist nifedipine (1), as therapeutic
agents to treat cardiovascular disorders,1 has prompted
studies to investigate the geometrical requirements at the
DHP binding site.2–5 Structure–activity relationships
indicate that the combination of the substituents at the
C-3, C-4, and C-5 positions of nifedipine modulated
activity,2 tissue selectivity,6–12 and the conformation13–15
of the 1,4-DHP ring system. The nature and position of
C-4 aryl ring substituents were determinants of calcium
channel antagonist activity where the potency order was
generally ortho P meta ꢁ para.3 Hantzsch 1,4-DHPs, in
the solid state, exist in a boat conformation where the
C-4 substituted-phenyl ring is perpendicular (pseudo-
axial) to the 1,4-DHP ring. Strain due to nonbonded
interactions between the C-3, C-4, and C-5 1,4-DHP
Keywords: 1,4-Dihydropyridines; Dihalocarbenes; Calcium channel
antagonists.
* Corresponding author. Tel.: +1-780-492-5993; fax: +1-780-492-1217;
e-mail: eknaus@pharmacy.ualberta.ca
0968-0896/$ - see front matter ꢀ 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmc.2004.03.063

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J. S. Mojarrad et al. / Bioorg. Med. Chem. 12 (2004) 3215–3220
Figure 1. Structures of nifedipine (1), CGP 28 392 (2) and Bay K 8644
(3).
substituent.17 It would ultimately be of interest to re-
place one of the 2-methyl-3-methoxycarbonyl-2,3-vinyl
moieties of nifedipine (1) by a potentially bioisosteric
dihalocyclopropyl moiety to determine the effect on
calcium channel modulation. In this regard, we now
report the synthesis and calcium channel antagonist
activities for a group of bicyclic methyl 2-methyl-7,7-
dihalo-5-phenyl-2-azabicyclo[4.1.0]hept-3-ene-4-carb-
oxylates (7–8) that are structurally related to nifedipine
(Fig. 1).
2. Chemistry
The piperidine catalyzed condendation18 of 4-nitrocin-
namaldehyde (4a),19 3-nitrocinnamaldehyde (4b),20 or 2-
nitrocinnamaldehyde (4c) with methyl 3-aminoacrylate
(5), prepared by reaction of methylamine with methyl
propiolate,21;22 afforded the respective methyl 1-methyl-
4-(4-, 3-, or 2-nitrophenyl)-1,4-dihydropyridine-3-car-
boxylate (6a, 30%; 6b, 8%; 6c, 27%) as illustrated in
Scheme 1. Methyl 1-methyl-4-phenyl-1,4-dihydropyr-
idine-3-carboxylate (6d) was prepared by the CuI cata-
lyzed regioselective reaction of phenylmagnesium
chloride with 3-methoxycarbonyl-1-methylpyridinium
iodide according to literature procedures.23;24 This latter
reaction was not suitable for the preparation of 6a–c
since 4-, 3-, or 2-chloronitrobenzene did not react with
magnesium metal to prepare the required Grignard
reagent.
Scheme 1. Reagents and conditions: (i) piperidine, MeOH, reflux, 12 h;
(ii) PhHgCBr3, dry benzene, reflux, 3 h; (iii) PhHgCBrCl2, dry benzene,
reflux, 3 h.
7–13% chemical yield (see Scheme 1). Electronegative
halogen substituents decrease the rate of reaction of
carbenes, which are electrophilic species.35;36 Accord-
ingly, it was expected that dihalocyclopropanation
(:CX2) would occur exclusively at the C5–C6 olefinic
bond of 6a–d, rather than the deactivated C2–C3 olefinic
bond to which the 3-methoxycarbonyl substituent is
attached. Regiospecific dihalocyclopropanation of the
C5–C6 olefinic bond, rather than the C@O bond of the
3-methoxycarbonyl substituent, is also in agreement
with the observation that dihalocarbenes rarely add to
the C@O bond of aldehydes or lactones.37 1,4-Dihy-
dropyridines such as 6a–d exist in a boat conformation
with the C-4 aryl ring pseudoaxial to the 1,4-DHP
ring.3;13;24;33 The concerted addition of :CX2 should
therefore occur from the sterically least hindered lower
face of the boat-shaped 1,4-DHP ring where the orien-
tation of the C-4 aryl ring remains unchanged. In this
context, these stereochemical and regiochemical assign-
ments are in agreement with the X-ray structure of 2-
benzoyl-5-benzyl-7,7-dibromo-4-ethoxycarbonyl-2-aza-
bicyclo[4.1.0]hept-3-ene that was prepared by reaction
Due to their extreme reactivity, carbenes often undergo
contraindicated insertion reactions that decrease the
yield of the olefin addition product.25 On the other hand,
dihalocarbenes (:CX2) are much less reactive species that
do not furnish insertion products.26–28 Singlet state
carbenes afford stereospecific syn addition products
upon reaction with olefins29;30 that likely proceeds via a
concerted mechanism.31 In this regard, the thermal in
situ generation of dihalocarbenes (:CX2, X ¼ Br, Cl)32;33
from the Seyferth reagents34 PhHgCBr3, or
PhHgCBrCl2, in the presence of the methyl 1-methyl-4-
(substituted-phenyl)-1,4-dihydropyridine-3-carboxylates
(6a–d) yielded the respective methyl 2-methyl-7,7-di-
halo-5-(substituted-phenyl)-2-azabicyclo[4.1.0]hept-3-
ene-4-carboxylates (7a–d, X ¼ Br; 8a–d, X ¼ Cl) in
of
1-benzoyl-4-benzyl-3-ethoxycarbonyl-1,4-dihydro-

J. S. Mojarrad et al. / Bioorg. Med. Chem. 12 (2004) 3215–3220
3217
Table 1. In vitro calcium channel antagonist activities for methyl 2-
methyl-7,7-dihalo-5-substituted-phenyl-2-azabicyclo[4.1.0]hept-3-ene-
4-carboxylates (7–8)
pyridine with :CBr2, in which the C@O moiety of the C-
4 CO2Et substituent is antiperiplanar (ap) to the C3–C4
olefinic bond.38
3. Results and discussion
As part of an ongoing program to design novel calcium
channel modulators, it was anticipated that replacement
of the C5–C6 olefinic bond of 1-methyl-3-methoxycar-
bonyl-4-(substituted-phenyl)-1,4-dihydropyridines (6a–
d) by a potentially bioisosteric dihalocyclopropyl moiety
would provide a novel class of methyl 2-methyl-7,7-di-
halo-5-(4-, 3-, or 2-nitrophenyl)-2-azabicyclo[4.1.0]hept-
3-ene-4-carboxylates (7–8) that bear some structural
relationship to the calcium channel antagonist nifedi-
pine (1). This drug design concept is based on the fact
that cyclopropyl C–C bonds have a number of similar-
ities to olefinic bonds that include: (i) the hybridization
of cyclopropyl C–C bonds is intermediate in character
between a sigma ðrÞ and a pi ðpÞ bond,37 (ii) a cyclo-
propyl C–C bond, like a C@C bond, is able to conjugate
with an olefinic bond to which it is attached,37 but unlike
a C@C it does not transmit electronic effects,39 and (iii) a
cyclopropyl ring interacts with adjacent p-electron sys-
tems and p-electron centers much like a vinyl group.40;41
In this regard, a cyclopropane group has been investi-
gated as a alkene bioisostere.42–44 Rigid tetracyclic
compounds derived from structural analogs of the cal-
cium channel antagonist nifedipine having a fused
cyclopropane ring have been synthesized but no phar-
macological properties were reported.45 It was therefore
anticipated that the fused dihalocyclopropyl ring in the
bicyclic compounds (7–8), which is oriented below the
plane of the boat-shaped tetrahydropyridine ring, may
serve as a bioisostere of the 2-methyl-3-methoxycar-
bonyl-2,3-olefinic moiety present in nifedipine (1). In
compounds 7–8, one C-7 halo substituent on the fused
planar cyclopropyl ring system is syn to the H-1 and H-6
hydrogen atoms, while the other C-7 halogen sub-
stituent is syn to the C3–C4 vinyl bond.
Compd
R
X
Calcium channel
antagonist activity
GPILSM: IC50 (M)a
7a
7b
4-NO2
3-NO2
2-NO2
H
Br
Br
Br
Br
Cl
Cl
Cl
Cl
8.82 0.65 · 10ꢀ6
5.85 1.19 · 10ꢀ6
2.25 0.11 · 10ꢀ6
7.17 1.26 · 10ꢀ6
2.01 0.36 · 10ꢀ5
5.79 0.33 · 10ꢀ6
4.55 0.26 · 10ꢀ6
7.97 1.02 · 10ꢀ6
1.40 0.19 · 10ꢀ8
7c
7d
8a
8b
4-NO2
3-NO2
2-NO2
H
8c
8d
Nifedipine
a The molar concentration of the test compound causing a 50% de-
crease in the slow component or tonic contractile response
(IC50 SEM, n ¼ 3) in guinea pig ileum longitudinal smooth muscle
(GPILSM) induced by the muscarinic agonist carbachol
(1.6 · 10ꢀ7 M) was determined graphically from the dose–response
curve.
4. Conclusions
A geminal-dihalocyclopropyl moiety (i) is a potential
bioisostere for the 2-methyl-3-methoxycarbonylvinyl
moiety of nifedipine (1), and (ii) the dihalocyclopropyl
compounds 7–8 provides further structure–activity data
that may be of value to probe the structure–function
relationship of calcium channel modulation.
The in vitro calcium channel antagonist activities exhib-
ited by compounds 7–8 were determined using a guinea
pig ileum longitudinal smooth muscle (GPILSM) assay,6
and the results are summarized in Table 1. Compounds
7–8 exhibited weaker calcium channel antagonist activity
(10ꢀ5–10ꢀ6 M range) relative to the reference drug
nifedipine (IC50 ¼ 1.40 · 10ꢀ8 M). Structure–activity
relationships showed that the position of a nitro sub-
stituent on the C-5 phenyl ring was a determinant of
calcium channel antagonist activity where the potency
5. Experimental
Melting points were determined using a Thomas–Hoo-
ver capillary apparatus and are uncorrected. Infrared
(IR) spectra were recorded using a Nicolet 550 Series II
Magna FT-IR spectrometer. 1H NMR nuclear magnetic
resonance spectra were recorded on a Bruker AM-300
spectrophotometer. Silica gel column chromatography
was performed using Silicycleꢂ (silica gel 70–230 mesh).
Elemental analyses were determined for C, H, and N
(microanalytical service laboratory, Department of
Chemistry, University of Alberta). 4-Nitrocinnamalde-
hyde (4a),19 3-nitrocinnamaldehyde (4b),20 methyl
3-aminoacrylate (5),21;22 methyl 1-methyl-4-phenyl-1,4-
dihydropyridine-3-carboxylate (6d),23;24 phenyl(tribro-
profile
was
ortho > meta > para
(7c > 7b > 7a;
8c > 8b > 8a). It appears that the size (van der Waal’s
ꢀ
radius for Br and Cl are 1.95 and 1.80 A, respectively),
and/or electronegativity (Cl > Br) of the C-7 halogen
atoms may be a determinant of CC antagonist activity.
Although the differences in antagonist activity were
small, compounds having C-7 geminal-bromo substitu-
ents were generally more potent that the corresponding
C-7 chloro derivatives (7a > 8a; 7bꢂ8b; 7c > 8c; 7d P 8d).
This class of compounds 7–8 did not exhibit an inotropic
effect (antagonist or agonist) on guinea pig left atria.
momethyl)mercury
yl(bromodichloromethyl)mercury
were prepared according to the literature procedures.
(PhHgCBr3),34
and
phen-
(PhHgCBrCl2),34

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J. S. Mojarrad et al. / Bioorg. Med. Chem. 12 (2004) 3215–3220
All other reagents, including 2-nitrocinnamaldehyde
(4c), were purchased from Aldrich Chemical (Milwau-
kee, WI) and used without further purification. In vitro
calcium channel antagonist activities were determined
using protocols approved by the Health Sciences Animal
Welfare Committee at the University of Alberta.
(d, J4;5 ¼ 4:2 Hz, 1H, DHP H-4), 5.27 (dd, J5;6 ¼ 9:9,
J4;5 ¼ 4:5 Hz, 1H, DHP H-5), 3.73 (s, 3H, OCH3), 2.86
(s, 3H, NCH3). Anal. Calcd for C14H14N2O4: C, 61.31;
H, 5.15; N, 10.21. Found: C, 60.99; H, 5.49; N, 10.25.
Compound 6c is sensitive to light, and it should be
stored in a dark container in a cool place prior to use.
5.1. General method for the synthesis of methyl 1-methyl-
4-(substituted-phenyl)-1,4-dihydropyridine-3-carboxylates
(6a–c)
5.2. General method for the preparation of methyl 2-
methyl-7,7-dihalo-5-(4-, 3-, or 2-nitrophenyl)-2-azabicy-
clo[4.1.0]hept-3-ene-4-carboxylates (7a–d, 8a–d)
A mixture of the nitrocinnamaldehyde (4a, 4b, or 4c;
4.43 g, 25 mmol), methyl 3-methylaminoacrylate (5,
2.88 g, 25 mmol), and piperidine (120 lL, 1.02 mmol) in
methanol (12 mL) was refluxed for 2 h. The solvent was
removed in vacuo, and the respective product (6a, 6b, or
6c) was purified by elution from a silica gel column using
ethyl acetate–hexanes (25:75, v/v) as eluent. Some
physical and spectroscopic data for 6a–c are listed
below.
Phenyl(tribromomethyl)mercury (1.38 g, 2.6 mmol), or
phenyl(bromodichloromethyl)mercury (1.15 g, 2.6 mmol),
was added to stirred solution of 6a, 6b, 6c, or 6d
(2.6 mmol) in dry benzene (20 mL), the reaction flask
was sealed with a rubber septum, and the mixture was
refluxed for 3 h. The reaction mixture was cooled to
25 ꢁC, and the PhHgBr, which precipitated during the
reaction was removed by filtration. Removal of the
solvent in vacuo gave a brownish oil, which was purified
by silica gel column chromatography using ethyl ace-
tate–hexane (25:75, v/v) as eluent to afford the respective
product 7a–d using phenyl(tribromomethyl)mercury,
or 8a–d using phenyl(bromodichloromethyl)mercury.
Physical and spectral data for these products are listed
below.
5.1.1. Methyl 1-methyl-4-(4-nitrophenyl)-1,4-dihydropyr-
idine-3-carboxylate (6a). Oil; yield 30.5%; IR (NaCl) m
1688 (C@O), 1589 (C@C, aromatic), 1523, 1341 (NO2)
1
cmꢀ1; H NMR (CDCl3): d 8.24 (d, Jortho ¼ 8:7 Hz, 2H,
phenyl H-3, H-5), 7.54 (d, Jortho ¼ 8:7 Hz, 2H, phenyl H-
2, H-6), 7.40 (s, 1H, DHP H-2), 6.49 (d, 1H,
J5;6 ¼ 9:9 Hz, DHP H-6), 5.14 (d, J4;5 ¼ 4:2 Hz, 1H,
DHP H-4), 5.04 (dd, J5;6 ¼ 9:9, J4;5 ¼ 4:2 Hz, 1H, DHP
H-5), 3.73 (s, 3H, OCH3), 2.85 (s, 3H, NCH3). Com-
pound 6a is sensitive to light and it should be used as
soon as possible after purification. When 6a is stored, it
should be placed in a dark container in a cool place
prior to use.
5.2.1. Methyl 7,7-dibromo-2-methyl-5-(4-nitrophenyl)-2-
azabicyclo[4.1.0]hept-3-ene-4-carboxylate (7a). Yellow
crystals (Et2O); mp 194–195 ꢁC (decomp.); yield 7.5%;
IR (NaCl) m 1686 (C@O), 1621 (C@C, aromatic), 1511,
1346 (NO2) cmꢀ1
;
1H NMR (CDCl3): d 8.26 (d,
Jortho ¼ 9:0 Hz, 2H, phenyl H-3, H-5), 7.50 (s, 1H, H-3),
7.46 (d, Jortho ¼ 9:0 Hz, 2H, phenyl H-2, H-6), 4.29 (s,
1H, H-5), 3.80 (s, 3H, OCH3), 2.85 (d, J1;6 ¼ 11:1 Hz,
1H, H-1), 2.76 (s, 3H, NCH3), 2.16 (d, J1;6 ¼ 11:1 Hz,
1H, H-6). Anal. Calcd for C15H14Br2N2O4: C, 40.39; H,
3.16; N, 6.28. Found: C, 40.40; H, 2.98; N, 6.05.
5.1.2. Methyl 1-methyl-4-(3-nitrophenyl)-1,4-dihydropyr-
idine-3-carboxylate (6b). Oil; yield 8%; IR (NaCl) m 1685
(C@O), 1637 (C@C, aromatic), 1527, 1348 (NO2) cmꢀ1
;
1H NMR (CDCl3): d 8.19 (d, J4;5 ¼ 8:1 Hz, 1H, phenyl
H-4), 8.16 (s, 1H, phenyl H-2), 7.77 (d, J5;6 ¼ 7:5 Hz,
1H, phenyl H-6), 7.58 (dd, J4;5 ¼ 8:1, J5;6 ¼ 7:5 Hz, 1H,
phenyl H-5), 7.39 (s, 1H, DHP H-2), 6.51 (d,
J5;6 ¼ 10:2 Hz, 1H, DHP H-6), 5.25 (d, J4;5 ¼ 3:9 Hz,
1H, DHP H-4), 5.06 (dd, J5;6 ¼ 10:2, J4;5 ¼ 3:9 Hz, 1H,
DHP H-5), 3.73 (s, 3H, OCH3), 2.86 (s, 3H, NCH3).
Compound 6b is sensitive to light and it should be used
as soon as possible after purification. When 6b is stored,
it should be placed in a dark container in a cool place
prior to use.
5.2.2. Methyl 7,7-dibromo-2-methyl-5-(3-nitrophenyl)-2-
azabicyclo[4.1.0]hept-3-ene-4-carboxylate (7b). Yellow
crystals (Et2O–hexane); mp 154–156 ꢁC (decomp.); yield
11%; IR (NaCl) m 1683 (C@O), 1621 (C@C, aromatic),
1
1530, 1346 (NO2) cmꢀ1; H NMR (CDCl3): d 8.20–8.24
(m, 1H, phenyl H-4), 8.14 (s, 1H, phenyl H-2), 7.57–7.64
(m, 2H, phenyl H-5, H-6), 7.51 (s, 1H, H-3), 4.30 (s, 1H,
H-5), 3.80 (s, 3H, OCH3), 2.86 (d, J1;6 ¼ 11:1 Hz, 1H, H-
1), 2.77 (s, 3H, NCH3), 2.18 (d, J1;6 ¼ 11:1 Hz, 1H, H-6).
Anal. Calcd for C15H14Br2N2O4: C, 40.39; H, 3.16; N,
6.28. Found: C, 40.76; H, 3.03; N, 6.00.
5.1.3. Methyl 1-methyl-4-(2-nitrophenyl)-1,4-dihydropyr-
idine-3-carboxylate (6c). Red crystals; mp 112–114 ꢁC
(MeOH/H2O); yield 27.5%; IR (NaCl) m 1696 (C@O),
5.2.3. Methyl 7,7-dibromo-2-methyl-5-(2-nitrophenyl)-2-
azabicyclo[4.1.0]hept-3-ene-4-carboxylate (7c). Yellow
crystals (Et2O–hexanes); mp 122–124 ꢁC (decomp.);
yield 10%; IR (NaCl) m 1686 (C@O), 1621 (C@C, aro-
1642 (C@C, aromatic), 1528, 1307 (NO2) cmꢀ1 1H
;
NMR (CDCl3): d 7.91 (d, J3;4 ¼ 8:1 Hz, 1H, phenyl H-
3), 7.86 (d, J5;6 ¼ 8:1 Hz, 1H, phenyl H-6), 7.67 (dd,
J4;5 ¼ 7:2, J5;6 ¼ 8:1 Hz, 1H, phenyl H-5), 7.48 (s, 1H,
DHP H-2), 7.45 (dd, J3;4 ¼ 8:1, J4;5 ¼ 7:2 Hz, 1H, phenyl
H-4), 6.45 (d, J5;6 ¼ 9:9 Hz, 1H, DHP H-6), 5.83
1
matic), 1523, 1341 (NO2) cmꢀ1; H NMR (CDCl3): d
8.02 (d, J3;4 ¼ 8:4 Hz, 1H, phenyl H-3), 7.64 (t,
J5;6 ¼ 7:5, J4;5 ¼ 7:5 Hz, 1H, phenyl H-5), 7.55 (s, 1H, H-
3), 7.51 (dd, J4;5 ¼ 7:5, J3;4 ¼ 8:4 Hz, 1H, phenyl H-4),

J. S. Mojarrad et al. / Bioorg. Med. Chem. 12 (2004) 3215–3220
3219
7.38 (dd, J5;6 ¼ 7:5, J4;6 ¼ 0:9 Hz, 1H, phenyl H-6), 4.83
(s, 1H, H-5), 3.80 (s, 3H, OCH3), 2.78 (d, J1;6 ¼ 11:1 Hz,
1H, H-1), 2.75 (s, 3H, NCH3), 2.33 (d, J1;6 ¼ 11:1 Hz,
1H, H-6). Anal. Calcd for C15H14Br2N2O4: C, 40.39; H,
3.16; N, 6.28. Found: C, 40.31; H, 2.96; N, 6.01.
5.2.8. Methyl 7,7-dichloro-2-methyl-5-phenyl-2-azabicy-
clo[4.1.0]hept-3-ene-4-carboxylate (8d). White crystals
after purification by silica gel column chromatography
using ethyl acetate–hexanes (15:85, v/v) as eluent; mp
95–96 ꢁC (Et2O–hexanes); yield 12%; IR (NaCl) m 1688
(C@O), 1622 (C@C, aromatic) cmꢀ1; 1H NMR (CDCl3):
d 7.33 (s, 1H, H-3), 7.16–7.31 (m, 5H, phenyl hydro-
gens), 3.99 (s, 1H, H-5), 3.53 (s, 3H, OCH3), 3.22 (s, 3H,
NCH3), 3.04 (d, J1;6 ¼ 11:1 Hz, 1H, H-1), 2.14 (d,
5.2.4. Methyl 7,7-dibromo-2-methyl-5-phenyl-2-azabicy-
clo[4.1.0]hept-3-ene-4-carboxylate (7d). White crystals
(Et2O–hexanes) after purification by elution from a sil-
ica gel column using ethyl acetate–hexanes (15:85, v/v)
as eluent; mp 96–98 ꢁC; yield 13%; IR (NaCl) m 1690
(C@O), 1630 (C@C, aromatic) cmꢀ1; 1H NMR (CDCl3):
d 7.33 (s, 1H, H-3), 7.16-7.29 (m, 5H, phenyl hydro-
gens), 3.92 (s, 1H, H-5), 3.53 (s, 3H,OCH3), 3.25 (s, 3H,
NCH3), 3.11 (d, J1;6 ¼ 11:1 Hz, 1H, H-1), 2.24 (d,
J1;6 ¼ 11:1 Hz, 1H, H-6). Anal. Calcd for C15H15Br2NO :
C, 44.92; H, 3.77; N, 3.49. Found: C, 44.86; H, 3.67; N,
3.43.
J1;6 ¼ 11:1 Hz,
1H,
H-6).
Anal.
Calcd
for
C15H15Cl2NO2: C, 57.71; H, 4.84; N, 4.49. Found: C,
57.84; H, 4.72; N, 4.39.
5.3. In vitro calcium channel antagonist assay
Smooth muscle calcium channel antagonist activity was
determined as the molar (M) concentration of the test
compound required to produce 50% inhibition of the
muscarinic receptor-mediated (carbachol, 1.6 · 10ꢀ7 M)
Caþ2-dependent contraction (tonic response) of guinea
pig ileum longitudinal smooth muscle (GPILSM) using
the procedure previously reported.6 The IC50 ( SEM,
n ¼ 3) was determined graphically from the dose–
response curve.
5.2.5. Methyl 7,7-dichloro-2-methyl-5-(4-nitrophenyl)-2-
azabicyclo[4.1.0]hept-3-ene-4-carboxylate (8a). Yellow
crystals (Et2O); mp 197–199 ꢁC (decomp.); yield 9.3%;
IR (NaCl) m 1686 (C@O), 1631 (C@C, aromatic), 1520,
1346 (NO2) cmꢀ1
;
1H NMR (CDCl3): d 8.20 (d,
Jortho ¼ 8:7 Hz, 2H, phenyl H-3, H-5), 7.49 (s, 1H, H-3),
7.46 (d, Jortho ¼ 8:7 Hz, 2H, phenyl H-2, H-6), 4.39 (s,
1H, H-5), 3.80 (s, 3H, OCH3), 2.82 (d, J1;6 ¼ 11:1 Hz,
1H, H-1), 2.77 (s, 3H, NCH3), 2.08 (d, J1;6 ¼ 11:1 Hz,
1H, H-6). Anal. Calcd for C15H14Cl2N2O4: C, 50.44; H,
3.95; N, 7.84. Found: C, 50.17; H, 3.77; N, 7.62.
Acknowledgements
We are grateful to the Canadian Institutes of Health
Research for financial support of this research, and to
the Government of Tehran for an Iranian Ministry of
Health & Medical Education for a six-month scholar-
ship to one of us (J.S.M.).
5.2.6. Methyl 7,7-dichloro-2-methyl-5-(3-nitrophenyl)-2-
azabicyclo[4.1.0]hept-3-ene-4-carboxylate (8b). Yellow
crystals (Et2O–hexanes); mp 163–165 ꢁC (decomp.);
yield 10.4%; IR (NaCl) m 1683 (C@O), 1623 (C@C,
aromatic), 1525, 1353 (NO2) cmꢀ1; 1H NMR (CDCl3): d
8.20–8.23 (m, 1H, phenyl H-4), 8.14 (s, 1H, phenyl H-2),
7.57–7.64 (m, 2H, phenyl H-5, H-6), 7.50 (s, 1H, H-3),
4.41 (s, 1H, H-5), 3.80 (s, 3H, OCH3), 2.82 (d,
J1;6 ¼ 11:1 Hz, 1H, H-1), 2.78 (s, 3H, NCH3), 2.10 (d,
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H-6).
Anal.
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C15H14Cl2N2O4: C, 50.44; H, 3.95; N, 7.84. Found: C,
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