3-Deoxyclocinnamox: The first high-affinity, nonpeptide μ-opioid antagonist lacking a phenolic hydroxyl group

Article abstract of DOI:10.1021/jm0009641

The C₃-substituent in morphinan opioids is of critical importance; the 3-OH group is usually associated with very much higher affinity for μ-receptors than H or -OMe. However in this series of 14β-cinnamoylamino derivatives the codeinones (e.g.

Full text of DOI:10.1021/jm0009641

3348
J . Med. Chem. 2000, 43, 3348-3350
3-Deoxyclocin n a m ox: Th e F ir st High -Affin ity, Non p ep tid e µ-Op ioid An ta gon ist
La ck in g a P h en olic Hyd r oxyl Gr ou p
Ian Derrick,† Claire L. Neilan,‡ J ennifer Andes,‡ Stephen M. Husbands,† J ames H. Woods,‡
J ohn R. Traynor,‡ and J ohn W. Lewis*,†
School of Chemistry, University of Bristol, Bristol BS8 1TS, U.K., and Department of Pharmacology, University of Michigan,
Ann Arbor, Michigan
Received April 5, 2000
The C3-substituent in morphinan opioids is of critical importance; the 3-OH group is usually
associated with very much higher affinity for µ-receptors than H or -OMe. However in this
series of 14â-cinnamoylamino derivatives the codeinones (e.g. methoclocinnamox, MC-CAM)
had unexpectedly high µ-opioid receptor affinity, similar to that of the morphinone (clocinnamox,
C-CAM). The current report relates to the synthesis and in vitro evaluation of deoxyclocinnamox
(DOC-CAM) which acted as a high-affinity opioid antagonist similar to C-CAM but with greater
µ selectivity. Thus it appears that the C3-substituent does not play a major role in the binding
of the 14â-cinnamoyl series and that the cinnamoyl group itself may in fact be the dominant
binding feature.
In tr od u ction
The phenolic hydroxyl group in morphine (1) and
related series of opioids is recognized as one of the key
structural features for binding to the µ-receptor and for
in vivo opioid activity. The µ binding of equivalent
methyl ethers is very much lower with codeine (2)
having 200-fold lower affinity than morphine.1 When
the phenolic hydroxy was removed to give 3-deoxymor-
phine (3), binding was also markedly reduced (30-fold)
though in vivo antinociceptive potency was much less
one (7),2 protected as the formylamino derivative 8, was
affected (3-8-fold).3 The relationship between morphi-
3-O-demethylated with boron tribromide10 to the mor-
none (3-OH) and codeinone (3-OMe) in the 14â-cin-
phinone 9 and converted to the phenyltetrazolyl ether
namoylamino series is unusual as exemplified by clo-
10. Hydrogenolysis11 afforded the 3-deoxy-14-formyl-
cinnamox (C-CAM, 4) and methoclocinnamox (MC-
aminomorphinone derivative 11 which was hydrolyzed
CAM, 5).4,5 The latter has very high affinity for µ-opioid
and re-acylated to give DOC-CAM (6) in 13% yield over
receptors, very similar to that of C-CAM. Thus the
six steps. The oxalate salt of 6 was formed prior to
cinnamoylamino group appeared to have a greater
pharmacological testing.
influence on opioid binding than the presence of a
phenolic hydroxyl group. It could be active as a Michael
Resu lts a n d Discu ssion
acceptor in forming a covalent bond to a receptor thiol
The affinity and selectivity of DOC-CAM for the three
group, but in vitro investigation failed to demonstrate
types of opioid receptor were determined in a displace-
such activity.2 Nevertheless C-CAM, MC-CAM, and
ment binding assay in monkey brain membranes in
their analogues display irreversible µ-antagonist actions
which the displaced radioligands were [3H]DAMGO (µ),
in in vitro and in vivo assays of opioid function.2,7,12-16
[3H]DPDPE (δ), and [3H]U69593 (κ).6 DOC-CAM bound
It was thus of interest to synthesize and evaluate
with very high affinity at µ-receptors (Ki 0.54 nM) with
deoxyclocinnamox (DOC-CAM, 6) to determine whether
lower affinity for δ (Ki 36.8 nM) and κ (Ki 11.9 nM)
high affinity for µ-receptors is maintained when there
receptors (Table 1). Though data in monkey brain
is no 3-oxygen function to form a hydrogen bond to the
binding assays are not available for C-CAM and MC-
receptor. We here report the synthesis of DOC-CAM and
CAM, comparable data for opioid binding in a mouse
its evaluation in displacement binding and in vitro
brain membrane preparation have been reported.7 The
Ki values for µ-receptor binding were 0.25 and 0.46 nM
functional assays.
for C-CAM and MC-CAM, respectively. It is thus clear
that DOC-CAM, as well as MC-CAM, has unusually
Syn th esis
The procedure shown in Scheme 1 was followed.
N-Cyclopropylmethyl-14â-amino-7,8-dihydronorcodein-
high µ affinity. The functional activity of DOC-CAM at
µ-receptors was determined for stimulation of [35S]-
GTPγS binding in cloned human µ-opioid receptors
transfected into a rat glioma cell line.8 DOC-CAM failed
to stimulate the binding of [35S]GTPγS up to a concen-
tration of 1 µM. A similar result was found with C-CAM,
* To whom correspondence should be addressed. Tel: 44 117 928
9933. Fax: 44 117 929 8611. E-mail: J .Lewis@bristol.ac.uk.
† University of Bristol.
‡ University of Michigan.
10.1021/jm0009641 CCC: $19.00 © 2000 American Chemical Society
Published on Web 08/09/2000

Brief Articles
J ournal of Medicinal Chemistry, 2000, Vol. 43, No. 17 3349
Sch em e 1a
a
(i) HCO2H, acetic anhydride; (ii) BBr3, DCM; (iii) 5-Cl-1-phenyltetrazole, K2CO3, DMF; (iv) 10% Pd/C, AcOH, 45 psi H2; (v) 4 N HCl,
reflux; (vi) p-Cl-cinnamoyl chloride, NEt3, CH2Cl2.
Ta ble 1. Binding of DOC-CAM, C-CAM, and MC-CAM to
Opioid Receptors
Ki (nM)
compound [3H]DAMGO (µ) [3H]DPDPE (δ) [3H]U69593 (κ)
DOC-CAM, 6 0.54 (0.32-0.91) 36.8 (34.0-43.2) 11.9 (9.7-14.2)
C-CAM, 4a
0.25
1.6
4.5
7.2b
29b
MC-CAM, 5a 0.46
a
b
Values taken from ref 7 (no confidence limits given). Dis-
placement of [3H]bremazocine in the presence of 1 µM DAMGO
and 1 µM DPDPE.
Exp er im en ta l Section
Infrared spectra were obtained on a Perkin-Elmer 881
spectrophotometer. The proton (300 MHz) and carbon-13 (75
MHz) NMR spectra were obtained on a J EOL J NM-GX FT
300 MHz spectrometer at 20 °C in CDCl3 unless otherwise
stated. Tetramethylsilane was used as the internal standard.
Mass spectra were obtained on a Fisons Autosampler instru-
ment with electron impact ionization (70 eV). Melting points
were determined on a Reicher hot-stage microscope and are
uncorrected. Elemental analyses were obtained on a Perkin-
Elmer 240C analyzer. All reagents were used as supplied by
Aldrich. Column chromatography employed flash silica gel
(Fluka, Silica gel 60). Thin-layer chromatography was per-
Ta ble 2. Antagonism of the µ-Opioid Agonist Fentanyl in the
[
35S]GTPγS Assay
DOC-CAM, 6
0.28 ( 0.13
C-CAM, 4
MC-CAM, 5
6.37 ( 2.7
Ke (nM)
0.37 ( 0.17
but MC-CAM acted as a very weak partial agonist
having a maximum stimulation of 12% relative to the
full µ-agonist fentanyl. All the cinnamoylamino deriva-
tives were able to antagonize the action of fentanyl in
this preparation with Ke values of 0.28, 0.37, and 6.37
nM, respectively, for DOC-CAM, C-CAM, and MC-CAM.
Thus DOC-CAM in these in vitro binding and func-
tional assays is a high-affinity µ-antagonist equivalent
to C-CAM but more selective. The very similar µ-opioid
receptor affinities displayed by all members of the
C-CAM series suggest that the cinnamoyl side chain is
now the dominant binding motif, certainly of more
importance than the phenolic hydroxyl. The only other
µ-antagonists lacking a 3-phenol group are cyprodime
(13) and its 14-O-benzyl analogue (14). However the in
vitro µ-antagonist potency of cyprodime is 200-fold lower
and that of the O-benzyl analogue over 40-fold lower
than that of DOC-CAM which is thus the first nonphe-
nolic, high-affinity µ-antagonist to be reported.9
formed on aluminum sheets coated with silica gel F254
.
N-Cyclop r op ylm eth yl-14-for m a m id ocod ein on e (8). A
solution of 7 (4.42 g, 12.5 mmol) in formic acid (97%, 45 mL)
was stirred at 5 °C under nitrogen. Acetic anhydride (18 mL,
180 mmol) was added dropwise and the yellow solution stirred
for a further 4 h before quenching with NH4OH and extracting
with DCM (3 × 100 mL). The combined organics were dried
(Na2SO4) and the solvent was removed in vacuo to leave a
cream foam. The product was purified by column chromatog-
raphy (5-10% MeOH:DCM): yield 3.82 g (66%); Rf 0.35 (10%
MeOH:DCM); EIMS m/z 382 (M+, 70%); δH 8.37 (1 H, d, J )
2 Hz, NCHO), 6.81 (1 H, br, s, NHCO), 6.72 (1 H, d, J ) 8 Hz,
2-H), 6.63 (1 H, d, J ) 8 Hz, 1-H), 4.94 (1 H, s, 5-H), 3.88 (3 H,
s, 3-OCH3); δC 207.50, 162.10, 145.34, 142.96, 128.46, 125.07,
119.11, 114.97, 89.77, 60.19, 59.35, 56.83, 56.56, 48.53, 44.06,
37.00, 30.55, 29.98, 21.41, 9.43, 4.10, 3.66; HRMS calcd for
C
22H26N2O4 382.1893, found 382.1885.

3350 J ournal of Medicinal Chemistry, 2000, Vol. 43, No. 17
Brief Articles
N-Cyclop r op ylm eth yl-14-for m a m id om or p h in on e (9). A
solution of 8 (4.53 g, 11.86 mmol) in dry DCM (100 mL) was
cooled to -30 °C under an atmosphere of nitrogen. Boron
tribromide solution (100 mL, 1 M, 100 mmol) was added
dropwise and the reaction stirred at this temperature for 4 h
before allowing to come to room temperature over 0.5 h. The
solution was poured onto a 1:1 mixture of ice and concentrated
ammonium hydroxide (200 mL) and stirred for 15 min. After
extraction with 3:1 DCM:MeOH (3 × 250 mL) the combined
organics were dried (Na2SO4) and the solvent was removed
under reduced pressure to yield the crude product which was
purified by column chromatography (2-5% MeOH:DCM):
yield 3.30 g (76%); mp 220 °C dec; Rf 0.23 (10% MeOH:DCM);
EIMS m/z 368 (M+, 100%); δH complex due to presence of
rotomers; δC 208.14, 161.09, 143.48, 139.29, 128.39, 124.19,
119.05, 117.23, 88.54, 58.94, 56.76, 48.38, 43.56, 36.23, 29.05,
28.15, 21.22, 9.27, 3.74, 3.53; HRMS calcd for C21H24N2O4
368.1736, found 368.1734.
mL, 11.5 mmol) followed by 4-chlorocinnamoyl chloride (0.92
g, 4.6 mmol) dropwise, as a solution in DCM (5 mL). After 3.5
h of vigorous stirring the solvent was removed in vacuo. The
crude product was purified by column chromatography (2.5%
MeOH:DCM): yield 0.69 g (62%); mp 117-119 °C; Rf 0.53 (5%
MeOH:DCM); νmax 3321 (NHCO), 1718 (CO), 1673 (NHCO)
cm-1; EIMS m/z 488 (M+, 60%); δH 7.58 (1 H, d, J ) 16 Hz,
CdCH), 7.46 (2 H, m, Ph), 7.38(1 H, br, s, NHCO), 7.34 (2 H,
m, Ph), 7.10 (1 H, m, 3-H), 6.72 (2 H, m, 2-H and 1-H), 6.58 (1
H, d, J ) 16 Hz, CdCH), 4.95 (1 H, s, 5-H); δC 207.18, 166.58,
157.57, 139.99, 135.63, 133.64, 133.36, 129.53, 129.18, 129.16,
127.36, 121.79, 118.64, 107.92, 89.29, 60.29, 59.36, 56.20,
47.83, 44.04, 36.80, 30.49, 30.20, 22.21, 9.67, 4.27, 3.91; HRMS
calcd for
C29H29N2O3Cl 488.1867, found 488.1874. Anal.
(C29H29N2O3Cl‚(CO2H)2‚1.5H2O) C, H, N.
Ack n ow led gm en t. This work was supported by the
National Institute on Drug Abuse (NIDA) Grants DA
00254 and DA 07315.
N-Cyclop r op ylm eth yl-14-for m a m id o-3-(1-p h en yl-1H-5-
tetr a zolyl)m or p h in on e (10). A mixture of 9 (3.14 g, 8.53
mmol), 5-chloro-1-phenyl-1H-tetrazole (1.85 g, 10.2 mmol) and
anhydrous potasium carbonate (2.40 g, 17.07 mmol) in anhy-
drous DMF (35 mL) was stirred at room temperature for 22
h. Water (150 mL) was added and the mixture extracted with
3:1 CHCl3:MeOH (3 × 200 mL). The combined organics were
combined and dried (Na2SO4) and the solvent was removed in
vacuo. The crude product was recrystallized (×2) from MeOH
to yield off-white crystals: yield 3.19 g (73%); mp 137-139
°C; Rf 0.25 (5% MeOH:DCM); νmax (CHCl3) 3333 (NHCHO),
1721 (CO), 1693 (NHCHO) cm-1; EIMS m/z 512 (M+, 10%); δH
8.38 (1 H, d, J ) 2 Hz, NCHO), 7.50-7.90 (5 H, m, N-Ph),
7.22 (1 H, d, J ) 8 Hz, 2-H), 6.7822 (1 H, d, J ) 8 Hz, 1-H),
5.03 (1 H, s, 5-H), 3.48 (1 H, d, J ) 4 Hz, NHCO); δC 205.67,
162.21, 159.29, 146.97, 135.61, 133.00, 131.54, 130.18, 129.70,
129.67, 129.38, 122.37, 122.31, 121.57, 119.61, 90.43, 59.79,
59.25, 56.02, 48.46, 43.86, 36.52, 30.17, 29.89, 21.72, 9.18, 4.17,
3.60; HRMS calcd for C28H28N6O4 512.2172, found 512.2179.
N-Cyclop r op ylm eth yl-14-for m a m id o-3-d eoxym or p h i-
n on e (11). A mixture of 10 (2.68 g, 5.23 mmol) and 10% Pd/C
in glacial acetic acid was hydrogentaed at room temperature
at 45 psi for 72 h. The Pd/C was removed by filtration and the
acetic acid then removed in vacuo. The solid was stirred with
35% NH4OH solution, the organics were extracted with 3:1
CHCl3:MeOH and dried (Na2SO4), and the solvent was then
removed in vacuo to yield an off-white foam (column chroma-
tography, 2.5-5% MeOH:DCM): yield 1.63 g (89%); mp 171-
173 °C; Rf 0.25 (5% MeOH:DCM); νmax (CHCl3) 3336 (NHCHO)
1716 (CO), 1692 (NHCHO) cm-1; EIMS m/z 352 (M+, 80%); δH
8.38 (1 H, d, J ) 2 Hz, NCHO), 6.93-7.18 (2 H, m, 3-H and
NHCO), 6.69-6.73 (2 H, m, 2-H and 1-H), 4.91 (1 H, s, 5-H);
δC 207.95, 162.05, 157.26, 133.37, 129.23, 126.73, 118.44,
107.71, 89.00, 59.60, 59.19, 56.34, 47.58, 43.76, 36.62, 30.03,
29.82, 21.93, 9.19, 3.91, 3.55; HRMS calcd for C21H24N2O3
352.1787, found 352.1794.
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N-Cyclop r op ylm et h yl-14-a m in o-3-d eoxym or p h in on e
(12). A solution of 11 (1.04 g, 2.95 mmol) in 4 N HCl (60 mL)
was refluxed for 2 h. The solution was allowed to cool to room
temperature and made basic with 35% NH4OH solution; before
extracting with DCM (3 × 125 mL), the combined organics
were dried (Na2SO4) and the solvent was removed in vacuo to
yield an off-white foam. This was purified by column chroma-
tography (10% MeOH:DCM): yield 0.59 g (62%); mp 135-137
°C; Rf 0.11 (5% MeOH:DCM); νmax 3671 (NH), 1723 (CO) cm-1
;
EIMS m/z 324 (M+, 32%); δH 7.05 (1 H, m, 3-H), 6.73 (1 H, d,
J ) 8 Hz, 2-H), 6.67 (1 H, d, J ) 8 Hz, 1-H), 4.65 (1 H, s, 5-H);
δC 209.26, 157.32, 133.79, 128.69, 128.17, 118.53, 107.74, 89.53,
63.75, 59.47, 52.77, 49.32, 43.86, 36.48, 32.01, 29.93, 22.88,
9.46, 3.77, 3.73; HRMS calcd for C20H24N2O2 324.1838, found
324.1836.
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N-Cyclop r op ylm eth yl-14-(4-ch lor ocin n a m oyla m id o)-3-
d eoxym or p h in on e (6, DOC-CAM). To a stirred solution of
12 (0.74 g, 2.29 mmol) in DCM (15 mL) was added NEt3 (1.6
J M0009641