μ-Opioid/5-HT4 dual pharmacologically active agents-Efforts towards an effective opioid analgesic with less GI and respiratory side effects (Part I)

Article abstract of DOI:10.1016/j.bmcl.2009.08.016

Novel compounds were prepared that united the pharmacologies of the μ-opioid tramadol with the 5-HT4 agonists metoclopramide and norcisapride. The synthesis, chiral separation and in vitro activity of the new compounds is described.

Full text of DOI:10.1016/j.bmcl.2009.08.016

Bioorganic & Medicinal Chemistry Letters 19 (2009) 5679–5683
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Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
l-Opioid/5-HT4 dual pharmacologically active agents—Efforts towards an
effective opioid analgesic with less GI and respiratory side effects (Part I)
*
Liming Shao , Fengjiang Wang, Michael C. Hewitt, Timothy J. Barberich
Sepracor Inc., 84 Waterford Drive, Marlborough, MA 01752, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
Novel compounds were prepared that united the pharmacologies of the
HT4 agonists metoclopramide and norcisapride. The synthesis, chiral separation and in vitro activity of
the new compounds is described.
l-opioid tramadol with the 5-
Received 13 July 2009
Revised 1 August 2009
Accepted 4 August 2009
Available online 8 August 2009
Ó 2009 Elsevier Ltd. All rights reserved.
Keywords:
Tramadol
Metoclopramide
Norcisapride
Designed multiple ligand
Hundreds of years after the discovery of morphine and its appli-
cation to pain treatment, opioids remain the most effective and
most widely prescribed analgesic class. For many decades scien-
tists around the world have been diligently working to uncouple
the analgesic potency from the concomitant side effects that occur
after chronic use.
Constipation is the most common adverse effect of chronic opi-
oid therapy,1 and typically afflicts at least 41% of patients receiving
long-term therapy.2 It is known that opioid-induced constipation is
and D2/5-HT2a antagonists5 for schizophrenia. This general concept
has been coined ‘designed multiple ligands (DML)’6 and can be de-
fined as taking two selective ligands and combining them into a
single molecular entity with dual activity. There are a number of
advantages to the DML approach over multicomponent drugs such
as Caudet7 or Vytorin,8 including a reduced risk of drug-drug inter-
actions and a less complex PK/PD relationship. Most importantly,
the success of marketed dual acting drugs such as the selective
serotonin and norepinephrine reuptake inhibitor Duloxetine has
validated this approach as a potential solution to patients who
are not responding to their current (selective) medications.
largely peripherally mediated—
on gut smooth muscle play a large role in gastrointestinal motility,
with
directly affecting the myenteric plexus.3 Prevention and
l and delta opioid receptors located
l
( )-cis Tramadol is used for the treatment of moderate to mod-
erately severe pain.9,10 The analgesic activity of tramadol is
thought to be the result of a dual mechanism—the parent (1) acts
as an inhibitor of norepinephrine and serotonin reuptake and the
treatment of opioid-induced constipation includes both non-phar-
macologic options such as hydration, diet and exercise, and phar-
macologic intervention such as laxatives, opioid-receptor
antagonists, and prokinetics.
The idea of combining multiple pharmacologies into a single
molecular entity (i.e. polypharmacology) was the common para-
digm for drug discovery when animal models of disease were the
main drivers of compound selection, but fell out of vogue with
the growth of in vitro biology and single target (selective) drugs.
The failure of the single target approach to adequately treat psychi-
atric diseases such as depression and schizophrenia led to drug dis-
covery programs against multiple targets such as the triple (5-HT,
Norepinephrine and dopamine) reuptake inhibitors4 for depression
major O-desmethyl metabolite (2) is a potent
l-opioid receptor
agonist (Fig. 1).11 Not unlike other opioids, tramadol also causes
OCH3
OH
OH
OH
CH3
CH3
N
N
CH3
CH3
1
2
* Corresponding author. Tel./fax: +1 5083577467.
E-mail address: liming.shao@sepracor.com (L. Shao).
Figure 1. ( )-Tramadol 1 and metabolite ( )-2.
0960-894X/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2009.08.016

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L. Shao et al. / Bioorg. Med. Chem. Lett. 19 (2009) 5679–5683
a number of side effects including constipation, nausea, dizziness,
and somnolence. Sepracor has maintained an active research pro-
gram targeted toward development of improved version of trama-
dol for a number of years, and our previous efforts to improve the
phamarcokinetics12 and potency13 of Tramadol have already been
disclosed. While the complex pharmacology of Tramadol presented
some difficulties in the development of DMLs, our familiarity with
the Tramadol scaffold gave us a competitive advantage and al-
lowed us more rapid entry into analog sets using Tramadol as
prokinetic agent before it was voluntarily withdrawn by Janssen
in 2000 because of reports of QT prolongation. Both compounds
are thought to work via 5-HT4 agonism; it is known that (+)-norc-
isapride, one of the primary de-alkylated metabolites of the parent
drug,14 is a potent 5-HT4 agonist/5-HT3 antagonist and has activity
in animals models of constipation such as MgSO4 induced intesti-
nal lavage.15 Furthermore, norcisapride is devoid of inhibitory
activity at the potassium hERG channel in vitro. Our idea was to
combine the pharmacophores of Tramadol with Metoclopramide
or norcisapride to create a novel analgesic that would cause less
constipation after chronic treatment (Fig. 2). It is also worth
mentioning that BIMU8, a selective 5-HT4 agonist, was shown to
the l-opioid component.
Metoclopramide (Reglan, Fig. 2) is used clinically to induce
gastric emptying; cisapride (Prepulsid) was on the market as a
µ
agonist
Prokinetic
O
HN
O
O
NH
OH
N
Cl
NH2
Cl
NH2
O
N
H
N
O
O
( ) - Tramadol
Metoclopramide
(+)-Norcisapride
3a
3b
Cl
NH2
OH
O
O
O
O
OH
H
N
N
O
N
N
H
O
O
NH2
Cl
Figure 2. Designed dual l-opioid agonist/prokinetic compounds 3a and 3b.
O
O
NH2
1. Mesyl-Cl, Et3N, CH2Cl2, RT
1. CDI, THF, rt
OH
O
N
O
N
OH
2.
2. Phthlamide, CsCO3, DMF, 90°C
3. N2H4, EtOH/THF, RT
OH
THF, rt
N
H
4
5
Wang resin
Cl
Cl
O
HO
O
NH2
NH2
H
N
N
O
6
H
O
1. PyBOP, NMM, DMF, rt
2. TFA/CH2Cl2
7
Scheme 1. Synthesis of methyl amine 7.
Cl
NH2
Br
1. Ph3P, B r 2, DMF
H
1. Mg, THF
OH
OH
RO
N
RO
N
OH
2. 7, K2CO3, CH3CN, 60 o
C
2. THF, rt
O
RO
O
O
8
R = CH3
9 R = Bn
10 (cis-racemic) R = CH3
11 (cis-racemic) R = Bn
3a R = CH3 (cis-racemic)
OH
13
R = Bn (cis-racemic)
H2 Pd/C, EtOH
14
R = H (cis-racemic)
Scheme 2. Synthesis of DML 3a and 14.

L. Shao et al. / Bioorg. Med. Chem. Lett. 19 (2009) 5679–5683
5681
Cl
Cl
O
NH2
NH2
OH
H
N
H
N
OH
+
O
O
AD, 80/20/0.1
hex/IPA/D EA
N
N
3a
O
O
O
15 (FME)
16 (SME)
Cl
O
Cl
NH2
NH2
1. AD,80/20/0.1
hex/IPA/D EA
OH
H
N
H
N
OH
+
HO
HO
N
N
13
2. H2, Pd/C, EtOH
O
O
O
17 (FME)
18 (SME)
Scheme 3. Separation of enantiomers of 3a and 13.
O
O
HN
OH
O
RO
OH
N
Cl
NH2
RO
O
O
N
K2CO3, CH3CN 60°C
Br
H
Cl
NH2
N
H
O
20
R = CH3 (cis racemic)
21 R = Bn (cis racemic)
19
(cis racemic)
3b R = CH3
23 R = Bn
Scheme 4. Preparation of racemic DMLs 3b and 23.
OH
O
RO
N
O
Cl
NH2
N
H
O
3b
R = CH3
23 R = Bn
AD 90/10 hex/IPA R = CH3
AD 87/13/0.1 hex/IPA/DEA R = Bn
OH
OH
O
O
RO
RO
N
N
O
O
Cl
Cl
N
H
N
H
O
NH2
O
NH2
24
R = CH3
27
R = CH3
28 R = Bn
25 R = Bn
H2 Pd/C, EtOH
26 R = H
29 R = H
OH
N
OH
O
O
RO
RO
N
O
O
Cl
NH2
Cl
N
H
N
H
O
O
NH2
30 R = CH3
33 R = CH3
34
31
R = Bn
R = Bn
35 R = H
H2 Pd/C, EtOH
32 R = H
Scheme 5. Chiral separation of piperdines.

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L. Shao et al. / Bioorg. Med. Chem. Lett. 19 (2009) 5679–5683
Table 1
In vitro binding and functional data for DMLs at 5-HT3, 5-HT4 and
l-opioid receptors
Binding
Functional
5-HT4 (IC50
,
l
M)
5-HT3 (IC50
lM)
l(IC50
,
l
M)
5-HT4 (EC50
,
lM)
5-HT3 (EC50 lM)
19 Norcisapride
1.6
0.019
3.9
9.9
3.5
5
>10
>10
>10
>10
>10
6.1
NT
0.290 (ag)
0.120 (ag)
0.090 (ag)
2.3 (antag)
>10
NT
33
32
12
15
16
14
17
18
24
27
30
26
29
35
0.159
0.018
3.3
3.5
4.9
2.8
3.1
2.5
2.8
0.79
1.70
1.6
0.39
1.4
>10
0.41
>10
4.5
>10
0.19
0.34
5.1
>10
>10
>10
>10
>10
>10
4.6
>10
>10
>10
reverse opioid-induced respiratory depression without loss of anal-
gesia.16 That made the
-5-HT4 combination even more attractive.
Functionality analysis showed that both agonist pharmaco-
33 and phenol 32. Both compounds were shown to be potent
agonists at the 5-HT4 receptor, with EC50’s of 120 and 90 nM,
respectively. Phenol 32 also showed reasonable potency against
l
l
phore (tramadol) and prokinetics pharmacophore (metaclopra-
mide and (+)-norcisapride) contained a basic amine critical for
activity. Our approach was to use this nitrogen as a merge point
(Fig. 2). Following this principal, we could not only preserve the ba-
sic amine functionality for both but also allow the pharmacophores
to be a substitution group for the other. This would offer us the
best chance to obtain all desired activities.
the l-opioid receptor (410 nM), and may provide a reasonable
starting point for further optimization efforts. The metoclopro-
mide scaffold did not provide significant 5-HT4 and 5-HT3 po-
tency when linked to the tramadol scaffold, although the DML
phenols such as single enantiomer 17 provided nanomolar
l-
opioid potency (340 nM).
Our DMLs based on the
l-opioid agonist tramadol and the
Synthesis of metoclopramide DML 3a was conducted on solid
phase and began with functionalization of Wang resin with CDI fol-
lowed by 2-methylamino methanol to give resin bound 4 (Scheme
1). Mesylation, displacement with phthlamide and deprotection
with hydrazine in EtOH/THF gave primary amine 5, which was
coupled to substituted benzoic acid 6. Treatment of the resin with
TFA in CH2Cl2 gave pure 7.
prokinetic agent norcisapride were designed to combine 5-HT4/5-
HT3 and mu activity into a single compound. We succeeded in unit-
ing the 5-HT4 and
agonist activity and nanomolar potency for the
l
activity with 32, which showed potent 5-HT4
-opioid receptor.
l
Future efforts will be focused on incorporating 5-HT3 antagonist
activity and determining the in vivo profile of 32 in models of pain
and constipation.
DML 3a was synthesized starting from 3-bromo anisole or 1-
(benzyloxy)-3-bromobenzene, which were converted to Grignard
reagents and added to 2-hydroxymethylcyclohexanone (Scheme
2). Cis-racemic diols 10 and 11 were selectively brominated and
condensed with amine 7 to give racemic DML 3a and 13. Benzyoxy
DML 13 could be converted to phenol 14 via hydrogenation over
Pd/C.
References and notes
1. Fallon, M.; O’Neill, B. Br. J. Med. 1997, 315, 1293.
2. Goodheart, C. R., Leavitt, S. B. Pain Treatment Topics, August, 2006.
3. Panchal, S. J.; Muller-Schwefe, P.; Wurzelmann, J. I. Int. J. Clin. Pract. 2007, 61,
1181.
4. Skolnick, P.; Popik, P.; Janowsky, A.; Beer, B.; Lippa, A. S. Eur. J. Pharmacol. 2003,
461, 99.
Racemic 3a was separated into enantiomers 15 (Fast Moving
Enantiomer) and 16 (Slow Moving Enantiomer) using a Chiral
Technologies AD column and a solvent system of 80/20/0.1 hex-
anes/IPA/diethylamine. Benzyl-oxy protected 13 could be similarly
separated; hydrogenation on Pd/C gave enantiomeric phenols 17
FME and 18 SME (Scheme 3).
Norcisapride was the starting point for DML 3b (Scheme 4).
Coupling of norcisapride with tramadol-derived bromides 20 and
21 gave tertiary amines 3b and 23, which could be separated by
chiral HPLC (Scheme 5).
The enantiomers of 3b and 23 could be obtained using an AD
column (Scheme 5) - the absolute configuration of the pure chiral
compounds was not determined, but was arbitrarily assigned.
Hydrogenation on Pd/C of benzyl ethers 25, 28, 31 and 34 provided
the pure phenols 26, 29, 32 and 35 (Scheme 5).
5. Jones, H. M.; Pilowsky, L. S. Exp. Rev. Neurother. 2002, 2, 61.
6. (a) Morphy, R.; Rankovic, Z. J. Med. Chem. 2005, 48, 6523; (b) Morphy, R.;
Rankovic, Z. In The Practice of Medicinal Chemistry; Wermuth, C. G., Ed., 3rd ed.;
Academic Press: Burlington, MA, 2008; pp 549–571; (c) Contreras, J. – M.;
Sippl, W. In The Practice of Medicinal Chemistry, 3rd ed.; Wermuth, C. G. Ed.;
Academic Press: Burlington, MA, 2008; pp 380–314.
7. Frishman, W. H.; Zuckerman, A. L. Exp. Rev. Cardiovas. Ther. 2004, 2, 675.
8. Flores, N. A. Curr. Opin. Invest. Drugs 2004, 5, 984.
9. (a) Raffa, R. B.; Friderichs, E.; Reimann, W.; Shank, R. P.; Good, E. E.; Vaught, J. L.
J. Pharmacol. Exp. Ther. 1992, 260, 275; (b) Gibson, T. P. Am. J. Med. 1996, 101,
47S; (c) Radbruch, L.; Grond, S.; Lehmann, K. Drug Safety 1996, 15, 8; (d) Raffa,
R. B. Am. J. Med. 1996, 101, 41S; (e) Garrido, M.; Valle, M.; Campanero, M. A.;
Calvo, R.; Troconiz, I. F. J. Pharmacol. Exp. Ther. 2000, 295, 352; (f)
Subrahmanyam, V.; Renwick, A. B.; Walters, D. G.; Young, P. J.; Price, R. J.;
Tonelli, A. P.; Lake, B. G. Drug Metab. Dispos. 2001, 29, 1146; (g) Wu, W. N.;
McKown, L. A.; Liao, S. Xenobiotica 2002, 32, 411; (h) Leppert, W.; Luczak, J.
Support Care Cancer 2005, 13, 5; (i) Duhmke, R. M.; Cornblath, D. D.;
Hollingshead, J. R. Cochrane Database Syst. Rev. 2004, 2, CD003726; (j) Grond,
S.; Sablotzki, A. Clin. Pharmacokinetics 2004, 43, 879; (k) Klotz, U.
Arzneimittelforschung 2003, 53, 681.
10. PDR Electronic Library, Thomson Scientific, http://www.thomsonhc.com/pdrel/
librarian, reference for UltramÒ tablets (Ortho-McNeil).
11. Raffa, R. B.; Nayak, R. K.; Liao, S.; Minn, F. L. Rev. Contemp. Pharmacother. 1995,
6, 485.
12. Shao, L.; Abolin, C.; Hewitt, M. C.; Koch, P.; Varney, M. Bioorg. Med. Chem. Lett.
2006, 16, 691.
13. Shao, L. S.; Hewitt, M. C.; Jurussi, T. P.; Wu, F.; Malcolm, S. C.; Grover, P.; Fang,
K.; Koch, P.; Senanayake, C.; Bhongle, N.; Ribe, S.; Bakale, R.; Currie, M. Bioorg.
Med. Chem. Lett. 2008, 18, 1674.
The designed single enantiomer DMLs were tested initially for
18
binding potency at 5-HT3,17 5-HT4 and
l-opioid receptors (Ta-
ble 1).19 Several of the most potent ligands were also tested in a
functional assay to determine if the compounds were agonists or
antagonists at the given receptor. It was clear from the data in
Table 1 that the norcisapride series of compounds were much
more potent against the 5-HT4 receptor and provided the two
compounds tested in the functional assay, methoxy substituted

L. Shao et al. / Bioorg. Med. Chem. Lett. 19 (2009) 5679–5683
5683
14. Meuldermans, W.; Hendrickx, J.; Lauwers, W.; Hurkmans, R.; Mostmans, E.;
Swysen, E.; Bracke, J.; Knaeps, A.; Heykants, J. Drug Metab. Dispos. 1998, 16, 410.
15. Heykants, J.; Megens, A.; Meuldermans, W.; Schuurkes, J. WO Patent
Publication 1999/002496.
17. Hope, A. G.; Peters, J. A.; Brown, A. M.; Lambert, J. J.; Blackburn, T. P. Br. J.
Pharmacol. 1996, 118, 1237.
18. Mialet, J.; Berque-Bestel, I.; Sicsic, S.; Langlois, M.; Fischmeister, R.; Lezoualc’h,
F. Br. J. Pharmacol. 2000, 129, 771.
16. Manzke, T.; Guenther, U.; Ponimaskin, E.; Haller, M.; Dutschmann, M.;
Schwarzacher, S.; Richter, D. Science 2003, 301, 226.
19. Wang, J.-B.; Johnson, P. S.; Persico, A. M.; Hawkins, A. L.; Griffin, C. A.; Uhl, G. R.
FEBS Lett. 1994, 338, 217.