Synthesis, rotamer orientation, and calcium channel modulation activities of alkyl and 2-phenethyl 1,4-dihydro-2,6-dimethyl-3-nitro-4-(3- or 6-substituted-2-pyridyl)-5-pyridinecarboxylates

Article abstract of DOI:10.1021/jm970529f

A group of racemic alkyl and 2-phenethyl 1,4-dihydro-2,6-dimethyl-3- nitro-4-(3- or 6-substituted-2-pyridyl)-5-pyridinecarboxylates (13a-q) was prepared using a modified Hantzsch reaction that involved the condensation of a 3- or 6-substituted-2-pyridinecarboxaldehyde (7a-j) with an alkyl or 2- phenethyl 3-aminocrotonate (11a-d) and nitroacetone (12). Nuclear Overhauser (NOE) studies indicated there is a significant rotamer fraction in solution where the pyridyl nitrogen is oriented above the 1,4-dihydropyridine ring, irrespective of whether a substituent is located at the 3- or 6-position. A potential H-bonding interaction between the pyridyl nitrogen free electron pair and the suitably positioned 1,4-dihydropyridine NH moiety may stablize this rotamer orientation. In vitro calcium channel antagonist and agonist activities were determined using guinea pig ileum longitudinal smooth muscle (GPILSM) and guinea pig left atrium (GPLA) assays, respectively. Compounds having an i-Pr ester substituent acted as dual cardioselective calcium channel agonists (GPLA)/smooth muscle-selective calcium channel antagonists (GPILSM), except for the C-4 3-nitro-2-pyridyl compound which exhibited an antagonist effect on both GPLA and GPILSM. In contrast, the compounds with a phenethyl ester group, which exhibited antagonist activity (IC₅₀ = 10^-5- 10^-7 M range) on GPILSM, were devoid of cardiac agonist activity on GPLA. Structure-activity relationships showing the effect of a substituent (Me, CF₃, C1, NO₂, Ph) at the 3- or 6-position of a C-4 2-pyridyl moiety and a variety of ester substituents (Me, Et, i-Pr, PhCH₂CH₂-) upon calcium channel modulation are described. Compounds possessing a 3- or 6-substituted- 2-pyridyl moiety, in conjuction with an i-Pr ester substituent, are novel 1,4-dihydropyridine calcium channel modulators that offer a new drug design approach directed to the treatment of congestive heart failure and may also be useful as probes to study the structure-function relationships of calcium channels.

Full text of DOI:10.1021/jm970529f

J . Med. Chem. 1998, 41, 1827-1837
1827
Syn th esis, Rota m er Or ien ta tion , a n d Ca lciu m Ch a n n el Mod u la tion Activities of
Alk yl a n d 2-P h en eth yl 1,4-Dih yd r o-2,6-d im eth yl-3-n itr o-4-(3- or
6-su bstitu ted -2-p yr id yl)-5-p yr id in eca r boxyla tes†
Nadeem Iqbal, Murthy R. Akula, Dean Vo, Wandikayi C. Matowe, Carol-Anne McEwen,
Michael W. Wolowyk,‡ and Edward E. Knaus*
Faculty of Pharmacy and Pharmaceutical Sciences, University of Alberta, Edmonton, Alberta, Canada T6G 2N8
Received August 12, 1997
A group of racemic alkyl and 2-phenethyl 1,4-dihydro-2,6-dimethyl-3-nitro-4-(3- or 6-substituted-
2-pyridyl)-5-pyridinecarboxylates (13a -q) was prepared using a modified Hantzsch reaction
that involved the condensation of a 3- or 6-substituted-2-pyridinecarboxaldehyde (7a -j) with
an alkyl or 2-phenethyl 3-aminocrotonate (11a -d ) and nitroacetone (12). Nuclear Overhauser
(NOE) studies indicated there is a significant rotamer fraction in solution where the pyridyl
nitrogen is oriented above the 1,4-dihydropyridine ring, irrespective of whether a substituent
is located at the 3- or 6-position. A potential H-bonding interaction between the pyridyl nitrogen
free electron pair and the suitably positioned 1,4-dihydropyridine NH moiety may stablize this
rotamer orientation. In vitro calcium channel antagonist and agonist activities were determined
using guinea pig ileum longitudinal smooth muscle (GPILSM) and guinea pig left atrium (GPLA)
assays, respectively. Compounds having an i-Pr ester substituent acted as dual cardioselective
calcium channel agonists (GPLA)/smooth muscle-selective calcium channel antagonists
(GPILSM), except for the C-4 3-nitro-2-pyridyl compound which exhibited an antagonist effect
on both GPLA and GPILSM. In contrast, the compounds with a phenethyl ester group, which
exhibited antagonist activity (IC50 ) 10-5-10-7 M range) on GPILSM, were devoid of cardiac
agonist activity on GPLA. Structure-activity relationships showing the effect of a substituent
(Me, CF3, Cl, NO2, Ph) at the 3- or 6-position of a C-4 2-pyridyl moiety and a variety of ester
substituents (Me, Et, i-Pr, PhCH2CH2-) upon calcium channel modulation are described.
Compounds possessing a 3- or 6-substituted-2-pyridyl moiety, in conjuction with an i-Pr ester
substituent, are novel 1,4-dihydropyridine calcium channel modulators that offer a new drug
design approach directed to the treatment of congestive heart failure and may also be useful
as probes to study the structure-function relationships of calcium channels.
The structure-activity relationships for Hantzsch
type 1,4-dihydropyridines, with respect to calcium chan-
nel antagonist-agonist modulation, have presented a
significant challenge.1-14 The calcium ion channel is an
important drug design target since it possesses specific
drug binding sites for both antagonist and agonist
ligands that are modulated by the closed or open
conformational state of the channel. Different states
of the channel have different affinities and/or access for
drugs, and drugs may exhibit both quantitative and
qualitative differences in structure-activity relation-
ships, including stereoselectivity between channel
states.14 Accordingly, ion channels can be viewed as
multiple drug binding receptors that typically have 4-8
discrete binding sites which may be individually linked
to each other and to the gating and permeation ma-
chinery of the ion channel by complex allosteric interac-
tions.15
dihydropyridine ring exists in a flat-boat conformation
with the C-4 aryl moiety in a pseudoaxial position and
orthogonal to the plane of the 1,4-dihydropyridine ring.
In addition, two rotamers may exist if the C-4 aryl ring
is substituted at its ortho or meta position (X * H). The
X-substituent either could then be on the same side as
the C-4H as in 1b [synperiplanar (sp) to the C-4H or
distal to the 1,4-dihydropyridine ring] or, following
rotation of the phenyl ring, could be oriented above the
1,4-dihydropyridine ring as in 1c [antiperiplanar (ap)
to the C-4H or proximal to the 1,4-dihydropyridine
ring].16 Although the rotation barrier about the C(4)-
C(phenyl) central C-C single bond is small, molecular
mechanics calculations for Hantzsch 1,4-dihydropyri-
dines show the rotational barrier separating the distal
(sp) and proximal (ap) rotamers is higher for a C-4
phenyl ring having an ortho-substituent relative to
analogues having a meta- or para-substituent.17 Ab
initio STO-3G calculations similarly showed that an
o-phenyl substituent also favors the sp rotamer orienta-
tion, although the energy difference or rotational barrier
between the sp and ap rotamers is not sufficiently large
to exclude the ap rotamer from participation in binding
to the calcium channel receptor.18 The observation that
the fraction of the sp rotamer in solution showed a
positive correlation with vasorelaxant activity and
1,4-Dihydropyridines of the nifedipine class [dialkyl
1,4-dih ydr o-2,6-dim et h yl-4-(su bst it u t ed-a r yl)-3,5-
pyridinedicarboxylates] are flexible molecules (1a ), in
which the C-4 aryl moiety and the C-3/C-5 ester sub-
stituents can rotate and the conformation of the 1,4-
dihydropyridine ring can change (Figure 1). The 1,4-
† Dedicated in the memory of Professor Michael Wolowyk.
‡ Deceased J anuary 31, 1992.
S0022-2623(97)00529-3 CCC: $15.00 © 1998 American Chemical Society
Published on Web 04/28/1998

1828 J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 11
Iqbal et al.
F igu r e 1. Rotation of the C-4 aryl moiety and the C-3/C-5 ester substituents (1a ) to give the two rotamers [synperiplanar (distal)
1b and antiperiplanar (proximal) 1c].
F igu r e 2. Structures of (S)-Bay K 8644, the isomeric isopropyl 1,4-dihydro-2,6-dimethyl-3-nitro-4-(pyridyl)-5-pyridinecarboxylates
2a -c, Bay K 8643, and nifedipine.
receptor binding affinity suggests the sp rotamer of
nonrigid unsymmetrically substituted 4-phenyl-1,4-di-
hydropyridine calcium antagonists is the receptor-bound
conformation.19
acted as calcium channel agonists on both cardiac and
smooth muscle. The (+)-2-pyridyl enantiomer (+)-2a
exhibited agonist activity on both cardiac and smooth
muscle, whereas the (-)-2-pyridyl enantiomer (-)-2a
exhibited cardiac agonist and smooth muscle antagonist
actions. It was therefore of interest to extend these
structure-activity data by replacing the isopropyl moi-
ety of 2a by a 2-phenethyl substituent and/or introduc-
ing a 3- or 6-substituent (CH3, CF3, Cl, NO2, C6H5) into
the 2-pyridyl ring since this novel type of 1,4-DHP
calcium channel modulator could provide a potentially
new approach directed toward the treatment of conges-
tive heart failure (CHF) and for use as probes to study
the structure-function relationships of calcium chan-
nels. We now report the synthesis of alkyl and 2-phen-
ethyl 1,4-dihydro-2,6-dimethyl-3-nitro-4-(3- or 6-substi-
tuted-2-pyridyl)-5-pyridinecarboxylates (13a -q), their
rotameric orientation, and their in vitro calcium channel
modulating actions on guinea pig smooth muscle and
left atrium.
A normal vs capsized DHP boat model was recently
proposed to explain structural and conformational
requirements for modulation of calcium channel action
where a left-hand-side alkoxy (cis) carbonyl interaction
is required for maximal DHP receptor affinity, and the
effect on channel action is determined by the orientation
of the 4-aryl moiety. Thus enantiomers having an up-
oriented pseudoaxial aryl group (normal DHP boat)
elicit antagonist activity, while enantiomers having a
down-oriented pseudoaxial aryl group (capsized DHP
boat) exhibit agonist activity.20 However, the issue of
antagonism or agonism is dependent not only on the
structure and stereochemistry of the 1,4-DHP but also
upon the state of the calcium channel due to its
membrane potential.15 This latter phenomenon is clearly
illustrated by the potent Ca2+ agonist (S)-Bay K 8644
(see Figure 2) which acts as an agonist at polarized
membrane potentials and as an antagonist at depolar-
ized membrane levels, respectively.21 Although the
interaction of calcium antagonists with Ca2+ has re-
ceived little attention, a recent study employing nicar-
dipine showed the predominant species to be a 2:1 drug:
Ca2+ sandwich complex that involved coordination of
Ca2+ to oxygen of the m-nitrophenyl substituent and the
carbonyl moiety of the C-3 ester substituent. Based on
this result, it was suggested that the Ca2+-bound form
of DHP drugs may constitute their biological active
species in the nonpolar milieu of a lipid bilayer.22
A novel third-generation class of isomeric 1,4-dihydro-
2,6-dim et h yl-3-n it r o-4-(pyr idyl)-5-pyr idin eca r box-
ylates (2a -c; see Figure 2) with different calcium
channel modulation activities was recently discovered.23
The 2-pyridyl isomer (()-2a acted as a dual cardio-
selective calcium channel agonist/smooth muscle-selec-
tive calcium channel antagonist. On the other hand,
the 3-pyridyl [(()-2b] and 4-pyridyl [(()-2c] isomers
Ch em istr y
The 3- and 6-substituted-2-pyridinecarboxaldehydes
7a -e, required for the modified Hantzsch 1,4-dihydro-
pyridine reaction, were prepared using a four-step
synthetic sequence as illustrated in Scheme 1. Thus,
oxidation of the 3- or 6-substituted-2-methylpyridines
3b-e with H2O2 in AcOH yielded the corresponding
N-oxide derivatives 4a -d in 55-89% yields. Reaction
of 4a -d with acetic anhydride afforded the respective
2-(acetoxymethyl)-3(or 6)-substituted-pyridines 5a -d in
75-81% yields. Hydrolysis of the acetate derivatives
5a -d with either 1 N NaOH or K2CO3/MeOH afforded
the corresponding 2-(hydroxymethyl)-3(or 6)-substituted-
pyridines 6a -d in 51-86% yields. In contrast, 3-chloro-
2-(hydroxymethyl)pyridine (6e) was prepared by oxida-
tion of 3-chloro-2-methylpyridine (3f) with KMnO4 to
yield 3-chloro-2-pyridinecarboxylic acid (5e; 45%) which
on treatment with ClCO2Et to form the mixed anhydride
and reduction with NaBH4 gave 6e (67%). Oxidation

Alkyl and Phenethyl Dihydropyridinecarboxylates
J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 11 1829
Sch em e 1a
a
Reagents and conditions: (a) benzene, C6H5B(OH)2 in EtOH, 2 M aqueous Na2CO3, Pd[P(Ph)3]4, reflux, 24 h; (b) AcOH, 35% H2O2,
70-80 °C, 12 h; (c) Ac2O, reflux, 1 h; (d) KMnO4, water, reflux, 22 h; (e) 1 N NaOH, 25 °C, 1.5 h (products 6a -c), K2CO3, MeOH, 25 °C,
1.5 h (product 6d ), or ClCO2Et, THF, Et3N, 5 °C, 30 min and then NaBH4, H2O, 10-15 °C, 4 h (product 6e); (f) dicyclohexylcarbodiimide,
DMF, H3PO4, 25 °C, 1.5 h (products 7a -c,e) or MnO2, CHCl3, 25 °C, 24 h (product 7d ).
Sch em e 2a
a
Reagents and conditions: (a) Et3N catalyst, 80 °C, 1 h; (b) NH3, MeOH, 25 °C, 6 h.
of the 2-(hydroxymethyl)-3(or 6)-substituted-pyridines
6a -e using either dicyclohexylcarbodiimide (DCC) or
MnO2 yielded the respective 3(or 6)-substituted-2-pyri-
dinecarboxaldehydes 7a -e (36-52%).
The Et3N-catalyzed reaction of 2-phenylethanol (9)
with diketene (8) afforded 2-phenethyl acetoacetate (10;
73%) which was elaborated to 2-phenethyl 3-amino-
crotonate (11d ; 90%) on treatment with NH3 in MeOH
(see Scheme 2).
The racemic alkyl or 2-phenethyl 1,4-dihydro-2,6-
dimethyl-3-nitro-4-(3- or 6-substituted-2-pyridyl)-5-pyri-
dinecarboxylates 13a -q were prepared by a modified
Hantzsch reaction. Accordingly, condensation of the
respective aldehyde (7a -j) with the respective alkyl or
2-phenethyl 3-aminocrotonate (11a -d ) and nitroacetone
(12) afforded the title compounds (13a -q) in 24-71%
yields as illustrated in Scheme 3 and summarized in
Table 1.
antagonists showed a positive potential in this region.25
In addition, the effect of aromatic substituents on the
C-4 phenyl ring of 1,4-dihydropyridine agonists and
antagonists is also different.26 These observations, in
conjunction with the dual cardioselective agonist/smooth
muscle-selective antagonist calcium channel-modulating
effects exhibited by isopropyl 1,4-dihydro-2,6-dimethyl-
3-nitro-4-(2-pyridyl)-5-pyridinecarboxylate
(2a ),23
prompted us to study analogues of 2a where the
isopropyl substituent is replaced by other alkyls or a
2-phenethyl substituent and a substituent is introduced
at the 3- or 6-position of the C-4 2-pyridyl moiety.
The nature (electronic properties, steric size) and
position (3 or 6) of the substituent on the 2-pyridyl ring
system was expected to be a determinant of the elec-
tronic charge distribution at the pyridyl ring carbons,
the global conformation of the molecule due to non-
bonded interactions between the C-3, C-4, and C-5
substituents, and the rotameric orientation and/or
preference (sp/ ap) of the substituted-2-pyridyl moiety.
These factors may provide an approach to optimize
calcium channel binding, calcium channel modulation,
and/or tissue specificity.
Resu lts a n d Discu ssion
The development of calcium channel modulators that
are useful for treating CHF will be dependent upon the
separation and/or elimination of their vasoconstrictor
effect from their cardiostimulant-positive inotropic prop-
erty.24 Differences in the molecular electrostatic po-
tentials between agonist and antagonist structures, with
respect to binding of the C-3 and C-5 DHP regions, have
been observed, which may provide a mechanism by
which the receptor differentiates between agonist and
antagonist ligands. In this regard, calcium channel
agonists have been shown to possess a strong negative
potential in the region of the C-3 nitro substituent, while
It has been suggested that molar refraction (MR)
values are a crude, but useful, measure of substituent
bulk (size) which have been used in some quantitative
structure-activity relationship (QSAR) studies.27
A
series of 1,4-dihydropyridines 13a -q were prepared
wherein the 3- or 6-substituent on the C-4 2-pyridyl
moiety possesses a broad range of MR values (H, 1.03;
CF3, 5.02; CH3, 5.65; Cl, 6.03; NO2, 7.36; C6H5-, 25.36).27
The van der Waals radi for H, Cl, and CH3 are 1.2, 1.8,

1830 J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 11
Iqbal et al.
Sch em e 3a
a
Reagents and conditions: (a) EtOH, 1 h at 25 °C and then 16 h at reflux (products 13a -e,g,h ,m ) or Me2CHOH, 9 h at 40 °C and then
13 h at 25 °C (products 13f,i-l,n -q).
1
and 2.0 Å, respectively. Examination of the H NMR
spectra for 13a -q indicated that the 1,4-DHP H-4
proton appeared in the δ 5.32-6.49 range (CDCl3). The
H-4 proton was always more shielded (higher field)
when a C-6 pyridyl R1-substituent was present (δ 5.32-
5.66 range) as compared to the same C-3 pyridyl R2-
solvent, compounds 13a ,h showed NOE enhancements
from the 1,4-DHP NH proton to the C-6 Me substituent
on the pyridyl ring of 1.6% and 3.0%, respectively.
However, a NOE from the NH hydrogen to the pyridyl
H-3 hydrogen of 13a or 13h was not observed (CDCl3,
22 °C), which suggests a rotamer in which the pyridyl
H-3 hydrogen is oriented above the 1,4-DHP moiety and
the pyridyl nitrogen atom is sp to the 1,4-DHP H-4
hydrogen either is not present or is a less predominant
rotamer in solution. Rovnyak et al.29 have elegantly
determined the fraction of ap rotamer by measurement
of NOEs from the NH hydrogen to an o-phenyl hydrogen
(interatomic distances of 3.2-3.5 Å) for Hantzsch 1,4-
1
substituent (δ 5.74-6.49 range). Low-temperature H
NMR studies (300 MHz) of 13a -q at -50 °C in CDCl3
did not give rise to any dual resonances. Although this
absence of dual resonances indicates the possibility that
a single rotamer and/or preference for the C-4 2-pyridyl
moiety exists in solution, it is equally plausible that the
rotation barrier is too small to stop rotation at -50 °C
or that there is a thermodynamic preference for one
rotamer regardless of the magnitude of the energy
barrier to rotation. However, Goldmann and Geiger28
reported that the two o-methyl resonances for dimethyl
1,4-dihydro-2,6-dimethyl-4-(2,4,6-trimethylphenyl)-3,5-
pyridinedicarboxylate appear as a broad singlet in
CDCl3 at 25 °C, coalescence occurred at -18 °C
(∆G(-18 °C) ) 51.1 kJ /mol), and two separate reso-
nances were observed at -50 °C. 1H NMR difference
nuclear Overhauser enhancement (NOE) studies were
performed for 13g and the three pairs of isomers 13a
and 13d , 13h and 13i, and 13p and 13q to acquire
information pertaining to the rotamer orientation of the
C-4 2-pyridyl moiety. The percent NOE enhancements
(DMSO-d6, 22 °C) clearly show that a significant rota-
mer fraction is present in which the pyridyl nitrogen
atom is oriented above the 1,4-DHP ring in all these
cases irrespective of whether the substituent (H, Me,
Ph) is located at the C-3 or C-6 position of the 2-pyridyl
moiety (see Figure 3).
1
DHPs. Variable temperature H NMR spectroscopy is
a useful method to study H-bonding interactions. Low-
ering temperature may stop NH exchange (gives rise
to a sharp, or coupled, NH resonance) which can
enhance H-bonding that results in a deshielding (down-
field shift) of the NH proton. Conversely, increasing
temperature may disrupt H-bonding resulting in a more
rapid rate of NH exchange (gives rise to a broader
resonance) that results in an upfield shift (shielding
effect) for the NH proton due to disruption of H-
bonding.30 Accordingly, it was also observed (1H NMR
spectra) that the chemical shift of the NH proton in
13a ,h in CDCl3 was highly temperature-dependent. For
example, the NH proton for 13a appeared at δ 10.28
(sharp singlet, 10 °C), 9.66 (sharp singlet, 22 °C), and
7.67 (broad singlet, 61 °C). Similarly, 13h showed NH
resonances at δ 10.13 (sharp singlet, 10 °C), 9.37 (sharp
singlet, 22 °C), and 8.11 (broad singlet, 50 °C). All other
resonances for 13a or 13h showed minor changes in
chemical shift positions of less than δ 0.09, irrespective
of temperature. These NH chemical shift dependence
data indicate that the NH group must be H-bonded
(sharp NH, more deshielded) at 10 and 22 °C and that
H-bonding is disrupted (broad NH, more shielded) upon
heating to 61 °C (13a ) or 50 °C (13h ).
Similar NOE enhancement studies (CDCl3, 22 °C)
were performed for 13a , 13h (see Figure 4) since the
H-bonding potential between the compound 13 and bulk
solvent differs significantly between CDCl3 and DMSO.
In contrast to the NOE studies using DMSO-d6 as

Alkyl and Phenethyl Dihydropyridinecarboxylates
J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 11 1831
F igu r e 3. Some NOE determinations to study the rotameric orientation of the 4-(2-pyridyl) moiety for the 1,4-dihydropyridine
compounds 13a ,d ,g-i,p ,q in DMSO-d6 at 22 °C.
occur in the ap orientation.6 Accordingly, the ap rota-
mer for Bay K 8643 may be stablized by an electronic
attraction between the nitro group on the phenyl ring
and the 1,4-DHP moiety. In methyl 1,4-dihydro-2,6-
dimethyl-3-nitro-4-(aryl)-5-pyridinecarboxylates such as
Bay K 8644 and Bay K 8643, the structure is stablized
by a H-bond (2.94 ( 0.04 Å) between the NH and the
3-nitro oxygen atom which is cis to the C(2)dC(3) double
bond.8 The amine group of Bay K 8644 is significantly
more acidic, due to electron delocalization, and is more
capable of forming a stronger H-bond than the related
antagonists having ester substituents at the 3- and
5-positions of the 1,4-DHP ring.6 It was therefore of
interest to investigate the conformation of 13a , which
exhibited the best calcium channel agonist activity on
guinea pig left atrium, to gain further information
pertaining to the H-bonding effect observed for the NH
hydrogen in CDCl3 at 22 °C and the rotamer orientation
of the pyridyl ring system. Weaver et al.31 have shown
that AM1 semiempircal molecular orbital conforma-
tional analyses of 1,4-DHP calcium channel modulators
are best suited to the modeling of DHP geometry.31
F igu r e 4. Some NOE determinations to study the rotameric
orientation of the 4-(6-methyl-2-pyridyl) moiety for the 1,4-
dihydropyridine compounds 13a ,h in CDCl3 at 22 °C.
Some interatomic distances for the AM1-minimized
structure of 13a are shown in Figure 5. The distance
between the amine and pyridyl nitrogen atoms (3.47 Å)
is shorter than that between the amine nitrogen and
nitro oxygen atom that is cis to the C(2)dC(3) double
bond (4.18 Å) or the carbonyl oxygen atom (4.49 Å).
These data suggest there may be a possibility for the
amine NH hydrogen atom to H-bond to the pyridyl
nitrogen free electon pair. A H-bond of this type would
position the NH hydrogen closer to the pyridyl nitrogen
free electron pair where the donor NH distance is less
than 3.2 Å and the angle made by covalent bonds to the
donor and acceptor atoms is less than 120°. Although
the preferred geometry of the amine nitrogen is trigonal
with the NH hydrogen projected away from the DHP
ring, the formation of a H-bond between the NH and
pyridyl nitrogen free electron pair may compensate for
the decrease in energy resulting from a change in the
It has been reported, using a group of dimethyl 1,4-
dihydro-2,6-dimethyl-4-(2-halogenophenyl)-3,5-pyridinedi-
carboxylates, that the fraction of sp rotamer (fs) in-
creased with increasing van der Waals radius of the
halogen substituent (F, 0.69; Cl, 0.84; Br, 0.92; I, 0.95)
in solution.19 The calcium channel antagonist nife-
dipine29 and agonist Bay K 86446 both exist as sp
rotamers. In contrast, the 4-(3-nitrophenyl) moiety
present in the agonist Bay K 8643 has the unexpected
ap rotamer orientation (X-ray structure), which places
the m-nitro substituent on the phenyl ring directly
above the 1,4-DHP ring (see structures in Figure 2).8
The restricted 2-(trifluoromethyl)phenyl ring sp orienta-
tion of Bay K 8644 in the solid state is primarily due to
steric contacts between the CF3 fluorine atoms and the
carbonyl ester and nitro oxygen atoms which would

1832 J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 11
Iqbal et al.
respectively. The calcium channel antagonist activities
of 13a -q determined as the concentration required to
produce 50% inhibition of GPILSM contractility are
presented in Table 1. Compounds 13a -q exhibited
weaker antagonist activity (IC50 ) 10-5-10-7 M range)
than the reference drug nifedipine (IC50 ) 1.40 × 10-8
M). The R3-ester substituent was a determinant of
antagonist activity for compounds possessing a C-4
6-methyl-2-pyridyl moiety where the potency order was
Me (13c) > PhCH2CH2 (13h ) > Et (13b) and i-Pr (13a ).
A similar activity profile was observed for compounds
possessing a C-4 6-chloro-2-pyridyl moiety [PhCH2CH2-
(13l) > i-Pr (13e)]. In contrast, for compounds having
a C-4 3-nitro-2-pyridyl moiety, the i-Pr ester (13f) was
more active than the PhCH2CH2- ester (13o). In the
isopropyl ester group of compounds, the nature of the
R1-substituent at the 6-position [Me (13a ) ≈ Cl (13e)],
or the R2-substituent at the 3-position [Me (13d ) ≈ NO2
(13f)], of the 2-pyridyl moiety was not a determinant of
antagonist activity. In the phenethyl ester group of
compounds 13g-q, incorporation of a substituent (Me,
CF3, Cl, NO2, Ph) at either the 3- or 6-position of the
C-4 2-pyridyl moiety decreased antagonist activity (IC50
) 1.51 × 10-6 to >5.96 × 10-5 M range) relative to the
unsubstituted 2-pyridyl compound 13g (IC50 ) 6.39 ×
10-7 M). In this latter series of compounds 13h -q, the
nature of the R1-substituent at the 6-position of the
2-pyridyl ring (13h ,j,l,n ,p ) had a small effect on an-
F igu r e 5. Some interatomic distances for the AM1-minimized
structure of isopropyl 1,4-dihydro-2,6-dimethyl-3-nitro-4-(6-
methyl-2-pyridyl)-5-pyridinecarboxylate (13a ) (panel A) and
perspective of the AM1-minimized structure for 13a (panel B).
NH orientation. Accordingly, a H-bond between the
pyridyl nitrogen free electron pair and the 1,4-DHP NH,
which would place the pyridyl nitrogen atom above the
1,4-DHP ring, would remove the requirement for a high-
energy rotational barrier that would be necessary to
exclusively, or preferentially, favor this rotameric ori-
entation. It is also possible that an electronic attraction
between the pyridyl ring and the 1,4-DHP moiety would
increase the fraction of this rotamer population. The
interatomic distance between the amine nitrogen and
pyridyl CH3 of 4.81 Å is consistent with the NOE effect
(1.6%) shown in Figure 4. For the purpose of compari-
son, the distance between the amine nitrogen and H-3
on the pyridyl ring, when 13a is minimized (AM1) with
the pyridyl nitrogen sp to H-4, was 3.26 Å. The
observation that no NOE effect was observed from NH
to the pyridyl H-3 in 13a also suggests that 13a exists
preferentially as the ap rotamer shown in Figure 4. The
nitro group of 13a in the AM1-minimized structure is
in the plane of the C(2)dC(3) bond to which it is
attached since the C(2)dC(3)-N-O (cis-oxygen) and
C(2)dC(3)-N-O (trans-oxygen) torsion angles are -2.9°
and 176.2°, respectively. AM1 geometry optimizations
for compounds 13a ,d ,g-i,p ,q (see ap rotamer orienta-
tion shown in Figure 3) were performed for both the
preferred ap rotamer (pyridyl N anti to H-4) and the
less favored sp rotamer (pyridyl N syn to H-4). In all
cases, the preferential ap rotamer orientation showed
a thermodynamic preference, viz.: 13a (6-Me), 3.00 kcal;
13d (3-Me), 7.47 kcal; 13g (3-H), 3.54 kcal; 13h (6-Me),
3.59 kcal; 13i (3-Me), 7.92 kcal; 13p (6-phenyl), 2.96
kcal; and 13q (3-phenyl), 6.37 kcal. The observation
that the energy differences between the two rotamer
orientations were greater for 13i (3-Me) and 13q (3-
phenyl) is attributed to the larger steric interactions
between the 1,4-dihydropyridine C-3, C-4, and C-5
substituents. Thermodynamic preferences g 3 kcal are
considered to be significant with respect to rotamer
orientation. The results of these studies do not indicate
whether the NH is H-bonded to the cis-oxygen atom of
the 3-nitro substituent or the pyridyl nitrogen free
electron pair. An X-ray structure for 13a will be
required to distinguish between these two potential
alternatives.
tagonist activity (IC50 ) 1.41 × 10-6 to 9.98 × 10-6
M
range). In contrast, the effect of a R2-substituent at the
3-position of the 2-pyridyl ring (13i,k ,m ,o,q) produced
a larger effect on antagonist activity (IC50 ) 3.35 × 10-6
to >5.96 × 10-5 M range) where the relative potency
order was Ph g Cl and Me > NO2 > CF3. The effect
which the position of the substituent on the C-4 2-pyr-
idyl moiety (6-R1 versus 3-R2) had upon antagonist
activity was variable where R2 > R1 [Me (13d ) > Me
(13a ); Me (13i) > Me (13h ); Ph (13q > Ph (13p )], but
in other cases R1 > R2 [CF3 (13j) > CF3 (13k ); Cl (13l)
> Cl (13m ); NO2 (13n ) > NO2 (13o)]. These isomeric
differences in antagonist activities for the ortho-like-
R2-substituent that is sp to the 1,4-DHP H-4 versus the
meta-like-R1-substituent that is ap to the 1,4-DHP H-4
(see Figure 2) could be due to a number of possibilities
which include differences in the drug-receptor interac-
tion or preferential affinity or access to the R1-subunit
binding site of the L-type calcium channel.14
In vitro calcium channel agonist (positive inotropic)
activities were determined as the molar concentration
eliciting 50% (EC50) of the maximum contractile re-
sponse produced by the racemic test drug on GPLA, as
determined from the dose-response curve. In this
assay, the reference drugs (()-Bay K 8644 and (()-2-
pyridyl 2a showed agonist EC50 values of 7.7 × 10-7 and
9.67 × 10-6 M, respectively.23 A comparison of the C-4
6-methyl-2-pyridyl compounds 13a -c showed the R3-
ester substituent was a determinant of GPLA agonist
activity where the activity profile was i-Pr (13a , EC50
) 1.81 × 10-6 M) > Et (13b, EC50 ) 1.23 × 10-5 M) >
Me (13c, 10% increase in contractile force at 4.50 × 10-5
M). In the R3-i-Pr ester series, the 6-methyl-2-pyridyl
compound 13a (EC50 ) 1.81 × 10-6 M) was a more
potent agonist than the 3-methyl-2-pyridyl isomer 13d
(EC50 ) 9.97 × 10-6 M). These latter results, in
The in vitro calcium channel antagonist- and agonist-
modulating activities of racemic compounds 13a -q were
determined using guinea pig ileum longitudinal smooth
muscle (GPILSM) and guinea pig left atrium (GPLA),

Alkyl and Phenethyl Dihydropyridinecarboxylates
J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 11 1833
Ta ble 1. Physical and Calcium Channel Antagonist Activities of Alkyl or 2-Phenethyl 1,4-Dihydro-2,6-dimethyl-3-nitro-4-(3- or
6-substituted-2-pyridyl)-5-pyridinecarboxylates 13a -q
mp
(°C)
yield
(%)
calcium channel
antagonist act: IC50b
calcium channel
agonist act: EC50
c
compd
13a
13b
13c
13d
13e
13f
13g
13h
13i
13j
13k
13l
13m
13n
13o
13p
13q
nifedipine
2a e
R1
Me
Me
Me
H
Cl
H
H
Me
H
CF3
H
Cl
H
NO2
H
R2
R3
cryst. solvent
formulaa
H
H
H
i-Pr
Et
Me
i-Pr
i-Pr
EtOAc-hexane 189-190 53 C17H21N3O4
2.51 ( 0.35 × 10-5 (5) 1.81 ( 0.92 × 10-6 (3)
1.72 ( 0.12 × 10-5 (3) 1.23 ( 0.58 × 10-5 (3)
2.29 ( 0.10 × 10-6 (3) weak agonistd
2.82 ( 0.66 × 10-6 (3) 9.97 ( 1.87 × 10-6 (3)
1.67 ( 0.57 × 10-5 (3) 5.96 ( 2.13 × 10-6 (3)
3.77 ( 1.86 × 10-6 (3) weak antagonist
6.39 ( 2.63 × 10-7 (3)
EtOAc-hexane 170-171 33
EtOAc-hexane 199-200 43
C
C
16H19N3O4
16H19N3O4
Me
H
NO2 i-Pr
EtOAc-hexane 240-241 29 C17H21N3O4
EtOAc-hexane 173-175 71
C16H18ClN3O4
EtOAc-hexane 205-206 27 C16H18N4O6
H
H
PhCH2CH2- EtOAc-hexane 184-185 24 C21H21N3O4
PhCH2CH2- EtOAc-ether
PhCH2CH2- EtOAc
193-194 73 C22H23N3O4
233-235 35 C22H23N3O4
9.98 ( 0.56 × 10-6 (3)
Me
H
CF3
H
Cl
H
5.43 ( 0.51 × 10-6 (3)
PhCH2CH2- EtOAc-hexane 134-135 37 C22H20F3N3O4 1.41 ( 0.24 × 10-6 (3)
PhCH2CH2- EtOAc
207-209 33 C22H20F3N3O4 >5.98 × 10-5 (3)
PhCH2CH2- EtOAc-hexane 167-168 53 C21H20ClN3O4
1.51 ( 0.06 × 10-6 (3)
PhCH2CH2- EtOAc-hexane 209-211 48 C21H20ClN3O4
5.17 ( 0.76 × 10-6 (3)
PhCH2CH2- EtOAc
171-172 28 C21H20N4O6
205-206 30 C21H20N4O6
80-81
4.74 ( 0.26 × 10-6 (3)
a
NO2 PhCH2CH2- EtOAc
PhCH2CH2- CHCl3-hexane
7.77 ( 0.61 × 10-5 (3)
C6H5- H
H
45 C27H25N3O4
8.38 ( 0.73 × 10-6 (3)
C6H5- PhCH2CH2- EtOAc-hexane 207-209 44 C27H25N3O4
3.35 ( 0.08 × 10-6 (3)
1.40 ( 0.19 × 10-8 (18)
4.87 ( 2.06 × 10-6 (3) 9.67 ( 1.27 × 10-6 (3)
a
b
Microanalytical analyses were within (0.4% of theoretical values, except for compound 13o: N, calcd, 13.20; found, 12.77. The
molar concentration of antagonist test compound causing a 50% decrease in the slow component or tonic contractile response (IC50
(
SEM) in guinea pig ileal longitudinal smooth muscle by the muscarinic agonist carbachol (1.6 × 10-7 M) was determined graphically
from the dose-response curve. The number of experiments is shown in parentheses. c The molar concentration of the agonist test compound
causing a 50% increase of the maximum contractile response (EC50 ( SEM) on guinea pig left atrium was determined graphically from
d
the dose-response curves. The number of experiments is shown in parentheses. A 10% increase in contractile force was observed at
4.50 × 10-5 M. e Data for racemic 2a taken from Vo et al.23
conjunction with the observation that the 6-chloro-2-
pyridyl 13e (EC50 ) 5.96 × 10-6 M) exhibited a positive
inotropic agonist effect, whereas the 3-nitro-2-pyridyl
13f exhibited a negative inotropic effect on GPLA,
suggest that a substituent at the 6-position of the
2-pyridyl moiety provides superior cardiac agonist activ-
ity compared to compounds having a 3-substituted-2-
pyridyl moiety. A group of R3-phenethyl ester com-
pounds (13g-q), having Me, CF3, Cl, NO2, and Ph
substituents at either the 3- or 6-position of the C-4
2-pyridyl moiety, was investigated as cardiac agonists
in an attempt to increase the dual cardiac agonist/
smooth muscle potency profile since the C-4 2-pyridyl
compound 13g was the most potent antagonist on
GPILSM (IC50 ) 6.39 × 10-7 M) among the group of
compounds 13a -q. However, all of the R3-phenethyl
esters 13h -q, including the unsubstituted 2-pyridyl
compound 13g, were devoid of cardiac agonist activity
on GPLA. The most potent agonist on GPLA 13a ,
having a C-4 6-methyl-2-pyridyl moiety and an isopropyl
ester group, was 2-3-fold less active than (()-Bay K
8644.
cate a significant rotamer fraction exists in solution
where the pyridyl nitrogen atom is oriented above the
1,4-DHP ring, irrespective of whether a substituent is
located at the 3- or 6-pyridyl position. This rotamer
orientation may possibly be the result of a H-bonding
interaction between the pyridyl nitrogen free electron
pair and the suitably positioned 1,4-DHP NH moiety.
The absence of a second rotamer in which the pyridyl
nitrogen atom is sp to the DHP H-4 hydrogen and the
pyridyl H-3 hydrogen is oriented above the 1,4-DHP ring
has not been proven. However, the failure to observe a
NOE effect from the NH hydrogen to the pyridyl H-3
hydrogen indicates this second rotamer is certainly less
predominant, if present in solution. The orientation of
the 6-substituted-2-pyridyl group differs from that of an
ortho-substituted-phenyl ring in Hantzsch 1,4-DHP
calcium channel antagonists since the rotamer where
the o-phenyl ring substituent is sp to the 1,4-DHP H-4
is generally thermodynamically more preferential.19
Isopropyl 1,4-dihydro-2,6-dimethyl-3-nitro-4-(6-methyl-
2-pyridyl)-5-pyridinecarboxylate (13a ), a novel type of
1,4-DHP calcium channel modulator, possesses the most
favorable activities and function profile (GPILSM an-
Su m m a r y
tagonist, IC50 ) 2.51 × 10-5 M; GPLA agonist, EC50
)
1.81 × 10-6 M). Compounds such as 13a offer a
potentially new approach in drug design directed toward
the treatment of congestive heart failure, and it could
be a useful probe to investigate the structure-function
relationship of calcium channels.
The alkyl and 2-phenethyl 1,4-dihydro-2,6-dimethyl-
3-nitro-4-(3- or 6-substituted-2-pyridyl)-5-pyridinecar-
boxylates 13a -q constitute a novel group of compounds
with different calcium channel modulation activities.
Nuclear Overhauser enhancement (NOE) studies indi-

1834 J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 11
Iqbal et al.
Gen er a l Met h od for t h e P r ep a r a t ion of 2-(Acet oxy-
m eth yl)-3(or 6)-su bstitu ted -p yr id in es 5a -d . A solution
of the 2-methyl-1-oxido-3(or 6)-substituted-pyridine (4a , 4b,
4c or 4d ; 6 mmol) in acetic anhydride (4.32 g, 42 mmol, 4 mL)
was refluxed for 1 h using a modified literature procedure.34
Ethanol (3 mL) was added to the reaction mixture, and the
reaction was allowed to proceed at reflux for 10 min. The
reaction mixture was cooled in an ice-water bath, poured onto
water (10 mL), and neutralized with 10% aqueous NaHCO3.
Extraction with ether (2 × 25 mL), washing the extract with
brine solution (10 mL), drying the organic fraction (Na2SO4),
and removal of the solvent in vacuo gave a residue. Purifica-
tion of the residue by silica gel column chromatography using
EtOAc-hexane (30:70, v/v) as eluent afforded the respective
product 5a (80%), 5b (75%), 5c (81%), or 5d (77%) as an oil
which was subsequently used for the preparation of 6a -d .
Representative spectral data (IR, 1H NMR) for compounds
5b,5c are provided since the spectral data are qualitatively
similar.
Exp er im en ta l Section
Melting points were determined using a Thomas-Hoover
capillary apparatus and are uncorrected. 1H NMR spectra
were recorded and nuclear Overhauser enhancement (NOE)
experiments were performed using a Bruker AM-300 spec-
trometer (300 MHz). The assignment of exchangeable protons
(NH, OH) was confirmed by the addition of D2O. The NOE
studies were performed under steady-state conditions using
the Bruker NOE DIFF.AU software program (signal:noise
ratio of 136 for a single pulse). DMSO-d6 was dried using
molecular sieves (type 3A, 1.6-mm pellets) and degassed by
passage of dry argon gas at 22 °C just prior to use. CDCl3
was similarly dried, treated with neutral alumina to remove
acidic impurities, and degassed likewise just prior to use.
Molecular tumbling time was not altered. Infrared spectra
were acquired using a Nicolet IR-500 Series II spectrometer.
Silica gel column chromatography was carried out using Merck
7734 (60-200 mesh) silica gel. Microanalyses were within (
0.4% of theoretical values for all elements listed, unless
otherwise stated. 2,3-Lutidine (3d ), 6-chloro-2-methylpyridine
(3e), 6-methyl-2-pyridinecarboxaldehyde (7f), and alkyl 3-ami-
nocrotonates (11a -c) were purchased from the Aldrich Chemi-
cal Co. 3-Bromo-2-methylpyridine (3a ),32 2-methyl-6-phenyl-
pyridine (3c),33 3-chloro-2-methylpyridine (3f),32 3-(trifluoro-
methyl)-2-pyridinecarboxaldehyde (7g),34 6-(trifluoromethyl)-
2-pyridinecarboxaldehyde (7h ),34 3-nitro-2-pyridinecarboxal-
dehyde (7i),34 6-nitro-2-pyridinecarboxaldehyde (7j),34 and
nitroacetone (12)35 were prepared according to the reported
procedures. The semiempirical AM1-minimized structure of
13a was determined using the HyperChem molecular visual-
ization and simulation program, Release 4 (Hypercube Inc.,
Waterloo, Canada).
2-(Acetoxym eth yl)-6-p h en ylp yr id in e (5b): IR (neat)
1
1753 (CdO) cm-1; H NMR (CDCl3) δ 2.20 (s, 3H, CH3), 5.32
(s, 2H, CH2), 7.30-8.02 (m, 8H, phenyl and pyridyl hydrogens).
2-(Acetoxym eth yl)-3-m eth ylp yr id in e (5c): IR (neat)
1737 (CdO) cm-1 1H NMR (CDCl3) δ 2.16 (s, 3H, COCH3),
;
2.34 (s, 3H, C-3 CH3), 5.11 (s, 2H, CH2), 7.14 (dd, J 4,5 ) 8.0
Hz, J 5,6 ) 4.5 Hz, 1H, H-5), 7.46 (d, J 4,5 ) 8.0 Hz, 1H, H-4),
8.40 (d, J 5,6 ) 4.5 Hz, 1H, H-6).
3-Ch lor o-2-p yr id in eca r boxylic Acid (5e). Potassium
permanganate (1.58 g, 10 mmol) was added to a mixture of
3-chloro-2-methylpyridine (3f; 1.27 g, 10 mmol) and water (45
mL) according to the method of Ashimori et al.,34 and the
reaction mixture was refluxed for 1.5 h. An additional aliquot
of KMnO4 (1.58 g, 10 mmol) was added, and the reaction was
allowed to proceed for 20 h at reflux temperature prior to
cooling to 25 °C. The reaction mixture was filtered to remove
the precipitated MnO2, and the volume of the filtrate was
reduced to 50% of its original volume in vacuo. Acidification
of the clear solution obtained with 35% (w/v) HCl to pH 3,
extraction with EtOAc (2 × 50 mL), drying the EtOAc extracts
(Na2SO4), and removal of the solvent in vacuo afforded 5e (706
mg, 45%): mp 120-124 °C; IR (KBr) 2491-2857 (CO2H), 1712
2-Meth yl-3-p h en ylp yr id in e (3b). A solution of phenyl-
boronic acid (9.90 g, 27 mmol) in EtOH (18 mL), aqueous
Na2CO3 (36 mL of 2 M), and Pd[P(Ph)3]4 (1.26 g, 10.8 mmol)
were added to a solution of 3-bromo-2-methylpyridine (3a ; 1.55
g, 9.0 mmol), prepared from 3-amino-2-methylpyridine,36 in
benzene (90 mL) with stirring using a modified procedure.37
The heterogeneous mixture obtained was purged with nitrogen
and heated at reflux with stirring for 24 h. After cooling to
25 °C, the organic layer was separated and the aqueous
solution was extracted with ether (2 × 100 mL). The combined
organic solutions were dried (MgSO4), the solvent was removed
in vacuo, and the residue was distilled to yield 3b as an oil
(1.07 g, 70%): bp 75-77 °C/1 mmHg (lit.38 bp 67-68 °C/0.5
(CdO) cm-1; 1H NMR (CDCl3) δ 7.54 (dd, J 4,5 ) 8.0 Hz, J 5,6
)
4.5 Hz, 1H, H-5), 8.04 (d, J 4,5 ) 8.0 Hz, 1H, H-4), 8.52 (d, J 5,6
) 4.5 Hz, 1H, H-6). The product 5e was used in a subsequent
reaction for the preparation of compound 6e.
1
Gen er a l Meth od for th e P r ep a r a tion of 2-(Hyd r oxy-
m eth yl)-3(or 6)-su bstitu ted -p yr id in es 6a-d . A mixture of
a 2-(acetoxymethyl)-3(or 6)-substituted-pyridine (5a , 5b, or 5c;
5 mmol), 1 N NaOH (6 mL), and MeOH (12 mL) was stirred
at 25 °C for 1.5 h according to a literature method,34 and the
reaction mixture was poured onto water (30 mL). Extraction
with EtOAc (2 × 50 mL), washing the EtOAc extract with
brine (10 mL), drying the EtOAc fraction (Na2SO4), and
removal of the solvent in vacuo gave a residue. Purification
of the residue by silica gel column chromatography using
EtOAc-hexane (40:60, v/v) as eluent afforded the respective
product 6a (86%), 6b (55%), or 6c (81%) as oils which were
subsequently used for the preparation of the respective
products 7a -c. Product 6d was prepared (51%) using a
similar procedure by treatment of 5d with K2CO3 in MeOH,
in the place of 1 N NaOH used for the preparation of 6a -c as
described above. Representative 1H NMR spectral data for
compounds 6a ,d are provided since the spectral data for 6a -d
are qualitatively similar.
mmHg); H NMR (CDCl3) δ 2.51 (s, 3H, CH3), 7.16-7.56 (m,
7H, phenyl hydrogens, pyridyl H-4 and H-5), 8.50 (dd, J 5,6
5.0 Hz, J 4,6 ) 2.0 Hz, 1H, pyridyl H-6).
)
Gen er a l Meth od for th e P r ep a r a tion of 2-Meth yl-1-
oxid o-3(or 6)-su bstitu ted -p yr id in es 4a -d . Hydrogen per-
oxide (1 mL of 35%, w/v, 10 mmol) was added to a solution of
the pyridine compound (3b, 3c, 3d , or 3e; 10 mmol) in glacial
AcOH (6 mL), and the mixture was heated at 70-80 °C with
stirring for 3 h according to the method of Ochiai.39 An
additional aliquot of 35% (w/v) H2O2 (1 mL) was added, and
the reaction was allowed to proceed for 9 h at 70-80 °C. The
volume of the reaction mixture was reduced in vacuo, water
(2 mL) was added, the mixture was concentrated in vacuo, and
the residue was made alkaline using dry Na2CO3. Chloroform
(5 mL) was added, this mixture was allowed to stand at 25 °C
for 5 min, and the insoluble Na2CO3 and NaOAc were removed
by filtration. Drying the filtrate (Na2SO4) and removal of the
solvent in vacuo gave the target product 4a (85%), 4b (60%),
4c (89%), or 4d (55%) as oils that were used in subsequent
reactions for the preparation of products 5a -d , respectively.
Representative 1H NMR spectral data for compounds 4a ,4d
are provided since the spectral data are qualitatively similar.
2-Meth yl-1-oxido-3-ph en ylpyr idin e (4a): 1H NMR (CDCl3)
δ 2.49 (s, 3H, CH3), 7.18-7.50 (m, 7H, phenyl hydrogens, H-3,
H-4), 8.32 (d, J 5,6 ) 4.5 Hz, 1H, H-6).
2-(H yd r oxym et h yl)-3-p h en yp yr id in e (6a ): 1H NMR
(CDCl3) δ 4.60 (s, 1H, OH), 4.68 (s, 2H, CH2), 7.28-7.50 (m,
6H, phenyl hydrogens, H-5), 7.62 (dd, J 4,5 ) 8.0 Hz, J 4,6 ) 2.0
Hz, 1H, H-4), 8.60 (d, J 5,6 ) 4.5 Hz, J 4,6 ) 2.0 Hz, 1H, H-6).
6-Ch lor o-2-(h yd r oxym eth yl)p yr id in e (6d ): 1H NMR
(CDCl3) δ 3.60 (s, 1H, OH), 4.74 (s, 2H, CH2), 7.24 (d, J 3,4
)
6-Ch lor o-2-m et h yl-1-oxid op yr id in e (4d ): 1H NMR
(CDCl3) δ 2.46 (s, 3H, CH3), 7.03 (dd, J 3,4 ) J 4,5 ) 8.0 Hz, 1H,
H-4), 7.15 (d, J 3,4 ) 8.0 Hz, 1H, H-3), 7.31 (d, J 4,5 ) 8.0 Hz,
1H, H-5).
8.0 Hz, 1H, H-3), 7.29 (d, J 4,5 ) 8.0 Hz, 1H, H-5), 7.64 (dd, J 3,4
) 8.0 Hz, J 4,5 ) 8.0 Hz, 1H, H-4).
3-Ch lor o-2-(h yd r oxym eth yl)p yr id in e (6e). A solution of
ethyl chloroformate (0.54 g, 5 mmol) in THF (2 mL) was added

Alkyl and Phenethyl Dihydropyridinecarboxylates
J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 11 1835
(neat) 3451 (NH2), 1663 (CdO), 1620 (CdC) cm-1 1H NMR
(CDCl3) δ 1.90 (s, 3H, CH3), 2.96 (t, J ) 7.0 Hz, 2H, CH2Ph),
4.28 (t, J ) 7.0 Hz, 2H, OCH2), 4.33 (s, 1H, dCH), 7.20-7.36
(m, 5H, phenyl hydrogens), 7.80 (br s, 2H, NH2).
to a solution of 3-chloro-2-pyridinecarboxylic acid (5e; 0.79 g,
5 mmol) and Et3N (0.5 g, 5 mmol) in THF (8 mL) at 5 °C during
30 min with stirring, according to the procedure of Ishizumi
et al.,40 and then the reaction was allowed to proceed for 30
min at 5 °C with stirring. The white precipitate (Et3N+Cl-)
was filtered and washed with THF (5 mL). The combined
filtrate and THF wash solution were added slowly during 30
min to a solution of NaBH4 (0.473 g, 12.5 mmol) in water (4
mL) at 10-15 °C with external cooling. A rapid evolution of
gas was observed after addition of the latter solutions was
completed. The reaction mixture was stirred for 4 h at 25 °C
prior to acidification with 10% (w/v) HCl which separated into
two layers. The aqueous solution was extracted with ether (2
× 30 mL), and the combined ether extracts and organic THF
layer were washed consecutively with 10% (w/v) NaOH and
water. Drying the organic fraction (Na2SO4) and removal of
the solvent in vacuo gave a residue that was purified by silica
gel column chromatography using EtOAc-hexane (30:70, v/v)
as eluent to afford 6e as an oil (0.48 g, 67%); IR (neat) 3172
;
Gen er a l Meth od for th e P r ep a r a tion of Alk yl or
2-P h en et h yl 1,4-Dih yd r o-2,6-d im et h yl-3-n it r o-4-(3- or
6-su bstitu ted -2-p yr id yl)-5-p yr id in eca r boxyla tes 13a -q.
A mixture of the respective aldehyde (7a -j; 1 mmol), either
an alkyl 3-aminocrotonate (11a , 11b, or 11c; 1 mmol) or
2-phenethyl 3-aminocrotonate (11d ; 1 mmol), and nitroacetone
(12; 103 mg, 1 mmol) in 2-propanol (5 mL) was stirred at 40
°C for 9 h and then at 25 °C for 13 h (products 13f,i-l,n -q).
For products 13a -e,g,h ,m , equimolar quantities of 7, 11, and
12 were used but the reaction was allowed to proceed for 1 h
at 25 °C and then for 16 h at reflux using EtOH as solvent.
Removal of the solvent in vacuo gave a residue which was
purified by silica gel column chromatography using EtOAc-
hexane (70:30, v/v) for compounds 13a -f,j,n ,p or EtOAc-
hexane (90:10, v/v) for products 13g-i,k -m ,o,q to afford the
respective product 13a -q. The recrystallization solvent, mp,
and % yield for products 13a -q are listed in Table 1. The
spectral data (IR, 1H NMR) for representative products
13a ,d ,g-j,m ,p ,q are listed below.
1
(OH) cm-1; H NMR (CDCl3) δ 4.04 (s, 1H, OH), 4.78 (s, 2H,
CH2), 7.20 (dd, J 4,5 ) 8.0 Hz, J 5,6 ) 4.5 Hz, 1H, H-5), 7.66 (d,
J 4,5 ) 8.0 Hz, 1H, H-4), 8.44 (d, J 5,6 ) 4.5 Hz, 1H, H-6).
Gen er a l Met h od for t h e P r ep a r a t ion of 3(or 6)-
Su bstitu ted -2-p yr id in eca r boxa ld eh yd es 7a-c,e). A solu-
tion of anhydrous H3PO4 in DMSO (1.5 mL of 1.0 M) was added
to a solution of the 3- or 6-substituted-2-(hydroxymethyl)-
pyridine (6a , 6b, 6c, or 6e; 3 mmol) and N,N′-dicyclohexyl-
carbodiimide (1.86 g, 9 mmol) in DMSO (7 mL), and the
reaction was allowed to proceed with stirring at 25 °C for 1.5
h. The precipitated dicyclohexylurea was filtered, the filtered
solid was washed with ether (15 mL) and water (15 mL), and
the aqueous wash was extracted with ether (2 × 30 mL). The
combined organic solutions were washed with brine (10 mL),
the organic fraction was dried (Na2SO4), and the solvent was
removed in vacuo. The residue obtained was purified by silica
gel column chromatography using ether-hexane (40:60, v/v)
as eluent to afford the respective product 7a (36%), 7b (40%),
7c (52%), or 7e (47%) as an oil. Representative spectral data
(IR, 1H NMR) for compounds 7b,c are provided since the
spectral data for 7a -c,e are qualitatively similar.
Isop r op yl 1,4-d ih yd r o-2,6-d im eth yl-3-n itr o-4-(6-m eth -
yl-2-p yr id yl)-5-p yr id in eca r boxyla te (13a ): IR (KBr) 3057
1
and 3180 (NH), 1704 (CO2) cm-1; H NMR (DMSO-d6, 22 °C)
δ 1.15 and 1.24 (two d, J CH,Me ) 6.0 Hz, 3H each, CHMe2), 2.27
(s, 3H, C-6 Me), 2.37 (s, 3H, pyridyl Me), 2.52 (s, 3H, C-2 Me),
4.93 (septet, J CH,Me ) 6.0 Hz, 1H, CHMe2), 5.35 (s, 1H, H-4),
7.04 (two coincidental d, J 3,4 and J 4,5 ) 7.5 Hz, 2H total, pyridyl
H-3 and H-5), 7.49 (dd, J 3,4 ) J 4,5 ) 7.5 Hz, 1H, pyridyl H-4),
9.51 (sharp s, 1H, NH); 1H NMR (CDCl3, 22 °C) δ 1.09 and
1.23 (two d, J CH,Me ) 6.0 Hz, 3H each, CHMe2), 2.27 (s, 3H,
C-6 Me), 2.49 (s, 3H, C-2 Me), 2.52 (s, 3H, pyridyl Me), 4.94
(septet, J CH,Me ) 6.0 Hz, 1H, CHMe2), 5.66 (s, 1H, H-4), 7.05
(d, J 4,5 ) 7.5 Hz, 1H, pyridyl H-5), 7.42 (d, J 3,4 ) 7.5 Hz, 1H,
pyridyl H-3), 7.57 (dd, J 3,4 ) J 4,5 ) 7.5 Hz, 1H, pyridyl H-4),
9.66 (sharp s, 1H, NH). Acquisition of 1H NMR spectra for
13a in CDCl3 at 10 °C (sharp singlet for NH at δ 10.28) and
at 61 °C (broad singlet for NH at δ 7.67) showed that the NH
resonance is temperature-dependent, while all other reso-
nances showed minor changes in chemical shift positions of
less than δ 0.09. Anal. (C17H21N3O4) C, H, N.
6-P h en yl-2-pyr idin ecar boxaldeh yde (7b): IR (neat) 1704
(CdO) cm-1 1H NMR (CDCl3) δ 7.50-8.12 (m, 8H, phenyl
;
hydrogens, H-3, H-4, H-5), 10.20 (s, 1H, CHO).
3-Meth yl-2-pyr idin ecar boxaldeh yde (7c): IR (neat) 1712
Isop r op yl 1,4-d ih yd r o-2,6-d im eth yl-3-n itr o-4-(3-m eth -
1
(CdO) cm-1; H NMR (CDCl3) δ 2.68 (s, 3H, CH3), 7.36 (dd,
yl-2-p yr id yl)-5-p yr id in eca r boxyla te (13d ): IR (KBr) 3057
1
and 3180 (NH), 1704 (CO2) cm-1; H NMR (DMSO-d6, 22 °C)
J 4,5 ) 8.0 Hz, J 5,6 ) 4.5 Hz, 1H, H-5), 7.62 (d, J 4,5 ) 8.0 Hz,
1H, H-4), 8.62 (d, J 5,6 ) 4.5 Hz, 1H, H-6), 10.16 (s, 1H, CHO).
δ 1.05 and 1.16 (two d, J ) 6.0 Hz, 3H each, CHMe2), 2.27 (s,
3H, C-6 Me), 2.47 (s, 3H, C-2 Me), 2.62 (s, 3H, pyridyl Me),
4.89 (septet, J ) 6.0 Hz, 1H, CHMe2), 5.48 (s, 1H, H-4), 7.07
(dd, J 4,5 ) 9.5 Hz, J 5,6 ) 6.0 Hz, 1H, pyridyl H-5), 7.46 (d, J 4,5
) 9.5 Hz, 1H, pyridyl H-4), 8.27 (d, J 5,6 ) 6.0 Hz, 1H, pyridyl
H-6), 9.50 (sharp s, 1H, NH). Anal. (C17H21N3O4) C, H, N.
6-Ch lor o-2-p yr id in eca r boxa ld eh yd e (7d ). MnO2 (16 g,
184 mmol) was added in eight equal aliquots to a solution of
6-chloro-2-(hydroxymethyl)pyridine (6d ; 2.8 g, 20 mmol) in
chloroform (100 mL), the resulting suspension was stirred at
25 °C for 24 h, and the reaction mixture was filtered through
a thoroughly packed Celite pad. Removal of the solvent in
vacuo gave a residue which was purified by silica gel column
chromatography using EtOAc-hexane (1:3, v/v) as eluent to
afford 7d as an oil (1.46 g, 52%) which was used immediately
for the synthesis of 13e,l.
2-P h en et h yl
p yr id yl)-5-p yr id in eca r boxyla te (13g): IR (KBr) 3057 and
3180 (NH), 1704 (CO2) cm-1 1H NMR (DMSO-d6) δ 2.18 (s,
3H, C-6 Me), 2.43 (s, 3H, C-2 Me), 2.82-3.02 (m, 2H, CH2Ph),
4.20-4.32 (m, 2H, CH2CO2), 5.28 (s, 1H, H-4), 7.02 (d, J 3,4
1,4-d ih yd r o-2,6-d im et h yl-3-n it r o-4-(2-
;
)
7.5 Hz, 1H, pyridyl H-3), 7.10 (dd, J 4,5 ) 7.5 Hz, J 5,6 ) 4.5 Hz,
1H, pyridyl H-5), 7.20-7.30 (m, 5H, phenyl hydrogens), 7.63
(dd, J 4,5 ) J 3,4 ) 7.5 Hz, 1H, pyridyl H-4), 8.48 (d, J 5,6 ) 4.5
Hz, 1H, pyridyl H-6), 9.82 (sharp s, 1H, NH). Anal.
(C21H21N3O4) C, H, N.
2-P h en eth yl Acetoa ceta te (10). Diketene (8; 0.84 g, 10
mmol) was added dropwise with stirring to 2-phenylethanol
(9; 1.22 g, 10 mmol) preheated to 50-60 °C in the presence of
a catalytic amount of Et3N (5 drops). Diketene was added at
a rate such the temperature of the reaction mixture did not
exceed 80 °C, and then the reaction was allowed to proceed
for 1 h at 80 °C. Distillation of the mixture afforded 10 as an
oil which was used immediately in the subsequent reaction
(bp 230 °C/1 mmHg; 1.5 g, 73%): IR (neat) 1745 (CO2), 1720
(CdO) cm-1; 1H NMR (CDCl3) δ 2.21 (s, 3H, CH3), 2.99 (t, J )
7.0 Hz, 2H, CH2Ph), 3.44 (s, 2H, COCH2CO2), 4.38 (t, J ) 7.0
Hz, 2H, OCH2), 7.22-7.36 (m, 5H, phenyl hydrogens).
2-P h en eth yl 3-Am in ocr oton a te (11d ). Ammonia gas was
bubbled slowly into a solution of 2-phenethyl acetoacetate (10;
1.5 g) in MeOH (10 mL) at 25 °C with stirring for 6 h, the
solvent was removed in vacuo, and the residue was distilled
to yield 11d as an oil (bp 285 °C/1 mmHg; 1.35 g, 90%): IR
2-P h en eth yl 1,4-dih ydr o-2,6-dim eth yl-3-n itr o-4-(6-m eth -
yl-2-p yr id yl)-5-p yr id in eca r boxyla te (13h ): IR (KBr) 3180
1
(NH), 1696 (CO2), 1450, 1294 (NO2) cm-1; H NMR (DMSO-
d6, 22 °C) δ 2.17 (s, 3H, C-6 Me), 2.34 (s, 3H, pyridyl Me), 2.49
(s, 3H, C-2 Me), 2.83-3.01 (m, 2H, CH2Ph), 4.25 (t, J ) 7.0
Hz, 2H, OCH2), 5.32 (s, 1H, H-4), 6.82 (d, J 3,4 ) 8.0 Hz, 1H,
pyridyl H-3), 7.00 (d, J 4,5 ) 8.0 Hz, 1H, pyridyl H-5), 7.18-
7.34 (m, 5H, phenyl hydrogens), 7.45 (dd, J 3,4 ) J 4,5 ) 8.0 Hz,
1H, pyridyl H-4), 9.54 (sharp s, 1H, NH); 1H NMR (CDCl3, 22
°C) δ 2.23 (s, 3H, C-6 Me), 2.49 (s, 3H, C-2 Me), 2.53 (s, 3H,
pyridyl Me), 2.83-3.02 (m, 2H, CH2Ph), 4.19-4.27 and 4.31-
4.42 (two m, 1H each, OCH2), 5.62 (s, 1H, H-4), 7.0 (d, J 4,5
)

1836 J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 11
8.0 Hz, 1H, pyridyl H-5), 7.13 (d, J 3,4 ) 8.0 Hz, 1H, pyridyl
Iqbal et al.
Ack n ow led gm en t. We are grateful to the Medical
Research Council of Canada (Grant MT-8892) for finan-
cial support of this research.
H-3), 7.15-7.36 (m, 5H, phenyl hydrogens), 7.47 (dd, J 3,4
)
J 4,5 ) 8.0 Hz, 1H, pyridyl H-4), 9.37 (sharp s, 1H, NH).
Acquisition of 1H NMR spectra for 13h in CDCl3 at 10 °C
(sharp singlet for NH at δ 10.13) and at 50 °C (broad singlet
for NH at δ 8.11) showed that the NH resonance is tempera-
ture-dependent, while all other resonances showed minor
changes in chemical shift positions of less than δ 0.09. Anal.
(C22H23N3O4) C, H, N.
Refer en ces
(1) Loev, B.; Goodman, M. M.; Snader, K. M.; Tedeschi, R.; Macko,
E. “Hantzsch-type” dihydropyridine hypotensive agents. J . Med.
Chem. 1974, 17, 956-965.
2-P h en eth yl 1,4-dih ydr o-2,6-dim eth yl-3-n itr o-4-(3-m eth -
yl-2-p yr id yl)-5-p yr id in eca r boxyla te (13i): IR (KBr) 3325
(2) J anis, R. A.; Triggle, D. J . New developments in Ca2+ antago-
nists. J . Med. Chem. 1983, 26, 775-785.
(NH), 1696 (CO2), 1515, 1498, 1392 (NO2) cm-1 1H NMR
;
(DMSO-d6, 22 °C) δ 2.19 (s, 3H, C-6 Me), 2.46 (s, 3H, C-2 Me),
2.53 (s, 3H, pyridyl Me), 2.74-2.91 (m, 2H, CH2Ph), 4.12-4.32
(m, 2H, OCH2), 5.46 (s, 1H, H-4), 7.07 (dd, J 4,5 ) 8.0 Hz, J 5,6
) 5.0 Hz, 1H, pyridyl H-5), 7.12-7.33 (m, 5H, phenyl hydro-
(3) Dagnino, L.; Li-Kwong-Ken, M. C.; Wolowyk, M. W.; Wynn, H.;
Triggle, C. R.; Knaus, E. E. Synthesis and calcium channel
antagonist activity of dialkyl 1,4-dihydro-2,6-dimethyl-4-(pyridi-
nyl)-3,5-pyridinedicarboxylates. J . Med. Chem. 1986, 29, 2524-
2529.
(4) Iqbal, N.; Knaus, E. E. Synthesis and calcium channel modulat-
ing effects of alkyl 1,4-dihydro-2,6-dimethyl-4-(pyridinyl or 2-tri-
fluoromethylphenyl)-5-(1H-tetrazol-5-yl)-3-pyridinecarbox-
ylates. Arch. Pharm. (Weinheim, Ger.) 1995, 328, 750-754.
(5) Miri, R.; Howlett, S. E.; Knaus, E. E. Synthesis and calcium
channel modulating effects of isopropyl 1,4-dihydro-2,6-dimethyl-
3-nitro-4-(thienyl)-5-pyridinecarboxylates. Arch. Pharm. Pharm.
Med. Chem. 1997, 330, 290-294.
(6) Langs, D. A.; Triggle, D. J . Conformational Features of Calcium
Channel Agonist and Antagonist Analogues of Nifedipine. Mol.
Pharmacol. 1985, 27, 544-548.
(7) Langs, D. A.; Strong, P. D.; Triggle, D. J . Receptor model for
the molecular basis of tissue selectivity of 1,4-dihydropyridine
calcium channel drugs. J . Comput.-Aided Mol. Des. 1990, 4,
215-230.
(8) Langs, D. A.; Kwon, Y. W.; Strong, P. D.; Triggle, D. J . Molecular
Level Model for the Agonist/Antagonist Selectivity of the 1,4-
Dihydropyridine Calcium Channel Receptor. J . Comput.-Aided
Mol. Des. 1991, 5, 95-106.
(9) Mager, P.; Coburn, R. A.; Solo, A. J .; Triggle, D. J .; Rothe, H.
QSAR, diagnostic statistics and molecular modeling of 1,4-
dihydropyridine calcium channel antagonists: A difficult road
ahead. Drug Dev. Res. 1992, 8, 273-289.
(10) Schramm, M.; Thomas, G.; Franchowiak, G. Novel dihydro-
pyridines with positive inotropic action through activation of
Ca2+ channels. Nature 1983, 303, 535-537.
(11) Hof, R. P.; Ruegg, U. T.; Hof, A.; Vogel, A. Stereoselectivity at
the calcium channel: Opposite action of the enantiomers of a
1,4-dihydropyridine. J . Cardiovasc. Pharmacol. 1985, 7, 689-
693.
gens), 7.42 (d, J 4,5 ) 8.0 Hz, 1H, pyridyl H-4), 8.29 (d, J 5,6
)
5.0 Hz, 1H, pyridyl H-6), 9.47 (sharp s, 1H, NH). Anal.
(C22H23N3O4) C, H, N.
2-P h en eth yl 1,4-d ih yd r o-2,6-d im eth yl-3-n itr o-4-[6-(tr i-
flu or om eth yl)-2-p yr id yl]-5-p yr id in eca r boxyla te (13j): IR
(KBr) 3303 (NH), 1704 (CO2), 1515, 1310 (NO2) cm-1; 1H NMR
[CDCl3 (not dried with molecular sieves or treated with neutral
alumina), 22 °C] δ 2.29 (s, 3H, C-6 Me), 2.55 (s, 3H, C-2 Me),
2.86-3.02 (m, 2H, CH2Ph), 4.24-4.41 (m, 2H, OCH2), 5.48 (s,
1H, H-4), 6.15 (s, 1H, NH), 7.14-7.34 (m, 6H, phenyl hydro-
gens, pyridyl H-5), 7.41 (d, J 4,5 ) 7.5 Hz, 1H, pyridyl H-3),
7.57 (dd, J 3,4 ) J 4,5 ) 7.5 Hz, 1H, pyridyl H-4). Anal.
(C22H20F3N3O4) C, H, N.
2-P h en eth yl 1,4-dih ydr o-2,6-dim eth yl-3-n itr o-4-(3-ch lo-
r o-2-p yr id yl)-5-p yr id in eca r boxyla te (13m ): IR (KBr) 3264
(NH), 1704 (CO2), 1507, 1315 (NO2) cm-1; 1H NMR [CDCl3 (not
dried with molecular sieves or treated with neutral alumina),
22 °C] δ 2.25 (s, 3H, C-6 Me), 2.49 (s, 3H, C-2 Me), 2.82-3.0
(m, 2H, CH2Ph), 4.26-4.36 (m, 2H, OCH2), 5.99 (s, 1H, H-4),
6.04 (s, 1H, NH), 7.07-7.26 (m, 6H, pyridyl H-5 and phenyl
hydrogens), 7.30 (dd, J 4,5 ) 7.5 Hz, J 4,6 ) 1.5 Hz, 1H, pyridyl
H-4), 8.32 (dd, J 5,6 ) 5.0 Hz, J 4,6 ) 1.5 Hz, 1H, pyridyl H-6).
Anal. (C21H20ClN3O4) C, H, N.
2-P h en eth yl 1,4-dih ydr o-2,6-dim eth yl-3-n itr o-4-(6-ph en -
yl-2-p yr id yl)-5-p yr id in eca r boxyla te (13p ): IR (KBr) 3320
(NH), 1687 (CO2), 1591, 1450, 1318 (NO2) cm-1 1H NMR
;
(DMSO-d6) δ 2.20 (s, 3H, C-6 Me), 2.56 (s, 3H, C-2 Me), 2.86-
3.02 (m, 2H, CH2Ph), 4.35 (t, J ) 7.0 Hz, 2H, OCH2), 5.36 (s,
1H, H-4), 7.02 (d, J 3,4 ) 7.5 Hz, 1H, pyridyl H-3), 7.15-7.30
(m, 5H, aryl hydrogens of CH2CH2Ph), 7.35-7.50 (m, 3H, m-
and p-aryl hydrogens of 6-phenyl-2-pyridyl moiety), 7.70 (dd,
J 3,4 ) J 4,5 ) 7.5 Hz, 1H, pyridyl H-4), 7.80 (d, J 4,5 ) 7.5 Hz,
1H, pyridyl H-5), 8.02 (dd, J ortho ) 7.5 Hz, J meta ) 1.5 Hz, 2H,
o-phenyl hydrogens of 6-phenyl-2-pyridyl moiety), 9.80 (sharp
s, 1H, NH). Anal. (C27H25N3O4) C, H, N.
(12) Holland, D. R.; Wikel, J . H.; Kauffman, R. F.; Smallwood, J . K.;
Zimmerman, K. M.; Utterback, B. G.; Turk, J . A.; Steinbert, M.
I. LY249933: A cardioselective 1,4-dihydropyridine with positive
inotropic activity. J . Cardiovasc. Pharmacol. 1989, 14, 483-491.
(13) Erne, P.; Burgisser, E.; Buhler, F. R.; Duback, B.; Kuhnis, H.;
Meier, M.; Rogg, H. Enhancement of calcium influx in human
platelets by CGP 28392, a novel dihydropyridine. Biochem.
Biophys. Res. Commun. 1984, 118, 842-847.
(14) Perez-Reyes, E.; Schneider, T. Calcium Channels: Structure,
Function and Classification. Drug Dev. Res. 1994, 33, 295-318.
(15) Triggle, D. J . Ion Channels as Pharmacologic Receptors. The
Chirality of Drug Interactions. Chirality 1996, 8, 35-38 and
references therein.
2-P h en eth yl 1,4-dih ydr o-2,6-dim eth yl-3-n itr o-4-(3-ph en -
yl-2-p yr id yl)-5-p yr id in eca r boxyla te (13q): IR (KBr) 3271
(NH), 1704 (CO2), 1590, 1458, 1340 (NO2) cm-1 1H NMR
;
(16) Goldmann, S.; Stoltefuss, J . 1,4-Dihydropyridines: Effects of
Chirality and Conformation on the Calcium Antagonist and
Calcium Agonist Activities. Angew. Chem., Int. Ed. Engl. 1991,
30, 1559-1578.
(17) Scholz, G. H.; Vieweg, S.; Uhlig, M.; Thormann, M.; Klossek,
P.; Goldmann, S.; Hofmann, H. J . Inhibition of Thyroid Hormone
Uptake by Calcium Antagonists of the Dihydropyridine Class.
J . Med. Chem. 1997, 40, 1530-1538.
(18) Hofmann, H. J .; Cimiraglia, R. Reference conformations for
calcium antagonists and agonists of dihydropyridine type. J . Mol.
Struct. (THEOCHEM) 1990, 205, 1-11.
(19) Rovnyak, G.; Andersen, N.; Gougoutas, J .; Hedberg, A.; Kimball,
S. D.; Malley, M.; Moreland, S.; Porubcan, M.; Pudzianowski,
A. Active Conformation of 1,4-Dihydropyridine Calcium Entry
Blockers. Effect of Size of 2-Aryl Substituent on Rotameric
Equilibria and Receptor Binding. J . Med. Chem. 1991, 34, 2521-
2524.
(DMSO-d6) δ 2.01 (s, 3H, C-6 Me), 2.40 (s, 3H, C-2 Me), 2.50-
2.72 (m, 2H, CH2Ph), 3.76-3.84 and 4.08-4.20 (two m, 1H
each, OCH2), 5.88 (s, 1H, H-4), 7.04-7.50 (m, 10H, CH2CH2Ph,
m- and p-hydrogens of 3-phenyl-2-pyridyl moiety, pyridyl H-4
and H-5), 7.65 (d, J ortho ) 7.5 Hz, 2H, o-phenyl hydrogens of
3-phenyl-2-pyridyl moiety), 8.44 (d, J 5,6 ) 4.5 Hz, 1H, pyridyl
H-6), 9.50 (sharp s, 1H, NH). Anal. (C27H25N3O4) C, H, N.
In Vitr o Ca lciu m Ch a n n el An ta gon ist a n d Agon ist
Assa ys. The calcium channel antagonist activities were
determined as the molar concentration of the test compound
required to produce 50% inhibition of the muscarinic receptor-
mediated (carbachol, 1.6 × 10-7 M) Ca2+-dependent contraction
(tonic response) of guinea pig ileum longitudinal smooth
muscle (GPILSM) using the procedure reported previously.41
The IC50 value ((SEM, n ) 3-18) was determined graphically
from the dose-response curve.
(20) Rovnyak, G. C.; Kimball, S. D.; Beyer, B.; Cucinotta, G.; DiMarco,
J . D.; Gougoutas, J .; Hedberg, A.; Malley, M.; McCarty, J . P.;
Zhang, R.; Moreland, S. Calcium Entry Blockers and Activa-
tors: Conformational and Structural Determinants of Dihydro-
pyrimidine Calcium Channel Modulators. J . Med. Chem. 1995,
38, 119-129.
Calcium channel agonist activity (positive inotropic re-
sponse) was calculated as the percentage increase in contrac-
tile force of isolated guinea pig left atrium (GPLA) relative to
its basal contractile force in the absence of test compound.23

Alkyl and Phenethyl Dihydropyridinecarboxylates
J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 11 1837
(21) Kass, R. S. Voltage Dependent Modulation of Cardiac Channel
Current by Optical Isomers of Bay K 8644: Implications for
Channel Gating. Circ. Res. 1987, 61 (Suppl. 1), 1-5.
(22) Belciug, M.-P.; Ananthanarayanan, V. S. Interaction of Calcium
Channel Antagonists with Calcium: Structural Studies on
Nicardipine and Its Ca2+ Complex. J . Med. Chem. 1994, 37,
4392-4399.
(31) Bikker, J . A.; Weaver, D. F. Theoretical Studies Applicable to
the Design of Novel Anticonvulsants. Part 2. A Comparison of
AM1, MNDO, and PM3 Semiempirical Molecular Orbital Con-
formational Analyses of Dihydropyridine Calcium Channel
Blockers. J . Mol. Struct. (THEOCHEM) 1993, 281, 173-184.
(32) Talik, T.; Koszalka, L.; Brekiesz-Lewandowska, B. Production
of 3-Chloro and 3-Bromopicolines. Pr. Nauk. Akad. Ekon. Im
Oskara Langego Wroclawiu 1980, 167, 191-195; Chem. Abstr.
1981, 95, 115214b.
(33) Young, R. N.; Zamboni, R.; Gauthier, J . Y. Preparation of
Pyridylstyrenedialkanoic Acids as Leukotriene Antagonists. U.S.
Patent 5004743, April 2, 1991; Chem. Abstr. 1991, 115, 92082x.
(34) Ashimori, A.; Ono, T.; Uchida, T.; Ohtaki, Y.; Fukaya, C.;
Watanabe, M.; Yokoyama, K. Synthesis and Hypotensive Activ-
ity of 4-(Substituted-pyridyl)-1,4-dihydropyridine Derivatives.
Chem. Pharm. Bull. 1990, 38, 2446-2458.
(35) Hurd, C. D.; Nilson, M. E. Aliphatic Nitro Ketones. J . Org. Chem.
1955, 20, 927-936.
(36) Deady L. W.; Stillman, D. C. Mechanism for the Acetylation of
Aminopyridines. Aust. J . Chem. 1978, 31, 1725-1730.
(37) Miura, Y.; Oka, H.; Momoki, M. A Convenient and Efficient
Synthesis of Polyphenylmono-, -di- and Triaminobenzenes.
Synthesis 1995, 1419-1422.
(38) Pillai, K. M. R.; Kapil, R. S.; Nand, N. Synthesis of 2-Hydroxy-
methyl-3-phenyl-piperidine and Related Compounds. Ind. J .
Chem. 1990, 29B, 892-894.
(39) Ochiai, E. Recent J apanese Work on the Chemistry of Pyridine
1-Oxide and Related Compounds. J . Org. Chem. 1953, 18, 534-
551.
(23) Vo, D.; Matowe, W. C.; Ramesh, M.; Iqbal, N.; Wolowyk, M. W.;
Howlett, S. E.; Knaus, E. E. Syntheses, Calcium Channel
Agonist-Antagonist Modulation Activities, and Voltage-Clamp
Studies of Isopropyl 1,4-Dihydro-2,6-dimethyl-3-nitro-4-pyridi-
nylpyridine-5-carboxylate Racemates and Enantiomers. J . Med.
Chem. 1995, 38, 2851-2859.
(24) Bechem, M.; Hebisch, S.; Schramm, M. Ca2+ Agonists. New
Sensitive Probes for Ca2+ Channels. Trends Pharmacol. Sci.
1988, 9, 257-261.
(25) Holtje, H.-D.; Marrer, S.
A Molecular Graphics Study on
Structure-Action Relationships of Calcium Antagonistic and
Agonistic 1,4-Dihydropyridines. J . Comput.-Aided Mol. Des.
1987, 1, 23-30.
(26) Kwon, Y. W.; Franckowiak, G.; Langs, D. A.; Hawthorn, N.;
J oslyn, A.; Triggle, D. J . Pharmacologic and Radioligand Binding
Analysis of the Actions of 1,4-Dihydropyridine Activators Related
to Bay K 8644 in Smooth Muscle, Cardiac Muscle and Neuronal
Preparations. Naunyn-Schmiedeberg’s Arch. Pharmacol. 1989,
339, 19-30.
(27) Hansch, C.; Leo, A.; Unger, S. H.; Kim, K.-H.; Nikaitani, D.; Lien,
E. J . “Aromatic” Substituent Constants for Structure-Activity
Correlations. J . Med. Chem. 1973, 16, 1207-1216 and references
therein.
(40) Ishizumi, K.; Koga, K.; Yamada, S. I. Chemistry of Sodium
Borohydride and Diborane. IV. Reduction of Carboxylic Acids
to Alcohols With Sodium Borohydride. Chem. Pharm. Bull. 1968,
16, 492-497.
(41) Dagnino, L.; Li-Kwong-Ken, M. C.; Wynn, H.; Wolowyk, M. W.;
Triggle, C. R.; Knaus, E. E. Synthesis and Calcium Channel
Antagonist Activities of Dialkyl 4-(Dihydropyridyl)-1,4-dihydro-
2,6-dimethyl-3,5-pyridinedicarboxylates. J . Med. Chem. 1987, 30,
640-646.
(28) Goldmann, S.; Geiger, W. Rotational Barriers of 4-Aryl-1,4-
dihydropyridines. Angew. Chem., Int. Ed. Engl. 1984, 23, 301-
302.
(29) Rovnyak, G.; Andersen, N.; Gougoutas, J .; Hedberg, A.; Kimball,
S. D.; Malley, M.; Moreland, S.; Porubcan, M.; Pudzianowski,
A. Studies Directred Toward Ascertaining the Active Conforma-
tion of 1,4-Dihydropyridine Calcium Entry Blockers. J . Med.
Chem. 1988, 31, 936-944.
(30) J ackman, L. M.; Sternhell, S. Applications of Nuclear Magnetic
Resonance Spectroscopy in Organic Chemistry, 2nd ed.; Perga-
mon Press: Toronto, 1969; pp 358-361.
J M970529F