Novel pyridylmethylamines as highly selective 5-HT1A superagonists

Article abstract of DOI:10.1021/jm100835q

To further improve the maximal serotonergic efficacy and better understand the configurational requirements for 5-HT_1A binding and activation, we generated and biologically investigated structural variants of the lead structure befiradol. For a bioisosteric replacement of the 3-chloro-4-fluoro moiety, a focused library of 63 compounds by solution phase parallel synthesis was developed. Target binding of our compound collection was investigated, and their affinities for 5-HT₂, α₁, and α₂-adrenergic as well as D₁-D₄ dopamine receptors were compared. For particularly interesting test compounds, intrinsic activities at 5-HT_1A were examined in vitro employing a GTPγS assay. The investigation guided us to highly selective 5HT_1A superagonists. The benzothiophene-3-carboxamide 8bt revealed almost exclusive 5HT_1A recognition with a K_i value of 2.7 nM and a maximal efficacy of 124%. To get insights into the bioactive conformation of our compound collection, we synthesized conformationally constrained bicyclic scaffolds when SAR data indicated a chair-type geometry and an equatorially dispositioned aminomethyl substituent for the 4,4-disubstituted piperidine moiety.

Full text of DOI:10.1021/jm100835q

J. Med. Chem. 2010, 53, 7167–7179 7167
DOI: 10.1021/jm100835q
Novel Pyridylmethylamines as Highly Selective 5-HT1A Superagonists
†
Stefan Bollinger, Harald Hubner, Frank W. Heinemann, Karsten Meyer, and Peter Gmeiner*
†
‡
‡
,†
€
†Department of Chemistry and Pharmacy, Emil Fischer Center, Friedrich Alexander University, Schuhstrasse 19, D-91052 Erlangen,
Germany, and Department of Chemistry and Pharmacy, Friedrich Alexander University, Egerlandstrasse 1, D-91058 Erlangen, Germany
‡
Received July 5, 2010
To further improve the maximal serotonergic efficacy and better understand the configurational
requirements for 5-HT1A binding and activation, we generated and biologically investigated structural
variants of the lead structure befiradol. For a bioisosteric replacement of the 3-chloro-4-fluoro moiety, a
focused library of 63 compounds by solution phase parallel synthesis was developed. Target binding of
our compound collection was investigated, and their affinities for 5-HT2, R1, and R2-adrenergic as well as
D1-D4 dopamine receptors were compared. For particularly interesting test compounds, intrinsic
activities at 5-HT1A were examined in vitro employing a GTPγS assay. The investigation guided us to
highly selective 5HT1A superagonists. The benzothiophene-3-carboxamide 8bt revealed almost exclusive
5HT1A recognition with a Ki value of 2.7 nM and a maximal efficacy of 124%. To get insights into the
bioactive conformation of our compound collection, we synthesized conformationally constrained
bicyclic scaffolds when SAR data indicated a chair-type geometry and an equatorially dispositioned
aminomethyl substituent for the 4,4-disubstituted piperidine moiety.
Introduction
Serotonin (5-HTa) is the endogenous ligand of a ligand-gated
ion channel (5-HT3) and 14 serotonergic G-protein-coupled
receptors (GPCRs) grouped into six subfamilies (5-HT1-2
,
5-HT4-7).1 The serotonin receptor 5-HT1A has been investi-
gated intensively and was the first subtype to be cloned.2
Showing a fast onset of action and high intrinsic activity, the
5-HT1A receptor can be activated to produce maximally
effective antidepressant-like activity, opening new perspectives
for the treatment of depressive disorders.3-8 There is strong
evidence that the target protein 5-HT1A can be also addressed
for the treatment of further central nervous system (CNS)
disorders including tardive dyskinesia and neuropathic
pain.9,10 Within the family of aminergic GPCR ligands, 1,4-
Figure 1. CNS active 1,4-disubstituted aromatic piperidines and
piperazines (1,4-DAPs).
disubstituted aromatic piperidines and piperazines (1,4-DAPs,
Figure 1)11 are known as privileged structural moieties simu-
lating endogenous neurotransmitters including dopamine,
serotonin, and (nor)epinephrine. Representative examples of
this huge family of bioactive compounds are the CNS active
drug haloperidol, the drug candidates WAY-100635,12 BP
897,13 and the recently discovered 2-pyridinylmethylamine
derivative befiradol (F-13640), a highly selective 5-HT1A re-
ceptor agonist that shows remarkable effects and is currently
undergoing clinical trials for the treatment of severe, chronic
pain.10,14-16 Befiradol shows high binding affinity and selec-
tivity as well as strong partial agonist properties in vitro. As an
example, subtype selectivity over 5-HT1B was shown to be
greater than 10 000.17 Efforts to advance ligand efficacy have
been performed recently.18
*To whom correspondence should be addressed. Phone: þ49 9131
85-29383. Fax: þ49 9131 85-22585. E-mail: peter.gmeiner@medchem.
uni-erlangen.de.
aAbbreviations: 5-HT, serotonin (5-hydroxytryptamine); 5-HT1A
,
serotonin 1A receptor; GPCR, G-protein-coupled receptor; Ki, inhibi-
tion constant; t-BuOK, potassium tert-butoxide; CHO, Chinese hamster
ovary; comp, compound; 1,4-DAPs, 1,4-disubstituted aromatic piper-
idines and piperazines; DIPEA, diisopropylethylamine; DMEA, di-
methylethylamine; DMF, dimethylformamide; DMSO, dimethyl-
sulfoxide; GTPγS, guanosine 50-O-[γ-thio]triphosphate; HF Pyr, poly-
3
(hydrogen fluoride)pyridine; HSQC, heteronuclear single quantum
coherence; HPLC, high performance liquid chromatography; m-CPBA,
m-chloroperbenzoic acid; MHz, megahertz; MS, mass spectrometry;
NBS, N-bromosuccinimide; NOE, nuclear Overhauser effect; PPh3,
triphenylphosphine; mp, melting point; tR, retention time; TBTU,
O-(benzotriazol-1-yl)-N,N,N0,N0-tetramethyluronium tetrafluorborate;
Tf, trifluoromethylsulfonyl; CNS, central nervous system; TMS, tri-
methylsilyl; THF, tetrahydrofuran; Ph, phenyl; RT, room temperature;
Ms, methanesulfonyl; Pr, propyl; SAR, structure-activity relationship;
SEM, standard error of the mean; TM, transmembrane helix; (HR-)
EIMS, (high resolution) electron ionization based mass spectrometry;
FTIR, Fourier transform infrared spectroscopy; TFA, trifluoroacetic
acid.
To further improve the maximal serotonergic efficacy
and better understand the configurational requirements for
5-HT1A binding and activation, we aimed to generate and
biologically investigate structural variants of the lead struc-
ture befiradol. Intending a bioisosteric replacement of the
r
2010 American Chemical Society
Published on Web 09/22/2010
pubs.acs.org/jmc

7168 Journal of Medicinal Chemistry, 2010, Vol. 53, No. 19
Bollinger et al.
3-chloro-4-fluoro moiety, we developed a focused library of
63 compounds by solution phase parallel synthesis. Inspired
by the 4-hydroxypiperidine partial structure of haloperidol,
we further envisioned increasing hydrophilicity of some final
products by a fluoride to hydroxyl exchange. Our program
involved the investigation of target binding of our compound
collection and comparison to the affinities for 5-HT2, R1- and
R2-adrenergic, and D1-D4-dopaminergic receptors. For par-
ticularly interesting test compounds, intrinsic activities at
5-HT1A should be examined in vitro employing a guanosine
50-O-[γ-thio]triphosphate (GTPγS) assay. To get insights into
the bioactive conformation of our compound collection, we
planned to synthesize bicyclic scaffolds in which the geometry of
the central piperidine moiety was conformationally restrained
by a bridge of two or three CH2 units. Whereas azabicyclo-
[3.2.1]octanes were chosen to simulate equatorially and
axially substituted chair conformations of the piperidine
unit, endo-substituted azabicyclo[3.3.1]nonanes should represent
boat-type analogues.
carboxamides 14 and 15 (Scheme 3). Subsequent methenyla-
tion gave the epoxides 16 and 17. Ring-opening with poly-
(hydrogen fluoride)pyridine22-25 stereospecifically produced
the isomers 18 and 19 displaying an endo positioned hydro-
xymethyl group. The relative stereochemistry was unambigu-
ously determined by NMR spectroscopy when a combination
of heteronuclear single quantum coherence (HSQC) and nucle-
ar Overhauser effect (NOE) experiments displayed proximity
between the hydroxymethyl group and the methylene bridge.
O-Activation gave the mesylates 20 and 21 which were trans-
formed into the azides 22 and 23, respectively, and subsequently
reduced and alkylated to yield the test compounds 24 and 25.
For the preparation of the 3-chloro-4-fluorobenzamide
30, we evaluated an alternative synthetic approach by initi-
ally treating the piperidone 26 (Scheme 4) with methyltri-
phenylphosphonium bromide. The thus formed olefin 27
was subjected to a bromofluorination29,30 reaction to give
the endo bromomethyl derivative 28 diastereoselectively.
Subsequent conversion into the azidomethyl derivative 29,
Staudinger reduction,26 and reductive alkylation yielded the
conformationally restrained befiradol analogue 30.
Results and Discussion
In the course of our preparation of the conformationally
restrained bicyclic 4-hydroxypiperidine derivatives (Scheme 5),
we intended to approach the endo alcohols 34, 35, and 36 and
the exo alcohol 38. Thus, Corey-Chaykovsky methenyla-
tion19,20 of the tropinones 14, 15, and 26 led to selective
oxirane formation with an endo positioned oxygen, whereas
epoxidation of the corresponding olefins led to a 2:3 mixture
of oxiranes with endo and exo oxygens, respectively. The
isomers could be separated by column chromatography.
The endo alcohols 31-33 were prepared from the epoxides
with endo oxygen according to the synthesis of the 4-hydro-
xypiperidines 10-12. For the synthesis of the phenyl substi-
tuted derivative 34, oxirane ring-opening of 31 was done with
sodium azide, followed by a one pot synthesis leading to the
target compound 34, whereas the ring-opening for the synth-
esis of the 3-chloro-4-fluorophenyl substituted derivative 36
was achieved by heating the precursor 33 in ammonia in
methanol. This modification was necessary because of the
tendency of the aromatic fluoro substituent to be substituted
byanazide group. Starting from the 3-thienylcarboxamide32,
the heterocyclic test compound 35 was prepared analogously.
The exo alcohol 38 was synthesized from 15 via a ring-opening
reaction of an exo-epoxide intermediate with sodium azide
resulting in formation of the azidoalcohol 37. The relative
stereochemistry was determinded on the stage of the ring-
opening products employing a combination of HSQC and
NOE experiments.
To modify the structural properties of our bicyclic scaf-
fold, we also synthesized a pair of homologous diastereomers
incorporating a propylene bridge (Scheme 6). Starting with
N-Boc azabicyclo[3.3.1]nonane-3-one (39), the synthesis of
the test compounds 41 and 43 was accomplished via the
intermediates 40 and 42, respectively, by benzoylation, epo-
xidation, selective ring-opening, reduction with Pd(OH)2/
C/H2, and reductive alkylation. The synthesis of the two iso-
mers differed only in the epoxidation step. Whereas the
epoxide with endo oxygen was synthesized under Corey-
Chaykovsky conditions,19,20 a Prileschajew reaction31 with
the appropriate olefin yielded the epoxide with exo oxygen
selectively.
Chemistry. For the development of a focused library based
on befiradol, the central intermediate 77,8 was synthesized
employing N-benzoyl protection (Scheme 1). In detail,
Corey-Chaykovsky methenylation19-21 of the piperidone
1 led to the oxirane 2 which was subsequently subjected
to ring-opening by poly(hydrogen fluoride)pyridine22-25 to
afford the fluoro alcohol 3, regioselectively. Activation of
the alcohol function and substitution of the thus formed
triflate 4 with sodium azide followed by a one pot reaction in
which the azide function was first reduced under Staudinger
conditions26 and then reductively alkylated with 5-methyl-
pyridine-2-carbaldehyde gave the pyridylmethylamine 6.
The central intermediate 7 was accessed as the corresponding
trihydrochloride by removal of the benzoyl protective group
with hydrochloric acid.27,28 For the envisioned structural
variations of the benzamide moiety, we selected commer-
cially available biphenyl, (tetrahydro)naphthyl, paracyclo-
phanyl, ferrocenyl, and (nor)adamantyl carboxylic acid deri-
vatives as representatives for saturated and unsaturated
carbocyclic and heterocyclic analogues. Moreover, mono-
cyclic and fused heteroarene carboxylic acids and analogous
heterobiarenes were employed. Thus, activation of a collec-
tion of 63 carboxylic acids with O-(benzotriazol-1-yl)-N,N,
N0,N0-tetramethyluroniumtetrafluorborate (TBTU) and sub-
sequent amide formation with the central building block 7 was
performed in parallel to afford the target compounds 8aa-cj
(Scheme 1). The synthesis of the N-methyl derivative 9 was
done by N-acylation and subsequent reductive methylation
with paraformaldehyde.
To study the influence of the 4-fluoro substituent of the
piperidine ring onto receptor binding, 4-hydroxy analogues
were synthesized (Scheme 2). Thus, the oxirane 2 was sub-
jected to ring-opening with a saturated solution of ammonia
in methanol to afford the respective aminomethylpiperidine.
Subsequent reductive alkylation with the methylpyridine-2-
carbaldehyde led to the test compound 10, which was de-
protected and acylated with thienyl-3-carboxylic acid and
3-chloro-4-fluorobenzoic acid to yield the final products
11 and 12, respectively.
For the preparation of the conformationally restrained
4-fluoropiperidine derivatives incorporating an ethylene bridge
(24 and 25), nortropinone (13) was N-acylated to give the
In the case of azabicyclo[3.2.1]octane derivatives, endo
methylene groups are axial and exo methylene groups are
equatorial because of the chair conformation of the central

Article
Journal of Medicinal Chemistry, 2010, Vol. 53, No. 19 7169
Scheme 1a
a Reagents and conditions: (a) trimethylsulfoxonium iodide, NaH, DMSO, RT, 1.5 h; (b) HF Pyr, CH2Cl2, -10 °C, 3 h; (c) trifluoromethanesulfonic
3
acid anhydride, pyridine, RT, 2 h; (d) NaN3, DMF, 80 °C, 15 h; (e) (i) PPh3, 5-methylpyridine-2-carbaldehyde, MeOH, reflux, 3 h; (ii) NaCNBH3, RT,
15 h; (f) 6 N HCl, reflux, 15 h; (g) carboxylic acid, TBTU, DIPEA, DMF, CH2Cl2, RT, 2 h; (h) (i) 3-chloro-4-fluorobenzoic acid, TBTU, DIPEA, DMF,
CH2Cl2, RT, 2 h; (ii) paraformaldehyde, NaCNBH3, RT, 16 h.
six-membered ring.32-34 Because of a boat type conformation
of the piperidine ring, thus avoiding 1,4-interactions with the
propylene bridge, azabizyclo[3.3.1]nonane derivatives usually
have equatorially oriented endo methylene group. To esta-
blish the configuration of our azabizyclo[3.3.1]nonanes, we
recorded an X-ray structure of the intermediate 42, which
is depicted in Figure 2. In fact, a boat conformation of the
4-substituted piperidine substructure could be observed.
Receptor Binding. Radioligand binding assays were em-
ployed to analyze affinity and selectivity profiles of the target
compounds. The binding data were generated by measuring
their ability to compete with [3H]WAY-100635, [3H]-
ketanserin, [3H]prazosin, and [3H]RX821002 when employ-
ing porcine 5-HT1A, 5-HT2, R1, and R2 receptors, respec-
tively.35 The ligands were also investigated for their potency
to displace [3H]spiperone for the cloned human dopamine
receptor subtypes D2long, D2short,
36 D3,37 and D4.438 stably
expressed in Chinese hamster ovary cells (CHO).39 D1
receptor affinities were determined utilizing porcine striatal
membranes and the D1 selective radioligand [3H]SCH23390.

7170 Journal of Medicinal Chemistry, 2010, Vol. 53, No. 19
Bollinger et al.
Scheme 2a
Scheme 5a
a Reagents and conditions: (a) (i) saturated solution of NH3 in
MeOH, RT, 1 d; (ii) 5-methylpyridine-2-carbaldehyde, NaCNBH3,
MeOH, RT, 16 h; (b) (i) 6 N HCl, reflux, 16 h; (ii) carboxylic acid,
TBTU, DIPEA, CH2Cl2, DMF, RT, 16 h.
Scheme 3a
a Reagents and conditions. (a) Method 1 (in the cases of 14 and 26):
(i) trimethylsulfoxonium iodide, NaH, DMSO, 60 °C, 3.5 h; (ii) satu-
rated solution of NH3 in MeOH, 60 °C, 5 d. Method 2 (in the case of 15):
(i) t-BuOK, MePPh3Br, THF, 80 °C, 2 h, then addition of 15, RT, 16 h;
(ii) m-CPBA, CH2Cl2, RT, 16 h, separation; (iii) NaN3, DMF, 120 °C,
2 d; (b) (i) Pd(OH)2/C, H2, MeOH, RT, 2 h; (ii) 5-methylpyridine-2-
carbaldehyde, NaCNBH3, MeOH, RT, 16 h; (c) 5-methylpyridine-2-
carbaldehyde, NaCNBH3, MeOH, RT, 18 h; (d) (i) t-BuOK, MePPh3Br,
THF, 80 °C for 2 h, then addition of 15, RT for 16 h; (ii) m-CPBA,
CH2Cl2, RT, 16 h, separation; (iii) NaN3, DMF, 120 °C, 2 d.
Scheme 6a
a Reagents and conditions. (a) Method 1: benzoyl chloride, Et3N, CH2Cl2,
0 °C to RT, 5 h. Method 2: carboxylic acid, TBTU, CH2Cl2, DMF, 0 °C to
RT, 2 h. (b) Trimethylsulfoxonium iodide, NaH, DMSO, 60 °C, 3.5 h;
(c) HF Pyr, CH2Cl2, -10 °C to RT; 16 h; (d) MsCl, CH2Cl2, THF, 0 °C to
3
RT, 3 h; (e) NaN3, DMF, 120 °C; 2 d; (f) (i) PPh3, 5-methylpyridine-2-
carbaldehyde, MeOH, reflux, 3 h; (ii) NaCNBH3, RT, 18 h.
Scheme 4a
a Reagents and conditions: (a) (i) 50% TFA in CH2Cl2, RT, 16 h; (ii)
BzCl, TEA, CH2Cl2, RT, 2 h; (iii) trimethylsulfoxonium iodide, NaH,
60 °C, 3 h; (iv) NaN3, DMF, 120 °C, 2 d; (b) (i) Pd(OH)2/C, H2, MeOH,
RT, 20 h; (ii) 5-methylpyridine-2-carbaldehyde, Na(AcO)3BH (in the
case of 41) or NaCNBH3 (in the case of 43), MeOH, RT, 16 h; (c) (i) 50%
TFA in CH2Cl2, RT, 16 h; (ii) BzCl, TEA, CH2Cl2, RT, 2 h; (iii) t-BuOK,
MePPh3Br, THF, 80 °C, 2 h, then addition of 9-benzoyl-9-azabicyclo-
[3.3.1]nonan-3-one, RT, 16 h; (iv) m-CPBA, CH2Cl2, RT, 2 h; (v) NaN3,
DMF, 120 °C, 2 d.
human 5-HT1A were employed.35 Ligand efficacy was com-
pared to the full agonist serotonin (Table 1).
a Reagents and conditions: (a) t-BuOK, MePPh3Br, THF, 80 °C for
2 h, then addition of 26, RT for 16 h; (b) HF Pyr, NBS, CH2Cl2, 0 °C, 1
3
Our initial investigations were directed to the ligand
binding properties of the test compounds 8aa-ag incorpor-
ating unsaturated carbocyclic substituents. When these mo-
lecular probes were compared with the unsubstituted phenyl-
carboxamide 6 (Ki=15 nM), a significant reduction of the
affinity was observed. As an exception, the naphthylcarbox-
amide 8ad showed comparable affinity. Interestingly, the
h; (c) NaN3, DMF, 80 °C, 2 d; (d) (i) PPh3, 5-methylpyridine-2-
carbaldehyde, MeOH, reflux, 3 h; (ii) NaCNBH3, 4 h, RT.
Compared to the lead compound befiradol, the resulting
Ki values are listed in Tables 1-4. Representative serotoner-
gic ligands were tested for their ability to stimulate [35S]-
GTPγS binding when CHO cells stably transfected with the

Article
Journal of Medicinal Chemistry, 2010, Vol. 53, No. 19 7171
nonaromatic, adamantane derived carboxamides 8ah-aq
showed also significant 5-HT1A binding with Ki values in the
submicromolar and nanomolar ranges for most representa-
tives. For this group of test compounds, the noradamantane
derivative 8aj displayed the highest affinity (Ki = 11 nM).
Surprisingly, both the naphthalene and the noradamantane
derived test compounds 8ad and 8aj gave superior intrinsic
activities when compared to our lead befiradol (Emax=84%),
resulting in Emax values of 110% and 96%, respectively. Within
the groups of unsubstituted monoheteroarenes, the thiophenes
8ar and 8as indicated the most advantageous binding proper-
ties (Ki=27 nM). On the other hand, the aza-analogues 8av
and 8aw and the hydroxyadamantane derivative 8an, incorpor-
ating an H-bond donating group, showed only poor receptor
recognition.
Starting from the thiophene and furan core structures, the
introductionofsubstituents, especiallyhalogen atoms, proved
to be a suitable means to further increase 5-HT1A binding
Figure 2. X-ray structure of the synthetic intermediate 42 displaying
a boat-type conformation of the hydroxypiperidine partial structure
and an endo configuration for the azidomethyl substituent.
Table 1. Receptor Binding Dataa and Intrinsic Activitiesb for Compounds of the Library 8aa-cjc in Comparison to Befiradol, 6, and 9 Employing
5-HT1A Receptors
[3H]WAY100635
[
35S]GTPγS
[3H]WAY100635
[
35S]GTPγS
compd
Ki ( SD/SEM [nM]
EC50 [nM]
Emax [%]
compd
Ki ( SD/SEM [nM]
EC50 [nM]
Emax [%]
befiradol
6
1.1 ( 0.45e
15 ( 1.3e
300 ( 120e
330 ( 92e
69 ( 24e
3.3
13
nd
nd
nd
52
nd
nd
37
11
26
47
48
nd
nd
600
nd
nd
nd
18
12
15
240
nd
nd
17
30
20
nd
nd
20
42
35
84
8bf
8bg
8bh
8bi
21 ( 1.4d
25 ( 5.7d
35 ( 2.1d
18 ( 0.71d
56 ( 2.8d
4.8 ( 0.64d
8.9 ( 0.64d
17 ( 3.5d
18 ( 3.5d
500 ( 170e
420 ( 120e
470 ( 180e
450 ( 21d
360 ( 28d
2.7 ( 0.39e
190 ( 33e
220 ( 35d
4.2 ( 0.92e
64 ( 15d
46
101
99
96
30
8aa
8ab
8ac
8ad
8ae
8af
nd
nd
nd
110
nd
nd
99
nd
54
nd
91
8bj
99
93
15 ( 1.7e
160 ( 21d
320 ( 78d
46 ( 8.9e
17 ( 1.9e
19 ( 1.4d
11 ( 0.71d
92 ( 28e
8bk
8bl
nd
nd
62
nd
nd
95
8bm
8bn
8bo
8bp
8bq
8br
8bs
8bt
8bu
8bv
8bw
8bx
8by
8bz
8ca
8cb
8cc
8 cd
8ce
8cf
8ag
8ah
8ai
50
102
nd
nd
nd
nd
nd
124
116
nd
101
87
98
nd
nd
nd
nd
nd
10
96
8aj
96
8ak
8al
91
120 ( 35e
29 ( 5.7d
1 300 ( 190e
1 300 ( 350e
470 ( 42d
460 ( 0d
nd
nd
90
8am
8an
8ao
8ap
8aq
8ar
8as
8at
240
nd
16
nd
nd
nd
91
34
27 ( 6.8e
27 ( 6.4d
62 ( 3.5d
182 ( 50e
660 ( 12e
910 ( 97e
6.2 ( 1.3d
19 ( 0d
93 ( 24d
310
93
96
95
180 ( 21d
51 ( 2.8d
94 ( 0d
80
81
36
46
8au
8av
8aw
8ax
8ay
8az
8ba
8bb
8bc
8bd
8be
99
nd
100
nd
nd
86
nd
94
nd
nd
116
95
380 ( 78d
910 ( 130d
3 500 ( 140d
20 ( 1.4d
32 ( 9.9d
37 ( 1.4d
46 ( 9.9d
25 ( 0.71d
74 ( 7.1d
nd
nd
104
102
100
103
97
32 ( 8.5d
16 ( 1.4d
26 ( 0.71d
8.3 ( 0.66e
14 ( 3.5d
26 ( 2.1d
104
nd
nd
101
104
96
8cg
8ch
8ci
63
130
39
8cj
59
9
8.6
77
a Binding data are the mean values of two to nine individual experiments with 5-HT1A receptors from porcine cortex membranes each done in
triplicate. nd=not determined. b Agonist stimulated [35S]GTPγS binding derived from a mean curve out of four experiments with human 5-HT1A
receptors stably expressed in CHO cells; Emax is displayed relative to the maximum effect of serotonin. c R according to Scheme 1. d Ki ( SD. e Ki ( SEM.

7172 Journal of Medicinal Chemistry, 2010, Vol. 53, No. 19
Bollinger et al.
Table 2. Selectivity Pattern for Selected Compounds from the Library 8bt, 8ax, and 8bw in Comparison to the Lead Befiradol Employing Porcine
5-HT1A, 5-HT2, D1, R1, R2, and Human D2long, D2short, D3, and D4.4 Receptors
Ki a ( SD/SEM [nM]
b
c
d
e
D1
f
f
f
f
g
h
compd
5-HT1A
5-HT1A
5-HT2
D2long
D2short
D3
D4.4
R1
R2
befiradol
8ax
8bt
1.1j
6.2i
2.7j
4.2j
0.33 j
1.8 j
0.86 j
1.1 j
23 000 j
18 000 i
22 000 j
53 000 j
26 000 j
34 000i
45 000i
48 000i
15 000 j
73 000i
20 000i
27 000i
46 000j
100 000i
54 000i
28 000i
10 000 j
19 000i
8 700i
2 000i
2 000i
460i
4 500 j
2 300i
2 000i
2 800i
3 700i
3 500i
1 700i
2 800i
8bw
12 000i
590i
a Binding data are the mean values of two to nine experiments each done in triplicate. b [3H]WAY-100635. c [3H]8-OH-DPAT. d [3H]Ketanserin.
e [3H]SCH23390. f [3H]Spiperone. g [3H]Prazosin. h [3H]RX821002. i SD < 30%. j SEM < 30%.
Table 3. Receptor Binding Dataa and Intrinsic Activitiesb for the
4-Hydroxylated Analogues 10-12 Employing 5-HT1A Receptors
Table 4. Receptor Binding Dataa and Intrinsic Activitiesb for
Azabicyclo[3.2.1]octane and Azabicyclo[3.3.1]nonane Derivatives
Employing 5-HT1A Receptors
[3H]WAY100635
[
35S]GTPγS
[3H]WAY100635
[
35S]GTPγS
compd
Ki ( SEM [nM]
EC50 [nM]
Emax [%]
compd
Ki ( SD/SEM [nM]
EC50 [nM]
Emax [%]
10
11
12
79 ( 9.0
120 ( 11
11 ( 2.4
nd
nd
6.6
nd
nd
24
25
30
34
35
36
38
41
43
260 ( 55d
340 ( 160d
110 ( 17c
100 ( 44d
43 ( 5.3d
17 ( 7.3d
63 ( 33d
nd
nd
nd
270
32
nd
nd
109
nd
a Derived from four to six individual experiments with porcine
5-HT1A receptors each done in triplicate. b Average of data from four
experiments with human 5-HT1A receptors. Emax relative to the max-
imum effect of serotonin.
113
101
121
<10
nd
18
150 ( 47d
nd
nd
when Ki values of 6.2 and 4.8 nM could be observed for the
monobromo- and the dibromothiophene carboxamide 8ax
and 8bk, respectively. On the other hand, unsaturated cyclic
substituents at the thiophene unit (8bo-bs) resulted in a
significant reduction of affinity.
1 600 ( 350c
nd
a Ki values are the mean of two to eight experiments with porcine
5-HT1A receptors each done in triplicate. b Average of functional data
from four experiments with human 5-HT1A receptors. Emax relative to
the maximum effect of serotonin. c Ki ( SD. d Ki ( SEM.
Finally, 17 fused heteroarenes were investigated (8bt-cj).
The evaluation of this family of compounds led to the identi-
fication of two further serotonergic ligands with Ki values in
the single digit nanomolar range. Thus, the benzothiophene-
3-carboxamide 8bt and its oxa-analogue 8bw displayed Ki
values of 2.7 and 4.2 nM, respectively. Whereas the benzo-
furan 8bw gave a ligand efficacy that was comparable to that
of serotonin, the benzothiophene 8bt revealed superpotent
properties with a maximal efficacy of 124%. Compared to
84% that we measured for the lead compound befiradol, this
means an improvement of about 50%. Table 1 also displays a
Ki value of the tertiary amine 9, indicating an NH group of
the aminomethylpiperidine moiety is important for high
5-HT1A binding.
Thus, the corresponding azabicyclo[3.2.1]octanes 34 and 38
simulating the chair conformation of the piperidine with
the aminomethyl substituent in the equatorial and axial
positions, respectively, showed Ki values of 100 and 63 nM
(Table 4). The structural analogues 35 and 36 displayed Ki
values of 43 and 17 nM, respectively, indicating superior
binding when compared to their surrogate 34. Interestingly,
the intrinsic activity strongly depended on the stereochemistry
of the bicyclic scaffold. Whereas the diastereomer 34 displayed
113% ligand efficacy, the endo-aminomethyl substituted iso-
mer 38 proved to be a neutral antagonist (Emax < 10%). Thus, the
bioactive conformation of the family of aminomethylpiper-
idines, which is responsible for their 5-HT1A agonist proper-
ties, adopts obviously an equatorial orientation of the crucial
basic element. The azabicyclo[3.3.1]nonanes 41 and 43 gave Ki
values of 150 and 1600 nM, respectively. The similarity between
the Ki values of 34 and its homologue 41 reflects that both
compounds adopt a chair type structure for the hydroxypiperidine
unit with an equatorially positioned aminomethyl group. In
the 5HT1A binding pocket, however, the entropy advantage of
conformational rigidization is obviously compensated by repul-
sive interactions with the bridging moieties. The boatlike confor-
mation of the endo-aminomethyl substituted bicyclononane 43
leads to a significantly lower binding affinity in the micromolar
range.
For the most promising test compounds 8ax, 8bt, and 8bw
and the reference agent befiradol, the ability to displace the
agonist radioligand [3H]8-OH-DPAT was investigated re-
vealing Ki values that were similar to those determined for
the displacement of [3H]WAY100635. Binding selectivities
over 5-HT2, the dopaminergic subtypes D1, D2long, D2short
,
D3, and D4, and the R-adrenergic receptors R1 and R2
were also studied. Besides the D4 affinities of 8bt and 8bw
(Ki = 500 and 590 nm, respectively), all Ki values were in the
single digit and double digit micromolar range, indicating
excellent selectivity ratios (Table 2).
To investigate a bioisosteric replacement of the fluoro
substituent in the 4-position of the piperidine ring by a more
hydrophilic hydroxy substituent, 5-HT1A binding of the pi-
peridinols 10, 11, and 12 was compared to the properties of
the fluoro analogues 6, 8as, and befiradol, respectively.
Interestingly, only a weak reduction of affinity (4- to
11-fold) was observed (Table 3).
Whereas the conformational restriction of the hydroxy-
piperidines in the chair conformation led to maintenance of
binding affinity, conformational restriction of the fluoropi-
peridines leading to the azabicyclooctanes 24, 25, and 30
even led to a reduction of binding affinity (Table 4).
This work concentrates on the characterization of in vitro
pharmacodynamic properties. Pharmacokinetic studies are
not involved. The critical metabolic elements are identical to
our lead compound befiradol. Although minor structural
In comparison to the 4,4-disubstituted benzoylpiperidine
10 (Ki = 79 nm), the consequence of conformational rigidi-
zation by an ethylene or propylene bridge was investigated.

Article
Journal of Medicinal Chemistry, 2010, Vol. 53, No. 19 7173
modifications can influence the metabolic fate, we expect
preferred biotransformation to the respective pyridine-3-
carboxylates as the major metabolites.18 However, different
appendages that have been introduced are expected to
influence lipophilicity and, thus, distribution and elimina-
tion. As an example, the 3-benzothiophenyl and the benzo-
furanyl derived bioisosteres 8bt and 8bw display clogP
values that significantly differ from befiradol (for befiradol
clogP = 2.61, for 8bt clogP = 3.64, and for 8bw clogP =
1.93).40 To optimize skin penetration, fine-tuning of lipo-
philicity will be necessary for the development of transdermal
therapeutic systems (TDS), which become more and more
important for the treatment of pain. Preliminary results mea-
suring the reduction of licking time in a formalin induced paw
pain assay (second phase at 1 mg/kg test compound admini-
strated intraperitoneally) for representative test compounds
indicated substantial antinociceptive activity (70% for 8ag,
45% for 8ar, 35% for 8at) and bioavailability.41
10% for 3 min, ascending to 100% in 15 min, 100% for 6 min:
flowrate, 0.5mL/min; λ =254nm. SystemB startedwith MeOH
30% for 1 min, ascending to 100% in 11 min, 100% for 4 min:
flow rate, 0.5 mL/min; λ = 254 nm. The purity of all test com-
pounds and key intermediates was determined to be >95%.
6-Benzoyl-1-oxa-6-azaspiro[2.5]octane (2). A suspension of
NaH (19.6 g, 490 mmol, 60% in oil) in DMSO (600 mL) was
stirred at 65 °C for 2 h. After the mixture was cooled to RT,
trimethylsulfoxonium iodide (108 g, 490 mmol) was added and
stirring at RT was continued for 15 min. Then 1-benzoylpiper-
idin-4-one (95 g, 470 mmol) dissolved in DMSO (300 mL) was
added to the mixture within 30 min and the solution was stirred
for 45 min. The reaction mixture was poured into water and
extracted with ethyl acetate three times. The combined organic
layers were washed with water and brine, dried (Na2SO4), and
evaporated and the residue was purified by flash chromatogra-
phy (CHCl3-ethyl acetate 9:1) to give pure 2 (84 g, 83%) as a
yellow solid (mp 55-60 °C). IR 3492, 3253, 3053, 3001, 2954,
2922, 2868, 1633, 1433, 1277 cm-1. 1H NMR (CDCl3, 600 MHz)
δ (ppm) 1.35-1.60 (m, 2H), 1.76-2.68 (m, 2H), 2.74 (bs, 2H),
3.43-3.72 (m, 3H), 4.18-4.36 (m, 1H), 7.37-7.46 (m, 5H). 13
C
NMR (CDCl3, 90 MHz) δ (ppm) 33.0, 33.7, 40.9, 46.2, 53.8,
57.0, 126.9 (2C), 128.6 (2C), 129.7, 136.0, 170.9. APCI-MS m/z
218 [M þ 1]þ.
Conclusion
A focused library of 5-HT1A agonists was synthesized.
Among the 63 test compounds, several derivatives with
excellent 5-HT1A affinities and superior potency could be
found. Our SAR studies showed that the 3-chloro-4-fluoro-
phenyl group of befiradol can be successfully replaced by both
unsaturated and saturated lipophilic moieties. The benzothio-
phene-3-carboxamide 8bt revealed almost exclusive 5-HT1A
recognition with a Ki value of 2.7 nM and a maximal efficacy
of 124%. To get insights into the bioactive conformation of
our compound collection, we synthesized bicyclic scaffolds in
which the geometry of the central piperidine moiety was
conformationally restrained. The substantial reduction of bind-
ing of the boatlike azabicyclo[3.3.1]nonanes 43 indicated a
chair-type conformation for the 4,4-disubstituted piperidine
scaffold. 5-HT1A binding experiments showed that both equa-
torial and axial disposition of the aminomethyl substitution of
the central piperidine chair leads to comparable receptor
binding. However the stereochemical outcome of the synthesis
is crucial for ligand efficacy. Thus, comparison of the azabicyclo-
[3.2.1]octanes 34-36 and 38 proved that only the equatorially
(1-Benzoyl-4-fluoropiperidin-4-yl)methanol (3). To a cooled
(-10 °C) solution of 2 (84 g, 385 mmol) in 200 mL of CH2Cl2,
poly(hydrogene fluoride)pyridine 70% (100 mL, 1160 mmol) was
added dropwise in 3 h at -10 °C. The solution was warmed to
RT, poured into water, which was neutralized with 50% K2CO3
to pH 7, and extracted with CH2Cl2 three times. The combined
organic layers were washed with water, 1 N HCl, and brine, dried
(Na2SO4), and concentrated in vacuo to get crude brown oil
which was purified by flash chromatography (CH2Cl2-MeOH
98:2) togive pure 3 (53g, 60%) as a white solid. 1H NMR (CDCl3,
360 MHz) δ (ppm) 1.46-2.13 (m, 4H), 2.96-3.53 (m, 3H), 3.64
(dd, J = 19.6 Hz, J = 4.2 Hz, 2H), 4.42-4.76 (m, 1H), 7.37-7.51
(m, 5H). APCI-MS m/z 238 [M þ 1]þ.
(1-Benzoyl-4-fluoropiperidin-4-yl)methyltrifluoromethanesulfonic
Acid (4). A solution of 3 (71 g, 300 mmol) in pyridine (1400 mL)
was cooled to 0 °C. Trifluoromethanesulfonic acid anhydride
(75 mL, 450 mmol) was added dropwise within 70 min. The mix-
ture was stirred for 1 h at RT and then poured into water. The
aqueous layer was extracted with CH2Cl2 three times, and the
combined organic layers were washed with 5 N HCl, dried
(Na2SO4), and concentrated under reduced pressure to yield 4
(78 g, 60%) as a white solid, which was used without further
purification in the next step. 1H NMR (CDCl3, 360 MHz)
δ (ppm) 1.63-2.13 (m, 4H), 3.10-4.02 (m, 3H), 4.48 (d, J =
18.9 Hz, 2H), 4.58-4.87 (m, 1H), 7.39-7.48 (m, 5H). APCI-MS m/
z 370 [M þ 1]þ. HPLC/MS system A purity 93% (tR = 0.1 min).
4-(Azidomethyl)-1-benzoyl-4-fluoropiperidine (5). To a solu-
tion of 4 (78 g, 212 mmol) in DMF (1000 mL) was added NaN3
(110 g, 1700 mmol), and the mixture was heated at 80 °C for 15 h.
The solvent was reduced by evaporation in vacuo, and 1000 mL
of dichloromethane was added. Then the organic layer was
washed with brine three times, dried (Na2SO4), and concen-
trated in vacuo to yield dark brown oil, which was purified by
flash chromatography (CH2Cl2-MeOH 98:2) to give 5 (28 g,
36%) as a white solid (mp 75-77 °C). IR 3411, 2962, 2925, 2870,
substituted diastereomers 34-36 act as agonists (Emax
101-121%). On the other hand, ligand efficacy below 10%
was observed for 38, the axially substituted diastereomer of 34.
=
Experimental Section
Chemistry. All reactions were carried out under nitrogen
atmosphere. Dry solvents and reagents were of commercial
quality and were used as purchased. Melting points have been
€
measured on a Buchi 510. MS experiments were run on a
Finnigan MAT TSQ 700 spectrometer by EI (70 eV) with solid
inlet. HR-EIMS experiments were run on a JEOL GCmateII
with a resolution of M/ΔM > 5000. NMR spectra were ob-
tained on a Bruker Avance 360 or a Bruker Avance 600 spectro-
meter relative to TMS in the solvents indicated (J value in Hz).
IR spectra were performed on a Jasco FT/IR 410 spectrometer.
Purification by flash chromatography was performed using silica
gel 60 if not stated otherwise. TLC analyses were performed
using Merck 60 F254 aluminum sheets and analyzed by UV light
(254 nm) or by spraying with ninhydrin reagent. Preparative
and analytical HPLC was performed on Agilent 1100 HPLC
systems employing a VWL detector. As column, a Zorbax
Eclipse XDB-C8 (4.6 mm ꢀ 150 mm, 5 μm) was used. HPLC
was run with MeOH (eluent I) and 0.1% aqueous formic acid
(eluent II) and the following gradients: System A was MeOH
2103, 1633, 1435, 1284 cm-1 1H NMR (CDCl3, 360 MHz)
.
δ (ppm) 1.48-2.14 (m, 4H), 3.05-3.48 (m, 4H), 3.58-3.83 (m,
1H), 4.48-4.79 (m, 1H), 7.38-7.47 (m, 5H). 13C NMR (CDCl3,
90 MHz) δ (ppm) 32.4, 32.9, 37.7, 43.2, 58.2 (d, J = 23.8 Hz),
93.7 (d, J = 175.7 Hz), 126.9 (2C), 128.6 (2C), 129.9, 135.7,
170.5. APCI-MS m/z 263 [M þ 1]þ. HPLC/MS system A purity
>99% (tR = 13.4 min).
N-(1-Benzoyl-4-fluoropiperidin-4-yl)methyl-N-(5-methylpyri-
din-2-yl)methylamine (6). A solution of 5 (41 g, 156 mmol),
5-methylpyridine-2-carbaldehyde (19 g, 160 mmol), and triphe-
nylphosphine (41 g, 160 mmol) in MeOH (2800 mL) was heated

7174 Journal of Medicinal Chemistry, 2010, Vol. 53, No. 19
Bollinger et al.
to reflux for 3 h. After the mixture was cooled to RT, NaCNBH3
(31 g, 50 mmol) was added and the solution was stirred at RT for
15 h. The solvent was evaporated in vacuo, and the remaining
residue was poured into water. The aqueous layer was extracted
with CH2Cl2 three times, and the combined organic layers were
washed with water, brine, dried (Na2SO4), and concentrated in
vacuo to obtain 101 g of a brown oil. The product was purified by
flash chromatography (CH2Cl2 supplemented with MeOH from
0% to 4%) to give 6 (44g, 82%) as a brown oil. 1H NMR (CDCl3,
360 MHz) δ (ppm) 1.45-2.15 (m, 4H), 2.32 (s, 3H), 2.79 (d, J =
20.2Hz, 2H), 3.08-3.75 (m, 2H), 3.90(s, 2H), 4.41-4.67 (m, 2H),
7.20 (d, J = 8.0Hz, 1H), 7.35-7.43 (m, 5H), 7.45 (dd, J = 7.8 Hz,
1.7 Hz, 1H), 8.34-8.40 (m, 1H). APCI-MS m/z 342 [M þ 1]þ.
HPLC/MS system A purity 97% (tR = 13.7 min).
13C NMR (CDCl3, 150 MHz) δ (ppm) 18.1, 33.1, 33.9, 38.0, 43.3,
55.1, 56.9 (d, J = 23.1 Hz), 94.5 (d, J = 171.2 Hz), 121.6, 122.6,
122.9, 124.9, 125.0, 126.4, 131.4, 131.8, 136.9, 137.1, 139.8, 149.6,
156.5, 164.4. APCI-MS m/z 398 [M þ 1]þ. HR-EIMS m/z
397.1624. HPLC/MS system A purity 96% (tR = 15.6 min).
N-[1-[(1-Benzofuran-3-yl)carbonyl]-4-fluoropiperidin-4-yl]-
methyl-N-(5-methylpyridin-2-yl)methyl]amine (8bw). Synthesis
was performed according to general procedure 1 employing
1-benzofuran-3-carboxylic acid (10.4 mg, 0.064 mmol), yielding
8bw (15.5 mg, 71%) as a pale yellow oil. IR 3332, 2923, 1631,
1565, 1446, 1103, 752 cm-1. 1H NMR(600 MHz, CDCl3) δ (ppm)
1.50-1.87 (m, 2H), 1.95-2.15 (m, 2H), 2.32 (s, 3H), 2.79 (d, J =
20.6 Hz, 2H), 3.21-3.55 (m, 2H), 3.90 (s, 2H), 4.06-4.91(m, 2H),
7.19 (d, J = 7.9 Hz, 1H), 7.31 (ddd, J = 7.4 Hz, J = 7.6 Hz, J =
1.0 Hz, 1H), 7.35 (ddd, J = 8.1 Hz, J = 7.2 Hz, J = 1.0 Hz, 1H),
7.45 (dd, J = 7.9 Hz, J = 1.5 Hz, 1H), 7.53 (d, J = 8.3 Hz, 1H),
7.63 (d, J = 7.6 Hz, 1H), 7.86 (s, 1H), 8.36-8.39 (m, 1H). APCI-
MS m/z 382 [M þ 1]þ. HR-EIMS m/z 381.1853. HPLC/MS
system A purity 98% (tR = 15.1 min).
N-(4-Fluoropiperidin-4-yl)methyl-N-(5-methylpyridin-2-yl)-
methylamine Trihydrochloride (7). A solution of 6 (43 g, 125
mmol) in 6 N HCl (4800 mL) was heated to reflux for 15 h. The
reaction mixture was washed with diethyl ether three times. The
aqueous layer was evaporated under reduced pressure to obtain a
viscid oil, which was washed with acetonitrile for several times to
obtain a solid. The solid was washed with diethyl ether, suspended
in a small amount of MeOH, and concentrated in vacuo to give
N-[1-(3-Chloro-4-fluorobenzoyl)-4-fluoropiperidin-4-yl]methyl-
N-methyl-N-(5-methylpyridin-2-yl)methylamine (9). 3-Chloro-4-
fluorobenzoic acid (56.0 mg, 0.321 mmol) and DIPEA (0.35 mL)
were dissolved in CH2Cl2 (10 mL) and cooled to 0 °C. TBTU
(98.3 mg, 0.306 mmol) was dissolved in DMF (3 mL) and was
added to the reaction mixture which was then warmed to RT.
Compound 7 (100.0 mg, 0.288 mmol) was dissolved in CH2Cl2
supplemented with DIPEA and was added to the solution.
Stirring was continued for 2 h. Paraformaldehyde (10.2 mg)
and NaCNBH3 (54.3 mg, 0.864 mmol) were added, and stirring
was continued for another 16 h at RT. The solvent was removed in
vacuo, and the residue was poured into ice-water. The aqueous
phase was then extracted with CH2Cl2 several times. The com-
bined organic layers were washed with brine, dried (Na2SO4),
filtered, and the solvent was evaporated in vacuo. The crude
product was purified by flash chromatography (CH2Cl2-
MeOH 95:5) to give pure 9 (55.3 mg, 47%) as a greenish oil.
IR 3002, 2952, 2925, 2875, 2845, 2806, 1673, 1437, 1285, 1258
cm-1. 1H NMR (600 MHz, CDCl3) δ (ppm) 1.37-1.68 (m, 2H),
1.86-2.16 (m, 2H), 2.33 (s, 3H), 2.38 (s, 3H), 2.62 (d, J = 23.0
Hz, 2H), 3.09-3.24 (m, 1H), 3.30-3.44 (m, 1H), 3.46-3.60 (m,
1H), 3.71 (s, 2H), 3.35-4.54 (m, 1H), 7.17 (dd, J = 8.5 Hz, J =
8.5 Hz, 1H), 7.27 (ddd, J = 8.4 Hz, J = 4.5 Hz, J = 1.9 Hz, 1H),
7.32 (d, J = 7.9 Hz, 1H), 7.44-7.49 (m, 2H), 8.34-8.38 (m, 1H).
13C NMR (CDCl3, 150 MHz) δ (ppm) 18.2, 32.9, 33.8, 38.2, 43.7,
44.8, 64.1 (d, J = 20.9 Hz), 65.1, 95.2 (d, J = 174.5 Hz), 116.8 (d,
J = 20.9Hz), 121.5 (d, J = 17.6 Hz), 122.7, 127.1 (d, J = 7.7Hz),
129.7, 131.5, 133.0 (d, J = 4.4 Hz), 137.1, 149.4, 156.3, 158.8 (d,
J = 252.5 Hz), 168.0. APCI-MS m/z 408 [M þ 1]þ. HR-EIMS
m/z 407.1576. HPLC/MS system A purity 96% (tR = 16.3 min).
1-Benzoyl-4-[[[(5-methylpyridin-2-yl)methyl]amino]methyl]-
piperidin-4-ol (10). 4-(Aminomethyl)-1-benzoylpiperidin-4-ol 42
(108 mg, 0.462 mmol), 5-methylpyridine-2-carbaldehyde
(53.3 mg, 0.440 mmol), and NaCNBH3 (77.9 mg, 1.240 mmol)
were dissolved in MeOH (10 mL) and stirred for 16 h at RT.
The solvent was subsequently removed in vacuo, and the crude
product was poured into water and extracted with CH2Cl2. The
organic layer was washed with water and brine, dried (Na2SO4),
and the solvent was removed in vacuo. The product was puri-
fied by flash chromatography (hexane-ethyl acetate 6:4, then
CH2Cl2-MeOH 98:2) to give pure 10 (81.7 mg, 52%) as a pale
yellow oil. IR 3358, 2921, 1625, 1574, 1489, 1444, 1280 cm-1. 1H
NMR (360 MHz, CDCl3) δ (ppm) 1.36-1.74 (m, 4H), 2.33 (s,
3H), 2.60 (s, 2H), 3.20-3.60 (m, 3H), 3.92 (s, 2H), 4.39-4.58 (m,
1H), 7.13 (d, J = 7.7 Hz, 1H), 7.35-7.41 (m, 5H), 7.46 (dd, J =
7.9 Hz, J = 1.8 Hz, 1H), 8.36-8.40 (m, 1H). 13C NMR (90 MHz,
CDCl3) δ (ppm) 18.2, 35.3, 36.2, 38.4, 43.9, 55.3, 59.1, 68.5, 121.8,
126.9 (2C), 128.4 (2C), 129.4, 131.7, 136.3, 137.2, 149.6, 156.4,
170.4. APCI-MS m/z 394 [M þ 1]þ. HR-EIMS m/z 339.1946.
HPLC/MS system A purity 97% (tR = 13.6 min).
1
7 (31 g, 89%) as a yellow solid. H NMR (CDCl3, 360 MHz)
δ (ppm) 1.96-2.23 (m, 4H), 2.35 (s, 3H), 2.91-3.02 (m, 2H),
3.18-3.28 (m, 2H), 3.35 (d, J = 21.5Hz, 2H), 4.37 (s, 2H), 7.70 (d,
J = 7.9 Hz, 1H), 7.89 (d, J = 7.6 Hz, 1H), 8.56 (s, 1H), 9.43
(bs, 2H). 13C NMR (CDCl3, 150 MHz) δ (ppm) 18.1, 29.4 (d,
J = 22.0 Hz), 39.1, 50.1, 52.8 (d, J = 22.0 Hz), 90.9 (d, J =
176.7 Hz), 125.1, 134.9, 140.4, 147.7. APCI-MS m/z 238 [M þ 1]þ
(free base).
General Procedure 1 for the Synthesis of 8aa-cj. The appro-
priate aromatic or aliphatic carboxylic acid (0.064 mmol) and
DIPEA (0.07 mL) were dissolved in dry CH2Cl2 (2 mL) and
cooled to 0 °C. TBTU (20.2 mg, 0.062 mmol) was dissolved in
DMF (0.2 mL) and added dropwise to the reaction mixture. The
mixture was warmed to RT. Compound 7 (20.0 mg, 0.057 mmol)
and DIPEA (0.4 mL) were dissolved in CH2Cl2 and added to the
reaction mixture. Stirring was continued until TLC showed com-
plete conversion (generally 2 h). The mixture was washed with
brine, dried (Na2SO4), and the solvent was removed in vacuo. The
product was purified by flash chromatography (CH2Cl2-MeOH
98:2).
If other amounts of carboxylic acid were used, all the other
reactants were adjusted stoichiometrical equally.
N-[1-[(4-Bromo-2-thienyl)carbonyl]-4-fluoropiperidin-4-yl]-
methyl-N-(5-methylpyridin-2-yl)methylamine 8ax. Synthesis
was performed according to general procedure 1 employing
4-bromothiophene-2-carboxylic acid (13.3 mg, 0.064 mmol),
yielding 8ax (14.8 mg, 61%) as a pale yellow oil. IR 3324,
2923, 1619, 1434, 1373, 1272, 968, 812, 759 cm-1. 1H NMR (360
MHz, CDCl3) δ (ppm) 1.82-1.95 (m, 2H), 2.00-2.14 (m, 2H),
2.32 (s, 3H), 2.79 (d, J = 20.2 Hz, 2H), 3.23-3.47 (m, 2H), 3.90
(s, 2H), 4.12-4.43 (m, 2H), 7.21 (d, J = 1.2 Hz, 1H), 7.20 (d, J =
8.0 Hz, 1H), 7.34 (d, J= 1.4Hz, 1H), 7.45 (dd, J =7.9Hz, J= 1.8
Hz, 1H), 8.35-8.40 (m, 1H). 13C NMR (CDCl3, 150 MHz)
δ (ppm) 18.1, 33.3 (2C), 40.1, 43.5, 55.1, 56.9 (d, J = 22.0 Hz),
94.4 (d, J = 172.3 Hz), 109.3, 121.7, 125.9, 130.6, 131.4, 137.0,
138.5, 149.7, 156.5, 162.0. APCI-MS m/z 427 [M þ 1]þ. HR-EIMS
m/z 425.0573. HPLC/MS system A purity 98% (tR = 15.0 min).
N-[1-[(1-Benzothien-3-yl)carbonyl]-4-fluoropiperidin-4-yl]-
methyl-N-(5-methylpyridin-2-yl)methylamine (8bt). Synthesis was
performed according to general procedure 1 employing 1-ben-
zothiophene-3-carboxylic acid (11.4 mg, 0.064 mmol), yielding
8bt (19.4 mg, 86%) as a pale yellow oil. IR 3332, 2923, 1631, 1515,
1
1434, 1272, 1238, 1126, 763, 748 cm-1. H NMR (360 MHz,
CDCl3) δ (ppm) 1.47-1.78 (m, 2H), 1.92-2.17 (m, 2H), 2.32 (s,
3H), 2.80 (d, J = 20.2 Hz, 2H), 3.23-3.42 (m, 2H), 3.53-3.80 (m,
1H), 3.90 (s, 2H), 4.18-5.03 (m, 1H), 7.20 (d, J = 7.7 Hz, 1H),
7.36-7.44 (m, 2H), 7.45 (dd, J = 7.8 Hz, J = 1.7 Hz, 1H), 7.55 (s,
1H), 7.76-7.83 (m, 1H), 7.84-7.90 (m, 1H), 8.36-8.40 (m, 1H).

Article
8-Benzoyl-8-azabicyclo[3.2.1]octan-3-one (15). Nortropinone
Journal of Medicinal Chemistry, 2010, Vol. 53, No. 19 7175
(ppm) 18.1, 27.3, 29.0, 39.4, 40.5, 50.1, 55.0, 58.8 (d, J = 24.4
Hz), 95.2 (d, J = 170.4 Hz), 121.8, 127.1 (2C), 128.4 (2C), 130.1,
131.4, 136.2, 137.1, 149.6, 156.8, 168.1. APCI-MS m/z 368
[M þ 1]þ. HPLC/MS system A purity 98% (tR = 13.7 min).
3-(Azidomethyl)-8-benzoyl-8-azabicyclo[3.2.1]octan-3-ol (exo-CH2)
(31). The three step synthesis started with the preparation of the
first intermediate 8-benzoyl-3-methylen-8-azabicyclo[3.2.1]octane,
which was done by stirring a solution of t-BuOK (221.3 mg,
1.972 mmol) and methyltriphenylphosphonium bromide (715.6 mg,
2.003 mmol) in THF (8 mL) for 2 h at 80 °C. Then a solution
of 15 (342.7 mg, 1.495 mmol) in THF was added and stirring was
continued for 16 h at RT. After addition of diethyl ether the precipitate
was filtered and washed twice with diethyl ether. The filtrate was
evaporated under reduced pressure and purified by flash chromato-
graphy (hexane-acetone 8:2) to give pure product (205.7 mg (61%) as
a pale oil. IR 3467, 3249, 3068, 2978, 2947, 2897, 2831, 1631, 1577,
hydrochloride (13) (560.0 mg, 3.465 mmol) was dissolved in
CH2Cl2 (25 mL) supplemented with Et3N (5 mL) and was cooled
to 0 °C. Benzoyl chloride (487.0 mg, 3.465 mmol) was added
dropwise. The reaction mixture was warmed to RT and stirred
for 5 h. The solvent was removed in vacuo, and purification by
flash chromatography (hexane-ethyl acetate 6:4) gave pure 15
(730.1 mg, 92%) as a colorless oil. IR 3059, 2958, 2923, 2885,
1
1717, 1635, 1577, 1409 cm-1. H NMR (360 MHz, CDCl3) δ
(ppm) 1.72-1.87 (m, 2H), 2.07-2.26 (m, 2H), 2.27-2.70 (m,
3H), 2.79-3.12 (m, 1H), 4.26-4.62 (m, 1H), 4.88-5.22 (m, 1H),
7.40-7.60 (m, 5H). 13C NMR (90 MHz, CDCl3) δ (ppm) 28.2,
29.7, 48.9, 49.7, 51.5, 56.1, 127.1 (2C), 128.6 (2C), 130.7, 135.6,
169.0, 207.4. APCI-MS m/z 230 [M þ 1]þ. HR-EIMS m/z
229.1103. HPLC/MS system B purity >99% (tR = 10.1 min).
8-Benzoylspiro[8-azabicyclo[3.2.1]octane-3,20-oxirane] (endo-O)
(17). Synthesis was done according to 16 when using pretreated
trimethylsulfoxonium iodide (1432.7 mg, 6.510 mmol) and 15
(710.2 mg, 3.098 mmol) to give pure 17 (660.3 mg, 88%) as a pale
1
1421 cm-1. H NMR (360 MHz, CDCl3) δ (ppm) 1.59-1.75 (m,
2H), 1.82-2.02 (m, 2H), 2.02-2.30 (m, 2H), 2.35-2.48 (m, 1H),
2.63-2.77 (m, 1H), 4.05-4.20 (m, 1H), 4.81-4.98 (m, 3H),
7.37-7.45 (m, 3H), 7.46-7.54 (m, 2H). 13C NMR (150 MHz,
CDCl3) δ (ppm) 27.2, 28.7, 40.8, 42.4, 52.5, 57.2, 114.3, 127.1 (2C),
128.4 (2C), 129.9, 136.6, 141.5, 168.2. APCI-MS m/z 228 [M þ 1]þ.
HR-EIMS m/z 227.1310. HPLC/MS system A purity >99% (tR =
20.0 min).
yellow oil. IR 3564, 3485, 3032, 2983, 2949, 2916, 1631, 1419 cm-1
.
1H NMR (600 MHz, CDCl3) δ (ppm) 1.18-1.28 (m, 1H),
1.32-1.42 (m, 1H), 1.98-2.24 (m, 4H), 2.26-2.35 (m, 1H), 2.48
(d, J = 26.8 Hz, 2H), 2.56-2.67 (m, 1H), 4.11-4.28 (m, 1H),
4.83-5.01 (m, 1H), 7.37-7.52 (m, 5H). 13C NMR (150 MHz,
CDCl3) δ (ppm) 26.9, 28.2, 38.8, 40.8, 48.3, 51.7, 51.7, 54.5, 56.5,
127.0 (2C), 128.5 (2C), 130.1, 136.3, 168.2. APCI-MS m/z 244
[M þ 1]þ. HR-EIMS m/z 243.1259. HPLC/MS system B purity
99% (tR = 12.2 min).
In a second step a mixture of endo-O and exo-O 8-benzoyl-
spiro[8-azabicyclo[3.2.1]octane-3,20-oxirane] was synthesized
by stirring a solution of 8-benzoyl-3-methylen-8-azabicyclo-
[3.2.1]octane (406.0 mg, 1.786 mmol) and m-CPBA (488.8 mg,
2.832 mmol) in CH2CCl2 (6 mL) at RT for 16 h. The reaction
mixture was washed with a saturated solution of NaHCO3,
dried (Na2SO4), and evaporated under reduced pressure. Both
isomers (endo-O and exo-O) were separated by flash chroma-
tography (hexane-acetone 85:15).
Analytical Data of the endo-O Isomer. Yield 210.8 mg (49%),
pale oil. IR 3477, 3249, 3055, 3033, 2983, 2951, 2916, 1630, 1419
cm-1. 1H NMR (600 MHz, CDCl3) δ (ppm) 1.26-1.41 (m, 2H),
1.99-2.12 (m, 2H), 2.12-2.25 (m, 2H), 2.26-2.34 (m, 1H), 2.45
(d, J = 4.0 Hz, 1H), 2.50 (d, J = 4.0 Hz, 1H), 2.56-2.66 (m, 1H),
4.14-4.25 (m, 1H), 4.82-5.00 (m, 1H), 7.39-7.46 (m, 3H),
7.47-7.51 (m, 2H). 13C NMR (CDCl3, 150 MHz) δ (ppm) 26.9,
28.2, 38.9, 40.8, 48.3, 51.8, 54.5, 56.5, 127.1 (2C), 128.5 (2C),
130.0, 136.3, 168.2. APCI-MS m/z 244 [M þ 1]þ. HR-EIMS m/z
243.1259. HPLC/MS system A purity >99% (tR = 17.7 min).
Analytical Data of the exo-O Isomer. Yield 144.8 mg (33%),
pale oil. IR 3479, 3248, 3055, 2979, 2952, 2921, 2879, 2854, 1633,
1423 cm-1. 1H NMR (360 MHz, CDCl3) δ (ppm) 1.20-1.50 (m,
2H), 1.75-1.90 (m, 2H), 1.97-2.13 (m, 2H), 2.13-2.26 (m, 1H),
2.34-2.56 (m, 1H), 2.76 (s, 2H), 4.10-4.34 (m, 1H), 4.86-5.09
(m, 1H), 7.37-7.46 (m, 3H), 7.37-7.54 (m, 2H). 13C NMR
(CDCl3, 150 MHz) δ (ppm) 27.2, 28.7, 38.8, 40.5, 51.6, 54.4,
56.3, 57.3, 127.1 (2C), 128.5 (2C), 130.2, 136.1, 168.2. APCI-MS
m/z 244 [M þ 1]þ. HR-EIMS m/z 243.1259. HPLC/MS system
A purity 99% (tR = 16.8 min).
(8-Benzoyl-3-fluoro-8-azabicyclo[3.2.1]oct-3-yl)methanol (endo-
CH2) (19). Synthesis was done according to 18 using 17 (400.0 mg,
1.644 mmol). Purification was performed with preparative HPLC
(MeOH/0.1% aqueous formic acid, gradient (MeOH) 30-59% in
10 min, 59% for 2.5 min, 59-95% in 0.5 min, 95% for 2 min, tR =
10.5 min) togive pure 19 (200.0mg, 46%) asapalecolorlessoil.1H
NMR (600 MHz, CDCl3) δ (ppm) 1.59-1.72 (m, 2H), 1.95-2.22
(m, 5H), 2.32-2.47 (m, 1H), 3.62-3.78 (m, 2H), 4.08-4.22 (m,
1H), 4.82-4.97 (m, 1H), 7.38-7.54 (m, 5H). 13C NMR (CDCl3,
150 MHz) δ (ppm) 27.5, 29.0, 37.8 (d, J = 22.0 Hz), 39.0 (d, J =
22.0 Hz), 50.1 (d, J = 7.7 Hz)., 54.9 (d, J = 7.7 Hz), 69.2 (d, J =
25.0 Hz), 95.0 (d, J = 170.2 Hz), 127.0 (2C), 128.6 (2C), 130.5,
135.3, 168.6. APCI-MS m/z 265 [M þ 1]þ. HR-EIMS m/z
263.1322. HPLC/MS system B purity 100% (tR = 10.5 min).
(8-Benzoyl-3-fluoro-8-azabicyclo[3.2.1]oct-3-yl)methylmetha-
nesulfonic Acid (endo-CH2) (21). Synthesis was done according
to 20 using the alcohol 19 (178.6 mg, 0.678 mmol) to give crude
21 (231.5 mg, 100%) as a yellowish oil. No further purification
was performed. APCI-MS m/z 342 [M þ 1]þ. HPLC/MS system
B purity 92% (tR = 11.2 min).
3-(Azidomethyl)-8-benzoyl-3-fluoro-8-azabicyclo[3.2.1]octane
(endo-CH2) (23). Synthesis was done according to 22 using 21
(52.2 mg, 0.160 mmol). Purification was performed using flash
chromatography (hexane-ethyl acetate 1:1) to yield pure 23
(37.7 mg, 82%) as a pale oil. 1H NMR (360 MHz, CDCl3)
δ (ppm) 1.54-1.64 (m, 2H), 1.96-2.22 (m, 5H), 2.37-2.61 (m,
1H), 3.44 (d, J = 23.4 Hz, 2H), 4.06-4.24 (m, 1H), 4.78-4.99
(m, 1H), 7.39-7.47 (m, 3H), 7.47-7.53 (m, 2H). 13C NMR
(CDCl3, 90 MHz) δ (ppm) 27.4, 29.2, 39.0, 40.1, 49.8, 54.7, 59.7
(d, J = 25.8 Hz), 94.4 (d, J = 175.0 Hz), 127.1 (2C), 128.6 (2C),
130.3, 135.9, 168.3. APCI-MS m/z 289 [M þ 1]þ. HPLC/MS
system B purity 96% (tR = 13.5 min).
Finally, a solution of the endo-O isomer of 8-benzoylspiro[8-
azabicyclo[3.2.1]octane-3,20-oxirane] (182.7 mg, 0.751 mmol)
and NaN3 (390.5 mg, 6.007 mmol) in DMF (5 mL) was stirred
at 120 °C for 2 days. After the mixture was cooled to RT, ethyl
acetate (20 mL) was added to the solution and the organic layer
was washed with brine. The aqueous layer was extracted with
ethyl acetate, the combined organic layers were dried (Na2SO4),
and the solvent was evaporated under reduced pressure. The
crude product was purified by flash chromatography (hexane-
ethyl acetate 1:1) to give pure 31 (147.5 mg, 69%) as a pale oil. IR
N-(8-Benzoyl-3-fluoro-8-azabicyclo[3.2.1]oct-3-yl)methyl-N-
(5-methylpyridin-2-yl)methylamine (endo-CH2) (25). The synth-
esis was done according to 24 using 23 (65.7 mg, 0.228 mmol).
The product was purified by flash chromatography (CH2Cl2-
MeOH 98:2) to give pure 25 (53.4 mg, 64%) as a brown oil. IR
3329, 3057, 2962, 2925, 2883, 2852, 1631, 1489, 1425, 1107
cm-1. 1H NMR (360 MHz, CDCl3) δ (ppm) 1.51-2.48 (m, 8H),
2.32 (s, 3H), 2.89 (d, J = 27.3 Hz, 2H), 3.92 (s, 2H), 4.02-4.16
(m, 1H), 4.79-4.92 (m, 1H), 7.22 (d, J = 7.9 Hz, 1H), 7.36-
7.53 (m, 6H), 8.35-8.41 (m, 1H). 13C NMR (90 MHz, CDCl3) δ
3375, 2980, 2952, 2921, 2864, 2101, 1667, 1608, 1575, 1496 cm-1
.
1H NMR (360 MHz, CDCl3) δ (ppm) 1.67-2.11 (m, 6H),
2.15-2.33 (m, 2H), 2.52 (s, 1H), 3.11-3.24 (m, 2H), 4.03-4.20
(m, 1H), 4.76-4.88 (m, 1H), 7.36-7.51 (m, 5H). 13C NMR
(CDCl3, 90 MHz) δ (ppm) 26.8, 28.2, 40.2, 42.0, 50.9,
55.8, 63.9, 71.0, 127.0 (2C), 128.5 (2C), 130.0, 136.2, 168.1.

7176 Journal of Medicinal Chemistry, 2010, Vol. 53, No. 19
Bollinger et al.
APCI-MS m/z 287 [M þ 1]þ. HR-EIMS m/z 286.1430. HPLC/
MS system A purity 95% (tR = 18.0 min).
(100 mL) and Et3N (25 mL), the mixture was cooled to 0 °C and
benzoyl chloride (2412 mg, 17.2 mmol) was added dropwise. The
solution was allowed to warm to RT and was stirred for a further
2 h. The solvent was removed in vacuo and the crude product was
purified by flash chromatography (hexane-ethyl acetate 6:4) to
give 9-benzoyl-9-azabicyclo[3.3.1]nonan-3-one (3.53 g, 85%) as a
white solid. IR3058, 2947, 2880, 1710, 1630, 1420 cm-1. 1H NMR
(360 MHz, CDCl3) δ (ppm) 1.63-1.99 (m, 6H), 2.28-2.40 (m,
1H), 2.44-2.59 (m, 2H), 2.75-2.89 (m, 1H), 4.23-4.42 (m, 1H),
5.19-5.35 (m, 1H), 7.39-7.51 (m, 5H). 13C NMR (CDCl3, 150
MHz) δ (ppm) 16.5, 30.4, 31.3, 45.3, 45.7, 45.8, 51.8, 126.5 (2C),
128.8 (2C), 130.2, 135.6, 170.1, 208.5. APCI-MS m/z 244
[M þ 1]þ. HR-EIMS m/z 243.1259. HPLC/MS system A purity
>99% (tR = 16.9 min).
Methenylation reaction to get the endo-O isomer of 9-benzoyl-
spiro[9-azabicyclo[3.3.1]nonane-3,20-oxirane] was done accord-
ing to the synthesis of 32 employing trimethylsulfoxonium iodide
(575 mg, 2.61 mmol) and 9-benzoyl-9-azabicyclo[3.3.1]nonane-3-
one (1096 mg, 4.40 mmol). Purification was performed by flash
chromatography (hexane-acetone 85:15) to give pure product
(456.6 mg, 40%) as a pale resin. IR 3479, 3244, 3053, 3030, 2973,
3941, 2906, 2850, 1627, 1421 cm-1. 1H NMR (360 MHz, CDCl3)
δ (ppm) 1.22-1.31 (m, 1H), 1.37-1.47 (m, 1H), 1.62-1.72 (m,
2H), 1.76-1.89 (m, 2H), 1.92-2.04 (m, 1H), 2.34-2.45 (m, 1H),
2.60-2.70 (m, 2H), 2.70-2.80 (m, 2H), 3.98-4.08 (m, 1H),
5.00-5.09 (m, 1H), 7.40-7.49 (m, 5H). 13C NMR (CDCl3, 90
MHz) δ (ppm) 16.1, 29.2, 30.2, 36.2, 37.5, 43.9, 50.3, 53.7, 53.9,
126.4 (2C), 128.6 (2C), 129.5, 136.4, 169.6. APCI-MS m/z 258
[M þ 1]þ. HR-EIMS m/z 257.1416. HPLC/MS system A purity
98% (tR = 18.7 min).
Finally, a solution of 9-benzoylspiro[9-azabicyclo[3.3.1]nonane-
3,20-oxirane] (endo-O) (228.5 mg, 0.888 mmol) and NaN3 (467.0
mg, 7.185 mmol) in DMF (5 mL) was stirred at 120 °C for 2 days.
Workup was done as described for 31. The crude product was
purified by flash chromatography (hexane-ethyl acetate 1:1). The
product was crystallized from a mixture of CH2Cl2 and diisopropyl
ether to give pure 40 (84.2 mg, 32%) as colorless crystals (mp 110-
112 °C). IR 3377, 3059, 2933, 2854, 2102, 1608, 1446, 1365, 1269
cm-1. 1H NMR (360 MHz, CDCl3) δ (ppm) 1.47-1.65 (m, 3H),
1.66-1.80 (m, 3H), 1.84-1.98 (m, 2H), 2.04-2.15 (m, 1H), 2.21 (s,
1H), 2.53-2.71 (m, 1H), 3.22-3.36 (m, 2H), 3.88-4.01 (m, 1H),
4.90-5.00 (m, 1H), 7.33-7.46 (m, 5H). 13C NMR (CDCl3, 150
MHz) δ (ppm) 15.4, 29.1, 30.2, 37.9, 38.6, 42.6, 49.0, 64.1, 68.7,
126.3 (2C), 128.7 (2C), 129.6, 136.1, 169.4. APCI-MS m/z 301
[M þ 1]þ. HR-EIMS m/z 300.1587. HPLC/MS system A purity
97% (tR = 19.2 min).
8-Benzoyl-3-[[[(5-methylpyridin-2-yl)methyl]amino]methyl]-8-
azabicyclo[3.2.1]octan-3-ol (exo-CH2) (34). A suspension of 31
(31.8 mg, 0.111 mmol) and Pd(OH)2/C (14.2 mg) in MeOH
(4 mL) was stirred for 2 h under hydrogen atmosphere. Sub-
sequent filtration over a short column of Celite and following
evaporation of the main part of the MeOH was performed to
concentrate the solution to 4 mL. 5-Methylpyridine-2-carbalde-
hyde (14.1 mg, 0.117 mmol) and NaCNBH3 (22.3 mg, 0.355
mmol) were added, and stirring at RT was continued for 16 h.
The solvent was evaporated in vacuo, and the residue was
poured into ice-water. The aqueous layer was then extracted
with CH2Cl2. The combined organic layer was washed with
water and brine and was dried (Na2SO4). Filtration and eva-
poration in vacuo gave crude product which was purified by
flash chromatography (CH2Cl2-MeOH 98:2) to give pure 34
(9.5 mg, 23%) as a pale yellow oil. IR 3349, 2977, 2938, 2868,
2235, 1614, 1574, 1434 cm-1 1H NMR (360 MHz, CDCl3)
.
δ (ppm) 1.60-1.73 (m, 2H), 1.75-1.84 (m, 1H), 1.87-2.02 (m,
3H), 2.24-2.38 (m, 5H), 2.46 (s, 2H), 3.88 (s, 2H), 4.00-4.14 (m,
1H), 4.72-4.89 (m, 1H), 7.12 (d, J = 7.7 Hz, 1H), 7.34-7.49 (m,
6H), 8.36-8.42 (m, 1H). 13C NMR (CDCl3, 150 MHz) δ (ppm)
18.2, 26.9, 28.2, 41.4, 43.2, 51.2, 55.0, 56.2, 62.0, 69.4, 121.9,
127.0 (2C), 128.4 (2C), 129.8, 131.7, 136.5, 137.2, 149.8, 156.1,
167.8. APCI-MS m/z 366 [M þ 1]þ. HR-EIMS m/z 365.2103.
HPLC/MS system B purity 97% (tR = 14.6 min).
3-(Azidomethyl)-8-benzoyl-8-azabicyclo[3.2.1]octan-3-ol (endo-
CH2) (37). A solution of the exo-O isomer of 8-benzoylspiro[8-
azabicyclo[3.2.1]octane-3,20-oxirane] (118.4 mg, 0.487 mmol),
which can be synthesized as described for the preparation of 31,
and NaN3 (253.0 mg, 3.89 mmol) in DMF (5 mL) was stirred at
120 °C for 2 days. After the mixture was cooled to RT, ethyl
acetate (20 mL) was added to the solution, the mixture was
washed with brine, the aqueous layer was extracted with ethyl
acetate, the combined organic layers were dried (Na2SO4), and
the solvent was evaporated under reduced pressure. The crude
product was purified by flash chromatography (hexane-ethyl
acetate 1:1) to give pure 37 (56.8 mg, 41%) as a pale oil. IR 3376,
3060, 2967, 2929, 2889, 2855, 2101, 1612, 1448 cm-1. 1H NMR
(360 MHz, CDCl3) δ (ppm) 1.63-1.70 (m, 2H), 1.77-2.15 (m,
5H), 2.16-2.32 (m, 1H), 2.43 (s, 1H), 3.42 (s, 2H), 4.00-4.24 (m,
1H), 4.73-4.95 (m, 1H), 7.37-7.47 (m, 3H), 7.48-7.54 (m, 2H).
13C NMR (CDCl3, 150 MHz) δ (ppm) 27.8, 29.4, 41.4, 42.6, 50.1,
55.0, 61.8, 70.5, 127.0, 128.5, 130.3, 136.0, 168.4. APCI-MS m/z
287 [M þ 1]þ. HR-EIMS m/z 286.1430. HPLC/MS system A
purity 93% (tR = 18.0 min).
9-Benzoyl-3-[[[(5-methylpyridin-2-yl)methyl]amino]methyl]-9-
azabicyclo[3.3.1]nonan-3-ol (exo-CH2) (41). A suspension of 40
(19.8 mg, 0.07 mmol) and Pd(OH)2/C (8.5 mg) in MeOH (2 mL)
was stirred for 20 h under hydrogen atmosphere. After subse-
quent filtration over a short column of Celite a small amount of
poly(4-vinylpyridine) resin was added and stirring was contin-
ued at RT for 1 h. Another filtration step over Celite was needed
to remove the resin. 5-Methylpyridine-2-carbaldehyde (7.9 mg,
0.07 mmol) and Na(AcO)3BH (20.6 mg, 0.10 mmol) were added
to the filtrate, and stirring at RT was continued for 16 h. The
solvent was evaporated in vacuo, and the residue was poured
into ice-water. The aqueous layer was then extracted with
CH2Cl2, and the combined organic layer was washed with water
and brine and was dried (Na2SO4). Filtration and evaporation
in vacuo gave crude product which was purified by flash chro-
matography (CH2Cl2-MeOH 98:2 to 95:5) to give pure 41
(5.6 mg, 23%) as a pale oil. IR 3419, 2925, 2848, 1621, 1430,
1197 cm-1. 1H NMR(360 MHz, CDCl3) δ (ppm) 1.43-1.53 (m,
1H), 1.56-1.66 (m, 2H), 1.67-1.80 (m, 3H), 1.84-1.95 (m, 1H),
1.95-2.04 (m, 2H), 2.33 (s, 3H), 2.48-2.58 (m, 2H), 2.75-2.92
(m, 1H), 3.86-3.94 (m, 3H), 4.88-4.96 (m, 1H), 7.13 (d, J = 7.7
Hz, 1H), 7.13-7.41 (m, 5H), 7.44-7.49 (m, 1H), 8.36-8.42 (m,
1H). 13C NMR (150 MHz, CDCl3) δ (ppm) 15.5, 18.2, 29.1, 30.3,
39.1, 40.2, 43.1, 49.6, 55.1, 62.5, 66.7, 121.9, 126.2 (2C), 128.4
8-Benzoyl-3-[[[(5-methylpyridin-2-yl)methyl]amino]methyl]-8-
azabicyclo[3.2.1]octan-3-ol (endo-CH2) (38). Compound 37
(41.2 mg, 0.144 mmol) was reacted as described for 34.
Purification by flash chromatography (CH2Cl2-MeOH 95:5)
gave pure 38 (13.9 mg, 26%) as a pale yellow oil. IR 3335, 2968,
2925, 2851, 2235, 1618, 1575, 1446 cm-1. 1H NMR (360 MHz,
CDCl3) δ (ppm) 1.57-1.71 (m, 2H), 1.74-1.86 (m, 1H),
1.86-2.10 (m, 3H), 1.78-2.29 (m, 2H), 2.32 (s, 3H), 2.82 (bs,
2H), 3.95 (s, 2H), 4.00-4.15 (m, 1H), 4.73-4.93 (m, 1H), 7.16
(d, J = 7.9 Hz, 1H), 7.34-7.43 (m, 3H), 7.43-7.56 (m, 3H),
8.34-8.41 (m, 1H). 13C NMR (CDCl3, 150 MHz) δ (ppm) 18.1,
27.6, 29.2, 42.1, 43.4, 50.5, 54.8, 55.4, 62.0, 69.2, 121.9, 127.1
(2C), 128.4 (2C), 129.9, 131.8, 136.3, 137.3, 149.6, 156.0, 167.9.
APCI-MS m/z 366[M þ 1]þ. HR-EIMS m/z 365.2104. HPLC/
MS system A purity 96% (tR = 14.5 min).
3-(Azidomethyl)-9-benzoyl-9-azabicyclo[3.3.1]nonan-3-ol (exo-
CH2) (40). The synthesis of 40 was achieved in a four-step
reaction sequence starting with the deprotection of N-butyloxy-
carbonyl-9-azabicyclo[3.3.1]nonan-3-one (39). The boc deriva-
tive 39 (4156 mg, 17.2 mmol) was stirred in a mixture of CH2Cl2
(15 mL) and TFA (15 mL) for 16 h at RT. The reaction mixture
was frozen with liquid nitrogen, and the solvent was removed by
sublimation in vacuo. After the residue was dissolved in CH2Cl2

Article
Journal of Medicinal Chemistry, 2010, Vol. 53, No. 19 7177
(2C), 129.4, 131.7, 136.6, 137.2, 149.8, 156.1, 169.2. APCI-MS
m/z 380 [M þ 1]þ. HR-EIMS m/z 379.2259. HPLC/MS system B
purity 96% (tR = 9.5 min).
1.47-1.68 (m, 4H), 1.73-1.91 (m, 2H), 1.91-2.02 (m, 1H),
2.18-2.29 (m, 1H), 2.32 (s, 3H), 2.54-2.64 (m, 2H), 3.90 (s, 2H),
4.00-4.09 (m, 1H), 5.04-5.16 (m, 1H), 7.17 (d, J = 7.9 Hz, 1H),
7.33-7.41 (m, 3H), 7.44-7.55 (m, 3H), 8.38-8.40 (m, 1H). 13
C
3-(Azidomethyl)-9-benzoyl-9-azabicyclo[3.3.1]nonan-3-ol (endo-
CH2) (42). Synthesis of 42 was achieved in a multistep reaction
starting from 9-benzoyl-9-azabicyclo[3.3.1]nonan-3-one (see syn-
thesis of 40). A solution of t-BuOK (502 mg, 4.55 mmol) and
methyltriphenylphosphonium bromide (1652 mg, 4.62 mmol) in
THF (15 mL) was stirred for 2 h at 80 °C. A solution of 9-benzoyl-
9-azabicyclo[3.3.1]nonan-3-one (840.0 mg, 3.452 mmol) in THF
was added and was stirred for 16 h at RT. After addition of diethyl
ether, the precipitate was filtered and washed with diethyl ether
twice. The filtrate was evaporated under reduced pressure and
purified by flash chromatography (hexane-acetone 8:2) to give
pure 9-benzoyl-3-methylene-9-azabicyclo[3.3.1]nonane (758.0 mg,
91%) as a pale resin. IR 3246, 3068, 3027, 2963, 2932, 2877, 2848,
NMR (150 MHz, CDCl3) δ (ppm) 14.3, 18.1, 31.2, 32.3, 35.8,
36.3, 40.9, 47.9, 55.4, 60.2, 69.2, 121.8, 126.6 (2C), 128.3 (2C),
129.0, 131.5, 137.1, 137.2, 149.7, 156.5, 170.0. APCI-MS m/z 380
[M þ 1]þ. HR-EIMS m/z 379.2261. HPLC/MS system A purity
95% (tR = 15.2 min).
Receptor Binding Studies. Receptor binding studies were
carried out as previously described.39 In brief, the dopamine
D1 receptor assay was done with porcine striatal membranes at a
final protein concentration of 40 μg/assay tube and the radio-
ligand [3H]SCH 23390 at 0.3 nM (KD = 0.41-0.56 nM). Com-
36
petition experiments with human D2long
,
D
,
36 D3,37 and
2short
D4.438 receptors were run with preparations of membranes from
CHO cells stably expressing the corresponding receptor and
[3H]spiperone at a final concentration of 0.1-0.4 nM. The
assays were carried out at a protein concentration of 5-20 μg/
assay tube and KD values of 0.04-0.14, 0.04-0.24, 0.11-0.28,
and 0.17-0.35 nM for the D2long, D2short, D3, and D4.4 recep-
tors, respectively. 5-HT and R1 receptor binding experiments
were performed with homogenates prepared from porcine cere-
bral cortex as described.35 Assays were run with membranes at a
protein concentration per assay tube of 100, 80, and 60 μg/assay
tube for 5-HT1A, 5-HT2, and R1 receptor, respectively, and
radioligand concentrations of 0.2-0.3 nM ([3H]WAY100635
and [3H]prazosin) and 0.5 nM ([3H]ketanserin) with KD values
of 0.03-0.15 nM for 5-HT1A, 0.67-1.6 nM for 5-HT2, and
0.07-0.16 nM for the R1 receptor. Binding affinities to the agonist
labeled high affinity binding site of the 5-HT1A receptor were
determined similar to the protocol for R1 in 24-well microplates at
a final volume of 800 μL employing membranes from porcine
cerebral cortex at 320 μg/assay tube and the selective agonist
radioligand [3H]8-OH-DPAT (Biotrend, Cologne, Germany,
with a specific activity of 187 Ci/mmol) at a final concentration
of 0.5 nM and with KD values of 0.66-1.1 nM. Binding affinities
to R2 receptors were determined similarly (total volume of 800 μL,
homogenates from porcine cerebral cortex at 240 μg/assay tube)
using the subtype selective radioligand [3H]RX82100243 at 0.2-
0.5 nM and considering KD values of 0.21-0.52 nM. Unspecific
binding was determined in the presence of 10 μM RX821002.
Protein concentration was established by the method of
Lowry using bovine serum albumin as standard.44
1
2821, 1628, 1419 cm-1. H NMR (360 MHz, CDCl3) δ (ppm)
1.40-1.52 (m, 1H), 1.60-1.70 (m, 1H), 1.70-1.85 (m, 2H), 1.86-
2.00 (m, 1H), 2.23-2.56 (m, 4H), 2.65-2.77 (m, 1H), 3.89-3.97
(m, 1H), 3.76-3.87 (m, 2H), 4.92-5.02 (m, 1H), 7.34-7.47 (m,
5H). 13C NMR (CDCl3, 90 MHz) δ (ppm) 18.1, 30.5, 31.5, 38.2,
39.3, 45.0, 51.3, 110.0, 126.4 (2C), 128,6 (2C), 129.4, 136.6, 145.1,
169.7. APCI-MS m/z 242 [M þ 1]þ. HR-EIMS 241.1466. HPLC/
MS system A purity 100% (tR = 18.8 min).
Stereoselective epoxidation of the methylene derivative was
done when a solution of 9-benzoyl-3-methylen-9-azabicyclo-
[3.3.1]nonane (440 mg, 1.825 mmol) and m-CPBA (500 mg, 2.90
mmol) in CH2Cl2 (6 mL) was stirred at RT for 2 h. The mixture
was washed with a saturated solution of NaHCO3, dried
(Na2SO4), and evaporated under reduced pressure. Purification
was performed by flash chromatography (hexane-acetone 85:15)
to give the pure exo-O isomer of 9-benzoylspiro[9-azabicyclo-
[3.3.1]nonan-3,20-oxirane] (388.2 mg, 83%) as a yellowish solid.
IR 3481, 3057, 3028, 2939, 2881, 2850, 1628, 1423 cm-1. 1H NMR
(360 MHz, CDCl3) δ (ppm) 1.26-1.34 (m, 1H), 1.41-1.50 (m,
1H), 1.53-1.61 (m, 1H), 1.71-1.88 (m, 3H), 1.91-2.04 (m, 2H),
2.19-2.30 (m, 1H), 2.41-2.52 (m, 1H), 2.77-2.88 (m, 2H), 4.03-
4.12 (m, 1H), 5.05-5.15 (m, 1H), 7.39-7.46 (m, 5H). 13C NMR
(CDCl3, 90 MHz) δ (ppm) 19.4, 29.3, 30.4, 36.8, 37.9, 45.0, 51.3,
55.7, 59.6, 126.4 (2C), 128.7 (2C), 129.7, 136.2, 169.5. APCI-MS
m/z 258 [M þ 1]þ. HR-EIMS m/z 257.1416. HPLC/MS system A
purity 98% (tR = 17.8 min).
A solution of 9-benzoylspiro[9-azabicyclo[3.3.1]nonan-3,20-
oxirane] (exo-O) (193.6 mg, 0.752 mmol) and NaN3 (396.2 mg,
6.095 mmol) in DMF (5 mL) was stirred at 120 °C for 2 days.
After the mixture was cooled to RT, ethyl acetate (20 mL) was
added to the solution, which was washed with brine to remove
the DMF. The aqueous layer was extracted with ethyl acetate, the
combined organic layers were dried (Na2SO4), and the solvent was
evaporated under reduced pressure. The crude product was
purified by flash chromatography (hexane-ethyl acetate 1:1).
The product crystallized from a mixture of CH2Cl2 and diisopro-
pyl ether to give pure 42 (171.7 mg, 76%) as colorless crystals (mp
Determination of [35S]GTPγS Binding. The [35S]GTPγS bind-
ing assay for functional activity was done as described in the
literature.45 In brief, ligand induced binding of the radioligand
[35S]GTPγS (specific activity of 1250 Ci/mmol, Perkin-Elmer) to
membranes of CHO cells stably expressing the human 5-HT1A
receptor was determined at a radioligand concentration of
0.1 nM and in the presence of test compounds in eight diff-
erent concentration (0.01-10000 nM) as hexaduplicates at a final
volume of 200 μL. Maximum stimulation (=100%) of [35S]GTPγS
binding was measured using the reference quinpirole (10 μM).
Data Analysis. The resulting competition curves of the re-
ceptor binding experiments were analyzed by nonlinear regres-
sion using the algorithms in PRISM 3.0 (GraphPad Software,
San Diego, CA). The data were fit using a sigmoid model to
provide an IC50 value, representing the concentration corre-
sponding to 50% of maximal inhibition. IC50 values were
transformed to Ki values according to the equation of Cheng
and Prusoff.46
1
140-142 °C). H NMR (360 MHz, CDCl3) δ (ppm) 1.32-1.49
(m, 2H), 1.49-1.57 (m, 1H), 1.57-1.70 (m, 3H), 1.75-1.90 (m,
2H), 1.91-2.03 (m, 1H), 2.13-2.27 (m, 1H), 2.91 (s, 1H),
3.18-3.30 (m, 2H), 4.02-4.13 (m, 1H), 4.97-5.08 (m, 1H),
7.33-7.43 (m, 3H), 7.45-7.53 (m, 2H). 13C NMR (CDCl3,
90 MHz) δ (ppm) 14.2, 31.1, 32.4, 34.3, 35.3, 41.1, 47.9, 61.8,
70.7, 126.7 (2C), 128.4 (2C), 129.5, 136.4, 170.5. APCI-MS
m/z 301 [M þ 1]þ. HPLC/MS system B purity 97% (tR
=
13.8 min).
9-Benzoyl-3-[[[(5-methylpyridin-2-yl)methyl]amino]methyl]-9-
azabicyclo[3.3.1]nonan-3-ol (endo-CH2) (43). Synthesis of 43 was
achieved according to 41 employing 42 (31.4 mg, 0.11 mmol),
5-methylpyridine-2-carbaldehyde (20.5 mg, 0.17 mmol), and
NaCNBH3 (21.1 mg, 0.34 mmol). Purification by flash chro-
matography (CH2Cl2-MeOH 98:2 to 95:5) gave pure 43 (16.0
mg, 40%) as a pale oil. IR 3419, 2931, 2852, 1614, 1446, 1197
Binding curves resulting from the [35S]GTPγS binding assay
were analyzed by nonlinear regression. The data were normal-
ized (basal effect of 0%, maximum effect of the full agonist
quinpirole of 100%) and then combined to get a mean curve.
Nonlinear regression analysis of this curve provided the EC50
values representing the concentration corresponding to 50% of
maximal stimulation as a measure of potency.
cm-1 1H NMR (360 MHz, CDCl3) 1.31-1.43 (m, 2H),
.

7178 Journal of Medicinal Chemistry, 2010, Vol. 53, No. 19
Bollinger et al.
ꢀ
Acknowledgment. The authors thank Dr. H. H. M. Van Tol
(Clarke Institute of Psychiatry, Toronto, Canada), Dr. J.-C.
Schwartz and Dr. P. Sokoloff (INSERM, Paris, France),
and Dr. J. Shine (The Garvan Institute of Medical Research,
Sydney, Australia) for providing dopamine D4, D3, and D2
receptor expressing cell lines, respectively, and Dr. P. Strange
(University of Reading, U.K.) for providing human 5-HT1A
receptor expressing CHO cells. PD Dr. Reinhard Berkels (UCB
Pharma GmbH, Germany) is acknowledged for providing us
with results of in vivo pharmacological experiments (formalin
induced paw pain assay).
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Supporting Information Available: Experimental and spetro-
scopic data of nonkey target compounds 8aa-8aw, 8ay-bs,
8bu, 8bv, 8bx-cj, 11, 12, 24, 30, 35, and 36 and the respective
precursors thereof; receptor binding data employing porcine
5-HT2, D1, R1, and R2 and the human D2long, D2short, D3, and
D4.4 receptors; X-ray crystal structure determination details.
This material is available free of charge via the Internet at http://
pubs.acs.org.
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