Piperidine-based nocaine/modafinil hybrid ligands as highly potent monoamine transporter inhibitors: Efficient drug discovery by rational lead hybridization

Article abstract of DOI:10.1021/jm040117o

Some piperidine-based nocaine/modafinil hybrid ligands have been designed, synthesized, and found to display an improved potency at all three monoamine transporters and particularly for DAT and/or NET. Some highly active and selective monoamine transporte

Full text of DOI:10.1021/jm040117o

© Copyright 2004 by the American Chemical Society
Volume 47, Number 24
November 18, 2004
Letters
attention deficit hyperactivity disorder (ADHD), anxiety,
Piperidine-Based Nocaine/Modafinil
Hybrid Ligands as Highly Potent
Monoamine Transporter Inhibitors:
Efficient Drug Discovery by Rational
Lead Hybridization
mood problems, Parkinson’s disease, Alzheimer’s dis-
ease, schizophrenia, bipolar disorder, chronic pain,
migraine, epilepsy, multiple sclerosis, stroke, trauma,
mania, obesity, and narcolepsy.3-8 However, important
issues regarding the selectivity and mechanisms of
action of these drugs remain unresolved. Research with
novel ligands that vary in their selectivity profiles and
potency at each of these three transporter sites may be
of value to unraveling the relevant pharmacological
mechanisms and thus aid in the discovery of new
medications with fewer side effects.
Jia Zhou,† Rong He,‡ Kenneth M. Johnson,§
Yanping Ye,§ and Alan P. Kozikowski*,†,‡
Acenta Discovery, Inc., 9030 S. Rita Road, Suite 300,
Tucson, Arizona 85747-9101, Department of Medicinal
Chemistry and Pharmacognosy, College of Pharmacy
(M/C781), University of Illinois at Chicago, 833 S. Wood
Street, Chicago, Illinois 60612-7230, and Department of
Pharmacology and Toxicology, University of Texas Medical
Branch, Galveston, Texas 77555-1031
Previously, we reported on the synthesis and phar-
macology of some 3,4-substituted piperidine-based co-
caine analogues.9 After extensive in vitro studies,
together with assays of locomotor activity, and self-
administration and drug discrimination studies, the
DAT/NET selective ligand (+)-methyl 4â-(4-chloro-
phenyl)-1-methylpiperidine-3R-carboxylate [(+)-CPCA,
1, nocaine] was chosen for advancement to human
clinical studies for the treatment of cocaine addiction10,11
Nocaine has lower potency and efficacy compared with
cocaine in increasing locomotor activity in rodents and
produces partial methamphetamine-like discriminative
stimulus effects, although it is fully cocaine-like in
cocaine-trained animals. Moreover, it shows reduced
reinforcing effects in nonhuman primates. Nocaine dose-
dependently antagonizes cocaine-induced locomotor ac-
tivation and potentiates the discriminative stimulus
effects of a low dose of cocaine. On the other hand,
modafinil (provigil) 2, a non-amphetamine-like wake-
promoting agent, has been approved recently for the
treatment of narcolepsy. However, modafinil has been
linked to side effects that include nausea, infection,
nervousness, anxiety, and insomnia. It shows a low but
selective affinity to the DAT in canine brain mem-
branes.12 Modafinil’s mode of action is complex and still
uncertain, although studies suggest that it increases
wakefulness by activating R-1 noradrenergic transmis-
sion13 or hypothalamic cells that contain the peptide
hypocretin14 or that it may work by modulating GABAer-
gic tone.15 Other research suggests that the presynaptic
Received June 21, 2004
Abstract: Some piperidine-based nocaine/modafinil hybrid
ligands have been designed, synthesized, and found to display
an improved potency at all three monoamine transporters and
particularly for DAT and/or NET. Some highly active and
selective monoamine transporter inhibitors with low nano-
molar to subnanomolar potency were identified. Ligands of this
type may find important applications as positron emission
tomography imaging tools and in the treatment of central
nervous system disorders such as depression and sleep apnea.
In the central nervous system (CNS), monoamines
such as dopamine (DA), serotonin (5-HT), and norepine-
phrine (NE) have an important modulatory role in
neurotransmission and are intimately involved in a
variety of physiological functions and pathological con-
ditions.1,2 Selective monoamine transporter (DAT, SERT,
or NET) inhibitors (e.g., GBR 12909, mazindol, fluoxe-
tine, paroxetine, reboxetine, amoxapine, desipramine,
imipramine, bupropion, and nisoxetine) have been
developed to treat a number of psychological and
neurological disorders such as depression, drug abuse,
* To whom correspondence should be addressed. Phone: 312-996-
7577. Fax: 312-996-7107. E-mail: kozikowa@uic.edu.
† Acenta Discovery, Inc.
‡ University of Illinois at Chicago.
§ University of Texas Medical Branch.
10.1021/jm040117o CCC: $27.50 © 2004 American Chemical Society
Published on Web 10/15/2004

5822 Journal of Medicinal Chemistry, 2004, Vol. 47, No. 24
Letters
Chart 1. Rational Design of Nocaine/Modafinil Hybrid
Ligands
Scheme 2a
Scheme 1a
a Reagents and conditions: (a) (for 16a and 21) NH3 (liquid),
t-BuOH, 90-95%; (b) (for 16b) hydroxylamine, KOH in MeOH,
76%; (c) (for 16c-f) HNR1R2 in MeOH, 72-92%; (d) 35% H2O2,
HOAc, 64-87%; (e) acetamide oxime, NaH, 4 Å molecular seives,
THF, 79%; (f) 1-chloroethyl chloroformate, CH2Cl2; (g) MeOH,
reflux, 80% (for two steps).
Table 1. Inhibition at Monoamine Transporters (Ki ( SEM
(nM))a
compd
[3H]-DA uptake [3H]-5-HT uptake [3H]-NE uptake
cocaine
(+)-CPCAb
modafinilc
4b
423 ( 147
233 ( 62
3800
155 ( 0.4
108 ( 3.5
252 ( 43
>10000
198 ( 53
424 ( 53
25 ( 6
8490 ( 1430
497 ( 58
376 ( 54
80 ( 23
231 ( 93
16 ( 5
1550 ( 360
238 ( 49
208 ( 47
809 ( 36
158 ( 5
5
6
7
53 ( 16
0.94 ( 0.27
42 ( 16
6 ( 2
a Reagents and conditions: (a) LiAlH4, 92%; (b) Ph3P/I2/imida-
zole, 86%; (c) methyl thioglycolate, Cs2CO3, 88%; (d) 35% H2O2,
HOAc, 61-80%; (e) LiAlH4, 82%; (f) NaH, MeI, THF, 65%; (g)
Ac2O/pyridine, DMAP, 70%; (h) benzoyl chloride, Et3N, DMAP,
68%.
8
9
12 (1
2183 ( 373
191 ( 57
469 ( 36
57 ( 18
10
50 ( 15
15 ( 5
11
25 ( 6
12
35 ( 11
9 ( 3
3.6 ( 1.5
29 ( 4
13
87 ( 17
14
68 ( 22
32 ( 12
159 ( 19
85 ( 19
13 ( 3
6.7 ( 1.5
199 ( 14
557 ( 150
227 ( 7
4.5 ( 1.2
18 ( 6
activation of DA transmission is a key pharmacological
event in mediating the wake-promoting effects of cur-
rently available CNS stimulants and that it is critical
for the pharmacological control of wakefulness, while
activation of the NE system is critical for rapid eye
movement sleep regulation.16 Experiments using DAT
knock-out mice appear to support an important role for
the DAT in sleep regulation and thus in the wake-
promoting action of modafinil.17
15
16a
16b
16c
16d
16e
16f
17a
17b
17c
17d
17e
17f
18
39 ( 5
15 ( 2
110 ( 45
88 ( 22
25 ( 2
116 ( 46
1.0 ( 0.2
83 ( 1
209 ( 25
55 ( 8
164 ( 28
2884 ( 654
248 (78
379 ( 90
126 ( 15
1653 ( 56
51 ( 16
114 ( 32
108 ( 29
27 ( 7
1.1 ( 0.4
4.5 ( 0.8
5790 ( 1712
1795 ( 67
2033 ( 573
924 ( 139
473 ( 60
825 ( 99
221 ( 46
1079 ( 269
13 ( 3
0.8 ( 0.1
0.68 ( 0.25
178 ( 49
12 ( 1
86 ( 2
1249 ( 19
20 ( 3
460 ( 11
32 ( 10
218 ( 14
0.56 ( 0.09
10 ( 0.1
31 ( 3
Since valuable therapies have emerged from com-
pounds exhibiting varying levels of transporter selectiv-
ity, we sought to examine the effect of creating hybrid
molecules combining structural features of nocaine and
modafinil. Specifically, we decided to explore the effect
of replacement of the hydrolyzable ester function of
nocaine with the same type of sulfur-containing side
chain as found in modafinil. This alteration to one of
the key pharmacophore elements of nocaine was antici-
pated to further reduce its reinforcing properties while
possibly improving its half-life (Chart 1).
Our synthetic approach to these hybrid structures
starting from arecoline9 is outlined in Schemes 1 and
2. The requisite steps are quite straightforward and
based in part on the methods devised for the synthesis
of nocaine itself. In the course of oxidation of the sulfide
intermediates to the corresponding sulfoxides, an ad-
ditional chiral center is created at the sulfur atom.
Typically, two diastereoisomers are generated in a ratio
of approximately 1:1, which is readily observable by
NMR. Possible separation of the sulfoxides by HPLC
19
20
21
170 ( 6
775 ( 96
22
a Data are the mean ( standard error of at least three
experiments as described in ref 6a. b Data taken from ref 18. c Data
taken from ref 16.
was attempted but was unsuccessful. However, in light
of the fact that the sulfoxides have substantially lower
activity compared with the sulfides (see Table 1) and
that the commercial drug modafinil itself is used in
racemic form, further efforts to bring about the prefer-
ential formation of one stereoisomer over the other by
optimizing the oxidation conditions using selective
oxidizing agents have not been made.
The newly synthesized ligands were evaluated for the
ability to inhibit high affinity uptake of DA, 5-HT, and
NE using rat synaptosomal nerve endings.6a From the

Letters
Journal of Medicinal Chemistry, 2004, Vol. 47, No. 24 5823
uptake inhibition data (Table 1), it is surmised that the
replacement of the hydrolyzable ester function of nocaine
with the sulfur appendage found in modafinil leads in
general to a substantial enhancement in DAT/NET
inhibitory potency for many of the ligands. In addition,
some of the ligands display unique levels of transporter
selectivity and potency.
The conversion of the carboxylic ester of nocaine into
the intermediate alcohol 4 and iodide 5 improves
activity at the SERT without causing any significant
alteration in potency at the DAT or NET. However, the
introduction of the sulfur appendage into nocaine
significantly enhances the inhibitory activity at the DAT
and NET. Thus, the key intermediate 6, a hybrid ligand,
displays fairly good activity at the NET (Ki ) 25 nM)
and at the DAT (Ki ) 80 nM) while at the same time
exhibiting moderate activity at the SERT (Ki ) 208 nM).
The oxidation of sulfide 6 to sulfoxide 7 leads to a
reduced transporter activity. Alcohol 8 exhibits a re-
markable potency at the NET (Ki ) 0.94 nM) and at
the DAT (Ki ) 16 nM) as well as a 170-fold and 10-fold
selectivity vs the SERT, respectively. The corresponding
alcohol 9 containing a sulfoxide function has a lower
potency (Ki ) 42 nM) at the NET and a 50-fold
selectivity vs the SERT, but it displays a higher potency
(Ki ) 12 nM) at the DAT and a 180-fold selectivity vs
the SERT. In comparison to alcohol 8, the methyl ether
analogues 10 and 11 exhibit a lower but still fairly good
DAT/NET activity. Among the inverse acyl and benzoyl
esters, ligands 12, 13, and 15 are good DAT/NET
inhibitors while ligand 14 is interestingly a good SERT
and NET inhibitor with potencies of 6.7 and 4.5 nM,
respectively. Among the amide analogues, ligands 16a-d
display a similar and fairly potent NET activity while
16c is also a good DAT inhibitor. Interestingly, ligand
16e exhibits outstanding activity with approximately
1 nM potency at all three monoamine transporters.
Ligand 16f is an outstanding SERT and NET inhibitor
with potencies of 4.5 and 0.68 nM, respectively. In
comparison to the sulfide ligands 16a-f, the corre-
sponding sulfoxide-amide analogues 17a-f generally
display a reduced activity except compound 17b, which
exhibits a slightly improved potency at the NET (Ki )
12 nM) and the DAT (Ki ) 55 nM) and a much better
selectivity vs the SERT (Ki ) 1795 nM). While oxadia-
zole analogues are of interest because of their antici-
pated prolonged action and high metabolic stability,
ligands 18 and 19 display only a moderate to low
activity at the NET. Interestingly, the N-demethylated
ligands 20-22 exhibit a remarkable activity at the NET
with Ki down to 0.56 nM (20), a result that likely reflects
the change from a tertiary to a secondary amine.
Figure 1. Effect of cocaine and ligand 8 (JZ-III-84) on
horizontal locomotor activity. Following a 30 min habituation
period, saline (0.9%), cocaine, and ligand 8 were injected ip (1
cm3/kg) in the doses indicated and total locomotor activity was
automatically recorded for 90 min as infrared beam breaks in
a 16 in. × 16 in. photobeam activity system (San Diego
Instruments). Cocaine and ligand 8 significantly increased
total activity counts as indicated by one-way analysis of
variance (F4,14 ) 28.4, p < 0.001). The asterisk (/) indicates
that the individual treatment group is significantly different
from saline control (p < 0.05, Tukey’s post hoc test).
ment to the small-molecule-directed brain imaging and
therapy program. To assess the bioavailability and
initial cocaine-like behavioral activity of 8, we compared
two doses of cocaine and 8 in an open-field locomotor
activity study (Figure 1). Ligand 8 was more potent than
cocaine and appeared to be somewhat more efficacious
as well. Although much more extensive testing is needed
to fully characterize the behavioral effects of 8, these
differences are consistent with its 17-fold NET vs DAT
selectivity and its virtual lack of activity at SERT.20
Further behavioral testing of some of the ligands in this
series is currently underway.
In summary, some piperidine-based nocaine/modafinil
hybrid ligands have been synthesized and found to
display an improved potency at all three monoamine
transporters but particularly for DAT and/or NET. Some
highly active and selective monoamine transporter
inhibitors with low nanomolar to subnanomolar potency
were identified including 8 and 20 (NET), 9, 11, 13, 15,
16c, and 17b (DAT/NET), 14 and 16f (SERT/NET), and
16e (DAT/SERT/NET). Because many of these ligands
have ClogP values in the range deemed suitable for
penetration of the blood-brain barrier, they can be
examined for their in vivo actions and radiolabeled as
possible positron emission tomography (PET) imaging
tools. The potency and selectivity profiles of these hybrid
molecules may allow us to gain a better understanding
of the relation between transporter activity and biologi-
cal effect. This knowledge may allow for an improved
design of CNS therapeutics.
In regard to their druglike properties, many of these
ligands have ClogP values (see the Supporting Informa-
tion) in the range deemed suitable for penetration of
the blood-brain barrier, as per Lipinski’s “rule of five”.19
On the basis of results in hand, we intend to focus on
ligands displaying improved NET activity with Ki values
less than 1 nM. Specifically, given the fact that ligands
8 and 16f exhibit remarkable NET inhibitory activity
(Ki values for NET are 0.94 and 0.68 nM, respectively)
while also exhibiting suitable lipophilicity (ClogP in the
range of 2-4), we believe that they may be good NET-
selective ligands primed for C-11 labeling for advance-
Acknowledgment. We are indebted to the NIMH,
STTR (Grant 1R41MH070083-01), and the NIH Na-
tional Institute on Drug Abuse (Grant DA10458,
DA11548) for their support of these studies.
Supporting Information Available: Experimental de-
tails, spectral data, and ClogP data for all new compounds.
This material is available free of charge via the Internet at
http://pubs.acs.org.

5824 Journal of Medicinal Chemistry, 2004, Vol. 47, No. 24
Letters
(10) Woolverton, W. L.; Ranaldi, R.; Wang, Z.; Ordway, G. A.; Paul,
I. A.; Petukhov, P.; Kozikowski, A. P. Reinforcing strength of a
novel dopamine transporter ligand: Pharmacodynamic and
pharmacokinetic mechanisms. J. Pharmacol. Exp. Ther. 2002,
303, 211-217.
(11) Kozikowski, A. P.; Johnson, K. M.; Deschaux, O.; Bandyo-
padhyay, B. C.; Araldi, G. L.; Carmone, G.; Munzar, P.; Smith,
M. P.; Balster, R. L.; Beardsley, P. M.; Tella, S. R. Mixed cocaine
agonist/antagonist properties of (+)-methyl 4â-(4-chlorophenyl)-
1-methylpiperidine-3R-carboxylate, a piperidine based analog of
cocaine. J. Pharmacol. Exp. Ther. 2003, 305, 143-150.
(12) Mignot, E.; Nishino, S.; Guilleminault, C.; Dement, W. C.
Modafinil binds to the dopamine uptake carrier site with low
affinity. Sleep 1994, 17, 436-437.
(13) Duteil, J.; Rambert, F. A.; Pessonnier, J.; Hermant, J. F.;
Gombert, R.; Assous, E. Central alpha 1-adrenergic stimulation
in relation to the behaviour stimulating effect of modafinil;
studies with experimental animals. Eur. J. Pharmacol. 1990,
180, 49-58.
(14) Chemelli, R. M.; Willie, J. T.; Sinton, C. M.; Elmquist, J. K.;
Scammell, T.; Lee, C.; Richardson, J. A.; Williams, S. C.; Xiong,
Y.; Kisanuki, Y.; Fitch, T. E.; Nakazato, M.; Hammer, R. E.;
Saper, C. B.; Yanagisawa, M. Narcolepsy in orexin knockout
mice: molecular genetics of sleep regulation. Cell 1999, 98, 437-
451.
(15) Ferraro, L.; Tanganelli, S.; O’Connor, W. T.; Antonelli, T.;
Rambert, F.; Fuxe, K. The vigilance promoting drug modafinil
increases dopamine release in the rat nucleus accumbens via
the involvement of a local GABAergic mechanism. Eur. J.
Pharmacol. 1996, 306, 33-39.
(16) Nishino, S.; Mao, J.; Sampathkumaran, R.; Shelton, J.; Mignot,
E. Increased Dopaminergic Transmission Mediates the Wake-
Promoting Effects of CNS Stimulants. Sleep Res. Online 1998,
1, 49-61.
(17) Wisor, J. P.; Nishino, S.; Sora, I.; Uhl, G. H.; Mignot, E.; Edgar,
D. M. Dopaminergic role in stimulant-induced wakefulness. J.
Neurosci. 2001, 21, 1787-1794.
References
(1) Greengard, P. The neurobiology of slow synaptic transmission.
Science 2001, 294, 1024-1030.
(2) Gainetdinov, R. R.; Sotnikova, T. D.; Caron, M. G. Monoamine
transporter pharmacology and mutant mice. Trends Pharmacol.
Sci. 2002, 23, 367-373.
(3) Nemeroff, C. B.; Owens, M. J. Treatment of mood disorders. Nat.
Neurosci. 2002, 5, 1068-1070.
(4) Carroll, F. I.; Howell, L. L.; Kuhar, M. J. Pharmacotherapies
for treatment of cocaine abuse: Preclinical aspects. J. Med.
Chem. 1999, 42, 2721-2736.
(5) (a) Olivier, B.; Soudijn, W.; van Wijngaarden, I. Serotonin,
dopamine and norepinephrine transporters in the central ner-
vous system and their inhibitors. Prog. Drug Res. 2000, 54, 59-
119. (b) Van Moffaert, M.; Dierick, M. Noradrenaline (norepi-
nephrine) and depression: Role in aetiology and therapeutic
implications. CNS Drugs 1999, 12, 293-305.
(6) (a) Zhou, J.; Zhang, A.; Kla¨ss, T.; Johnson, K. M.; Wang, C. Z.;
Ye, Y.; Kozikowski, A. P. Biaryl analogues of conformationally
constrained tricyclic tropanes as potent and selective norepi-
nephrine reuptake inhibitors: Synthesis and evaluation of their
uptake inhibition at monoamine transporter sites. J. Med. Chem.
2003, 46, 1997-2007. (b) Zhou, J.; Kla¨ss, T.; Zhang, A.; Johnson,
K. M.; Wang, C. Z.; Ye, Y.; Kozikowski, A. P. Synthesis and
pharmacological evaluation of (Z)-9-(heteroarylmethylene)-7-
azatricyclo[4.3.1.03,7]decanes: Thiophene analogues as potent
norepinephrine transporter inhibitors. Bioorg. Med. Chem. Lett.
2003, 13, 3565-3569. (c) Smith, M. P.; Hoepping, A.; Johnson,
K. M.; Trzcinska, M.; Kozikowski, A. P. Dopaminergic agents
for the treatment of cocaine abuse. Drug Discovery Today 1999,
4, 322-332.
(7) (a) Versiani, M.; Cassano, G.; Perugi, G.; Benedetti, A.; Mastalli,
L.; Nardi, A.; Savino, M. Reboxetine, a selective norepinephrine
reuptake inhibitor, is an effective and well-tolerated treatment
for panic disorder. J. Clin. Psychiatry 2002, 63, 31-37. (b) Arai,
S.; Morita, K.; Kitayama, S.; Kumagai, K.; Kumagai, M.; Kihira,
K.; Dohi, T. Chronic inhibition of the norepinephrine transporter
in the brain participates in seizure sensitization to cocaine and
local anesthetics. Brain Res. 2003, 964, 83-90.
(8) Friedman, J. I.; Adler, D. N.; Davis, K. L. The role of norepi-
nephrine in the pathophysiology of cognitive disorders: Potential
applications to the treatment of cognitive dysfunction in schizo-
phrenia and Alzheimer’s disease. Biol. Psychiatry 1999, 46,
1243-1252.
(9) Kozikowski, A. P.; Araldi, G. L.; Boja, J.; Meil, W. M.; Johnson,
K. M.; Flippen-Anderson, J. L.; George, C.; Saiah, E. Chemistry
and pharmacology of the piperidine-based analogues of cocaine.
Identification of potent DAT inhibitors lacking the tropane
skeleton. J. Med. Chem. 1998, 41, 1962-1969.
(18) Petukhov, P. A.; Zhang, J.; Kozikowski, A. P.; Wang, C. Z.; Ye,
Y. P.; Johnson, K. M.; Tella, S. R. SAR Studies of piperidine-
based analogues of cocaine. 4. Effect of N-modification and ester
replacement. J. Med. Chem. 2002, 45, 3161-3170.
(19) Lipinski, C. A. The design of drug-like properties. Presented at
the Lipinski Advanced Chemistry Development (ACD) European
Workshop, 2001. For details, see the following website: http://
www.acdlabs.com/download/publ/eum_lipinski.pdf.
(20) Uhl, G. R.; Hall, F. S.; Sora, I. Cocaine, reward, movement and
monoamine transporters. Mol. Psychiatry 2002, 7, 21-26.
JM040117O