Rapid access towards follow-up NOP receptor agonists using a knowledge based approach

Article abstract of DOI:10.1016/j.bmcl.2009.09.028

A knowledge based approach has been adopted to identify novel NOP receptor agonists with simplified hydrophobes. Substitution of the benzimidazol-2-one piperidine motif with a range of hydrophobic groups and pharmacophore guided bio-isosteric replacement

Full text of DOI:10.1016/j.bmcl.2009.09.028

Bioorganic & Medicinal Chemistry Letters 19 (2009) 6441–6446
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Rapid access towards follow-up NOP receptor agonists using a knowledge
based approach
a
b
a
a
a
Ronald Palin a, , John K. Clark , Louise Evans , Helen Feilden , Dan Fletcher , Niall M. Hamilton ,
Andrea K. Houghton b, Philip S. Jones a, Duncan McArthur a, Brian Montgomery a, Paul D. Ratcliffe a,
Alasdair R. C. Smith a, Aaron Sutherland c, Mark A. Weston a, Grant Wishart a
*
a Department of Chemistry, Schering-Plough Research Institute, Newhouse, Lanarkshire ML1 5SH, UK
b Department of Pharmacology, Schering-Plough Research Institute, Newhouse, Lanarkshire ML1 5SH, UK
c Department of Molecular Pharmacology, Schering-Plough Research Institute, Newhouse, Lanarkshire ML1 5SH, UK
a r t i c l e i n f o
a b s t r a c t
Article history:
A knowledge based approach has been adopted to identify novel NOP receptor agonists with simplified
hydrophobes. Substitution of the benzimidazol-2-one piperidine motif with a range of hydrophobic
groups and pharmacophore guided bio-isosteric replacement of the benzimidazol-2-one moiety was
explored. Compound 51 was found to be a high affinity, potent NOP receptor agonist with reduced affin-
ity for the hERG channel.
Received 13 August 2009
Revised 8 September 2009
Accepted 9 September 2009
Available online 12 September 2009
Ó 2009 Elsevier Ltd. All rights reserved.
Keywords:
NOP/ORL1 agonist
Antinociception
hERG
Pharmacophore
The ORL1 receptor (opioid receptor like-1 receptor, known as
NOP) and its endogenous ligand nociceptin (NC, also known as
orphanin FQ), a 17-amino acid neuropeptide, was discovered in
1994.1–4 Although its sequence is closely related to traditional opi-
oid receptors, the NOP receptor shows low binding affinities for
selective opioid agonists and antagonists (such as dynorphin
A).5,6 Furthermore, the NOP ligand NC does not bind to the three
traditional opioid receptors (MOP, DOP, KOP). Activation of the G
protein-coupled NOP receptor inhibits adenylate cyclase activity,
reduces intracellular cAMP and regulates ion channels. The NOP
receptor and NC have been implicated in several physiological
pathways including cognition, pain, locomotion, anxiety, neuroen-
docrine control and modulation of cardiovascular and respiratory
function.7 Supraspinal administration of nociceptin in rodents pro-
duces hyperalgesia8 whereas spinal intrathecal administration
causes hyperalgesia in low doses and analgesia in high doses.9 In
addition to complex biological data there are limitations in using
NC because of the inherent poor metabolic stability. Therefore,
the development of highly selective and potent NOP ligands could
help elucidate the role of the NOP receptor in pain. Several research
groups have disclosed their efforts in the search for small molecule
NOP agonists and antagonists.10–13 Some of these ligands (1, 2 and
3) have high selectivity and potency for the NOP receptor versus
the other opioid receptors (Fig. 1). Many different classes of NOP
ligands have been reported however only 3, has progressed into
clinical trials for multiple target indications using an experimental
medicine approach.14
In earlier work we had identified a series of 3-phenoxypropyl
piperidine benzimidazol-2-ones that led to the optimised com-
pounds 4 and 5.15–17 These agonists have high affinity for NOP
(Ki = 0.5 nM and 2 nM, respectively) with excellent selectivity over
the other opioid receptors, in particular MOP (Ki = 54 nM, NOP/
MOP = 108 for 4). We attributed the higher affinity and selectivity
of 4 to both the H-bond donating and accepting capacity of the ter-
minal amide appended from the N-3 position of the benzimidazol-
2-one and have since capitalised on these properties with a host of
bio-isosteric replacements.18 The synthetic feasibility of these
compounds is a key issue. The route is a four step process involving
an asymmetric hydrogenation and a moderate yielding Mitsunobu
coupling even after extensive optimisation.16 In this Letter we re-
port a knowledge based strategy to rapidly access a back-up series
focussing on simplified hydrophobes and pharmacophoric replace-
ments of the benzimidazol-2-one to simplify the synthetic route,
maintain NOP affinity and selectivity.
Simplified hydrophobes were selected for synthesis on the
basis of literature precedent for NOP ligands and appropriate
physicochemical properties for known CNS active drugs. A 3D
* Corresponding author. Tel.: +44 1698 736128; fax: +44 1698 736187.
E-mail address: ronald.palin@spcorp.com (R. Palin).
0960-894X/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2009.09.028

6442
R. Palin et al. / Bioorg. Med. Chem. Lett. 19 (2009) 6441–6446
O
R
N
H
NH
O
OMe
O
N
O
O
N
N
N
N
N
O
N
OH
N
N
O
N
OH
R = CH2C(O)NHMe (+)-4
R = CH2CH2OMe (+)-5
2 NNC 63-0532
1 Ro 64-6198
3 J-113397
Figure 1. Structure of NOP lead compounds.
pharmacophore approach was adopted to aid the prioritisation of
potential bio-isosteric replacements for the benzimidazol-2-one
piperidine of 4. Previous superposition analysis between the ben-
zimidazol-2-one piperidine moiety of 4 and the 1-phenyl-1,3,8-tri-
aza-spiro[4.5]decan-4-one moiety characteristic of a number of
known NOP receptor ligands such as 1 highlighted the aromatic
hydrophobe, basic amine and associated acceptor site as the key
common pharmacophoric features.17 Two 3-D pharmacophore
queries were generated based on the superposition model. Both
queries contained the common aromatic hydrophobe, basic amine
and associated acceptor site. One query had an additional acceptor
atom functionality derived from the carbonyl of the benzimidazol-
2-one piperidine, the other query had an additional acceptor atom
functionality derived from the carbonyl of the 1-phenyl-1,3,8-tri-
aza-spiro[4.5]decan-4-one moiety. The two queries were used to
search a database of approximately 60 potential benzimidazol-2-
one piperidine bio-isosteres using Unity flexible 3D searching.19
Pharmacophore model hits were prioritised on the basis of fit to
the query, conformational penalties and the ability to bear a po-
tential potency and selectivity enhancing amide substituent in a
similar direction to that of the benzimidazol-2-one piperidine.
Several of which have been synthesised. The fit of the 1,3-dihy-
dro-2,1,3-benzothiadiazol-2,2-dione piperidine moiety (core E)
with the benzimidazol-2-one piperidine and its derived 3D query
is shown in Figure 2.
H
N
O
H
N
O
N
i
N
HN
N
O
R
N
N
O
6-31
52
Scheme 1. Reagents and conditions: (i) NaBH(OAc)3, Ti(OiPr)4, EtOH, ketone/
aldehyde, microwave 180 °C, 300 s.
3,1-benzoxazine-4,40-piperidin]-2-(1H)-one 54. Compound 54
could be treated with ethyl chloroacetate followed by methylamine
in aqueous ethanol to install the N-methyl amide from N-1 to give
55. The hydrophobe could then be appended after deprotection of
55 to afford 32, 37, 41 and 44 using the previously mentioned
reductive amination conditions. Core B was constructed following
the protocols of Takai et al.21 2-Aminobenzamide 57 was treated
with 1-benzyl-4-piperidinone under reductive amination condi-
tions followed by reductive cleavage of the intermediate dihydro-
4-quinazoline to give the diamine 58 (Scheme 3). Cyclisation of
58 with N,N0-carbonyldiimidazole gave the protected quinazoline
59. In a similar manner to core A, the N-methyl amide can be in-
stalled onto 59 before attachment of the hydrophobe to give 33
and 46. Core C is described in the patent literature by Euroceltique
and is prepared starting from ethyl 1-benzyl piperidine-4-carboxyl-
ate 62 (Scheme 4).22 Deprotonation adjacent to the ester and
quenching with benzoyl chloride gave the keto ester 63. Compound
63 was then cyclised to the spiropyrazole 64 with a large excess of
hydrazine under microwave conditions. Previous attempts using
conventional heating in ethylene glycol gave disappointing yields
(ꢀ20%). Treatment of 64 with ethyl chloroacetate followed by
methylamine appended the N-methyl amide to afford 66. Subse-
quent deprotection and reductive amination to introduce the
hydrophobes gave 34, 38, 42, 45 and 47. With diamine 58 in hand
we were able to access 3,4-dihydro-1H-2,1,3-benzothiadiazin-2,2-
diones (core D). In a method described by Goehring et al.23 towards
similar NOP ligands, diamine 58 was treated with sulfamide in dig-
lyme at 170 °C to affect the cyclisation and afford 68 (Scheme 3).
Again the N-methyl amide can be installed in a similar manner to
previously described and a host of hydrophobes attached using
the reductive amination conditions to afford 35, 39 and 48. Synthe-
sis of 1,3-dihydro-2,1,3-benzothiadiazol-2,2-diones (core E) is also
described by Goehring et al.23 Firstly the diamine 73 is constructed
via a reductive amination between 1,2-phenylene diamine 72 and
(tert-butoxycarbonyl)piperidinone (Scheme 5). Refluxing 73 with
sulfamide in diglyme gave the desired cyclic material 74. Further-
more 74 could be transformed to the N-methyl amide 76 and the
hydrophobes added after deprotection to give 36, 40, 43 and 49.
The affinities (Ki values) of compounds at the opioid receptors
were determined by radioligand binding experiments performed
in triplicate. Compounds showing high NOP affinity were profiled
for selectivity over MOP, selected compounds were further evalu-
ated for NOP agonism in a cAMP functional assay and compared
to the reference NOP agonist nociceptin (NC). All assays were car-
ried out as described previously.17
The previously disclosed benzimidazol-2-one piperidine 5217
was treated with sodium triacetoxy borohydride in the presence
of titanium isopropoxide in ethanol with the appropriate ketone
or aldehyde at high temperature in a microwave reactor to give
compounds 6–31 (Scheme 1, Table 1). The cores A–E highlighted
from the pharmacophore analysis were constructed and the N-
methyl amide proven to give an enhancement in potency and selec-
tivity in the initial series was included before the attachment of a
selection of hydrophobes. Synthesis of core A was carried out
according to the protocol of Clark et al. (Scheme 2).20 Dilithiation
of (tert-butoxycarbonyl)aniline 53 and condensation with (tert-
butoxycarbonyl)piperidinone results in the protected spiro[4H-
Figure 2. Unity fit of the 1,3-dihydro-2,1,3-benzothiadiazol-2,2-dione piperidine
moiety (core E, orange) to the benzimidazol-2-one piperidine moiety of 4 (magenta)
and its derived 3D pharmacophore query.

R. Palin et al. / Bioorg. Med. Chem. Lett. 19 (2009) 6441–6446
6443
Table 1
H
N
O
O
N
N
N
R
No.
R
NOP Ki (nM)
MOP Ki (nM)
NOP/MOP
No.
R
NOP Ki (nM)
MOP Ki (nM)
NOP/MOP
*
*
6
470
NT
19
487
NT
*
*
7
8
227
35
NT
20
21
2560
259
NT
*
1794
51
41
55
26
5.6
54
118
14
10
1883
7.3
*
*
*
*
*
9
15
608
11
22
23
24
25
26
27
28
29
30
31
1118
471
186
29
NT
10
11
12
13
14
15
16
17
18
0.2
1.3
62
NT
*
*
*
34
2707
67
15
*
*
350
282
201
77
2.3
51
*
*
5.2
1.7
5.5
4.7
253
3.5
2.7
138
120
NT
*
*
18
6.7
OMe
*
1050
4082
454
16
N
*
*
*
*
N
47
NT
NT
NT
*
*
127
36
3.7
0.2
NT = not tested.

6444
R. Palin et al. / Bioorg. Med. Chem. Lett. 19 (2009) 6441–6446
O
upon comparison to the unsubstituted cyclopentyl 6. However
O
O
H
N
the 4,4-dimethyl substituted cyclohexyl 13 yielded a 44-fold in-
crease in NOP affinity compared to the parent cyclohexyl 7 result-
ing in a promising 54-fold selectivity over MOP for 13. This
suggested that additional steric bulk at the cyclohexyl 4 position
may be beneficial for NOP affinity. 4-Isopropyl cyclohexyl analogue
14 afforded a high affinity NOP ligand (Ki = 1.7 nM) with good
selectivity over MOP. However tert-butyl analogue 15 showed a
3.2-fold decrease in NOP affinity compared to 14 which coupled
with an increase in MOP affinity resulted in a significant decrease
in selectivity. Derivatives 16 and 18 also showed decreased NOP
affinity compared to 14 although 18 maintained a reasonable 36-
fold selectivity over NOP. Phenyl substituted cyclohexyl 17 exhib-
ited a profound decrease in NOP affinity as did norbornane ana-
logue 19. Methylene insertion between the piperidine nitrogen
and cycloalkyl resulted in poor NOP affinity for cyclobutyl 20 while
cyclohexyl 21 showed no improvement over the direct linked
analogue 7. Branched alkyl derivatives 22–24 all showed relatively
poor NOP affinities. Naphthyl analogue 25 exhibited reasonable
NOP affinity (Ki = 29 nM) indicating that both aliphatic and
O
HN
N
i
O
NH
O
ii
O
iii
N
N
R
R
53
R = Boc 54
R = Boc 55
R = H 56
iv
v
32, 37, 41, 44
Scheme 2. Reagents and conditions: (i) (tert-butoxycarbonyl)piperidinone, tBuLi,
THF, ꢁ78 °C; (ii) ethyl chloroacetate, NaH, DMF, NaI; (iii) 2 M methylamine in
methanol, ethanol, rt; (iv) 20% TFA, dichloromethane, rt; (v) NaBH(OAc)3, Ti(OiPr)4,
EtOH, ketone, microwave 180 °C, 300 s.
Table 1 shows the NOP and MOP binding affinities for the sim-
plified hydrophobes. Cycloalkyl systems 6–10 increase in affinity
with increasing ring size. The cyclodecyl derivative 10 exhibits
high NOP affinity (Ki = 0.2 nM) and 55-fold selectivity over MOP.
Spiro compound 11 maintains high NOP affinity however selectiv-
ity over MOP is decreased to 26-fold. 2,2-Dimethyl substituted
cyclopentyl 12 showed a modest 7.6-fold increase in NOP affinity
H
N
O
O
N
O
N
H
H2N
N
N
O
i
H
N
iv
v
iii
H2N
H2N
Bn
N
R N
Bn
N
ii
57
58
59
R = Bn 60
R = H 61
33, 46
vi
viii
vii
H
N
OEt
O
O
S
O
O
S
O
S
O
H
O
N
O
N
N
N
iv
v
Bn
N
N
N
R
N
Bn
N
69
68
R = Bn 70
R = H 71
35, 39, 48
vi
vii
Scheme 3. Reagents and conditions: (i) 1-benzyl-4-piperidinone, NaBH(OAc)3, AcOH, DCE, rt; (ii) LiAlH4, 1,4-dioxane, 0–100 °C; (iii) N,N0-carbonyldiimidazole,
dichloromethane, rt; (iv) ethyl chloroacetate, NaH, DMF, NaI; (v) 2 M methylamine in methanol, ethanol, rt; (vi) 10 wt % palladium on carbon, hydrogen, methanol, 2 M
HCl, 5 bar; (vii) NaBH(OAc)3, Ti(OiPr)4, EtOH, ketone/aldehyde, microwave 180 °C, 300 s; (viii) sulfamide, diglyme, 170 °C.
H
N
H
N
O
O
O
O
O
O
H
N
N
O
N
N
O
O
N
N
O
O
N
N
i
v
iv
ii
iii
O
O
N
N
N
N
N
R
N
Bn
Bn
Bn
Bn
Bn
R = H 67
34, 38, 42, 45, 47
66
65
vi
62
63
64
Scheme 4. Reagents and conditions: (i) benzoyl chloride, LDA, THF, ꢁ78 °C to rt; (ii) hydrazine hydrate, ethanol, microwave, 160 °C; (iii) ethyl chloroacetate, NaH, DMF, NaI;
(iv) 2 M methylamine in methanol, ethanol, rt; (v) 30 wt % palladium hydroxide, hydrogen, methanol, 5 bar; (vi) NaBH(OAc)3, Ti(OiPr)4, EtOH, ketone, microwave 180 °C,
300 s.
O
N
O
O
N
O
N
O
N
O
N
O
O
H2N
O
O
NH2
O
O
H
S
S
iii
S
H
iv
ii
N
i
N
NH2
NH
N
R N
N
N
OEt
O
O
72
74
73
75
R = Boc 76
R = H 77
R = 36, 40, 43, 49
v
vi
Scheme 5. Reagents and conditions: (i) (tert-butoxycarbonyl)piperidinone, NaBH(OAc)3, AcOH, DCE, rt; (ii) sulfamide, diglyme, 170 °C; (iii) ethyl chloroacetate, NaH, DMF,
NaI; (iv) 2 M methylamine in methanol, ethanol, rt; (v) 20% TFA, dichloromethane, rt; (vi) NaBH(OAc)3, Ti(OiPr)4, EtOH, ketone, microwave 180 °C, 300 s.

R. Palin et al. / Bioorg. Med. Chem. Lett. 19 (2009) 6441–6446
6445
aromatic ring systems are tolerated for NOP. 4-Methyl substitution
of the naphthyl ring gave an 11-fold increase in NOP affinity and a
2-fold decrease in MOP affinity resulting in 51-fold selectivity for
compound 26 but 4-methoxy naphthyl substitution to give 27
was less successful. Insertion of a nitrogen atom into the naphthyl
moiety to yield isoquinoline 28 gave a 36-fold decrease in NOP
affinity compared to naphthyl 25. Low NOP affinity was also ob-
served for the 2-naphthyl compound 30 and its quinoline analogue
29 however biphenyl 31 showed good NOP affinity (Ki = 16 nM)
but no selectivity over MOP.
The hydrophobes with the most promising selectivity over MOP
were selected for combination with the prioritised benzimidazol-
2-one bio-isosteres. tert-Butyl cyclohexyl was preferred over
4,4-dimethyl cyclohexyl based upon reagent availability and cost.
Results are detailed in Table 2 although not all combinations were
synthesised. Initially core C was evaluated with all hydrophobes
except the 4-methyl naphthyl. SAR for core C typically mirrored
that of the benzimidazol-2-one series where cycloheptyl and 4-
tert-butyl cyclohexyl show lower NOP affinities. SAR was expanded
around the 4-isopropyl cyclohexyl hydrophobe with all 5 cores
then followed up with selected analogues around the remaining
hydrophobes within the series. 4-Methyl naphthyl was only syn-
thesised with core B and failed to show any preliminary advantage
over 4-isopropyl cyclohexyl and was therefore not pursued further.
Core A showed a significant reduction in NOP affinity compared to
the equivalent benzimidazol-2-one analogues, ranging from 54-
fold for 44 to 140-fold for 37. High NOP affinity was achieved for
cores B, C and D with 3,4-dihydro-1H-2,1,3-benzothiadiazin-2,2-
dione core showing affinity similar to that of the ben-
D
zimidazol-2-one derivatives. However, surprisingly high MOP
affinities for compounds containing cores B, C and D resulted in
loss of selectivity. 1,3-Dihydro-2,1,3-benzothiadiazol-2,2-dione
core E showed lower NOP affinity than equivalent core D contain-
ing compounds but afforded appreciable selectivity over MOP per-
haps suggesting that core E maintained the N-methyl acetamide
substituent in an optimal location. Compounds 36, 40 and 49 all
showed high NOP affinity, greater than 35-fold selectivity over
MOP and good functional potency as NOP receptor agonists. It is
noteworthy that analogues of 35, 36, 48 and 49 without the
N-methyl acetamide substituent have been reported in the litera-
ture with differing SAR.23 Unsubstituted analogues of core E gener-
ally showed lower NOP affinity and limited selectivity over MOP
whereas the unsubstituted analogue of 35 (core D) exhibited high
NOP affinity and good selectivity over MOP. This suggests that
N-3 substitution of 1,3-dihydro-2,1,3-benzothiadiazol-2,2-dione
(core E) is preferred for high NOP affinity and selectivity but N-3
unsubstituted analogues are more favourable for 3,4-dihydro-1H-
2,1,3-benzothiadiazin-2,2-dione (core D).
The high affinity and highly selective benzimidazol-2-one 14
was selected for further profiling. Separation of the cis and trans
stereoisomers was achieved by preparative HPLC using a Chiralpak
AD column and 80:20 isohexane/propanol as eluant. Stereochemis-
try was assigned from spin–spin coupling constants and subse-
quent evaluation indicated that cis stereochemistry across the
Table 2
HN
H
N
HN
HN
O
O
O
S
O
O
O
O
S
N
N
O
H
N
N
N
O
N
O
N
O
O
N
N
N
O
N
R
N
N
N
R
N
R
R
R
A
B
C
E
D
No.
R
Core
NOP Ki (nM)
MOP Ki (nM)
NOP/MOP
cAMP IC50 (nM) (%NC resp.)
32
33
34
35
36
A
B
C
D
E
106
21
11
2.9
6.4
108
21
5.2
12
1.0
1.0
0.5
4.1
54
448 (78)
NT
53 (75)
16 (95)
21 (110)
*
346
37
38
39
40
A
C
D
E
28
27
1.0
0.5
3.7
43
103 (82)
9.6 (81)
5.2 (93)
7.5 (104)
*
2.3
0.6
2.5
1.1
2.2
107
41
42
43
A
C
E
2152
227
111
527
NT
3177
0.2
29
NT
NT
339 (81)
*
*
44
45
A
C
295
44
113
7.3
0.4
0.2
NT
685 (109)
*
46
B
22
19
0.9
NT
47
48
49
C
D
E
7.7
5.0
7.1
5.8
14
268
0.8
2.8
38
18 (74)
28 (84)
12 (104)
*
NT = not tested.

6446
R. Palin et al. / Bioorg. Med. Chem. Lett. 19 (2009) 6441–6446
Table 3
H
N
O
O
N
N
N
R
No.
R
NOP Ki (nM)
MOP Ki (nM)
NOP/MOP
1.0
cAMP IC50 (nM) (%NC resp.)
59 (92)
*
50
31
30
*
51
0.7
69
99
2.6 (101)
cyclohexyl ring was preferable (Table 3). Compound 5124 shows
high NOP affinity (Ki = 0.7 nM), almost 100-fold selectivity over
MOP and acts as a high potency NOP agonist in the cAMP func-
tional assay (IC50 = 2.6 nM). Furthermore 51 exhibited low affinity
3. Chen, Y.; Fan, Y.; Liu, J.; Mestek, A.; Tian, M.; Kozak, C.; Yu, L. FEBS Lett. 1994,
347, 279.
4. Wang, J.-B.; Johnson, P. S.; Imai, Y.; Persico, A. M.; Ozenberger, B. A.; Eppler, C.
M.; Uhl, G. R. FEBS Lett. 1994, 348, 75.
5. Reinscheid, R. K.; Nothacker, H. P.; Bourson, A.; Ardati, A.; Henningsen, R. A.;
Bunzow, J. R.; Grandy, D. K.; Langen, H.; Monsma, F. J.; Civelli, O., Jr. Science
1995, 270, 792.
for KOP (Ki = 2.7 lM) and DOP (Ki = 7.0 lM) receptors. During the
course of this work it was discovered that 4 prolonged (approx.
10%) the QTc interval in conscious dogs at therapeutic doses. hERG
channel inhibition is considered an indicator of the potential for a
compound to prolong the QT interval25 therefore 4 was subse-
quently evaluated for hERG channel affinity using a dofetilide
binding assay and found to exhibit high affinity (Ki = 56 nM).26
However 51 showed 75-fold decreased affinity for hERG
6. Meunier, J.-C.; Mollereau, C.; Toll, L.; Suaudeau, C.; Moisand, C.; Alvinerie, P.;
Butour, J. L.; Guillemot, J. C.; Fexrara, P.; Monsarrat, B.; Mazarguil, H.; Vussart,
G.; Parmentier, M.; Costentin, J. Nature 1995, 377, 532.
7. Meunier, J.-C. Exp. Opin. Ther. Patents 2000, 10, 371. and references cited
therein.
8. Yamamoto, Y.; Nozaki-Taquchi, N.; Kimura, S. Neuroscience 1997, 81, 249.
9. Mogil, J. S.; Pasternak, G. W. Pharmacol. Rev. 2001, 53, 381.
10. Ronzoni, S.; Peretto, I.; Giardina, G. A. M. Exp. Opin. Ther. Patents 2001, 11, 525.
11. Bignan, G. C.; Connolly, P. J.; Middleton, S. A. Exp. Opin. Ther. Patents 2005, 15,
357.
(Ki = 4.2
in vivo evaluation. The compound demonstrated an ED50 = 0.23
mol/kg (in comparison to 1.03 mol/kg for compound 4, iv
lM) compared to 4. Compound 51 was taken further for
12. Zaveri, N. Life Sci. 2003, 73, 663.
13. Barlocco, D.; Toma, L.; Cignarella, G. Mini-Rev. Med. Chem. 2001, 1, 363.
14. Satoh, A.; Sagara, T.; Sakoh, H.; Hashimoto, M.; Nakashima, H.; Kato, T.; Goto,
Y.; Mizutani, S.; Azuma-Kanoh, T.; Tani, T.; Okuda, S.; Okamoto, O.; Ozaki, S.;
Iwasawa, Y.; Ohta, H.; Kawamoto, H. J. Med. Chem. 2009, 52, 4091.
15. Palin, R.; Barn, D. R.; Clark, J. K.; Cottney, J. E.; Cowley, P. M.; Crockatt, M.;
Evans, L.; Feilden, H.; Goodwin, R. R.; Griekspoor, F.; Grove, S. J. A.; Houghton,
A. K.; Jones, P. S.; Morphy, R. J.; Smith, A. R. C.; Sundaram, H.; Vrolijk, D.;
Weston, M. A.; Wishart, G.; Wren, P. Bioorg. Med. Chem. Lett. 2005, 15, 589.
16. Clark, J. K.; Jones, P. S.; Palin, R.; Rosair, G.; Weston, M. Tetrahedron 2008, 64,
3119.
l
l
administration) in the second phase of the mouse formalin paw
test thus illustrating this compound has antinociceptive properties.
Furthermore evaluation of the sedative/anaesthetic effect follow-
ing iv administration in the loss of righting reflex (LRR) assay in
mice showed the compound to have a calculated HD50 value of
0.08 lmol/kg (compared to a HD50 = 4.7 lmol/kg for compound 4).
In summary we have developed a knowledge based strategy to
rapidly access simplified hydrophobes to replace the more complex
3-phenoxypropyl piperidine found in 4. Replacement of the ben-
zimidazol-2-one core resulted in ligands that demonstrated a lower
level of selectivity for NOP over MOP. Only core E afforded apprecia-
ble selectivity over MOP thus highlighting once again the impor-
tance of the orientation of the N-methyl acetamide for selectivity.
Compound 51 given iv produced antinociceptive effects comparable
to morphine in the formalin paw test and showed potent anaesthetic
activity in a loss of righting reflex assay. Furthermore 51 had a lower
propensity to bind the hERG channel. Compound 51 had the ideal
attributes as a follow-up compound to 4.
17. Palin, R.; Bom, A.; Clark, J. K.; Evans, L.; Feilden, H.; Houghton, A. K.; Jones, P. S.;
Montgomery, B.; Weston, M. A.; Wishart, G. Bioorg. Med. Chem. 2007, 15, 1828.
18. Palin, R.; Clark, J. K.; Evans, L.; Houghton, A. K.; Jones, P. S.; Prosser, A.; Wishart,
G.; Yoshiizumi, K. Bioorg. Med. Chem. 2008, 16, 2829.
19. Molecular modelling, pharmacophore query generation and 3D database
searching was carried out using Sybyl6.9 and Unity as distributed by Tripos
Inc. 1699 South Hanley Road, St. Louis, Missouri 63144-2913, USA.
20. Clark, R. D.; Caroon, J. M.; Kluge, A. F.; Repke, D. B.; Roszkowski, A. P.; Strosberg,
A. M.; Baker, S.; Bitter, S. M.; Okada, M. D. J. Med. Chem. 1983, 26, 657.
21. Takai, H.; Obase, H.; Nakamizo, N.; Teranishi, M.; Kubo, K.; Shuto, K.; Kasuya,
Y.; Shigenobu, K.; Hashikami, M.; Karashima, N. Chem. Pharm. Bull. 1985, 33,
1116.
22. Brogle, K. PCT Int. Appl. WO 2004103305 A2.
23. Goehring, R. R.; Whitehead, J. F. W.; Brown, K.; Islam, K.; Wen, X.; Zhou, X.;
Chen, Z.; Valenzano, K. J.; Miller, W. S.; Shan, S.; Kyle, D. J. Bioorg. Med. Chem.
Lett. 2004, 14, 5045.
24. Analytical data for compound 51: ESI-MS m/z = 413.3 [M+H]+. 1H NMR
(400 MHz, CDCl3): d 7.35–7.31 (m, 1H), 7.13–7.09 (m, 2H), 7.07–7.05 (m,
1H), 6.18 (br s, 1H), 4.49 (s, 2H), 4.33 (tt, J = 4.4 and 12.4 Hz, 1H), 3.16 (d,
J = 11.7 Hz, 2H), 2.78 (s, 3H), 2.42 (dq, J = 3.8 and 12.5 Hz, 2H), 2.32 (m, 1H),
2.21 (t, J = 12.0 Hz, 2H), 1.82 (d, J = 12.0 Hz, 2H), 1.74–1.59 (m, 5H), 1.57–1.48
(m, 2H), 1.42–1.35 (m, 2H), 1.17–1.10 (m, 1H), 0.9 (d, J = 6.6 Hz, 6H).
25. Jamieson, C.; Moir, E. M.; Rankovic, Z.; Wishart, G. J. Med. Chem. 2006, 49, 5029.
26. The affinity of test drugs for the hERG cardiac K+ channel was determined by
their ability to displace tritiated dofetilide (a class III antiarrhythmic and
potent hERG blocker) in membrane homogenates from HEK-293 cells
expressing the hERG channel.
Acknowledgements
We would like to thank our Analytical Chemistry colleagues for
structure and purity determination.
References and notes
1. Mollereau, C.; Parmentier, M.; Mailleux, P.; Butour, J.-L.; Moisand, C.; Chalon,
P.; Caput, D.; Vassart, G.; Meunier, J.-C. FEBS Lett. 1994, 341, 33.
2. Fukuda, K.; Kato, S.; Mori, K.; Nishi, M.; Takeshima, H.; Iwabe, N.; Miyata, T.;
Houtani, T.; Sugimoto, T. FEBS Lett. 1994, 343, 42.