Structural determinants of opioid activity in derivatives of 14-aminomorphinones: Effects of changes to the chain linking of the C 14-amino group to the aryl ring

Article abstract of DOI:10.1021/jm060595u

The 14-aminodihydromorphinone and codeinone series of opioid ligands have produced a number of ligands of substantial interest. To investigate the importance of the 14-substituent, a series of analogues in which the side chain length is varied and the ami

Full text of DOI:10.1021/jm060595u

6104
J. Med. Chem. 2006, 49, 6104-6110
Structural Determinants of Opioid Activity in Derivatives of 14-Aminomorphinones: Effects of
Changes to the Chain Linking of the C14-Amino Group to the Aryl Ring
David Rennison,†, Humphrey Moynihan,‡,§ John R. Traynor,| John W. Lewis, and Stephen M. Husbands*,
UniVersity of Bristol, Cantock’s Close, Bristol, BS8 1TS, United Kingdom, Department of Pharmacology, UniVersity of Michigan, Michigan
48109, and Department of Pharmacy and Pharmacology, UniVersity of Bath, Bath, BA2 7AY, United Kingdom
ReceiVed May 18, 2006
The 14-aminodihydromorphinone and codeinone series of opioid ligands have produced a number of ligands
of substantial interest. To investigate the importance of the 14-substituent, a series of analogues in which
the side chain length is varied and the amide and alkene functions are reduced have been prepared. Binding
affinity, particularly at the µ-opioid receptor (MOR), was largely determined by the aromatic group of the
side chain. In the [35S]GTPγS functional assay, the ligands having a three-carbon side chain were more
potent antagonists than their longer chain counterparts, while shorter, two-carbon chain analogues were of
higher MOR efficacy, an effect that was confirmed in vivo. Wash-resistant binding was observed within
this series and appeared to be unrelated to side-chain length.
Introduction
Among the close structural analogues of the opium alkaloids
morphine (1a) and codeine (1b), the dihydromorphinones (2)
have provided the major opportunities for therapeutic analogues
and the starting materials for a series of opioid ligands selective
for the individual types of opioid receptors.1 Introduction of a
hydroxyl at C14 provided the therapeutic analgesics oxymor-
phone (2a) and oxycodone (2b), but importantly, also in
naloxone (2c) and naltrexone (2d), the first “pure” opiate
antagonists2 that have become indispensable pharmacological
tools with therapeutic utility in treating narcotic overdose
(naloxone) and in maintenance therapy for opiate dependence
and alcoholism (naltrexone).3,4
For a number of years, we have studied derivatives in the
formally similar 14-aminodihydromorphinone series (3) and, in
particular, the cinnamoylamino derivatives (4).5 The lead com-
poundsfromthisseriesclocinnamox(C-CAM,4a)6,7andmethocin-
namox (M-CAM, 3b)8 are important pharmacological tools as
selective irreversible antagonists for the µ-opioid receptor (MOR),
having the advantage over the prototype MOR-irreversible anta-
gonist â-FNA that they have no short-term agonist activity. The
codeinone (MC-CAM, 5a) equivalent of 4a had long-duration
potent antinociceptive activity and, when this had waned,
irreversible MOR antagonist activity similar to that of 4a.9
Chemistry
This report relates to analogues of 4a and 5a, in which the
N-Cyclopropylmethyl-14â-amino-7,8-dihydronormorphino-
side chain has been extended or shortened (4f,k, 5e,f,k), together
ne (7a) and the equivalent codeinone (7b) were prepared via
with the equivalent ligands in which the side chain amide
ketals (6) from thebaine using established procedures (Scheme
function (-NHCO-) has been reduced to the equivalent amine
(-NHCH2-) (4h,i,l, 5h,i,l) and those having the alkene moiety
reduced (4g,j, 5g,j). Also included are the close relatives of 4a
and 5a with saturated side chains (4b, 5b) and with the amide
carbonyl reduced (4c,d, 5c,d), which were prepared earlier but
not reported in any detail.10
1).11,12 Acylated codeinone derivatives 5b, 5f, 5g, and 5k were
prepared from 7b and the appropriate acid chloride. Their
phenolic counterparts 4f, 4g, and 4k were prepared from 7a by
bisacylation with subsequent hydrolysis of the C3-phenolic ester
or for 4b by 3-O-demethylation of 5b (Scheme 1).
Direct alkylation of 7a and 7b using the corresponding alkyl
bromides gave target compounds 4h, 5h, 4l, and 5l (Scheme
1). Direct alkylation of ethylene ketals 6a and 6b, with
subsequent deprotection of the carbonyl group under acidic
conditions, gave the 14â-alkylaminocodeinone/morphinone
analogues 4i, 5i, 4j, and 5j. In these latter cases, this two-stage
strategy gave superior results to the direct alkylation of 7a and
7b (Scheme 1). Compound 6a was also used in the preparation
of 5d. Acylation of 6a to give 8, followed by LiAlH4 reduction
* Corresponding author. Tel.: 44 (0)1225 383103. Fax: 44 (0)1225
386114. E-mail: s.m.husbands@bath.ac.uk.
† Current address: Department of Chemistry, The University of Auck-
land, Auckland, New Zealand.
‡ Current address: Department of Chemistry, University College Cork,
Cork, Ireland.
§ University of Bristol.
| University of Michigan.
University of Bath.
10.1021/jm060595u CCC: $33.50 © 2006 American Chemical Society
Published on Web 09/06/2006

Structural Determinants of Opioid ActiVity
Journal of Medicinal Chemistry, 2006, Vol. 49, No. 20 6105
a
Scheme 1
a Reagents and conditions: (i) BBr3, DCM, -30 °C to rt, 0.5 h, 40% (6a to 6b) or 40% (7b to 7a); (ii) HCl (6 N), MeOH, reflux, 5 h, 50%; (iii) (a) alkyl
bromide, K2CO3, DMF, 90 °C, 24 h; (b) HCl (6 N), MeOH, reflux, 5 h; (iv) acid chloride, NEt3, DCM, rt, overnight; (v) K2CO3, MeOH, rt, overnight; (vi)
alkyl bromide, K2CO3, DMF, 90 °C, 3 h; (vii) LiAlH4, THF, reflux overnight, then HCl (1 N), MeOH, reflux, 5 h, 53%.
Scheme 2a
a Reagents and conditions: (i) (EtO)2P(O)CH2COCl, THF, -20 °C to rt, 0.5 h, 60%; (ii) (a) LDA, THF, -78 °C, 0.5 h, (b) 4-chlorophenylacetaldehyde,
THF, -78 °C to rt, 1 h, 28%.
of the amide and deprotection of the C6-carbonyl, gave 5d,
which could then be 3-O-demethylated to yield 4d.
fold) than that of the equivalent morphinones, as was DOR
affinity (e71-fold). Thus, the codeinones showed significant
MOR over DOR selectivity (e64-fold). MOR over KOR
selectivity was generally modest, but the four-carbon chain
arylalkyl substituents in 5i and 5j conferred a MOR selective
profile, and the three-carbon chain analogues 5c and 5d were
even more selective for MOR (Table 1).
Having discovered that 4-(4′-chlorophenyl)-2-butenoic acid
(10) could not readily be isolated, owing to its preference to
isomerize to 9, an alternative strategy to the routine acylation
approach was required for the preparation of 5e (Scheme 2).
The protocol selected involved the formation of the R,â-
unsaturated amide via a Horner-Wadsworth-Emmons-type
reaction.13 Acylation of 7b using diethoxyphosphorylacetyl
chloride14,15 afforded 11. Treatment of 11 with LDA at low
temperature in the presence of 4-chlorophenylacetaldehyde
afforded 5e exclusively in the (E)-configuration.
Compounds 4a and 5a with a three-carbon chain C14
substituent have similar MOR and DOR affinities (Table 1),
but the KOR affinity of 5a is 12-fold lower than that of 4a.
The equivalent new ligands, with a four-carbon side chain (4f,
5e, 5f), generally had similar binding affinities to 4a and 5a,
with the notable exception that the DOR affinity of 5e was 50-
fold lower and the DOR affinity of 5f was more than 20-fold
lower than that of 5a. Among the new ligands there was
relatively little effect on OR binding affinities resulting from
differences of chain length, though the new three-carbon chain
derivatives (4b, 4d, 5b, 5d) generally showed higher affinity
than their two- and four-carbon equivalents (4g, 4j, 4k, 4l, 5g,
5j, 5k, 5l). There was a similar lack of substantial effect from
introducing unsaturation into the side chain and replacing NHCO
in the side chain with NHCH2. It can be concluded that the
predominant entity in the side chain for OR binding affinity is
the aromatic group. The affinities of naltrexone (3d) were 25-
fold (DOR), 320-fold (KOR), and 430-fold (MOR) greater than
those of its 3-O-methyl ether (3e; Table 1). The big loss of KOR
and MOR affinities resulting from 3-O-methylation of naltrexone
is in sharp contrast to the modest differences in KOR and MOR
Results and Discussion
Affinity for the individual types of opioid receptors (OR) was
determined in displacement binding assays in recombinant
human opioid receptors transfected into chinese hamster ovary
(CHO) cells; the displaced selective radioligands were [3H]-
DAMGO (MOR), [3H]U69593 (κ; KOR), and [3H]Cl-DPDPE
(δ; DOR).16 All the morphinone and codeinone ligands had high
affinity for MOR, with the morphinones (4) having modestly
higher (e6-fold) affinity than the equivalent codeinones (5;
Table 1). KOR affinity of the codeinones was also lower (e59-

6106 Journal of Medicinal Chemistry, 2006, Vol. 49, No. 20
Rennison et al.
Table 1. Binding Affinities of Ligands to Human Opioid Receptor Transfected into CHO Cellsa
Ki/nM
compd
R
X
DOR
KOR
MOR
DOR/MOR
KOR/MOR
5a
5b
5c
5d
5e
5f
5g
5h
5i
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
H
H
H
H
H
H
H
H
H
COCHdCH
CO(CH2)2
CH2CHdCH
(CH2)3
COCHdCHCH2
COCH2CHdCH
CO(CH2)3
CH2CHdCHCH2
(CH2)2CHdCH
(CH2)4
COCH2
(CH2)2
COCHdCH
CO(CH2)2
CH2CHdCH
(CH2)3
4.79 ( 0.73
5.10 ( 0.14b
44.5 ( 4.6b
31.3 ( 1.8b
242 ( 50.0
104 ( 21.7
89.4 ( 20.0
94.9 ( 21.2
24.8 ( 5.15
55.9 ( 1.67
51.9 ( 15.6
33.8 ( 1.40
2.69 ( 0.23
0.60 ( 0.00b
0.63 ( 0.08c
1.10 ( 0.00b
3.25 ( 0.28
3.85 ( 0.25
6.65 ( 0.20
2.10 ( 0.79
2.18 ( 0.30
1.51 ( 0.17
1.91 ( 0.17
10.8 ( 3.0
16.4 ( 2.54
6.50 ( 0.26b
53.6 ( 0.95b
78.6 ( 32.8b
25.2 ( 4.14
21.5 ( 4.19
7.51 ( 0.43
25.9 ( 5.9
4.78 ( 0.58
0.24 ( 0.05b
0.70 ( 0.10b
0.59 ( 0.00b
8.07 ( 1.84
8.19 ( 0.94
3.88 ( 1.07
6.76 ( 2.39
1.15 ( 0.27
2.23 ( 0.80
2.64 ( 0.91
1.33 ( 0.24
2.98 ( 0.22
0.04 ( 0.00b
0.32 ( 0.03c
0.13 ( 0.08b
1.87 ( 0.45
1.34 ( 0.05
1.89 ( 0.01
1.00 ( 0.28
0.96 ( 0.35
0.73 ( 0.00
0.86 ( 0.20
0.2 ( 0.0
1.0
21.2
63.6
53.0
30.0
12.7
23.0
14.0
21.6
25.1
19.7
25.4
0.9
15.0
2.0
8.5
1.7
2.9
3.5
2.1
2.3
2.0
3.4
27.1
76.6
133
3.1
2.6
1.9
3.8
29.1
18.6
1.0
9.8
0.5
16.2
2.8
14.6
2.6
2.2
2.0
33.5 ( 4.15
41.5 ( 7.79
2.59 ( 0.22
13.1 ( 2.29
1.41 ( 0.52
0.65 ( 0.07b
0.91 ( 0.12c
1.90 ( 0.85b
4.94 ( 1.75
2.95 ( 0.16
3.72 ( 0.05
3.69 ( 1.31
5.27 ( 2.06
1.00 ( 0.14
1.53 ( 0.05
0.4 ( 0.1
5j
5k
5l
4a
4b
4c
4d
4f
4g
4h
4i
4j
4k
4l
3d
3d
3e
COCH2CHdCH
CO(CH2)3
CH2CHdCHCH2
(CH2)2CHdCH
(CH2)4
3.7
5.5
1.4
1.8
2.0
1.5
1.5
H
H
H
H
COCH2
(CH2)2
2.2
54.0
16.2
3.2
6.5 ( 1.3b
0.6 ( 0.1b
128 ( 23
0.4 ( 0.05b
85.6 ( 0.22
Me
272 ( 72
a Data are the average from two experiments, each carried out in triplicate. Tritiated ligands were [3H]DAMGO(µ), [3H]Cl-DPDPE(δ), and [3H]U69593(κ).
3
b Binding to guinea pig brain homogenates. c Displacement of H-diprenorphine from membranes of C6mu cells, C6delta cells or CHOkappa cells.
affinities between the series of morphinones (4) and codeinones
(5). That the presence of a free 3-OH group is not necessary
for high MOR affinity in series 4 and 5, but is necessary in
naltrexone-related ligands, confirms that the C14 substituent in
4 and 5 is relatively a more important determinant of MOR
affinity than the C3 substituent.17
three-carbon chain (4a, 4b, 4d and 5a, 5b, 5d) were antagonists
at each of the opioid receptors, with the more flexible, saturated
analogues (4b, 4d and 5b, 5d) being more potent than their
cinnamoyl counterparts (4a, 5a). This was most noticeable at
MOR and KOR, with antagonist potency at DOR least affected.
Thus, 4b, 4d, and 5b were more potent than 4a and 5a by around
20-40-fold at MOR and KOR and 10-fold at DOR. Compound
5d was a slight exception, being more potent than 5a by around
5-fold at each receptor. As expected, the morphinones (4a, 4b,
4d) were of higher antagonist potency than their codeinone
counterparts (5a, 5b, 5d) at KOR and DOR, with little or no
change seen at MOR. The most striking SAR is found in
comparison of the new ligands with three-carbon side chains
(4b, 4d, 5b, 5d) with their four-carbon counterparts (4g, 4j,
5g, 5j). At each of the three opioid receptors, the three-carbon
chain analogues were very much more potent (20-150-fold)
in the functional assay than their four-carbon homologues,
suggesting that it is at three carbons that optimal antagonist
potency is reached. In fact, the addition of the extra carbon in
codeinones 5g and 5j results in the introduction of some efficacy
at KOR.
The in vitro functional profiles of the new ligands with two-
carbon chain C14 substituents were notable insofar as they were
the only ligands tested that showed significant MOR efficacy
in the [35S]GTPγS assay (Table 2). Compounds 4k, 4l, 5k, and
5l were all potent MOR partial agonists, with the phenylacetyl-
aminomorphinone (4k) having the greatest potency, with EC50
) 0.26 nM. The codeinones 5k and 5l had marginally higher
MOR efficacy than the morphinones 4k and 4l, but 4k was over
thirty times more potent than 5k. The difference in potency
In vitro OR functional activity of the new ligands was
determined in assays in which stimulation of [35S]GTPγS
binding is measured for recombinant human OR transfected into
CHO cells.16,18 All the new ligands with four-carbon chain C14
substituents (4f-4j, 5e-5j) were potent MOR antagonists
(Table 2), with the codeinones having 4-7-fold lower potency
than the morphinones. The only exception was 5f, which was
equipotent as a MOR antagonist to 4f. The morphinones (4f-
4j) were also potent DOR antagonists, whereas the codeinones
were low potency DOR antagonists (5g, 5h, 5j) or low potency,
low efficacy DOR partial agonists (5f, 5i). Only the morphinones
with saturated four-carbon chains in the C14 substituent (4g, 4j)
were KOR antagonists; those with unsaturated four-carbon
chains (4f, 4h, 4i) were KOR low efficacy partial agonists of
moderate potency. The codeinones (5e-5j) were all KOR partial
agonists of generally low potency. As was found in the binding
assays, the in vitro functional profiles of the morphinones (4f-
4j) and codeinones (5e-5j) were relatively insensitive to the
change of C14-amide (NHCO) to amine (NHCH2) and to the
introduction of unsaturation into the side chain.
While the location of the double bond or degree of saturation
did not appear to greatly influence the potency of the compounds
having a four-carbon chain, differences were seen within the
series having a three-carbon chain. All the ligands having a

Structural Determinants of Opioid ActiVity
Journal of Medicinal Chemistry, 2006, Vol. 49, No. 20 6107
Table 2. Agonist and Antagonist Effects of Ligands at Opioid Receptors Measured by the [35S]GTPγS Binding Assaya
IC50/nM: % stim or Ke/nM
compd
R
X
DOR
KOR
MOR
5a
5b
5d
5e
5f
5g
5h
5i
5j
5k
5l
4a
4b
4d
4f
4g
4h
4i
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
H
H
H
H
H
H
H
H
H
COCHdCH
COCH2CH2
(CH2)3
COCHdCHCH2
COCH2CHdCH
CO(CH2)3
CH2CHdCHCH2
(CH2)2CHdCH
(CH2)4
COCH2
(CH2)2
COCHdCH
CO(CH2)2
(CH2)3
7.16 ( 0.57; ANT
0.76 ( 0.11; ANT
1.66 ( 0.17; ANT
NT
9.81 ( 0.88; ANT
0.29 ( 0.07; ANT
1.87 ( 1.00; ANT
26.2 ( 0.62; 23
106 ( 28.0; 41
0.97 ( 0.15; ANT
0.03 ( 0.003; ANT
0.12 ( 0.01; ANT
12.1 ( 0.38; ANT
1.27 ( 0.24; ANT
4.91 ( 0.54; ANT
4.98 ( 0.59; ANT
1.64 ( 0.28; ANT
1.45 ( 0.22; ANT
8.84 ( 0.22; 39
118 ( 21.0; 32
79.9 ( 6.19; ANT
96.8 ( 9.27; ANT
148 ( 47.0; 29
20.2 ( 8.3; 30
387 ( 47.0; 31
208 ( 66.0; 43
61.1 ( 6.71; ANT
88.7 ( 29.6; 32
63.0 ( 16.0; 44
0.19 ( 0.02; ANT
0.03 ( 0.006; ANT
0.02 ( 0.002; ANT
1.70 ( 0.45; ANT
1.37 ( 0.21; ANT
3.35 ( 0.42; ANT
1.17 ( 0.14; ANT
0.67 ( 0.04; ANT
2.41 ( 0.85; 50
1.59 ( 0.01; 27
5.44 ( 0.75; ANT
1000 ( 52; ANT
202 ( 47.7; 49
9.07 ( 2.53; 89
43.4 ( 11.5; 31
0.10 ( 0.006; ANT
0.003 ( 0.001; ANT
0.006 ( 0.002; ANT
13.8 ( 3.09; 33
0.59 ( 0.08; ANT
3.45 ( 0.41; 24
16.7 ( 2.34; 44
0.44 ( 0.06; ANT
1.12 ( 0.29; 23
0.34 ( 0.05; ANT
1.86 ( 0.16; ANT
410 ( 104; ANT
3.73 ( 0.91; 39
0.53 ( 0.13; ANT
0.028 ( 0.005; ANT
0.0125 ( 0.002; ANT
1.84 ( 0.32; ANT
0.87 ( 0.10; ANT
1.21 ( 0.06; ANT
0.24 ( 0.04; ANT
0.29 ( 0.01; ANT
0.26 ( 0.07; 29
COCH2CHdCH
CO(CH2)3
CH2CHdCHCH2
(CH2)2CHdCH
(CH2)4
4j
4k
4l
3d
3e
COCH2
(CH2)2
H
H
Me
1.56 ( 0.57; 34
0.59 ( 0.04; ANT
96.3 ( 18; ANT
a Values are means from five or six experiments. NT ) not tested. Efficacy is measured against the standards DPDPE (δ), U69593 (κ), and DAMGO (µ),
and antagonist potency is recorded as Ke values versus the same standards. ANT ) antagonist.
between 4l and 5l was only about 2-fold, in keeping with the
MOR affinities in the binding assays (Table 1). Compounds
4k and 4l were also potent DOR partial agonists and had potent,
very low efficacy, or antagonist KOR functional activity. The
efficacy of the phenylethylaminomorphinone (4l) for DOR and
KOR was somewhat lower than that of the phenylacetylami-
nomorphinone (4k). The equivalent codeinones (5k, 5e) had
low potency DOR partial agonist activity but, whereas 5l was
also a low potency KOR partial agonist, the phenylacetylami-
nocodeinone (5k) was a nearly full KOR agonist of significant
potency (Table 2).
Figure 1. Effect of preincubation with C-CAM (4a) followed by
extensive washing on the concentration effect curve for DAMGO in
C6 cells expressing a mu-opioid receptor.
Three of the new 14-aminodihydromorphinones (4f, 4g, 4k)
and 4a (C-CAM) were investigated in membranes from C6 cells
expressing MOR to determine whether evidence could be found
for irreversible binding to MOR. The test compound or vehicle-
treated membranes were incubated in Tris-HCl buffer for 1 h
at 25 °C, following which the membranes were collected by
centrifugation, resuspended, incubated at 37 °C to promote the
dissociation of the weakly bound ligand, and then collected by
recentrifugation and twice further washed. This procedure was
sufficient to cause complete washout of 10 µM of the reversible
antagonist naloxone (2c), whereas the test compounds (4a, 4f,
4g, 4k) remained bound to the membranes. This was confirmed
in experiments in which the test compound or vehicle-treated
membranes (15 µg) were incubated at 25 °C for 1 h with
increasing concentrations of DAMGO in the presence of
Figure 2. Effect of preincubation with C-CAM analogues (4f, 4g, 4k)
followed by extensive washing on the concentration effect curve for
DAMGO in C6 cells expressing a mu-opioid receptor.
buffered [35S]GTPγS to determine the effects of the ligand
combinations on [35S]GTPγS binding. The effects on DAMGO
concentration-effect curves for incubation with the test ligands
are shown in Figures 1 and 2. For 4a, a concentration of 10
nM had a relatively small effect in suppressing the stimulation
of [35S]GTPγS binding produced by DAMGO (Figure 1); a
concentration of 100 nM was fully effective (Figure 1). The
homologue (4f) had a similar effect as 4a at 10 nM concentra-
tion, but the phenylbutylamido derivative (4g) and phenylacetyl-

6108 Journal of Medicinal Chemistry, 2006, Vol. 49, No. 20
Rennison et al.
Experimental Section
Reagents and solvents were purchased from Aldrich or Lancaster
and used as received. Melting point: Gallenkamp MFB-595 melting
point apparatus; uncorrected. IR spectra: Perkin-Elmer 881 instru-
ment, in cm-1. NMR spectra: JEOL Lambda-270-MHz instru-
ment: 1H at 270 MHz, 13C at 67.5 MHz, δ in ppm, and J in Hz,
with TMS as an internal standard. EIMS: V.G.-Autospec instrument
equipped with a Fisons autosampler; EI at 70 eV; m/z (rel %).
Microanalysis: Perkin-Elmer 240C analyzer. Ligands were tested
as their oxalate salts, prepared by adding 1 equiv of oxalic acid to
an ethanolic solution of the compound.
Figure 3. Agonist effect of 4k compared to morphine in the 50 °C
General Procedure A: Preparation of Acid Chlorides and
the in situ Acylation of N-Cyclopropylmethyl-14â-amino-7,8-
dihydronorcodeinones/morphinones. A suspension of oxalyl
chloride (8.8 equiv) and the corresponding carboxylic acid (1.1
equiv) in anhydrous toluene was heated at reflux for 1 h. The
resulting solution was allowed to cool, and the solvent was re-
moved in vacuo. The residue was dissolved in anhydrous dichlo-
romethane and added dropwise to a solution of N-cyclopropyl-
methyl-14â-amino-7,8-dihydronorcodeinone (1 equiv) and tri-
ethylamine (1.1 equiv) in anhydrous dichloromethane, and the
mixture stirred at room temperature overnight. The solvent was
removed in vacuo, and the crude residue was purified by column
chromatography (5% CH3OH in CH2Cl2). In the acylation of
N-cyclopropylmethyl-14â-amino-7,8-dihydronormorphinone, a sec-
ond equivalent (total: 2 equiv) of the corresponding acid chlor-
ide was used to afford the bisacylated derivative. The crude resi-
due was dissolved in methanol/water (9:1) before adding potas-
sium carbonate (5 equiv), and the mixture was stirred at room
temperature overnight. The solvent was removed in vacuo, and the
crude residue was purified by column chromatography (5%
CH3OH in CH2Cl2).
General Procedure B: Alkylation of N-Cyclopropylmethyl-
14â-amino-7,8-dihydronorcodeinones/morphinones and Their
Ethylene Glycol Protected Derivatives. A stirring suspension of
N-cyclopropylmethyl-14â-amino-7,8-dihydronorcodeinone/morphi-
none or its ethylene ketal-protected derivative (1 equiv), potassium
carbonate (5 equiv), and the corresponding alkyl bromide (1.1 equiv)
in dimethylformamide was heated at 90 °C for 3-12 h. The solvent
was removed in vacuo and the crude residue purified by column
chromatography (5% CH3OH in CH2Cl2).
General Procedure C: Acid-Catalyzed Deprotection of
N-Cyclopropylmethyl-14â-amino-7,8-dihydronorcodeinone/mor-
phinone Ethylene Ketals. A solution of N-cyclopropylmethyl-14â-
amino-7,8-dihydronorcodeinone/morphinone ethylene ketal in metha-
nol and hydrochloric acid (6 N) was heated at reflux for 4 h. The
solvent was removed in vacuo and the crude residue was basified
with concentrated ammonia and extracted with dichloromethane.
The combined organic extracts were washed with water and dried
over anhydrous magnesium sulfate. The solvent was removed in
vacuo, and the crude residue was purified by column chromatog-
raphy (5% CH3OH in CH2Cl2).
N-Cyclopropylmethyl-14â-[3′-(4′′-chlorophenyl)propanamido]-
7,8-dihydronorcodeinone (5b). Compound 7b (1.57 g, 4.42 mmol)
was treated with 3-(4-chlorophenyl)propanoyl chloride (912 mg,
4.90 mmol), as described in general procedure A, to afford 5b as
a white foam (1.75 g, 3.37 mmol, 76%). Anal. (oxalate salt;
C32H35N2ClO8) C, H, N.
mouse tail-withdrawal test.
amino derivative (4k) at 10 nM concentration both produced a
greater effect than 4a (Figure 2). The effect of 4g at 1 nM was
at least as great as 4a at 10 nM (data not shown). The flattening
of the dose-response curve of an agonist in the presence of an
antagonist is an indication that the antagonist binds irreversibly
to the receptor responsible for the agonist effect,19 and in this
series, the magnitude of this effect was unrelated to side-chain
length.
The phenylacetylaminomorphinone (4k) was investigated in
vivo in the mouse tail withdrawal assay with water at 50 °C
(Figure 3).8 Compound 4k was fully active in this assay at a
dose of 1 mg/kg, representing 10 times greater potency than
morphine. The antinociceptive effect of 4k had gone by 24 h,
and at that pretreatment time, 4k did not affect the antinocicep-
tive dose-effect curve of morphine, which would have indicated
a delayed MOR-antagonist effect. The high efficacy agonist
effect of 4k in vivo is apparently at odds with its modest efficacy
(29% of DAMGO) in the [35S]GTPγS in vitro assay. However,
such disparity between activity in vitro and in vivo for lipophilic
ligands in the 14-substituted morphinone series has been noted
elsewhere.8 One explanation for this disparity is that the receptor
reserve in the 50 °C water antinociceptive assay is substantially
greater than in the MOR [35S]GTPγS assay. Differences are
also noted for antagonist activity where, for example, 4k was a
powerful noncompetitive antagonist of DAMGO in the [35S]-
GTPγS assay but had no discernible delayed antagonism in the
tail withdrawal assay. More work is needed to better understand
these disparities and whether the antagonism in vitro provides
any beneficial effects in the search for MOR agonists with
reduced abuse potential.
Conclusion
The lack of any agonist effect and the exceptional noncom-
petitive antagonism displayed in vivo by 4a cannot be explained
by covalent bond formation to the receptor20,21 but seems likely
to involve dominant lipophilic binding by the cinnamoyl
aromatic group. This could involve binding of the aromatic
group outside the helical loops of the receptor to the lipid bilayer.
In that case, the interaction could be sensitive to the length of
the C14 side chain. The data presented here indicate that, of the
new ligands that were more extensively studied in vitro, MOR
profiles of 4f and 4g, with 4 carbon C14 side chains, are similar
to that of the three-carbon chain analogues such as 4a and 4b,
whereas the ligand (4k) with a two-carbon chain is different in
having substantial MOR-agonist activity that was confirmed in
vivo. However, the in vitro data provide evidence that 4k is a
MOR partial agonist and show noncompetitive antagonist
activity in suppressing the agonist effects of the selective MOR-
agonist DAMGO. It is, therefore, unclear whether extra-helical
binding is responsible for the profile of 4a as a noncompetitive
antagonist.
N-Cyclopropylmethyl-14â-[3′-(4′′-chlorophenyl)propanamido]-
7,8-dihydronormorphinone (4b). A solution of BBr3 (17 mL, 1
M, 17 mmol) in CH2Cl2 was added at -78 °C under N2 to a solution
of 5b (1.48 g, 2.8 mmol) in CH2Cl2 (10 mL). The mixture was
allowed to warm to -20 °C and stirred for 1 h before again cooling
to -78°C and adding MeOH (30 mL). The mixture was then
basified using 2 M NaOH (to pH 12) and then neutralized with
dilute HCl. Extraction with CH2Cl2/MeOH (9:1, 3 × 20 mL), drying
(MgSO4), and evaporation gave a residue that was purified using
column chromatography (CH2Cl2/MeOH, 19:1) to yield 4b as a
white solid (990 mg, 1.98 mmol, 69%). Anal. (free base; C29H31N2-
ClO4.CH3OH) C, H, N.

Structural Determinants of Opioid ActiVity
Journal of Medicinal Chemistry, 2006, Vol. 49, No. 20 6109
N-Cyclopropylmethyl-14â-[3′-(4′′-chlorophenyl)propanamido]-
7,8-dihydronorcodeinone Ethylene Glycol Ketal (8). Compound
6a (1.65 g, 4.15 mmol), 3-(4-chlorophenyl)propanoyl chloride (0.97
g, 12.4 mmol), and NEt3 (0.58 mL) in dry CH2Cl2 (10 mL) were
stirred under N2 for 3 h before evaporation to dryness and
purification by silica gel column chromatography (CH2Cl2/MeOH,
19:1) to yield 8 as a white foam (1.92 g, 3.40 mmol, 82%).
N-Cyclopropylmethyl-14â-[3′-(4′′-chlorophenyl)propylamino]-
7,8-dihydronorcodeinone (5d). A solution of 8 (2.87 g, 5.08 mmol)
in dry THF (12 mL) was added to a suspension of LiAlH4 (500
mg, 13.0 mmol) in dry THF (33 mL) under N2. The mixture was
refluxed for 24 h and cooled, and the reaction was quenched by
the addition of Rochelle’s salt. The THF was removed in vacuo,
and CH2Cl2 and H2O were added, with the organic layer being
collected. The aqueous layer was further extracted with CH2Cl2/
MeOH (9:1, 3 × 20 mL), and the combined extracts were dried
(MgSO4) and evaporated in vacuo to give a white foam that was
immediately dissolved in MeOH (25 mL) and 1 M HCl (15 mL).
After refluxing for 5 h, the solution was cooled and neutralized
with Na2CO3, and the MeOH was evaporated. Extraction with CH2-
Cl2/MeOH (9:1, 3 × 15 mL), evaporation, and purification by silica
gel column chromatography (CH2Cl2/MeOH, 19:1) gave 5d as a
white foam (1.37 g, 2.71 mol, 53%). Anal. (oxalate; C32H37N2-
ClO7‚0.5H2O) C, H, N.
N-Cyclopropylmethyl-14â-[2′-(4′′-chlorophenyl)-ethanamido]-
7,8-dihydronormorphinone (4k). Compound 7a was treated with
2-(4′-chlorophenyl)acetyl chloride, as in general procedure A, to
afford 4k as a white solid (50 mg, 0.10 mmol, 51%). Anal. (oxalate;
C30H31N2ClO8‚0.5H2O) C, H, N.
N-Cyclopropylmethyl-14â-[2′-(4′′-chlorophenyl)-ethanamino]-
7,8-dihydronorcodeinone (5l). Compound 7b was treated with
2-(4′-chlorophenyl)ethyl iodide, as in general procedure B, to afford
5l as a pale brown solid (47 mg, 0.10 mmol, 48%). Anal. (oxalate;
C31H35N2ClO7‚0.5CH2Cl2) C, H, N.
N-Cyclopropylmethyl-14â-[2′-(4′′-chlorophenyl)-ethanamino]-
7,8-dihydronormorphinone (4l). Compound 7a was treated with
2-(4′-chlorophenyl)ethyl iodide, as in general procedure B, to afford
4l as a white solid (35 mg, 0.07 mmol, 37%). Anal. (oxalate;
C30H33N2ClO7‚0.5CH2Cl2) C, H, N.
N-Cyclopropylmethyl-14â-[4′-(4′′-chlorophenyl)-3′-butenami-
no]-7,8-dihydronorcodeinone (5i). Compound 6a was treated with
4-(4′-chlorophenyl)-3-butenyl bromide, as in general procedure B,
to afford N-cyclopropylmethyl-14â-[4′-(4′′-chlorophenyl)-3′-bute-
namino]-7,8-dihydronorcodeinone ethylene ketal as a colorless oil
(39 mg, 0.07 mmol, 50%).
This was treated as in general procedure C to afford 5i as a pale
yellow solid (21 mg, 0.04 mmol, 65%). Anal. (oxalate; C33H37N2-
ClO7‚1.5H2O) C, H, N.
N-Cyclopropylmethyl-14â-[4′-(4′′-chlorophenyl)-3′-butenami-
no]-7,8-dihydronormorphinone (4i). Compound 6b was treated
with 4-(4′-chlorophenyl)-3-butenyl bromide, as in general procedure
B, to afford N-cyclopropylmethyl-14â-[4′-(4′′-chlorophenyl)-3′-
butenamino]-7,8-dihydronormorphinone ethylene ketal as a colorless
oil (77 mg, 0.14 mmol, 44%).
This was treated as in general procedure C to afford 4i as a pale
yellow solid (36 mg, 0.07 mmol, 54%). Anal. (oxalate; C32H35N2-
ClO7‚1H2O) C, H, N.
N-Cyclopropylmethyl-14â-[4′-(4′′-chlorophenyl)-2′-butenami-
no]-7,8-dihydronorcodeinone (5h). Compound 7b was treated with
4-(4′-chlorophenyl)-2-butenyl bromide, as in general procedure B,
to afford 5h as a yellow solid (82 mg, 0.16 mmol, 79%). Anal.
(oxalate; C33H37N2ClO7‚1.5H2O) C, H, N.
N-Cyclopropylmethyl-14â-[4′-(4′′-chlorophenyl)-2′-butenami-
no]-7,8-dihydronormorphinone (4h). Compound 7a was treated
with 4-(4′-chlorophenyl)-2-butenyl bromide, as in general procedure
B, to afford 4h as a yellow solid (70 mg, 0.14 mmol, 69%). Anal.
(oxalate; C32H35N2ClO7‚1.25H2O) C, H, N.
N-Cyclopropylmethyl-14â-[4′-(4′′-chlorophenyl)-butanamino]-
7,8-dihydronorcodeinone (5j). Compound 6a was treated with
4-(4′-chlorophenyl)butyl bromide, as in general procedure B, to
afford N-cyclopropylmethyl-14â-[4′-(4′′-chlorophenyl)-butanamino]-
7,8-dihydronorcodeinone ethylene ketal as a colorless oil (51 mg,
0.09 mmol, 58%).
This was treated as in general procedure C to afford 5j as a pale
yellow solid (25 mg, 0.05 mmol, 63%). Anal. (oxalate; C33H39N2-
ClO7‚1.25H2O) C, H, N.
N-Cyclopropylmethyl-14â-[4′-(4′′-chlorophenyl)-butanamino]-
7,8-dihydronormorphinone (4j). Compound 6b was treated with
4-(4′-chlorophenyl)butyl bromide, as in general procedure B, to
afford N-cyclopropylmethyl-14â-[4′-(4′′-chlorophenyl)-butanamino]-
7,8-dihydronormorphinone ethylene ketal as a colorless oil (94 mg,
0.17 mmol, 49%).
This was treated as in general procedure C to afford 4j as a pale
yellow solid (40 mg, 0.08 mmol, 51%). Anal. (oxalate; C32H37N2-
ClO7‚1.5H2O) C, H, N.
N-Cyclopropylmethyl-14â-[3′-(4′′-chlorophenyl)propylamino]-
7,8-dihydronormorphinone (4d). Compound 5d (1.1 g; 2.2 mmol)
was treated with BBr3 (13 mL, 1 M, 13 mmol) as described for
4b. Column chromatography (CH2Cl2/MeOH, 19:1) yielded 4d as
a white solid. Anal. (oxalate; C31H35N2ClO7‚0.5H2O) C, H, N.
N-Cyclopropylmethyl-14â-[4′-(4′′-chlorophenyl)-3′-butena-
mido]-7,8-dihydronorcodeinone (5f). Compound 7b was treated
with 4-(4′-chlorophenyl)-3-butenoyl chloride, as in general proce-
dure A, to afford 5f as a pale yellow solid (68 mg, 0.13 mmol,
64%). Anal. (oxalate; C33H35N2ClO8‚0.5H2O) C, H, N.
N-Cyclopropylmethyl-14â-[4′-(4′′-chlorophenyl)-3′-butena-
mido]-7,8-dihydronormorphinone (4f). Compound 7a was treated
with 4-(4′-chlorophenyl)-3-butenoyl chloride, as in general proce-
dure A, to afford 4f as a white solid (50 mg, 0.10 mmol, 48%).
Anal. (oxalate; C32H33N2ClO8‚0.75H2O) C, H, N.
N-Cyclopropylmethyl-14â-[4′-(4′′-chlorophenyl)-butanamido]-
7,8-dihydronorcodeinone (5g). Compound 7b was treated with
4-(4′-chlorophenyl)butanoyl chloride, as in general procedure A,
to afford 5g as a yellow solid (76 mg, 0.14 mmol, 71%). Anal.
(oxalate; C33H37N2ClO8‚1H2O) C, H, N.
N-Cyclopropylmethyl-14â-[4′-(4′′-chlorophenyl)-butanamido]-
7,8-dihydronormorphinone (4g). Compound 7a was treated with
4-(4′-chlorophenyl)butanoyl chloride, as in general procedure A,
to afford 4g as a white solid (55 mg, 0.11 mmol, 53%). Anal.
(oxalate; C32H35N2ClO8‚0.75H2O) C, H, N.
N-Cyclopropylmethyl-14â-[4′-(4′′-chlorophenyl)-2′-butena-
mido]-7,8-dihydronorcodeinone (5e). To a solution of lithium
diisopropylamide [butyllithium 2.5 M in hexanes (100 µL, 0.24
mmol) and diisopropylamine (35 µL, 0.24 mmol)] in tetrahydrofuran
(1 mL) at -78 °C was added 11 (0.11 g, 0.20 mmol) in
tetrahydrofuran (1 mL), and the mixture was stirred for 0.5 h,
maintaining this temperature. A solution of 4-chlorophenylacetal-
dehyde (9; 0.04 g, 0.26 mmol) in tetrahydrofuran (1 mL) was added
dropwise at -78 °C, and the resulting mixture was stirred at room
temperature for 1 h. Water was added, and the aqueous layer was
extracted with diethyl ether and then dichloromethane. The
combined organic extracts were washed with water and dried over
anhydrous magnesium sulfate, and the solvent was removed in
vacuo. Purification by column chromatography (5% CH3OH in CH2-
Cl2) afforded 5e as a white solid (30 mg, 0.06 mmol, 28%). Anal.
(oxalate; C33H35N2ClO8) C, H, N.
N-Cyclopropylmethyl-14â-(2-diethoxyphosphoryl-1-oxoethyl)-
7,8-dihydronorcodeinone (11). To a stirring solution of N-cyclo-
propylmethyl-14â-amino-7,8-dihydronorcodeinone (7b; 140 mg,
0.40 mmol) in tetrahydrofuran (3 mL) at -20 °C was added
diethoxyphosphorylacetyl chloride (94 mg, 0.44 mmol) in tetrahy-
drofuran (1 mL). The mixture was allowed to warm and was stirred
at room temperature for 0.5 h. Water was added, and the mixture
was extracted with diethyl ether and then dichloromethane. The
combined organic extracts were washed with water, dried over
anhydrous magnesium sulfate, and the solvent was removed in
N-Cyclopropylmethyl-14â-[2′-(4′′-chlorophenyl)-ethanamido]-
7,8-dihydronorcodeinone (5k). Compound 7b was treated with
2-(4′-chlorophenyl)acetyl chloride, as in general procedure A, to
afford 5k as a white solid (70 mg, 0.14 mmol, 69%). Anal.
(C31H33N2ClO8‚1.5H2O) C, H, N.

6110 Journal of Medicinal Chemistry, 2006, Vol. 49, No. 20
Rennison et al.
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vacuo. Purification by column chromatography (5% CH3OH in CH2-
Cl2) afforded 17 as a colorless oil (128 mg, 0.24 mmol, 60%).
Acknowledgment. This work was funded through NIDA
grants DA00254 and DA07315, and the in vitro characterization
of compounds was carried out through the NIDA Abuse
Treatment Discovery Program (ATDP).
Supporting Information Available: 1H NMR, 13C NMR, mass
spectra, infrared, melting point, and microanalysis data. This
material is available free of charge via the Internet at http://
pubs.acs.org.
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