Novel α3β4 nicotinic acetylcholine receptor-selective ligands. discovery, structure-activity studies, and pharmacological evaluation

Article abstract of DOI:10.1021/jm1006148

Antagonist activity at the α3β4 nicotinic acetylcholine receptor (nAChR) is thought to contribute to the antiaddictive properties of several compounds. However, truly selective ligands for the α3β4 nAChR have not been available. We report the discovery an

Full text of DOI:10.1021/jm1006148

J. Med. Chem. 2010, 53, 8187–8191 8187
DOI: 10.1021/jm1006148
Novel r3β4 Nicotinic Acetylcholine Receptor-Selective Ligands. Discovery,
Structure-Activity Studies, and Pharmacological Evaluation
Nurulain Zaveri,* Faming Jiang, Cris Olsen, Willma Polgar, and Lawrence Toll
Biosciences Division, SRI International, 333 Ravenswood Avenue, Menlo Park, California 94025, United States
Received February 1, 2010
Antagonist activity at the R3β4 nicotinic acetylcholine receptor (nAChR) is thought to contribute to the
antiaddictive properties of several compounds. However, truly selective ligands for the R3β4 nAChR have
not been available. We report the discovery and SAR of a novel class of compounds that bind to the R3β4
nAChR and have no measurable affinity for the R4β2orR7 subtype. In functional assays the lead compound
antagonized epibatidine-induced Ca2þ flux in R3β4-transfected cells in a noncompetitive manner.
Introduction
nAChR”.6,15,16 In the CNS, R3β4 nAChR is present, although
not in large amounts, in the mesolimbic dopamine pathway,
which is known to be crucial for the rewarding effects of drugs
of abuse.4 Differences in desensitization rates may, however,
increase its relative influence in this brain region.4 It is abun-
dant, however, in the medial habenula and interpeduncular
nucleus, regions that receive inputs from the nucleus accum-
bens and send efferents to the ventral tegmental area
(VTA).4,6,16,17 As discussed below, these receptors may influ-
ence drug dependence. A recent study has further indicated
the importance of the R3β4 nAChR to nicotine addiction
by demonstrating that nicotine-induced hypolocomotion is
reduced in β4 null mice.18 Furthermore, after chronic nicotine
treatment, mecamylamine-induced withdrawal is greatly
diminished in β4 null mice but not in β2 null mice.18
Although recent studies seem to implicate a role for R3β4
nAChR in psychostimulant and drug-seeking behavior, re-
searchers have no good tools to explore this hypothesis. Some
compounds, such as epibatidine, have high affinity at this site,
but virtually no available compound has sufficient selectivity
for this site to allow the study of the pharmacological role of
R3β4 nAChR. 18-Methoxycoronaridine (18-MC), a semisyn-
thetic iboga alkaloid congener, has been shown to block
the R3β4 nAChR and has shown intriguing effectiveness in a
variety of animal models of drug dependence against morphine,
methamphetamine, and nicotine.19-24 Although 18-MC is an
antagonist at R3β4 nAChR,25 it is not particularly selective and
binds to opioid and other receptors. Studies by Glick and
colleagues, which include the synthesis and testing of more
selective congeners, have further implicated R3β4 nAChR in
dependence induced by nicotine and other drugs of abuse.22,26
Another nonselective R3β4 nAChR antagonist mecamyla-
mine is an antagonist at several nAChRs.27 Mecamylamine
has been evaluated previously in clinical trials as a smoking
cessation pharmacotherapy28 and as an antidepressant.29
Dextromethorphan has also been shown to have antagonist
activity at R3β4 nAChR;30 however, it is also an antagonist at
the NMDA receptor. Potent, selective ligands for the R3β4
nAChR have been unavailable thus far.
Nicotine, the addictive active ingredient in tobacco smoke,
acts by binding to nicotinic acetylcholine receptors (nAChRsa)
in the central and peripheral nervous system. nAChRs are
ligand-gated ion channels in the same family as the GABA and
glutamate receptors and mediate cation flux.1,2 The neuronal
nAChR is a pentameric protein made up of a combination of R
and β subunits,3 although fully functional homomeric proteins,
particularly the prominent R7 nAChR, are also present in the
brain. The R4β2 and the R7 nAChRs are by far the most
prevalent in the central nervous system (CNS),4,5 whereas the
R3β4 subtype is predominant in the sensory and autonomic
ganglia and in a subpopulation of neurons in the medial habenula
(MHN) and interpeduncular nucleus (IPN) in the CNS.6
Although nAChRs are implicated in nicotine reward, depen-
dence, and expression of withdrawal, little is known definitively
about which subtypes are involved in each of these aspects of
tobacco addiction. Since nicotine increases dopamine levels in
the mesocorticolimbic reward circuitry, most attention has been
focused on nAChR subtypes present in these pathways. Behav-
ioral and functional studies in knockout mice have shown that
the predominant R4β2 nAChR present in this circuitry is
required for nicotine addiction and dependence.7-9 The R4β2
nAChR is therefore an important target for the development of
smoking cessation medications, and significant efforts have been
directed toward the development of ligands selective for this
nAChR subtype. Indeed, the R4β2 nAChR partial agonist
varenicline, which was recently approved by the FDA as a
smoking cessation medication, is effective in reducing craving
and preventing relapse to smoking during abstinence.10-13
Although R4 and β2 subunits appear to be crucial for
nicotine dependence, other nAChR subtypes, particularly the
R3β4 nAChR, have also been implicated in addiction to
nicotine and other drugs of abuse.14 The R3β4 receptor, which
appears to predominate in sensory and autonomic ganglia and
in the adrenal gland, is sometimes referred to as the “ganglionic
*To whom correspondence should be addressed. Current address: Astraea
Therapeutics, LLC, 320 Logue Avenue, Mountain View, CA 94043. Phone:
650-254-0786. Fax: 650-254-0787. E-mail: nurulain@astraeatherapeutics.com.
a Abbreviations: nAChR, nicotinic acetylcholine receptor; CNS,
central nervous system; FDA, Food and Drug Administration; MHN,
medial habenula; IPN, interpeduncular nucleus; VTA, ventral tegmental
area; 18-MC, 18-methoxycoronaridine; FLIPR, fluorometric imaging
plate reader.
We recently discovered a novel compound, 5 (SR16584),
which binds to the R3β4 nAChR and has no apparent affinity
for R4β2 or R7 nAChR. We report here the structure-activity
relationships of 5and its congeners to understand the molecular
features that afford the selectivity toward the R3β4nAChR. We
r
2010 American Chemical Society
Published on Web 10/27/2010
pubs.acs.org/jmc

8188 Journal of Medicinal Chemistry, 2010, Vol. 53, No. 22
Zaveri et al.
also characterized the binding of these compounds to the R3β4
nAChR and compared them to epibatidine.
Table 1. Structures and Binding Affinities (Ki, nM)a of Selected Com-
pounds Screened for nAChR Affinity
Results and Discussion
Lead compound 5 was discovered from screening a limited,
selective library of small molecule compounds that possessed a
protonatable nitrogen in an alicyclic ring, keeping in mind the
three-point pharmacophoric features of the Sheridan nicotinic
pharmacophore.31 Most of the compounds screened contained a
piperidine core ring, monocyclic or bicyclic, with a lipophilic
substituent on the alicyclic nitrogen and a heterocyclic aromatic
substituent on the 4-position of the piperidine ring. These
compounds were screened against the R3β4 and R4β2 nAChR
transfected into HEK293 cells (obtained from the laboratory of
Dr. Kenneth Kellar, Georgetown University; Washington, DC).
Compounds were evaluated for binding affinity, determined by
inhibition of [3H]epibatidine binding to cell membranes, and for
functional activity, measuring stimulation or inhibition of cal-
cium flux using the fluorometric imaging plate reader (FLIPR).
Selected compounds were also tested for binding affinity to the R7
nAChR on rat brain membranes. Table 1 provides the structures
of some of the compounds screened and their binding affinities.
From the binding affinities in Table 1, it was apparent that
compounds that contain the essential protonatable nitrogen in a
monocyclic piperidine ring (1-3) have no affinity for the R3β4or
the R4β2 nAChR, whereas those in which the nitrogen is present
as part of a bicyclic core ring (4-13) possessed measurable
binding affinity at one or both nAChRs. This is not surprising
and is also a trend seen in the natural product nAChR ligands
such as epibatidine (Figure 1), which contains a bicyclic ring and
has a 1000-fold higher affinity for nAChR than does nicotine,
which contains a monocyclic pyrrolidine ring. In fact, several
potent nAChR ligands contain bicyclic core rings.32-35 From the
65 compounds we tested, we identified [3.2.1]azabicyclooctane-
containing 4 and [3.3.1]azabicyclononane-containing 5 as po-
tential lead compounds; both have binding affinity at the
R3β4 nAChR and no affinity for the R4β2 or R7 nAChR up to
100 μM. The binding affinity of 5 at R3β4 is similar to that of
nicotine and cytisine at R3β4 (see Table 1); however, 5 has over
200-fold selectivity for the R3β4 nAChR and offers a good
starting point for developing potent and selective R3β4 nAChR
ligands. More importantly, our SAR studies suggest insights into
the structural basis of subtype selectivity between the R3β4 and
R4β2 nAChRs.
Both 4 and 5 contain an azabicyclic core ring, with a
dihydroindolin-2-one ring distal to the protonatable nitrogen.
Although the azabicyclic rings differ by only one carbon
(azabicyclooctane vs azabicyclononane), 5 is more potent
than 4 by almost a whole order of magnitude at the R3β4
nAChR. Moreover, both these bicyclic rings are larger than
the azabicycloheptane ring of epibatidine, indicating that,
among other factors, the R3β4 receptor may have a larger
binding pocket than does R4β2, which may be distinguished
by compounds containing larger rings, like 5, in contrast to
epibatidine, which contains an optimally sized bicyclic ring
that fits into all the nAChRs and thus lacks selectivity.
We synthesized a small series of analogues to investigate the
importance of the three major pharmacophoric elements, (i) the
heteroaromatic ring, (ii) the bicyclic core ring, and (iii) the
nitrogen substituent, for selectivity to the R3β4 nAChR.
The synthesis of these analogues is shown in Schemes 1-3 and
followed standard methodology as shown. These analogues,
shown in Table 1, were tested for their binding affinity and
functional activity at the R3β4 and R4β2 nAChR and showed
a Binding affinities were determined by inhibition of [3H]epibatidine
binding to membranes derived from HEK cells transfected with rat R3β4
and R4β2 nAChR and rat brain membranes for R7 nAChR.
some interesting trends that suggested the basis for the selec-
tivity of lead 5 for the R3β4 nAChR.
The dihydroindolin-2-one ring plays a significant role in the
selectivity of 5 for R3β4 and, as discussed later, also on
conferring antagonist activity at the R3β4 nAChR. When
the indolinone ring of 5 was replaced with a 3-pyridyl ring, as
in 8, the compound retained affinity for R3β4 but now gained
significant affinity for the R4β2 receptor (10 nM) and was a
potent ligand for R4β2 nAChR. This surprising result indi-
cates that it is the dihydroindolinone ring of 5 that provides
selectivity for the R3β4 receptor. In the published SAR on
epibatidine, the 3-pyridylringis a favoredheteroaromatic ring
for several R4β2 ligands.32,35,36 The gain in R4β2 affinity by
introducing the 3-pyridyl ring onto the [3.3.1]azabicyclo core
ring of 8 agrees with published SAR trends and confirms our
observation that the dihydroindolinone ring somehow precludes
binding to the R4β2 receptor, thereby affording selectivity for

Brief Article
Journal of Medicinal Chemistry, 2010, Vol. 53, No. 22 8189
Scheme 1a
Figure 1. Structures of known nonselective nAChR ligands with
affinity for the R3β4 nAChR.
R3β4. Replacing the heteroaromatic ring with a quinoline, as
in 9, decreases binding affinity for R4β2 and R3β4, indicating
that the larger 3-quinolinyl ring is not optimal for binding at
either of these receptors.
We explored the effect of substitution on the basic nitrogen
and found that removal of the N-methyl group of 5 (as in 6)
retained the affinity and selectivity for R3β4. This finding agrees
with most reported observations for nAChR ligands.32,35
Interestingly, carbamate-type N-substituents, such as those
present in 7 (N-ethoxycarbamate analogue of 8), result in
complete loss of binding affinity for R3β4andR4β2, confirming
previous SAR that the protonatable basic nitrogen is an
important requisite for binding affinity at all nAChRs.
a Reagents and conditions: (a) aniline, molecular sieves, toluene, reflux,
sodium cyanoborohydride, methanol; (b) chloroacetyl chloride, triethyla-
mine, methylene chloride, reflux; (c) aluminum chloride, 130-160 °C.
Scheme 2a
We determined the mode of binding and functional activity of
5 at R3β4 nAChR. Saturation binding experiments at R3β4 using
[3H]epibatidine indicated that 5 and cytisine bind noncompeti-
tively with epibatidine, as indicated by a change in Kd and Bmax
when using increasing concentrations of 5 (Figure 2). However,
the moderate Ki of both compounds in displacing [3H]epibatidine
in binding experiments appears to indicate that both compounds
may bind at sites partially overlapping the epibatidine binding.
We used the high-throughput FLIPR and calcium flux to
evaluate the functional activity of these compounds. As seen in
Figure 3, addition of the nAChR agonist epibatidine leads to a
1000-fold increase in intracellular Ca2þ-induced fluorescence.
The potencies of epibatidine (0.030 ( 0.004 μM) and nicotine
(8.7 ( 0.9 μM, data not shown) are similar to those reported by
Fitch et al.37 Both 5 and its desmethyl analogue 6 were anta-
gonists in the FLIPR assay. They showed no agonist activity
alone and fully reversed the epibatidine-induced Ca2þ fluores-
cence, with potencies in the micromolar range (as shown for 5 in
Figure 3). The 3-pyridyl containing analogue 8, on the other
hand, showed partial agonist activity in the FLIPR assay. This
result supports our hypothesis that the larger bicyclic benzo-
fused dihydroindolinone ring not only plays a role in the selec-
tivity but also confers antagonistic activity to this class of azabi-
cyclononane-type nAChR ligands. To the best of our knowl-
edge, the dihydroindolinone ring is a new heterocyclic ring not
present in any nAChR ligands reported to date. Notably, 5 has
no affinity at the R7 nAChR (Table 1). Compound 5 therefore
represents a novel class of R3β4-selective nAChR ligands that
may be valuable for studying the pharmacological role of this
receptor in drug abuse and reward pathways.
From our screening efforts, we also identified a new bicyclic
core ring, the 2-azabicyclo[3.2.1]octane (an isomer of tropane)
that provided potent binding affinity for R4β2 nAChR. The
compound containing this isotropane core scaffold and the
R4β2-favored 3-pyridyl ring, 10 (Table 1), has a 2 nM binding
affinity for R4β2 and about 100-fold selectivity over R3β4
receptors and greater than 200-fold selectivity over R7 nAChR.
Interestingly, 10 contains an N-benzyl substituent on the basic
nitrogen. Furthermore, in functional assays, 10 is a partial
agonist at R4β2 nAChR. This is unusual because most SARs
on R4β2 show that for agonist activity, only small alkyl substit-
uents are tolerated at the basic nitrogen.32,35 Our results show
that in this isotropane class, the larger N-benzyl substituent can
still impart agonist activity at the R4β2 receptor. At R3β4
a Reagents and conditions: a. ethyl chloroformate, K2CO3, toluene, 90-
100 °C; b. NaN(TMS)2, N-(5-chloro-2-pyridyl)triflimide, THF, -78 °C; c.
3-pyridineboronic acid, Pd(PPh3)4, K3PO4, dioxane, 85 °C; d. LAH, THF.
Scheme 3a
a Reagents and conditions: (a) NaN(TMS)2, N-(5-chloro-2-pyridyl)-
triflimide, THF, -78 °C; (b) 3-pyridineboronic acid, Pd(PPh3)4, K3PO4,
dioxane, 85 °C.
nAChR, the 3-pyridyl containing 10 is also a partial agonist,
similar to the 3-pyridyl containing azabicyclononane 8
(Figure 3B). The 3-quinolinyl analogue 11 in the isotropane
series has decreased activity at both receptors, similar to the trend
also seen with the in the azabicyclononane series (9). However,
when the 3-pyridyl ring in the isotropane series is replaced with
the dihydroindolinone ring (12), it completely abolished affinity
at the R4β2 nAChR, although it did bind to the R3β4 nAChR,
albeit with lower affinity than the isotropane 10 or the azabicy-
clononane 5. This further confirms our SAR that the dihydroin-
dolinone ring somehow prevents binding to the R4β2 nAChR, a
trend also seen with the azabicyclononane series of ligands.
The SAR on the two pharmacophoric features, the hetero-
aromatic ring and the core bicyclic ring, provides approaches
to designing R3β4-selective nAChR ligands. The heteroaro-
matic dihydroindolinone ring precludes binding to the R4β2
nAChR when presentonanyof the core bicyclicrings(see4, 5,
and 12), thus conferring selectivity for the R3β4 nAChR.
Among the azabicyclic core rings, the larger azabicyclono-
nane affords good binding affinity for the R3β4 nAChR and
the possibility of preferential binding to the R3β4 nAChR,
with an appropriate heteroaromatic pharmacophore, as in 5.
We are currently optimizing the pharmacophoric elements of
the azabicyclononane class of R3β4 ligands to improve bind-
ing affinity, and these results will be reported in due course.
In summary, we have discovered a new class of nAChR
ligands that do not appear to bind other major nAChR

8190 Journal of Medicinal Chemistry, 2010, Vol. 53, No. 22
Zaveri et al.
Figure 2. Scatchard analysis of [3H]epibatidine binding at R3β4nAChR
alone and in the presence of various concentrations of the inhibitor 5.
subtypes at concentrations greater than 100 μM and therefore
show excellent selectivity (>200-fold) for the R3β4 nAChR.
Our SAR studies show that the azabicyclo[3.3.1]nonane core
ring and the dihydroindolinone heteroaromatic ring play a
role in conferring the selectivity for the R3β4 nAChR, whereas
only the dihydroindolinone-containing ligands possess an-
tagonist activity at R3β4 nAChR. These SARs may lead to
a better understanding of structuralfeatures for selectivityand
functional activity at the nAChR. Such selective and potent
R3β4 nAChR antagonists will be useful for testing the hypoth-
esis that R3β4 receptor antagonists can attenuate rewarding
properties of nicotine and other drugs of abuse.14,38
Figure 3. Ligand-induced Ca2þ fluorescence in R3β4 nAChR con-
taining HEK cells using FLIPR: (A) agonist activity of epibatidine
and antagonist activity of 5; (B) agonist activity of epibatidine and
the partial agonist activity of 10 and 8.
(t, J = 7.6 Hz, 1H, Ar-H8), 7.25-7.32 (m, 3H, Ar-H5, Ar-H6,
Ar-H7). MS (ESI) m/z: 271.2 (M þ H)þ.
Experimental Details
9-Methyl-3-(pyridin-3-yl)-9-azabicyclo[3.3.1]non-2-ene (8). To a
solution of 19 (67 mg, 0.25 mmol) in THF (10 mL) was added
lithium aluminum hydride (108 mg, 4.74 mmol). The resultant
mixture was stirred at room temperature for 30 min, and the excess
of lithium aluminum hydride was destroyed with ethyl acetate until
no gas was released. Then water (0.5 mL) was added. The mixture
was filtered and the solid washed with ethyl acetate (10 mL). The
filtrate and washings were combined, dried over sodium sulfate,
and evaporated to dryness. The residue was subjected to chroma-
tography on silica gel, eluting with a solvent mixture of dichloro-
methane and methanol (20%) to afford 14 mg of desired product
General. 1H and 13C NMR spectra were recorded on a Varian
Gemini 300 MHz spectrometer (300 and 75 MHz, respectively)
and are internally referenced to chloroform at δ 7.27. Data for
13C are reported in terms of chemical shift. Mass spectra were
obtained using a ThermoFinnigan LCQ Duo LC/MS/MS in-
strument and an electrospray ionization probe. Thin-layer
chromoatgraphy was run on Analtech Uniplate silica gel TLC
plates. Flash chromatography was carried out using silica gel,
Merck grade 9385, 230-400 mesh. The purity of the final
compounds reported was confirmed by HPLC and mass spec-
tra, using the following conditions: column, Phenomenex Syn-
ergi 4 m Fusion RP, 250 mm ꢀ 4.60 mm; mobile phase, (A)
MeCN (0.1% TFA)/(B) H2O (0.1% TFA) (gradient 20% A to
100% A, 15 min); flow rate, 1 mL/min; detection, PDA 254 nm.
The purity of all final compounds was greater than 95%.
Experimental details for intermediates in Schemes 1-3 are
reported in the Supporting Information.
1-(9-Methyl-9-azabicyclo[3.3.1]non-3-yl)-1,3-dihydro-2H-indol-
2-one (5). A mixture of 16 (576 mg, 1.88 mmol) and aluminum
chloride (1.00 g, 7.51 mmol) under argon was placed in a 160 °C
oil bath and stirred for 15 min and then allowed to cool to 130 °C
and kept at this temperature 1.75 h. A solution of 1 N sodium
hydroxide (10 mL) was added, and the resulting mass was soni-
cated to homogeneity and extracted three times with methylene
chloride, dried (sodium sulfate), and evaporated to an oil. The
oil was purified by flash chromatography, eluting with 0-6%
methanol containing 5% of 28% ammonium hydroxide/
methylene chloride to give 5 as a colorless oil (free base,
219 mg, 43%). This was treated with HCl in ether and eva-
porated to dryness to give an off-white solid, mp 268-269 °C.
1H NMR (HCl salt; 300 MHz, CD3OD) δ 1.63 (br d, J = 14.4
Hz, 2H, H-6ax, H-8ax), 1.75 (br d, J = 14.4 Hz, 1H, H-7ax), 2.22
(m, 2H, 2-H, H-4), 2.35-2.48 (m, 3H, H-6eq, H-7eq, H-8eq),
2.79 (ddd, J = 10.4, 10.1, 2.3 Hz, 2H, H-2, H-4), 2.98 (s, 3H,
N-CH3), 3.55 (s, 2H, indolinyl CH2), 3.74 and 3.77 (2 br s,
J = 11.2 Hz, 2H, H-1, H-5), 4.90-5.05 (m, 1H, H-3), 7.05
1
8 (35%) as a light yellow oil. H NMR (300 MHz, CDCl3) δ
1.36-1.62 (m, 4H, H-6, H-7, H-8), 1.78-1.96 (m, 2H, H-6, H-8),
2.03 (dd, J = 18.3, 1.5 Hz, 1H, H-4), 2.37 (s, 3H, N-CH3), 2.74
(ddd,J= 18.4, 6.9 Hz, 1.0 Hz, 1H, H-4), 3.14 (br, 1H, H-5), 3.37 (br,
1H, H-1), 6.06 (dt, J= 4.8, 2.1 Hz, 1H, H-2), 7.19 (ddd, J= 8.1, 4.8,
0.9 Hz, 1H, Ar-H5), 7.63 (ddd, J = 8.8, 2.4, 1.5 Hz, 1H, Ar-H4),
8.43 (dd, J = 4.8, 1.5 Hz, 1H, Ar-H6), 8.63 (d, J = 2.1 Hz, 1H, Ar-
H2). 13C NMR (300 MHz, CDCl3) δ15.4 (C-7), 26.5 (C-6), 28.1 (C-
8), 32.9 (C-4), 41.8 (C-9, N-CH3), 52.7 (C-1), 55.4 (C-5), 123.2 (Ar-
C5), 125.5 (C-2), 132.0 (Ar-C4), 133.9 (Ar-C3), 135.6 (C-3), 146.5
(Ar-C2), 148.3 (Ar-C6). MS (APCI) m/z: 215.1 (M þ H)þ.
6-Benzyl-3-(pyridin-3-yl)-6-azabicyclo[3.2.1]oct-2-ene (10). A
mixture of 21 (140 mg, 0.40 mmol), 3-pyridineboronic acid (55
mg, 0.45 mmol), Pd(PPh3)4 (23 mg, 0.02 mmol), K3PO4 (128 mg,
0.60 mmol), and dioxane (4 mL) was stirred at 85 °C overnight
(17 h). The mixture was treated with NaOH (2 M) until strongly
basic (pH>12) and extracted with ethyl acetate (3ꢀ10 mL).
The extract was washed with brine, dried over sodium sulfate,
and evaporated to dryness. The residue was subjected to chro-
matography on silica gel, eluting with a mixture solvent of ethyl
acetate/hexanes/methanol (5:5:1) to afford 36 mg of 10 (32%) as
a light yellow oil. 1H NMR (300 MHz, CDCl3) δ 1.71 (d, J =
10.5 Hz, 1H, H-8), 1.96-1.86 (m, 1H, H-8), 2.43 (d, J = 17.1 Hz,
1H, H-4), 2.55 (d, J = 17.1 Hz, 1H, H-4), 2.66-2.71 (m, 1H,
H-5), 2.83 (dd, J = 8.7, 4.8 Hz, 1H, H-7eq), 2.97 (d, J = 9.0 Hz,
1H, H-7ax), 3.46 (m, 1H, H-1), 3.74 (d, J = 10.5 Hz, 1H,

Brief Article
Journal of Medicinal Chemistry, 2010, Vol. 53, No. 22 8191
CH2-Ph), 3.87 (d, J = 10.5 Hz, 1H, CH2-Ph), 6.48 (d, J = 6.1,
1H, H-2), 7.10-7.36 (m, 6H, Ar-H, pyridyl H-5), 7.58 (ddd, J =
8.8, 2.3, 1.6 Hz, 1H, pyridyl H-4), 8.38 (dd, J = 5.0, 1.6 Hz, 1H,
pyridyl H-6), 8.58 (dd, J = 2.4, 0.6 Hz, 1H, pyridyl H-2). 13C
NMR (300 MHz, CDCl3) δ 32.8 (C-1), 35.7 (C-4), 35.8 (C-8),
57.6 (C-5), 59.6 (C-7), 62.4 (Ar-CH2-N), 123.0 (pyridyl C-5),
126.8 (Ar C-4), 128.2 (Ar C-3, Ar C-5,), 128.5 (Ar C-2), 131.6
(C-2), 131.7 (C-3), 131.9 (pyridyl C-4), 135.9 (pyridyl C-3),
146.5 (pyridyl C-2), 148.0 (pyridyl C-6). MS (APCI) m/z: 277.0
(M þ H)þ.
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Acknowledgment. This work was supported by a NIH-
NIDA Grant R01-DA020811.
Supporting Information Available: Experimental details and
analytical data for all intermediates in Schemes 1-3, biological
evaluation, and in vitro assay protocols. This material is avail-
able free of charge via the Internet at http://pubs.acs.org.
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