Synthesis of 2-(substituted phenyl)-3,5,5-trimethylmorpholine analogues and their effects on monoamine uptake, nicotinic acetylcholine receptor function, and behavioral effects of nicotine

Article abstract of DOI:10.1021/jm1014555

Toward development of smoking cessation aids superior to bupropion (2), we describe synthesis of 2-(substituted phenyl)-3,5,5-trimethylmorpholine analogues 5a-5h and their effects on inhibition of dopamine, norepinephrine, and serotonin uptake, nicotinic acetylcholine receptor (nAChR) function, acute actions of nicotine, and nicotine-conditioned place preference (CPP). Several analogues encompassing aryl substitutions, N-alkylation, and alkyl extensions of the morpholine ring 3-methyl group provided analogues more potent in vitro than (S,S)-hydroxybupropion (4a) as inhibitors of dopamine or norepinephrine uptake and antagonists of nAChR function. All of the new (S,S)-5 analogues had better potency than (S,S)-4a as blockers of acute nicotine analgesia in the tail-flick test. Two analogues with highest potency at α3β4-nAChR and among the most potent transporter inhibitors have better potency than (S,S)-4a in blocking nicotine-CPP. Collectively, these findings illuminate mechanisms of action of 2 analogues and identify deshydroxybupropion analogues 5a-5h as possibly superior candidates as aids to smoking cessation.

Full text of DOI:10.1021/jm1014555

ARTICLE
pubs.acs.org/jmc
Synthesis of 2-(Substituted Phenyl)-3,5,5-trimethylmorpholine
Analogues and Their Effects on Monoamine Uptake, Nicotinic
Acetylcholine Receptor Function, and Behavioral Effects of Nicotine
F. Ivy Carroll,*,† Ana Z. Muresan,† Bruce E. Blough,† Hernꢀan A. Navarro,† S. Wayne Mascarella,†
J. Brek Eaton,§ Xiaodong Huang,† M. Imad Damaj,‡ and Ronald J. Lukas§
†Center for Organic and Medicinal Chemistry, Research Triangle Institute, P. O Box 12194, Research Triangle Park, North Carolina
27709-2194, United States
‡Department of Pharmacology and Toxicology, Virginia Commonwealth University Medical Center, Richmond, Virginia 23298-0613,
United States
§Division of Neurobiology, Barrow Neurological Institute, 350 West Thomas Road, Phoenix, Arizona 85013, United States
S Supporting Information
b
ABSTRACT: Toward development of smoking cessation aids superior to bupropion (2), we describe synthesis
of 2-(substituted phenyl)-3,5,5-trimethylmorpholine analogues5a-5h and theireffects oninhibition of dopamine,
norepinephrine, and serotonin uptake, nicotinic acetylcholine receptor (nAChR) function, acute actions of
nicotine, and nicotine-conditioned place preference (CPP). Several analogues encompassing aryl substitutions, N-
alkylation, and alkyl extensions of the morpholine ring 3-methyl group provided analogues more potent in vitro
than (S,S)-hydroxybupropion (4a) as inhibitors of dopamine or norepinephrine uptake and antagonists of nAChR function. All of the
new (S,S)-5 analogues had better potency than (S,S)-4a as blockers of acute nicotine analgesia in the tail-flick test. Two analogues with
highest potency at R3β4*-nAChR and among the most potent transporter inhibitors have better potency than (S,S)-4a in blocking
nicotine-CPP. Collectively, these findingsilluminate mechanisms of action of2 analogues and identify deshydroxybupropionanalogues
5a-5h as possibly superior candidates as aids to smoking cessation.
’ INTRODUCTION
norepinephrine (NE) transporter (NET), and nicotinic acetyl-
choline receptor (nAChR) function is important to its therapeu-
tic efficacy as a smoking cessation agent.9,10 The model also
suggests that fine-tuning of effects on DA and NE availability and
on nAChR function could lead to superior aids to smoking
cessation. We have chosen 2 as a template for such work.
Our earlier work toward a goal of developing superior aids to
smoking cessation concerned analogues of 2, its (S,S)- or (R,R)-
hydroxymetabolites (S,S)-4a or (R,R)-4a, respectively, or 3-phe-
nyltropane-related compounds.8,11-13 Several of these agents
have superior activities relative to 2 or its active metabolite (S,S)-
4a as inhibitors of DA or NE uptake or of nAChR function and
have very promising In Vivo profiles as inhibitors of nicotine-
induced dependence behaviors.8,11-13
To explore potential utility as smoking cessation aids of
compounds having related structural topology and to define
possible mechanism(s) of action of these compounds, we now
describe the synthesis and in vitro and In Vivo effects of
2-(substituted phenyl)-3,5,5-trimethylmorpholine analogues
5a-5h. Compounds (S,S)- and (R,R)-5a are analogues of the
hydroxybupropion metabolites (S,S)- and (R,R)-4a, where the
hydroxy group has been replaced by a hydrogen. We also
synthesized and studied analogues (S,S)-5b-5h. In this study,
Tobacco product use, principally via cigarette smoking, is the
number one cause of premature death in the United States
(Centers for Disease Control and Prevention, 2002). There are
more than 440000 deaths due to cigarette smoking, and more
than $75 billion in annual medical costs is attributed to smoking
(NIDA, 2006; Centers for Disease Control and Prevention,
2008; Centers for Disease Control and Prevention, 2005). It is
now commonly accepted that smoking behavior is maintained to
a large extent by the reinforcing effects of nicotine (1) and
aversive effects of nicotine withdrawal.1-4 Both nonpharmaco-
logical and pharmacological interventions have demonstrated
efficacy in smoking cessation.5 At present, first-line pharmaceu-
tical treatments include nicotine replacement therapy or use of
bupropion (2) or varenicline (3).6,7 While these treatments are
useful in helping about 20% of smokers abstain long-term, new
pharmacotherapies are needed that are either more effective or
can impact those individuals not helped by existing treatments.
While nicotine replacement therapy and 3 act on nicotinic
receptors as their primary targets, 2 seems to engage additional
targets. We have hypothesized that 2, or more specifically its
active (S,S)-hydroxymetabolite (S,S)-4a (see Carroll et al.,
2010)8 fits the multiple molecular target model of drug action.
This model postulates that the combination of effects of 2 or
active metabolites on dopamine (DA) transporter (DAT),
Received: November 11, 2010
Published: February 14, 2011
r
2011 American Chemical Society
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ARTICLE
Scheme 1a
a Reagents: (a) NaBH4, CH3OH; (b) CH2Cl2, H2SO4; (c) MeI, DMF, 70 °C for 5d; (d) Na(OAc)3BH, acetaldehyde for 5e or propionaldehyde for 5f.
we report the identification of ligands with superior in vitro and
preliminary In Vivo activity profiles than those for (S,S)-4a.
(IC50 = 9900 nM) than (S,S)-4a. Compound (S,S)-5a, with IC50
values of 220, 100, and 390 nM for DA, NE, and 5HT uptake
inhibition, respectively, is a more potent inhibitor of uptake of all
three neurotransmitters than (S,S)-4a. The (R,R)-5a isomer is
less potent at all three transporters than (S,S)-5a, as was seen for
the pair of hydroxyl analogues, but was more potent than (R,R)-
4a for DA and NE uptake inhibition.
Replacement of the chloro group in (S,S)-5a with a fluoro
group to give (S,S)-5b results in a 3.7- and 3.2-fold increase in the
potency for inhibition of DA and NE uptake but a 12-fold
decrease in potency for inhibition of 5HT uptake (Table 1).
Compared to (S,S)-4a, 5b is 10- and 5.6-fold more potent as a
DA and NE uptake inhibitor. The arylbromo analogue 5c, with
an IC50 value of 44 nM for inhibition of DA uptake, is 5-fold more
potent than 5a at DAT but has essentially the same potency as 5a
for inhibition of NE and 5HT uptake.
’ CHEMISTRY
The addition of an N-methyl group to (S,S)-5a to give 5d had
little effect on monoamine uptake inhibition potency (Table 1).
In contrast, the addition of an N-ethyl or N-propyl group to 5a to
give 5e and 5f, respectively, resulted in a 4- to 7.8-fold increase in
potency (relative to (S,S)-5a) for DA and NE uptake inhibition
and a 4- to 7-fold decrease in 5HT uptake inhibition potency.
Compounds 5g and 5h, which have 3-ethyl and 3-propyl
groups in place of the 3-methyl group in (S,S)-5a, have IC50
values of 23 and 6.0 nM for DA uptake inhibition, 19 and 9 nM
for NE uptake inhibition, and 1800 and 300 nM for 5HT uptake
inhibition (Table 1). Thus, they are the most potent of the
analogues tested as DA uptake inhibitors and share with the
N-ethyl and N-propyl analogues highest potency as NE uptake
inhibitors.
The effects of 3,5,5-trimethylmorpholine analogues (S,S)- and
(R,R)-4a, (S,S)- and (R,R)-5a, and 5b-5h on function of diverse
human nAChR subtypes naturally or heterologously expressed
by human cell lines were assessed using 86Rbþ efflux assays that
are specific only for nAChR function in the cells used. None of
the analogues has activity as agonists at R1*-, R3β4*-, R4β2-, or
R4β4-nAChR because 86Rbþ efflux in the presence of these
ligands alone at concentrations from ∼5 nM to 100 μM (data not
shown here) was indistinguishable from responses in cells
exposed only to efflux buffer. 86Rbþ efflux assays also were used
Analogues 5a-5c, 5g, and 5h were synthesized in a fashion
similar to that reported in the literature for optically active
phenmetrazine (Scheme 1).14 The keto forms of the previously
reported hydroxymorpholines 4a-4c, 4g, and 4h were reduced
with sodium borohydride to afford mixtures of diastereomeric
diols 6a-6c, 6g, and 6h, varying at the benzylic hydroxyl
position. The morpholine ring structure could then be formed
by cyclization using sulfuric acid in methylene chloride to form
the optically active phenylmorpholines 5a-5c, 5g, and 5h. The
diastereomic benzyl alcohol is presumably removed forming a
benzylic cation, which is then trapped by the primary alcohol.
Cyclization afforded the thermodynamically and kinetically more
stable trans isomer. The optical activity is thus controlled by the
methyl group alpha to the nitrogen. N-Methylation of (S,S)-5a to
form 5d was done using methyl iodide in dimethylformamide at
70 °C. N-Alkylation of (S,S)-5a to form 5e and 5f was accom-
plished by standard reductive alkylation using acetaldehyde and
propionaldehyde, respectively, and sodium triacetoxyborohy-
dride in methylene chloride.
Analogue Characterization in Vitro. Compound (S,S)-4a
has IC50 values of 630 and 180 nM for DA and NE uptake
inhibition and is inactive for 5HT uptake inhibition (Table 1).
The (R,R)-isomer (R,R)-4a is inactive as a DA and 5HT uptake
inhibitor with much lower potency for NE uptake inhibition
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Table 1. Analogue Inhibition of Monoamine Uptake and Nicotinic Acetylcholine Receptor (nAChR) Function
monoamine uptake inhibitiona IC50 (nM)
nAChR inhibitionb IC50 (μM)
compd
2c
R1
R2
X
[3H]DA
[3H]NE
[3H]5HT
R3β4*-
R4β2-
R4β4-
R1*-
660 ( 180
630 ( 50
IA
1900 ( 300
180 ( 4
IA
1.8 (1.15)
11 (1.48)
6.5 (1.20)
3.3 (
12 (1.15)
3.3 (1.07)
31 (1.12)
20 (0.06)
17 (1.06)
23 (1.05)
12 (1.06)
16 (1.14)
7.2 (1.06)
12 (1.06)
14 (1.05)
9.5 (1.04)
15 (1.07)
30 (1.10)
41 (1.07)
30 (1.12)
12 (1.06)
55 (1.10)
11 (1.07)
23 (1.09)
6.4 (1.04)
5.8 (1.04)
15 (1.10)
8.0 (1.12)
7.9 (1.12)
28 (1.45)
7.5 (1.10)
NT
(S,S)-4ac
(R,R)-4ac
(S,S)-5a
(R,R)-5a
(S,S)-5b
(S,S)-5c
(S,S)-5d
(S,S)-5e
(S,S)-5f
(S,S)-5g
(S,S)-5h
IA
9900 ( 1400
100 ( 30
1200 ( 300
32 ( 3
IA
CH3
CH3
CH3
CH3
CH3
CH3
CH3
C2H5
C3H7
H
Cl
Cl
F
220 ( 60
1600 ( 270
61 ( 20
44 ( 3
387 ( 140
IA
H
1.6 (1.07)
5.6 (1.04)
1.4 (1.12)
2.8 (1.09)
0.79 (1.06)
0.98 (1.06)
5.6 (1.16)
3.1 (1.15)
9.4 (1.05)
34 (1.07)
7.3 (1.07)
21 (1.05)
14 (1.05)
5.5 (1.06)
13 (1.07)
5.0 (1.08)
H
4600 ( 430
390 ( 30
540 ( 130
1500 ( 300
2900 ( 400
1800 ( 30
300 ( 100
H
Br
Cl
Cl
Cl
Cl
Cl
150 ( 20
170 ( 20
24 ( 8
CH3
C2H5
C3H7
H
230 ( 60
44 ( 9
61 ( 20
23 ( 5
13 ( 3.6
19 ( 3
H
6.0 ( 1
9 ( 2
a Values for mean ( standard error of three independent experiments, each conducted with triplicate determination. b Mean micromolar IC50 values (to two
significant digits) for (S,S)-and(R,R)-hydroxybupropions (4a and 4b) and the indicated 2-(substituted phenyl)-3,5,5-trimethylmorpholine analogues from three
independent experiments for inhibition of functional responses to an EC80-EC90 concentration of carbamylcholine mediated by nAChR subtypes composed of
the indicated subunits (where * indicates that additional subunits are or may be additional assembly partners with the subunits specified; see Experimental
Section). Numbers in parentheses indicate SEM as a multiplication/division factor of the mean micromolar IC50 values shown (i.e., the value 1.8 (1.15) reflects a
mean IC50 value of 1.8 μM with an SEM range of 1.8 ꢀ 1.15 μM to 1.8/1.15 μM or 1.6-2.1 μM). IA: IC50 > 100 μM. NT: not determined. c Taken from ref 13.
to assess whether ligands had activity as antagonists at human
nAChR. Representative concentration-response curves for se-
lected ligands illustrate their nAChR in vitro inhibitory profiles
(Figure 1; see also Table 1). Other studies (not shown here)
indicate that each of the ligands acts via noncompetitive inhibi-
tion of nAChR function.
Compound (S,S)-4a has IC50 values of 11, 3.3, 30, and 28 μM
for functional antagonism of R3β4*-, R4β2-, R4β4-, and R1β1*-
nAChRs, respectively, meaning that it has 3-10-fold selectivity
for R4β2-nAChR over other subtypes. Its potency as a functional
antagonist of R4β2-nAChR, which are strongly implicated in
nicotine dependence, is ∼10-fold higher than that of (R,R)-4a,
which is slightly more potent than (S,S)-4a as an antagonist of
R3β4*- and R1*-nAChR. The (S,S)-deshydroxy analogue, (S,S)-
5a, with IC50 values of 3.3 μM at R3β4*-nAChR and 20 μM at
R4β2-nAChR, is three times more potent at R3β4*-nAChR and
seven times less potent at R4β2-nAChR than (S,S)-4a. Impor-
tantly, (S,S)-5a has selectivity for R3β4*-nAChR over R4β2-
nAChR as does (R,R)-4a but opposite to the R4β2-nAChR
Figure 1. Specific 86Rbþ efflux (ordinate; percentage of control) was
selectivity of the sister isomer, (S,S)-4a. Both (S,S)-4a and (S,S)-
determined for functional, human muscle-type R1β1γδ-nAChR (9),
5a have lower potencies at R4β4- and R1β1*-nAChR than at
ganglionic R3β4*-nAChR (O), R4β2-nAChR (2), or R4β4-nAChR
R3β4*- or R4β2-nAChR. Interestingly, (R,R)-5a has an IC50
(3) naturally or heterologously expressed in human cell lines in the
presence of a receptor subtype-specific, EC80-EC90 concentration of
the full agonist, carbamylcholine, either alone or in the presence of the
value of 1.6 μM at R3β4*-nAChR, making it the most potent at
this nAChR subtype of the 4a or 5a ligands, and is 11-, 7.4-, or
5.8-fold more selective for R3β4*-nAChR relative to R4β2-,
R4β4-, or R1*-nAChR subtypes. It is also 6.5- and 4-times more
potent as an R3β4*-nAChR antagonist than (S,S)- and (R,R)-4a.
Aryl halogen substitution of the chloro group in (S,S)-5a to a
fluoro group to give (S,S)-5b slightly decreased, whereas change
to a bromo group in 5c produced an ∼2-fold increase in
antagonist potency at R3β4*-nAChR but also had similar effects
indicated concentrations (abscissa, log molar) of (S,S)-5a, (R,R)-5a, 5e,
or 5f as indicated. Mean micromolar IC50 values and SEM as a multi-
plication/division factor of the mean micromolar IC50 value are pro-
vided in Table 1.
on the other nAChR subtypes tested, thus not markedly altering
nAChR selectivity.
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Table 2. Pharmacological Evaluation of 3,5,5-Trimethylmorpholine Analogues as Noncompetitive Nicotinic Antagonistsa,b
AD50 (mg/kg)
compd
2c
tail-flick
hot-plate
locomotion
hypothermia
CPP
1.2 (1-1.18)
15 (6-19)
4.9 (0.9-46)
0.9 (0.2-5.7)
IA
9.2 (4-23)
0.35
0.1
(S,S)-4ac
(R,R)-4ac
(S,S)-5a
(R,R)-5a
(S,S)-5b
(S,S)-5c
(S,S)-5d
(S,S)-5e
(S,S)-5f
(S,S)-5g
(S,S)-5h
0.2 (0.06-0.7)
1.0 (0.2-2.2)
1.5 (0.15-2.6)
2.5 (1.2-3.6)
10.3 (5.7-17.1)
IA
NT
NT
NT
NT
NT
NT
0.025
0.03
NT
NT
0.036 (0.012-0.1)
1.26 (0.39-4.1)
0.02 (0.008-0.03)
0.006 (0.003-0.01)
0.13 (0.03-0.6)
0.029 (0.004-0.23)
0.056 (0.018-0.17)
0.018 (0.009-0.03)
0.017 (0.002-0.15)
IA
IA
IA
3.9 (0.8-19)
IA
IA
IA
4.7 (1.2-19)
2.1 (0.9-4.8)
3.8 (1.2-12)
IA
IA
IA
IA
IA
IA
IA
IA
IA
IA
IA
9.6 (1.2-77)
2.7 (0.7-10.5)
0.49 (0.03-6.6)
2.5 (1.6-3.9)
IA
IA
a Results were expressed as AD50 (mg/kg) ( confidence limits (CL) or % effect at the highest dose tested. Dose-response curves were determined using
a minimum of four different doses of test compound, and at least eight mice were used per dose group. IA = AD50 > 20 mg/kg. b NT = not tested. c Taken
from ref 13.
Compound 5d, which is the N-methyl analogue of (S,S)-5a, has
an nAChR profile similar to that of (S,S)-5a, with similar selectivity
for R3β4*-nAChR over other subtypes but with slightly higher
potency at R3β4*-nAChR. The N-ethyl and N-propyl analogues
5e and 5f have IC50 values of 0.79 and 0.98 μM at the R3β4*-
nAChR, which makes them 4.2- and 3.4-fold more potent than
(S,S)-5a and about two times more potent than (R,R)-5a at R3β4*-
nAChRs. Compounds 5g and 5h have R3β4*-nAChR profiles
similar to that of (S,S)-5a, although the propyl analogue 5h has
slighty higher potency across all nAChR subtypes.
2-hydroxyl group has been replaced with a hydrogen and
assessed the abilities of these analogues to affect DA, NE, and
5HT uptake, function of four nAChR subtypes, and the acute
effects of nicotine and in CPP, which measures reward-related
phenomena. The (S,S) analogues of 5a to 5h have greater
potency than the reference compounds 2 and (S,S)-4a as
inhibitors of DA or NE uptake. All the compounds have higher
potency as antagonists of R3β4*-nAChR function than (S,S)-
4a, and four of the compounds, 5a, 5c, 5e, and 5f, are more
potent than 2. A comparison of the effects of aromatic substit-
uents on 5a-5h shows a rank order potency at R3β4*-nAChR of
alkyl-bromo > -chloro > -fluoro (5c > 5a > 5b). N-Alkylation of
(S,S)-5a provided the N-methyl, N-ethyl, and N-propyl analo-
gues 5d-5f. Whereas the N-methyl analogue 5d had about equal
potencies at all the in vitro assays tested, the N-ethyl and
N-propyl analogues 5e and 5f, respectively, had significantly
higher potency for DA and NE uptake inhibition as well as
antagonism of the R3β4*-nAChR. The carbon-3 extended
3-ethyl and 3-propyl analogues 5g and 5h, respectively, both
had significantly higher DA and NE uptake inhibition relative to
(S,S)-5a. Analogue 5g had slightly lower R3β4*-nAChR antago-
nist potency relative to (S,S)-5e, whereas 5h had about the same
R3β4*-nAChR antagonist potency as (S,S)-5a. With AD50 values
of 0.017 to 0.13 mg/kg, all N-substituted and carbon-3 extended
chain analogues 5d-5h are potent antagonists of nicotine-
induced antinociception in the tail-flick test. With AD50 values
of 0.018 and 0.017 mg/kg, the extended chain analogues 5g and
5h have the highest potency in the tail-flick test. Importantly, the
two analogues selected for further study based in part on in vitro
profiling results, N-ethyl and N-propyl derivatives 5e and 5f, with
AD50 values of 0.025 and 0.03 mg/kg, respectively, have better
potency as antagonists of nicotine-induced CPP than 2 and
(S,S)-4a, which have AD50 values of 0.35 and 0.1 mg/kg, respec-
tively. The antagonist activity of 2 in this assay is consistent with
its ability to promote smoking cessation, probably via its
hydroxymetabolite.
Behavioral Effects of Analogues. Compound (S,S)-4a blocks
nicotine-induced antinociception in the tail-flick, hot-plate, locomo-
tor depression, and hypothermia measures with AD50 values of 0.2,
1.0, 0.9, and 1.5 mg/kg, respectively (Table 2). None of the
analogues was more potent than (S,S)-4a in the hot-plate and
hypothermia tests, and only 5h with an AD50 of 0.49 mg/kg was
more potent than (S,S)-4a in the locomotor test. However, eight
analogues were more potent (AD50 values ranged from 0.006 to
0.13 mg/kg) in the tail-flick test than (S,S)-4a, with four of the
analogues also being substantially more potent than (S,S)-5a.
Compound (S,S)-5a with an AD50 of 0.036 mg/kg in the tail-flick
test is 5.5 times more potent than (S,S)-4a despite being inactive in
the other three tests of acute nicotine action in mice. The arylbromo
analogue 5c is six times more potent in the tail-flick test than (S,S)-
5a and ∼33 times more potent than (S,S)-4a and has an AD50 of 2.1
mg/kg in the locomotor test. The arylfluoro analogue 5b has slightly
lower potency than (S,S)-5c in the tail-flick and locomotor tasks.
Moreover, each of the N-substituted and the alkyl extended
analogues had higher potency than (S,S)-4a in the tail-flick assay.
In part because their in vitro potency as antagonists of R3β4*-
nAChR and as inhibitors of DA and NE uptake were nearly the
highest of the analogues tested, 5e and 5f were tested in mice for
the ability to block nicotine rewarding effects as measured in the
CPP test. Both compounds dose-dependently blocked the
development of nicotine-induced CPP, and they were 4- and
3-fold more potent in that assay than (S,S)-4a (Table 2).
In our previous studies,8,11-13 we succeeded in generating
analogues with reasonably higher inhibitory potency than 2 or
either of its hydroxymetabolite isomers (R,R)-4a and (S,S)-4a in
both the in vitro and In Vivo assays used in this study, whether on
’ DISCUSSION
We have generated the 3,5,5-trimethylmorpholine analogues
5a-5h of the hydroxybupropion isomer (S,S)-4a where the
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the 2, hydroxybupropion, or 3-phenyltropane backbones.8,12,13
The current studies show that several 3,5,5-morpholino analo-
gues 5a-5h also have higher potency than 2, (R,R)-4a, and
(S,S)-4a in the same test.
inhibitory potency at any single molecular target. The similarities
in the abilities of 5e and 5f to block nicotine-induced CPP (AD50 =
0.025 and 0.03 mg/kg, respectively) can be reconciled with the
similar activities of those agents at DA and NE uptake inhibition
and/or R3β4*-nAChR antagonism, as their 3-4-fold better
activity in nicotine-CPP blockade relative to (S,S)-4a could be
attributed to their ∼10-fold higher potency at these molecular
targets.
Interestingly, (S,S)-5a, which has a hydrogen in place of the
2-hydroxy group in (S,S)-4a, has a higher potency than (S,S)-4a
at the targets of interest, DAT, NET, and R3β4*-nAChR but not
at R4β2-nAChR, a subtype that has been implicated in nicotine
dependence. Because DA in the nucleus accumbens undoubtedly
plays a role in reinforcement and reward, and NE input from the
locus coeruleus can gate activity in dopaminergic nuclei and
enhance attention, inhibition of reuptake at either could con-
tribute to nicotine’s dependence-related behavioral effects.
Recent genetic studies suggest that R3β4*-nAChR subtypes
play an important role in nicotine dependence. Indeed, genetic
variants in the nAChR R3/β3/R5 subunit gene cluster are
associated with susceptibility to nicotine dependence in humans,
perhaps consistent with the presence of R3β4*-nAChR at key
portions in the extended reward circuit.15-17
Our earlier studies indicated that conversion of 2 to its (S,S)-
hydroxymetabolite (S,S)-4a was associated with an increase in
compound potency in inhibition of acute nicotine effects to the
same degree that the latter compound also displayed an increase
in potency as an inhibitor and selectivity for R4β2-nAChR.9 This
suggested that efforts to increase potency at R4β2-nAChR might
lead to discovery of better bupropion-related aids to smoking
cessation. It was not clear whether the hydroxy moiety itself, the
specific atomic topography of the (S,S)-hydroxymetabolite, or
some combination of both, contributed to the increased beha-
vioral and R4β2-nAChR potency of the compound relative to 2.
The current studies indicate that the hydroxy moiety could
contribute to enhanced selectivity of bupropion-related com-
pounds for R4β2-nAChR, as its removal from (S,S)-4a in (S,S)-
5a correlates with a decline in antagonist potency at R4β2-
nAChR. Interestingly, as opposed to the preference of (R,R)-4a
for R3β4*-nAChR and of (S,S)-4a for R4β2-nAChR, both
isomers (R,R)- and (S,S)-5a are slightly selective for R3β4*-
over R4β2-nAChR and have indistinguishable antagonists po-
tencies at R4β2-nAChR, although (S,S)-4a or -5a are both less
potent than their (R,R)-equivalents at R3β4*-nAChR. Moreover,
all of the other (S,S)-5 analogues have higher potency at R3β4*-
than at R4β2-nAChR.
With regard to activity as monoamine uptake inhibitors,
higher potency for (S,S) as opposed to (R,R)-4a and -5a is
evident at DAT and NET and there is a substantial increase in
potency when either isomeric form is changed from the hydroxyl-
to the hydrogen form. Moreover, each of the (S,S)-5a variants
has higher DA and NE uptake inhibitory potency except for the
N-methyl analogue 5d and the bromo-substituted analogue 5c
acting at the NET. The alkyl extension analogues 5g and 5h also
have higher potency for 5HT uptake inhibition.
It is possible that good activity in DA and/or NE uptake
inhibition and slight adjustments in activity at nAChR may be key
to developing a compound with desired, increased efficacy as a
smoking cessation aid. However, strong activity in either DA or
NE uptake inhibition also might be adequate to decrease nicotine
dependence measures. In no case is potency at nAChR greater
than that for DA or NE uptake inhibition for analogues 5b-5h.
Submicromolar IC50 values for inhibition of DA uptake is a
characteristic of the most potent inhibitors of nicotine effects in
the tail-flick assay. Comparative differences in activity in the tail-
flick assay do not match with comparative differences in
’ CONCLUSIONS
In summary, replacement of 2-hydroxyl groups in the (S,S)-
hydroxybupropion (4a) with a hydrogen to give (S,S)-5a re-
sulted in increased potency for inhibition of DA and NE uptake,
antagonism of R3β4*-nAChR, and increased potency for antag-
onizing nicotine-induced antinociception in the tail-flick test.
The N-ethyl and N-propyl analogues, 5e and 5f, respectively, of
(S,S)-5a were more potent DA and NE uptake inhibitors as well
as antagonists of R3β4*-nAChRs than (S,S)-4a and (S,S)-5a.
The aryl fluoro and bromo analogues 5b and 5c, respectively, and
carbon-3 extended chain analogues 5g and 5h all have higher DA
uptake inhibition potency than (S,S)-4a and (S,S)-5a. All (S,S)-5
analogues are more potent in the tail-flick test than (S,S)-4a. The
N-ethyl and N-propyl analogues 5e and 5f, respectively, which
have the highest antagonist potency at R3β4*-nAChR as well as
high potency for DA and NE uptake inhibition, also had better
potency than (S,S)-4a in the nicotine-CPP test. Thus, 2 and
(S,S)-4a analogues 5a-5h, particularly 5e and 5f, represent
exciting new lead structures for the development of new phar-
macotherapies to treat nicotine addiction (smokers).
’ EXPERIMENTAL SECTION
Nuclear magnetic resonance (1H NMR and 13C NMR) spectra were
recorded on a 300 MHz (Bruker AVANCE 300) unless otherwise noted.
Chemical shift data for the proton resonances were reported in parts per
million (δ) relative to internal (CH3)4Si (δ 0.0). Optical rotations were
measured on an AutoPol III polarimeter, purchased from Rudolf
Research. Elemental analyses were performed by Atlantic Microlab,
Norcross, GA. Purity of compounds (>95%) was established by
elemental analyses. Analytical thin-layer chromatography (TLC) was
carried out on plates precoated with silica gel GHLF (250 μM
thickness). TLC visualization was accomplished with a UV lamp or in
an iodine chamber. All moisture-sensitive reactions were performed
under a positive pressure of nitrogen maintained by a direct line from a
nitrogen source. Anhydrous solvents were purchased from Aldrich
Chemical Co.
(S,S)-2-(30-Chlorophenyl)-3,5,5-trimethylmorpholine [(S,S)-
5a] Hemi-D-tartrate. A solution of (S,S)-2-(30-chlorophenyl)-3,5,5-
trimethylmorpholine-2-ol [(S,S)-4a] hemi-D-tartrate (990 mg, 3.00 mmol)
in 12 mL of 50% aqueous ethanol was cooled at 0 °C and treated with
NaBH4 (450 mg, 12 mmol). The reaction mixture was stirred overnight at
room temperature. The reaction mixture was quenched at 0 °C by the
slow addition of 4.5 mL of concentrated HCl. The clear solution was
basified with saturated aqueous solution of NaCO3 and extracted twice
with ethyl acetate. The combined extracts were dried (Na2SO4), filtered,
and concentrated under reduced pressure, affording 470 mg of crude
mixture of diols. The crude reaction mixture was dissolved in 5 mL of
CH2Cl2, cooled to 0 °C, and treated dropwise with 4 mL of concentrated
H2SO4. The mixture was stirred overnight with warming to room
temperature. The reaction mixture was added to crushed ice, basified
with aqueous solution of sodium carbonate, and extracted with ether
(twice). The combined extracts were dried (Na2SO4), filtered, and
concentrated under reduced pressure. The resulting oil was purified by
1445
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Journal of Medicinal Chemistry
ARTICLE
flash chromatography using CH2Cl2-methanol (10:1) plus 1% ammo-
nium hydroxide as the eluent to afford 300 mg (42%) of (S,S)-5a. H
0.82 (d, 3H, J = 6.3 Hz). 13C NMR (CDCl3) δ 164.6, 142.7, 129.9 (d),
123.3 (d), 115.1 (d), 114.3 (d), 86.2, 77.4, 51.1, 49.2, 27.4, 23.5, 18.5.
MS (ESI) m/z 222.4 [(M - H)þ M = C13H18FNO].
A sample of free base (54 mg, 0.24 mmol) in 2 mL of ether was treated
with a solution of D-tartaric acid (18 mg, 0.12 mmol) in MeOH (1 mL)
1
NMR (CDCl3) δ 7.38-7.35 (m, 1H), 7.28-7.20 (m, 3H), 3.78 (d, 1H,
J = 9.3 Hz), 3.68 (d, 1H, J = 11.0 Hz), 3.34 (d, 1H, J = 11.0 Hz), 3.12-
3.01 (m, 1H), 1.39 (s, 3H), 1.07 (s, 3H), 0.82 (d, 3H, J = 6.3 Hz). 13
C
NMR (CDCl3) δ 142.2, 134.5, 129.8, 128.24, 127.7, 125.9, 86.2, 77.4,
51.1, 49.9, 27.4, 23.6, 18.5.
to give 61 mg (85% yield) of 5b tartrate as a white solid: mp 167-
3
1
168 °C; [R]20 þ9.1° (c 0.9, CH3OH). H NMR (methanol-d4) δ
D
A sample of the (S,S)-5a was converted to the hemi-D-tartrate salt: mp
209-210 °C; [R]20D þ7.6° (c 0.7, CH3OH). 1H NMR (methanol-d4) δ
7.48-7.45 (m, 1H), 7.41-7.35 (m, 3H), 4.37 (s, 1H), 4.29 (d, 1H, J =
10.0 Hz), 3.76 (dd, 2H, J = 30.5, J = 12.3 Hz), 3.58-3.50 (m, 1H), 1.58
(s, 3H), 1.35 (s, 3H), 1.04 (d, 3H, J = 6.5 Hz). 13C NMR (methanol-d4)
δ 177.6, 140.8, 135.6, 131.3, 130.2, 128.7, 127.3, 83.5, 74.9, 74.4, 55.1,
52.2, 23.8, 21.2, 15.4. MS (ESI) m/z 240.2 [(M - tartrate)þ; M =
C13H18ClNO 0.5C4H6O6]. Anal. (C15H21ClNO4 0.25 H2O) C, H, N.
7.45-7.36 (m, 1H), 7.25-7.09 (m, 3H), 4.36 (s, 1H), 4.28 (d, 1H, J =
10.0 Hz), 3.74 (dd, 2H, J = 30.4, J = 12.0 Hz), 3.52-3.43 (m, 1H), 1.56
(s, 3H), 1.32 (s, 3H), 1.02 (d, 3H, J = 6.5 Hz). 13C NMR (CD3OD) δ
165.9, 141.6, 131.5 (d), 124.7 (d), 116.7 (d) 115.4 (d), 83.8, 75.2, 74.7,
54.7, 52.2, 24.1, 21.4, 15.6. MS (ESI) m/z 224.3 [(M - tartrate)þ, M =
C13H18FNO 0.5C4H6O6]. Anal. (C15H21FNO4 0.25H2O) C, H, N.
3
3
(S,S)-2-(30-Bromophenyl)-3,5,5-trimethylmorpholine (5c)
Hemi-D-tartrate. A procedure similar to the one reported for (S,S)-
2-(30-chlorophenyl)-3,5,5-trimethylmorpholine (S,S)-5a was used to
synthesize 5c. A solution of (S,S)-2-(30-bromophenyl)-3,5,5-trimethyl-
morpholine-2-ol (4c) D-tartrate (265 mg, 0.710 mmol) in 4 mL of 50%
aqueous ethanol was treated with NaBH4 (107 mg, 2.83 mmol) to give
215 mg of a crude mixture of diols. The crude reaction mixture was
dissolved in CH2Cl2 (4 mL) and treated with 2 mL of concentrated
H2SO4 to afford 150 mg (74%) of (S,S)-5c. 1H NMR (CDCl3) δ 7.53-
7.50 (m, 1H), 7.44-7.40 (m, 1H), 7.25-7.17 (m, 2H), 3.75 (d, 1H, J =
9.3 Hz), 3.69 (d, 1H, J = 11.1 Hz), 3.33 (d, 1H, J = 11.4 Hz), 3.11-3.01
(m, 1H), 1.39 (s, 3H), 1.07 (s, 3H), 0.81 (d, 3H, J = 6.3 Hz). 13C NMR
(CDCl3) δ 142.5, 131.3, 130.5, 130.0, 126.4, 122.7, 86.1, 77.4, 50.8, 49.8,
27.4, 23.6, 18.6.
0 3
3
(R,R)-2-(3 -Chlorophenyl)-3,5,5-trimethylmorpholine[(R,R)-
5a] Hemi-L-tartrate. A procedure similar to the one reported for
(S,S)-2-(30-chlorophenyl)-3,5,5-trimethylmorpholine (S,S)-5a was used.
A sample of (R,R)-2-(30-chlorophenyl)-3,5,5-trimethylmorpholine-2-ol
[(R,R)-4a] hemi-D-tartrate (660 mg, 2.00 mmol) in 8 mL of 50%
aqueous ethanol was treated with NaBH4 (300 mg, 8.00 mmol) to give
540 mg of a crude mixture of diols 6a. A solution of the crude sample in
CH2Cl2 (6 mL) was treated with 3 mL of concentrated H2SO4 to afford
364 mg (76% yield) of (2R,3R)-5a. 1H NMR (CDCl3) δ 7.38-7.36 (m,
1H), 7.29-7.20 (m, 3H), 3.77 (d, 1H, J = 9.3 Hz), 3.69 (d, 1H,
J = 9.0 Hz), 3.34 (d, 1H, J = 12.0 Hz), 3.11- 3.02 (m, 1H), 1.43 (s, 3H),
1.07 (s, 3H), 0.81 (d, 3H, J = 6.0 Hz). 13C NMR (CDCl3) δ 142.2, 134.4,
129.7, 128.3, 127.7, 126.0, 86.2, 77.5, 51.1, 49.7, 27.4, 23.6, 18.5.
A sample of the (R,R)-5a was converted to the hemi-L-tartrate salt:
mp 210-211 °C; [R]20D -10.2° (c 0.5, CH3OH). 1H NMR (methanol-
d4) δ 7.47-7.43 (m, 1H), 7.40-7.31 (m, 3H), 4.35 (s, 1H), 4.26 (d, 1H,
J = 10.2 Hz), 3.74 (dd, 2H, J = 32.1, J = 12.2 Hz), 3.57-3.41 (m, 1H),
1.56 (s, 3H), 1.32 (s, 3H), 1.02 (d, 3H, J = 6.6 Hz). 13C NMR (methanol-
d4) δ 178.1, 141.2, 135.6, 131.2, 130.1, 128.7, 127.3, 83.8, 75.2, 74.7,
54.6, 52.2, 24.1, 21.4, 15.6. MS (ESI) m/z 240.1 [(M - tartrate)þ; M =
A sample of the free base was converted to the title compound: mp
212-213 °C; [R]20D þ7.6° (c 0.63, CH3OH). 1H NMR (methanol-d4)
δ 7.59-7.51 (m, 1H), 7.39-7.25 (m, 3H), 4.35 (s, 1H), 4.26 (d, 1H, J =
10.0 Hz), 3.79 (d, 1H, J = 12.2 Hz), 3.68 (d, 1H, J = 12.2 Hz), 3.51-3.45
(m, 1H), 1.56 (s, 3H), 1.32 (s, 3H), 1,02 (d, 3H, J = 6.6 Hz). 13C NMR
(methanol-d4) δ 177.8, 141.5, 133.0, 131.5 (d), 127.7, 123.5, 84.0, 75.4,
74.6, 54.3, 52.2, 24.3, 21.5, 15.8. MS (ESI) m/z 284.7 [(M - tartrate)þ;
M = C13H18BrNO 0.5C4H6O6]. Anal. (C15H21BrNO4) C, H, N.
3
C13H18ClNO 0.5C4H6O6]. Anal. (C15H21ClNO4) C, H, N.
(S,S)-2-(30-Chlorophenyl)-3,4,5,5-tetramethylmorpholine
(5d) Hydrochloride. A sample of (S,S)-2-(30-chlorophenyl)-3,5,5-
trimethylmorpholine (5a) (60 mg, 0.25 mmol) and potassium carbonate
(104 mg, 0.750 mmol) in 1.5 mL of DMF were charged in a sealed flask
apparatus and treated with CH3I (19 μL, 0.30 mmol). The reaction
vessel was sealed and stirred overnight at 70 °C. The reaction mixture
was cooled to room temperature, diluted with water, and extracted twice
with ether. The combined extracts were dried (Na2SO4), filtered, and
concentrated under reduced pressure. The resulting oil was purified by
column chromatography using CH2Cl2-methanol (30:1) as eluent,
afforded 45 mg (71%) of 5d. 1H NMR (CDCl3) δ 7.38-7.36 (m, 1H),
7.25-7.21 (m, 3H), 4.04 (d, 1H, J = 9.6 Hz), 3.54 (q, 1H, J = 11.1 Hz),
2.62-2.53 (m, 1H), 2.25 (s, 3H), 1.19 (s, 3H), 1.07 (s, 3H), 0.83 (d, 3H,
J = 6.3 Hz). 13C NMR (CDCl3) δ 142.6, 134.3, 129.5, 128.29, 128.04,
126.4, 85.5, 78.1, 57.3, 34.2, 25.0, 15.7, 14.1.
0 3
(S,S)-2-(3 -Fluorophenyl)-3,5,5-trimethylmorpholine (5b)
Hemi-D-tartrate. A solution of (S,S)-2-(30-fluorophenyl)-3,5,5-tri-
methylmorpholine (4b) hemi-D-tartrate (220 mg, 0.700 mmol) in
4 mL of EtOH/H2O (1:1) was cooled at 0 °C and treated with NaBH4
(106 mg, 2.80 mmol). The reaction mixture was stirred at room
temperature overnight. After cooling the reaction mixture at 0 °C,
1 mL of HCl 1.6 M solution in EtOH was added slowly to the reaction
vessel and the mixture was allowed to warm to room temperature. Ether
and NaHCO3 saturated aqueous solution were added to the reaction
vessel, and the organic layer was separated. The aqueous phase was
extracted with ether (three times). The combined organic extracts were
washed (water, brine), dried (Na2SO4), and concentrated to give 6b as a
1
white solid 124 mg (74% yield). H NMR (CDCl3) δ 7.33-7.27 (m,
1H), 7.11-7.04 (m, 2H), 6.98-6.89 (m, 1H), 4.58 (d, 1H, J = 4.0 Hz),
3.37 (dd, 2H, J = 26.2, J = 10.7 Hz), 3.13-3.02 (m, 1H), 1.12 (s, 3H),
1.10 (s, 3H), 0.85 (d, 3H, J = 6.7 Hz). 13C NMR (CDCl3) δ 129.4 (d),
121.9 (d), 114.1, 113.8, 113.5, 113.2, 75.5, 69.7, 54.3, 51.5, 25.2, 24.6,
18.2. MS (ESI) m/z 242.3 [(M þ H)þ, M = C13H18FNO2].
A sample of 5d was converted to the hydrochloride salt: mp 212-
213 °C; [R]20D þ51.9° (c 0.75, CH3OH); MS (ESI) m/z 254.6 [(M -
HCl)þ; M = C14H20ClNO HCl]. Anal. (C14H21Cl2NO) C, H, N.
3
(S,S)-2-(30-Chlorophenyl)-4-ethyl-3,5,5-trimethylmorpho-
line (5e) Di-p-toluoyl-L-tartrate. A sample of (S,S)-2-(30-chloro-
phenyl)-3,5,5-trimethylmorpholine (5a) (320 mg, 1.33 mmol) was
dissolved in 5 mL of dichloroethane and treated with NaBH(OAc)3
(117 mg, 2.66 mmol) and an excess amount of acetaldehyde. The
reaction mixture was stirred at room temperature overnight. The
reaction was quenched with aqueous solution of sodium carbonate
and extracted with ether. The combined organic layers were dried
(Na2SO4), filtered, and concentrated. The crude product was purified
by column chromatography on silica gel using cyclohexane-ethyl
acetate (5:1) with 1% NH4OH as the eluent to give 150 mg (42%) of
A solution of crude diol 6b (110 mg, 0.455 mmol) in CH2Cl2 (2 mL)
was cooled at 0 °C and treated with 1 mL of concentrated H2SO4. The
reaction mixture was stirred at room temperature overnight and then
poured into a flask with crushed ice. The mixture was neutralized with
NaHCO3 saturated aqueous solution, followed by extraction with ether
(three times). The organic layers were separated, combined, washed
(water, brine), separated, dried (Na2SO4), and concentrated to a white
1
solid 58 mg (57% yield). H NMR (CDCl3) δ 7.34-7.28 (m, 1H),
7.14-6.97 (m, 3H), 3.78 (d, 1H, J = 9.2 Hz), 3.70 (d, 1H, J = 11.0 Hz),
3.34 (d, 1H, J = 11.0 Hz), 3.10-3.01 (m, 1H), 1.39 (s, 3H), 1.08 (s, 3H),
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Journal of Medicinal Chemistry
ARTICLE
(S,S)-5e as colorless oil. 1H NMR (CDCl3) δ 7.36 (s, 1H), 7.25 (m, 3H),
4.00 (d, 1H), 3.50 (dd, 2H), 2.72 (m, 2H), 2.27 (m, 1H), 1.22 (s, 3H),
1.05 (t, 3H), 1.04 (s, 3H), 0.82 (d, 3H). 13C NMR (CDCl3) δ 142.9,
134.5, 129.8, 128.6, 128.4, 126.7, 86.2, 78.5, 57.5, 54.6, 42.6, 25.4, 19.3,
17.1, 16.4. m/z 268.0 [(M þ H)þ. M = C15H22ClNO].
nAChR Functional Assays. 86Rubidium ion efflux assays were
used as previously described8,12 to characterize functional effects of
analogues.
Behaviorial Assays. All animal experiments were conducted in
accordance with the NIH Guide for the Care and Use of Laboratory
Animals and Institutional Animal Care and Use Committee guidelines.
Male Institute of Cancer Research (ICR) mice (weighing 20-25 g)
obtained from Harlan (Indianapolis, IN) were used to test effects of
analogues on acute actions of nicotine (tail-flick, hot-plate, locomotor,
and body temperature studies) as previously described.8,12 Conditioned
place preference (CPP) assays also were conducted as specified earlier
respectively) or 3-phenyltropanes-related compounds.8,11
A sample of the 5e was converted to the di-p-toluoyl-L-tartrate salt:
mp 165-166 °C; [R]20 -81.4° (c 0.56, CH3OH). Anal. (C35H40-
D
ClNO9) C, H, N.
(S,S)-2-(30-Chlorophenyl)-3,5,5-trimethyl-4-propylmor-
pholine (5f) Di-p-toluoyl-L-tartrate. Compound 5f was prepared
in the same fashion as 5e, using (S,S)-2-(30-chlorophenyl)-3,5,5-tri-
methylmorpholine (5a) (320 mg, 1.33 mmol) in 5 mL of dichloroethane
and was treated with NaBH(OAc)3 (790 mg, 3.74 mmol) and an excess
1
amount of propionaldehyde to afford 220 mg (75%) of 5f. H NMR
’ ASSOCIATED CONTENT
(CDCl3) δ 7.36 (s, 1H), 7.23 (m, 3H), 4.00 (d, 1H), 3.50 (dd, 2H), 2.72
(m, 1H), 2.55 (m, 1H), 2.10 (m, 1H), 1.45 (m, 2H), 1.22 (s, 3H), 1.02
(s, 3H), 0.82 (t, 3H), 0.79 (d, 3H). 13C NMR (CDCl3) δ 142.9, 134.5,
129.8, 128.5, 128.4, 126.7, 86.1, 78.3, 57.7, 54.4, 51.2, 27.2, 25.5, 17.2,
16.1, 11.9. m/z 282.6 [(M þ H)þ, M = C16H24ClNO].
S
Supporting Information. Elemental analysis data. This
b
material is available free of charge via the Internet at http://
pubs.acs.org.
A sample of the 5f was converted to the di-p-toluoyl-L-tartrate salt: mp
144-145 °C; [R]20D -67.2° (c 0.6, CH3OH). Anal. (C36H42ClNO9)
C, H, N.
’ AUTHOR INFORMATION
Corresponding Author
*Phone: 1.919.541.6679. Fax: 1.919.541.8868. E-mail: fic@rti.org.
(S,S)-2-(30-Chlorophenyl)-3-ethyl-5,5-dimethylmorpholine
(5g) Hemi-D-tartrate. A procedure similar to the one described for
(S,S)-2-(30-chlorophenyl)-3,5,5-trimethylmorpholine (S,S)-5a was used
to synthesize (S,S)-5g. A sample of (S,S)-2-(30-chlorophenyl)-3-ethyl-
5,5-dimethylmorpholine-2-ol-D-tartrate (4g) (100 mg, 0.230 mmol) in
2 mL of 50% aqueous ethanol was treated with NaBH4 (45 mg, 1.2 mmol)
to give 74 mg of a crude mixture of diols 6g. A solution of the crude
sample in 2 mL of CH2Cl2 was treated with 1 mL of concentrated
sulfuric acid to afford 54 mg (98%) of (S,S)-5g. The free base was con-
verted to its hemi-D-tartrate salt by dissolving the free base on methanol
and adding 16.9 mg (0.5 equivalent) of D-tartaric acid dissolved in
methanol: mp 203-204 °C; [R]20D -4.2° (c 0.5, CH3OH). 1H NMR
(CD3OD) δ 7.47 (s, 1H), 7.39 (s, 3H), 4.36 (s, 1H), 4.27 (d, 1H), 3.76
(d, 1H), 3.66 (d, 1H), 1.56 (s, 3H), 1.40 (m, 2H), 1.32 (s, 3H), 0.75 (t,
3H). 13C NMR (CD3OD) δ 178.2, 141.8, 136.0, 131.7, 130.5, 129.3,
127.9, 83.7, 75.7, 74.9, 58.2, 55.0, 24.5, 21.9, 10.7. m/z 254.0 [(M -
’ ACKNOWLEDGMENT
This work was supported by National Institutes of Health
National Cooperative Drug Discovery Group grant U19
DA019377.
’ ABBREVIATIONS USED
NRT, nicotine replacement therapy; DA, dopamine; 5HT, ser-
otonin; NE, norepinephrine; HEK, human embryonic kidney;
DAT, dopamine transporter; SERT, serotonin transporter; NET,
norepinephrine transporter; nAChR, nicotine acetylcholine
receptor(s); VTA, ventral tegmental area; MPE, maximum pos-
sible effect; CPP, conditioned place preference
tartrate)þ. M=C16H23ClNO4] Anal. (C16H23ClNO4 0.25H2O) C, H, N.
3
(S,S)-2-(30-Chlorophenyl)-5,5-dimethyl-3-propylmorpho-
line (5h) Hemi-D-tartrate. A procedure similar to the one reported
for (S,S)-2-(30-chlorophenyl)-3,5,5-trimethylmorpholine (S,S)-5a was
used to synthesize 5h. Treatment of (S,S)-2-(30-chlorophenyl)-5,5-
dimethyl-3-propylmorpholine-2-ol (4h) hemi-D-tartrate (360 mg,1.00
mmol) in 6 mL of 50% aqueous ethanol with NaBH4 (151 mg, 4.00
mmol) afforded 295 mg of a crude mixture of diols. The crude sample
was dissolved in 4 mL of CH2Cl2 and treated with 2 mL of concentrated
H2SO4 to give 250 mg (98%) of 5h. Compound 5h was converted to its
hemi-D-tartrate salt: mp 232-233 °C; [R]20D -19.0° (c 1.1, CH3OH).
1H NMR (CD3OD) δ 7.47 (s, 1H), 7.40-7.36 (m, 3H), 4.36 (s, 1H),
4.30 (d, 1H), 3.78-3.66 (m, 2H), 3.37-3.29 (m, 2H), 1.57 (s, 3H), 1.33
(s, 3H), 1.26-1.40 (m, 1H), 0.94-0.92 (m, 1H), 0.74 (t, 3H). 13C
NMR (CD3OD) δ 178.4, 141.8, 136.0, 131.7, 130.5, 129.3, 83.7, 75.5,
75.1, 56.6, 55.1, 33.6, 24.4, 21.8, 20.1, 14.4; m/z 268.0 [(M - tartrate)þ.
M = C17H25ClNO4)]. Anal. (C17H25ClNO4) C, H, N.
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