Synthesis and opioid receptor affinity of morphinan and benzomorphan derivatives: Mixed κ agonists and μ agonists/antagonists as potential pharmacotherapeutics for cocaine dependence

Article abstract of DOI:10.1021/jm9903343

This report concerns the synthesis and preliminary pharmacological evaluation of a novel series of K agonists related to the morphinan (-)- cyclorphan (3a) and the benzomorphan (-)cyclazocine (2) as potential agents for the pharmacotherapy of cocaine abuse. Recent evidence suggests that agonists acting at κ opioid receptors may modulate the activity of dopaminergic neurons and alter the neurochemical and behavioral effects of cocaine. We describe the synthesis and chemical characterization of a series of morphinans 3a-c, structural analogues of cyclorphan [(-)-3-hydroxy-N- cyclopropylmethylmorphinan S(+)-mandelate, 3a], the 10-ketomorphinans 4a,b, and the 8-ketobenzomorphan 1b. Binding experiments demonstrated that the cyclobutyl analogue 3b [(-)-3-hydroxy-N-cyclobutylmethylmorphinan S(+)- mandelate, 3b, MCL-101] of cyclorphan (3a) had a high affinity for μ, δ, and κ opioid receptors in guinea pig brain membranes. Both 3a,b were approximately 2-fold more selective for the κ receptor than for the μ receptor. However 3b (the cyclobutyl analogue) was 18-fold more selective for the κ receptor in comparison to the δ receptor, while cyclorphan (3a) had only 4-fold greater affinity for the κ receptor in comparison to the δ receptor. These findings were confirmed in the antinociceptive tests (tail- flick and acetic acid writhing) in mice, which demonstrated that cyclorphan (3a) produced antinociception that was mediated by the δ receptor while 3b did not produce agonist or antagonist effects at the δ receptor. Both 3a,b had comparable κ agonist properties 3a,b had opposing effects at the μ receptor: 3b was a μ agonist whereas 3a was a μ antagonist.

Full text of DOI:10.1021/jm9903343

114
J . Med. Chem. 2000, 43, 114-122
Syn th esis a n d Op ioid Recep tor Affin ity of Mor p h in a n a n d Ben zom or p h a n
Der iva tives: Mixed K Agon ists a n d µ Agon ists/An ta gon ists a s P oten tia l
P h a r m a coth er a p eu tics for Coca in e Dep en d en ce†
J ohn L. Neumeyer,*,‡ J ean M. Bidlack,§ Rushi Zong,‡ Venkatesalu Bakthavachalam,| Peng Gao,| Dana J . Cohen,§
S. Stevens Negus,‡ and Nancy K. Mello‡
Department of Psychiatry, Harvard Medical School, McLean Hospital, Alcohol and Drug Abuse Research Center,
Belmont, Massachusetts 02478-9106, Department of Pharmacology and Physiology, University of Rochester School of Medicine
and Dentistry, Rochester, New York 14642-8711, and Research Biochemicals International (RBI), 1 Strathmore Road,
Natick, Massachusetts 01760
Received J une 28, 1999
This report concerns the synthesis and preliminary pharmacological evaluation of a novel series
of κ agonists related to the morphinan (-)-cyclorphan (3a ) and the benzomorphan (-)-
cyclazocine (2) as potential agents for the pharmacotherapy of cocaine abuse. Recent evidence
suggests that agonists acting at κ opioid receptors may modulate the activity of dopaminergic
neurons and alter the neurochemical and behavioral effects of cocaine. We describe the synthesis
and chemical characterization of a series of morphinans 3a -c, structural analogues of
cyclorphan [(-)-3-hydroxy-N-cyclopropylmethylmorphinan S(+)-mandelate, 3a ], the 10-keto-
morphinans 4a ,b, and the 8-ketobenzomorphan 1b. Binding experiments demonstrated that
the cyclobutyl analogue 3b [(-)-3-hydroxy-N-cyclobutylmethylmorphinan S(+)-mandelate, 3b,
MCL-101] of cyclorphan (3a ) had a high affinity for µ, δ, and κ opioid receptors in guinea pig
brain membranes. Both 3a ,b were approximately 2-fold more selective for the κ receptor than
for the µ receptor. However 3b (the cyclobutyl analogue) was 18-fold more selective for the κ
receptor in comparison to the δ receptor, while cyclorphan (3a ) had only 4-fold greater affinity
for the κ receptor in comparison to the δ receptor. These findings were confirmed in the
antinociceptive tests (tail-flick and acetic acid writhing) in mice, which demonstrated that
cyclorphan (3a ) produced antinociception that was mediated by the δ receptor while 3b did
not produce agonist or antagonist effects at the δ receptor. Both 3a ,b had comparable κ agonist
properties. 3a ,b had opposing effects at the µ receptor: 3b was a µ agonist whereas 3a was a
µ antagonist.
In tr od u ction
in rodents has been reported to block or decrease
cocaine-induced hyperactivity,11,12 sensitization to cocaine-
induced hyperactivity and stereotypies,13 and cocaine-
induced place preferences.11,13,14 κ Agonists also blocked
the effects of cocaine in squirrel monkeys in assays of
cocaine discrimination15,16 and scheduled-controlled re-
sponding.These findings suggest that activation of κ
opioid receptors may functionally antagonize some
abuse-related effects of cocaine, possibly by inhibiting
the release of dopamine from dopaminergic neurons,
and may provide a new approach to the continuing
search for effective treatment medications for cocaine
abuse and dependence.17 In an effort to evaluate this
hypothesis, the effects of eight benzomorphan and
arylacetamide κ agonists on cocaine self-administration
in rhesus monkeys were examined.18,19 Most of these κ
agonists produced dose-dependent decreases in cocaine
self-administration. Moreover, all κ agonists that re-
duced cocaine self-administration were compounds with
relatively high efficacy for κ receptors, whereas a low-
efficacy κ agonist (cyclazocine, 2) and a κ antagonist
(nor-binaltorphimine) were ineffective. Interestingly,
however, nonselective κ agonists such as ethylketocy-
clazocine (1c), which produce µ receptor-mediated effects
in addition to their κ agonist effects, decreased cocaine
self-administration more effectively and with fewer
κ Opioid receptors derive their name from the proto-
type benzomorphan, ketocyclazocine (1a ) (Chart 1),
which was found to produce behavioral effects that were
distinct from the behavioral effects of morphine but that
were antagonized by the opioid antagonist, naltrexone.1
Compounds from several structural classes, including
benzomorphans, arylacetamides, and morphinans have
been found to possess κ opioid agonist activity. A
growing body of evidence suggests that agonists at κ
opioid receptors may modulate the activity of dopam-
inergic neurons and alter the neurochemical and be-
havioral effects of cocaine. The nucleus accumbens
contains high levels of both κ opioid receptors2-4 and
dynorphin,5 an endogenous opioid peptide with high
affinity for κ receptors.6 In contrast to cocaine, κ agonists
have been shown to decrease striatal dopamine levels
in rats.7-9 κ Agonists also attenuated cocaine-induced
increases in dopamine levels in the nucleus accum-
bens.10 Behaviorally, the administration of κ agonists
† This manuscript is dedicated to the memory of Professor Sydney
Archer.
* Corresponding author: J ohn L. Neumeyer, Ph.D. Phone: (617)
855-3388. Fax: (617) 855-2519. E-mail: neumeyer@mclean.harvard.edu.
‡ Alcohol and Drug Abuse Research Center.
§ University of Rochester.
| RBI.
10.1021/jm9903343 CCC: $19.00 © 2000 American Chemical Society
Published on Web 12/21/1999

Morphinan and Benzomorphan Derivatives
J ournal of Medicinal Chemistry, 2000, Vol. 43, No. 1 115
Ch a r t 1. Structures of κ Agonists
undesirable side effects than highly selective κ agonists.
Antagonism studies also suggested that κ agonists
which are partial agonists at the µ receptor such as
ethylketocyclazocine (1c) may be especially effective in
decreasing cocaine self-administration in rhesus mon-
keys.18 Specifically, naloxone completely blocked the
effects of ethylketocyclazocine on cocaine self-adminis-
tration, but the κ-selective antagonist, nor-binaltor-
phimine, was only partially effective. In contrast, both
naloxone and nor-binaltorphimine completely blocked
the effects of the highly selective κ agonist U-50,488 on
cocaine self-administration.15,16,18,19 Taken together,
these earlier findings suggested that nonselective κ
agonists with additional activity at µ receptors may be
especially promising candidate medications for the
treatment of cocaine abuse.
ethylamine. The crude diacyl compound 9a was further
reduced with lithium aluminum hydride to yield 3a ,b
previously prepared by Gates and Montzka20 from (-)-
3-hydroxymorphinan. 3a ,b were further converted to
their white crystalline mandelate salts. The (S)-N-
tetrahydrofurfuryl derivative 3c was prepared from (S)-
tetrahydrofurfuryl (1R)-camphor-10-sulfonate (10) by
methods previously reported.21 The 10-ketomorphinans
were prepared by the oxidation22 of the morphinan 7
with CrO3/H2SO4 followed by alkylation with cyclopro-
pylmethyl bromide and O-demethylation to yield 4b
(Scheme 1). O-Demethylation of 11 to form 13 followed
by alkylation with (S)-tetrahydrofurfuryl (1R)-camphor-
10-sulfonate (10) led to 4a . The assignment of the
stereochemistry of 4a was based on the work of Merz
and Stockhaus.23
Ethylketocyclazocine (1c) has intermediate efficacy at
µ receptors and functions as a κ agonist/µ partial
agonist. The development of other κ agonists with higher
or lower efficacy at µ receptors would permit further
evaluation of the most favorable combination of κ and
µ opioid receptor-mediated effects for the reduction of
cocaine self-administation. Because both morphinans
and benzomorphans are known to include compounds
with mixed activity at µ and κ receptors, the purpose of
the present study was to develop novel morphinan and
benzomorphan κ agonists as candidate drug abuse
treatment medications. Accordingly, we describe here
the synthesis and preliminary evaluation of a series of
morphinans (3a -c), structural analogues of cyclorphan
3a , the 10-ketomorphinans 4a ,b, and the 8-ketobenzo-
morphan 1b, structurally related to ketocyclazocine
(1a ). The structures of these compounds are shown in
Chart 1.
The 8-ketobenzomorphan derivative 1b was prepared
from (-)-5,9-R-dimethyl-2-hydroxy-6,7-benzomorphan
(14) [(-)-nor-metazocine]24 as outlined in Scheme 2.
Protection of the amine with di-tert-butyl dicarbonate
(Boc) and O-methylation with dimethyl sulfate led to
16. Acid hydrolysis followed by oxidation of 17 with
CrO3/H2SO4 by the procedure of Michne and Albertson22
led to 18. O-Demethylation and alkylation with 5-tet-
rahydrofurfuryl (1R)-camphor-10-sulfonate (10) gave 1b
which was isolated as the HCl salt.
Resu lts
All compounds were examined for their affinity and
selectivity at µ, δ, and κ opioid receptors in guinea pig
brain membranes using the selective radioligands, [3H]-
DAMGO (µ), [3H]naltrindole (δ), and [3H]U69,593 (κ)
(Table 1). The antinociceptive activity of the two mor-
phinans with the highest affinity at the κ receptor was
examined further in the tail-flick and acetic acid writh-
ing tests in mice.
Ch em istr y
The synthesis of the morphinans 3a -c and the 10-
keto derivatives 4a ,b is shown in Scheme 1. The
compounds were all prepared from commercially avail-
able (-)-3-hydroxy-N-methylmorphinan (levorphanol,
3d ) which was converted to the O-methyl ether 6 and
N-dealkylated to (-)-3-methoxymorphinan (7). Alter-
natively, 3d was directly N-dealkylated to 8.
55° Wa r m -Wa ter Ta il-F lick Test. In the warm-
water tail-flick test, (-)-cyclorphan (3a ) produced 37 (
10% antinociception after an icv dose of 100 nmol. In
contrast, 3b produced a full dose-response curve with
an ED50 value and 95% confidence limits (CL) of 7.3
(5.7-9.4) nmol with testing taking place 20 min afer
an icv injection.
The intermediate 8 was N- and O-diacylated with
cyclopropanecarbonyl chloride in the presence of tri-
Because 3b generated a full dose-response curve in
the tail-flick test, the receptor selectivity of the agonist

116 J ournal of Medicinal Chemistry, 2000, Vol. 43, No. 1
Neumeyer et al.
Sch em e 1a
a
Reagents: (i) CH2N2; (ii) 1-chloroethyl chloroformate; (iii) MeOH; (iv) HBr/HOAc; (v) R′COCl; (vi) LiAlH4; (vii) (S)-tetrahydrofurfuryl
(1R)-camphor-10-sulfonate (10); (viii) CrO3-H2SO4; (ix) cyclopropylmethyl bromide; (x) BBr3/CH2Cl2.
Sch em e 2a
a
Reagents: (i) (t-Boc)2O, K2CO3, dioxane, H2O; (ii) (CH3O)2SO2, NaOH, H2O; (iii) HCl, H2O/EtOAc; (iv) CrO3, H2SO4; (v) 48% HBr; (vi)
(S)-tetrahydrofurfuryl (1R)-camphor-10-sulfonate.
effect was determined by using selective antagonists.
Figure 1 shows that in the tail-flick test, antinociception
induced by 3b was mediated by both κ and µ opioid
receptors.
Acetic Acid Wr ith in g Test. Because κ agonists often
do not produce full dose-response curves in the warm-
water tail-flick test,25 the effects of 3a ,b were character-
ized in the writhing test. Both 3a ,b produced full dose-
response curves in the writhing test, with ED50 values
and 95% CL of 0.65 (0.35-1.2) and 0.79 (0.48-1.3) nmol,
respectively, demonstrating that in this assay the two
compounds were equipotent.
The receptor selectivity for antinociception produced
by 3a ,b in the writhing test was also determined. Figure

Morphinan and Benzomorphan Derivatives
J ournal of Medicinal Chemistry, 2000, Vol. 43, No. 1 117
Ta ble 1. Ki Value Inhibition of µ, δ, and κ Opioid Binding to Guinea Pig Brain Membranes by Test Compoundsa
Ki (nM ( SE)
compound
[3H]DAMGO (µ)
[3H]naltrindole (δ)
[3H]U69,593 (κ)
selectivity κ:µ
selectivity κ: δ
U50,488
ethylketocyclazocine (1c)
220 ( 5.6
0.78 ( 0.1
2500 ( 170
3.4 ( 0.41
0.58 ( 0.06
0.22 ( 0.01
1.3 ( 0.06
0.27 ( 0.02
4.2 ( 0.45
1.0 ( 0.18
150 ( 71
0.36 ( 0.056
0.62 ( 0.11
0.052 ( 0.0009
0.053 ( 0.003
0.073 ( 0.012
0.15 ( 0.01
2.3 ( 0.26
610
1
2
2
6900
5
11
4
18
2
2
6
6
(-)-cyclazocine (2)
0.10 ( 0.03
0.092 ( 0.005
0.12 ( 0.012
0.010 ( 0.002
0.21 ( 0.017
0.38 ( 0.004
240 ( 89
(-)-cyclorphan (3a )
MCL-101 (3b)
2
3c
0.066
0.09
2
1
4
levorphanol (3d )
4a
4b
1b
0.18 ( 0.019
24 ( 1.6
2900 ( 58
>100000
720 ( 57
a
Guinea pig brain membranes, 0.5 mg of protein/sample, were incubated with 12 different concentrations of the compounds in the
presence of receptor-specific radioligands at 25 °C, in a final volume of 1 mL of 50 mM Tris-HCl, pH 7.5. Nonspecific binding was determined
using 1 µM naloxone. Data are the mean values SEM from three experiments, performed in triplicate.
F igu r e 1. Receptor selectivity of antinociception induced by
3b in the tail-flick test. Mice were pretreated either with the
µ-selective antagonist â-FNA for 24 h or with the κ antagonist
nor-BNI or the δ antagonist ICI 174,864, which were co-
injected with MCL-101 (3b), 20 min before testing. Each group
contained 10 mice. Data are the mean ( SE. **P < 0.01, in
comparison to the 3b alone group.
2A shows that 3a produced antinociception that was
mediated by κ and δ opioid receptors. In contrast, 3b
produced antinociception that was mediated by κ and µ
receptors, as shown in Figure 2B, and is in agreement
with the results from the tail-flick assay (Figure 1). The
receptor selectivity results in the writhing assay cor-
related with the binding results in Table 1, which
showed that 3a had a higher affinity than 3b for the δ
receptor.
An ta gon ist P r op er ties of (-)-Cyclor p h a n (3a )
a n d Com p ou n d 3b. Because 3a did not produce a full
dose-response curve in the 55 °C warm-water tail-flick
test, experiments were performed to determine if it
F igu r e 2. Receptor selectivity of antinociception induced by
(-)-cyclorphan (3a ) (A) and 3b (B) in the writhing test. Mice
would antagonize morphine-induced antinociception.
Mice were co-injected with 3 nmol of morphine and
varying doses of 3a . Antinociception was determined 20
min later. Figure 3A shows that 3a at a dose of 1 nmol
completely antagonized morphine-induced antinocice-
ption, indicating that 3a was a µ antagonist. In contrast,
3b was a weak µ antagonist, with only partial antago-
nism of morphine-induced antinociception, at a dose
that did not produce antinociception by itself (Figure
3B).
were pretreated either with the µ-selective antagonist â-FNA
for 24 h or with the κ antagonist nor-BNI or the δ antagonist
ICI 174,864, which were co-injected with (-)-cyclorphan or 3b.
After 20 min, the number of writhes was measured and
compared to a control group of mice that received icv saline.
Each group contained 10 mice. Data are the mean ( SE. *P <
0.05, **P < 0.01, in comparison to the (-)-cyclorphan (A) or
3b (B) alone group.
To determine the receptor selectivity of the antago-
nism induced by 3a , mice were co-injected with either

118 J ournal of Medicinal Chemistry, 2000, Vol. 43, No. 1
Neumeyer et al.
the δ or κ receptors but did antagonize morphine-
induced antinociception, demonstrating that 3a was a
µ-selective antagonist.
Con clu sion s
The major findings of this study were that cyclorphan
(3a ) and 3b (the N-cyclobutylmethyl analogue of 3a ) had
similar agonist effects mediated by κ opioid receptors
but produced different effects at µ opioid receptors.
Specifically, both cyclorphan (3a ) and 3b had high
affinity for κ opioid receptors and produced agonist
effects mediated by κ opioid receptors in mice. Both
compounds also bound to µ opioid receptors with affini-
ties approximately 2-fold lower than their affinities for
κ receptors. However, cyclorphan (3a ) had low efficacy
at µ receptors and acted as a µ antagonist, whereas 3b
had higher efficacy at µ receptors and acted as a µ
agonist. In addition to these effects at κ and µ receptors,
cyclorphan (3a ) also produced δ receptor-mediated ago-
nist effects, whereas 3b did not produce agonist or
antagonist effects at δ receptors.
These findings confirm and extend previous studies
that have evaluated opioid receptor binding profiles and
pharmacological activities of different N-substituted
morphinans. For example, in the present study, conver-
sion of the N-substituent from N-methyl (levorphanol,
3d ) to N-cyclopropylmethyl (cyclorphan, 3a ) increased
binding affinity to µ, κ, and δ receptors, and this increase
in affinity was most pronounced for κ receptors. Con-
sequently, levorphanol (3d ) had 10-20-fold selectivity
for µ vs κ and δ receptors, whereas cyclorphan (3a ) had
approximately 2-4-fold selectivity for κ vs µ and δ
receptors. Moreover, the conversion of the N-substituent
from N-methyl to N-cyclopropylmethyl also decreased
µ agonist efficacy, and cyclorphan acted as a µ antago-
nist. Previous studies also found that conversion of the
N-substituent from N-methyl to N-cyclopropylmethyl
increased µ, κ, and δ receptor affinity and decreased µ
receptor efficacy for morphinans [i.e. levorphanol (3d )
and cyclorphan (3a )] as well as for morphine itself (i.e.
morphine and N-cyclopropylmethyl-nor-morphine) and
benzomorphans (i.e. metazocine and cyclazocine).26 Pre-
vious in vivo preclinical studies also reported that
cyclorphan (3a ) displayed agonist effects at κ receptors
and low-efficacy effects at µ receptors in both pigeons
and primates.27-30
F igu r e 3. Antinociceptive effects of icv morphine (3 nmol, -20
min), alone or co-administered to mice with increasing doses
of icv (-)-cyclorphan (3a ) (A) or 3b (B) in the mouse tail-flick
assay. Data are the mean ( SE. *P < 0.05, **P < 0.01, in
comparison to the morphine alone group.
In the present study, further conversion of the N-
substituent from N-cyclopropylmethyl to N-cyclobutyl-
methyl had little effect on receptor affinity or selectivity
but increased µ agonist efficacy. To our knowledge,
previous studies have not provided a detailed pharma-
cological evaluation of this conversion in the morphinan
series. However, earlier studies did find that 3b was
approximately 40 times more potent than morphine in
suppressing abstinence in morphine-dependent mon-
keys, and this finding is consistent with the conclusion
that 3b has potent µ agonist effects.31 Moreover, conver-
sion of the N-substituent from N-cyclopropylmethyl to
N-cyclobutylmethyl has also been found to increase
µ agonist efficacy in other related chemical classes
including the 14-hydroxymorphinans,31 the nor-oxymor-
phones,32 and the 5-phenylbenzomorphans.33
F igu r e 4. Antinociceptive effects of icv morphine (3 nmol),
U50,488 (30 nmol), or DPDPE (10 nmol) in untreated mice
and mice co-administered with a single icv dose of (-)-
cyclorphan (1 nmol) in the warm-water tail-flick assay. Testing
was performed 20 min after the co-administration of the
compounds. **P < 0.01, in comparison to the morphine alone
group.
the µ agonist, morphine, the κ-selective agonist, U50,-
488, or the δ-selective peptide, DPDPE, along with
1-nmol of (-)-cyclorphan (3a ). Figure 4 shows that 3a
did not antagonize antinociception mediated by either
The present study also evaluated the effects of two
other modifications to cyclorphan (3a ). First, addition

Morphinan and Benzomorphan Derivatives
J ournal of Medicinal Chemistry, 2000, Vol. 43, No. 1 119
cautiously adding 3 mL of H2SO4 to 34 mL of water) was added
a solution of CrO3 in the remaining 17 mL of dilute H2SO4.
The resulting suspension was heated to reflux for 2 h. TLC
(9:1:0.01 CH2Cl2-MeOH-NH4OH) analysis indicated the dis-
appearance of the starting material. Upon cooling, NH3 (37%,
8 mL) was added, and the resulting emulsion was extracted
with ether (3 × 50 mL). Upon filtration the ether extracts were
washed with water, dried (MgSO4), and concentrated to
dryness to afford 11 (0.6 g, 92%). 1H NMR (CDCl3): δ 0.9-1.7
(m, 7H), 1.76-1.88 (m, 1H), 1.90-2.1 (m, 2H), 2.31-2.4 (m,
1H), 2.54-2.65 (m 1H), 2.71-2.79 (m, 1H), 3.22 (d, J ) 3.3
Hz, 1H), 3.89 (s, 3H), 6.82-6.88 (m, 2H), 8.07 (d, J ) 8.6 Hz).
10-Ket o-3-m et h oxy-N-cyclop r op ylm et h ylm or p h in a n
(12). A mixture of 11 (250 mg, 0.92 mmol), cyclopropylmethyl
bromide (0.1 mL, 1.03 mmol), and NaHCO3 (0.12 g, 1.4 mmol)
in dry DMF (3 mL) was heated under nitrogen at 75 °C for 4
h. Solvent was removed under reduced pressure. The remain-
ing material was taken up with CHCl3 (25 mL), washed with
water (2 × 25 mL), dried (MgSO4), and concentrated to dryness
to afford 12 (250 mg, 87%). 1H NMR (CDCl3): δ 0.02-0.15 (m,
2H), 0.45-0.49 (m, 2H), 0.82-0.98 (m, 1H), 1.03-1.7 (m, 9H),
1.86-2.03 (m, 3H), 2.08-2.15 (m, 1H), 2.66-2.74 (m, 1H), 2.9-
2.98 (m, 1H), 3.2 (d, J ) 2.9 Hz, 1H), 3.87 (s, 3H), 6.8-6.86
(m, 2H), 8.0 (d, J ) 8.5 Hz, 1H).
10-Ket o-3-h yd r oxy-N-cyclop r op ylm et h ylm or p h in a n
(4b). To a solution of 12 (220 mg, 0.67 mmol) in CH2Cl2 (15
mL) was added a solution of BBr3 in CH2Cl2 (1 M, 2.8 mL, 2.8
mmol), and the resulting solution was stirred at room tem-
perature overnight. TLC (CHCl3-EtOH, 95:5) indicated a
major transformation. MeOH (20 mL) was added, and the
resulting solution was allowed to reflux for 2 h. Solvent was
removed under reduced pressure. The remaining material was
taken up with CHCl3 (30 mL), washed with saturated NaHCO3
(to pH 8) and water, dried (MgSO4), and concentrated to
dryness. Column separation (silica gel, 30 g) eluting with
CHCl3-EtOH (99:1) afforded 4b (150 mg, 71%). 1H NMR
(CDCl3): δ 0.01-0.28 (m, 2H), 0.45-0.48 (m, 2H), 0.85-0.94
(m, 1H), 1.08-1.7 (m, 8H), 1.9-2.17 (m, 4H), 2.3-2.38 (m, 1H),
2.7-2.79 (m, 1H), 2.93-3.01 (m, 1H), 3.24 (d, J ) 2.8 Hz, 1H),
6.75-6.78 (m, 2H), 7.97 (d, J ) 9.2 Hz, 1H). Compound 4b
(150 mg, 0.48 mmol) was dissolved in EtOH (1 mL) and treated
with ethereal HCl (1 M, 0.5 mL). Solvent was removed under
reduced pressure. The remaining material was washed with
ether and collected as 4b HCl (100 mg, 60%): mp 174 °C
(sublime). Anal. (C20H25NO2HCl‚0.75H2O) C,H,N.
of a 10-keto group to cyclorphan (3a ) to produce 4b
decreased affinity at κ, µ, and δ receptors. Similarly,
addition of a 10-keto group to the benzomorphan cycla-
zocine to form ketocyclazocine also produced a decrease
in affinity for κ, µ, and δ receptors.34 Second, the further
substitution of N-cyclopropylmethyl to N-furfurylmethyl
to form 4a increased binding affinities to κ, µ, and δ
receptors. Thus, 4a retained high affinity for opioid
receptors. Interestingly, the comparable benzomorphan
1b did not retain affinity for opioid receptors.
Recent findings from our laboratory18,19 that some κ
agonists selectively decrease cocaine self-administration
by rhesus monkeys with minimal effects on food self-
administration support our further chemical and be-
havioral studies with these and other mixed κ/ µ opioids
as potential anticocaine medications.
Exp er im en ta l Section
Melting points were determined on a Thomas-Hoover capil-
lary tube apparatus and are reported uncorrected. 1H and 13C
NMR spectra were recorded on a Brucker AC300 spectrometer
using tetramethylsilane as an internal reference. All optical
rotations were measured at the sodium D line using a Rudolph
polarimeter (model DP 1A31, 10-cm cell). Elemental analyses,
performed by Atlantic Microlabs, Atlanta, GA, were within
(0.4% of theoretical values. Analytical thin-layer chromatog-
raphy (TLC) was carried out on 0.2-mm Kieselgel 60F 254
silica gel plastic sheets (EM Science, Newark) and visualiza-
tion was performed by illumination with 254-nm UV light or
by exposure to iodine vapor. Flash chromatography was used
for the routine purification of reaction products. The column
output was monitored with TLC. HPLC apparatus consisted
of a Rainin-Rabbit-HP pump, a Rheodyne injector, column
(Phenomenex Bondclone C18, 3.9 × 300 mm; or EMerk
Aluspher RP select B250-4), and a variable wavelength UV
detector.
(-)-3-Meth oxy-N-m eth ylm or p h in a n (6). (-)-3-Hydroxy-
N-methylmorphinan (levorphanol) (3d ) free base was made
from levorphanol tartrate (Mallinckrodt) by treating with
NaHCO3(aq) and extraction with CHCl3. To a solution of KOH
(8 g) in water (8 mL) and EtOH (25 mL) was added a solution
of Diazald (20 g) in ether (200 mL) at 65 °C. The resulting
mixture was subjected to distillation and the ether solution of
CH2N2 was collected in an ice-bath trap. Additional ether (50
mL) was added to maintain the distillation. This process was
stopped when the distillate solution became colorless (a total
of ∼120 mL was collected). It was then added to a solution of
3d (2.4 g, 9.3 mmol) in MeOH (25 mL) in a pressure tube. The
resulting solution was sealed and allowed to stay at room
temperature overnight. Pressure was released with caution.
Solvent was removed under reduced pressure to afford crude
6 (2.5 g, 99%) (lit.35 mp 109-111 °C). TLC [CHCl3-MeOH-
NH3H2O (1% in MeOH), 80-20].
(-)-3-Hyd r oxym or p h in a n (8). The procedure of Portogh-
ese37 was modified by using phenyl chloroformate for the
synthesis of 8 from 3d in 69% yield: mp 273-274 °C (lit.37
mp 260-262 °C).
(-)-3-Hyd r oxy-N-cyclop r op ylm eth ylm or p h in a n Ma n -
d ela te ((-)-Cyclor p h a n Ma n d ela te) (3a ). To 7.1 g of 8
dissolved in 400 mL of anhydrous CH2Cl2 were added cyclo-
propanecarbonyl chloride (9.4 g) and triethylamine 64 mL. The
reaction mixture was stirred and allowed to reflux for 14 h.
After cooling, 130 mL of water and 50 mL of ice were added
and the mixture was extracted with HCl (concentrated HCl
40 mL in 300 mL H2O), washed with 200 mL of H2O, and dried
over K2CO3 and the solvent removed to yield 12.5 g of crude
diacyl compound (9a ) as an oil. Without purification, the oil
was dissolved in 385 mL of anhydrous tetrahydrofuran, and
87 mL of 1 M lithium aluminum hydride in tetrahydrofuran
was added. The mixture was stirred at room temperature
under N2 overnight. To the reaction mixture was added 44 mL
of EtOAc and the mixture was stirred for an additional 10 min,
followed by the addition of 10 mL of H2O with stirring. The
mixture was then stirred vigorously with a solution of am-
monium L-tartrate (290 g in 700 mL of H2O) for 1 h. The
aqueous layer was extracted three times with 150-mL portions
of CH2Cl2. The organic layers were combined and dried over
sodium sulfate. The solvent was removed under reduced
pressure to yield 8.9 g of an oil, to which 7 mL of EtOAc was
added and the oil triturated until crystals formed. The product
was refrigerated, filtered, and washed with small volumes of
(-)-3-Meth oxym or p h in a n (7). The N-dealkylation was
carried out by the procedure of Olfoson et al.36 A mixture of 6
(5.2 g, 19.2 mmol), R-chloroethyl chloroformate (18 mL, 166
mmol), 1,2-dichloroethane (80 mL), and NaHCO3 (2.4 g) was
allowed to reflux for 48 h. Upon filtration, the filtrate was
concentrated to dryness under reduced pressure. MeOH (500
mL) was added, and the mixture was heated to reflux for 3 h.
Solvent was removed under reduced pressure, and the remain-
ing material was taken up with CHCl3 (50 mL). It was washed
with NaOH (1.8 N, 10 mL) and water (to pH 7), dried (MgSO4),
1
and concentrated to dryness to afford an oil 7 (5.1 g, 90%). H
NMR (CDCl3, free base): δ 1-1.6 (m, 8H), 2.05 (m, 1H), 2.18
(m, 1H), 2.37 (m, 1H), 2.75 (m, 1H), 3.1-3.25 (m, 3H), 3.72
(m, 1H), 3.8 (s, 3H), 6.75-6.81 (m, 2H), 7.09-7.12 (d, J ) 8.3
Hz, 1H).
10-Keto-3-m eth oxym or p h in a n (11). To a solution of 7
(0.7 g, 2.38 mmol) in 17 mL of dilute H2SO4 (prepared by

120 J ournal of Medicinal Chemistry, 2000, Vol. 43, No. 1
Neumeyer et al.
cold EtOAc to yield 4.5 g (51.8%) of crystalline free base: mp
precipitated solid was filtered, washed with water, and dried
to give 13 g of 15 as a white solid. The t-Boc derivative 15
was dissolved in 2 N NaOH (100 mL) and was treated with
10 mL of dimethyl sulfate. The mixture was stirred at 25 °C
for 6 h and was extracted with ether (3 × 50 mL). The ether
extract was washed with 2.5 N NaOH and brine and evapo-
rated to an oil. The oil was dissolved in EtOAc (100 mL) and
mixed with 6 N HCl (100 mL) and the mixture was stirred at
50 °C for 16 h. The volatiles were removed under vacuum to
give a foam 17 as the hydrochloride salt (8 g, 80% from 15).
Dilute sulfuric acid was prepared by dissolving 54 mL of
concentrated H2SO4 in 600 mL of ice-water. Compound 17 (8
g) was dissolved in 300 mL of this acid to give an orange
solution. To this was added a solution of CrO3 (7.2 g, 72 mmol)
in 300 mL of the dilute sulfuric acid in one portion. The
resulting mixture was stirred at 100 °C for 2 h, cooled in ice,
basified with NH4OH, and extracted with ether (4 × 100 mL).
The ether extract was washed with brine, dried, and evapo-
rated to a reddish brown oil 6.0 g (82%). Without further
purification 2 g of the product 18 was O-demethylated by
treating with 25 mL of 48% HBr at reflux for 2.5 h. The
solution was evaporated and the residue was dissolved in
water and basified with NH4OH to give 900 mg of 19 as a tan
solid. A mixture of compound 19 (1.0 g, 4.3 mmol), NaHCO3
(600 mg, 7.1 mmol), S-tetrahydrofurfuryl (1R)-camphor-10-
sulfonate (10) (1.52 g, 4.80 mmol), and anhydrous DMF (50
mL) was heated at 100 °C for 16 h. DMF was removed in
vacuum and the residue in water was extracted with ether,
dried, and evaporated. The residue was purified by column
chromatography (silica gel, CH2Cl2:MeOH:NH4OH, 90:9:1) to
187.5-189 °C (lit.20 mp 187.5-189 °C).
The free base of 3a was converted to the S(+)-mandelate
salt and recrystallized from isopropyl ether/ETOH. The prod-
uct obtained 17 g, mp 189-190 °C, is a white crystalline
powder: [R]25D -7.28° (MeOH, c 1.5). Anal. (C20H27NO‚C8H8O3)
C,H,N.
(-)-3-H yd r oxy-N-cyclob u t ylm et h ylm or p h in a n S(+)-
Ma n d ela te (3b). This compound was prepared as described
for 3a from 8 and cyclobutanecarbonyl chloride to yield a
crystalline base, mp 217.5-218 °C (lit.20 mp 219.2-219.8 °C),
which was converted to the S(+)-mandelate salt 3b: mp 201-
202 °C. Anal. (C21H29NO‚C8H8O3) C,H,N.
(-)-3-H yd r oxy-N-[(S)-t et r a h yd r ofu r fu r yl]m or p h in a n
Hyd r och lor id e (3c). A mixture of 0.65 g (2 mmol) of 8, 0.79
g (2 mmol) of 10, and NaHCO3 (0.6 g, 7 mmol) in DMF (10
mL) was stirred at 120 °C for 7 h. Solvent was removed under
reduced pressure. The remaining material was taken up with
CHCl3 (15 mL) and washed with water (to neutral), and the
organic layer was concentrated to dryness. The residue was
applied to a silica gel column (30 g) and eluted with CHCl3-
1
EtOH (95/5) to afford 0.4 g (58%). H NMR (CDCl3): δ 1-1.7
(m, 6H), 1.8-2.1 (m, 5H), 2.15-2.32 (m, 3H), 2.35-2.42 (t, J
) 7.2 Hz, 1H), 2.65-2.7 (m, 3H), 2.84-2.99 (m, 2H), 3.14-
3.23 (m, 1H), 3.38-3.43 (t, J ) 7.2 Hz, 1H), 3.7-3.8 (m, 1H),
3.85-3.92 (m, 1H), 4.05-4.15 (m, 1H), 6.61-6.66 (m, 1H),
6.74-6.77 (m, 1H), 6.94-6.98 (d, J ) 7.3 Hz, 1H). Compound
3c (400 mg, 1.17 mmol) was dissolved in EtOH (2 mL) and
treated with 1 M etheral HCl (1.5 mL, 1.5 mmol). Solvent was
removed under reduced pressure. The residue 3c was recrys-
talized from EtOH-ether to afford 190 mg (42%): mp 170 °C
give 1b which was isolated as the HCl salt: yield 75 mg (5%);
1
mp 212-214 °C; [R]25 +59.0° (CH3OH, c 0.2). H NMR (CD3-
dec; [R]25 -33.6° (MeOH, c 0.8). Anal. (C21H29NO2‚HCl‚
D
D
OD): δ 0.97-0.99 (d, 3H), 1.51 (s, 3H), 1.53-1.65 (m, 1H),
1.75-1.85 (br d, 1H), 1.9-2.0 (m, 2H), 2.1-2.5 (m, 3H), 2.78-
2.9 (m, 1H), 2.96-3.1 (m, 1H), 3.22-3.35 (m, 3H), 3.8-4.0 (m,
2H), 4.04 (br s, 1H), 4.55-4.65 (m, 1H), 6.84-6.87 (m, 2H),
7.95-8.0 (d, 1H). Anal. (C19H25NO3‚HCl‚0.25C4H10O) C,H,N.
0.25H2O) C,H,N.
(-)-(S)-Tetr a h yd r ofu r fu r yl (1R)-Ca m p h or -10-su lfon a te
(10).21 A solution of (1R)-camphor-10-sulfonyl chloride (75 g,
300 mmol) in 60 mL of anhydrous pyridine was stirred in an
ice bath. To this solution was added tetrahydrofurfuryl alcohol
(30.6 g, 300 mmol) dropwise over a period of 25 min. The
resulting mixture was stirred at 25 °C for 20 h. Then the
mixture was poured into 600 mL of ice-water, extracted with
3 × 250 mL of ether. The combined ether layer was washed
with 1 × 100 mL of water, 2 × 100 mL of 2 N HCl, and brine,
dried, and evaporated. The residue was recrystallized from
CCl4-petroleum ether (35-65 °C). After three crystallizations
18.1 g (16%) of (-)-(S)-tetrahydrofurfuryl (1R)-camphor-10-
Det er m in a t ion of K1 Va lu es a t µ, δ, a n d K Op ioid
Recep tor s. Guinea pig brain membranes were prepared from
frozen guinea pig brains, obtained from Harlan Bioproducts
(Indianapolis, IN). Brains were thawed and homogenized in
10 times the wet weight of tissue in cold 50 mM Tris-HCl, pH
7.5, followed by centrifugation at 39000g for 20 min at 4 °C.
The membranes were resuspended in the original volume of
buffer and incubated at 37 °C for 30 min, followed by
centrifugation at 39000g for 20 min at 4 °C. The membranes
were resuspended at a protein concentration of 8-12 mg/mL
in 50 mM Tris-HCl, pH 7.5, and stored at -80 °C until use.
The protein concentration of membranes was determined by
the method of Bradford,38 using bovine serum albumin as
standard.
sulfonate was obtained: mp 66-67 °C; [R]25 -14.7° (MeOH,
D
c 1).
(-)-10-Keto-3-h yd r oxy-N-[(S)-tetr a h yd r ofu r fu r yl]m or -
p h in a n Hyd r och lor id e (4a ). A mixture of 13 (1.5 g, 4.4
mmol), 10 (1.54 g, 4.8 mmol), and NaHCO3 (0.74 g, 8.8 mmol)
in DMF (15 mL) was stirred at 120 °C for 12 h. Solvent was
removed under reduced pressure. The residue was taken up
with CHCl3 (25 mL), washed with NH4Cl (10%, 10 mL) to pH
5, followed by washing with water (2 × 20 mL). The CHCl3
layer was separated and concentrated to dryness under
reduced pressure. Column separation (silica gel, 45 g) eluting
with CHCl3-EtOH (96/4) afforded 4a (290 mg, 19%). 1H NMR
(CDCl3): δ 1.04-1.68 (m, 6H), 1.78-2.09 (m, 4H), 2.14-2.31
(m, 2H), 2.39 (t, J ) 9.7 Hz, 1H), 2.64-2.8 (m, 3H), 2.85-2.99
(m, 2H), 3.15-3.24 (m, 1H), 3.39 (t, J ) 6.4 Hz, 1H), 3.7-3.79
(m, 1H), 3.85-3.93 (m, 1H), 4.05-4.14 (m, 1H), 6.62-6.77 (m,
1H), 6.74 (m, 1H), 6.94-6.97 (d, J ) 7.4 Hz, 1H). Compound
4a (290 mg, 0.85 mmol) was dissolved with EtOH (1.5 mL)
and treated with etheral HCl (1 M, 0.9 mL, 0.9 mmol). Solvent
was removed to dryness. The residue was recrystalized from
EtOH-ether to afford 4a HCl (200 mg, 62%): mp 255 °C dec;
Guinea pig brain membranes, 500 µg of membrane protein,
were incubated with 12 different concentrations of the com-
pound in the presence of either 0.25 nM [3H]DAMGO (µ), 0.2
nM [3H]naltrindole (δ), or 1 nM [3H]U69,593 (κ) in a final
volume of 1 mL of 50 mM Tris-HCl, pH 7.5 at 25 °C. Naloxone
at
a final concentration of 1 µM was used to measure
nonspecific binding. Samples incubated with either [3H]-
DAMGO or [3H]U69,593 were incubated at 25 °C for 60 min.
To measure binding to δ receptors, 5 mL of MgCl2 and 1 mM
PMSF were included with [3H]naltrindole and the test com-
pound. These samples were incubated at 25 °C for 3 h. Binding
was terminated by filteirng samples through Schleicher &
Scheull No. 32 glass fiber filters. The filters were subsequently
washed three times with 3 mL of cold 50 mM Tris-HCl, pH
7.5, and were counted in 2 mL of Ecoscint A scintillation fluid.
For [3H]naltrindole and [3H]U69,593 binding, the filters were
soaked in 0.25% poly(ethylenimine) for at least 60 min before
use.
25
[R]D -0.13° (MeOH, c 0.75). Anal. (C21H28NO3HCl‚0.25H2O)
C,H,N.
(+)-N -[(S )-Te t r a h yd r ofu r fu r yl]-8-k e t o-n or -m e t a zo-
cin e (1b). A mixture of (-)-nor-metazocine (RBI) (14) (11.6
g, 40 mmol) and K2CO3 (11 g, 80 mmol) in water (160 mL)
was stirred at 25 °C. To this was added a solution of di-tert-
butyl dicarbonate (8.7 g, 40 mmol) in dioxane (80 mL) dropwise
and the stirring was continued at 25 °C for 16 h. The
IC50 values were detrmined using the least-squares fit to a
logarithm probit analysis reported by Cheng and Prusoff.39 The
Kd values for [3H]DAMGO, [3H]naltrindole, and [3H]U69,593
binding to guinea pig membranes were 0.45, 0.086, and 0.46
nM, respectively.

Morphinan and Benzomorphan Derivatives
J ournal of Medicinal Chemistry, 2000, Vol. 43, No. 1 121
Mou se An tin ocicep tive Assa ys. All antinociceptive ex-
periments used male, ICR mice (20-24 g; Harlan Sprague-
Dawley, Inc., Indianapolis, IN). Mice were kept in groups of 8
in a temperature-controlled room with a 12-h light-dark cycle.
Food and water were available ad libitum until the time of
the experiment. Intracerebroventricular injections were made
directly into the lateral ventricle according to the modified
method of Haley and McCormick.40 The volume of all icv
injections was 5 µL, using a 10-µL Hamilton microliter syringe.
The mouse was lightly anesthetized with ether, an incision
was made in the scalp, and the injection was made 2 mm
lateral and 2 mm caudal to bregma at a depth of 3 mm.
these κ agonists was suggested by the late Sydney
Archer to whom this manuscript is dedicated.
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described in McLaughlin et al.41 The thermal nociceptive
stimulus was 55 °C water, with the latency to tail-flick or
withdrawal taken as the endpoint.42 After determining control
latencies, the mice received graded icv doses of either 3a or
3b. Morphine sulfate, DPDPE, U50,488, 3a , and 3b were given
as single icv injections with antinociceptive effect measured
20 min after injection. In the antagonist study, various doses
of 3a and 3b were co-administered with 3 nmol of morphine
by icv injection, 20 min before testing. In the receptor selectiv-
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that time, the tail was removed from the water and the animal
assigned a maximal antinociceptive score of 100%. Mice who
showed no response within 5 s in the initial control test were
eliminated from the experiment. At each time point, antinoci-
ception was calculated according to the following formula: %
antinociception ) 100 × (test latency - control latency)/(15 -
control latency).
Mou se Wr ith in g Assa y. Since antinociception of κ opioid
agonists has been difficult to evaluate in the tail-flick test,25
we also investigated the action of 3a ,b in the mouse acetic
acid writhing test, which was performed as described in Xu et
al.43 After receiving graded icv doses of opioid agonists and
antagonists at various times, an ip injection of 0.6% acetic acid
(10 mL/kg) was administered to each mouse. Five minutes
after administration, the number of writhing signs displayed
by each mouse was counted for an additional 5 min. Antinoci-
ception for each tested mouse was calculated by comparing
the test group to a control group in which mice were treated
with icv vehicle solution.
Sta tistics. IC50 values for the radioligand binding experi-
ments were calculated by least-squares fit to a logarithm probit
analysis. Saturation [3H]DAMGO binding data were analyzed
by nonlinear regression analysis using the LIGAND program.44
All dose-response lines were analyzed, using the regression
methods described by Tallarida and Murray.45 Regression
lines, D50 (dose producing 50% antinociception) values, and
95% confidence limits were determined with each individual
data point.45 All data points shown are the mean of 7-10 mice,
with standard error of the mean represented by error bars.
Ch em ica ls. [3H]DAMGO (60 Ci/mmol) and [3H]U69,593 (64
Ci/mmol) were purchased from Amersham (Arlington Heights,
IL). [3H]Naltrindole (40 Ci/mmol) was obtained from New
England Nuclear (Boston, MA). Morphine sulfate was pur-
chased from Mallinckrodt Chemical Co. (St. Louis, MO).
DPDPEP, U50,488, nor-BNI, ICI 174,964, and â-FNA were
purchased from Research Biochemicals International (Natick,
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Ack n ow led gm en t . Supported by NIDA Grants
DA00360, U-19-DA11007, and K05-DA00101 and from
funds provided by Dr. Saal van Zwanenbergstichtung
to Raoul Fisser. Levorphanol tartrate was generously
donated by Mallinckrodt Inc. The capable technical
assistance of Bregiete Luinge and Raoul Fisser is also
gratefully acknowledged. The synthesis of a number of

122 J ournal of Medicinal Chemistry, 2000, Vol. 43, No. 1
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