Identification of the first trans-(3R,4R)-Dimethyl-4-(3-hydroxyphenyl)piperidine derivative to possess highly potent and selective opioid κ receptor antagonist activity

Full text of DOI:10.1021/jm015521r

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J . Med. Chem. 2001, 44, 2687-2690
2687
Ch a r t 1
Id en tifica tion of th e F ir st tr a n s-(3R,4R)-
Dim eth yl-4-(3-h yd r oxyp h en yl)p ip er id in e
Der iva tive To P ossess High ly P oten t a n d
Selective Op ioid K Recep tor An ta gon ist
Activity
J ames B. Thomas,† Robert N. Atkinson,†
Richard B. Rothman,‡ Scott E. Fix,†
S. Wayne Mascarella,† N. Ariane Vinson,† Heng Xu,‡
Christina M. Dersch,‡ Y. -F. Lu,‡ Buddy E. Cantrell,§
Dennis M. Zimmerman,§ and F. Ivy Carroll*,†
Chemistry and Life Sciences, Research Triangle Institute,
Research Triangle Park, North Carolina 27709, Clinical
Psychopharmacology Section, NIDA/ NIH Addiction
Research Center, 5500 Nathan Shock Drive, Baltimore,
Maryland 21224, and Lilly Research Laboratories, Eli Lilly
and Company, Lilly Corporate Center, Indianapolis,
Indiana 46285
Received April 5, 2001
Abstr a ct: A structurally novel opioid κ receptor selective
ligand has been identified. This compound, (3R)-7-hydroxy-
N-((1S)-1-{[(3R,4R)-4-(3-hydroxyphenyl)-3,4-dimethyl-1-piperi-
dinyl]methyl}-2-methylpropyl)-1,2,3,4-tetrahydro-3-isoquino-
linecarboxamide (J DTic, 10) demonstrated high affinity for the
κ receptor in the binding assay (κ Ki ) 0.3 nM) and highly
potent and selective κ antagonism in the [35S]GTP-γ-S assay
using cloned opioid receptors (κ Ki ) 0.006 nM, µ/κ ratio )
570, δ/κ ratio > 16600).
In tr od u ction . Compounds that exert their actions
via the opioid receptor system have been studied
intensely for many years in an effort to eliminate the
unwanted side effects produced by the most frequently
used or abused opiates morphine (1) and heroin (2).
Among the many side effects produced by these com-
pounds, addiction, tolerance, and respiratory depression
are of greatest concern. While many agonists have been
identified for the opioid receptor system, very few
antagonists have appeared, and of these, naltrexone (3a )
and naloxone (3b) have found the greatest application
and have received the most attention particularly as it
relates to the development of receptor subtype selective
antagonists.1 By applying the message-address concept
of Schwyzer2 to naltrexone (3a ), Portoghese has devel-
oped receptor subtype selective antagonists for both the
δ and the κ opioid receptors. In the case of the δ receptor,
attachment of a properly aligned phenyl ring (δ address)
to naltrexone (the opioid message) to act as a mimic for
Phe4 of the enkephalins provided the potent and δ
selective antagonist naltrindole (NTI, 4).3
assertion has been supported by a variety of different
experiments, but perhaps the most notable example was
the demonstration that addition of a basic 5′-methyl-
eneamidino group to NTI (4) resulted in a remarkable
change of receptor preference from δ to κ for the ligand
5′-[(N2-butylamidino)methyl]naltrindole (6).5 Further
refinements of this concept lead to the discovery of 7,
C5′-guanidinylnaltrindole (GNTI), which displays even
greater potency and selectivity for the κ receptor com-
pared with its predecessors.6
From this brief review it is clear that the oxymor-
phone framework of naltrexone (3b) has provided a
reliable scaffold upon which to build receptor subtype
selective antagonists. We have studied modifications of
the trans-(3,4)-dimethyl-4-(3-hydroxyphenyl)piperidine
class of opioid antagonist such as 8a ,b as an alternate
approach to developing potent and selective κ opioid
antagonists.7-10 This class of compounds has long been
considered novel relative to the classical antagonists
such as 3a ,b because unlike the oxymorphone-based
compounds, the opioid antagonist activity in this class
of compounds (e.g., 8a ,b ) is not mediated by the
structure of the N-substituent. Thus, while only N-allyl
and N-cyclopropylmethyl substituents exhibit potent
pure antagonist activity in the oxymorphone series
The κ selectivity of the antagonist nor-binaltorph-
imine (nor-BNI, 5)4 has also been explained according
to the message-address concept. In this case, it is the
N-17′ nitrogen (marked by an asterisk in Chart 1) that
is responsible for conferring selectivity by interacting
with an acidic residue specific to the κ receptor. This
* Phone: 919 541-6679. Fax: 919 541-8868. E-mail: fic@rti.org.
† Research Triangle Institute.
‡ NIDA/NIH Addiction Research Center.
§ Eli Lilly and Company.
10.1021/jm015521r CCC: $20.00 © 2001 American Chemical Society
Published on Web 07/14/2001

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2688 J ournal of Medicinal Chemistry, 2001, Vol. 44, No. 17
Letters
Sch em e 1a
Ta ble 1. Radioligand Binding Results at the µ, δ, and κ Opioid
Receptors for Compound 9, the Standard κ Antagonist nor-BNI
(5), and the Novel κ Antagonist 10
Ki (nM ( SD)
µ
δ
κ
compd
[3H]DAMGOa [3H]DADLEb [3H]U69,593c µ/κ
δ/κ
79
5, nor-BNI 65.06 ( 5.6
86 ( 7.3 1.09 ( 0.14
>3400
301 ( 50
60
9
10
171 ( 15
3.73 ( 0.17
3.84 ( 0.26
0.32 ( 0.05
45 >885
12 940
a
[3H]DAMGO [(D-Ala2,MePhe4,Gly-ol5)enkephalin]. Tritiated
ligand selective for µ opioid receptor. [3H]DADLE [(D-Ala2,D-
Leu5)enkephalin]. Tritiated ligand selective for δ opioid receptor.
c [3H]U69,593 {[3H](5R,7R,8â)-(-)-N-methyl-N-[7-(1-pyrrolidinyl)-
1-oxaspiro[4,5]dec-8-yl]benzeneacetamide}. Tritiated ligand selec-
tive for κ opioid receptor.
b
a
Reagents: (a) Boc-D-7-hydroxy-1,2,3,4-tetrahydroisoquinoline-
3-carboxylic acid, BOP, TEA, THF; (b) TFA, CH2Cl2.
(3a ,b), all N-substituted derivatives of trans-(3,4)-di-
methyl-4-(3-hydroxyphenyl)piperidine, thus far re-
ported, show antagonist activity.7,8
Ta ble 2. Antagonist Activity of nor-BNI (5), RTI5989-29 (9),
and Compound 10 on Agonist Stimulated [35S]GTP-γ-S Binding
in Guinea Pig Caudate Membranes
Recently we reported the discovery of 9 as the first
trans-(3,4)-dimethyl-4-(3-hydroxyphenyl)piperidine ana-
logue11 to display a preference for the opioid κ receptor.
Obtained from the screening of libraries biased for
opioid antagonist activity through incorporation of
trans-(3,4)-dimethyl-4-(3-hydroxyphenyl)piperidine into
each ligand, compound 9 (RTI-5989-29) was found to be
κ selective in binding but not in functional assays.11 We
now report the discovery of (3R)-7-hydroxy-N-((1S)-1-
{[(3R,4R)-4-(3-hydroxyphenyl)-3,4-dimethyl-1-piperidi-
nyl]methyl}-2-methylpropyl)-1,2,3,4-tetrahydro-3-iso-
quinolinecarboxamide (J DTic, 10) which behaves in a
manner opposite to that observed for 9. Thus, compound
10 shows minimal µ versus κ selectivity in binding
assays but excellent selectivity and κ antagonist potency
in functional assays. A comparison of the behaviors of
compound 9, its methylenamino-bridged analogue J DTic
(10), and the prototypical κ antagonist nor-BNI (5) as
determined in biological assays is provided herein.
Ch em istr y. The synthesis of the novel antagonist 10
was accomplished by coupling the previously reported
amine 3-[1-(2S-amino-3-methylbutyl)-3R,4R-dimethyl-
4-piperidinyl]phenol (11)11 with Boc-D-7-hydroxy-1,2,3,4-
tetrahydroisoquinoline-3-carboxylic acid using benzo-
triazol-1-yl-oxy-tris-(dimethylamino)phosphonium hexa-
fluorophosphate (BOP reagent) in THF followed by
removal of the Boc-protecting group with trifluoroacetic
acid (TFA) in dry methylene chloride as shown in
Scheme 1.
apparent functional Ki
(nM ( SD)
µ
δ
κ
compd
DAMGOa
SNC-80b
U69,593c
µ/κ
δ/κ
268
96
>15000
5, nor-BNId 16.7 ( 1.5
10.2 ( 1.0 0.038 ( 0.005 439
9d
10
7.25 ( 0.52 450 ( 74.1
2.16 ( 0.75 >300
4.7 ( 0.56
1.5
0.02 ( 0.002 108
a
Apparent functional Ki (vs 10 µM DAMGO, an agonist selective
b
for µ opioid receptor). Apparent functional Ki (vs 10 µM SNC-
80, an agonist selective for δ opioid receptor). c Apparent functional
Ki (vs 10 µM U69,593, an agonist selective for κ opioid receptor).
The apparent functional Ki is calculated by the Cheng-Prusoff
equation where Ki ) IC50/(1 + [L]/ED50), and the experimentally
determined ED50 values are as follows: DAMGO, 592 nM; SNC-
d
80, 317 nM; U69,593, 684 nM. Data taken from ref 11.
Ta ble 3. Antagonist Activity of nor-BNI (5) and Compound 10
on Agonist Stimulated [35S]GTP-γ-S Binding in Cloned Opioid
Receptors
apparent functional Ki
(nM ( SD)
µ
δ
κ
compd
DAMGOa
SNC-80b
U50,488c
µ/κ
δ/κ
172
5, nor-BNI 15.8 ( 5.7
10
12.1 ( 3.1
0.07 ( 0.03
0.006 ( 0.001 570 >16600
225
3.42 ( 0.83 >100
a
Apparent functional Ki (vs 1 µM DAMGO, an agonist selective
b
for µ opioid receptor). Apparent functional Ki (vs 200 nM SNC-
80, an agonist selective for δ opioid receptor). c Apparent functional
Ki (vs 2 µM U50,488, an agonist selective for κ opioid receptor).
The apparent functional Ki is calculated as illustrated in Table 2
where the experimentally determined ED50 values are as follows:
DAMGO, 59 nM; SNC-80, 2 nM; U50,488, 24 nM.
Biologica l. The binding affinities of the novel κ
antagonist 10, the lead compound 9, and the standard
κ antagonist 5 for the µ, δ, and κ opioid receptors were
determined using competitive binding assays following
previously reported procedures (Table 1).12 In the bind-
ing assay, µ and δ receptors were obtained from rat
brain while κ receptors were obtained from guinea pig
brain. Measures of antagonism were obtained by moni-
toring the test compound’s ability to inhibit stimulation
of [35S]GTP-γ-S binding produced by the selective ago-
nists (D-Ala2,MePhe4,Gly-ol5)enkephalin (DAMGO, µ
receptor), (+)-4-[(RR)-R-(2S,5R)-4-allyl-2,5-dimethyl-1-
piperazinyl)-3-methoxybenzyl]-N,N-diethylbenzamide
(SNC-80, δ receptor), and 5R,7R,8â-(-)-N-methyl-N-[7-
(1-pyrrolidinyl)-1-oxaspiro[4,5]dec-8-yl]benzeneacet-
amide (U69,593, κ receptor) in guinea pig caudate (Table
2).13 Compounds 10 and nor-BNI (5) were further
studied in cloned human (δ, κ) and rat (µ) receptors
using the same selective agonists mentioned above with
the exception that 2-(3,4-dichlorophenyl)-N-methyl-N-
[(1R,2R)-2-(1-pyrrolidinyl)cyclohexyl]acetamide [(-)-
U50,488] was used as the selective κ agonist (Table 3).
Resu lts a n d Discu ssion . Comparison of the data for
compounds 9 and 10 (Table 1) reveals that 9 with a µ/κ
and δ/κ ratio of 45 and >885, respectively, is superior
to 10 which possesses ratios of 12 and 940. Indeed,
compound 9 possesses a µ/κ Ki ratio comparable to the
standard antagonist 5 and a far superior δ/κ Ki ratio
and is thus selective for the κ opioid receptor over either
the µ or the δ receptor. In contrast, J DTic (10) shows
very little κ versus µ selectivity in this assay relative to
the analogue 9. The principal reason for this is the 46-
fold greater affinity of 10 for the µ receptor relative to
compound 9. The difference in affinity at this site
overshadows the 10-fold improvement that 10 shows for
the κ receptor relative to 9. The overall result is that
10 possesses low κ versus µ selectivity in the binding
assay.

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Letters
J ournal of Medicinal Chemistry, 2001, Vol. 44, No. 17 2689
In the functional assay using guinea pig membranes
(Table 2), the standard antagonist nor-BNI (5) with a
Ki value of 0.038 nM shows a 28-fold increase in its κ
receptor Ki value relative to that seen in the binding
assay. At the µ and δ receptors, however, the Ki values
for nor-BNI of 16.7 nM and 10.2 nM represent only 4-
and 8.5-fold increases, respectively. Overall this trans-
lates into a significant increase in µ versus κ and δ
versus κ selectivity in this assay relative to that
observed in the binding assay.
arrangement raises the possibility that two independent
tyrosine binding subsites may exist within the κ recep-
tor.
While providing answers to these questions lies
beyond the scope of this communication, the establish-
ment of a new structural class of compounds exhibiting
potent and selective κ antagonist activity holds the
promise to expand fundamentally our understanding of
the κ receptor. Such information in turn could provide
new opportunities for the development of treatments for
substance abuse. Further studies focused on addressing
the questions and possibilities related above are cur-
rently underway and will be reported shortly.
Compound 9 also shows significant changes in be-
havior between these two assays, but these do not
parallel those found for nor-BNI (5). Instead, the trans-
(3,4)-dimethyl-4-(3-hydroxyphenyl)piperidine (9) shows
no µ versus κ selectivity compared with its 45-fold
selectivity seen in the binding assay; an effect driven
primarily by its 25-fold increase in µ receptor Ki.
Overall, compound 9 is not selective in this functional
assay and does not compare favorably with the standard
κ antagonist nor-BNI (5).
Ack n ow led gm en t. The National Institute on Drug
Abuse supported this research under Grant DA09045.
IUPAC names for the final compounds and intermedi-
ates were obtained from ACD Laboratories.
Su p p or tin g In for m a tion Ava ila ble: Data for compound
10 includes (1) HPLC trace, (2) 1H NMR spectra, and (3)
electrospray mass spectra. This material is available free of
charge via the Internet at http://pubs.acs.org.
In stark contrast, the novel ligand J DTic (10), like
nor-BNI (5), shows a 16-fold improvement in its κ
receptor Ki value in the functional assay relative to the
binding assay (0.02 nM versus 0.3 nM). Since the Ki
values for 10 in the µ and δ assays do not increase
substantially, the shift to higher potency for 10 in the
κ receptor functional assay results in greater than 100-
fold µ versus κ selectivity and a remarkable >15000-
fold selectivity for the δ versus κ receptor.
In the [35S]GTP-γ-S functional assay using cloned
opioid receptors (Table 3), compound 10 with a Ki value
of 0.006 nM demonstrates a 3.4-fold increase in κ
antagonist potency relative to the functional assay
utilizing guinea pig membranes. This represents a 53-
fold overall improvement in the κ receptor Ki value
compared with the binding assay, and as before there
is little shift in Ki values for either the µ or δ receptors.
This effectively boosts the selectivities of 10 to 570 and
>16000-fold for µ versus κ and δ versus κ, respectively.
In this assay, the novel antagonist 10 is observed to be
an order of magnitude more potent and considerably
more selective than the prototypical antagonist nor-BNI
(5), which shows µ versus κ and δ versus κ selectivities
of 225- and 172-fold, respectively.
Refer en ces
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Con clu sion s. The discovery of the potent and selec-
tive κ opioid receptor antagonist (3R)-7-hydroxy-N-((1S)-
1-{[(3R,4R)-4-(3-hydroxyphenyl)-3,4-dimethyl-1-pipe-
ridinyl]methyl}-2-methylpropyl)-1,2,3,4-tetrahydro-3-
isoquinolinecarboxamide (J DTic, 10) represents a sig-
nificant advancement in the development of the trans-
(3,4)-dimethyl-4-(3-hydroxyphenyl)piperidine class of
opioid antagonist. However, it also raises many ques-
tions. Of particular interest is the nature of the rela-
tionship between compound 10 and the oxymorphone-
based κ antagonists such as 5 or 6. For example, do both
classes of antagonist utilize the same recognition loci
within the κ receptor to express antagonist activity and
selectivity? Also, what physical event in the κ receptor/
ligand interaction gives rise to the conundrum whereby
some κ antagonists show an inverse relationship be-
tween selectivity in binding and selectivity in functional
potency?11,14,15 Additionally, the presence of the two
independent tyrosyl mimicking moieties within the
structure of J DTic (10) is intriguing as this tandem
(13) Xu, H.; Hashimoto, A.; Rice, K. C.; J acobson, A. E.; Thomas, J .
B.; Carroll, F. I.; Lai, J .; Rothman, R. B. Opioid peptide receptor
studies. 14. Stereochemistry determines agonist efficacy and
intrinsic efficacy in the [(35)S]GTP-gamma-S functional binding
assay. Synapse 2001, 39 (1), 64-69.

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2690 J ournal of Medicinal Chemistry, 2001, Vol. 44, No. 17
Letters
(14) Portoghese, P. S.; Lin, C. E.; Farouz-Grant, F.; Takemori, A. E.
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