Synthesis of novel GABA uptake inhibitors. 4. Bioisosteric transformation and successive optimization of known GABA uptake inhibitors leading to a series of potent anticonvulsant drug candidates

Article abstract of DOI:10.1021/jm980492e

By bioisosteric transformations and successive optimization of known GABA uptake inhibitors, several series of novel GABA uptake inhibitors have been prepared by different synthetic approaches. These compounds are derivatives of nipecotic acid and guvacine, substituted at the nitrogen of these amino acids by various lipophilic moieties such as diarylaminoalkoxyalkyl or diarylalkoxyalkyl. The in vitro values for inhibition of [³H]GABA uptake in rat synaptosomes was determined for each compound, and it was found that the most potent compound from this series, (R)-1-(2-(3,3-diphenyl-1-propyloxy)ethyl)-3-piperidinecarboxylic acid hydrochloride (29), is so far the most potent parent compound inhibiting GABA uptake into synaptosomes. Structure-activity results confirm our earlier observations, that an electronegative center in the chain connecting the amino acid and diaryl moiety is very critical in order to obtain high in vitro potency. Several of the novel compounds were also evaluated for their ability in vivo to inhibit clonic seizures induced by a 15 mg/kg (ip) dose of methyl 6,7-dimethoxy-4-ethyl-β-carboline-3-carboxylate (DMCM). Some of the compounds tested show a high in vivo potency comparable with that of the recently launched anticonvulsant product 6 ((R)-1-(4,4-bis(3-methyl-2- thienyl)-3-butenyl)-3-piperidinecarboxylic acid).

Full text of DOI:10.1021/jm980492e

J . Med. Chem. 1999, 42, 4281-4291
4281
Articles
Syn th esis of Novel GABA Up ta k e In h ibitor s. 4.1 Bioisoster ic Tr a n sfor m a tion
a n d Su ccessive Op tim iza tion of Kn ow n GABA Up ta k e In h ibitor s Lea d in g to a
Ser ies of P oten t An ticon vu lsa n t Dr u g Ca n d id a tes
Knud Erik Andersen,* J an L. Sørensen, Per O. Huusfeldt, Lars J . S. Knutsen,† J esper Lau, Behrend F. Lundt,
Hans Petersen,‡ Peter D. Suzdak,§ and Michael D. B. Swedberg
Health Care Discovery, Novo Nordisk A/ S, Novo Nordisk Park, DK 2760 Måløv, Denmark
Received August 24, 1998
By bioisosteric transformations and successive optimization of known GABA uptake inhibitors,
several series of novel GABA uptake inhibitors have been prepared by different synthetic
approaches. These compounds are derivatives of nipecotic acid and guvacine, substituted at
the nitrogen of these amino acids by various lipophilic moieties such as diarylaminoalkoxyalkyl
or diarylalkoxyalkyl. The in vitro values for inhibition of [3H]GABA uptake in rat synaptosomes
was determined for each compound, and it was found that the most potent compound from
this series, (R)-1-(2-(3,3-diphenyl-1-propyloxy)ethyl)-3-piperidinecarboxylic acid hydrochloride
(29), is so far the most potent parent compound inhibiting GABA uptake into synaptosomes.
Structure-activity results confirm our earlier observations, that an electronegative center in
the chain connecting the amino acid and diaryl moiety is very critical in order to obtain high
in vitro potency. Several of the novel compounds were also evaluated for their ability in vivo
to inhibit clonic seizures induced by a 15 mg/kg (ip) dose of methyl 6,7-dimethoxy-4-ethyl-â-
carboline-3-carboxylate (DMCM). Some of the compounds tested show a high in vivo potency
comparable with that of the recently launched anticonvulsant product 6 ((R)-1-(4,4-bis(3-methyl-
2-thienyl)-3-butenyl)-3-piperidinecarboxylic acid).
In tr od u ction
γ-Aminobutyric acid (GABA) is a major inhibitory
neurotransmitter in the mammalian central nervous
system (CNS).2-6 GABA has been estimated to be
present in 60-70% of all synapses in the CNS.7
A
decrease in GABA-ergic neurotransmission appears to
be involved in the etiology of several neurological
disorders, including anxiety, pain, and epilepsy.4,5,8-10
Thus, numerous investigations have focused on finding
novel approaches to modulate GABA-ergic function in
human. These approaches include direct agonism of the
GABA receptors,11,12 inhibition of enzymatic breakdown
of GABA,13,14 or inhibition of the uptake of GABA into
neuronal and glial cell bodies.5,15 It is well-documented
that GABA agonists are responsible for a number of
unacceptable side effects in humans.16 However, in
principle, GABA uptake inhibitors should exert a more
therapeutically useful influence than GABA agonists.
This is because a major enhancement of GABA-ergic
neurotransmission would only take place under condi-
tions where GABA is already being released physiologi-
cally. GABA can be removed from the synapse either
F igu r e 1. Three cyclic amino acids which act as GABA uptake
inhibitors: nipecotic acid (1), guvacine (2), and homo-â-proline
(3).
by a high-affinity sodium-dependent GABA uptake
carrier into neuronal or glial cells or by diffusion from
the synapse. The GABA uptake system has traditionally
been classified as either neuronal or glial on the basis
of pharmacological selectivity of cyclic amino acid GABA
uptake inhibitors.5 However, several investigators have
recently cloned and sequenced subtypes of the GABA
uptake carrier, and the selectivity of novel and hitherto
known GABA uptake inhibitors on these subtypes has
been investigated.17 It was found that the type of GABA
uptake inhibitors described in this paper is binding to
the GAT-1 subtype.
Nipecotic acid (1), guvacine (2), and homo-â-proline
(3)18,19 (Figure 1) which can be considered as conforma-
tionally restricted GABA analogues20 display in vitro
activity as inhibitors of [3H]GABA uptake. However,
compounds 1-3 do not readily cross the blood-brain
barrier.18,21,22 In the 1980s, novel series of lipophilic
GABA uptake inhibitors that possess potent activity in
vitro and in vivo were described.23-26 These compounds
* Corresponding author. Tel: +45 4444 4898. Fax: +45 4466 3450.
E-mail: kea@novo.dk.
† Cerebrus Ltd., Oakdene Ct, Winnersh, Wokingham, Berkshire
RG41 5UA, England.
‡ H. Lundbeck A/S, Ottiliavej 9, DK-2500 Copenhagen, Denmark.
§ Department of Research, Guildford Pharmaceuticals, 6611 Tribu-
tary St, Baltimore, MD 21224.
Astra Pain Control, S-15185 Sødertalje, Sweden.
10.1021/jm980492e CCC: $18.00 © 1999 American Chemical Society
Published on Web 09/24/1999

4282 J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 21
Andersen et al.
During the development of this new drug we have
continuously searched for GABA uptake inhibitors with
improved properties as second-generation compounds.
This resulted in a series of novel and highly potent
GABA uptake inhibitors, of which 7 and 8 are examples1
(Figure 3). In this type of compound we applied the
electronegative principle in the chain and thereby
improved in vitro GABA uptake inhibition considerably
compared to compounds such as 4-6. In our continued
search for GABA uptake inhibitors with improved
biological properties, we have investigated other struc-
tural features around these reference compounds. In one
of these investigations we have modified compounds 4
and 933,35,38 (analogue of 5, Figure 3) by successive
isosteric replacement, optimization of chain length, and
electrostatic optimization into a series of new GABA
uptake inhibitors. The synthesis45 and biological activity
of this series of GABA uptake inhibitors 10-35 (Table
1) will now be reported.
F igu r e 2. Lipophilic reference GABA uptake inhibitors.
Ch em istr y
The overall general strategy used for the preparation
of the new compounds presented in Table 1 was via
N-alkylation of the parent cyclic amino acids 1 or 2,46
with the appropriate halogenide (Schemes 1-3, method
B1) or mesylate or tosylate (Scheme 4, method B2). The
parent cyclic amino acids were protected as their ester
derivatives for this reaction. The separate enantiomers
of 1 could be prepared by the published procedure
involving resolution with either L-(+)- or with D-(-)-
tartaric acid giving (R)- or (S)-ethyl nipecotate, respec-
tively.47,48
The N-alkylated amino acid ester derivatives were
saponified under basic conditions (Schemes 1-4, method
C) to provide the free N-alkylated amino acids featured
in Table 1, isolated generally as their crystalline hy-
drochloride salts. Preparation of the various halides or
mesylates of the diaryl chains used are further il-
lustrated in Schemes 1-4.
F igu r e 3. Potent GABA uptake inhibitors with an electro-
negative moiety introduced in the chain.
Starting from diphenylamine several different meth-
ods were used to produce the desired chains in one or
several steps (Scheme 1). N-Alkylation of diphenylamine
with a bis-halogenide furnished the desired halogenide
directly (method A1). For this N-alkylation NaH was
used in a high-boiling solvent like dibutyl ether. This
method was applicable for straight alkyl chains or the
diethyl ether chain, as bis-chloroethyl ether is readily
available. Alternatively, when oxygen was desired in the
chain a two-step sequence was employed (methods A2
and A3) in which the chain was built in successive
alkylation steps (Scheme 1). N-Alkylation of diphenyl-
amine with the appropriate haloalkyl tetrahydro-2-
pyranyl ether49-51 using NaH in a high-boiling solvent
like diethylene glycol diethyl ether followed by removal
of the THP group by hydrolysis in dilute acid furnished
2-(diphenylamino)ethanol52 and 3-(diphenylamino)-1-
propanol53 (method A2). These alcohols were elongated
by O-alkylation with a dihaloalkane in a high boiling
solvent like dibutyl ether in the presence of NaH to give
the desired diphenylaminoalkoxyalkyl halides (method
A3). The halides were then converted into 10-15 and
17-20 by the general methods B1 and C described
above.
differ from compounds 1-3 in that they readily cross
the blood-brain barrier probably due to the attachment
of a lipophilic anchor to the nitrogen in compounds 1-3.
In the early 1980s, such lipophilic derivatives of
amino acids 1-3 were described for the first time. These
compounds, an example of which is 4 (SKF 89976A,
Figure 2), exhibited promising seizure protection23,27,28
in some animal models predictive of anticonvulsant
activity.29 The compounds also displayed reduced CNS
depressant effects compared with some commonly used
anticonvulsant drugs, such as diazepam.30 These ob-
servations have also stimulated others to investigate
this field,31-36 leading to the discovery of a highly
lipophilic GABA uptake inhibitor with CNS activity, 5
(CI-966). This compound was discovered at Parke-Davis/
Warner-Lambert and has been investigated in a phase
I clinical trial.37 From our laboratory we have previously
reported on the structure-activity studies leading to the
choice of 6 (tiagabine, NO-328, or NNC 05-0328) as an
anticonvulsant drug candidate.24-26,38-40 Extensive phar-
macological41,42 and clinical investigations have been
completed on 6 with proven anticonvulsant efficacy in
humans.43,44 This novel antiepileptic agent has now been
launched for add-on therapy in the treatment of epi-
lepsy.
In general, aryl-substituted diphenylamines were not
employed in the structure-activity studies concerning

Synthesis of Novel GABA Uptake Inhibitors
J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 21 4283
Sch em e 1. Synthesis of (R)-1-(Diphenylaminoalkyl)-
3-piperidinecarboxylic acids 10-15 and
(R)-1-(Diphenylaminoalkoxyalkyl)-3-piperidinecarboxylic
Acids 17-20a
Sch em e 2. Synthesis of (R)-1-(8-(Diphenylamino)-
8-oxo-1-octyl)-3-piperidinecarboxylic Acid 16a
a
Method A4: NaH, dibutyl ether, reflux. Method B1: K2CO3,
acetone, (R)-3-piperidinecarboxylic acid ethyl ester, reflux. Method
C: (1) NaOH, EtOH, room temperature; (2) HCl.
bromides used were prepared by known methods54-57
from the appropriate propiophenone and an arylmag-
nesium reagent followed by dehydration in dilute acid
and then bromination by NBS/peroxide. To elongate the
chain in the allyl bromides, O-alkylation of a diol was
employed (method A5). A solution of n-butyllithium in
hexanes was carefully added at 10 °C to either ethylene
glycol or 1,3-propanediol through which a steady stream
of dry nitrogen was passed. This afforded a suspension
of the corresponding lithiate salt to which the appropri-
ate allyl bromide was added. The reaction mixture was
then allowed to react for several days and worked up
to give the diarylpropenyloxy alcohols. Further reaction
of these alcohols via their mesylates or tosylates by the
general methods B2 and C described above produced the
acids 21-26 with an unsaturated chain.
Preparation of compounds with a saturated chain can
be accomplished in three different ways. The most
convenient and direct route to produce chain-saturated
derivatives is by catalytic hydrogenation of the corre-
sponding acids holding an unsaturated chain (method
D2). Hydrogenation of the acid hydrochlorides 22 and
23 in the presence of 10% Pd/C in methanol afforded
the corresponding saturated acid hydrochlorides 31 and
32. However, it was observed that the ether linkage of
the starting allyl ether was partly cleaved during
hydrogenation.58 This cleavage resulted in a byproduct
with comparable polarity as in the product which made
workup more tedious. To circumvent this problem, an
alternative method was used in which hydrogenation
was performed at an earlier step in the synthesis
(method D1). Hydrogenation of the hydroxyalkyl allyl
ethers in the presence of 10% Pd/C in dioxane afforded
the corresponding hydroxyalkyl alkyl ethers. Further
a
Y, Y′ ) Cl or Br; 10-15: X ) CH2; r ) 2-5; s ) 0; 17-20:
X ) O, OCH2CH2O; r ) 2-3; s ) 2-4. Methods A1, A2, and A3:
NaH, dibutyl ether, reflux. Method B1: K2CO3, dibutyl ether or
acetone, (R)-3-piperidinecarboxylic acid ethyl ester, reflux. Method
C: (1) NaOH, EtOH, room temperature; (2) HCl.
substitution pattern on the aryl moieties. The reason
being that this type of substituted starting amine is not
very accessible, illustrated by tedious methods for their
preparation and the low number of publications describ-
ing only a poor diversity of such derivatives of diphen-
ylamine. Therefore, this type of structure-activity
investigation was made on the diarylallyl or diarylalkyl
derivatives described below, as aryl-substituted starting
materials for this type of compound are much more
accessible.
In the preparation of the more rigid amide analogue
16 of the above diphenylamine derivatives, the sodium
salt of diphenylamine was acylated with 8-bromo-
octanoyl chloride in dibutyl ether (Scheme 2, method
A4). This furnished the desired 8-bromo-N,N-diphenyl-
octanamide which was converted into 16 by the general
methods B1 and C described above.
In Scheme 3, several methods for the preparation of
diarylpropenyloxyalkyl and diarylpropoxyalkyl deriva-
tives of 1 and 2 are illustrated. The preferred and
general method utilized the appropriate diarylallyl
bromide as starting material (method A5). The allyl

4284 J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 21
Andersen et al.
reaction of these saturated ethers by the general
methods B2 and C described above produced the acids
30 and 33. This method is also critical for the prepara-
tion of derivatives of 2, as the double bond in 1,2,5,6-
tetrahydro-3-pyridinecarboxylic acid is easily hydroge-
nated. Therefore, the reductive step in the preparation
of 33 must be performed before this amino acid is
introduced in the synthesis.
To investigate whether a basic moiety was allowed
in the chain, compound 35 was prepared (Scheme 5).
1-Bromo-3,3-diphenylpropane was treated with a 33%
ethanolic methylamine solution at room temperature to
give N-(3,3-diphenyl-1-propyl)-N-methylamine.59 This
secondary amine was then alkylated with (R)-1-(2-
bromoethyl)-3-piperidinecarboxylic acid ethyl ester60 in
acetone in the presence of K2CO3 to give the ethyl ester
derivative of 35 (method B3). Hydrolysis of the ester by
the general method C afforded the desired acid deriva-
tive 35.
The third method used for the preparation of diaryl-
propoxyalkyl derivatives employs 3,3-diphenyl-1-pro-
panol as starting material (method A6). O-Alkylation of
this alcohol with 2-bromoethyl tetrahydro-2-pyranyl
ether in the presence of NaH in dibutyl ether followed
by hydrolysis in dilute acid furnished the 2-(3,3-diphen-
yl-1-propyloxy)ethanol in a moderate yield. Further
reaction of this alcohol by the general methods B2 and
C described above gave the acid 29. However, this
method was not generally employed, as the appropriate
propanols are less available than the allyl bromides.
The diphenylalkenyl derivatives 27 and 28 were
prepared via the diphenylalkenyl bromides (Scheme 4).
Addition of 2 equiv of phenyllithium at low temperature
to ethyl 6-bromohexanoate or ethyl 8-bromooctanoate
followed by dehydration in dilute acid furnished the
desired diphenylalkenyl bromides (method A7). The use
of these bromides in the general methods B1 and C
described above produced the acids 27 and 28. The
double bonds in these acids could then be hydrogenated
at normal pressure using 10% Pd/C in aqueous solution
(method D3) to give the corresponding diphenylalkyl
derivatives, exemplified by 34.
Biologica l Resu lts a n d Discu ssion
With the aim to identify GABA uptake inhibitors with
improved pharmacological properties, a large range of
new GABA uptake inhibitors have been prepared.45
Some representative examples of these compounds are
included in Table 1. Their IC50 values for in vitro
inhibition of [3H]GABA uptake determined essentially
by Fjalland’s method61 are included (mean of two
determinations is given).
In the compounds 10-35, steric and electronic prop-
erties of the aryl moieties as well as the chain linking
the aryl and amino acid parts of the molecules have been
varied in order to probe the requirements for inhibiting
GABA transport at the site62-65 involved in the uptake
of GABA from the synaptic cleft into neuronal and glial
cell bodies.
In the first series of diphenylamine derivatives rep-
resented by compounds 10-15 (Table 1), the central
chain moieties (>CdCH- or >CH-O-) between the
Sch em e 3. Synthesis of (1,1-Diaryl-1-propen-3-yl)oxyalkyl Amino Acids 21-26 and (3,3-Diaryl-1-propyl)oxyalkyl
Amino Acids 29-33a
a
s ) 2-3; R1 and R2, see Table 1. Method A5: n-BuLi, ethylene glycol or 1,3-propanediol, room temperature. Method A6: (1) NaH,
dibutyl ether, reflux; (2) 2-bromoethyl tetrahydropyranyl ether, reflux; (3) H2SO4, i-PrOH, 60 °C. Method B2: (1) n-BuLi, THF or toluene,
10 °C; (2) p-tosyl chloride, room temperature; (3) K2CO3, (R)-3-piperidinecarboxylic acid ethyl ester or 1,2,5,6-tetrahydro-3-pyridinecarboxylic
acid ethyl ester, reflux. Method C: (1) NaOH, EtOH, room temperature; (2) HCl. Method D1: H2, 10% Pd/C, 1 atm, dioxane. Method D2:
H2, 10% Pd/C, 1 atm, MeOH.

Synthesis of Novel GABA Uptake Inhibitors
J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 21 4285
Sch em e 4. Synthesis of (R)-1-(Diphenylalkenyl)-
3-piperidinecarboxylic Acids 27 and 28 and
(R)-1-(6,6-Diphenyl-5-hexen-1-yl)-3-piperidinecarboxylic
Acid 34a
Sch em e 5. Synthesis of (R)-1-(2-(N-(3,3-Diphenyl-
1-propyl)-N-methylamino)ethyl)-3-piperidinecarboxylic
Acid 35a
a
Method B3: K2CO3, acetone, room temperature. Method C: (1)
NaOH, EtOH, room temperature; (2) HCl.
obtain potency optimization in this series, it is beneficial
to shorten the chain length as illustrated by example
17.
Having applied the electronegative principle and
having optimized the chain length in the diphenylamine
series as discussed above, which resulted in the most
potent compound 17 for the above-mentioned series, a
reversed isosteric transformation was made from the
>N-CH2- moiety in this compound to a >CdCH-
group represented in the corresponding allyl ether
derivative 21. Comparing the potency of this compound
with that of the reference compounds 4 and 9, this
reverse change does not affect the potency significantly,
as compound 21 is only moderately weaker than com-
pound 17. In the third series of allyl ether derivatives
21-26 prepared around 21, the substitution pattern has
been varied. As we have shown earlier,1,38 an o-methyl
substitution on both phenyl groups, as in example 23,
is beneficial for potency. As these methyl substituents
only allow the out-of-plane conformations of the aryl
groups in this compound, they may introduce the
preferred conformations of the aryl groups in the
binding site. One o-methyl substituent, as in example
22, seems not to create enough strain in the diaryl
moiety of this compound to improve potency compared
to the parent compound 21. As can be seen from the
examples 25 and 26, substitution in the para position
affects binding negatively, although it does not abolish
potency totally.
a
t ) 4 (27, 34) or 6 (28). Method A7: (1) 2 PhLi, Et2O, -60 °C;
(2) H2SO4, i-PrOH, reflux. Method B1: K2CO3, (R)-3-piperidine-
carboxylic acid ethyl ester, reflux. Method C: (1) NaOH, EtOH,
room temperature; (2) HCl. Method D3: H2, 10% Pd/C, 1 atm, H2O.
aryl groups in 4 or 9, respectively, have been replaced
by the isosteric >N-CH2- moiety. It is obvious from
the data presented in Table 1 that direct replacement
is not allowed as potency is completely lost when
comparing the activity of compound 10 with that 4 and
9. However, successive elongation of the chain in
compound 10 leads to improved potency as shown in
examples 11-14. With an optimum of seven carbon
atoms, as in example 14, potency has been totally
recovered again compared to the reference compounds.
Further extension of the chain leads to a decrease in
potency as shown by example 15. Introduction of the
conformationally more restricted amide moiety, as in
example 16, leads to a complete loss in affinity for the
GABA uptake site.
With the optimized length of the chain we now applied
the electronegative principle which we have described
earlier.1 In the second series of diphenylamine deriva-
tives represented by compounds 17-20 (Table 1), an
oxygen has been introduced in the chain. In this series
the placement of the oxygen is very critical as can be
seen by comparison of examples 18 and 19. Further, to
In the series of hydrogenated ether derivatives 29-
33 a very different SAR is observed compared to the
allyl ethers discussed above. Examples 29 and 30 from

4286 J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 21
Andersen et al.
Ta ble 1. Chemical and Biological Data of the Novel GABA Uptake Inhibitors 10-35
inhibition of
GABA uptake
IC50(nM)c
method for
synthesis
no.
r
s
R1
R2
X
R3a
mp (°C)
formula
microanalysesb
4
6
7
8
9
330
67
137
d
e
e
d
104
1407
>9000
2608
1381
659
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
3
4
5
6
7
8
(R)-N
(R)-N
(R)-N
(R)-N
(R)-N
(R)-N
(R)-N
(R)-N
(R)-N
(R)-N
A1B1C
A1B1C
A1B1C
A1B1C
A1B1C
A1B1C
A4B1C
A1B1C
A2A3B1C
A2A3B2C
A1B1C
A5B2C
A5B2C
A5B2C
A5B2C
A5B2C
A5B2C
A7B1C
A7B1C
A6B2C
138-140f
196-198f
175-178f
143-146g
115-120f
80-86f
C21H26N2O2,HCl
C22H28N2O2,HCl
C23H30N2O2,HCl,2H2O
C24H32N2O2,HCl
C25H34N2O2,HCl
C26H36N2O2,HCl
C,H,N,Cl
C,H,N,Cl
C,H,N,Cl
C,H,N,Cl
C,H,N,Cl
C,H,N,Cl
C,H,N
C,H,N,Cl
C,H,N,Cl
C,H,N,Cl
C,H,N,Cl
C,H,N,Cl
C,H,N,Cl
C,H,N
C,H,N
C,H,N,Cl
C,H,N
C,H,N,Cl
C,H,N,Cl
C,H,N,Cl
C,H,N,Cl
C,H,N,Cl
C,H,N
232
1293
>9000
90
amorphous C26H34N2O3,HCl,H2O
2
2
3
2
2
4
3
2
2
2
2
3
2
2
2
4
2
2
2
2
2
2
2
-O-
-O-
-O-
145-148f
oil
C22H28N2O3,HCl,2H2O
C24H32N2O3,HCl
C24H32N2O3,HCl
C24H32N2O4,HCl,H2O
C23H27NO3,HCl,2H2O
C24H29NO3,HCl
300
138-140f
oil
>3000
>9000
258
-OCH2CH2O- (R)-N
H
2-CH3
H
H
-O-
-O-
(R)-N
(R)-N
(R)-N
(R)-N
(R)-N
(R)-N
(R)-N
(R)-N
(R)-N
GUV
(R)-N
(R)-N
(R)-N
(R)-N
(R)-N
160-165f
145-150h
188-190i
156-158i
203-204f
184-186f
164-168h
90-95j
236
114
75
955
1462
2256
1359
55
48
86
2-CH3 2-CH3 -O-
C25H31NO3,HCl
C26H33NO3,HCl
2-CH3 2-CH3 -O-
4-Cl
4-F
H
H
H
4-Cl
4-F
H
H
H
-O-
-O-
C23H25Cl2NO3,HCl,H2O
C23H25F2NO3,HCl
C24H29NO2,HCl
C26H33NO2,HCl,2H2O
C23H29NO3,HCl,2H2O
C23H27NO3,HCl
C24H29NO3,HCl,2H2O
C25H33NO3,HCl
C23H27F2NO3,HCl
C24H31NO2,HCl,4H2O
C24H32N2O2,2HCl
-CH2-
-CH2-
-O-
178-179f
H
2-CH3
H
H
-O-
-O-
A5D1B2C 155-156h
A5B2CD2 137-140h
A5B2CD2 193-196h
A5D1B2C 154-156j
A7B1CD3 148-150f
2-CH3 2-CH3 -O-
358
675
1585
5699
4-F
H
H
4-F
H
H
-O-
-CH2-
>NCH3
C,H,N
C,H,N,Cl
C,H,N,Cl
B3C
232-234k
a
b
N represents nipecotic acid (see 1); GUV represents guvacine (see 2); both are alkylated on nitrogen. All compounds were analyzed
for C, H, and N and are within (0.4% of the theoretical values. c Inhibition of GABA uptake in synaptosomes: IC50 (nM), mean of two
determinations. Ref 38. e Ref 1. Compounds were crystallized from acetone; gCH2Cl2; hEtOAc/acetone; iMeOH/PhCH3; jEtOAc; k2-PrOH.
d
f
this series are so far the most potent parent compounds
inhibiting GABA uptake into synaptosomes. Opposite
to the observations made above, the effects of o-methyl
substituents on the phenyl groups are very different in
this series. One o-methyl substituent, as in example 31,
lowers the potency to some extent, but o-methyl sub-
stituents on both phenyl groups, as in example 32, lower
the potency considerably in this series. The explanation
for this missing ortho effect may be the change in the
strain between the aryl groups going from a strained
sp2 system in the allyl ethers to a less strained sp3
system in the hydrogenated analogues. In the former
series, the methyl substituents are needed in order to
bring the aryl groups in a preferred out-of-plane con-
formation, whereas in the latter series, the aryl groups
are easily oriented in the preferred conformations due
to the sp3 system. Again, para substitution is not
beneficial in this series either as exemplified by com-
pound 33.
the oxygen may be an important pharmacophoric ele-
ment which participates in binding to the GABA uptake
site. On the other hand, oxygen in the chain instead of
a methylene group will create a much higher degree of
rotational freedom, which may increase the probability
for the molecule to populate more preferred conforma-
tions for binding to the GABA uptake site. Another
exchange of oxygen is shown in example 35 where the
oxygen atom of 29 was replaced by >NMe. The low
affinity of 35 shows that this replacement is not
beneficial; however, the major loss of activity may be
due to the steric bulk introduced by the methyl group.
Attempts to prepare the nonmethylated compound have
so far been unsuccessful.
In Table 2 the in vivo anticonvulsant effect in mice
(expressed as ED50 values in mg/kg) for representative
compounds which inhibited [3H]GABA uptake is il-
lustrated. The anticonvulsant effect is measured as
observed inhibition of clonic seizures induced by a 15
mg/kg intraperitoneal (ip) dose of the chemoconvulsant
methyl 6,7-dimethoxy-4-ethyl-â-carboline-3-carboxylate
(DMCM), an inverse benzodiazepine agonist. The ex-
perimental procedure has been described previously.26
In Table 2 we have also listed the ED50 values found in
the rotarod performance test and calculated the protec-
tive index as the ratio between ED50 values found in
To further investigate the importance on potency of
the oxygen in the chain, oxygen has been replaced by a
methylene group, as in examples 27, 28, and 34.
Inspection of the data in Table 1 show that this
replacement lowers the potency 10 times in the allyl
ether series (27 compared to 21) and 50 times in the
hydrogenated series (34 compared to 29) indicating that

Synthesis of Novel GABA Uptake Inhibitors
J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 21 4287
Ta ble 2. Anticonvulsant Properties of Selected Compounds
were obtained within ( 0.4% of theoretical values where given.
Elemental C, H, and N were determined with a Perkin-Elmer
model 240 elemental analyzer; Cl were determined by the
Scho¨niger combustion method. 1H NMR spectra were recorded
on a Bruker WM400 spectrometer with TMS as internal
standard, with illustrative chemical shifts quoted in ppm (δ)
in the solvents indicated. Compounds used as starting materi-
als are either known compounds or compounds which can be
prepared by methods known per se.49-57 Column chromatog-
raphy was carried out using the technique described by Still
et al.,66 on Merck silica gel 60 (Art. 9385) using thick-walled
glass columns and TLCs on Merck silica gel 60, 5 × 20 cm
plates (Art. 5714).
Syn a p tosom a l [3H]GABA Up ta k e. Uptake of [3H]GABA
into synaptosomal preparations was assayed by a filtration
assay.61 Rat forebrain was rapidly excised and homogenized
in 20 mL of ice-cold 0.32 M sucrose with a hand-driven Teflon/
glass Potter-Elvehjem homogenizer. The homogenate was
centrifuged for 10 min at 600g at 4 °C. The pellet was
resuspended in 50 volumes of ice-cold buffer (120 mM NaCl,
0.18 mM KCl, 2.30 mM CaCl2, 4.0 mM MgSO4, 12.66 mM Na2-
HPO4, 2.97 mM NaH2PO4, and 10.0 mM glucose, pH 7.4) at 4
°C; 50 µL of this synaptosomal suspension (0.1 mg of protein),
diluted into 300 µL of phosphate buffer and 100 µL of test
substance solutions in water, was preincubated for 8 min at
30 °C. Then 50 µL of [3H]GABA (final concentration 0.9 nM)
and unlabeled GABA (final concentration 0.9 nM) were added
before continuing incubation for another 8 min. Synaptosomes
were then recovered by rapid filtration through Whatman
GF/F glass fiber filters under vacuum. Filters were washed
twice, each time with 10 mL of ice-cold isotonic saline, and
the tritium trapped on the filters was assessed by conventional
scintillation counting in 4 mL of Filter-Count (Packard). Non-
carrier-mediated uptake was determined in the presence of
nipecotic acid (500 µM) and was subtracted from total binding
to give carrier-mediated [3H]GABA uptake. The IC50 value
obtained for each example is shown in Table 1.
DMCM
rotarod
protective
indexc
no.
ED50 (mg/kg)a
ED50 (mg/kg)b
4
6
7
8
9
3.1
1.2
3.2
1.5
6.0
36
5.5
5.4
4.6
3.6
12
13
14
17
18
21
22
23
24
25
28
29
30
31
32
33
36
12
10
34
16
1.6
3.8
5.4
3.4
5.0
>60
75
1.7
1.6
4.4
6.8
21
23
21
14
24
6.1
3.9
4.1
4.8
>90
9.0
6.8
19
30
54
>1.2
5.3
4.3
4.3
4.4
2.6
a
Inhibition of DMCM-induced seizures in mice: ED50 (mg/kg)
b
after ip administration. Rotarod in mice: ED50 (mg/kg) after ip
administration. c Ratio for ED50 values for inhibition of rotarod
and inhibition of DMCM-induced convulsions in mice.
the rotarod performance test and inhibition of DMCM-
induced convulsions in mice. As can be seen from Table
2 the compounds with highest affinity for the GABA
uptake site, generally, also show a high in vivo potency.
Further, the two most potent compounds (24 and 29)
show an in vivo potency and protective index compa-
rable to that of reference compounds such as 6 and 8.
An ta gon ism of Seizu r es In d u ced by DMCM in Mice.26
Female NMRI mice were used. The test drug was injected ip
30 min prior to the seizure test. In this test the animals were
injected ip with 15 mg/kg DMCM and were observed for the
next 30 min for the presence of clonic seizures and death
(N ) 5-10/dose). The ED50 value obtained for each example
is shown in Table 2.
Rota r od Test in Mice.26 The animals were pretrained in
the rotarod apparatus (Ugo-Basile, Italy) for 2 min before
testing (speed: 6 rpm). The rod diameter was 3 cm. In the
test procedure, the animals were placed on the rotating rod.
If the animal fell from the rod, the animal was immediately
picked up by the tail and again placed on the rod. Testing was
stopped when a total of 10 failures were obtained or 2 min
had elapsed.
Con clu sion
In our initial communication38 we concluded on some
of the reasoning behind the selection of 6 as an anti-
convulsant drug candidate. However, during develop-
ment of this compound, a demand for a second genera-
tion compound with a longer duration of action and
broader therapeutic window became clear. Therefore we
initiated the search for novel series of compounds which
could be selected and optimized with respect to these
features. With the compounds described in this publica-
tion, we have now identified several series of GABA
uptake inhibitors with high in vitro potency and in vivo
efficacy which are comparable with those found for
compound 6. These new anticonvulsant compounds
could therefore potentially serve as second-generation
drug candidates. A broad range of compounds from
these novel series45 as well as those described earlier1
have now been put through extended investigations for
a longer duration of action and metabolism studies as
well as for a broader therapeutic ratio. However, these
investigations have not revealed any suitable com-
pounds for further development so far. The effort to
refine the pharmacological profile of this type of com-
pound has therefore been continued and resulted in the
identification of new classes of compounds which will
be reported at a later date.
Ch em istr y. Each of the methods A-D is illustrated by the
preparation of the following derivatives. Although the methods
are illustrated for specific compounds, the methods have been
found to be general for the examples in Table 1.
Meth od A1B1: (R)-1-(6-(Dip h en yla m in o)-1-h exyl)-3-p i-
p er id in eca r boxylic Acid Eth yl Ester (36). A mixture of
NaH (0.7 g, 0.023 mol, 80% oil dispersion) and diphenylamine
(3.4 g, 0.020 mol) in dry dibutyl ether (30 mL) was heated at
reflux for 1 h under N2. The reaction mixture was cooled and
1,6-dibromohexane (3.1 mL) was added. The mixture was
heated at reflux for 3 h and then cooled to 40 °C. Ethyl (R)-
3-piperidinecarboxylate (3.5 g, 0.022 mol) and K2CO3 (3.1 g,
0.022 mol) were added and the mixture was heated at reflux
for 16 h under N2. EtOAc (50 mL) was added, the mixture was
filtered, and the solvent was evaporated. The residue was
purified by chromatography on silica gel (200 g, n-heptane/
THF ) 4:1) to give 3.4 g (42%) of 36 as an oil: TLC Rf 0.26
(SiO2; n-heptane/THF ) 7:3); 1H NMR (CDCl3, 400 MHz) δ
1.25 (t, 3H, CH2CH3), 1.2-2.1 (m, 14H, NCH2CH2CH2CH and
CH2(CH2)4CH2), 2.29 (t, 2H, NCH2(CH2)5), 2.54 (m, 1H, CHCO2-
Et), 2.74 (d, 1H, NCH2CH), 2.97 (d, 1H, NCH2CH), 3.67 (t, 2H,
Exp er im en ta l Section
Gen er a l. Melting points were determined in open capillary
tubes on
a Bu¨chi 535 melting point apparatus and are
uncorrected. The structures of all compounds are consistent
with spectroscopic data and satisfactory elemental analyses

4288 J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 21
Andersen et al.
Ph2NCH2), 4.12 (q, 2H, CH2CH3), 6.94 (t, 2H, p-ArH), 6.98 (d,
4H, o-ArH), 7.26 (t, 4H, m-ArH).
(150 g, n-heptane/EtOAc ) 3:7) to give 1.3 g of 40 (29%) as an
oil: 1H NMR (CDCl3, 400 MHz) δ 1.23 (t, 3H, CH2CH3), 1.2-
2.1 (m, 16H, NCH2CH2CH2CH and CH2(CH2)5CH2), 2.25 (t, 2H,
CH2CdO), 2.27 (t, 2H, N CH2(CH2)6), 2.55 (m, 1H, CHCO2-
Et), 2.76 (d, 1H, NCH2CH), 2.98 (d, 1H, NCH2CH), 4.12 (q,
2H, CH2CH3), 7.2-7.4 (m, 10H, ArH).
Meth od A2: 2-(Dip h en yla m in o)eth a n ol (37).52 A mixture
of NaH (2.0 g, 0.050 mol, 60% oil dispersion), diphenylamine
(7.6 g, 0.045 mol), and dry diethylene glycol dimethyl ether
(30 mL) was stirred for 3 h at 135 °C under N2. The reaction
mixture was cooled and placed on an ice-bath. 2-Bromoethyl
tetrahydropyran-2-yl ether (10.5 g, 0.050 mol) in dry dibutyl
ether (15 mL) was added and the mixture was stirred for 3 h
at 120 °C. The mixture was cooled, poured into water (300 mL),
and extracted with EtOAc (2 × 200 mL). The combined organic
extracts were dried (Na2SO4) and the solvent was evaporated.
The residue was dissolved in 2-propanol (150 mL) and 4 N
H2SO4 (30 mL) was added. The mixture was stirred at 60 °C
for 30 min and 4 N NaOH was added until pH 7. The
neutralized mixture was poured into H2O (1 L) and extracted
with EtOAc (2 × 250 mL). The combined organic extracts were
dried (Na2SO4) and the solvent was evaporated. The residue
was purified by chromatography on silica gel (200 g, n-heptane/
THF ) 4:1) to give 5.4 g (56%) of 37 as an oil: 1H NMR (CDCl3,
400 MHz) δ 1.84 (t, 1H, OH), 3.83 (q, 2H, CH2O), 3.93 (t, 2H,
NCH2), 6.99 (t, 2H, p-ArH), 7.07 (d, 4H, o-ArH), 7.30 (t, 4H,
m-ArH).
Meth od A5: 2-((1-(2-Meth ylp h en yl)-1-p h en yl-1-p r op en -
3-yl)oxy)eth a n ol (41). A solution of n-BuLi in hexanes (13.0
mL, 2.5 M) was added dropwise under N2 to ethylene glycol
(30 mL) at 10 °C. When addition was complete the mixture
was stirred 0.5 h at room temperature. 3-Bromo-1-(2-meth-
ylphenyl)-1-phenyl-1-propene (9.3 g, 32 mmol) was added and
the reaction mixture was stirred at room temperature for 100
h. The mixture was poured in H2O (200 mL) and extracted
with EtOAc (3 × 75 mL). The combined organic extracts were
dried (Na2SO4) and the solvent was evaporated. Chromatog-
raphy of the residue on silica gel (200 g, n-heptane/THF ) 4:1)
provided 3.9 g (45%) of 41: TLC Rf 0.20 (SiO2; n-heptane/
THF ) 7:3); 1H NMR (CDCl3, 400 MHz shows mixture (1:9) of
the two E/ Z isomers) δ major isomer 2.06 (s, 3H, CH3), 3.47
(t, 2H, CH2CH2OH), 3.69 (t, 2H, CH2OH), 3.93 (br m, 2H, d
CHCH2), 6.36 (t, 1H, dCH), 7.1-7.3 (m, 9H, ArH); δ minor
isomer 2.02 (s, 3H, CH3), 3.56 (t, 2H, CH2CH2OH), 3.74 (t, 2H,
CH2OH), 4.27 (d, 2H, dCHCH2), 5.86 (t, 1H, dCH), 7.1-7.3
(m, 9H, ArH).
3-((1,1-Bis(2-m eth ylp h en yl)-1-p r op en -3-yl)oxy)-1-p r o-
p a n ol (42). A solution of n-BuLi in hexanes (15.2 mL, 2.5 M)
was added dropwise under N2 to 1,3-propanediol (31 mL) on
an ice bath. When addition was complete the mixture was
stirred 0.5 h at room temperature. 3-Bromo-1,1-bis(2-meth-
ylphenyl)-1-propene (11.5 g, 38 mmol) was added and the
reaction mixture was stirred at room temperature for 48 h and
at 75 °C for 36 h. H2O (100 mL) was added and the mixture
was extracted with EtOAc (100 mL). The phases were sepa-
rated and the organic phase was washed with H2O (2 × 50
mL) and dried (MgSO4) and the solvent evaporated. Chroma-
tography of the residue on silica gel (300 g) using a gradient
of n-heptane in EtOAc as eluent provided 3.5 g (31%) of 42:
1H NMR (CDCl3, 400 MHz) δ 1.80 (quint, 2H, CH2CH2CH2),
2.07 (s, 3H, CH3), 2.26 (s, 3H, CH3), 2.36 (t, 1H, OH), 3.57 (t,
2H, OCH2CH2), 3.76 (q, 2H, CH2OH), 3.97 (d, 2H, dCHCH2O),
5.93 (t, 1H, dCH), 7.1-7.2 (m, 8H, ArH).
3-(Dip h en yla m in o)-1-p r op a n ol (38).53 Prepared in 46%
yield from 3-bromo-1-propyl tetrahydro-2-pyranyl ether by a
method similar to that described above: 1H NMR (CDCl3, 80
MHz) δ 1.55 (s, 1H, OH), 1.85 (quint, 2H, CH2CH2CH2), 3.66
(t, 2H, CH2OH), 3.80 (t, 2H, NCH2), 6.8-7.4 (m, 10H, ArH).
Meth od A3B1: (R)-1-(4-(2-(Dip h en yla m in o)eth oxy)-1-
bu tyl)-3-p ip er id in eca r boxylic Acid Eth yl Ester (39). NaH
(0.4 g, 10.0 mmol, 60% oil dispersion) was suspended in dry
dibutyl ether (25 mL) under N2 and 37 (2.1 g, 10.0 mmol) was
added. The mixture was stirred for 1 h at room temperature
and then heated at 130 °C for 1 h. LiH (0.1 g) was added and
the mixture was heated at reflux for 1 h. The mixture was
cooled to 80 °C and 1-bromo-4-chlorobutane (2.0 g, 12 mmol)
was added. The reaction mixture was heated at reflux for 12
h and then another portion of 1-bromo-4-chlorobutane (4.0 g,
23 mmol) was added. Heating was continued for another 24
h. Dibutyl ether (25 mL) was added to the cooled reaction
mixture and then, carefully, H2O (25 mL) was added. The
organic phase was separated and dried (K2CO3) and the solvent
evaporated. The residue was purified by chromatography on
silica gel (100 g, n-heptane/THF ) 4:1) to give 2.0 g of 1-chloro-
4-(2-(diphenylamino)ethoxy)butane. A suspension of the above
chloride (2.0 g, 6.6 mmol), ethyl (R)-3-piperidinecarboxylate
(1.1 g, 7.0 mmol), K2CO3 (1.0 g, 7.2 mmol), and dry dibutyl
ether (25 mL) was heated at 150 °C for 4 h. The mixture was
cooled and filtered and the solvent evaporated. The residue
was purified by chromatography on silica gel (150 g, n-heptane/
THF ) 4:1) to give 1.5 g (34%) of 39 as an oil: TLC Rf 0.23
(SiO2; n-heptane/THF ) 7:3); 1H NMR (CDCl3, 400 MHz) δ
1.26 (t, 3H, CH2CH3), 1.4-2.1 (m, 10H, N CH2CH2CH2CH and
N CH2CH2CH2CH2O), 2.34 (t, 2H, NCH2CH2CH2CH2O), 2.56
(m, 1H, CHCO2Et), 2.75 (d, 1H, NCH2CH), 2.98 (d, 1H, NCH2-
CH), 3.44 (t, 2H, NCH2CH2CH2CH2O), 3.65 (t, 2H, N CH2CH2O),
3.95 (t, 2H, NCH2CH2O), 4.15 (q, 2H, CH2CH3), 6.96 (t, 2H,
p-ArH), 7.06 (d, 4H, o-ArH), 7.29 (t, 4H, m-ArH).
Meth od A4B1: (R)-1-(8-(Dip h en yla m in o)-8-oxo-1-octyl)-
3-p ip er id in eca r boxylic Acid Eth yl Ester (40). A mixture
of NaH (0.40 g, 0.010 mol, 60% oil dispersion), diphenylamine
(1.7 g, 0.010 mol), and dry dibutyl ether (25 mL) was stirred
for 3 h at reflux under N2. The reaction mixture was allowed
to cool to 60 °C and 8-bromooctanoyl chloride (2.4 g, 10 mmol)
was added. Then the mixture was heated at reflux for 3 h. To
the cooled mixture were added ice-cold 2 N HCl (50 mL) and
EtOAc (50 mL). The phases were separated, the organic phase
was dried (Na2SO4), and the solvent was evaporated. The
residue was dissolved in acetone (25 mL) and ethyl (R)-
piperidinecarboxylate (2.0 g, 12.7 mmol) and K2CO3 (1.8 g, 13
mmol) were added. The mixture was heated at reflux for 8 h
and then stirred at room temperature for 2 days. The reaction
mixture was filtered and the solvent evaporated to give an oily
residue which was purified by chromatography on silica gel
Meth od A6: 2-(3,3-Dip h en yl-1-p r op yloxy)eth a n ol (43).
A mixture of NaH (0.80 g, 0.020 mol, 60% oil dispersion) and
3,3-diphenyl-1-propanol (4.25 g, 0.020 mol) in dry dibutyl ether
(30 mL) was stirred at room temperature for 30 min and then
heated at reflux for 2.5 h under N2. The reaction mixture was
cooled to 60 °C, 2-bromoethyl tetrahydro-2-pyranyl ether (4.2
g, 0.020 mol) was added, and the mixture was heated at reflux
for 16 h under N2. The reaction mixture was cooled and washed
with H2O and the organic solvent evaporated. Chromatography
of the residue on silica gel (150 g, n-heptane/THF ) 4:1)
provided 2.6 g of an oil, which was dissolved in 2-propanol (25
mL). 4 N H2SO4 (10 mL) was added and the mixture was
stirred at 60 °C for 1 h. CH2Cl2 (250 mL) was introduced and
the separated organic phase was washed with H2O (2 × 100
mL) and 5% aqueous NaHCO3 (100 mL). The organic phase
was dried (Na2SO4) and the solvent evaporated. This afforded
1
2.5 g (49%) of 43 as an oil. The H NMR spectra was identical
with that obtained from the material prepared by method D1.
Meth od A7: 8-Br om o-1,1-d ip h en yl-1-octen e (44). A so-
lution of ethyl 8-bromooctanoate (2.5 g, 10 mmol) in dry Et2O
(5 mL) was added at -35 °C to a mixture of phenyllithium
(12 mL, 24 mmol, 2 M in c-hexane/Et2O) and dry Et2O (15 mL)
kept under N2. When addition was complete the mixture was
stirred at -35 °C for 1 h and then at -60 °C for 5 h. 4 N H2-
SO4 (10 mL) was added at -60 °C and the reaction mixture
was allowed to warm to 10 °C. The phases were separated and
from the organic phase the solvent was evaporated. The oily
residue was dissolved in a mixture of 2-propanol (50 mL) and
4 N H2SO4 (20 mL) and heated at reflux for 1 h. The mixture
was allowed to cool and the volatiles were removed to give a
residue which was diluted with water and then extracted with
Et2O (2 × 50 mL). The combined organic extracts were dried

Synthesis of Novel GABA Uptake Inhibitors
J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 21 4289
(Na2SO4) and the solvent was evaporated to give 3.1 g of 44
(90%): 1H NMR (CDCl3, 400 MHz) δ 1.2-1.9 (m, 8H, d
CHCH2CH2CH2CH2CH2CH2Br), 2.11 (q, 2H, dCHCH2), 3.35
(t, 2H, CH2Br), 6.07 (t, 1H, dCH), 7.15-7.6 (m, 10 H, ArH).
(m, 2H, OCH2CH2CH2N), 3.85 (d, 2H, dCHCH2), 4.03 (q, 2H,
CH2CH3), 5.85 (t, 1H, dCHCH2), 7.0-7.2 (m, 8H, ArH).
Meth od B3: (R)-1-(2-(N-(3,3-Diph en yl-1-pr opyl)-N-m eth -
yla m in o)eth yl)-3-p ip er id in eca r boxylic Acid Eth yl Ester
(48). A suspension of (3,3-diphenyl-1-propyl)(methyl)amine59
(1.1 g, 4.7 mmol), K2CO3 (1.9 g, 14 mmol), and (R)-1-(2-
bromoethyl)-3-piperidinecarboxylic acid ethyl ester60 (1.6, 4.7
mmol) in acetone (25 mL) was stirred at room temperature
for 3 weeks. The reaction mixture was filtered and the solvent
was evaporated. The oily residue was purified by chromatog-
raphy on silica gel (200 g, n-heptane/THF ) 1:1) to give 0.7 g
(36%) of 48 as an oil: Rf 0.07 (SiO2; n-heptane/THF ) 1:1); 1H
NMR (DMSO-d6, 400 MHz) δ 1.15 (t, 3H, CH2CH3), 1.37 (m,
1H, NCH2CH2CH2CH), 1.58 (m, 1H, NCH2CH2CH2CH), 1.75
(m, 1H, NCH2CH2CH2CH), 1.95 (t, 1H, NCH2CH2CH2CH),
2.08-2.35 (m, 13H, NCH2CH2CH2CH and CHCH2CH2N(CH3)-
CH2CH2), 2.42 (m, 1H, CHCO2Et), 2.57 (d, 1H, NCH2CH), 2.78
(d, 1H, NCH2CH), 3.99 (t, 1H, Ph2CH), 4.03 (q, 2H, CH2CH3),
7.1-7.3 (m, 10H, ArH).
Meth od B1: (R)-1-(8,8-Dip h en yl-7-octen -1-yl)-3-p ip e-
r id in eca r boxylic Acid Eth yl Ester (45). A suspension of
44 (3.1 g, 9.0 mmol), ethyl (R)-piperidinecarboxylate (2.0 g,
12.7 mmol), K2CO3 (1.9 g, 13.5 mmol), and KI (0.2 g) in acetone
(30 mL) was stirred at room temperature for 4 days. The
mixture was filtered and the solvent evaporated. The oily
residue was purified by chromatography on silica gel (200 g,
n-heptane/EtOAc ) 7:3) to give 1.6 g (42%) of 45 as an oil:
TLC Rf 0.20 (SiO2; n-heptane/EtOAc ) 7:3); 1H NMR (CDCl3,
400 MHz) δ 1.25 (t, 3H, CH2CH3), 1.3-2.1 (m, 14H, NCH2-
CH2CH2CH and dCHCH2CH2CH2CH2CH2CH2), 2.10 (q, 2H,
dCHCH2), 2.28 (t, 2H, NCH2CH2CH2CH2CH2), 2.55 (m, 1H,
CHCO2Et), 2.76 (d, 1H, NCH2CH), 2.99 (d, 1H, NCH2CH), 4.11
(q, 2H, CH2CH3), 6.06 (t, 1H, dCH), 7.15-7.4 (m, 10H, ArH).
Meth od B2: (R)-1-(2-((1-(2-Meth ylp h en yl)-1-p h en yl-1-
p r op en -3-yl)oxy)eth yl)-3-p ip er id in eca r boxylic Acid Eth -
yl Ester (46). A solution of 41 (3.4 g, 12.5 mmol) in dry THF
(30 mL) kept under N2 was cooled to 10 °C. A solution of
n-BuLi in hexanes (5.5 mL, 2.5 M) was added dropwise and
the reaction mixture was stirred for 0.5 h at room temperature.
p-Toluenesulfonyl chloride (2.6 g, 13.8 mmol) was added and
the mixture was stirred at room temperature for 1.5 h. Ethyl
(R)-3-piperidinecarboxylate (2.9 g, 18.8 mmol) and K2CO3 (2.6
g, 18.8 mmol) were added and the mixture was heated at reflux
for 18 h. The cooled reaction mixture was poured into ice-
water (200 mL) and extracted with EtOAc (2 × 100 mL). The
combined organic extracts were washed with a 10% sodium
citrate buffer solution (2 × 100 mL, pH 6). The organic phase
was extracted with a 5% citric acid solution (4 × 75 mL) and
the combined acidic aqueous extracts were washed with
toluene (50 mL). To the acidic aqueous solution was added 4
N NaOH until pH 9 and this solution was immediately
extracted with EtOAc (2 × 100 mL). The combined organic
extracts were dried (Na2SO4) and the solvent was evaporated
to give 2.3 g (45%) of 46 as an oil: TLC Rf 0.23 (SiO2;
n-heptane/THF ) 7:3); 1H NMR (CDCl3, 400 MHz shows a
mixture (1:9) of the two E/ Z isomers) δ major isomer 1.25 (t,
3H, CH2CH3), 1.35-1.75 (m, 3H, N CH2CH2CH2CH), 1.95-
2.05 (m, 5H, NCH2CH2CH2CH and ArCH3), 2.57 (m, 3H,
CHCO2Et and OCH2CH2N), 2.80 (d, 1H, NCH2CH), 3.03 (d,
1H, NCH2CH), 3.50 (t, 2H, OCH2CH2N), 3.90 (brs, 2H, dCH
CH2), 4.12 (q, 2H, CH2CH3), 6.35 (t, 1H, dCHCH2), 7.1-7.3
(m, 9H, ArH); δ minor isomer 1.25 (t, 3H, CH2CH3), 1.35-
1.75 (m, 3H, NCH2CH2CH2CH), 1.95-2.05 (m, 5H, N CH2CH2-
CH2CH and ArCH3), 2.57 (m, 3H, CHCO2Et and O CH2CH2N),
2.80 (d, 1H, NCH2CH), 3.03 (d, 1H, NCH2CH), 3.58 (t, 2H,
OCH2CH2N), 4.12 (q, 2H, CH2CH3), 4.26 (d, 2H, dCHCH2),
5.85 (t, 1H, dCHCH2), 7.1-7.3 (m, 9H, ArH).
(R)-1-(3-((1,1-Bis(2-m eth ylp h en yl)-1-p r op en -3-yl)oxy)-
1-p r op yl)-3-p ip er id in eca r boxylic Acid Eth yl Ester (47).
A solution of 42 (3.45 g, 11.6 mmol) in dry toluene (150 mL)
was cooled on an ice bath and a solution of n-BuLi in hexanes
(5.1 mL, 2.5 M) was added dropwise. The reaction mixture was
stirred for 15 min at room temperature, p-toluenesulfonyl
chloride (2.44 g, 12.8 mmol) was added, and the mixture was
stirred at room temperature for 3 h. Ethyl (R)-3-piperidine-
carboxylate (4.5 g, 23.3 mmol) and K2CO3 (3.2 g, 23.3 mmol)
were added and the mixture was stirred at room temperature
for 0.5 h and then at 75 °C for 12 h. KI (1.0 g) and acetone (40
mL) were added and the mixture was heated at reflux for 15
h. The reaction mixture was diluted with acetone (50 mL) and
cooled and the solvent evaporated. Chromatography of the
residue on silica gel (280 g) using a gradient of n-heptane in
EtOAc as eluent afforded 2.6 g (52%) of 47 as an oil: TLC Rf
0.52 (SiO2; MeOH/EtOAc ) 1:9); 1H NMR (DMSO-d6, 400
MHz) δ 1.17 (t, 3H, CH2CH3), 1.35-1.75 (m, 6H, NCH2CH2CH2-
CH and O CH2CH2CH2N), 1.95 (m, 1H, NCH2CH2CH2CH),
2.02 (s, 3H, ArCH3), 2.13 (m, 1H, NCH2CH2CH2CH), 2.22 (s,
3H, ArCH3), 2.27 (m, 2H, OCH2CH2CH2N), 2.42 (m, 1H,
CHCO2Et), 2.55 (d, 1H, NCH2CH), 2.71 (d, 1H, NCH2CH), 3.35
Meth od C: Hyd r olysis of 3-P ip er id in e- a n d 1,2,5,6-
Tetr a h yd r o-3-p yr id in eca r boxylic Acid Ester Der iva tives
10-30, 33, a n d 35. The ester under consideration (1.0 mmol)
was dissolved in ethanol (3 mL) and 3 mmol of 4 or 12 N NaOH
was added. The reaction mixture was stirred at room temper-
ature until TLC indicated complete reaction (3-6 h). A
concentrated aqueous HCl solution was added with cooling on
an ice bath until pH 1. Then CH2Cl2 (100 mL) was added and
the resulting emulsion was dried (Na2SO4). The solvent was
evaporated to give a residue which was crystallized from
acetone. Recrystallization afforded the pure acid hydrochlo-
rides for which the data are shown in Table 1.
Meth od D1: 2-(3,3-Dip h en yl-1-p r op yloxy)eth a n ol (43).
2-((1,1-Diphenyl-1-propen-3-yl)oxy)ethanol (4.0 g, 15.7 mmol)
was dissolved in dry dioxane (80 mL) and stirred under an
atmosphere of hydrogen for 3 h at room temperature in the
presence of 10% Pd/C catalyst (50% aqueous paste) and then
filtered. The solvent was evaporated to give 4.0 g (100%) of
43: 1H NMR (CDCl3, 400 MHz) δ 2.23 (brs, 1H, OH), 2.34 (q,
2H, CH2CH2CH2), 3.39 (t, 2H, CHCH2CH2O), 3.42 (t, 2H, CH2-
CH2OH), 3.65 (t, 2H, CH2OH), 4.10 (t, 1H, CH), 7.15-7.25 (m,
10H, ArH).
Meth od D2: (R)-1-(2-(3,3-Bis(2-m eth ylp h en yl)-1-p r o-
p yloxy)eth yl)-3-p ip er id in eca r boxylic Acid Hyd r och lo-
r id e (32). A solution of 23 (1.1 g, 2.6 mmol) in MeOH (25 mL)
was stirred under an atmosphere of hydrogen for 1 h at room
temperature in the presence of 10% Pd/C catalyst (35%
aqueous paste) and then filtered. The filtrate was evaporated
to dryness leaving a residue which was treated with a mixture
of EtOAc and acetone to give a solid which was recrystallized
from a mixture of MeOH and toluene to give 0.75 g (67%) of
32 as a solid (Table 1): 1H NMR (DMSO-d6, 400 MHz) δ 1.43
(brs, 1H, NCH2CH2CH2CH), 1.83 (m, 2H, NCH2CH2CH2CH),
2.00 (brs, 1H, NCH2CH2CH2CH), 2.15 (q, 2H, Ph2CHCH2), 2.24
(s, 6H, 2 x CH3), 2.95 (m, 3H, CHCO2Et and NCH2CH2CH2),
3.25 (brs, 2H, NCH2CH2O), 3.40 (t, 2H, CHCH2CH2O), 3.45
(brs, 1H, NCH2CH), 3.62 (brs, 1H, NCH2CH), 3.75 (brs, 2H,
NCH2CH2O), 4.38 (t, 1H, Ph2CH), 7.05-7.15 (m, 8H, ArH),
10.75 (brs, 1H, NH), 12.85 (brs, 1H, COOH).
Meth od D3: (R)-1-(6,6-Dip h en yl-1-h exyl)-3-p ip er id in e-
ca r boxylic Acid Hyd r och lor id e (34). A solution of 27 (0.6
g, 1.5 mmol) in H2O (25 mL) was stirred under an atmosphere
of hydrogen for 16 h at room temperature in the presence of
10% Pd/C catalyst (50% aqueous paste). The mixture was
filtered and the solvent was evaporated to give an oily residue
which was reevaporated with acetone and then crystallized
from a mixture of Et2O and acetone. This afforded 0.5 g (83%)
of 34 (Table 1): 1H NMR (DMSO-d6, 400 MHz) δ 1.15-1.35
(m, 4H, CHCH2(CH2)3), 1.48 (brs, 1H, NCH2CH2CH2CH), 1.65
(m, 2H, CHCH2(CH2)3), 1.80 (m, 2H, NCH2CH2CH2CH), 1.95
(brs, 1H, NCH2CH2CH2CH), 2.03 (q, 2H, Ph2CHCH2), 2.75 (m,
1H, CHCO2Et), 2.9 (m, 4H, CH2NCH2CH2CH2CH), 3.30 (brs,
1H, NCH2CH), 3.40 (brs, 1H, NCH2CH), 3.90 (t, 1H, Ph2CH),
7.1-7.3 (m, 10H, ArH).

4290 J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 21
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