Conformationally constrained nicotines: Polycyclic, bridged, and spiro-annulated analogues as novel ligands for the nicotinic acetylcholine receptor

Article abstract of DOI:10.1021/jm020916b

A set of novel nicotine-related, conformationally constrained compounds, including tetracyclic, bridged (4), and tricyclic, spiro-annulated (5) structures, were synthesized in a straightforward manner and optically resolved in a convenient fashion with (+)- and (-)-O,O′-di-p-toluoyltartaric acids. Absolute configurations were determined by X-ray crystallography. These compounds were evaluated for their ability to displace [³H]cytisine in a rat forebrain preparation and compared to (-)-nicotine. Three substances emerged With high affinity in the low nanomolar range. Moreover, one of these compounds ((+)-5b) showed not only high binding affinity (K_i = 4.79 nM) but also significant enantioselectivity over its antipode (K_i = 148 nM), supporting the hypothesis that conformational restraint can lead to high-affinity ligands, which are stereochemically discriminated by the nicotinic acetylcholine receptor and may feature optimum locations of the active sites of the pharmacophore.

Full text of DOI:10.1021/jm020916b

J . Med. Chem. 2002, 45, 4047-4054
4047
Con for m a tion a lly Con str a in ed Nicotin es: P olycyclic, Br id ged , a n d
Sp ir o-An n u la ted An a logu es a s Novel Liga n d s for th e Nicotin ic Acetylch olin e
Recep tor
Thomas Ullrich,*,† Sylvia Krich,† Dieter Binder,† Kurt Mereiter,‡ David J . Anderson,§ Michael D. Meyer,§ and
Michael Pyerin†
Institute of Applied Synthetic Chemistry, Vienna University of Technology, Getreidemarkt 9/ E163,
A-1060 Vienna, Austria, Institute of Chemical Technologies and Analytics, Vienna University of Technology,
Getreidemarkt 9/ E164, A-1060 Vienna, Austria, and Neurological and Urological Diseases Research,
Pharmaceutical Products Division, Abbott Laboratories, Department 47W, Building AP-9A/ 311,
100 Abbott Park Road, Abbott Park, Illinois 60064-6125
Received April 19, 2002
A set of novel nicotine-related, conformationally constrained compounds, including tetracyclic,
bridged (4), and tricyclic, spiro-annulated (5) structures, were synthesized in a straightforward
manner and optically resolved in a convenient fashion with (+)- and (-)-O,O′-di-p-toluoyltartaric
acids. Absolute configurations were determined by X-ray crystallography. These compounds
were evaluated for their ability to displace [3H]cytisine in a rat forebrain preparation and
compared to (-)-nicotine. Three substances emerged with high affinity in the low nanomolar
range. Moreover, one of these compounds ((+)-5b) showed not only high binding affinity (Ki )
4.79 nM) but also significant enantioselectivity over its antipode (Ki ) 148 nM), supporting
the hypothesis that conformational restraint can lead to high-affinity ligands, which are
stereochemically discriminated by the nicotinic acetylcholine receptor and may feature optimum
locations of the active sites of the pharmacophore.
Ch a r t 1. Nicotine (1) and Selected Conformationally
Restricted Analogues
In tr od u ction
Central nicotinic acetylcholine receptors (nAChRs)
have been implicated in a number of cognitive and
learning processes, making them a potential target for
the treatment of Alzheimer’s and other neurodegenera-
tive diseases.1 Other findings suggest that activation of
these receptors also plays a critical role in the antinoci-
ceptive effects of cholinergic channel modulators.2 Alz-
heimer’s disease has received the most attention as a
therapeutic target for nicotinic drugs, as nicotinic recep-
tor binding was found to be significantly reduced in
distinct brain regions of Alzheimer’s patients.3 Because
the identification of various adverse physiological ef-
fects3,4 of the alkaloid (S)-nicotine (1, Chart 1), synthetic
modifications of its structure have been performed in
order to improve potency and selectivity while reducing
the toxicity.
A worldwide search for nAChR agonists for the R4â2
receptor, the predominant nAChR subtype in the brain,
has already led to a number of promising substances,
many of them closely related to nicotine.5 In particular,
nicotine analogues with rigid structures have become
interesting targets stimulated by recent findings related
to the highly active alkaloid, epibatidine.6 Glassco et al.7
and several others8 pursued the concept of conforma-
tional restriction in nicotine with the objective of forcing
both pharmacophore nitrogen atoms into well-defined
angles (“up” and “down” conformations), which would
help in elucidating the “active” conformation of nicotine
on one hand and obtaining a tool to study receptor
subtype specificity on the other hand. These endeavors
led to, among others, the class of hexahydropyrroloiso-
quinolines (2). The correct stereochemistry began to play
an increasingly decisive role: while the relatively low
enantioselectivity of nicotine (the affinity of (S)-nicotine
is 10-100 times higher than that of (R)-nicotine)9 has
been an intriguing phenomenon for many years,10 the
premise that conformational restraint of nicotine should
enhance enantioselectivity has been well-established.11
The (-)-enantiomer of 2 shows low relative affinity
(Ki ) 605 nM) for the nAChR [3H]nicotine binding site,
whereas the (+)-enantiomer fails to displace the radio-
ligand even at 10 µM concentrations.8 Looking for
similar enantioselectivities but higher binding affinities,
* To whom correspondence should be addressed. Tel:
+43(1)86634-436. Fax: +43(1)86634-285. E-mail: thomas.ullrich@
pharma.novartis.com.
† Institute of Applied Synthetic Chemistry, Vienna University of
Technology.
‡ Institute of Chemical Technologies and Analytics, Vienna Univer-
sity of Technology.
§ Abbott Laboratories.
10.1021/jm020916b CCC: $22.00 © 2002 American Chemical Society
Published on Web 08/07/2002

4048 J ournal of Medicinal Chemistry, 2002, Vol. 45, No. 18
Sch em e 1. Retrosynthetic Approach to Racemic 4
Ullrich et al.
Sch em e 2a
there has been a continuing effort in our group to extend
the concept of conformational restriction in nicotinoid
molecules either by imposing more rigidity on the
nicotinic ligands or by achieving constraint in different
molecule locations. The goal of our endeavors was to
eventually find a structure, which is deprived of flex-
ibility, binds with high affinity to the receptor, and is
essentially more active than its stereoisomer. Without
taking advantage of the possible predictability of bind-
ing provided by several pharmacophore models,5,12 we
found Glassco’s research on isoquinolines (2) an intrigu-
ing concept and decided to focus on its structural
variation. Recently, we have reported an enantioselec-
tive synthesis of azabicyclo[2.2.1]heptanes (3)13 in which
the pyrrolidine ring of nicotine is conformationally
constrained into a bicyclic ring system. In the course of
the present studies, we developed a synthetic route to
combine the structural features of 3 with those of 2,
resulting in a novel class of tetracyclic nicotine-like
compounds 4. This novel chemical entity features a five-
membered central ring (to keep the flexibility of the
molecule at a minimum) and a bridge of variable chain
length (n ) 1, 2).
a
Reagents: (i) HC(OMe)3, H2SO4 (catalytic), MeOH. (ii) Pyr-
rolidine, NH4Cl (catalytic), reflux. (iii) (a) LDA, BrCH2Cl, THF;
(b) NaI, acetone. (iv) (a) Zn, LiCl, Cu, THF; (b) 3-bromopyridine,
ClCOOEt, THF, -40 °C; (c) sulfur, xylene, reflux. (v), n-BuLi, THF,
-78 °C. (vi) LDA, ICH2CN, THF, -78 °C. (vii) Raney-cobalt,
MeOH, 50 °C. (viii) (a) 62% HBr, reflux; (b) Na2CO3, H2O, reflux.
introduced early in the synthesis. For this reason, the
multifunctional precursors 8 (Scheme 2) were built up
in an efficient pathway that took its course from a
methanolysis of γ-butyrolactone and δ-valerolactone,14
respectively. Thus, the chain length present in the
azabicyclic unit rooted in the commercial starting mate-
rial, and its variation at a later stage was not possible.
After esters 6 were aminolyzed with neat pyrrolidine,
an iodomethyl substituent had to be introduced into the
R-position of amides 7, which appeared to be the
bottleneck of the pathway. Lithiation of 7 with LDA in
tetrahydrofuran (THF) and direct treatment with di-
iodomethane15 resulted in poor yields, due to side
reactions, such as elimination and dimerization. Cir-
cumvention of this problem was achieved by reacting
the lithium enolate with bromochloromethane, giving
reasonable yields of chloromethyl-substituted interme-
diate, and conversion into iodides 8 was easily ac-
complished under Finkelstein conditions.
Chemo- and regioselective 1,4-addition of soft nucleo-
philes to pyridinium salts (Knochel reaction) has been
extensively reported in the literature.16a-c Thus, iodides
8 had to be transformed into activated, mixed zinc,
copper organometallic species and were in situ combined
with 3-bromopyridinium ethylformate at low tempera-
tures. The dihydropyridines formed quantitatively, ac-
cording to thin-layer chromatography (TLC), and were
aromatized without prior purification, employing ele-
mental sulfur in refluxing xylene.16c In good overall
yields (50-60%), 4-substituted pyridines 9 were ob-
tained . Metal-halogen exchange of the 3-bromo sub-
stituent was accomplished with n-BuLi and led to
immediate and chemoselective, intramolecular cycliza-
In yet another approach, closely related to the syn-
thesis of 4, it was our objective to create a second set of
conformationally restricted molecules by introducing
spiro-connection between the pyrrolidine ring and the
pyridine-bearing unit. This approach led to compounds
5, which represent, to the best of our knowledge, the
first spiro-annulated nicotine analogues ever reported.
Ch em istr y
(a ) Syn th esis of Br id ged An a logu es 4a ,b. Follow-
ing a basic concept, compound class 4 was aimed to be
synthesized as a mixture of stereoisomers that would
easily undergo optical resolution, due to the high strain
of the molecule. As it was neither known nor anticipated
which of the isomers would elicit any activity in biologi-
cal assays, an early determination of the stereochem-
istry appeared disadvantageous. Optical resolution at
the final stage of the pathway, on the other hand, would
provide quick availability of any desired isomer.
The retrosynthetic approach toward racemic com-
pounds 4 was based on successive ring closure steps,
starting with a commercial pyridine derivative and
approaching the final azabicyclic system step by step
(Scheme 1). The variable chain length (n ) 1, 2) that
determined the size of the bicyclic ring had to be

Conformationally Constrained Nicotines
J ournal of Medicinal Chemistry, 2002, Vol. 45, No. 18 4049
Sch em e 3. Retrosynthetic Approach to Racemic 5a
F igu r e 1. Thermal ellipsoid plot (20% ellipsoids) of (R)-(-)-
4a in its crystalline salt 16. Crystallographic atom numbering.
Sch em e 4a
F igu r e 2. Thermal ellipsoid plot (20% ellipsoids) of (4aS)-
(+)-4b in its crystalline salt 17. Crystallographic atom num-
bering.
tion with the amide unit, affording the first ring closure
in the synthetic route to give pyrindinones 10. For this
step, THF was first chosen as an appropriate solvent
and gave good yields (68%) of 10b, whereas 10a could
only be isolated among a number of byproducts. Com-
pound 10a , however, was obtained in equally good yields
when THF was substituted for toluene to modulate the
reactivity of n-BuLi. R-Substitution of the ketones with
iodoacetonitrile was achieved after forming the lithium
enolate with LDA, and catalytic hydrogenation of ni-
triles 11 led to a reaction cascade, assumably via
subsequent, stereoselective formation of a primary
amine and a cyclic hemiaminal, followed by reduction
to the secondary amine. Whereas employment of Raney
nickel gave inferior results, Raney cobalt, prepared from
a commercially available Co-Al alloy,17 furnished yields
between 40 and 50%. Thus, only cis-annulated pyrro-
lidines 12 were obtained, with no traces of trans
products determined. The mixtures of both diastereo-
mers, respectively, underwent ether cleavage under
acidic conditions followed by alkaline treatment under
heating, upon which the last cyclization to the azabi-
cyclic ring systems 4 took place.13 The five-membered
ring in 4a (from methoxyethyl substitution) formed as
easily as its six-membered analogue in 4b (from meth-
oxypropyl substitution), despite the considerably higher
ring strain, and little material was lost due to the harsh
reaction conditions.
a
Reagents: (i) (a) Zn, LiCl, Cu, THF; (b) 3-bromopyridine,
ClCOOEt, THF, -40 °C; (c) sulfur, xylene, reflux. (ii) N-Vinylpyr-
rolidone, NaH, THF, °C. (iii) (a) 6 N HCl; (b) Na2CO3. (iv) n-BuLi,
THF, -78 °C. (v) HCHO, NaBH3CN, CH3CN.
enantiomer (+)-4a . The absolute configuration of (+)-
4b was found to be 4aS; hence, the 4aR configuration
was assigned to its stereoisomer (-)-4b.
(b) Syn th esis of Spir o-An n u lated An alogu es 5a,b.
In a similar manner, the spiro-system present in
compounds 5 was designed in a straightforward, sym-
metric sequence, with 3-bromopyridine as the starting
material. In this approach, spiro-annulation was gener-
ated from a pyrroline key intermediate (Scheme 3).
In analogy with the pathway described above, a
â-iodocarboxylic acid derivative was introduced into
position 4 of 3-bromopyridine via 1,4-addition under the
same experimental conditions as described above
(Scheme 4). Ethyl ester 13 was then transformed in two
steps into a cyclic imine that was considered essentially
reactive toward intramolecular reaction with an orga-
nolithium species: Pyrroline 15 was obtained following
conditions described by Haslego et al.19 In this manner,
reaction with deprotonated N-vinylpyrrolidone led to
â-ketolactam 14, which was not isolated but directly
N-dealkylated with HCl under concomitant lactam
hydrolysis and decarboxylation, yielding a γ-aminoke-
tone that finally cyclized upon basification. Pyrroline
15 was simply treated with n-BuLi in toluene to trigger
metal-halogen exchange and intramolecular addition
across the C-N double bond. Spiro-compound 5a was
obtained in moderate yield as a racemate, which could
be optically resolved again by salt formation with chiral
O,O′-di-p-toluoyltartaric acid and fractional recrystal-
lization. For both enantiomers, an optical purity of the
free base of >95% ee was observed after derivatization
Compounds 4a ,b (as mixtures of two diastereomers,
respectively) were optically resolved by salt formation
with chiral O,O′-di-p-toluoyltartaric acid and fractional
recrystallization. In both cases, an optical purity of the
free base of >95% de was observed by employment of
(R)-(-)-1,1′-binaphthyl-2,2′-diyl hydrogen phosphate as
1
an appropriate H NMR shift reagent.18 Absolute con-
figurations were determined by single-crystal X-ray
diffraction analysis for (-)-4a via its (2R,3R)-(-)-O,O′-
di-p-toluoyltartrate 16 (Figure 1) and for (+)-4b via its
(2S,3S)-(+)-O,O′-di-p-toluoyltartrate 17 (Figure 2). In
the crystal structure images, the high conformational
strain of the molecules becomes evident, and the spatial
arrangement of the bridged unit can be easily contem-
plated. The absolute configuration of (-)-4a was found
to be R; hence, the S configuration was assigned to its
1
with (S)-(-)-phenylethylisocyanate and H NMR analy-
sis of the resulting ureas. N-Methylation on each of the

4050 J ournal of Medicinal Chemistry, 2002, Vol. 45, No. 18
Ullrich et al.
remarkable enantioselectivity was observed. We con-
clude that either the extreme conformational constraint
imposed on these molecules forced their molecular
shapes in a disfavorable position, in which binding was
impaired, or the high spatial demand that now charac-
terized compounds 4 was not tolerated by the receptor.
Spiro-annulated compounds 5a ,b exhibited much higher
binding affinities. nor-Derivative (+)-5a bound at Ki )
53.1 nM with a 10-fold higher affinity than its enanti-
omer (Ki ) 533 nM). Introduction of the N-methyl
substituent resulted in a significant improvement, prob-
ably due to the gain of fortified receptor interaction: (+)-
5b (Ki ) 4.79 nM) appeared to be the most interesting
ligand of this set as it not only bound in the low
nanomolar range but also exhibited a 30-fold higher
affinity than its enantiomer (Ki ) 148 nM).
F igu r e 3. Thermal ellipsoid plot (20% ellipsoids) of crystalline
(R)-(-)-5b‚2HCl. Only one of the two independent molecules
in the crystal structure is shown. Crystallographic atom
numbering.
Ta ble 1. Relative Affinities of Nicotine and Conformationally
Constrained Analogues for the [3H]Cytisine Binding Site
Ki, [3H]cytisine (nM)a
Nb
It can also be concluded from the data that with the
exception of 3 all compounds featuring the S configu-
ration show higher binding affinities than their R
isomers, which indicates analogy with nicotine and
suggests that the compounds bind in a nicotine-like
manner. In the case of (+)-5b, not only a successful
approach toward conformational restriction was found
but also the beneficial effects of an N-methyl group
present in the unbridged pyrrolidine ring were demon-
strated. In compound (+)-5b, a conformation that comes
close to the ideal conformation of a nicotinic ligand at
the receptor may have been found, representing a rigid
structure that provides nearly optimum locations of the
active sites of the pharmacophore. These findings have
the potential to give more insight to receptor-ligand
interactions. Compound (+)-5b is a potential candidate
for further investigation, such as peripheral binding and
antinociceptive behavior, and may result in a new lead
structure for the development of novel nAChR agonists
and lead optimization, correspondingly.
compd
1 (nicotine)
(+)-3
0.94 ( 0.26
2.32 ( 0.36
1.89 ( 0.16
962 ( 170
1360 ( 180
318 ( 34
1040 ( 92
53.1 ( 6.3
533 ( 11
4.79 ( 0.44
148 ( 32
3
3
3
3
3
3
3
3
3
3
3
(-)-3
(S)-(+)-4a
(R)-(-)-4a
(4aS)-(+)-4b
(4aR)-(-)-4b
(S)-(+)-5a
(R)-(-)-5a
(S)-(+)-5b
(R)-(-)-5b
a
All numbers are mean values ( SEM. Assay details are given
in the Experimental Section. b Number of separate determinations.
enantiomers was easily accomplished following a modi-
fied Eschweiler-Clarke protocol to afford 5b.20
The absolute configuration was determined in (-)-
5b by X-ray diffraction analysis of its dihydrochloride
(Figure 3) and found to be R. The S configuration was
hence assigned to its enantiomer (+)-5b, and precursor
molecules (+)-5a and (-)-5a were assigned their abso-
lute configurations likewise.
Con clu sion
Convenient synthetic routes to a set of novel nicotinic
ligands with a focus on conformational constraint were
established in the present study. The chemistry com-
bined modern and traditional methods fit for multigram
synthetic scales, including efficient optical resolution,
and was supported by X-ray crystallography. The new
compounds were evaluated in a preliminary radioligand
displacement assay, and several substances showed low
nanomolar binding affinities. The most promising can-
didate, compound (+)-5b, exhibited distinct enantiose-
lectivity and is considered worthy of further investiga-
tion. The present structure-activity relationship study
represents a valuable tool in our search for the develop-
ment of improved nicotinic ligands.
P h a r m a cology
Each stereoisomer of compounds 3-5 (no binding data
for compounds 3 have been previously published) was
evaluated in an in vitro radioligand displacement assay
and compared to nicotine, which was considered most
appropriate for a first screening in order to determine
binding ability of the ligands in central nervous system
(CNS) tissue. In a procedure described by Pabreza et
al.,21 rat forebrain membrane was treated with the
radioligand [3H]cytisine that binds preferentially to the
R4â2 receptor.
The relative binding constants (Ki) of each compound
for the [3H]cytisine binding site are provided in Table
1. None of the tested substances was superior to
nicotine; however, low nanomolar binding affinity was
determined for (+)-3 (Ki ) 2.32 nM), (-)-3 (Ki ) 1.89
nM), and (+)-5b (Ki ) 4.79 nM). It is evident that both
enantiomers of 3, which show the highest structural
resemblance to nicotine, exhibit a binding profile most
similar to the alkaloid. The conformational restriction
accomplished by inserting a bridge in the pyrrolidine
ring did not lead to significant enantioselectivity in this
case, as both enantiomers show equally high affinity.
The stereoisomers of bridged analogues 4a ,b did not
achieve quite a similar profile; all four compounds bound
in a low micromolar or submicromolar range, and no
Exp er im en ta l Section
Unless otherwise indicated, all reagents were purchased
from commercial suppliers and used without further purifica-
tion. TLC analyses were carried out on precoated silica gel
plates (Merck 60 F254), and signals were visualized with UV
light. Flash chromatography refers to Fluka silica gel 60, 220-
240 mesh. Melting points were recorded on a Kofler apparatus
1
and are uncorrected. H and 13C NMR spectra were recorded
on a Bruker 200FS FT-NMR spectrometer. 1H spectra are
reported as parts per million downfield from Me4Si with
multiplicity, number of protons, and coupling constant(s) in
Hertz indicated parenthetically.13C NMR spectral data are
indicated as carbon units with the number of hydrogen atoms

Conformationally Constrained Nicotines
J ournal of Medicinal Chemistry, 2002, Vol. 45, No. 18 4051
attached. The following abbreviations are used to indicate spin
multiplicities: s (singlet), bs (broad singlet), d (doublet), dd
(doublet of doublets), t (triplet), q (quartet), quin (quintet), or
m (multiplet). Elemental analyses were performed at the
Microanalytical Laboratory, Institute of Physical Chemistry
at Vienna University, Austria.
(0.9 mmol; predried at 120-130 °C in vacuo for at least 2 h)
was mixed with CuCN (1 mmol), dissolved quickly in dry THF
(20% solution), and cooled to -40 °C. The organozinc suspen-
sion was decanted quickly into a dropping funnel and added
to the copper solution. After 5 min at 0 °C, the resulting
mixture was cooled to -50 °C (flask 1). 3-Bromopyridine (0.75
mmol) in anhydrous THF (20% solution) was reacted with
ethyl chloroformate (0.75 mmol) in anhydrous THF (20%
solution) at 0 °C under nitrogen (flask 2). After 1 h, the
contents of flask 2 were transferred into a dropping funnel
and quickly added to flask 1 under vigorous stirring. The
resulting mixture was allowed to reach room temperature.
After 25% NH4OH was added until a dark blue color prevailed,
the obtained suspension was stirred for 1 h and filtered
through Celite. After the solvent was removed, the residue was
extracted with Et2O (3×). The combined organic layers were
washed with 2 N HCl and H2O, dried (Na2SO4), filtered, and
evaporated. The crude intermediate was dissolved in anhy-
drous xylene (20% solution), and elemental sulfur (1.3 mmol)
was added. The mixture was refluxed for 72 h, cooled, poured
on 2 N HCl, and washed with Et2O. The aqueous layer was
neutralized with NaHCO3 and extracted 3× with Et2O. The
combined organic layers were dried (Na2SO4), filtered, and
evaporated. The crude product was purified by flash chroma-
tography (CH2Cl2/MeOH ) 15:1). Yields are given referring
to 3-bromopyridine as the starting material.
Ester Am in olysis. Gen er a l P r oced u r e. A mixture of the
appropriate ester (6a ,b) (1.00 mol), NH4Cl (280 mmol), and
pyrrolidine (2.00 mol) was refluxed for 4 h. After excess
pyrrolidine was removed by distillation (first without reduced
pressure, then at 300 mbar), the residue was cooled and taken
up in Et2O, and the precipitated salt was filtered off. The
filtrate was concentrated, and the product was obtained by
fractional distillation in a 25 cm Vigreux-column (0.5 mbar).
1-[4-(Meth oxy)-1-oxobu tyl]p yr r olid in e (7a ). The product
was obtained as a colorless liquid (97%): Kp 100 °C (0.5 mbar).
1H NMR (CDCl3): δ 3.50-3.36 (m, 6H), 3.30 (s, 3H), 2.33 (t, J
) 8, 2H), 2.01-1.72 (m, 6H). 13C NMR (CDCl3): δ 171.2 (C),
71.9 (CH2), 58.4 (CH3), 46.5 (CH2), 45.5 (CH2), 31.0 (CH2), 26.0
(CH2), 24.8 (CH2), 24.3 (CH2). Anal. (C9H17NO2‚0.17H2O) C,
H, N.
1-[5-(Meth oxy)-1-oxop en tyl]p yr r olid in e (7b). The prod-
uct was obtained as a colorless liquid (95%): Kp 110 °C (0.5
mbar). 1H NMR (CDCl3): δ 3.52-3.32 (m, 6H), 3.30 (s, 3H),
2.29 (t, J ) 8 Hz, 2H), 1.88 (quin, J ) 8, 4H), 1.78-1.52 (m,
4H). 13C NMR (CDCl3): δ 171.7 (C), 72.3 (CH2), 58.6 (CH3),
46.7 (CH2), 45.8 (CH2), 35.2 (CH2), 30.8 (CH2), 27.3 (CH2), 26.0
(CH2), 24.3 (CH2). Anal. (C10H19NO2‚0.22H2O) C, H, N.
1-[2-[(3-Br om o-4-p yr id yl)m eth yl]-4-m eth oxy-1-oxobu -
tyl]p yr r olid in e (9a ). The product was obtained as a yellow
1
oil (52%): Rf ) 0.5 (CH2Cl2/MeOH ) 15:1). H NMR (CDCl3):
Iod om eth yla tion . Gen er a l P r oced u r e. To a solution of
diisopropylamine (502 mmol) in anhydrous THF (500 mL) was
added n-BuLi (2.5 M solution in n-hexane; 502 mmol) at 0 °C
and stirred for 1 h. The appropriate amide (7a ,b) (502 mmol)
in anhydrous THF (200 mL) was added dropwise at 0 °C and
stirred for 2 h at 25 °C. The mixture was cooled to -80 °C,
and bromochloromethane (502 mmol) was added at once. After
it reached room temperature and was stirred for 2 h, the
solution was partitioned between 2 N HCl (500 mL) and EtOAc
(500 mL). The aqueous layer was extracted with 3 × 300 mL
of EtOAc. The combined organic layers were dried (Na2SO4,
activated charcoal), filtered, and evaporated. The crude product
was dried thoroughly in vacuo and taken up in a solution of
anhydrous NaI (468 mmol) in dry acetone (1 L). After it was
refluxed for 48 h and the solvent was removed, the residue
was diluted with 200 mL of Et2O. Precipitated NaCl was
filtered off, and the filtrate was evaporated. The crude product
was purified by flash chromatography (1.5 kg of silica gel;
EtOAc).
δ 8.60 (s, 1H), 8.29 (d, J ) 6, 1H), 7.12 (d, J ) 6, 1H), 3.43-
3.02 (m, 7H), 3.22 (s, 3H), 3.02-2.74 (m, 2H), 2.05-1.49 (m,
6H). 13C NMR (CDCl3): δ 172.1 (C), 151.5 (CH), 147.9 (C),
147.8 (CH), 126.2 (CH), 122.8 (C), 69.9 (CH2), 58.3 (CH3), 46.2
(CH2), 45.3 (CH2), 39.5 (CH), 38.2 (CH2), 32.6 (CH2), 25.7 (CH2),
24.0 (CH2). Anal. (C15H21BrN2O2) C, H, N.
1-[2-[(3-Br om o-4-p yr id yl)m eth yl]-4-m eth oxy-1-oxop en -
tyl]p yr r olid in e (9b). The product was obtained as a yellow
1
oil (62%): Rf ) 0.5 (CH2Cl2/MeOH ) 15:1). H NMR (CDCl3):
δ 8.62 (s, 1H), 8.33 (d, J ) 6, 1H), 7.13 (d, J ) 6, 1H), 3.50-
3.30 (m, 7H), 3.28 (s, 3H), 3.00-2.79 (m, 2H), 1.98-1.42 (m,
8H). 13C NMR (CDCl3): δ 172.3 (C), 151.6 (CH), 148.2 (C),
147.9 (CH), 126.4 (CH), 122.9 (C), 72.4 (CH2), 58.5 (CH3), 46.4
(CH2), 45.6 (CH2), 42.7 (CH), 38.4 (CH2), 29.5 (CH2), 27.4 (CH2),
25.8 (CH2), 24.1 (CH2). Anal. (C16H23BrN2O2) C, H, N.
3-(3-Br om o-4-p yr id yl)p r op ion ic Acid Eth yl Ester (13).
The product was obtained as a yellow oil (49%): Kp 102-105
°C (0.1 mbar); Rf ) 0.25 (petroleum ether/EtOAc ) 4:1). 1H
NMR (CDCl3): δ 8.63 (s, 1H), 8.39 (d, J ) 6, 1H), 7.18 (d, J )
6, 1H), 4.10 (q, J ) 7.1, 2H), 3.02 (t, J ) 7.5, 2H), 2.63 (t, J )
7.5, 2H), 1.21 (t, J ) 7.1, 3H). 13C NMR (CDCl3): δ 171.8 (C),
151.8 (CH), 148.6 (C), 148.2 (CH), 125.1 (CH), 122.9 (C), 60.7
(CH2), 32.7 (CH2), 30.4 (CH2), 14.1 (CH3). Anal. (C10H12BrNO2)
C, H, N.
1-[2-(Iod om e t h yl)-4-(m e t h oxy)-1-oxob u t yl]p yr r oli-
d in e (8a ). The product was obtained as a yellowish oil (36%):
Rf ) 0.3 (ethyl acetate). 1H NMR (CDCl3): δ 3.69-3.32 (m,
8H), 3.28 (s, 3H), 3.31-3.08 (m, 1H), 2.05-1.69 (m, 6H). 13C
NMR (CDCl3): δ 171.5 (C), 69.8 (CH2), 58.3 (CH3), 46.6 (CH2),
45.6 (CH2), 43.9 (CH), 33.9 (CH2), 25.9 (CH2), 24.3 (CH2), 6.2
(CH2). Anal. (C10H18INO2) C, H, N.
5,6-Dih yd r o-6-[2-(m e t h oxy)e t h yl]-7H -2-p yr in d in -7-
on e (10a ). To a solution of n-BuLi (2.5 M in n-hexane; 64 mL;
159 mmol) in anhydrous toluene (500 mL), 9a (49.2 g; 144
mmol) in anhydrous toluene (500 mL) was added dropwise at
-90 °C. The mixture was stirred for 30 min, with the
temperature allowed to rise to -50 °C. After it was cooled to
-90 °C, a second portion of n-BuLi (2.5 M in n-hexane; 64 mL;
159 mmol) was added to the mixture, followed by another 30
min of stirring. The cold solution was poured on 2 N HCl (13
mL) and ice (100 g). After the organic layer was separated,
the aqueous phase was washed with EtOAc (5 × 200 mL). The
combined organic layers were dried (Na2SO4), filtered, and
evaporated. The crude product was purified by flash chroma-
tography (1 kg of silica gel; EtOAc) to give 21.5 g (78%) of a
yellow oil: Rf ) 0.3 (EtOAc). 1H NMR (CDCl3): δ 8.88 (s, 1H),
8.64 (d, J ) 6, 1H), 7.38 (d, J ) 6, 1H), 3.50 (t, J ) 8, 2H),
3.32 (dd, J ) 17, 6, 1H), 3.23 (s, 3H), 2.89 (dd, J ) 17, 9, 1H),
1-[2-(Iod om et h yl)-5-(m et h oxy)-1-oxop en t yl]p yr r oli-
d in e (8b). The product was obtained as a red oil (49%): Rf )
0.5 (ethyl acetate). 1H NMR (CDCl3): δ 3.72-3.32 (m, 7H),
3.28 (s, 3H), 3.13 (dd, J ) 17, 8, 1H), 3.06-2.88 (m, 1H), 2.02-
1.78 (m, 4H), 1.78-1.43 (m, 4H). 13C NMR (CDCl3): δ 171.7
(C), 72.3 (CH2), 58.6 (CH3), 47.0 (CH), 46.7 (CH2), 45.8 (CH2),
30.8 (CH2), 27.3 (CH2), 26.0 (CH2), 24.3 (CH2), 6.1 (CH2). Anal.
(C11H20INO2) C, H, N.
P yr id in iu m 1,4-Ad d ition . Gen er a l P r oced u r e. Zinc
powder (1.3 mmol) was suspended in a 50% solution of 1,2-
dibromoethane (0.15 mmol) in anhydrous THF under nitrogen
and briefly heated until gas began to evolve. This procedure
was repeated twice, followed by addition of a few drops of
chloro(trimethyl)silane. The mixture was stirred for 30 min
at room temperature. Then, a 50% solution of the appropriate
halide (8a ,b or ethyl â-iodopropionate; 1 mmol) in anhydrous
THF was carefully added. After it was stirred for 10 min and
briefly heated to reflux temperature three times, the resulting
suspension was allowed to stand for 1 h. Thoroughly dried LiCl
2.80-2.67 (m, 1H), 2.25-2.08 (m, 1H), 1.78-1.58 (m, 1H). 13
C
NMR (CDCl3): δ 206.8 (C), 161.4 (C), 153.4 (CH), 146.3 (CH),
132.2 (C), 121.7 (CH), 70.3 (CH2), 58.4 (CH3), 44.5 (CH), 32.7
(CH2), 30.6 (CH2). Anal. (C11H13NO2‚0.09H2O) C, H, N.

4052 J ournal of Medicinal Chemistry, 2002, Vol. 45, No. 18
Ullrich et al.
5,6-Dih yd r o-6-[3-(m et h oxy)p r op yl]-7H -2-p yr in d in -7-
on e (10b). To a solution of 9b (77.0 g; 217 mmol) in anhydrous
THF (1.4 L), n-BuLi (2.5 M in n-hexane; 87.0 mL; 217 mmol)
was added at -78 °C. The mixture was stirred for 30 min,
allowing the temperature to rise to -60 °C. The cold solution
was quenched with 2 N HCl (500 mL). After the organic
solvent was separated, the aqueous phase was washed with
EtOAc (2 × 200 mL), neutralized with NaHCO3, and extracted
with Et2O (5 × 300 mL). The combined organic layers were
dried (Na2SO4), filtered, and evaporated. The crude product
was purified by flash chromatography (500 g of silica gel; CH2-
Cl2/MeOH ) 15:1) to give 30.3 g (68%) of a yellow oil: Rf )
[3a r,8bâ]-1,2,3,3a ,4,8b-Hexa h yd r o-3a -[(3-m eth oxy)p r o-
p yl]p yr r olo[3′,2′:4,5]cyclop en ta [1,2-c]-p yr id in e (12b). The
product was obtained as a yellow oil (41%): Rf ) 0.4 (MeOH/
NH4OH ) 50:1). 1H NMR (CDCl3): δ 8.40 (s, 1H), 8.38 (d, J )
6, 1H), 7.06 (d, J ) 6, 1H), 4.38 (s, 1H), 3.38 (t, J ) 8, 2H),
3.31 (s, 3H), 3.13-2.98 (m, 1H), 3.00-2.87 (m, 2H), 2.78-2.64
(m, 1H), 2.34 (bs, 1H), 1.77-1.53 (m, 6H). 13C NMR (CDCl3):
δ 152.2 (C), 148.3 (CH), 147.1 (CH), 140.4 (C), 119.8 (CH), 72.8
(CH), 72.2 (CH2), 58.4 (CH3), 53.7 (C), 46.6 (CH2), 43.3 (CH2),
40.4 (CH2), 36.4 (CH2), 25.9 (CH2). Anal. (C14H20N2O‚0.06H2O)
C, H, N.
Eth er Clea va ge a n d Cycliza tion . Gen er a l P r oced u r e.
A solution of the appropriate pyrrolidine (12a ,b, 10 mmol) in
62% HBr (10 mL) was refluxed in a glass autoclave for 4 h.
After water (1 mL) and Na2CO3 (pH 8-9) were added, the
mixture was refluxed for 2 h and concentrated in vacuo. The
residue was triturated 5× with hot EtOAc, and the combined,
decanted organic layers were dried (Na2SO4), filtered, and
concentrated. The crude product was purified by flash chro-
matography (MeOH) and crystallized from Et2O.
1
0.4 (EtOAc). H NMR (CDCl3): δ 8.98 (s, 1H), 8.70 (d, J ) 6,
1H), 7.42 (d, J ) 6, 1H), 3.41 (t, J ) 8, 2H), 3.38 (dd, J ) 17,
9, 1H), 3.31 (s, 3H), 2.87 (dd, J ) 17, 6, 1H), 2.78-2.63 (m,
1H), 2.08-1.90 (m, 1H), 1.79-1.48 (m, 3H). 13C NMR
(CDCl3): δ 207.0 (C), 161.6 (C), 153.5 (CH), 146.5 (CH), 132.5
(C), 121.9 (CH), 72.3 (CH2), 58.5 (CH3), 46.9 (CH), 32.7 (CH2),
27.9 (CH2), 27.2 (CH2). Anal. (C12H15NO2‚0.15H2O) C, H, N.
Cya n om eth yla tion . Gen er a l P r oced u r e. To a 5% solu-
tion of diisopropylamine (1 mmol) in anhydrous THF, n-BuLi
(2.5 M solution in n-hexane; 1 mmol) was added at -30 °C
and stirred for 30 min. A 10% solution of the appropriate
pyrindinone (10a ,b, 1 mmol) in anhydrous THF was added
dropwise at -20 °C and stirred for 1 h at 0 °C. The mixture
was cooled to -90 °C, and a 20% solution of iodoacetonitrile
(1 mmol) in anhydrous THF was added quickly. After it was
stirred for 1 h at room temperature, the mixture was extracted
with 2 N HCl. The aqueous phase was washed with EtOAc,
neutralized with Na2CO3, and extracted 3× with EtOAc. The
combined organic layers were dried (Na2SO4), filtered, and
evaporated. The crude product was purified by flash chroma-
tography (EtOAc).
(()-1,3a -E t h a n o-1,2,3,3a ,4,8b -h exa h yd r op yr r olo[3′,2′:
4,5]cyclop en ta [1,2-c]-p yr id in e (4a ). The product was ob-
tained as colorless crystals (60%): mp 104-107 °C; Rf ) 0.3
(MeOH/NH4OH ) 50:1). 1H NMR (CDCl3): δ 8.52 (s, 1H), 8.40
(d, J ) 6, 1H), 7.15 (d, J ) 6, 1H), 3.93 (s, 1H), 3.57-3.30 (m,
1H), 3.08-2.63 (m, 3H), 2.98-2.80 (m, 2H), 1.82-1.61 (m, 1H),
1.51-1.38 (m, 1H), 1.38-1.20 (m, 1H), 1.19-1.00 (m, 1H). 13
C
NMR (CDCl3): δ 158.3 (C), 148.7 (CH), 145.6 (CH), 135.0 (C),
122.2 (CH), 82.6 (CH), 61.8 (CH2), 57.9 (CH2), 55.0 (C), 35.2
(CH2), 34.1 (CH2), 32.1 (CH2). Anal. (C12H14N2‚0.03H2O) C, H,
N.
(()-[4a r,9b â]-2H -1,4a -E t h a n o-3,4,5,9b -t et r a h yd r o-1H -
cyclop en ta [2,1-b:3,4-c’]d ip yr id in e (4b). The product was
obtained as colorless crystals (46%): mp 84-86 °C; Rf ) 0.3
(MeOH/NH4OH ) 50:1). 1H NMR (CDCl3): δ 8.52 (s, 1H), 8.42
(d, J ) 6, 1H), 7.13 (d, J ) 6, 1H), 3.95 (s, 1H), 3.12-2.65 (m,
6H), 2.08-1.60 (m, 4H), 1.60-1.38 (m, 1H), 1.34-1.09 (m, 1H).
13C NMR (CDCl3): δ 151.9 (C), 148.5 (CH), 145.6 (CH), 138.4
(C), 121.2 (CH), 78.9 (CH), 56.1 (CH2), 52.2 (CH2), 51.1 (C),
40.3 (CH2), 36.2 (CH2), 35.0 (CH2), 19.4 (CH2). Anal. (C13H16N2‚
0.49H2O) C, H, N.
Op tica l Resolu tion of 4a . Step 1: A solution of (+)-O,O′-
di-p-toluoyltartaric (0.5 mmol) in anhydrous EtOH (1 mL) was
added to (()-4a (1 mmol) in anhydrous EtOH. The solution
was stored at -20 °C until precipitation of the chiral salt was
completed. The product was obtained by filtration, washed
with EtOH, and dried in vacuo. Step 2: The crude product
was recrystallized 2× from EtOH. The optically resolved
material (ee > 95%) was free-based with 0.1 N NaOH,
extracted with CHCl3, dried (Na2SO4), and concentrated to give
crystalline (-)-4a . Step 3: The mother liquor from step 1 was
free-based and worked up in the same manner and submitted
to derivatization with (-)-O,O′-di-p-toluoyltartaric acid, as
described above, to afford (+)-4a (ee > 95%).
Op tica l Resolu tion of 4b. Step 1: A solution of (+)-O,O′-
di-p-toluoyltartaric acid (0.5 mmol) in anhydrous EtOH (1 mL)
was added to (()-4b (1 mmol) in anhydrous EtOH. The
solution was stored at -20 °C until precipitation of the chiral
salt was completed. The product was obtained by filtration,
washed with EtOH, and dried in vacuo. Step 2: The crude
product was recrystallized 2× from MeOH. The optically
resolved material (de > 95%) was free-based with 0.1 N NaOH,
extracted with CHCl3, dried (Na2SO4), and concentrated to give
an amorphous solid that was dissolved in 8 N methanolic HCl
and concentrated in vacuo. Treatment with methanolic HCl
in this manner was repeated twice, and (-)-4b‚2HCl precipi-
tated from the methanolic solution upon storage at -20 °C
for 3 days. Step 3: The mother liquor from step 1 was free-
based and worked up in the same manner and submitted to
derivatization with (-)-O,O′-di-p-toluoyltartaric acid, as de-
scribed above, to afford (+)-4b‚2HCl (de > 95%).
6,7-Dih yd r o-6-(2-m eth oxyeth yl)-7-oxo-5H-2-p yr in d in e-
6-a ceton itr ile (11a ). The product was obtained as a yellow
1
oil (78%): Rf ) 0.3 (EtOAc). H NMR (CDCl3): δ 8.92 (s, 1H),
8.70 (d, J ) 6, 1H), 7.42 (d, J ) 6, 1H), 3.32-3.12 (m, 2H),
3.28 (t, J ) 8, 2H), 2.97 (s, 3H), 2.72-2.58 (m, 1H), 2.12-1.80
(m, 2H). 13C NMR (CDCl3): δ 204.7 (C), 159.3 (C), 154.1 (CH),
146.7 (CH), 131.0 (C), 121.6 (CH), 116.8 (C), 67.9 (CH2), 58.2
(CH3), 48.8 (CH), 37.2 (CH2), 36.2 (CH2), 25.2 (CH2). Anal.
(C13H14N2O2‚0.14H2O) C, H, N.
6,7-Dih ydr o-6-(3-m eth oxypr opyl)-7-oxo-5H-2-pyr in din e-
6-a ceton itr ile (11b). The product was obtained as a yellow
1
oil (78%): Rf ) 0.4 (EtOAc). H NMR (CDCl3): δ 9.03 (s, 1H),
8.75 (d, J ) 6, 1H), 7.48 (d, J ) 6, 1H), 3.32-3.18 (m, 4H),
3.20 (t, J ) 8, 2H), 2.70-2.57 (m, 2H), 1.82-1.78 (m, 2H),
1.53-1.22 (m, 2H). 13C NMR (CDCl3): δ 205.1 (C), 159.7 (C),
154.8 (CH), 147.0 (CH), 131.1 (C), 121.8 (CH), 116.8 (C), 71.7
(CH2), 58.4 (CH3), 49.7 (CH), 37.4 (CH2), 33.8 (CH2), 24.9 (CH2),
24.3 (CH2). Anal. (C14H16N2O2‚0.05H2O) C, H, N.
Red u ctive Am in a tion of Keton es. Gen er a l P r oced u r e.
The appropriate nitrile (11a ,b, 10 mmol) was dissolved in
anhydrous MeOH (10 mL), treated with activated charcoal,
and filtered. Activated Raney cobalt (3 equiv of weight) was
added to the filtrate. The mixture was transferred into a Parr
hydrogenator and shaken for 12 h at 50 °C (90 psi H2). The
procedure was repeated with another equivalent of weight of
Raney cobalt. After the reaction was completed (by TLC), the
catalyst was filtered through Celite. The solvent was removed
in vacuo, and the residue was purified by flash chromatogra-
phy (MeOH/NH4OH ) 50:1). The product was dissolved in CH2-
Cl2, dried (Na2SO4), filtered, and concentrated.
[3a r,8bâ]-1,2,3,3a ,4,8b-Hexa h yd r o-3a -[(2-m eth oxy)eth -
yl]p yr r olo[3′,2′:4,5]cyclop en ta [1,2-c]p yr id in e (12a ). The
product was obtained as a yellow oil (55%): Rf ) 0.4 (MeOH/
NH4OH ) 50:1). 1H NMR (CDCl3): δ 8.52 (s, 1H), 8.41 (d, J )
6, 1H), 7.09 (d, J ) 6, 1H), 4.47 (s, 1H), 3.49 (t, J ) 8, 2H),
3.29 (s, 3H), 3.15-2.98 (m, 1H), 3.05-2.90 (m, 2H), 2.79-2.63
(m, 1H), 2.30 (bs, 1H), 2.00-1.63 (m, 4H). 13C NMR (CDCl3):
δ 152.0 (C), 148.5 (CH), 147.3 (CH), 141.0 (C), 120.3 (CH), 72.5
(CH), 70.3 (CH2), 58.6 (CH3), 52.7 (C), 46.6 (CH2), 43.6 (CH2),
40.4 (CH2), 39.2 (CH2). Anal. (C13H18N2O‚0.05H2O) C, H, N.
(R)-(-)-1,3a -E t h a n o-1,2,3,3a ,4,8b -h exa h yd r op yr r olo-
[3′,2′:4,5]cyclop en ta [1,2-c]-p yr id in e (4a ). The product was
obtained as colorless crystals (20%): [R]D20 -51.2° (c 1, MeOH).

Conformationally Constrained Nicotines
J ournal of Medicinal Chemistry, 2002, Vol. 45, No. 18 4053
Anal. (C12H14N2‚0.04H2O) C, H, N. All other analytical data
were identical with those of (()-4a .
(S)-(+)-1,3a -E t h a n o-1,2,3,3a ,4,8b -h exa h yd r op yr r olo-
[3′,2′:4,5]cyclop en ta [1,2-c]-p yr id in e (4a ). The product was
obtained as colorless crystals (23%): [R]D20 +50.7° (c 1, MeOH).
Anal. (C12H14N2‚0.12H2O) C, H, N. All other analytical data
were identical with those of (()-4a .
with methanolic HCl in this manner was repeated twice, and
(-)-5a ‚2HCl precipitated from acetone/EtOH upon storage at
-20 °C for 3 days. Step 3: The combined mother liquors from
step 1 were free-based and worked up in the same manner
and submitted to derivatization with (-)-O,O′-di-p-toluoyltar-
taric acid, as described above, to afford (+)-5a ‚2HCl (ee >
95%).
(R)-(-)-1,2,3,4,10,11-Hexa h yd r osp ir o[7H-2-p yr in d in e-
7,2′-2H-p yr r ole]d ih yd r och lor id e (5a ). The product was
obtained as colorless, hygroscopic crystals (26%): mp not
measurable; [R]D20 -23.1° (c 1, MeOH). 1H NMR (D2O): δ 8.94
(s, 1H), 8.77 (d, J ) 6, 1H), 8.10 (d, J ) 6, 1H), 3.71-3.52 (m,
2H), 3.52-3.36 (m, 2H), 2.84-2.26 (m, 6H). 13C NMR (D2O):
δ 169.4 (C), 144.2 (CH), 142.1 (C), 139.5 (CH), 126.6 (CH), 76.6
(C), 47.2 (CH2), 38.1 (CH2), 37.9 (CH2), 33.3 (CH2), 24.8 (CH2).
Anal. (C11H16Cl2N2‚0.3H2O) C, H, N.
(S)-(+)-1,2,3,4,10,11-H exa h yd r osp ir o[7H -2-p yr in d in e-
7,2′-2H-p yr r ole]d ih yd r och lor id e (5a ). The product was
obtained as colorless, hygroscopic crystals (22%): mp not
measurable; [R]D20 +24.0° (c 1, MeOH). Anal. (C11H16Cl2N2) C,
H, N. All other analytical data were identical with those of
(-)-5a ‚2HCl.
N-Meth yla tion . Gen er a l P r oced u r e. A solution of the
appropriate pyrrolidine ((+)-5a or (-)-5a ) (650 mg, 3.73 mmol)
and 35% aqueous formaldehyde (3.1 mL, 36.1 mmol) in
anhydrous CH3CN (30 mL) was treated with NaBH3CN (540
mg, 8.58 mmol) and stirred for 30 min at room temperature.
The mixture was quenched with 2 N HCl until pH 1. The
resulting slurry was washed with CH2Cl2 (2 × 50 mL),
alkalified with 6 N NaOH (pH 10), and extracted with CH2-
Cl2 (4 × 50 mL). The combined organic layers were dried (Na2-
SO4), filtered, and evaporated to give a solid (Rf ) 0.5/MeOH)
that was dissolved in 8 N methanolic HCl and concentrated
in vacuo. Treatment with methanolic HCl in this manner was
repeated twice, and the product was precipitated from acetone/
EtOH upon storage at -20 °C for 3 days.
[4aR-(4ar,9bâ)]-(-)-2H-1,4a-Eth an o-3,4,5,9b-tetr ah ydr o-
1H-cyclop en ta [2,1-b:3,4-c’]d ip yr id in e, Dih yd r och lor id e
(4b). The product was obtained as colorless, hygroscopic
crystals (18%): mp not measurable; [R]D20 -44.6° (c 1, MeOH).
1H NMR (D2O): δ 8.82 (s, 1H), 8.73 (d, J ) 6, 1H), 8.09 (d, J
) 6, 1H), 4.91 (s, 1H), 3.70-3.20 (m, 6H), 2.38-1.97 (m, 5H),
1.72-1.51 (m, 1H). 13C NMR (D2O): δ 166.7 (C), 144.1 (CH),
139.1 (CH), 137.3 (C), 127.2 (CH), 76.7 (CH), 56.5 (CH2), 54.2
(CH2), 52.5 (C), 42.4 (CH2), 33.6 (CH2), 33.0 (CH2), 18.6 (CH2).
Anal. (C13H18Cl2N2‚0.35H2O) C, H, N.
[4aS-(4ar,9bâ)]-(+)-2H-1,4a-Eth an o-3,4,5,9b-tetr ah ydr o-
1H-cyclop en ta [2,1-b:3,4-c’]d ip yr id in e, Dih yd r och lor id e
(4b). The product was obtained as colorless, hygroscopic
crystals (27%): [R]D20 +44.3° (c 1, MeOH). Anal. (C13H18Cl2N2‚
0.37H2O) C, H, N. All other analytical data were identical with
those of (-)-4b.
3-Br om o-4-[2-(4,5-d ih yd r o-3H -p yr r ol-2-yl)et h yl]p yr i-
d in e (15). A solution of freshly distilled N-vinyl-2-pyrrolidi-
none (18.2 g, 164 mmol) and 13 (40.0 g, 155 mmol) in
anhydrous THF (300 mL) was added to a suspension of NaH
(4.30 g, 179 mmol) in anhydrous THF (300 mL) in a N2
atmosphere. The mixture was refluxed for 1 h and poured on
a saturated NH4Cl solution (300 mL). After THF was removed
in vacuo, the aqueous mixture was extracted with Et2O (3 ×
500 mL). The combined organic layers were dried (Na2SO4),
filtered, and evaporated. The crude intermediate (14) was not
further purified but taken up in 8 N HCl (650 mL) and refluxed
for 12 h. The mixture was cooled with an ice bath, alkalified
with 50% NaOH until pH 10, and extracted with CH2Cl2 (4 ×
500 mL). The combined organic layers were dried (Na2SO4),
filtered, and evaporated. The crude product was purified by
flash chromatography (450 g of silica gel; CH2Cl2/acetone )
2:1) to give 16.3 g (42%) of a yellow oil: Rf ) 0.35 (CH2Cl2/
(R)-(-)-1,2,3,4,10,11-1-Hexa h yd r o-1-m eth ylsp ir o[7H-2-
pyr in din e-7,2′-2H-pyr r ole]dih ydr och lor ide (5b). The prod-
uct was obtained as colorless, hygroscopic crystals (78%): mp
20
1
not measurable; [R]D -39.9° (c 1, MeOH). H NMR (D2O): δ
8.93 (s, 1H), 8.74 (d, J ) 6, 1H), 8.04 (d, J ) 6, 1H), 3.92-3.23
(m, 4H), 2.88-2.21 (m, 6H), 2.68 (s, 3H). 13C NMR (D2O): δ
170.4 (C), 144.7 (CH), 140.5 (CH), 139.4 (C), 126.9 (CH), 81.6
(C), 56.1 (CH3), 38.1 (CH2), 36.5 (CH2), 36.2 (CH2), 33.8 (CH2),
22.1 (CH2). Anal. (C12H18Cl2N2) C, H, N.
1
acetone ) 2:1). H NMR (CDCl3): δ 8.65 (s, 1H), 8.39 (d, J )
6, 1H), 7.19 (d, J ) 6, 1H), 3.90-3.78 (m, 2H), 3.12-3.01 (m,
2H), 2.63 (t, J ) 8, 2H), 2.50 (t, J ) 8, 2H), 2.00-1.83 (m,
2H). 13C NMR (CDCl3): δ 176.1 (C), 151.7 (CH), 149.5 (C),
148.1 (CH), 124.9 (CH), 122.8 (C), 60.7 (CH2), 37.5 (CH2), 32.2
(CH2), 31.7 (CH2), 22.3 (CH2). Anal. (C11H13BrN2) C, H, N.
(S)-(+)-1,2,3,4,10,11-1-Hexa h yd r o-1-m eth ylsp ir o[7H-2-
pyr in din e-7,2′-2H-pyr r ole]dih ydr och lor ide (5b). The prod-
uct was obtained as colorless, hygroscopic crystals (82%): mp
not measurable; [R]D20 +39.8° (c 1, MeOH). Anal. (C12H18Cl2N2)
C, H, N. All other analytical data were identical with those of
(-)-5b‚2HCl.
(()-1,2,3,4,10,11-Hexa h yd r osp ir o[7H-2-p yr in d in e-7,2′-
2H-p yr r ole] (5a ). n-BuLi (2.5 M solution in n-hexane, 97.5
mmol) was added to 15 (24.5 g, 96.8 mmol) in anhydrous
toluene (350 mL) at -78 °C under a N2 atmosphere. After it
was stirred for 30 min, the mixture was poured on 2 N NaOH
(400 mL) and extracted with Et2O (5 × 500 mL). The combined
organic layers were dried (Na2SO4), filtered, and evaporated.
The crude product was purified by flash chromatography (400
g of silica gel; MeOH) to give 7.44 g (44%) of a yellow oil: Rf
X-r a y Str u ctu r e Deter m in a tion s. X-ray data collection
was carried out with a Bruker SMART CCD area detector
diffractometer and graphite monochromatized Mo KR radia-
tion, λ(Mo - KR) ) 0.71073 Å. For each crystal, four sets of
frames were measured, which covered complete spheres of the
reciprocal space (4 × 606 frames, ω-scans, ∆ω ) 0.3°).
Corrections for absorption was with program SADABS, struc-
ture solution was with direct methods and the program
1
) 0.3 (MeOH). H NMR (CDCl3): δ 8.46 (s, 1H), 8.38 (d, J )
6, 1H), 7.11 (d, J ) 6, 1H), 3.26-2.99 (m, 2H), 2.99-2.70 (m,
2H), 2.23-1.89 (m, 7H). 13C NMR (CDCl3): δ 152.5 (C), 148.2
(CH), 145.3 (C), 144.4 (CH), 120.0 (CH), 71.6 (C), 46.5 (CH2),
2
41.0 (CH2), 38.2 (CH2), 29.9 (CH2), 25.9 (CH2). Anal. (C11H16
Cl2N2) C, H, N.
-
SHELXS97, and structure refinement on F was with the
program SHELXL97.22 All nonhydrogen atoms were refined
anisotropically. Hydrogen atoms had isotropic temperature
factors and rided on the C atoms to which they were bonded
or, if N- or O-bound, were refined in x,y,z without restraints.
Com p ou n d 16 [(2R,3R)-(-)-O,O′-Di-p-tolu oylta r tr a te of
(R)-(-)-4a ]. Crystal data: C32H32N2O8, Mr ) 572.60, colorless
prism (0.24 mm × 0.20 mm × 0.18 mm) from ethanol,
orthorhombic, space group P212121 (no. 19), a ) 12.277(5) Å, b
) 15.126(5) Å, c ) 15.957(5) Å, V ) 2963.2(18) Å3, Z ) 4, Dx
) 1.283 Mg/m-3, µ ) 0.093 mm-1, T ) 295(2) K. A total of
29 164 reflections with θ < 25.0° measured and merged to 5177
unique reflections, Rint ) 0.074. The final refinement varied
388 parameters and converged at R1 ) ∑||Fo| - |Fc||/∑|Fo| )
0.080, wR2 ) [∑(w(Fo2-Fc2)2)/∑(w(Fo2)2)]1/2 ) 0.097, and S )
Op tica l Resolu tion of 5a . Step 1: A solution of (()-5a
(3.30 g, 18.9 mmol) in EtOH (20 mL) was treated with (-)-
O,O′-di-p-toluoyltartaric acid (7.31 g, 18.9 mmol). The resulting
solution was diluted with acetone (10 mL) and H2O (7 mL)
and stored at -20 °C until precipitation of the chiral salt was
completed. The product was obtained by filtration, washed
with hot MeOH, and dried in vacuo. Step 2: The residue was
free-based with 0.1 N NaOH, extracted with Et2O, dried (Na2-
SO4), and concentrated to give partially resolved material (ee
) 70%) that underwent the same procedure twice with
equimolar amounts of (-)-O,O′-di-p-toluoyltartaric acid, to
furnish optically resolved (-)-5a (ee > 95%) that was dissolved
in 8 N methanolic HCl and concentrated in vacuo. Treatment

4054 J ournal of Medicinal Chemistry, 2002, Vol. 45, No. 18
Ullrich et al.
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1.10 for the 5177 unique reflections; R1 ) 0.056 for the 4078
observed data [I > 2σ(I)].
Com p ou n d 17 [(2S,3S)-(+)-O,O′-Di-p-tolu oylta r tr a te of
(4a S)-(+)-4b]. Crystal data: C33H34N2O8, Mr ) 586.62, color-
less prism of poor quality and low scattering power (0.32 mm
× 0.24 mm × 0.24 mm) from ethanol, orthorhombic, space
group P212121 (no. 19), a ) 12.369(8) Å, b ) 15.446(8) Å, c )
15.711(8) Å, V ) 3002(3) Å3, Z ) 4, Dx ) 1.298 mg/m-3, µ )
0.093 mm-1, T ) 295(2) K. A total of 23 123 reflections with θ
< 22.5° measured and merged to 3871 unique reflections, Rint
) 0.122. The final refinement varied 397 parameters and
converged at R1 ) 0.085, wR2 ) 0.141, and S ) 1.18 for the
3871 unique reflections; R1 ) 0.069 for the 3273 observed data
[I>2σ(I)].
(R)-(-)-5b‚2HCl. Crystal data: C12H18Cl2N2, Mr ) 586.62,
colorless block (0.65 mm × 0.4 mm × 0.4 mm) from ethanol,
monoclinic, space group P21 (no. 4), a ) 11.225(3) Å, b )
10.221(4) Å, c ) 11.617(4) Å, V ) 1330.6(8) Å3, Z ) 4 (two
independent molecules per asymmetric unit), Dx ) 1.304 mg/
m-3, µ ) 0.464 mm-1, T ) 295(2) K. A total of 19 244 reflections
with θ < 30° measured and merged to 7549 unique reflections,
Rint ) 0.019. The final refinement varied 3â2 parameters and
converged at R1 ) 0.041, wR2 ) 0.093, and S ) 1.07 for the
7549 unique reflections; R1 ) 0.037 for the 6940 observed data
[I > 2σ(I)].
Compounds 16 and 17 form an enantiomeric pair of almost
identical structures, which differ only by one ring CH2 group
but not in the basic spatial arrangement, orientation, and
mutual hydrogen bonding of their constituents. In each
compound, the nonaromatic N atom is protonated and donates
a hydrogen bond to a COO- oxygen atom whereas the second
active hydrogen atom remains part of a toluoyltartaric acid
COOH group and forms a hydrogen bond to the pyridine
nitrogen as the acceptor. In the structure of (R)-(-)-5b‚2HCl,
the two active hydrogen atoms are bonded to both N atoms of
the 5b molecule and form hydrogen bonds to the Cl- anions
as acceptors. Further details on all structures are given in the
Supporting Information.
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May, E. L.; Rosecrans, J . A.; Collins, A. C.; Martin, B. R.
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Hexahydro-1-methyl-1H-pyrrolo[3,2-h]isoquinoline, a Bridged-
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a
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N-Methylcarbamylcholine. J . Comput. Mol. Des. 2001, 15, 247-
258.
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modification of the method described by Pabreza et al.21
Membrane-enriched fractions from rat brain minus cerebellum
(ABS Inc., Wilmington, DE) were slowly thawed at 4 °C,
washed, and resuspended in 30 volumes of BSS-Tris buffer
(120 mM NaCl, 5 mM KCl, 2 mM CaCl2, 2 mM MgCl2, and 50
mM Tris-Cl, pH 7.4, 4 °C). Seven log-dilution concentrations
of test compounds (10-5 to 10-11 M) containing 100-200 µg of
protein and 0.75 nM [3H] cytisine (30 Ci/mmol; Perkin-Elmer-
NEN, Boston, MA) were incubated in a final volume of 500
µL for 75 min at 4 °C in duplicate. Nonspecific binding was
determined in the presence of 10 µM (-)-nicotine. Incubations
were terminated by vacuum filtration through Whatman GF/C
filters that were prewet with 0.5% polyethylenimine. Bound
radioactivity was collected on Millipore MultiScreen harvest
plates FB using a Packard cell harvester, and radioactivity
was determined using a Packard TopCount Microplate beta
counter. IC50 values were determined by nonlinear regression
in Microsoft Excel. Ki values were calculated from the IC50
values using the Cheng-Prusoff equation, where Ki ) IC50/1
+ [ligand]/KD]. Average Ki values were derived from a mini-
mum of three separate determinations (N).
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(22) (a) Sheldrick, G. M. SADABS: Program for Absorption Correc-
tion, University of Go¨ttingen, Germany, 1996. (b) Sheldrick, G.
M. SHELXS97: Program for the Solution of Crystal Structures,
University of Go¨ttingen, Germany, 1997. (c) Sheldrick, G. M.
SHELXL97: Program for Crystal Structure Refinement, Uni-
versity of Go¨ttingen, Germany, 1997.
Ack n ow led gm en t. We thank C. Adelwo¨hrer and A.
Ro¨gner for their support in the synthetic work.
Su p p or tin g In for m a tion Ava ila ble: Tables of X-ray
structural data, including data collection parameters, posi-
tional and thermal parameters, and bond distances and angles
for compounds 16, 17, and (R)-(-)-5b‚2HCl. This material is
available free of charge via the Internet at http://pubs.acs.org.
Refer en ces
(1) Schmitt, J . D.; Bencherif, M. Chapter 5: Targeting Nicotinic
Acetylcholine Receptors: Advances in Molecular Design and
Therapies. Ann. Rep. Med. Chem. 2000, 35, 41-45.
J M020916B