Synthesis and structure-activity relationships of N-substituted spiropiperidines as nociceptin receptor ligands: Part 2

Article abstract of DOI:10.1016/j.bmcl.2008.12.092

A series of N-8 substituted analogs based upon the spiropiperidine core of the original lead compound 1 was synthesized. This lead has been elaborated to compounds to give compounds 2 and 3 (R = H) that exhibited high NOP binding affinity as well as selec

Full text of DOI:10.1016/j.bmcl.2008.12.092

Bioorganic & Medicinal Chemistry Letters 19 (2009) 1164–1167
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Synthesis and structure–activity relationships of N-substituted
spiropiperidines as nociceptin receptor ligands: Part 2
a
b
b
b
John P. Caldwell a, , Julius J. Matasi , Xiomara Fernandez , Robbie L. McLeod , Hongtao Zhang ,
*
Ahmad Fawzi b, Deen B. Tulshian a
a CV & CNS Department of Chemical Research, Schering Plough Research Institute, 2015 Galloping Hill Road, Kenilworth, NJ 07033, USA
b CV & CNS Department of Biological Research, Schering Plough Research Institute, 2015 Galloping Hill Road, Kenilworth, NJ 07033, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of N-8 substituted analogs based upon the spiropiperidine core of the original lead compound 1
was synthesized. This lead has been elaborated to compounds to give compounds 2 and 3 (R = H) that
exhibited high NOP binding affinity as well as selectivity against other known opioid receptors. These
two series have been further functionalized at the amido nitrogen. The synthesis and structure–activity
relationship (SAR) of these and related compounds are discussed.
Received 6 November 2008
Revised 18 December 2008
Accepted 19 December 2008
Available online 29 December 2008
Ó 2009 Elsevier Ltd. All rights reserved.
Keywords:
Nociceptin
NOP
ORL1
Antitussive
Opioid
From high-throughput screening of our chemical library, com-
pound 1 was identified as a lead showing moderate affinity for
NOP with a Ki of 500 nM. Our previous paper1a detailed the initial
efforts to explore modifications at the piperidine nitrogen resulting
in compounds such as 2 and 3 which exhibited high NOP binding
affinity as well as selectivity against the other known opioid recep-
tors. It is worth noting that others have incorporated this spiropi-
peridine motif in similar efforts exploring NOP agonism.1b
However, despite the treasure trove of data focused around sub-
stitution of the piperidine nitrogen, it was apparent that explora-
tion was rather limited with respect to substitution on the amido
nitrogen. Capitalizing on this opportunity, we set forth to investi-
gate the SAR focusing on substitution at the amido nitrogen of
the spiropiperidine core of 1 using the optimized moieties we have
previously discussed.1a
product is 7. The chloride of 7 may be readily displaced by second-
ary or primary amines to produce compounds such as 8.
N
N
HN
O
F
F
1
NOP Ki= 500 nM
As summarized in Scheme 1, the commercially available 1-phe-
nyl-1,3,8-triazaspiro-[4,5]deacan-4-one, 4, was either alkylated in
the presence of various benzyl halides or treated under reductive
amination conditions with benzyl aldehydes to produce 5, where
R1 consists of primarily benzhydryl, benzyl, and tetralinyl analogs.
The amido nitrogen of 5 was further functionalized under phase-
transfer alkylation conditions to produce derivatives such as 6.2
When 5 is subjected under the phase-transfer alkylation conditions
using 1,2-bromochloroethane as the alkylating agent, the resultant
Cl
N
N
N
N
RN
RN
Cl
O
O
2
3
(R= H)
NOP Ki= 11 nM
(R= H)
NOP Ki= 1.3 nM
* Corresponding author. Tel.: +1 908 740 5199.
E-mail address: john.caldwell@spcorp.com (J.P. Caldwell).
0960-894X/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2008.12.092

J. P. Caldwell et al. / Bioorg. Med. Chem. Lett. 19 (2009) 1164–1167
1165
receptor expressing Chinese hamster ovary (CHO) cell membranes
as described.3a Ki values for human
l-, j-, and d-opioid receptors
were determined using [3H]diprenorphine and CHO cell mem-
branes expressing the opioid receptors as described.3b In cases
where the products yielded an enantiomeric mixture, the resultant
mixture was screened as such.
a
b
N
N
N
HN
HN
R2
N
NH
NR1
NR1
O
O
O
The SAR of the spiropiperidine analogs are shown in Table 1.
The SAR exploration began using the unsubstituted benzhydryl
moiety at the piperdinyl nitrogen (R1 = A). In general, alkylation at
the amido nitrogen (10–19) decreased potency at the NOP receptor
while retaining good selectivity over DOP and only marginal selec-
tivities over KOP and MOP throughout the series.
6
4
5
c
d
5
N
N
N
N
We turned to the 1,10-bischlorobenzhydryl substituent (R1 = B)
which was proven to provide excellent potency at NOP with high
selectivity over the opioid receptors (2). Substitution at the amido
nitrogen with simple alkyl (20, 21) as well as oxygen containing
derivatives (22–24) displayed a decrease in NOP potency. How-
ever, potency at NOP was regained by introduction of an alkylami-
noalkyl side chain (26–39) while maintaining an acceptable
selectivity profile.
R4
NR1
NR1
Cl
O
N
O
R3
8
7
Scheme 1. Reagents and conditions: (a) R1Br, K2CO3, CH3CN, reflux or R1Cl, K2CO3,
KI, CH3CN, reflux or R1CHO, Na(OAc)3BH, CH2Cl2; (b) R2Br, NaOH, K2CO3, Bu4NHSO4,
toluene, 70 °C; (c) Cl(CH2)2Br, NaOH, K2CO3, Bu4NHSO4, toluene, 70 °C; (d) NR3R4,
EtOH, reflux.
In light of this finding, the 2,6-dichlorobenzyl substituted coun-
terparts (R1 = C) were explored. The incorporation of the alkylami-
noethyl units resulted in numerous examples (41–49) of
subnanomolar potency at NOP; yet, these compounds were also
highly potent at KOP.
The compounds described were evaluated in radioligand binding
assays. Ki values against the human NOP receptor were determined
from competition binding assays using [125I]nociceptin and h-NOP
Table 1
Binding affinities of spiropiperidine analogs
N
R2
N
NR1
O
where R1 =
Cl
Cl
A
B
Cl
Cl
H3C CH3
C
D
Compound
R1
R2
Ki (nM)
NOP
DOP
37,890
33,095
23,175
15,325
59,420
9111
KOP
137
150
506
1342
773
543
MOP
489
9
A
A
A
A
A
A
A
A
A
A
A
B
B
B
B
H–
Me
Et
Pr
Bu
i-Pr
23
31
84
34
57
66
83
53
89
234
203
6.8
48.7
56
19.5
10
11
12
13
14
15
16
17
18
19
2
692
2283
11,755
8438
4042
5279
nt
c-PrCH2–
c-BuCH2–
c-HexylCH2–
Propargyl
Allyl
H–
Bu–
i-Amyl
CH3OC(O)CH2–
5412
8210
633
1846
2316
1268
694
5887
81,010
46,515
2274
187,050
44,025
45,335
150,385
192,050
60,980
122,080
nt
4314
63,020
5945
33,120
13,000
683
20
21
22
(continued on next page)

1166
J. P. Caldwell et al. / Bioorg. Med. Chem. Lett. 19 (2009) 1164–1167
Table 1 (continued)
Compound
R1
R2
Ki (nM)
NOP
18.5
26
47.8
DOP
5612
28,990
32
578
868
955
1525
759
KOP
1747
MOP
483
726
886
1069
776
745
625
400
421
978
23
24
25
26
27
28
29
30
31
32
33
34
35
36
B
B
B
B
B
B
B
B
B
B
B
B
B
B
HO(CH2)2–
MeO(CH2)2–
NH2(CH2)2–
CH3NH(CH2)2–
EtNH(CH2)2–
i-PrNH(CH2)2–
c-PentylNH(CH2)2–
c-HexylNH(CH2)2–
(CH3)2N(CH2)2–
c-PrNH(CH2)2–
(i-Pr)2N(CH2)2–
BuNH(CH2)2–
1830
852
871
497
469
247
224
320
1014
674
165
238
271
4.05
2.1
2.55
8.65
5
3.5
3.7
933
1136
4758
1033
878
12.1
1921
2546
1376
1800
2.15
2.75
3.8
i-BuNH(CH2)2–
c-HexylCH2NH(CH2)2–
1535
37
38
39
B
B
B
2.25
3.2
8
906
2381
3176
254
436
436
683
N
N
(CH2)2-
(CH2)3-
(CH2)2-
64
279
N
40
41
42
43
44
45
46
47
48
49
C
C
C
C
C
C
C
C
C
C
H–
2.3
0.8
0.7
0.7
0.5
0.5
0.6
0.5
0.4
1.0
1633
2270
1676
1080
445
370
516
376
867
52
68
54
40
25
29
13
8
29
146
167
136
89
112
28
26
CH3NH(CH2)2–
EtNH(CH2)2–
i-PrNH(CH2)2–
c-PrCH2NH(CH2)2–
c-BuNH(CH2)2–
PrNH(CH2)2–
i-BuNH(CH2)2–
BuNH(CH2)2–
Et2N(CH2)2–
10
56
36
122
379
50
C
2.3
538
15
37
N
(CH2)2-
3
D
D
D
D
D
D
D
D
D
D
D
D
D
D
D
H–
Pr–
1.3
5.4
4.5
1.7
2.1
1.6
1.4
0.9
0.9
1.0
0.9
1.5
0.8
0.5
6.7
1790
3103
795
540
1392
56
655
48
39
68
49
33
45
208
45
174
65
86
48
142
14
59
35
37
69
96
120
43
51
52
53
54
55
56
57
58
59
60
61
62
63
64
CH3C(O)CH2–
HO(CH2)2–
2639
1298
2064
5016
1615
1951
2340
2515
2096
2879
1802
2980
CH3NH(CH2)2–
EtNH(CH2)2–
i-PrNH(CH2)2–
c-PentylNH(CH2)2–
c-HexylNH(CH2)2–
PrNH(CH2)2–
CH2@CHCH2NH(CH2)2–
c-BuNH(CH2)2–
c-PrCH2NH(CH2)2–
i-BuNH(CH2)2–
(i-Pr)2NH(CH2)2–
198
64
239
61
82
65
D
1.4
1224
169
69
N
(CH2)2-
66
67
68
69
D
D
D
D
BuNH(CH2)2–
0.5
0.4
0.7
3.6
3948
2600
1693
1279
138
82
26
66
204
102
139
i-AmylNH(CH2)2–
c-HexylCH2NH(CH2)2–
BnNH(CH2)2–
151
Values are means of 2–3 experiments. nt, not tested.
Additionally, we pursued the SAR of the gem-dimethyltetralinyl
analogs (R1 = D). In this SAR, single-digit nanomolar potency was
achieved at NOP regardless of the amido substitution. Indeed, the
alkylaminoalkyl side chain could be replaced by other amido mod-
ifications which were tolerated, as well (51–53). Several examples
in this series displayed subnanomolar potency at NOP while exhib-
iting tremendous selectivity over the other opioids (60, 62, 66, and
67).
Although NOP potency ranged from subnanomolar (72) to low
double digit nanomolar (70 and 73), the selectivity against KOP
for all compounds in this series decreased markedly relative to
compound 66.
Compound 66 was selected for further profiling. Compound 66
increases [35S]GTP
cS binding thereby acting as a full agonist in the
h-NOP functional assay as shown in Table 3. Compound 66 pos-
sessed an acceptable pharmacokinetic profile at a 10 mpk oral dose
in rat with an AUC(0–6 h) of 1165 nM h and a Cmax at 6 h = 279 nM.
Moreover, compound 66 had improved solubility compared to
the parent compound 3 (data not shown). Additionally, compound
The SAR of various tetralinyl analogs was explored where the
amido nitrogen was substituted with the butylaminoethyl side
chain as in compound 66. The results are shown in Table 2.

J. P. Caldwell et al. / Bioorg. Med. Chem. Lett. 19 (2009) 1164–1167
1167
Table 2
66 was efficacious in a pharmacological model of cough, namely
the capsaicin-induced guinea pig model,4a,b and displayed antitus-
sive activity with an ED50 < 3 mg/kg, po at 2 h. Furthermore, com-
pound 66 was tested in a hERG rubidium efflux FLIPR assay and
exhibited modest activity of 40% inhibition at a concentration of
Binding affinities of tetralinyl analogs
5
l
g/ml.
N
NR1
In summary, we have developed several small-molecule NOP
N
agonists through two-point modification which display excellent
selectivity over the other opiate receptors. Furthermore, com-
pound 66 was identified as a compound displaying in vivo efficacy
in the guinea pig model of capsaicin-induced cough.
BuHN
O
Compound
R1
Ki (nM)
Compound 32: 1H NMR (CDCl3, 400 MHz) d 7.63 (t, 2H); 7.30–
7.37 (m, 4H); 7.24 (t, 2H); 7.14 (t, 2H); 6.98 (d, 2H); 6.90 (t, 1H);
7.63 (t, 2H); 5.49 (s, 1H); 7.63 (t, 2H); 4.69 (s, 2H); 3.52 (t, 2H);
3.04 (t, 2H); 7.63 (t, 2H); 2.95 (t, 2H); 2.69 (d, 2H); 7.63 (t, 2H);
2.58 (t, 2H); 2.17 (m, 1H); 1.63 (br s, 1H); 0.43 (dt, 2H); 0.29 (dt,
2H). Mass Spec. ESI (M+1) = 549.1 (100), 315.1 (52).
NOP
15.9
DOP
KOP
11
MOP
297
Cl
70
71
1062
1316
Compound 66: 1H NMR (CDCl3, 400 MHz) d 7.87 (t, 1H); 7.33 (m,
4H); 7.19 (m,1H); 7.01 (d, 2H); 6.88 (t, 1H); 4.77 (q, 2H); 3.84 (t,
1H); 3.55 (t, 2H); 3.52 (t, 2H); 2.88 (t, 2H); 2.85 (m, 3H); 2.64 (t,
2H); 2.44 (m, 1H); 1.93 (m, 2H); 1.76 (d, 2H); 1.63 (m, 1H); 1.58
(d,1H); 1.45 (t, 2H); 1.35 (m, 2H); 1.32 (s, 3H); 1.24 (s, 3H); 0.89
(t, 3H). Mass Spec. ESI (M+1) = 489.1 (92), 331.1 (100).
1.8
0.6
14
25
141
50
Cl
72
73
883
Acknowledgments
Cl
We would like to thank Dr. William Greenlee for his support and
guidance of this work, Dr. Steven Sorota for performing the hERG
activity assay, and Dr. Jesse Wong for preparation of intermediates.
Cl
Cl
12.2
5022
158
306
References and notes
1. (a) Caldwell, J. P.; Matasi, J. J.; Zhang, H.; Fawzi, A.; Tulshian, D. B. Bioorg. Med.
Chem. Lett. 2007, 17, 2281; (b) Roever, Stephan; Adam, Geo; Cesura, Andrea M.;
Galley, Guido; Jenck, Francois; Monsma, Frederick J.; Wichmann, Juergen;
Dautzenberg, Frank M. J. Med. Chem. 2000, 43, 1329. EP 0856514B1.
Values are means of 2–3 experiments.
2. Reuschling, D.; Pietsch, H.; Linkies, A. Tetrahedron Lett. 1978, 7, 615.
3. (a) Fawzi, Ahmad B.; Zhang, Hongtao; Weig, Blair; Hawes, Brian; Graziano,
Michael P. Eur. J. Pharmacol. 1997, 336, 233; (b) Corboz, M. R.; Rivelli, M. A.; Egan,
R. W.; Tulshian, D.; Matasi, J.; Fawzi, A. B.; Benbow, L.; Smith-Torhan, A.; Zhang,
H.; Hey, J. A. Eur. J. Pharmacol. 2000, 402, 171.
Table 3
Functional activity of compound 66
% stimulation of [35S]GTP
c
S
At [lM]
4. (a) Mcleod, R. L.; Parra, L. E.; Mutter, J. C.; Erickson, C. H.; Carey, G. J.; Tulshian, D. B.;
Fawzi, A. B.;Smith-Torhan, A.; Egan, R. W.;Cuss, F. M.; Hey, J. Br. J. Pharmacol. 2001,
1326, 1175;(b)Mcleod, R. L.;Bolster, D. C.; Jia, Y.; Parra, L. E.; Mutter, J. C.;Wang, X.;
Tulshian, D. B.; Egan, R. W.; Hey, J. A. Pulm. Pharmacol. Ther. 2002, 153, 213.
119
92
60
10
1
0.1