Design, synthesis, and preliminary pharmacological evaluation of new quinoline derivatives as nicotinic ligands

Article abstract of DOI:10.1021/jm070325r

A series of nicotinic ligands, carrying a quinoline nucleus, and characterized by a pharmacophoric distance between the quinoline nitrogen (H-bond acceptor) and the cationic nitrogen atoms higher than that proposed in the classical pharmacophoric models,

Full text of DOI:10.1021/jm070325r

J. Med. Chem. 2007, 50, 4993-5002
4993
Design, Synthesis, and Preliminary Pharmacological Evaluation of New Quinoline Derivatives as
Nicotinic Ligands
Luca Guandalini,† Monica Norcini,‡ Katia Varani,§ Marco Pistolozzi,| Cecilia Gotti, Carla Bazzicalupi,# Elisabetta Martini,†
Silvia Dei,† Dina Manetti,† Serena Scapecchi,† Elisabetta Teodori,† Carlo Bertucci,| Carla Ghelardini,‡ and
Maria Novella Romanelli*,†
Laboratory of Design, Synthesis and Study of Biologically ActiVe Heterocycles (HeteroBioLab), Department of Pharmaceutical Sciences,
UniVersity of Florence, Via Ugo Schiff 6, I-50019 Sesto Fiorentino, Italy, Department of Preclinical and Clinical Pharmacology,
UniVersity of Florence, Viale Pieraccini 6, I-50139 Firenze, Italy, Institute of Pharmacology, UniVersity of Ferrara, Via Fossato di Mortara
17-19, I-44100 Ferrara, Italy, Department of Pharmaceutical Sciences, UniVersity of Bologna, Via Belmeloro 6, I-40126 Bologna, Italy, CNR,
Institute of Neuroscience, Molecular and Cellular Pharmacology, Via VanVitelli 32, I-20129 Milano, Italy, Department of Chemistry, UniVersity
of Florence, Via della Lastruccia 3, I-50019 Sesto Fiorentino, Italy
ReceiVed March 21, 2007
A series of nicotinic ligands, carrying a quinoline nucleus, and characterized by a pharmacophoric distance
between the quinoline nitrogen (H-bond acceptor) and the cationic nitrogen atoms higher than that proposed
in the classical pharmacophoric models, have been synthesized and tested for their affinity for the central
nicotinic receptor. The enantiomers of the nicotine analogue 1-methyl-2-pyrrolidinyl-6-quinoline and of its
methiodide display enantioselectivity in binding studies, but not when tested in vivo; on R7* nicotinic receptor
enantioselectivity is inverted with respect to the R4â2* subtype. N,N,N-Trimethyl-4-(quinolin-6-yl)but-3-
yn-1-ammonium iodide (3c) and trans-N,N,N-trimethyl-4-(quinolin-6-yl)but-3-en-1-ammonium iodide (4c),
showing pharmacophoric distances in the range 8.5-10.4 Å, interact with the R4â2* nicotinic receptor
with Ki in the µM range; compound 3c shows preference for the R7* subtype.
Introduction
is made difficult by the high number of subunits that can co-
assemble in many different ways, by the low abundance of some
of them in the brain, and by the lack of selective ligands to
study the role of nAChR under physiological or pathological
conditions. Therefore, it is important to find new selective
nicotinic ligands. On the other hand, there is evidence that some
therapeutic effects are shared by nicotinic modulators selective
for different subtypes: for instance, both R4â2* and R7*
agonists are able to improve cognition,8,9 or to induce analge-
sia,10 also suggesting that agonists with broader activity could
be useful, at least as cognition-enhancers or as analgesics.
Nicotinic acetylcholine receptors (nAChRa) belong to the
family of ligand-gated ion channels (LGIC). They are composed
of five subunits assembled around a central channel and are
permeable to cations such as Na+, K+, or Ca++.1 nAChR have
been divided into muscle-type receptors found at the skeletal
neuromuscular junction, where they mediate neuromuscular
transmission, and neuronal receptors, found throughout the
central and peripheral nervous system, but also in non-neuronal
tissues.2 To date, 17 different subunits have been cloned and
of these, five (R1, â1, γ, δ, and ꢀ) are found in the muscle-type
receptor and 12 (R2-10 and â2-4) are found in neuronal
receptors; these subunits are differently distributed in the areas
of the nervous system, some in low abundance, and the number
of possible combinations is not yet known.3,4 nAChR may have
presynaptic, postsynaptic, and nonsynaptic locations, suggesting
a modulatory role for these proteins in the brain.5
The therapeutic potential of nicotinic modulators can be
highlighted by the wide range of diseases in which nAChR have
been implicated, including Alzheimer’s and Parkinson’s disease,
autism, epilepsy, schizophrenia, depression, and addiction;
moreover, nAChR are involved in important functional mech-
anisms, such as pain control and cognition.6,7 It is obviously
important to determine which subtype of nicotinic receptor is
involved in each process to design specific modulators, but this
We have recently reported about a series of quinoline
derivatives designed on the basis of a 3D-database search
approach, endowed with good affinity for the R4â2* nicotinic
receptor.11 The most interesting compounds of this series (1a-
c, Chart 1)12 show a distance between the H-bond acceptor
aromatic nitrogen and the cationic nitrogen, which is higher (6.6
Å) than that proposed by the classical pharmacophoric models
(4.5-6.1 Å)13-15 but in the same range as that obtained by
applying the “water-extension concept” to classical ligands.16
On these bases, we thought it interesting to continue our work
in two directions: to study the enantioselectivity of compounds
1b and 1c and to test a new series of quinolinyl derivatives,
characterized by a pharmacophoric N-N distance greater than
6.6 Å. Compounds 2-4 were therefore designed (Chart 1),
which represent the product of hybridization between quinoline
and the basic portion of high affinity nicotinic ligands such as
A-84543,15 N-methyl-3-(4-aminobutynyl)pyridine,17,18 or trans-
metanicotine. Moreover, we decided to also test the cis-
derivative 5 and the analogues with a 3-C-atoms side chain
(compounds 6-8). For each compound, secondary, tertiary, and
quaternary derivatives were prepared. Preliminary results on
compounds 3-519 have also shown that “long” derivatives can
interact with, and activate, the central nicotinic receptor.
* To whom correspondence should be addressed. Tel.: +39 055
4573691. Fax: +39 055 4573671. E-mail: novella.romanelli@unifi.it.
† Department of Pharmaceutical Sciences, University of Florence.
‡ Department of Preclinical and Clinical Pharmacology, University of
Florence.
§ University of Ferrara.
| University of Bologna.
CNR, Institute of Neuroscience.
# Department of Chemistry, University of Florence.
a Abbreviations: nAChR, nicotinic acetylcholine receptors; LGIC, ligand-
gated ion channels; ee, enantiomeric excess; ER, eudismic ratio.
10.1021/jm070325r CCC: $37.00 © 2007 American Chemical Society
Published on Web 09/12/2007

4994 Journal of Medicinal Chemistry, 2007, Vol. 50, No. 20
Guandalini et al.
Chart 1
Scheme 1a
Scheme 2a
a Reagents: (a) (R)-2-benzoyloxypropionyl chloride; (b) chromatographic
separation; (c) HCl, AcOH; (d) ClCOOCH2Ph; (e) LiAlH4; (f) di-O,O′-p-
toluoyltartaric acid; (g) NaOH; (h) MeI.
a Reagents: (a) p-toluenesulfonyl chloride, Py; (b) 6-hydroxyquinoline,
NaH; (c) H2, Pd/C; (d) LiAlH4; (e) MeI. Starting from N-CBZ-(S)-prolinol,
the enantiomeric compounds (S)-11 and (S)-2a-c were obtained.
Chemistry
Scheme 3a
The enantiomers of 1b were obtained in two different ways
(Scheme 1). Derivatization of rac-1a11 with (R)-2-benzylox-
ypropionyl chloride (obtained by treating the commercially
available (R)-2-benzyloxypropionic acid with SOCl2) gave two
diastereomeric amides 9 and 10, which were separated by
chromatography, obtaining the first-eluted amide 9 as a single
isomer, as shown by the NMR spectrum, and a mixture of 9
and 10 in a 1:2 ratio. Four further chromatographic separations
gave again some amount of 9 (39% final yield) but did not allow
obtainment of pure 10, because in the NMR spectrum of this
compound (27% final yield) the presence of some amount (5%)
of 9 was detectable. Compounds 9 and 10 were hydrolyzed
under acidic conditions, giving, respectively, (-)-1a and (+)-
1a, which were transformed into (-)-1b and (+)-1b following
the same procedure used for the racemate.11
To improve enantiomeric excess (ee) and to obtain greater
amounts of compound, (()-1b was resolved also by fractional
crystallization of the diastereomeric salts formed with chiral
acids. Several acids were used, starting from those already
utilized for the resolution of enantiomeric mixtures of nicotine
or of its analogues;20-22 however, only O,O′-di-p-toluoyl-tartaric
acid gave a salt suitable for crystallization, making it possible
to obtain (+)-1b and (-)-1b, with high ee. The tertiary amines
(+)-1b and (-)-1b were transformed into the methiodides (+)-
1c and (-)-1c by treatment with MeI.
a Reagents: (a) Pd(PPh3)4, CuBr, NEt3; (b) CH3SO2Cl, pyridine; (c)
MeNHR, EtOH; (d) MeI; (e) LiAlH4; (f) H2/Pd/BaSO4. Ar ) 6-quinolinyl.
Mitsunobu method. Catalytic hydrogenation of (R)-11 gave the
secondary amine (R)-2a, while LiAlH4 reduction gave (R)-2b,
which was then treated with MeI to give (R)-2c. Compounds
(S)-2a-c were obtained in the same way starting from (S)-
benzyl 2-(hydroxymethyl)pyrrolidine-1-carboxylate.23
A preliminary report on the synthesis of compounds 3-5 has
been published in ref 19; the description of the experimental
work is reported as Supporting Information.
The synthesis of compounds 6-8 is reported in Scheme 3.
The Sonogashira reaction between 6-bromoquinoline and pro-
pargyl alcohol gave compound 12, which was transformed into
the methanesulfonate ester and reacted with methylamine or
dimethylamine, obtaining, respectively, 6a and 6b. LiAlH4
reduction of 12 gave only the trans-alcohol 13, while its cis-
The synthesis of compounds 2a-c is reported in Scheme 2.
Compound (R)-11 was obtained by reaction of (R)-benzyl
2-[(toluene-4-sulfonyloxy)methyl]pyrrolidine-1-carboxylate (ob-
tained by reaction of (R)-benzyl 2-(hydroxymethyl)pyrrolidine-
1-carboxylate23 with p-toluenesulfonyl chloride) with 6-hydrox-
yquinoline under basic conditions; this method allowed obtainment
of the desired compound with higher yields compared to the

Quinoline DeriVatiVes as Nicotinic Ligands
Journal of Medicinal Chemistry, 2007, Vol. 50, No. 20 4995
Figure 1. Ortep drawing of the two independent conformers of (S)-
1c (50% ellipsoid probability).
isomer 14 was obtained by catalytic hydrogenation over Pd/
BaSO4. Compounds 13 and 14 were directly transformed into
the amines 7a,b and 8a,b without isolation of their methane-
sulfonate esters. The tertiary amines 6b, 7b, and 8b were
transformed into the corresponding methiodides 6c, 7c, and 8c
by treatment with an excess of iodomethane in Et2O; as
expected, only quaternarization of the exocyclic nitrogen was
observed. Light or heat can catalyze the isomerization of
compound 14 as well as the other cis-derivatives 8a,b to the
trans-isomers 13 and 7a,b, respectively.
Enantiomeric Excess and Absolute Configuration. The ee
of compounds 1a-c was determined by enantioselective HPLC
analysis. The secondary amines (-)-1a and (+)-1a, obtained
from the hydrolysis of amides 9 and 10, were found to have ee
values of 96.7% and 94.8%, respectively (see Supporting
Information, Figure 1). The ee of (-)-1a is very close to that
of commercially available (R)-2-benzoyloxypropionic acid
(97%),24 indicating that the hydrolysis did not involve racem-
ization; the ee of (+)-1a was found to be higher than that
estimated from NMR (92%). The ee values of (-)-1b and (+)-
1b, obtained by fractional crystallization, were found to be
99.4% and >99%, respectively; the enantiomeric purity of (+)-
1b was estimated because the peak of the minor enantiomer
was too small to be integrated. (see Supporting Information,
Figure 2).
The absolute configuration was established by means of X-ray
diffraction analysis of the methiodide (-)-1c, by determining
the Flack’s parameter,25 which provides the fractional contribu-
tion of the inverted component of a “racemic twin” and it should
be zero if the absolute structure is correct. The stereogenic center
of (-)-1c shows a S-configuration (Figure 1), and, as a
consequence, amines (-)-1a and (-)-1b also have the same
S-configuration.
Two independent molecules (A and B) were found in the
asymmetric unit (Figure 1), representing two different confor-
mations: they both show a similar arrangement of the five-
membered ring, but they differ for the value of the N1-C7-
C8-C16 dihedral angle, which is +g in conformer A and -g
in conformer B.
Figure 2. Effect of (S)-1b (closed squares), (R)-1b (open square), (S)-
1c (closed circles), and (R)-1c (open circles) in the mouse hot-plate
test. The compounds were injected i.p. at the dose of 5 mg/kg. Each
point represents the mean ( SEM of at least three mice. Open
triangles: controls. *P < 0.05 vs pretest.
tested also in competition studies against [3H]-epibatidine and
[
125I]R-bungarotoxin according to the experimental procedure
reported in ref 27. Compounds 2a-c, 3a,b, 4a,b, and 5-8a-
c, which did not displace [3H]-cytisine from rat brain, and
compound 4c, were not tested further.
The enantiomers of compounds 1b and 1c were tested as
analgesic in the mice hot-plate test according to refs 26 and
28; the results are reported in Figures 2 and 3.
Results and Discussion
From the data reported in Table 1, it can be seen that (S)-1b
and (R)-1b show enantioselectivity in the interaction with the
nicotinic receptors. In fact, the affinity of (S)-1b measured
against [3H]cytisine or [3H]-epibatidine is, respectively, 22-fold
and 17-fold higher than that of (R)-1b; these values of
enantioselectivity are similar to those reported for nicotine in
other studies.29-31 The eudismic ratio (ER) of the methiodides
(S)-1c and (R)-1c has similar values (ER ) 14 and 33,
respectively), but in this case, no comparison with nicotine
derivatives can be made because only the Ki for (S)-1,1-
dimethyl-2-(3-pyridyl)pyrrolidinium iodide has been found in
the literature.18 The ER of the secondary amines (S)-1a and (R)-
1a has not been measured, due to the low affinity of rac-1a.19
In addition, enantioselectivity is usually low or absent for
nicotinic ligands having the pyrrolidine ring as a secondary
amine, while it is higher for bicyclic secondary amines such as
pyrido[3,4-b]homotropane or anatoxin-a, with the exception of
epibatidine and its derivatives.15,29-33
The enantiomers of 1b and 1c were also tested for their
affinity on R7* receptor; on this subtype, compounds (S)-1b
and (R)-1b have Ki values in the micromolar range. The lower
affinity on this subtype is in accord with the selectivity usually
displayed by nicotine and its analogues for the R4â2* receptor;7
surprisingly, the methiodide (R)-1c shows a preference for the
R7* subtype. As far as the R7* receptor is concerned, the
methiodides (S)- and (R)-1c show a higher enantioselectivity
than the tertiary amines (S)- and (R)-1b, their ER being 0.06
and 0.2, respectively. In both cases, the enantioselectivity is
inverted with respect to the R4â2* subtype, because the
R-isomers display higher affinity than the S-isomers. This is
Biological Tests. The synthesized compounds were tested
in vitro on rat cerebral cortex to evaluate their affinity for the
central nicotinic receptors; [3H]-cytisine was used as radioligand
to label R4â2* receptors, according to the experimental procedure
reported in ref 26. The results are reported in Table 1. All
compounds were tested up to a 10 µM concentration, but only
compounds (S)- and (R)-1b, (S)- and (R)-1c, 3c, and 4c were
able to displace [3H]-cytisine from the nicotinic receptors of
rat brain. The enantiomers of 1b and 1c and compound 3c were

4996 Journal of Medicinal Chemistry, 2007, Vol. 50, No. 20
Guandalini et al.
Figure 3. Effect of the enantiomers of 1b (left) and 1c (right) in the mouse hot-plate test, alone and after treatment with mecamylamine (4 mg/kg
i.p.). The compounds were injected icv at the dose of 5 µg/mouse. Each point represents the mean ( SEM of at least three mice. *P < 0.05 vs
pretest. ∧P < 0.05 vs treated mice.
Table 1. Binding Affinity of the Synthesized Compounds for the Nicotinic Receptors of Rat Cerebral Cortexa
Ki (nM)
( SEM
(n ) 3)
Ki (nM)
( SEM
(n ) 3)
Ki (nM)
( SEM
(n ) 3)
N
structure
X
Y
[3H]-cytisine
ERd
22
[3H]-epibatidine
ERd
17
[
125I]-R-bungarotoxin
ERd
0.2
rac-1bb
(S)-1b
(R)-1b
rac-1cb
(S)-1c
(R)-1c
3c
I
I
I
I
I
I
II
II
NMe
NMe
NMe
NMe2I
NMe2I
NMe2I
NMe3I
NMe3I
132 ( 8
90 ( 6
n.t.
n.d.
124 ( 50
2100 ( 966
n.d.
42 ( 15
1400 ( 644
6800 ( 2650e
n.t.f
42 000 ( 13 440
8100 ( 2592
n.d.
1570 ( 361
90 ( 21
142 ( 51e
n.t.
1950 ( 104
45 ( 2
16 ( 2
14
33
0.06
220 ( 12
500 ( 47c
1350 ( 165c
6.8 ( 0. 3
sCtCs
(E)sCHdCH
4c
nicotine
3.0 ( 1.0
450 ( 60
a Compounds 2(a-c), 3(a,b), 4(a,b), and 5-8(a-c) did not displace [3H]-cytisine from rat brain up to a 10 µM concentration and were not tested on R7
receptors nor against [3H]-epibatidine. b From reference 11. c From reference 19. d Ratio between the Ki values for the R- and the S-enantiomers. e Number
of experiments ) 5. f n.t.: not tested.
different from what happens for nicotine, because (S)-nicotine
shows higher affinity than (R)-nicotine on both R4â2* and R7*
receptor.30
lack of enantioselectivity in vivo between (R)-1c and (S)-1c,
but not that of (R)-1b and (S)-1b, which display similar nAChR
agonistic properties in vivo tests but different affinity in binding
studies. The possibility that (R)-1b and (S)-1b interact with other
nicotinic subtypes involved in pain perception will be considered
in further studies.
To assess the agonistic properties of the enantiomers of 1b
and 1c, their analgesic activity was measured in the hot plate
test.34 After i.p. injection, these compounds were able to increase
the pain threshold in a dose-dependent manner; the maximal
effect was obtained at 20 min after treatment (Figure 2);
compound (S)-1c was the most active in this test, although the
difference between it and the other tested compounds is at the
limit of significance. It must be noted that at the dose of 5 mg/
kg i.p. no significant difference in potency was found between
tertiary bases and methiodides, nor was enantioselectivity
observed. Because the antinociceptive activity of nicotinic
agonists can be due to interaction at both central and peripheral
sites35 and the CNS distribution of the methiodides (S)- and
(R)-1c is expected to be different from the tertiary bases (S)-
and (R)-1b, the analgesic test was repeated after i.c.v injection
(Figure 3). At the dose of 5 µg/mouse, (S)- and (R)-1b were
almost equipotent in their analgesic effect; analgesia was
prevented by mecamylamine, indicating that this is due to
activation of nicotinic receptors. Mecamylamine was also able
to reduce the analgesic effect of (S)-1c, but it failed to prevent
the effect of (R)-1c, indicating that, in this latter case, analgesia
does not have a nicotinic origin. This finding can explain the
The flexible compounds 2-8 were designed to provide
information about the possible values of the pharmacophoric
distance between the H-bond acceptor group and the cationic
nitrogen. In fact, it is known that compounds with an extended
side chain, such as trans-metanicotine, N-methyl-3-(4-aminobu-
tynyl)pyridine,18,36 or other more rigid nicotinic agonists, such
as 1,1-dimethyl-4-(3′-hydroxy)phenylpiperazinium iodide and
related compounds,26 can bind with high affinity with the R4â2*
receptor. Compounds 2-8 have limited conformational flex-
ibility and, at the same time, cover a wide range of possible
pharmacophoric N-N distances (Table 2). In this series of
compounds, only compounds 3c and 4c, the analogues of trans-
metanicotine and N-methyl-3-(4-aminobutynyl)pyridine, were
able to displace [3H]-cytisine from rat brain. The inactivity of
compounds 2a-c was unexpected; in fact, it is well-known that
the introduction of an oxymethylene bridge between the
pyrrolidine ring and the heterocycle of nicotinic ligands usually
gives compounds showing good to moderate affinity for the
nicotinic receptor of rat brain.15,37 In addition, it has been

Quinoline DeriVatiVes as Nicotinic Ligands
Journal of Medicinal Chemistry, 2007, Vol. 50, No. 20 4997
Table 2. Calculated Pharmacophoric Distances for the Conformers of
Compounds 2-8a
In conclusion, the study of the enantioselectivity of the
quinoline ligands reported in this paper has shown that the
R4â2* and the R7* nicotinic receptor subtypes have different
stereochemical requirements. In addition, a compound selective
for the R7* receptor has been disclosed (3c), which may
represent a new lead molecule for the development of ligands
to study this receptor subtype at the peripheral level.
N
distanceb (Å)
N
distance (Å)
2
3
4
5
6.2-8.8
8.7-10.4
8.5-10.2
7.5-9.1
6
7
8
8.8-9.0
8.3-9.0
5.6-7.8
a The compounds, in all the possible conformations, were built using
Spartan (V 1.01, wavefunction) and their geometry was optimized using
AM1. b Distance between the quinoline N atom (H-bond acceptor) and the
cationic nitrogen atom.
Experimental Section
(A) Chemistry. All melting points were taken on a Bu¨chi
apparatus and are uncorrected. NMR spectra were recorded on a
1
Brucker Avance 400 spectrometer (400 MHz for H NMR, 100
MHz for 13C). Optical rotation was measured at a concentration of
1 g/100 mL (c ) 1), unless otherwise stated, with a Perkin-Elmer
polarimeter (accuracy (0.002°). GC-MS analysis were performed
on a Perkin-Elmer Turbomass - Autosystem XL; alternatively, mass
spectra were recorded on a Linear Ion trap (LTQ)-Thermo-Finnigan
spectrometer. Chromatographic separations were performed on a
silica gel column by gravity chromatography (Kieselgel 40, 0.063-
0.200 mm; Merck) or flash chromatography (Kieselgel 40, 0.040-
0.063 mm; Merck). Yields are given after purification, unless
differently stated. Where analyses are indicated by symbols, the
analytical results are within 0.4% of the theoretical values. When
reactions were performed under anhydrous conditions, the mixtures
were maintained under nitrogen. Compounds were named following
IUPAC rules as applied by Beilstein-Institute AutoNom (version
2.1) software for systematic names in organic chemistry.
reported that (S)-7-(2-pyrrolidinyl)methoxyquinoline was able
to displace [3H]-cytisine from rat brain homogenate with low
affinity (Ki ) 5 µM),37 but for these compounds the shift of
the substituent from the 7- to the 6-position of the quinoline
ring did not increase the affinity as it happened for 6-(dimethyl-
amino)methylquinoline, the ring-opening analogue of compound
1b.11
The lack of affinity of the propyne (6a-c) or trans- and cis-
propene derivatives (7a-c and 8a-c, respectively) is in
agreement with the results of Cheng,38 who reported that
3-pyridyl-propynylamines and their cis- and trans-propenyl
analogues bind to the nicotinic receptor labeled by [3H]-nicotine
with lower affinity than their butyne or butene analogues. On
the contrary, the finding that only the methiodides 3c and 4c
bind to the nicotinic receptor labeled by [3H]-cytisine is
somewhat in contrast with other reports showing that in the
series of 3-pyridyl-butynyl or -butenyl derivatives, N-methyl
secondary amines are endowed with the highest affinity.18,36
While it is difficult to discuss the relationship between the
pharmacophoric distance and affinity (the majority of the
compounds do not interact with the nicotinic receptor labeled
by [3H]-cytisine), it is worth highlighting that affinity for R4â2*
receptors is found only for the compounds (3c and 4c) that can
assume, within this series, the greatest possible pharmacophoric
distance. It is obvious that this is not the only geometrical feature
that influences binding because the volume, shape, and elec-
tronic distribution of the molecules also play a crucial role in
the interaction with the receptor; docking studies have provided
a possible explanation for the binding mode on the R4â2 subtype
of 3c, as well as of compounds (S)-1b and (S)-1c.19 Interestingly,
compound 3c displays a 48-fold higher affinity for the receptor
subtype labeled by [125I]-R-bungarotoxin with respect to that
labeled by [3H]-epibatidine. Other quaternary ammonium com-
pounds have been reported so far to show a preference or
selectivity for the R7* compared to the R4â2* subtype;18,39,40
these compounds, being choline derivatives, belong to a
chemical class that is different from that of 3c.
As far as the Ki values obtained against [3H]-cytisine and
[3H]-epibatidine are concerned, it must be noted that, while the
enantiomers of 1b and 1c did not display a significant difference
in the displacement of these two radioligands, compound 3c
showed a 14-fold higher affinity for the site labeled by [3H]-
cytisine. [3H]-Epibatidine is reported to label a range of nAChR
subtypes, which is broader than that of [3H]-cytisine; it binds
with picomolar affinity to the subtypes containing R2, R3, R4,
R6, â2, â4 subunits and with nanomolar affinity with the R7
subtype,41,42-45 while [3H]-cytisine interacts with nanomolar
affinity with the subtypes containing R2, R4, â2, â4 subunits,42,43
and it is able to activate R6â2* receptors.46 The binding profile
of compound 3c suggests a selectivity for a receptor subtype
labeled by [3H]-cytisine, which cannot be identified in light of
the current knowledge.
2-(R)-Benzyloxy-1-(2-quinolin-6-yl-pyrrolidin-1-yl)-propan-
1-one (9 + 10). To a solution of commercially available (R)-(+)-
2-benzyloxy-propionic acid (0.216 g, 1.2 mmol) in ethanol-free
CHCl3 (2 mL), SOCl2 (2.8 g, 24 mmol) was added under N2
atmosphere, and the mixture was heated at 60 °C for 3 h;
evaporation of the solvent gave a residue ((R)-(+)-2-benzyloxy-
propionyl chloride) that was dissolved in ethanol-free CHCl3 (1
mL) and added dropwise to a solution of (()-1a11 (0.2 g, 1 mmol)
and Et3N (0.168 mL, 1.2 mmol) in ethanol-free CHCl3 (3 mL).
The mixture was left stirring at rt for 9 h and at 60 °C for 1 h, then
the solvent was evaporated under vacuum, and the residue
partitioned between 2 N HCl and Et2O. The aqueous layer was
made alkaline with NaOH al 10% and extracted with Et2O.
Anhydrification (Na2SO4) and removal of the solvent gave a residue
that was purified by flash chromatography (abs EtOH-NH4OH-
CHCl3-Et2O-pet. ether 45/2.5/180/180/450 as eluent). After five
separations, compound 9 (the first eluting isomer) was obtained in
39% yield, and a mixture of 9 and 10 (27%) in a 1:19 ratio
(estimated from the [1H]-NMR spectrum).
Compound 9. [1H]-NMR (CDCl3, 2 rotamers, A and B, in 50:
50 ratio) δ 1.08 (d, 3HA, J ) 6.4 Hz, CH3), 1.49 (d, 3HB, J ) 6.4
Hz, CH3), 1.82-2.05 (m, 3HA + 3HB), 2.24-2.35 (m, 1HA + 1HB,
CH2CH2), 3.65-3.90 (m, 2HA + 2HB, CH2N), 3.94 (q, 1HA, J )
6.4 Hz, CHOBz), 4.35 (q, 1HB, J ) 6.4 Hz, CHOBz), 4.39 (d,
1HA, J ) 12.0 Hz, CHHPh), 4.44 (d, 1HA, J ) 12.0 Hz, CHHPh),
4.48 (d, 1HB, J ) 11.6 Hz, CHHPh), 4.59 (d, 1HB, J ) 11.6 Hz,
CHHPh), 5.03 (d, 1HA, J ) 6.8 Hz, CHN), 5.38 (dd, 1HB, J ) 8.4
Hz, 3.2 Hz, CHN), 7.24-7.26 (m, 1HA + 1HB), 7.32-7.42 (m,
6HA + 6HB), 7.52-7.55 (m, 1HA + 1HB), 7.98-8.06 (m, 2HA
+
2HB), 8.84 (d, 1HB, J ) 2.8 Hz), 8.89 (d, 1HA, J ) 3.2 Hz,
aromatics) ppm; Anal. (C23H24N2O2) C, H, N.
Compound 10. [1H]-NMR (CDCl3 2 rotamers, A and B, in a
50:50 ratio) δ 1.32 (d, 3HA, J ) 6.4 Hz, CH3), 1.48 (d, 3HB, J )
6.4 Hz, CH3), 1.88-2.01 (m, 3HA + 3HB), 2.32-2.41 (m, 1HA +
1HB, CH2CH2), 3.68-3.78 (m, 1HA + 1HB), 3.94-3.99 (m, 1HA
+ 1HB, CH2N), 3.84 (d, 1HA, J ) 12.0 Hz, CHHPh), 3.96 (q, 1HA,
J ) 6.4 Hz, CHOBz), 4.29 (q, 1HB, J ) 6.8 Hz, CHOBz), 4.37 (d,
1HA, J ) 12.0 Hz, CHHPh), 4.47 (d, 1HB, J ) 11.6 Hz, CHHPh),
4.67 (d, 1HB, J ) 11.6 Hz, CHHPh), 5.16 (d, 1HA, J ) 8.0 Hz,
CHN), 5.38 (dd, 1HB, J ) 8.4 Hz, 4.8 Hz, CHN), 6.82-6.84 (m,
1HA + 1HB), 6.90-6.98 (m, 2HA + 1HB), 7.28-7.36 (m, 2HA
+
4HB), 7.39-7.47 (m, 1HA), 7.49-7.56 (m, 2HA + 2HB), 8.05 (m,

4998 Journal of Medicinal Chemistry, 2007, Vol. 50, No. 20
Guandalini et al.
2HA + 2HB), 8.83 (dd, 1HB, J ) 4.0 Hz, 2.0 Hz), 8.90 (dd, 1HA,
J ) 4.0 Hz, 1.6 Hz, aromatics) ppm; Anal. (C23H24N2O2) C, H, N.
4.98-5.14 (m, 4H, ArCH2O and CH2OSO2), 7.27-7.36 (m, 8H),
7.73-7.68 (m, 1H, aromatics) ppm.
6-Hydroxyquinoline (0.07 g, 0.5 mmol) in 1.5 mL of dry DMF
was treated with NaH (1 mmol) under nitrogen atmosphere; after
0.5 h of stirring at rt, a solution of the ester (0.2 g, 0.5 mmol) in
dry DMF (1.5 mL) was added dropwise. The mixture was left
stirring at rt for 1 h, heated at 80 °C for 4 h, cooled to rt, treated
with H2O, and extracted with Et2O. The organic phase was
anhydrified (Na2SO4), and the solvent was removed under vacuum
to yield a residue that was purified by column chromatography
(CHCl3-MeOH-NH3 98/2/0.5 as eluent), giving the title com-
pound as an oil (75% yield). The [1H]-NMR showed the presence
of two rotamers, A and B, in 1:1 ratio. [1H]-NMR (CDCl3) δ 1.92-
1.94 (m, 1HA+B), 2.05-2.14 (m, 3HA+B, CH2-CH2), 3.52-3.53
(m, 2HA+B, CH2-N), 3.90-3.96 (m, 1HA, CH-N), 4.10-4.16 (m,
1HB, CHB-N), 4.20-4.32 (m, 2HA+B, CHCH2O), 5.12-5.24 (m,
2HA+B, Ph-CH2O), 6.98 (s, 1HA), 7.18 (s, 1HB), 7.31-7.38 (m,
7HA+B), 7.81-7.82 (m, 1HA), 7.95-8.05 (m, 2HB + 1HA), 8.76
(dd, 1HA+B, J ) 4.0 Hz, 1.6 Hz, aromatics) ppm; MS (ESI) 363.27
(M + 1); [R]20D ) +45.9° (CHCl3); Anal. (C22H22N2O3) C, H, N.
(S)-2-(Quinolin-6-yloxymethyl)-pyrrolidine-1-carboxylic Acid
Benzyl Ester (S)-11. Following the same procedure used for (R)-
11, starting from (R)-(-)-phenylmethyl 2-(hydroxymethyl)pyrro-
lidine-1-carboxylate,23 the title compound was obtained in 85% yield
after flash chromatography (CHCl3-MeOH 99/1 as eluent). Chemi-
cal and physical characteristics are identical to those of (R)-11.
(S)-6-Pyrrolidin-2-yl-quinoline [(S)-(-)-1a]. Compound 9 (0.25
g, 0.69 mmol) was dissolved in 2.6 mL of a 1:1 mixture of HCl
(37% in H2O) and glacial acetic acid and heated at 100 °C for 48
h. After cooling, the mixture was made alkaline with 10% NaOH
and extracted with Et2O. Anhydrification (Na2SO4) and removal
of the solvent gave the title compound in 90% yield. Its [1H]-NMR
spectrum is identical to that of the racemate.11 [R]20 ) -43.0°
D
(CHCl3); Anal. (C15H16N2O4) C, H, N (as oxalate salt).
(R)-6-Pyrrolidin-2-yl-quinoline [(R)-(+)-1a]. Following the
same procedure, starting from 10, compound (+)-1a was obtained
in 78% yield. Its [1H]-NMR spectrum is identical to that of (-)-1a
and of the racemate. [R]20D ) +44.0° (CHCl3); Anal. (C15H16N2O4)
C, H, N (as oxalate salt).
(S)-6-(1-Methyl-pyrrolidin-2-yl)-quinoline [(S)-1b] and (R)-
6-(1-Methyl-pyrrolidin-2-yl)-quinoline [(R)-1b]. These com-
pounds were prepared from (S)-1a and (R)-1a, according to the
procedure previously reported for the racemate11 and both obtained
in 80% yield. The [1H]-NMR spectra are identical to that of the
racemate.11 (-)-1b [R]20D ) -153.9° (CHCl3); Anal. (C16H18N2O4)
C, H, N (as oxalate salt). (+)-1b [R]20D ) +152.8° (CHCl3); Anal.
(C16H18N2O4) C, H, N (as oxalate salt).
Resolution of rac-1b. A solution of (()-1b (0.63 g, 0.003 mol)
in absolute EtOH (10 mL) was added to a solution of (-)-O,O′-
di-p-toluyl-L-tartaric acid (1.15 g, 0.003 mol) in EtOH (10 mL),
and the resulting mixture was kept at 5-6 °C for 2 h. The brownish
precipitate was filtered off and crystallized twice from the same
solvent. Optical rotation and melting point appeared to be constant
[R]20 ) -46.0° (CHCl3); Anal. (C22H22N2O3) C, H, N.
D
(R)-6-(Pyrrolidin-2-ylmethoxy)-quinoline [(R)-2a]. Compound
(R)-11 (0.1 g), dissolved in abs. EtOH (15 mL), was hydrogenated
on Pd/C at 1 atm. Filtration and removal of the solvent under
vacuum gave a residue that was purified by flash chromatography
(CHCl3-MeOH-NH3 95/5/0.5 as eluent), giving 0.03 g of the title
compound as an oil (45% yield). [1H]-NMR (CDCl3) δ 1.61-1.64
(m, 1H), 1.80-1.89 (m, 2H), 1.97-2.16 (m, 1H, CH2CH2), 2.39
(bs, 1H, NH), 2.97-3.07 (m, 2H, CH2N), 3.58-3.61 (m, 1H, CHN),
3.98 (dd, 1H, J ) 8.8 Hz, 6.8 Hz, CHHO), 4.05 (dd, 1H, J ) 8.8
Hz, 4.8 Hz, CHHO), 7.07 (d, 1H, J ) 2.8 Hz, H-5), 7.31-7.39
(m, 2H, H-3 and H-7), 7.98 (d, 1H, J ) 9.2 Hz, H-8), 8.02 (d, 1H,
J ) 8.4 Hz, H-4), 8.75 (dd, 1H, J ) 4.0 Hz, 1.2 Hz, H-2) ppm.
The oxalate salt melted at 80 °C after crystallization from abs.
EtOH. [R]20D ) +48.2° (MeOH; oxalate salt); Anal. (C16H18N2O5)
C, H, N.
after the first crystallization: [R]20 -86.6° (CH3OH), mp )
D
154 °C. The salt obtained (0.50 g) was then treated with a solution
of NaOH 10% and extracted in CH2Cl2. Anhydrification (Na2SO4)
and evaporation of the organic phase gave 0.175 g of (R)-(+)-1b
([R]20 (CHCl3) ) +154.4°).
D
The mother liquors obtained from the three crystallizations were
evaporated, and the residue was treated with NaOH 10% and
extracted in CH2Cl2; anhydrification and removal of the solvent
gave 0.44 g (0.002 mol) of a residue that was dissolved in absolute
EtOH (8 mL) and added to a solution of (+)-O,O′-di-p-toluyl-D-
tartaric acid (0.80 g, 0.002 mol) in EtOH (8 mL). After 2 h at 5-
6 °C a solid precipitated, it was filtered and crystallized twice
(S)- 6-(Pyrrolidin-2-ylmethoxy)-quinoline [(S)-2a]. Following
the same procedure used for (R)-2a, starting from (S)-11, the title
compound was obtained in 35% yield. Chemical and physical
showing a [R]20 ) +86.6° (CH3OH) and a mp ) 154 °C. Also,
D
in this case, optical rotation and melting point did not change after
the first crystallization. The salt obtained (0.62 g) was then treated
with a solution of NaOH 10% and extracted in CH2Cl2. Anhydri-
fication (Na2SO4) and evaporation of the organic phase gave 0.218
g of (S)-(-)-1b ([R]20D ) -151.1° (CHCl3)). [1H] and [13C]- NMR
spectra of (+)-1b and (-)-1b are identical with those of the
racemate.
characteristics are identical to those of (R)-2a. [R]20 ) -48.1°
D
(MeOH; oxalate salt); Anal. (C16H18N2O5) C, H, N.
(R)-6-(1-Methyl-pyrrolidin-2-ylmethoxy)quinoline [(R)-2b]. A
solution of compound (R)-11 (0.4 g, 1.1 mmol) in anhydrous DME
(6 mL) was added dropwise, at 0 °C and under N2, to a suspension
of LiAlH4 (0.26 g, 6.93 mmol) in DME (3.7 mL). The mixture
was left stirring for 1 h at 0 °C, then it was allowed to warm to rt,
treated with ice, and extracted with CHCl3. Anhydrification (Na2-
SO4) and removal of the solvent gave a residue that was purified
by flash chromatography (CHCl3-MeOH-NH3 98/2/0.5 as eluent).
(S)-6-(1-Methyl-pyrrolidin-2-yl)-quinoline [(S)-(-)-1c] and
(R)-6-(1-Methyl-pyrrolidin-2-yl)-quinoline [(R)-(+)-1c]. The com-
pounds were obtained by treatment of (S)-1b and (R)-1b with MeI
in Et2O (see general procedure for the synthesis of methiodides).
Their [1H]- and [13C]-NMR spectra are identical with those of the
The title compound was obtained in 75% yield. [R]20 ) +64.2°
D
racemate.11 (S)-1c [R]20 ) -25.2° (CHCl3); mp ) 180-182 °C;
(CHCl3); [1H]-NMR (CDCl3) δ 1.76-1.93 (m, 3H), 2.03-2.12 (m,
1H, CH2CH2), 2.29-2.36 (m, 1H), 2.68-2.76 (m, 1H, CH2N), 2.52
(s, 3H, NCH3), 3.12-3.15 (m, 1H, CHN), 4.01 (dd, 1H, J ) 9.2
Hz, 5.6 Hz, CHHO), 4.10 (dd, 1H, J ) 9.2 Hz, 5.2 Hz, CHHO,
CH2O), 7.07 (d, 1H, J ) 2.6 Hz, H-5), 7.33 (dd, 1H, J ) 8.4 Hz,
4.4 Hz, H-3), 7.39 (dd, 1H, J ) 9.2 Hz, 2.6 Hz, H-7), 7.98 (d, 1H,
J ) 9.2 Hz, H-8), 8.03 (d, 1H, J ) 8.4 Hz, H-4), 8.76 (dd, 1H, J
) 4.4 Hz, 1.6 Hz, H-2) ppm; [13C]-NMR-APT (CD3OD) δ 23.18,
28.89, 41.88, 57.9, 64.38, 71.32, 106.05, 121.44, 122.68, 129.42,
130.90, 134.92, 144.55, 148.04, 157.29 ppm. The oxalate salt melted
at 110 °C. Anal. (C17H20N2O5) C, H, N.
D
Anal. (C15H19IN2) C, H, N. (R)-1c [R]20 ) +25.2° (CHCl3); mp
D
) 180-182 °C; Anal. (C15H19IN2) C, H, N.
(R)-2-(Quinolin-6-yloxymethyl)-pyrrolidine-1-carboxylic Acid
Benzyl Ester [(R)-11]. To a solution of (R)-(-)-phenylmethyl
2-(hydroxymethyl)pyrrolidine-1-carboxylate23 (1.59 g, 6.8 mmol)
in CHCl3 (10 mL) and anhydrous pyridine (4.6 mL, 57 mmol)
cooled a 0 °C and kept under nitrogen, para-toluenesulfonyl
chloride (1.54 g, 8.1 mmol) was slowly added, and the mixture
was allowed to warm to rt. After 2 h of stirring, the mixture was
treated with H2O and CHCl3; anhydrification (Na2SO4) and removal
of the solvent gave (R)-2-(toluene-4-sulfonyloxymethyl)-pyrrolidine-
1-carboxylic acid benzyl ester in 80% yield, which was used as
such in the next step. [1H]-NMR (CDCl3) δ 1.79-1.96 (m, 4H,
CH2-CH2), 2.41 (s, 3H, CH3), 3.36-4.17 (m, 3H, CH2N, CHN),
(S)-6-(1-Methyl-pyrrolidin-2-ylmethoxy)quinoline [(S)-2b].
Following the same procedure used for (R)-2b, starting from (S)-
11, the title compound was obtained in 60% yield. Chemical and
physical characteristics of the free base and its oxalate salts are

Quinoline DeriVatiVes as Nicotinic Ligands
Journal of Medicinal Chemistry, 2007, Vol. 50, No. 20 4999
Table 3. Experimental Details for the Synthesis of Compounds (R)- and (S)-2c, 6a-c, 7a-c, and 8a-c
yield
N
(%)
purification
crystallization from abs. ethanol
crystallization from abs. ethanol
column chromatography (CH2Cl2/MeOH 95:5)
none
mp °C
201
Anal.
(R)-2c
(S)-2c
6a
6b
6c
7a
7b
7c
8a
20
20
37
70
87
10
17
75
39
26
30
C16H21IN2O
C16H21IN2O
C15H14N2O4
C16H16N2O4
C15H17IN2
C15H16N2O4
C16H18N2O4
C15H19IN2
201
a
a
180a
155a
crystallization from abs. ethanol
>200 (dec)
a
a
column chromatography (CH2Cl2/MeOH 95:5)
column chromatography (CH2Cl2/MeOH 95:5)
crystallization from abs. ethanol
column chromatography (CHCl3/MeOH/NH4OH 98:2:0.5)
column chromatography(CHCl3/MeOH/NH4OH 95:5:0.5)
crystallization from abs. ethanol
110a
140a
169
a
a
115a,b
C15H16N2O4
C16H18N2O4
C15H19IN2
8b
8c
145a
c
a As oxalate salts, obtained by treatment of the amine with 1 equiv of oxalic acid in ethyl acetate. b The amine is an 82:18 mixture of 8a and 7a. c The
solid is a 1:1 mixture of 8c and 7c.
identical to those of (R)-2b. [R]20 ) -68.0° (CHCl3); Anal.
with Et2O, and extracted with a saturated solution of NH4Cl. The
aqueous layer was collected, made alkaline with NaOH (10%
solution in H2O), and extracted with Et2O. Anhydrification and
removal of the solvent gave the desired amine. The cis-amines 8a
and 8b spontaneously convert into the trans-isomers 7a and 7b
under light or heating. Other experimental details are reported in
Table 3.
D
(C17H20N2O5) C, H, N (as oxalate salt).
3-(Quinolin-6-yl)prop-2-yn-1-ol 12. To a solution of 6-bromo-
quinoline47 (0.2 g, 1 mmol) and propargyl alcohol (0.1 g, 2 mmol)
in 4 mL of anhydrous Et3N, CuBr (0.16 g, 2 mmol) and Pd-tetrakis-
triphenylphosphine (0.04 g, 0.4 mmol) were added under nitrogen,
and the mixture was heated at 90 °C for 2 h. After cooling, the
mixture was diluted with Et2O and washed with a saturated solution
of NH4Cl. The organic phase was then extracted with 1 N HCl;
the aqueous phase was collected, made alkaline with NaOH 10%,
and extracted with Et2O. Anhydrification (Na2SO4) and removal
of the solvent gave the title compound in 84% yield. Mp )
183 °C; [1H]-NMR (CDCl3) δ 4.56 (s, 2H, CH2O), 7.35 (dd, 1H,
J ) 8.0 Hz, 4.0 Hz, H-3), 7.59 (d, 1H, J ) 8.6 Hz, H-7), 7.85 (s,
1H, H-5), 8.02 (d, 1H, J ) 8.6 Hz H-8), 8.06 (d, 1H, J ) 8.0 Hz
H-4), 8.85 (d, 1H, J ) 4.0 Hz, H-2) ppm; GC-MS 183 (M+), 166,
154; Anal. (C12H9NO) C, H, N.
trans-3-Quinolin-6-yl-prop-2-en-1-ol 13. To a solution of
compound 12 (0.2 g, 1.1 mmol) in anhydrous THF (15 mL), LiAlH4
(0.06 g, 1.6 mmol) was added under N2. After 1 h heating under
reflux, the reaction was quenched with NH4OH 33%, the solvent
was evaporated, and the residue was partitioned between H2O and
CHCl3. The organic phase was collected, anhydrified (Na2SO4),
and the solvent was removed under vacuum, leaving a residue which
was purified by flash chromatography (CH2Cl2-MeOH 97/3 as
eluent), giving the title compound as an oil in 50% yield. [1H]-
NMR (CDCl3) δ 2.17 (bs, 1H, OH), 4.40 (d, 2H, J ) 5.6 Hz, CH2),
6.52 (dt, 1H, J ) 16.0 Hz, 5.6 Hz, ) CH-CH2), 6.78 (d, 1H, J )
16.0 Hz, ) CH-C), 7.38 (dd, 1H, J ) 8.4 Hz, J ) 4.4 Hz, H-3),
7.68 (s, 1H, H-5), 7.82 (d, 1H, J ) 8.8 Hz, H-7 or H-8), 8.05 (d,
1H, J ) 8.8 Hz, H-8 or H-7), 8.11 (d, 1H, J ) 8.4 Hz, H-4), 8.85
(d, 1H, J ) 4.4 Hz, H-2) ppm; Anal. (C12H11NO) C, H, N.
cis-3-Quinolin-6-yl-prop-2-en-1-ol 14. A suspension of 12 (0.1
g, 0.55 mmol) and Pd/BaSO4 (0.05 g) in anhydrous pyridine (10
mL) was hydrogenated at 1 atm; the reaction was stopped when 1
equiv of H2 (12.24 mL) was consumed. After filtration and removal
of the solvent, the residue was purified by flash chromatography
(CHCl3-MeOH-NH3 (99/1/0.1 as eluent), obtaining 0.04 g of the
title compound as an oil (40% yield) and a small amount (0.02 g)
of 12. [1H]-NMR (CDCl3) δ 4.52 (dd, 2H, J ) 6.4 Hz, 1.6 Hz,
CH2), 6.03 (dt, 1H, J ) 12.0 Hz, 6.4 Hz, dCHsCH2), 6.68
(d, 1H, J ) 11.6 Hz, CsCHd), 7.38 (dd, 1H, J ) 8.0 Hz, 4.0
Hz, H-3), 7.54 (d, 1H, J ) 8.6 Hz, H-7 or H-8), 7.59 (s, 1H,
H-5), 8.03 (d, 1H, J ) 8.6 Hz, H-8 or H-7), 8.11 (d, 1H, J ) 8.0
Hz, H-4), 8.86 (d, 1H, J ) 4.0 Hz, H-2) ppm; Anal. (C12H11NO)
C, H, N.
Compound 6a. [1H]-NMR (CDCl3) δ 1.89 (bs, 1H, NH), 2.59
(s, 3H, NCH3), 3.68 (s, 2H, CH2N), 7.40 (dd, 1H, J ) 8.4 Hz, 4.4
Hz, H-3), 7.70 (dd, 1H, J ) 8.8 Hz, J ) 1.4 Hz, H-7), 7.90 (d, 1H,
J ) 1.4 Hz, H-5), 8.02 (d, 1H, J ) 8.8 Hz, H-8), 8.09 (d, 1H, J )
8.4 Hz, H-4), 8.89 (dd, 1H, J ) 4.4 Hz, J ) 1.6 Hz, H-2) ppm;
[13C]-NMR-APT (CDCl3) δ 35.36, 40.79, 83.29, 88.73, 121.51,
121.66, 127.93, 129.45, 131.05, 132.27, 135.67, 147.49, 150.79
ppm.
Compound 6b. [1H]-NMR (CDCl3) δ 2.43 (s, 6H, NMe2), 3.55
(s, 2H, NCH2), 7.41 (dd, 1H, J ) 8.4 Hz, 4.4 Hz, H-3), 7.73 (dd,
1H, J ) 8.8 Hz, 1.4 Hz, H-7), 7.93 (d, 1H, J ) 1.4 Hz, H-5), 8.03
(d, 1H, J ) 8.8 Hz, H-8), 8.10 (d, 1H, J ) 8.4 Hz, H-4), 8.90 (dd,
1H, J ) 4.4 Hz, 1.6 Hz, H-2) ppm; [13C]-NMR-APT (CDCl3) δ
44.31, 48.64, 84.93, 86, 121.51, 121.68, 127.96, 129.51, 131.11,
132.36, 135.67, 147.58, 150.85 ppm.
Compound 7a. [1H]-NMR (CDCl3) δ 2.52 (s, 3H, NCH3), 2.75
(bs, 1H, NH), 3.47 (d, 2H, J ) 6.0 Hz, NCH2), 6.45 (dt, 1H, J )
16 Hz, 6.0 Hz, dCHsCH2), 6.72 (d, 1H, J ) 16 Hz, CdCH),
7.35 (dd, 1H, J ) 8.2 Hz, 4.4 Hz, H-3), 7.67 (s, 1H, H-5), 7.81
(dd, 1H, J ) 8.8 Hz, 1.6 Hz, H-7), 8.02 (d, 1H, J ) 8.8 Hz, H-8),
8.08 (d, 1H, J ) 8.2 Hz, H-4), 8.83 (dd, 1H, J ) 4.4 Hz, 1.6 Hz,
H-2) ppm; [13C]-NMR-APT (CDCl3) δ 35.06, 53.11, 121.54,
125.84, 125.85, 127.34, 127.53, 128.47, 129.78, 132.43, 134.91,
136.05, 148, 150.28 ppm.
Compound 7b. [1H]-NMR (CDCl3) δ 2.30 (s, 6H, NMe2), 3.14
(d, 2H J ) 6.6 Hz, NCH2), 6.41 (dt, 1H, J ) 15.8 Hz, 6.6 Hz,
dCHsCH2), 6.67 (d, 1H, J ) 15.8 Hz, 1H, dCHsC), 7.35 (dd,
1H, J ) 8.2 Hz, 3.5 Hz, H-3), 7.67 (s, 1H, H-5), 7.82 (d, 1H, J )
8.8 Hz, H-7), 8.02 (d, 1H, J ) 8.8 Hz, H-8), 8.08 (d, 1H, J ) 8.2
Hz, H-4), 8.83 (d, 1H, J ) 3.5 Hz, H-2) ppm; [13C]-NMR-APT
(CDCL3) δ 45.32, 62.03, 121.48, 125.59, 127.35, 128.48, 128.91,
129.7, 132.04, 135.23, 148.02, 150.12 ppm.
Compound 8a. [1H]-NMR (CDCl3) δ 2.07 (bs, 1H, NH), 2.46
(s, 3H, NCH3), 3.59 (d, 2H, J ) 5.6 Hz, NCH2), 5.92 (dt, 1H, J )
11.8 Hz, 5.6 Hz, dCHsCH2), 6.73 (d, 1H, J ) 11.8 Hz, CsCHd
), 7.39 (dd, 1H, J ) 8.4 Hz, 4.4 Hz, H-3), 7.61 (d, 1H, J ) 8.6 Hz,
H-7), 7.64 (s, 1H, H-5), 8.06 (d, 1H, J ) 8.6 Hz, H-8), 8.14 (d,
1H, J ) 8.4 Hz, H-4), 8.88 (d, 1H, J ) 4.4 Hz, 1.6 Hz, H-2) ppm;
[13C]-NMR-APT (CDCl3) δ 35.84, 49.40, 53.47, 121.38, 127.79,
129.3, 130.11, 130.27, 130.44, 131.67, 136.05, 150.34 ppm.
Compound 8b. [1H]-NMR (CDCl3) δ 2.32 (s, 6H, NMe2), 3.35
(d, 2H, J ) 6.4 Hz, CH2), 5.95-5.98 (dt, 1H, J ) 11.6 Hz, 6.4 Hz,
dCHsCH2), 6.78 (d, 1H, J ) 11.6 Hz, CsCHd), 7.40 (dd, 1H,
J ) 8.6 Hz, 4.0 Hz, H-3), 7.62 (dd, 1H, J ) 8.8 Hz, 1.6 Hz, H-7),
7.66 (s, 1H, H-5), 8.07 (d, 1H, J ) 8.8 Hz, H-8), 8.15 (d, 1H, J )
8.6 Hz, H-4), 8.89 (dd, 1H, J ) 4.0 Hz, 1.2 Hz, H-2) ppm; [13C]-
General Procedure for the Synthesis of Amines 6a,b, 7a,b,
and 8a,b. To a solution of the alcohol (1 equiv) and anhydrous
pyridine (9 equiv) in CHCl3, methanesolfonyl chloride (1.2 equiv)
was added at 0 °C. The mixture was allowed to warm to rt, left
under stirring for 1 h, then treated with an excess of methylamine
or dimethylamine (33% solution in ethanol). After 24 h of stirring
at rt, the solvent was removed under vacuum, the residue was treated

5000 Journal of Medicinal Chemistry, 2007, Vol. 50, No. 20
Guandalini et al.
Table 4. Crystal Data and Structure Refinement of (S)-1c (conformers
A and B)
NMR-APT (CDCl3) δ 45.43, 57.42, 121.42, 127.51, 128.05, 129.04,
129.21, 130.90, 131.58, 135.50, 136.12, 150.39 ppm.
General Procedure for the Synthesis of Methiodides. A
solution of the amine in Et2O (10 mL) was treated with 1-2 mL
of iodomethane and left stirring for 24 h in the dark. A solid material
was formed, which was collected by filtration, washed with Et2O,
and dried under vacuum. Other experimental details are reported
in Table 3.
Compound (R)-2c. [1H]-NMR (CD3OD) δ 2.21-2.31 (m,3H),
2.54-2.56 (m, 1H) (CH2CH2), 3.17 (s, 3H, NCH3), 3.45 (s, 3H,
NCH3), 3.73-3.82 (m, 2H, CH2N), 4.29-4.33 (m, 1H, CHN),
4.59-4.68 (m, 2H, CH2O), 7.51-7.56 (m, 3H, H-5, H-3, H-7),
7.98 (d, 1H, J ) 9.2 Hz, H-8), 8.35 (d, 1H, J ) 6.0 Hz, H-4), 8.72
(d, 1H, J ) 4.0 Hz, H-2) ppm; [13C]-NMR-APT (CD3OD) δ 20.98,
25.64, 46.59, 54.25, 66.18, 69.32, 75.20, 108.43, 123.07, 123.49,
130.90, 130.97, 137.5, 149.37, 157.08 ppm. The NMR spectra of
(S)-2c are identical to those of (R)-2c.
Compound 6c. [1H]-NMR (D2O) δ 3.28 (s, 9H, NMe3), 4.5 (s,
2H, NCH2), 7.50-7.53 (m, 1H, H-3), 7.74 (d, 1H, J ) 8.5, H-7),
7.88 (d, 1H, J ) 8.5, H-8), 8.05 (s, 1H, H-5), 8.24 (d, 1H, J ) 7.5
Hz, H-4), 8.77 (s, 1H, H-2) ppm; [13C]-NMR-APT (D2O) δ 52.70,
57.06, 77.34, 90.59, 118.68, 122.30, 127127.73, 127.83, 132.05,
132.73, 146.37, 151.35 ppm.
formula (A, B)
C15H19N2I
formula weight (A, B)
space group
a (Å)
354.25
P21
13.069 (2)
7.548 (1)
15.639 (2)
103.80 (1)
b (Å)
c (Å)
â (˚)
volume (Å3)
Z (A, B)
1498.2 (4)
2
1.57
16.66
Cu KR
density (g/cm3)
abs. coeff. (mm-1
radiation
)
theta range for data collection (˚)
reflns collected
No. of unique reflns
Rint
5.1-51.8
5834
2877
0.059
final R indices (I > 2σ(I))
final R indices (all data)
flack parameter
R1 ) 0.041, wR2 ) 0.090
R1 ) 0.053, wR2 ) 0.095
-0.01 (1)
largest diff. peak and hole (e Å3)
0.36 and -0.76
(C) Enantiomeric Excess. Chemicals. Stock solutions of
compounds 1b and 1a (racemates and enantiomers) were prepared
in 2-propanol at concentrations of 1.5-2.5 mg/mL and stored at
4 °C. Working solutions were prepared daily by a 50-fold dilution
of the stock solutions with hexane. 2-Propanol, hexane (HPLC
grade), and diethylamine were obtained from Sigma-Aldrich, Milan.
HPLC Analysis. The HPLC apparatus consisted of a Jasco PU-
2089 plus HPLC pump (Jasco, Tokyo), a Rheodyne injector system
with a 20 µL loop, and a Jasco MD-2010 plus (Jasco, Tokyo) diode
array detector. A wavelength of 314 nm was selected for both
compounds. Separations were carried out at room temperature using
a CHIRALCEL OD-H, 250 × 4.6 mm, 5 µm particle-size HPLC
column (Daicel Chemical Industries LTD). The mobile phases were
hexane/2-propanol 85:15 (v/v) for 1a and hexane/2-propanol 99:1
(v/v) for 1b. The eluents were modified with 0.1% diethylamine
(v/v) to improve the chromatographic resolution. Three injections
were performed for each sample. The chromatographic parameters
of 1a were t0, 3.0 min (flow 1 mL/min); k of (R)-1a, 2.77; k of
(S)-1a, 3.44; R, 1.24. The chromatographic parameters of 1b were
t0, 3.0 min (flow 1 mL/min), k of (R)-1b, 2.41; k of (S)-1b, 2.64;
R, 1.10.
The capacity factor (k) is defined as (tdrug - t0)/t0 (tdrug ) retention
time of the drug; t0 ) retention time of an unretained solute). The
enantioselectivity is calculated as R ) k2/k1, where k2 and k1 are
the capacity factors of the second and first eluted enantiomers,
respectively.
(D) Crystal Structure Determination and Refinement. Dif-
fraction data were collected at room temperature on an Oxford
Diffraction Xcalibur3 four circle diffractometer equipped with CCD
area detector graphite-monochromated Cu KR radiation, using an
ω scan technique.
The crystal data and details of the data collection and structure
refinement are summarized in Table 4. Correction for Lorentz and
polarization effects has been applied. Absorption correction has been
applied by ABSPACK program.48 The crystal structure was solved
by direct method using the SIR97 program.49 Two independent
molecules were found in the asymmetric unit. Refinement was
carried out using the SHELXL97 program.50 Anisotropic displace-
ment parameters were used for all nonhydrogen atoms. Hydrogen
atoms were introduced in calculated position and isotropically
refined in agreement with the linked carbon atom. The Flack
parameter at the end of refinement was -0.01(1) The crystal-
lographic data of the structure have been deposited in the Cambridge
Crystallographic Data Centre (www.ccdc.cam.ac.uk) and allocated
the deposition number CCDC-649134.
Compound 7c. [1H]-NMR (D2O) δ 3.20 (s, 9H, NMe3), 4.12
(d, J ) 7.6 Hz, 2H, NCH2), 6.51 (dt, 1H, J ) 15.6 Hz, 7.6 Hz,
dCHsCH2), 7.06 (d, 1H, J ) 15.6 Hz, CsCHd), 7.50 (dd, 1H,
J ) 8.2 Hz, 4.4 Hz, H-3), 7.85 (s, 1H, H-5), 7.90 (s, 2H, H-7 +
H-8), 8.27 (d, 1H, J ) 8.2 Hz, H-4), 8.75 (dd, 1H, J ) 4.4 Hz, 1.6
Hz, H-2) ppm; [13C]-NMR-APT (D2O) δ 52.34, 52.38, 52.42, 68,
116.52, 122.05, 127.66, 127.78, 128.15, 133.36, 137.97, 141.93,
146.67, 150.48 ppm.
Compound 8c. [1H]-NMR (CD3OD) δ 3.19 (s, 9H, NMe3), 4.34
(d, 2H, J ) 7.4 Hz, NCH2), 6.26 (dt, 1H, J ) 11.8 Hz, 7.4 Hz,
dCHsCH2), 7.38 (d, 1H, J ) 11.8 Hz, CsCHd), 7.66 (dd, 1H,
J ) 8.4 Hz, 4.4 Hz, H-3), 7.79 (dd, 1H, J ) 8.6 Hz, 1.6 Hz, H-7),
8.10 (s, 1H, H-5), 8.14 (d, 1H, J ) 8.6 Hz, H-8), 8.54 (d, 1H, J )
8.4 Hz, H-4), 8.94 (dd, 1H, J ) 4.4 Hz, 1.6 Hz, H-2) ppm; [13C]-
NMR-APT (CD3OD) δ 53.37, 69.25, 118.69, 120.33, 123.23,
129.10, 129.87, 132.06, 135.44, 139.53, 143.00, 148.23, 151.35
ppm.
(B) Pharmacology. Binding Studies. The affinity of the
synthesized compounds for the R4â2* receptor was measured on
rat cerebral cortex using [3H]-cytisine and [3H]-epibatidine as
radioligand, according to previously published protocols.26,27 The
affinity of compounds (S)- and (R)-1b, (S)- and (R)-1c, and 3c for
the R7* subtype was measured on rat cerebral cortex using [125I]R-
bungarotoxine as radioligand, according to ref 27. The subtype
selectivity was measured by comparing Ki values obtained through
displacement of [3H]-epibatidine and [125I]R-bungarotoxine from
the same tissue. Amines were tested as oxalate salts.
Hot-Plate Test. The method adopted was described by
O’Callaghan and Holtzman.28 The mice were placed inside a
stainless steel container, which was set thermostatically at 52.5 (
0.1 °C in a precision water bath from KW Mechanical Workshop,
Siena, Italy. Reaction times (s) were measured with a stopwatch
before and 15, 30, 45, and 60 min after administration of analgesic
drugs. The endpoint used was licking of the fore or hind paws.
Those mice scoring less than 12 and more than 18 s in the pretest
were rejected (30%). An arbitrary cutoff time of 45 s was adopted.
No sign of tissue injury was observed up to 45 s. Ten mice per
group were tested. The compounds were administered i.p. or icv.
The nicotinic origin of analgesia was checked by its reversion by
mecamylamine at the dose of 4 mg/kg i.p.
Statistical Analysis. All experimental results are given as the
mean ( S.E.M. Analysis of variance (ANOVA), followed by
Fisher’s protected least significant difference (PLSD) procedure for
post-hoc comparison, was used to verify significance between two
means. Data were analyzed with the StatView software for the
Macintosh (1992). P values of less than 0.05 were considered
significant.
Acknowledgment. This work was supported by the Italian
M.U.R. (Ministero dell’Universita` e della Ricerca).

Quinoline DeriVatiVes as Nicotinic Ligands
Journal of Medicinal Chemistry, 2007, Vol. 50, No. 20 5001
3-(1-methyl-2-pyrrolidinyl)pyridine maleate (SIB-1508Y). J. Org.
Chem. 1998, 63, 1109-1118.
Supporting Information Available: Experimental details of
the synthesis of compounds 3-5; assessment of enantiomeric
excess; and table of elemental analysis of the new compounds. This
material is available free of charge via the Internet at http://
pubs.acs.org.
(23) Dei, S.; Bellucci, C.; Buccioni, M.; Ferraroni, M.; Gualtieri, F.;
Guandalini, L.; Manetti, D.; Matucci, R.; Romanelli, M. N.; Scapec-
chi, S.; Teodori, E. Synthesis and cholinergic affinity of diastereo-
meric and enantiomeric isomers of 1-methyl-2-(2-methyl-1,3-dioxolan-
4-yl)-pyrrolidine, 1-methyl-2-(2-methyl-1,3-oxathiolan-5-yl)pyrrolidine,
and of their iodomethylates. Bioorg. Med. Chem. 2003, 11, 3153-
3164.
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