Carbamates as potent calcitonin gene-related peptide antagonists with improved solution stability

Article abstract of DOI:10.1016/j.bmcl.2009.04.150

The calcitonin gene-related peptide (CGRP) receptor has been implicated in the pathogenesis of migraine. A class of urethanamide derivatives has been identified as potent inhibitors of the CGRP receptor. Compound 20 was found to be among the most potent (

Full text of DOI:10.1016/j.bmcl.2009.04.150

Bioorganic & Medicinal Chemistry Letters 19 (2009) 3555–3558
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Carbamates as potent calcitonin gene-related peptide antagonists with
improved solution stability
b
c
c
a
Andrew P. Degnan a, , Charles M. Conway , Richard A. Dalterio , Robert Macci , Stephen E. Mercer ,
*
Richard Schartman c, Cen Xu b, Gene M. Dubowchik a, John E. Macor a
a Neuroscience Discovery Chemistry, Bristol-Myers Squibb Research and Development, 5 Research Parkway, Wallingford, CT 06492-7660, USA
b Neuroscience Discovery Biology, Bristol-Myers Squibb Research and Development, 5 Research Parkway, Wallingford, CT 06492-7660, USA
c Pharmaceutical Candidate Optimization, Bristol-Myers Squibb Research and Development, 5 Research Parkway, Wallingford, CT 06492-7660, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
The calcitonin gene-related peptide (CGRP) receptor has been implicated in the pathogenesis of migraine.
A class of urethanamide derivatives has been identified as potent inhibitors of the CGRP receptor. Com-
pound 20 was found to be among the most potent (IC50 = 17 pM). It was shown to retain excellent aque-
ous solubility (>50 mg/mL, pH 7) while dramatically improving solution stability as compared to our
previously disclosed development candidate, BMS-694153 (1).
Received 19 February 2009
Revised 27 April 2009
Accepted 30 April 2009
Available online 8 May 2009
Ó 2009 Elsevier Ltd. All rights reserved.
Keywords:
CGRP
Calcitonin gene-related peptide
Carbamates
Solution stability
Migraines are episodic headaches which typically last 4–72 h
and may be quite severe.1 The pain is often unilateral, throbbing,
and accompanied by symptoms such as nausea and heightened
sensitivity to light, sound, or odors. Migraine is the most common
cause of recurrent moderate to severe headache. Nationally,
migraines have a 1-year prevalence of 18% for women and 6% for
men. The current standard of care, the triptans, are believed to
act, in part, by the active, nonselective vasoconstriction of cranial
vessels.2 However, because they are nonselective vasoconstrictors,
they are associated with a number of unpleasant cardiovascular
side effects and are contraindicated in patients with hypertension
or ischemic heart disease.3
Calcitonin gene-related peptide (CGRP), has been implicated in
the pathogenesis of migraine.4 Studies have shown that plasma
levels of CGRP, a 37 amino-acid peptide, are elevated during
migraine attacks.5 Moreover, it has been shown that intravenous
(iv) administration of CGRP causes migraine-like headaches in
migraneurs.6 It has also been demonstrated that iv administration
of the potent CGRP receptor antagonist BIBN4096BS in migraneurs
was accompanied by the alleviation of pain without the cardiovas-
cular side effects associated with the use of triptans.7 Although
BIBN4096BS effectively demonstrated the first clinical proof of
concept, evidence of significant further development of the mole-
cule has been lacking. In this context, we undertook a medicinal
chemistry effort to identify a potent CGRP antagonist that could
be administered by a more convenient route.8
In an earlier Letter, we disclosed our intranasal (IN) develop-
ment candidate BMS-694153 (1).9 Compound 1 had a number of
desirable properties to support its selection. It was found to be a
potent competitive antagonist (IC50 = 26 pM). Additionally, it had
a favorable preclinical toxicology profile and outstanding aqueous
solubility (>500 mg/mL @ pH 7). Since we were pursuing an IN for-
mulation, solution stability had to be sufficient to support an
acceptable shelf life. Solution stability studies over time found that
three significant degradants were generated upon standing as an
aqueous solution (0.05 M, pH 5, 40 °C, 12 weeks) (Fig. 1). The
impurity formed to the greatest extent was that arising from oxi-
dation of the fluorodihydroquinazolinone (2%) to give hydroxyl-
ated derivative 2. Additionally, hydrolysis of the amide to give
acid 3 was also observed. Acid 3 underwent further hydrolysis to
compound 4 (presumably catalyzed by the newly formed adjacent
carboxylic acid), bringing the total hydrolytic degradation to 0.6%.
Although this stability profile met our development criteria, we
targeted improved solution stability for future development
candidates.
It was thought that some pendant functionality may be assist-
ing in the unanticipated hydrolysis. For example, intramolecular
protonation of the amide by the adjacent urea as depicted in
Scheme 1 (path A) might activate the amide toward nucleophilic
attack by water to give the corresponding acid. Alternately, cleav-
age of the amide bond might be assisted by internal nucleophilic
* Corresponding author. Tel.: +1 203 677 5750; fax: +1 203 677 7884.
E-mail address: andrew.degnan@bms.com (A.P. Degnan).
0960-894X/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2009.04.150

3556
A. P. Degnan et al. / Bioorg. Med. Chem. Lett. 19 (2009) 3555–3558
F
O
H
N
H
N
O
NR'2
R2N
N
O
AA
5
O
H
N
N
N
O
N
hydrolysis
O
path A
H+
path B
O
N
N
H
O
NR'2
1
oxidation
NR'2
O
F
F
H
N
H
N
O
N
NH
O
R2N
N
N
AA
6
O
AA
8
O
H
N
H
N
N
N
OH
HO
N
O
O
N
H2O
H2O
N
N
N
H
N
H
O
H
N
3 (0.2%)
NR'2
2 (2%)
HO
hydrolysis
AA
7
O
F
H
O
N
Scheme 1. Possible degradation pathways.
N
HN
4 (0.4%)
Figure 1. Compound 1 and aqueous degradation products.
to give
a
-hydroxy acid 13. The amide was formed by the action
of PyBOP to give 15. The carbamate was then prepared by conver-
sion of the alcohol to a p-nitrophenylcarbonate, followed by treat-
ment with piperidine 16 to furnish the carbamate in 60% yield.
Finally, removal of the SEM protecting group was cleanly accom-
plished by the action of trifluoroacetic acid in dichloromethane
to give analogue 17.
Our efforts were rewarded when it was found that 17 had out-
standing in vitro potency at the CGRP receptor (IC50 = 11 pM).
Structure–activity relationships in this new chemotype were
defined by generating two small libraries—first optimizing the
right hand heterocycle and subsequently varying the amide por-
tion of the molecule. Since oxidation of the quinazolinone was
the major degradant observed in solution stability studies, we
focused most of our efforts in the first library on the incorporation
of electron deficient heterocycles in an effort to reduce hydroxyl-
ation (Table 1). A number of different heterocycles were found to
maintain outstanding potency at the receptor.
attack of the urea to give oxazolone 8 which can undergo hydroly-
sis to give an identical carboxylic acid (path B).
In either event, we sought to reduce this undesirable hydrolysis
by converting the urea to a less basic and/or less nucleophilic func-
tionality such as a carbamate. This perturbation would decrease
both the nucleophilicity and Brønsted basicity of the compounds
while maintaining the Lewis basic site (assumed to be a hydrogen
bond acceptor)that wasthought tobe criticalfor maximumpotency.
The synthesis of the carbamate analogue of 1 began with a
Horner–Wadsworth–Emmons olefination of aldehyde 1010 with
phosphonate 911 (Scheme 2). The reaction gave olefin 11 as a 2:1
mixture of E- and Z-isomers which were used without separation.
This mixture was inconsequential as both isomers were reduced
with high levels of enantioselectivity to afford the same protected
Among the most potent analogues was quinolinone 20
(IC50 = 17 pM). In addition to its remarkable potency, this compound
a
-hydroxy ester (12) in 96% ee. Cleavage of both esters was
achieved in one chemical step by the action of lithium hydroxide
O
9
O
P
O
O
O
OEt
MeO
OEt
OBz
12
OH
OBz
11
MeO
HO
MeO
OBz
b
c
a
NSEM
NSEM
NSEM
O
NSEM
N
N
N
N
13
N
10
F
H
N
O
O
d
OH
e
f
N
O
N
O
O
N
N
NH
NH
F
NSEM
O
HN
N
N
N
14
15
N
16
N
N
H
17
Scheme 2. Reagents and conditions: (a) LiCl/TMG/THF (94%); (b) [(2R,5R)-Et-DuPhosRh]BF4/H2 (60 psi)/DCM/MeOH (98%); (c) LiOH/THF/MeOH/H2O (100%); (d) PyBOP/DIEA/
DMF/DCM (91%); (e) p-nitrophenylchloroformate/DIEA/DMAP/DCM then 16/DIEA/DMF (60%); (f) TFA/DCM (67%).

A. P. Degnan et al. / Bioorg. Med. Chem. Lett. 19 (2009) 3555–3558
3557
Table 1
Effect of the right-hand heterocycle on human CGRP receptor binding potency
Table 2
Effect of the left-hand amide on receptor potency
H
O
N
O
N
O
O
N
O
N
O
N
O
N
N
H
N
N
H
Compound
Heterocycle
CGRP IC50 (nM)
0.011
F
H
N
Compound
Amine
CGRP IC50 (nM)
0.017
O
17
N
N
20
N
N
N
N
N
H
N
O
28
29
30
31
32
33
1.8
18
19
20
21
0.010
0.022
0.017
0.057
0.053
0.044
0.020
0.063
0.13
H
N
O
O
F
MeN
N
N
N
N
H
N
N
F
N
N
F
H
N
N
N
O
The route developed to allow the incorporation of a variety of
amides at a later stage of the synthetic sequence is shown in
Scheme 3. Acid 13 was first selectively protected as its methyl ester
by treatment with diazomethane. The alcohol was converted to the
p-nitrophenylcarbonate and treated with piperidine 25 to afford
the corresponding carbamate (26). Removal of the indazole pro-
tecting group and hydrolysis of the ester gave acid 27. Finally,
amines were efficiently coupled by the action of PyBOP to afford
analogues in a single chemical step.
N
N
22
23
0.18
O
NH
0.068
had excellent aqueous solubility (>50 mg/mL, pH 7, amorphous
material) and no oxidizable benzylic methylene. As such, the quinoli-
none was incorporated into the subsequent amide library.
A number of amides were identified that maintained picomolar
potencies (Table 2). However, none were found to be more potent
than the original 4-piperidinyl-piperidine. Additionally, compounds
H
O
N
O
O
OH
b
OH
a
MeO
HO
O
N
O
O
NH
NSEM
NSEM
O
HN
MeO
N
N
25
13
24
NSEM
N
26
H
N
O
H
N
O
O
N
d
c, d
O
O
N
O
O
HO
O
N
NH
N
N
14
N
N
H
N
N
H
27
20
Scheme 3. Reagents and conditions: (a) CH2N2/Et2O (95%); (b) p-nitrophenylchloroformate/DIEA/DMAP/DCM then 25/DIEA/DMF (86%); (c) TFA/DCM (99%); (d) LiOH/THF/
MeOH/H2O (89%); (d) PyBOP/DIEA/DMF/DCM (88%).

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A. P. Degnan et al. / Bioorg. Med. Chem. Lett. 19 (2009) 3555–3558
H
N
In conclusion, we have demonstrated that the exchange of the
O
urea has been replaced
with a carbamate
backbone urea of 1 (IC50 = 26 pM) for a carbamate in 17 was well
tolerated, giving compounds with modestly improved potency
(IC50 = 11 pM). Similar potency (IC50 = 17 pM) was observed upon
exchange of the fluorodihydroquinazolinone for a quinolinone to
give compound 20. Compound 20 showed greatly improved
solution stability, generating significantly reduced amounts of
degradants in solution. In addition to its outstanding potency
and improved solution stability, 20 had excellent solubility
(>50 mg/mL, pH 7, amorphous material). Further characterization
of this compound and additional SAR will be reported in due
course.
O
N
O
N
O
site of hydroxylation in
a higher oxidation state
N
N
N
H
20
Compound
1
20
Hydrolytic
Stabilitya
(% remaining)
56%
72%
99%
References and notes
Oxidative
Stabilityb
(% remaining)
97%
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