Fused tricyclic pyrrolizinones that exhibit pseudo-irreversible blockade of the NK1 receptor

Article abstract of DOI:10.1016/j.bmcl.2010.07.058

Previously, we had disclosed a novel class of hNK₁ antagonists based on the 5,5-fused pyrrolidine core. These compounds displayed subnanomolar hNK₁ affinity along with good efficacy in a gerbil foot-tapping (GFT) model, but unfortunately they had low to moderate functional antagonist (IP-1) activity. To elaborate on the SAR of this class of hNK₁ compounds and to improve functional activity, we have designed and synthesized a new class of hNK₁ antagonist with a third fused ring. Compared to the 5,5-fused pyrrolidine class, these 5,5,5-fused tricyclic hNK₁ antagonists maintain subnanomolar hNK₁ binding affinity with highly improved functional IP-1 activity (<10% SP remaining). A fused tricyclic methyl, hydroxyl geminally substituted pyrrolizinone (compound 20) had excellent functional IP (<2% SP remaining), hNK₁ binding affinity, off-target selectivity, pharmacokinetic profile and in vivo activity. Complete inhibition of agonist activity was observed at both 0 and 24 h in the gerbil foot-tapping model with an ID₅₀ of 0.02 mpk at both 0 and 24 h, respectively.

Full text of DOI:10.1016/j.bmcl.2010.07.058

Bioorganic & Medicinal Chemistry Letters 20 (2010) 5925–5932
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Fused tricyclic pyrrolizinones that exhibit pseudo-irreversible blockade
of the NK1 receptor
b
a
a
b
b
Gregori J. Morriello a, , Gary Chicchi , Tricia Johnson , Sander G. Mills , Julie DeMartino , Marc Kurtz ,
K. L. C. Tsao b, Song Zheng c, Xinchun Tong c, Emma Carlson d, Karen Townson d, Alan Wheeldon d,
Susan Boyce d, Neil Collinson d, Nadia Rupniak d, Robert J. DeVita a
*
a Department of Medicinal Chemistry, Merck Research Laboratories, PO Box 2000, Rahway, NJ 07065, USA
b Department of Immunology, Merck Research Laboratories, PO Box 2000, Rahway, NJ 07065, USA
c Department of Drug Metabolism, Merck Research Laboratories, PO Box 2000, Rahway, NJ 07065, USA
d Department of Behavioral Neuroscience, Merck Research Laboratories, Terlings Park, UK
a r t i c l e i n f o
a b s t r a c t
Article history:
Previously, we had disclosed a novel class of hNK1 antagonists based on the 5,5-fused pyrrolidine core.
These compounds displayed subnanomolar hNK1 affinity along with good efficacy in a gerbil foot-tapping
(GFT) model, but unfortunately they had low to moderate functional antagonist (IP-1) activity. To elabo-
rate on the SAR of this class of hNK1 compounds and to improve functional activity, we have designed and
synthesized a new class of hNK1 antagonist with a third fused ring. Compared to the 5,5-fused pyrrolidine
class, these 5,5,5-fused tricyclic hNK1 antagonists maintain subnanomolar hNK1 binding affinity with
highly improved functional IP-1 activity (<10% SP remaining). A fused tricyclic methyl, hydroxyl geminally
substituted pyrrolizinone (compound 20) had excellent functional IP (<2% SP remaining), hNK1 binding
affinity, off-target selectivity, pharmacokinetic profile and in vivo activity. Complete inhibition of agonist
activity was observed at both 0 and 24 h in the gerbil foot-tapping model with an ID50 of 0.02 mpk at both
0 and 24 h, respectively.
Received 19 February 2010
Revised 12 July 2010
Accepted 14 July 2010
Available online 19 July 2010
Keywords:
Neurokinin
Neurokinin-1 antagonists
Functional IP
Ó 2010 Elsevier Ltd. All rights reserved.
Interest in neurokinin-1 (NK1) antagonists for treatment of CNS
disorders greatly increased in the 1990s and resulted in the discov-
ery of EmendÒ for the treatment of chemotherapy induced nausea
and vomiting.1 Considerable research has been done in the last
decade on the physiological effects of substance P (SP) on the
NK1 receptor, which led to other potential medicinal uses for
hNK1 antagonists including the treatment of anxiety, depression,
and urge urinary incontinence.2
Therefore, compounds with poor functional IP-1 require high-
er drug levels to maintain high receptor occupancy (RO), and
thus necessitates a higher initial dose of the compound. This,
in turn, could reduce the safety margins due to the higher drug
concentrations. It was desired to find compounds with greater
functional IP-1 that in turn would lead to a higher RO at much
lower drug concentrations and thereby increasing the margin
of safety.
Previously, we had disclosed a new structurally diverse class of
5,5-fused pyrrolidine-based NK1 antagonists that displayed good
binding affinity, bioavailability, and efficacy profiles.3 However,
these compounds proved to have low to moderate activity in the
functional IP-1 assay.3,4 The functional IP-1 assay,5 measures the
In an attempt to improve functional activity, it was proposed that
a more rigid structure might be advantageous since substituents at
the
a and b positions of the cyclic lactam fused to the pyrrolidine
core exhibited moderate increases in functional IP-1 activity.4
A
more rigid structure may also give the desired steric interactions
which may enable it to bind more tightly to the receptor, in essence,
improving the functional activity of NK1 antagonism. In addition,
other series of fused bicyclic tetrahydroquinoline NK1 antagonists7
and 5,5-fused pyrrolidines inspired our interest in fused tricyclic
pyrrolidines. (Fig. 1) Thus, chemistry was developed to make fused
tricyclic pyrrolidines in the hopes that this modification would re-
tain NK1 binding affinity while improving other physical–chemical
and pharmacological properties.
activity of substance P (at 10 lM concentrations) remaining in
hNK1 overexpressing CHO cells after pre-treatment with the antag-
onist at 100 nM. We find that those compounds with low substance
P response remaining (<10% SPRR) display pseudo-irreversible
blockade of the NK1 receptor. In turn, we have found that this prop-
erty (low SPRR) correlates well with receptor off-rates,6 leading to
lower plasma concentrations necessary for high central receptor
occupancy in an in vivo rhesus receptor occupancy model.1,17
Two types of tricyclic compounds were of interest to us: (1) the
fusion of a pyrrolidine ring and (2) the fusion of a cyclopentyl ring
with the ability for addition of substitutions on each ring. The
* Corresponding author. Tel.: +1 732 594 3867; fax: +1 732 594 5350.
E-mail address: greg_morriello@merck.com (G.J. Morriello).
0960-894X/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2010.07.058

5926
G. J. Morriello et al. / Bioorg. Med. Chem. Lett. 20 (2010) 5925–5932
CF3
CF3
CF3
O
O
CF3
CF3
O
CF3
O
Boc
N
N
O
N
H
OH
X
X= O, N, C
R'
(H,F)
X
R
(H,F)
5,5,5 fused tricyclic pyrrolidine
Figure 1. Tricyclic design derived from bicyclic scaffold.
R
(H,F)
1
5,5 fused pyrrolidine
Figure 2. Enantiomerically pure starting material.
The cyclopentyl lactam compounds were slightly more compli-
cated to prepare: however, the a,b-unsaturated ester intermediate
chemistry was first developed in which a pyrrolidine was incorpo-
rated as the third fused ring (Scheme 1).
3 from the synthesis of the pyrrolidine compounds could be uti-
lized for the cyclopentyl series, by reaction with 2-[(trimethyl-
silyl)methyl]prop-2-en-1-yl acetate in the presence of palladium
acetate and tri-isopropoxy-phosphite refluxed in toluene for 5 h12
(Scheme 2). This afforded a cyclopentyl ring with an exo-double
bond 7 that could be manipulated into different functional groups.
Oxidation of the methylene with ozone followed by reduction of
the ozonide with triphenylphosphine afforded the cyclopentyl ke-
tone 8. Then, using the conditions similar to the prior chemistry,
acidic deprotection and EDC coupling of the amino acid gave the
tricyclic fused cyclopentyl lactam 9. Separation of the two cis
cyclopentyl diastereomers (9a,b)11 at this stage was accomplished
via MPLC purification using a Biotage flash 40 + silica gel cartridge
and eluting with a gradient of 10–60% ethyl acetate in hexane. The
primary amino compounds were prepared via treatment of the ke-
tones with sodium(triacetoxy)borohydride in the presence of ben-
zyl amine and molecular sieves to afford the benzyl protected
amines 10a,b and 12a,b. Then the resulting benzyl protected
amines were hydrogenated to give 11a,b and 13a,b as a mixture
of amino diastereomers. The alcohol compounds were also of
The more active enantiomerically pure alcohol (intermediate 1)
was already determined from previous chemistry in the synthesis
of the 5,5-fused pyrrolidine compounds,3 Figure 2. Therefore, sim-
ple chemical manipulations of this known intermediate 1 led to the
desired fused tricyclic pyrrolidine core hNK1 antagonists.
First, the alcohol 1 was oxidized to the aldehyde 2 via Swern oxi-
dation.8 This intermediate was then immediately used without puri-
fication in a Wittig reaction9 to give the
a,b-unsaturated ester 3.
Treatment of the unsaturated ester with N-benzyl-1-methoxy-N-
[(trimethylsilyl)methyl]methanamine, in the presence of 0.4 M e-
quiv of TFA overnight afforded the cyclic N-benzyl pyrrolidine 4.10
Simultaneous removal of the Boc and t-butyl ester with 4 N HCl in
dioxane followed by treatment with EDC and DMAP in the presence
of DIEA gave the penultimate tricyclic fused pyrrolidine lactam 5.
The benzyl group was then removed via hydrogenolysis to afford
the 5,5,5-fused cis pyrrolidine lactam diastereomers 6a,b.11 Other
analogs were synthesized via substitutions on the available nitrogen
of the pyrrolidine ring.
F3C
F3C
O
CF3
O
CF3
a
b
Boc
N
Boc
N
O
F
F
O
O
N
2
3
F3C
F3C
O
CF3
O
CF3
O
Boc
N
c,d
e
H
N
N
F
O
F
O
5
4
F3C
F3C
O
CF3
O
CF3
O
O
N
N
H
H
N
H
F
F
N
R
6a, b
Scheme 1. Reagents and conditions: (a) (t-butoxycarbonylmethylene)triphenylphosphorane, DCM rt overnight (78%); (b) N-benzyl-1-methoxy-N-[(trimethyl-
silyl)methyl]methanamine, TFA, DCM, rt overnight (89%); (c) 4 N HCl in dioxane, 1 h quantitative; (d) EDC, DMAP, DIEA, DCM, rt, overnight (65%); (e) 10% palladium on
carbon, H2, MeOH, 1 equiv HCl, 3 h (82%).

G. J. Morriello et al. / Bioorg. Med. Chem. Lett. 20 (2010) 5925–5932
5927
F3C
F3C
F3C
F3C
O
CF3
O
O
CF3
O
CF3
CF3
Boc
N
O
Boc
Boc
h, i
N
N
N
g
j
f
O
F
O
F
O
F
F
O
O
3
7
O
O
O
8
9
F3C
CF3
CF3
O
CF3
O
O
CF3
CF3
O
H
O
m
O
N
N
N
H
H
H
H
H
H
H
H
F
F
F
9b
O
9a
O
14a and 14b
HO
k
CF3
k
F3C
CF3
F3C
O
CF3
O
H
O
CF3
N
O
O
CF3
CF3
O
N
O
O
l
N
N
l
H
H
H
H
H
H
H
H
H
F
H
H
F
H2N
F
F
11 a,b
10a, b
H2N
13a, b
12 a, b
HN
HN
Scheme 2. Reagents and conditions: (f) 2-[(trimethylsilyl)methyl]prop-2-en-1-yl acetate, Pd(OAc)2, P(OiPr)3, toluene, reflux 5 h (74%); (g) ozone, DCM À78 °C followed by
PPh3 rt overnight (78%); (h) 4 N HCl in dioxane, 1 h. (quantitative); (i) EDC, DMAP, DIEA, DCM, rt, overnight (74% mixture of isomers); (j) separation of isomers by MPLC
eluting with 100% ethyl acetate; (k) benzyl amine, Na(OAc)3BH, DCM, 4 Å MS rt 16 h (59–70%); (l) 10% Pd/C, methanol, 1 equiv HCl under H2 atm 2 h (82–94%); (m) NaBH4,
methanol, rt 5 h (54–61%).
Table 1
Sample structural activity relationship (SAR) from 5,5-fused bicyclic pyrrolidinones
a
b
Compounda,4
Structure
hNK1 IC50
IP-1c% SP
remaining
hPXR inductiond
IC50 M) (%max)
Ion channelsd
IC50 M)
Gerbil foot-tappinge (GFT)
(nM)/50% HS
(
l
(l
F3C
CF3
Ikr: 6.5
Dz: 0.21
100% inh. at 3 mpk (24 h)
ED50 = 0.61 mpk (24 h)
15
O
0.06/0.38
59
>25 (7)
O
N
Na: 0.24
H
H2N
F
F3C
CF3
16
0.09/0.60
75
>25 (1)
O
Ikr: 9.5
Dz: 1.88
Na: 7.72
100% inh. at 3 mpk (24 h)
ED50 = 0.92 mpk (24 h)
O
N
H
NH2
F
(continued on next page)

5928
G. J. Morriello et al. / Bioorg. Med. Chem. Lett. 20 (2010) 5925–5932
Table 1 (continued)
a
b
Compounda,4
Structure
hNK1 IC50
IP-1c% SP
remaining
hPXR inductiond
IC50 M) (%max)
Ion channelsd
IC50 M)
Gerbil foot-tappinge (GFT)
(nM)/50% HS
(
l
(l
F3C
CF3
Ikr: 5.7
Dz: 1.58
Na: 1.75
100% inh. at 3 mpk (24 h)
ED50 = 0.20 mpk (24 h)
17
0.06/2.20
88
4.8 (50)
O
O
N
H
F
a
All compounds gave satisfactory 1H NMR and mass spectral data.
b
c
Displacement of [125I]SP from the human hNK1 receptor expressed in CHO cells. See also Ref. 13 and note 14.
IP-1 assay: measures the response of inositol phosphate generation to substance P (10 mM) and is reported as the percentage of substance P remaining (SPRR) at 100 nM
NK1 antagonist concentration; Ref. 5.
d
Ion channels: binding assay in which IC50’s are calculated for both sodium and calcium (Dlz) channels. hPXR induction %max at 10 lM.
Inhibition of GR73632 induced foot tapping in gerbils at concentration and time point given in the table (i.e., 3 mpk (24 h)); Ref. 15.
e
interest, and therefore, reduction of ketone 9a to the corresponding
alcohols 14a,b11 was completed upon treatment with sodium
borohydride. Further manipulations of the desired isomer of the
ketone intermediate (9a) with Grignard reagents offered another
modification to the compounds as exhibited in the examples
shown in Table 4.
Table 1 shows a subset of 5,5-fused pyrrolidine hNK1 antago-
nists previously disclosed in the literature.3,4 They proved to have
excellent hNK1 binding affinity along with moderate efficacy as
exhibited in the GFT15 assay. However, the major concern with
these compounds was the high percent of substance P remaining
in the functional IP-1 assay. High percentage numbers in this assay
Table 2
SAR of the tri-cyclic fused pyrroline/pyrrolidinone
Compounda
Structurea
hNK1 IC50 (nM)/50% HS
IP-1c% SP remaining
Ion channelsd IC50
(l
M)
Gerbil foot tappinge (GFT)
b
O
H
CF3
N
O
HN
n/af
n/af
H
6a
1.5/15.0
46
H
CF3
F
O
CF3
H
N
O
HN
12% inh. at 3 mpk (24 h)
H
Ikr: 2.71
Dz: 0.31
6b
0.31/3.2
60
H
CF3
F
O
CF3
H
N
O
N
18ad
0.17/1.9
11
O
O
H
Ikr: 1.43
Dz: 8.81
32% inh. at 3 mpk (24 h)
H
CF3
F
O
H
CF3
H
N
O
N
18be
0.09/1.0
7
92% inh. at 1 mpk (1 h)
74% inh. at 3 mpk (24 h)
H
Ikr: 0.73
Dz: 4.81
CF3
F
a
All compounds gave satisfactory mass spectral data. Stereochemistry was not assigned and isomers were labeled in order of retention (a: first isomer eluded, b: second
isomer).
b
Displacement of [125I]SP from the human hNK1 receptor expressed in CHO cells. See also Ref. 13 and note 14.
IP-1 assay: measures the response of inositol phosphate generation to substance P (10 mM) and is reported as the percentage of substance P remaining (SPRR) at 100 nM
c
NK1 antagonist concentration; Ref. 5.
d
Ion channels: binding assay in which IC50’s are calculated for both sodium and calcium (Dlz) channels.
Inhibition of GR73632 induced foot tapping in gerbils at concentration and time point given in the table (i.e., 3 mpk (24 h)); Ref. 15.
n/a stands for no data available.
e
f

G. J. Morriello et al. / Bioorg. Med. Chem. Lett. 20 (2010) 5925–5932
5929
were associated with fast off-rates on the hNK1 receptor which cor-
related to the need for much higher dosing levels for good duration
of pharmodynamic (PD) activity.16
This is illustrated by compound 16 with a measured receptor
occupancy off-rate of less than 100 min. To maintain good receptor
occupancy, the dose of drug would have to be rather high which
would drastically reduce safety margins. As can also be seen in
the functional antagonist IP-1 assay. In vivo efficacy for compound
(18b) was 74% inh. at 3 mpk seen at 24 h, a promising result; how-
ever, loss of IKr selectivity proved to be a liability for this series of
compounds. Having demonstrated that an additional ring substan-
tially increased the functional receptor blockade, exploration of the
substituted cyclopentane ring was deemed important to reduce
Dlz binding affinity.
Table 1,
a
(15) and b (16) substitutions on the fused bicyclic series
Table 3 contains the data for the key compounds synthesized in
the cyclopentane 5,5,5-fused tricyclic hNK1 antagonist series. As
can be seen, the conformational differences of the diastereomers
had a great impact on the observed functional IP-1 activity.
The desired (more active) conformation greatly enhanced func-
tional activity exhibiting less than 5% substance P remaining. In the
case of the amino substituted compounds, all four diastereomers
were synthesized. After inspection of the intrinsic binding data,
only the diastereomers of the hydroxyl compounds formed from
intermediate 9a were selected to be assayed for hNK1 binding
affinity.
did give slightly better functional IP numbers. As we extended the
substitution out, the numbers seem to improve.4 Thus, we decided
to explore the 5,5,5-fused tricyclic pyrrolidines in the hope of
seeing improvement in the functional activity of these hNK1
antagonist to less than 10% remaining.
The first series of compounds, shown in Table 2, contained the
fused pyrrolidine ring as the third fused ring. During formation
of the pyrrolidine ring, two diastereomers were formed and sepa-
rated during the synthesis of pyrrolidine compound 6. Compounds
6a and 6b displayed slightly increased IP-1 functional activity (60%
and 46% SP remaining, respectively). The addition of a substituent,
such as the vinylogous amide moiety, greatly improved results in
Analogs 12a and 12b, in which the fused ring was in the less ac-
tive stereochemical series, had reasonable intrinsic binding activ-
Table 3
SAR of the tri-cyclic fused substituted cyclopentane/pyrrolidinone
Compounda
Structurea,g
hNK1 IC50
IP-1c% SP
remaining
PXR Induction
IC50 M) (%max)
Ion channelsd
IC50 M)
Gerbil foot
b
(nM)/50% HS
(
l
(
l
tappinge (GFT)
O
H
CF3
H
N
O
12a
1.2/13.0
94
n/af
n/af
n/af
N
H
H
CF3
F
O
H
CF3
H
N
O
81% inh. at 1 mpk (1 h)
6% inh. at 3 mpk (24 h)
N
H
H
12b
10a
10b
0.14/2.3
0.14/1.3
0.17/1.8
58
n/af
n/af
CF3
F
O
H
CF3
H
N
Ikr: 0.30
Dz: 0.21
Na: 0.21
94% inh. at 3 mpk (24 h)
O
O
N
H
H
4
>25 (0)
CF3
F
F
O
H
CF3
H
N
Ikr: 0.28
Dz: 0.14
Na: n/a
100% inh. at 3 mpk (24 h)
ED50 = 0.47 mpk (24 h)
N
H
H
2
>25 (0)
CF3
O
CF3
H
N
O
H2N
H
13a
1.5 /47.0
93
n/a
n/a
n/a
CF3
H
F
(continued on next page)

5930
G. J. Morriello et al. / Bioorg. Med. Chem. Lett. 20 (2010) 5925–5932
Table 3 (continued)
b
Compounda
Structurea,g
hNK1 IC50
IP-1c% SP
remaining
PXR Induction
IC50 M) (%max)
Ion channelsd
IC50 M)
Gerbil foot
(nM)/50% HS
(
l
(
l
tappinge (GFT)
O
CF3
H
H
H
N
O
H2N
H
13b
0.66/13.0
61
n/a
n/a
n/a
H
CF3
F
O
CF3
N
Ikr: 1.73
Dz: 0.59
Na: 0.52
100% inh. at 3 mpk (24 h)
ED50 = 1.33 mpk (24 h)
O
H2N
H
11a
0.11/1.0
10
>25 (0)
H
CF3
F
O
H
CF3
N
O
91% inh. at 3 mpk (24 h)
Ikr: 0.99
Dz: 1.23
H2N
HO
HO
H
11b
0.09/1.0
0.06/0.77
0.08/1.7
6
>25 (0)
4.5 (65)
n/af
CF3
Na: 0.71
F
O
H
CF3
H
N
O
n/af
100% inh. at 1 mpk (1 h)
100% inh. at 3 mpk (24 h)
H
14a
3
CF3
F
O
CF3
H
N
O
14b
35
n/af
n/af
H
H
CF3
F
All compounds gave satisfactory 1H NMR and mass spectral data.
a
b
c
Displacement of [125I]SP from the human hNK1 receptor expressed in CHO cells. See also Ref. 13 and note 14.
IP-1 assay: measures the response of inositol phosphate generation to substance P (10 mM) and is reported as the percentage of substance P remaining (SPRR) at 100 nM
NK1 antagonist concentration; Ref. 5.
d
Ion channels: binding assay in which IC50’s are calculated for both sodium and calcium (Dlz) channels. hPXR induction %max at 10 lM.
Inhibition of GR73632 induced foot tapping in gerbils at concentration and time point given in the table (i.e., 3 mpk (24 h)); Ref. 15.
n/a stands for no data available.
e
f
g
Stereochemistry of the amino substituent was not confirmed and are drawn on the assumption that they follow the same stereochemistry as their related hydroxyl
substituted compounds. (i.e., 14a known stereochemistry relative to 11b since they are the more potent diastereomers in their related series).
ity, however, they were shown to be ineffective at blocking the ef-
fects of substance P in the IP-1 assay with 58–94% substance P
remaining. Analog 12b also proved to have a short duration of
activity in the GFT assay with good response of 81% inh. at
1 mpk at 1 h but only 6% inh. at 3 mpk at the 24 h time point. As
for the diastereomers, analogs 10a and 10b had similar, if not
slightly better, binding affinities and were able to block the sub-
stance P response by greater than 95% (4% and 2% SPRR) at
100 nM. This also correlated with excellent efficacy and duration
of activity with 100% inh. at 3 mpk at 24 h with an IC50 of
0.47 mpk. This compound demonstrated rapid brain penetration
with a good duration of action in blocking the agonist induced foot
tapping response in the gerbil model. Although, the ion channel
selectivity was greatly compromised with both IKr and calcium
channel (Dlz) activity of less than 300 nM.
Analogs 11a and 11b IKr selectivity had significantly improved
along with their sodium and calcium channel selectivity. However,
the in vivo efficacy was disappointing and, therefore, we moved on
to examining the hydroxyl substitution.
Since we had now determined the desired, more active diaste-
reomer from the amino compounds, the corresponding ketone
intermediate (9a) was taken on to the hydroxyl analogs via simple
sodium borohydride reduction to give a mixture of two isomers
(14a and 14b) which were separated via chiral HPLC purification
on a ChiralCel OD column. The two analogs exhibited excellent
intrinsic binding activity with minimal serum shifts. The functional
IP-1 assay distinguished the superior isomer (14a) with 3% sub-
stance P remaining (as compared to 14b with 35%). The GFT proved
to be extremely promising with 100% inhibition of the foot-tapping
response at both 1 h (1 mpk dose) and 24 h (3 mpk dose) time

G. J. Morriello et al. / Bioorg. Med. Chem. Lett. 20 (2010) 5925–5932
5931
Table 4
SAR of the Grignard addition products
b
Compound
Structurea
hNK1 IC50
IP-1c% SP
remaining
hPXR induction
IC50 M) (%max)
Ion channelsd
IC50 M)
Gerbil foot tapping
e(GFT) IC50
M)
(nM)/50% HS
(
l
(
l
(l
O
CF3
H
H
H
H
N
O
O
O
O
HO
HO
H
19
0.066/1.20
0.061/0.70
0.21/2.3
24
n/af
n/af
n/af
H
CF3
F
F
F
F
O
H
CF3
N
H
20
21
22
3
8.4 (37)
Ikr: 2.47
Dz: >10
Na: >10
100% inh. at 3 mpk (24 h)
ED50 = 0.02 mpk (24 h)
CF3
O
H
CF3
N
HO
HO
H
31
n/af
n/af
n/af
CF3
O
H
CF3
N
H
0.16/1.7
4
3.3 (51)
Ikr: 1.77
Dz: 8.42
100% inh. at 3 mpk (24 h)
ED50 = 0.06 mpk (24 h)
CF3
Na: n/a
a
b
c
All compounds gave satisfactory 1H NMR and mass spectral data.
Displacement of [125I]SP from the human hNK1 receptor expressed in CHO cells. See also Ref. 13 and note 14.
IP-1 assay: measures the response of inositol phosphate generation to substance P (10 mM) and is reported as the percentage of substance P remaining (SPRR) at 100 nM
NK1 antagonist concentration; Ref. 5.
d
Ion channels: binding assay in which IC50’s are calculated for both sodium and calcium (Dlz) channels. hPXR induction %max at 10 lM.
Inhibition of GR73632 induced foot tapping in gerbils at concentration and time point given in the table (i.e., 3 mpk (24 h)); Ref. 15.
n/a stands for no data available.
e
f
points. Unfortunately, the off-target activity proved to be a concern
with the hPXR inhibition at IC50 of 4.5 M with 65% inhibition seen
at 10 M concentration.
Table 5 summarizes the activity and pK profile of the gem
substituted hydroxyl, methyl analog 20. The cross species intrinsic
binding affinities in the presence of 50% serum were surprisingly
equipotent with IC50’s still less than 2 nM. The functional IP was ti-
trated down to 1 nM with a receptor blockade of 64% (36% SPRR).
Microsomal stability was excellent across species with greater
than 90% parent remaining after a 60 min incubation with micro-
somes. The ancillary activity was minimal and the compound’s
brain/plasma ratio was 0.5 in the gerbil PK/PD study. Looking at
the pK values in rat, the clearance was very low and the compound
had an excellent half life of 14.6 h with bioavailability of ꢀ88%. The
dog pK also proved to have a particularly long half-life of 58 h. The
compound proved to have long duration of activity in vivo and the
pK profile seemed to justify this result with long half-lives and low
clearance in two species.
Thus, we have presented a series of 5,5,5-tricyclic fused pyrrol-
idines that displayed excellent hNK1 intrinsic binding affinity and
good functional IP-1 activities with the better diastereomers hav-
ing less than 5% substance P remaining. This series clearly showed
much improvement in functional activity versus the prior 5,5-
fused compounds. Compound 20 in particular exhibited drug-like
pharmacokinetics with reduced potential for inhibition or induc-
tion of the CYP enzymes and good off-target activity. The pK profile
across species was also extremely promising.
l
l
As stated previously, a Grignard addition to the ketone gave an-
other set of analogs that could be examined in the functional IP-1
assay. Grignard addition to the desired ketone intermediate (9a)
with both methyl and ethyl magnesium bromide was carried out
to give the four geminal substituted analogs shown in Table 4.
The two sets of diastereomers 19, 20 and 21, 22 were equipotent
in terms of the receptor binding affinity, however, analogs 20
and 22 demonstrated superior functional receptor blockade with
3% and 4% substance P remaining, respectively. Both compounds
proved to be extremely efficacious in the GFT assay with ID50’s of
0.02 and 0.06 mpk at 24 h. Ion channels for both were much im-
proved versus the amino compounds along with a minimal po-
tency shift in the presence of 50% human serum. The difference
in the two finally became apparent with the measurement of hPXR
induction. The ethyl substituted compound 22 had twice the po-
tency of the methyl substituted compound 20 with an IC50 of 3.3
versus 8.4 lM, respectively. Thus, compound 22, with intrinsic
hNK1 activity of 0.16 nM, had sevenfold worst off-target selectivity
on hPXR than compound 20, with 0.06 nM hNK1 activity. There-
fore, compound 20 was selected for further follow-up assays to
determine its viability as a drug candidate.

5932
G. J. Morriello et al. / Bioorg. Med. Chem. Lett. 20 (2010) 5925–5932
Table 5
Lead compound of tricyclic hNK1 antagonists
O
CF3
H
N
O
HO
H
H
CF3
F
IC50: 0.06 nM
IC50 + 50% serum:
Human: 0.7 nM
Dog: 1.5 nM
Rhesus: 0.4 nM
Rat: 0.4 nM
Ancillary activity:
CYP inhibition
2D6: 17.38
3A4: 22.68
2C9: 43.12
hPXR: 3.77 lM (38%)
lM
lM
lM
Gerbil: 1.9 nM
*
IP-1: 2% SP remaining (36%SP at 1 nM dose)
GFT:
Gerbil PK/PD iv study:
IC50 = 2.2 nM (1 h brain)
IC50 = 4.3 nM (1 h plasma)
ID50 = 0.02 mg/kg (1 h)
ID50 = 0.02 mg/kg (24 h)
Microsomal stability % remaining (60 min)
Dog: 90%
Human: 96%
Rat: 96%
Rhesus: 99%
Pharmocokinetics
Rat
Dog
0.50
58.02
n/a
Clp (ml/min/kg)
t1/2: (h)
MRT: (h)
Vd: (L/Kg)
F%
3.24
14.60
4.67
4.03
88.83
n/a
BSA for 15 min. Antagonists (100 nM) or anhydrous DMSO were added for
30 min before substance P (up to 10 M) was added for another 30 min. The
reaction was terminated by removal of the medium and addition of formic acid.
The supernatant was aged for 60 min at 22 °C. Lysates (15 L) were incubated
m) SPA beads (Amersham) in
Acknowledgments
l
The authors thank George Doss for the NMR characterizations of
compounds 1, 9a,9b, 14a, 14b, 20, and Paul Finke for his assistance
in the preparation of this Letter.
l
with 1 mg RNA Binding Yittrium Silicate (2–5
l
Optiplates with shaking for 2 h. [H3]-inositol phosphate generation was
quantitated on a Packard Topcount and the data were analyzed using Prism
(GraphPad).
6. Young, J. R.; Eid, R.; Turner, C.; DeVita, R. J.; Kurtz, M. M.; Tsao, K.-L. C.; Chicchi,
G. G.; Wheeldon, A.; Carlson, E.; Mills, S. G. Bioorg. Med. Chem. Lett. 2007, 17,
5310.
7. (a) Devita, R.; Mills, S. G.; Jiang, J.; et al. World Patent 2006/060344, 2006.; (b)
Devita, R.; Mills, S. G.; Jiang, J.; et al. World Patent 2006/060346, 2006.
8. (a) Mancuso, A. J.; Huang, S. L.; Swern, D. J. Org. Chem. 1978, 43, 2480; (b)
Mancuso, A. J.; Swern, D. Synthesis 1981, 3, 165.
Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.bmcl.2010.07.058.
9. (a) Wittig, G.; Geissler, G. Liebigs Ann. Chem. 1953, 580, 44; (b) Wadsworth, W.
S.; Emmons, W. D. J. Am. Chem. Soc. 1961, 7, 1733.
References and notes
10. (a) Terao, Y.; Kotaki, H.; Imai, N.; Achiwa, K. Chem. Pharm. Bull. 1985, 33, 2762;
(b) Luci, D. K.; Santulli, R. J.; Gauthier, D. A.; Tounge, B. A.; Ghosh, S.; Proost, J.
C.; Kinney, W. A.; De Corte, B.; Galemmo, R. A.; Lewis, J. M.; Dorsch, W. E.;
Wagaman, M. W.; Daimiano, B. P.; Maryanoff, B. E. Heterocycles 2004, 62, 543.
11. Compounds 1, 6a, 6b, 9a, 9b, 14a, and 14b relative stereochemistry was
assigned via NOEsy, HMQC, 1H NMR, and 13C NMR. Isomers were compared to
one another and assignments were based on the observation (or absence) of
NOE signal in relation to the surrounding hydrogens of known
stereochemistry.
12. (a) Cossy, J.; Belotti, D.; Pete, J. P. Tetrahedron Lett. 1987, 28, 4547; (b) Trost, B.
M.; Crawley, M. L. J. Am. Chem. Soc. 2002, 124, 9328.
13. Cascieri, M. A.; Ber, E.; Fong, T. M.; Sadowski, S.; Bansal, A.; Swain, C. J.; Seward,
E. M.; Frances, B.; Burns, D.; Strader, C. D. Mol. Pharmacol. 1992, 42, 458.
14. All values represent the average of 2–6 independent experiments. Variability
between experiments was typically less than twofold.
15. (a) Rupniak, N. M. J.; Williams, A. R. Eur. J. Pharmcol. 1994, 265, 179; (b)
Rupniac, N. M. J.; Tattersall, F. D.; Williams, A. R.; Rycroft, W.; Carlson, E. J.;
Cascieri, M. A.; Sadowski, S.; Ber, E.; Hale, J. J.; Mills, S. G.; MacCoss, M.; Seward,
E.; Huscroft, I.; Owen, S.; Swain, C. J.; Hill, R. G.; Hargreaves, R. J. Eur. J.
Pharmcol. 1997, 326, 201.
16. Lin, P.; Chang, L.; DeVita, R. J.; Young, J. R.; Eid, R.; Tong, X.; Zheng, S.; Ball, R. G.;
Tsou, N. N.; Chicchi, G.; Kurtz, M.; Tsao, K.-L. C.; Wheeldon, A.; Carlson, E. J.;
Eng, W.; Burns, D. H.; Hargreaves, R. J.; Mills, S. G. Bioorg. Med. Chem. Lett. 2007,
17, 5191.
17. Jiang, J.; Bunda, J. L.; Doss, G. A.; Chicchi, G. G.; Kurtz, M. M.; Tsao, K.-L. C.; Tong,
X.; Zheng, S.; Upthagrove, A.; Samuel, K.; Tschirret-Guth, R.; Kumar, S.;
Wheeldon, A.; Carlson, E. J.; Hargreaves, R.; Burns, D.; Hamill, T.; Ryan, C.;
Krause, S. M.; End, W.; Devita, R. J.; Mills, S. G. J. Med. Chem. 2009, 52, 3039.
1. (a) Hale, J. J.; Mills, S. G.; MacCoss, M.; Shah, S. K.; Qi, H.; Mathre, D. J.; Cascieri,
M. A.; Sadowski, S.; Strader, C. D.; MacIntyre, D. E.; Metzger, J. M. J. Med. Chem.
1996, 39, 1760; (b) Campos, D.; Pereira, J. R.; Reinhardt, R. R.; Carracedo, C.;
Poli, S.; Vogel, C., et al J. Clin. Oncol. 2001, 19, 1759; (c) Poli-Bigelli, S.;
Rodrigues-Pereira, J.; Carides, A. D.; Ma, G. J.; Eldridge, K.; Hipple, A., et al
Cancer 2003, 97, 3090; (d) Gale, J. D.; O’Neill, B. T.; Humphrey, J. M. Exp. Opin.
Ther. Pat. 2001, 11, 1837.
2. (a) Stahl, S. M. J. Clin. Psychiatry [Brainstorms] 1990, 60, 77; (b) Quatara, L.;
Maggi, C. A. Neuropeptide 1998, 32, 1; (c) Kramer, M. S.; Cutler, N.; Feighner, J.;
Shrivastava, R.; Carmen, J.; Sramek, J. J.; Reines, S. A.; Liu, G.; Snavely, D.;
Wyatt-Knowles, E.; Hale, J. J.; Mills, S. G.; MacCoss, M.; Swain, C. J.; Harrison, T.;
Hill, R. G.; Hefto, F.; Scolnick, E. M.; Cascieri, M. A.; Chicchi, G. G.; Sadowski, S.;
Williams, A. R.; Hewson, L.; Smith, D.; Carlson, E. J.; Hargreaves, R. J.; Rupniak,
N. M. J. Science 1998, 22, 1640; (d) Rupniak, N. M. J.; Kramer, M. S. Trends
Pharmocol. Sci. 1999, 20, 485; (e) Green, S. A.; Alon, A.; Ianus, J.; McNaughton, K.
S.; Tozzi, C. A.; Reiss, T. F. J. Urol. 2006, 176, 2535.
3. Morriello, G. J.; DeVita, R. J.; Mills, S. G.; Young, J. R.; Lin, P.; Doss, G.; Chicchi, G.
G.; DeMartino, J.; Kurzt, M. M.; Tsao, K.-L. C.; Carlson, E.; Townson, K.;
Wheeldon, A.; Boyce, S.; Collinson, N.; Rupniak, N.; Moore, S. Bioorg. Med. Chem.
2008, 16 5, 2156.
4. Morriello, G. J.; DeVita, R. J.; Mills, S. G.; Young, J. R.; Lin, P.; Doss, G.; Chicchi, G. G.;
DeMartino, J.; Kurzt, M. M.; Tsao, K.-L. C.; Carlson, E.; Townson, K.; Wheeldon, A.;
Boyce, S.; Collinson, N.; Rupniak, N.; Moore, S. Bioorg. Med Chem. Lett. 2010.
5. CHO cells (2.5 Â 104) expressing recombinant human NK1 receptors were
plated in 96-well tissue culture dishes and left overnight. This was then
followed by prelabeling overnight with [H3]-myo-inositol (10–25 Ci/mmol) in
inositol-free medium with 0.02% BSA at 37 °C. The cells were then incubated
with 10 mM LiCl in Hepes-buffered inositol-free (DMEM) medium with 0.02%