(2S,3S,5R)-2-(3,5-difluorophenyl)-3,5-dimethyl-2-morpholinol: a novel antidepressant agent and selective inhibitor of norepinephrine uptake.

Article abstract of DOI:10.1021/jm950630p

(2S,3S,5R)-2-(3,5-difluorophenyl)-3,5-dimethyl-2-morpholinol: a novel antidepressant agent and selective inhibitor of norepinephrine uptake.

Full text of DOI:10.1021/jm950630p

J . Med. Chem. 1996, 39, 347-349
347
Research on phenylmorpholinols has led to the
discovery of (3,5-difluorophenyl)morpholinol 4 (BW
1555U88), a potent, selective inhibitor of norepinephrine
uptake. The compound is active in the anti-tetrabena-
zine animal behavioral model that responds to clinically
effective antidepressant drugs, at doses that are free of
other significant pharmacological activities. Compound
4 represents a novel, potent, selective inhibitor of
norepinephrine uptake with antidepressant properties
and, as such, may provide a therapeutic alternative to
the serotonin uptake inhibitors currently used in clinical
practice.
(2S,3S,5R)-2-(3,5-Diflu or op h en yl)-3,5-
d im eth yl-2-m or p h olin ol: A Novel
An tid ep r essa n t Agen t a n d Selective
In h ibitor of Nor ep in ep h r in e Up ta k e
J ames L. Kelley,*,† David L. Musso,†
G. Evan Boswell,† Francis E. Soroko,‡ and
Barrett R. Cooper*,‡
Divisions of Organic Chemistry and Pharmacology,
Burroughs Wellcome Co., Research Triangle Park,
North Carolina 27709
Ch em istr y. Compound 4 was prepared in three
steps from 3,5-difluorobenzonitrile (5) (Scheme 1). The
nitrile 5 was reacted with ethylmagnesium bromide in
diethyl ether to give propiophenone 6 in high yield as
an oil. Ketone 6 was brominated with dioxane dibro-
mide25 in dioxane to provide racemic bromide 7 as an
oil in quantitative yield. An analytical sample of 7 was
prepared by Kugelrohr distillation, bp 60-62 °C (0.3
mmHg). The crude bromopropiophenone 7 was reacted
with (R)-(-)-2-amino-1-propanol in acetonitrile in the
presence of 2,6-lutidine to give amino ketone 8, which
cyclized in situ to provide the cyclic ketal 4 as the
hydrobromide salt, mp 240-241 °C dec. The hydrobro-
mide salt was converted to the free base of 4 with
aqueous sodium hydroxide in high yield, mp 113-115
°C. The free base of 4 was converted to the hydrochlo-
ride salt with ethereal hydrogen chloride to give
(2S,3S,5R)-2-(3,5-difluorophenyl)-3,5-dimethyl-2-mor-
pholinol hydrochloride (4) as a white solid, mp 255-
257 °C.26,27
P h a r m a cology. The effects of 4 and three clinical
antidepressant drugs on inhibition of biogenic amine
uptake28 are tabulated in Table 1. In a synaptosomal
preparation of rat brain, 4 competitively inhibited
biogenic amine uptake, with an IC50 of 0.07 µM for
norepinephrine (NE) and 1.0 µM for dopamine (DA), and
caused no significant inhibition of serotonin (5HT)
uptake at 10 µM. Compound 4 was 30-fold more active
than bupropion as an inhibitor of NE uptake and
displayed inhibitory activity comparable to nomifensine
and imipramine. The profile for inhibition of DA uptake
(IC50 of 1.0 µM) with no effect on 5HT uptake is similar
to that of nomifensine and bupropion. These data
indicate that morpholinol 4 appears to be a potent
inhibitor of NE uptake with weak affinity for DA uptake
and no effect on 5HT uptake.
Compound 4 was active in the anti-tetrabenazine test,
an animal model that is predictive for antidepressant
activity in humans (Table 1). The compound prevented
tetrabenazine-induced sedation29 in rats and mice: oral
ED50s were 1.4 and 6.2 mg/kg, respectively. In rats 4
was more potent than the clinical antidepressant drugs
nomifensine, imipramine, and bupropion, whereas in
mice 4 was more potent than imipramine or bupropion
and one-half as active as nomifensine. Compound 4
shows comparable potency to nomifensine in an animal
model that is predictive for antidepressant activity in
humans.
Compound 4 was evaluated in numerous receptor-
binding, enzyme inhibition, and biogenic amine release
test systems. Other than in the norepinephrine trans-
port system, 4 exhibited no action that could explain
its pharmacological effects in the anti-tetrabenazine
Received August 25, 1995
In tr od u ction . Clinical depression is a common
neurological disorder with a 1-year prevalence of 5-8%
in clinical and community populations.1,2 Until recently
the tricyclic antidepressants and monoamine oxidase
(MAO) inhibitors were the principal drugs in the
psychiatrist’s armamentarium. Because both classes of
drugs suffer from side effects and other problems
associated with their use, new antidepressant agents
with greater efficacy and safety are needed.3,4 Within
the past 2 decades, a second generation of antidepres-
sant agents has emerged. These new agents include
bupropion (1, Wellbutrin), an amino ketone with a
mechanism of action not explained by biochemical
mechanisms common to other antidepressants,5-9 and
the serotonin-selective drugs such as fluoxetine and
sertraline.10 Efforts to develop new antidepressants
that are selective for the noradrenergic system have
been less successful. Nomifensine, a norepinephrine
uptake inhibitor with promising clinical effects, was
withdrawn from the market because of bone marrow
suppression associated with its use.11 Imipramine and
related tricyclic drugs are norepinephrine-selective but
have anticholinergic effects and the potential to cause
cardiac depression.12
Bupropion (1) is a clinically efficacious, antidepres-
sant agent that was first marketed in the United States
in 1989 for the treatment of depressed patients unre-
sponsive to, or intolerant of, other antidepressant
therapy.13-16 The potential of bupropion as an antide-
pressant agent was initially established through its
activity in the anti-tetrabenazine test model in mice.5
It is metabolized to several acidic and basic products
that vary according to the species used to study me-
tabolism. Welch et al.17 reported that the rat metabo-
lizes bupropion primarily by side-chain cleavage to
acidic metabolites, whereas mice, dogs, and humans
primarily form the basic, side-chain-hydroxylated prod-
uct BW 306U. The structure of BW 306U was initially
reported to be that of 2, a noncyclic hydroxy ketone,18,19
but a subsequent report revealed that BW 306U is the
2-phenylmorpholinol 3.17,20 Although the role of 3 in
the clinical profile of bupropion is unresolved,17,21,22
recent reports suggest that 3 may contribute to the
antidepressant profile of bupropion in depressed pa-
tients.23,24 Consequently, we initiated a program to
study the structure-activity relationships of 2-phenyl-
morpholinols in animal models that are predictive of
antidepressant activity in humans.
† Division of Organic Chemistry.
‡ Division of Pharmacology.
0022-2623/96/1839-0347$12.00/0 © 1996 American Chemical Society

348 J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 2
Communications to the Editor
F igu r e 1.
Sch em e 1a
a
(a) EtMgBr, Et2O; (b) dioxane‚Br2, dioxane; (c) (R)-(-)-2-amino-1-propanol, 2,6-lutidine, CH3CN; (d) 40% aqueous NaOH, Et2O; (e)
Et2O‚HCl.
Ta ble 1. Inhibition of Biogenic Amine Uptake and Anti-tetrabenazine Activity of 4 and Three Clinical Antidepressant Drugs
in vitro inhibition of biogenic amine uptake
(IC50, µM)a-c
inhibition of tetrabenazine-induced sedation
(po, ED50, mg/kg)d
compd
NE
DA
5HT
rat
mouse
4
0.07 ( 0.02
0.05 ( 0.02
0.04 ( 0.01
2.4 ( 1.4
1.0 ( 0.4
0.5 ( 0.1
>10
>10
>10
0.5 ( 0.1
>10
1.4 ( 0.2
3.3 ( 0.6
13.4 ( 0.2
e
6.2 ( 0.3
3.3 ( 0.4
9.0 ( 0.6
32 ( 6
nomifensine
imipramine
bupropion
0.9 ( 0.3
a
IC50 values ( SEM were calculated using data from at least five separate experiments. In each experiment, the IC50 value was
b
determined from the concentration-effect curve using duplicate samples as described in ref 28. Designation >10 means the IC50 value
is >10 µM. c NE ) norepinephrine, DA ) dopamine, 5HT ) serotonin. The compounds were tested as described in ref 29. ED50 values
d
( SEM were calculated using data from at least eight determinations of the ED50 in separate experiments. In each experiment doses
from 0.5 to 5.0 µM were evaluated in a minimum of 5 animals/dose. e At doses up to 100 mg/kg po, bupropion failed to produce a 50%
antagonism of tetrabenazine-induced sedation in rats.
models. At a concentration of 10 µM, 4 had no signifi-
cant effects on the following receptor-binding assays:
R-1 and R-2 noradrenergic, â-noradrenergic, dopamine
1 and 2, serotonin 1A and 2, benzodiazepine, substance
P, leukotriene D4, muscarinic M1 and M2, and chole-
cystokinin. The A and B forms of monoamine oxidase
were not inhibited at 10 µM, although modest inhibition
(15% and 8%, respectively) of these enzymes was
observed in ex vivo studies. Compound 4 did not cause
release of NE from hypothalamic synaptosomes or
dopamine from striatal synaptosomes at concentrations
up to 10 µM.
The general central nervous system (CNS) effects of
4 were studied over a large range of oral doses in both
rats (0.5, 1.0, 5.0, 15, 40, 250, and 500 mg/kg) and mice
(15, 40, 100, 250, and 500 mg/kg po). Other than
activity in the antidepressant screen, the lower doses
(g5 mg/kg in rats, g15 mg/kg in mice) increased
locomotion and produced dose-related stereotyped be-
haviors such as sniffing, licking, and biting in both
species. Behavioral reflexes, nociception, body temper-
ature, and weight gain were affected at doses of g250
mg/kg in both rats and mice. Doses of 250 mg/kg
resulted in coarse tremors in both species. Deaths
occurred at 500 mg/kg in mice (1/4) and at 250 mg/kg
(1/4) and 500 mg/kg (1/4) in rats. A large separation
exists between doses producing significant neurological
effects and lethality in rodents and those showing
activity in the antidepressant screening test.
Compound 4 produced only transient, dose-dependent
changes in blood pressure at multiples of the active dose.
Blood pressure responses to NE injection were potenti-
ated, consistent with NE uptake inhibition. Unlike the
tricyclic antidepressants or fluoxetine, 4 did not block
electrical conduction in the cardiac Perkinje fiber system
at concentrations up to 1 mM.
In summary, 4 is a potent, selective inhibitor of NE
uptake and demonstrates much weaker effects on
dopamine and serotonin uptake. The compound is
active in behavioral tests that respond to clinically
effective antidepressant drugs; this is true at doses that
do not produce other significant pharmacological activi-
ties. Unlike the tricyclic antidepressants, 4 does not
bind to M1 or M2 receptors, nor does it block electrical
conduction in cardiac tissue at 1 mM. Cardiovascular
studies in dogs indicate that 4 is unlikely to produce
adverse effects at plasma levels associated with the
therapeutic effect. Increased locomotion activity is the
first observable CNS effect in rodents. This effect occurs
at doses 16-fold above those that provide plasma levels
equal to the IC50 for NE transport inhibition. These
doses are expected to produce antidepressant activity
during chronic treatment. The pharmacological profile
of 4 suggests that it will display antidepressant activity
in humans and that this activity will involve inhibition
of the NE uptake mechanism but without the cholin-
ergic and cardiac depression effects associated with
tricyclic antidepressants.

Communications to the Editor
J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 2 349
(12) Blackwell, B. Adverse Effects of Antidepressant Drugs Part 1:
Monoamine Oxidase Inhibitors and Tricyclics. Drugs 1981, 21,
201-219.
(13) Fann, W. E.; Schroeder, D. H.; Mehta, N. B.; Soroko, F. E.;
Maxwell, R. A. Clinical Trial of Bupropion HCl in Treatment of
Depression. Curr. Ther. Res. 1978, 23, 222-229.
(14) Fabre, L. R., J r.; McLendon, D. M. Double-Blind Placebo-
Controlled Study of Bupropion Hydrochloride (Wellbutrin®) in
the Treatment of Depressed In-Patients. Curr. Ther. Res. 1978,
23, 393-402.
(15) Davidson, J .; Miller, R.; Fleet, J . V. W.; Strickland, R.; Manberg,
P.; Allen, S.; Parrott, R. A Double-Blind Comparison of Bupro-
pion and Amitriptyline in Depressed Inpatients. J . Clin. Psy-
chiatry 1983, 44 (5), 115-117.
(16) Feighner, J . P.; Meredith, C. H.; Stern, W. C.; Hendrickson, G.;
Miller, L. L. A Double-Blind Study of Bupropion and Placebo in
Depression. Am. J . Psychiatry 1984, 141, 525-529.
(17) Welch, R. M.; Lai, A. A.; Schroeder, D. H. Pharmacological
Significance of the Species Differences in Bupropion Metabolism.
Xenobiotica 1987, 17, 287-298.
(18) Schroeder, D. H.; Eiseman, J . L.; Mehta, N. B.; Brent, D. A.;
Soroko, F. E.; Welch, R. M. The Isolation and Identification of
Some Basic Urinary Metabolites of Bupropion.HCl in Man.
Pharmacologist 1979, 21, 191 (Abstract).
Ack n ow led gm en t. We acknowledge the assistance
of Ms. S. J ones-Humble and Mr. B. T. Kenney, who
performed the biogenic amine uptake and anti-tetra-
benazine experiments. The development of 4 was
supported with the secondary studies of Dr. P. Morgan
and Ms. F. Tang (receptor-binding assays), Dr. H. White
(monoamine oxidase assays), Ms. S. J ones-Humble
(effect on synaptosomes), Dr. C. Wang (Perkinje fiber
system measurements), Mr. O. Beek (cardiovascular
studies in dogs), and Ms. V. M. Boncek (locomotor
activity studies). Mr. R. C. Crouch assigned the correct
2-phenylmorpholinol structure for 3. We thank Ms. D.
T. Staton for the art work, the Burroughs Wellcome Co.
Research Document Center for assistance in preparation
of the manuscript, and Laura Mansberg for proofreading
the final draft. The support and encouragement of Dr.
R. M. Ferris and Dr. R. W. Morrison are greatly
appreciated.
(19) Schroeder, D. H. Metabolism and Kinetics of Bupropion. J . Clin.
Psychiatry 1983, 44 (5), 79-81.
Refer en ces
(20) Crouch, R. C. Personal communication.
(1) Boyd, J . H.; Weissman, M. M. Epidemiology of Affective Disor-
ders. Arch. Gen. Psychiatry 1981, 38, 1039-1046.
(21) Laizure, S. C.; DeVane, C. L.; Stewart, J . T.; Dommisse, C. S.;
Lai, A. A. Pharmacokinetics of Bupropion and its Major Basic
(2) Hirschfeld, R. M. A.; Cross, C. K. Epidemiology of Affective
Disorders. Psychosocial Risk Factors. Arch. Gen. Psychiatry
1982, 39, 35-46.
Metabolites in Normal Subjects after
a Single Dose. Clin.
Pharmacol. Ther. 1985, 38, 586-589.
(3) Weisman, M. M.; Klerman, G. L. The Chronic Depressive in the
Community: Unrecognized and Poorly Treated. Compr. Psy-
chiatry 1977, 18, 523-532.
(22) Golden, R. N.; DeVane, C. L.; Laizure, S. C.; Rudorfer, M. V.;
Sherer, M. A.; Potter, W. Z. Bupropion in Depression II. The
Role of Metabolites in Clinical Outcome. Arch. Gen. Psychiatry
1988, 45, 145-149.
(4) Maxwell, R. A. Second Generation Antidepressants: The Phar-
macological and Clinical Significance of Selected Examples. Drug
Dev. Res. 1983, 3, 203-211.
(23) Ferris, R. M.; Cooper, B. R. Mechanism of Antidepressant
Activity of bupropion. J . Clin. Psychiatry, in press.
(24) Cooper, B. R.; Wang, C. M.; Cox, R. F.; Norton, R.; Shea, V.;
Ferris, R. Evidence that the Acute Behavioral and Electrophysi-
ological Effects of Bupropion (Wellbutrin®) are Mediated by a
Noradrenergic Mechanism. Unpublished data.
(5) Soroko, F. E.; Mehta, N. B.; Maxwell, R. A.; Ferris, R. M.;
Schroeder, D. H. Bupropion hydrochloride ((()R-t-butylamino-
3-chloropropiophenone HCl): a novel antidepressant agent. J .
Pharm. Pharmacol. 1977, 29, 767-770.
(6) Cooper, B. R.; Hester, T. J .; Maxwell, R. A. Behavioral and
Biochemical Effects of the Antidepressant Bupropion (Well-
butrin): Evidence for Selective Blockade of Dopamine Uptake
in vivo. J . Pharmacol. Exp. Ther. 1980, 215, 127-134.
(7) Ferris, R. M.; White, H. L.; Cooper, B. R.; Maxwell, R. A.; Tang,
F. L. M.; Beaman, O. J .; Russell, A. Some Neurochemical
Properties of a New Antidepressant, Bupropion Hydrochloride
(Wellbutrin®). Drug Dev. Res. 1981, 1, 21-35.
(25) Pasaribu, S. J .; Williams, L. R. Selective Bromination of
Substituted Acetophenones With Dioxan Dibromide. Aust. J .
Chem. 1973, 26, 1327-1331.
(26) Physical data for 4: [R]20 ) +42.1° (c ) 0.687, 95% EtOH); 1
H
D
NMR (DMSO-d6) δ 0.97 (d, 3H, CH3), 1.20 (d, 3H, CH3), 3.49 (br
m, 2H, CH), 3.83 (m, 2H, CH2), 7.17-7.34 (m, 3H, ArH), 7.62 (s,
1H, OH), 8.75 and 10.10 (br s, 2H, NH, HCl). Anal. (C12H16ClF2-
NO2) C, H, N.
(8) Ferris, R. M.; Cooper, B. R.; Maxwell, R. A. Studies of Bupro-
pion’s Mechanism of Antidepressant Activity. J . Clin. Psychiatry
1983, 44 (5), 74-78.
(27) The relative configuration of the three stereocenters of 4 was
confirmed by X-ray crystallography.
(9) Ferris, R. M.; Beaman, O. J . Bupropion: A New Antidepressant
Drug, the Mechanism of Action of Which is Not Associated with
Down-Regulation of Postsynaptic â-Adrenergic, Serotonergic (5-
HT2), R2-Adrenergic, Imipramine and Dopaminergic Receptors
in Brain. Neuropharmacology 1983, 22, 1257-1267.
(10) 5-HT Blockers and All That. Lancet 1990, 336, 345-346 (Edito-
rial).
(11) Salama, A.; Mueller-Eckhardt, C. Rh Blood Group-Specific
Antibodies in Immune Hemolytic Anemia Induced by Nomi-
fensine. Blood 1986, 68, 1285-1288.
(28) Musso, D. L.; Mehta, N. B.; Soroko, F. E.; Ferris, R. M.;
Hollingsworth, E. B.; Kenney, B. T. Synthesis and Evaluation
of the Antidepressant Activity of the Enantiomers of Bupropion.
Chirality 1993, 5, 495-500.
(29) Sulser, F.; Soroko, F. On the role of rate of brain norepinephrine
release in the antibenzoquinolizine action of desipramine. Psy-
chopharmacologia 1965, 8, 191-200.
J M950630P