The synthesis and SAR of calcitonin gene-related peptide (CGRP) receptor antagonists derived from tyrosine surrogates. Part 1

Article abstract of DOI:10.1016/j.bmcl.2012.05.074

We have systematically studied the effects of varying the central unnatural amino acid moiety on CGRP receptor antagonist potency and CYP inhibition in a series of ureidoamides. In this Letter, we report the discovery of compound 23, a potent CGRP recepto

Full text of DOI:10.1016/j.bmcl.2012.05.074

Bioorganic & Medicinal Chemistry Letters 22 (2012) 4723–4727
Contents lists available at SciVerse ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
The synthesis and SAR of calcitonin gene-related peptide (CGRP) receptor
antagonists derived from tyrosine surrogates. Part 1
⇑
Xiaojun Han , Rita L. Civiello, Charles M. Conway, Deborah A. Cook, Carl D. Davis, Robert Macci,
Sokhom S. Pin, Shelly X. Ren, Richard Schartman, Laura J. Signor, George Thalody, Kimberly A. Widmann,
Cen Xu, Prasad V. Chaturvedula, John E. Macor, Gene M. Dubowchik
Department of Molecular Sciences and Candidate Optimization (MSCO), Bristol-Myers Squibb Research & Development, 5 Research Parkway, Wallingford, CT 06492, USA
Department of Neuroscience Biology, Bristol-Myers Squibb Research & Development, 5 Research Parkway, Wallingford, CT 06492, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
We have systematically studied the effects of varying the central unnatural amino acid moiety on CGRP
receptor antagonist potency and CYP inhibition in a series of ureidoamides. In this Letter, we report the
discovery of compound 23, a potent CGRP receptor antagonist with only weak CYP3A4 inhibition. Unlike
the triptans, compound 23 did not cause active constriction of ex vivo human cerebral arteries. At doses
of 0.3–1 mg/kg (sc), 23 showed robust inhibition of CGRP-induced increases in marmoset facial blood
flow, a validated migraine model. Ureidoamide 23 derives from a novel amino acid, 1H-indazol-5-yl
substituted alanine as a tyrosine surrogate.
Received 17 April 2012
Revised 17 May 2012
Accepted 18 May 2012
Available online 1 June 2012
Keywords:
CGRP receptor antagonist
Calcitonin gene-related peptide (CGRP)
Migraine headache
Ó 2012 Elsevier Ltd. All rights reserved.
Tyrosine surrogates
CYP3A4 inhibition
Migraines are severe episodic headaches which can last 4–72 h.
The pain is often accompanied by nausea and heightened sensitiv-
ity to light, sound or odors.1 It is estimated that 18% of women and
7% of men suffer from migraine and 23% of households have at least
one migraneur. Annually, 12% of the general population suffers
from this disabling condition.2 The current standard of care for
migraine are triptans (5-HT1B/D agonists). Because triptans are
non-selective vasoconstrictitors, they are contraindicated in
patients with cardiovascular disease and hypertention.3 This limi-
tation and the somewhat limited efficacy of triptans4 underscores
the need to develop new migraine drugs that are more effective
and do not cause active vasoconstriction.
Calcitonin gene-related peptide (CGRP) is a 37-amino acid neu-
ropeptide that is expressed in the trigeminal ganglia, and has been
implicated in the pathogenesis of migraine.5 Increased levels of
CGRP are observed during a migraine attack, and intravenous
administration of CGRP can induce headache in migraineurs.6 In
a Phase II clinical trial, intravenous administration of the potent
CGRP receptor antagonist BIBN4096BS (olcegepant, 1) demon-
strated efficacy in treating migraines that was comparable to that
of the triptans, but without the cardiovascular side effects.7 This
result motivated us and others8,9 to commence a medicinal chem-
istry effort to identify potent CGRP antagonists that could be
administered by other routes of administration, including intrana-
sal10 and oral8 administrations.
Previously we reported the identification and SAR of novel CGRP
receptor antagonists derived from thiophenylalanines.11 Com-
pound 2 was found to be a potent CGRP antagonist, but it also
was a potent inhibitor of cytochrome P450 3A4 (CYP3A4). In this
Letter, we report the structure–activity relationship effort that led
to the discovery of BMS-694153,10 and optimization of compound
23 (Fig. 1), a potent CGRP antagonist with only weak CYP3A4 inhi-
bition. We also describe its activity in a validated in vivo migraine
model.10
Our medicinal chemistry strategy was to study the effects of
varying the central unnatural amino acid moiety on CGRP receptor
antagonist potency and CYP inhibition.12 Our initial observations
indicated an important influence of the unnatural D-amino acid
on the extent of the CYP3A4 interaction. These results are summa-
rized in Table 1.
From Table 1 it is clear that the human CGRP receptor shows a
clear preference for hydrophobic aromatic residues that optimally
contain a hydrogen-bond donating group (i.e., 23) that can spa-
tially mimic a
D-tyrosine hydroxyl, such as the 2,6,-dibromo-D-
tyrosine (10) found in BIBN-4096-BS (1). The best CGRP potency
was achieved when the aromatic ring was attached to the amino
acid backbone by one methylene group (4 vs 5 and 6, and 7 vs
8). Comparing aniline 12 with phenol 7 suggested that a stronger
hydrogen bond donor increased CGRP binding affinity. Ether 9
⇑
Corresponding author.
E-mail address: xiaojun.han@bms.com (X. Han).
0960-894X/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.bmcl.2012.05.074

4724
X. Han et al. / Bioorg. Med. Chem. Lett. 22 (2012) 4723–4727
O
ing pocket or simply from a steric effect. In the absence of a
O
H
N
hydrogen-bonding group, fused aromatics or pendant biaryls
tended to improve CGRP binding potency. In the case of the biphe-
nyl (16) or naphthyl groups (14 and 15), 1-naphthyl substitution
(14) was clearly superior. N-methyl-3-indole 18 was comparable
to 14, while the des-methyl analog, 17, was somewhat less active.
Compared to the 2-naphthyl compound (15), the 5-indolyl (19)
and 5-indazolyl (20) derivatives were more potent, presumably
due to the hydrogen bond donating N–H. In the absence of an aro-
matic spacer, glutamate (21) or glutamine (22) side chains offered
no advantage.
N
HN
O
N
N
N
NH
N
O
Br
H2N
Br
HO
olcegepant, 1
O
N
N
O
NH
NH
hCGRP Ki (nM)
CYP3A4-BFC IC50 (µM) 0.87
CYP3A4-BZR IC50 (µM) 0.084
0.55
N
N
Selected compounds were tested for in vitro CYP3A4 inhibition
using benzyloxyresorufin (BZR) as the substrate. In general,
CYP3A4 inhibition correlated with lipophilicity of the aromatic
O
S
2
D
-amino acid side chains. Both naphthyl derivatives 14 and 15
O
N
N
O
N
were potent inhibitors, each showing sub-micromolar potency.
Addition of a polar OH (7) or an NH in 3-indolyl (17) dramatically
reduced inhibition, but the 5-indolyl group (19) had a much
smaller effect on CYP3A4 activity, suggesting specific spatial pref-
erences. Inhibition could be exacerbated by increasing lipophilicity
in 10 with the dibromo addition to 7, and capping the NH of 17
with methyl in 18. On the other hand, increasing polarity from
indole 19 to indazole 20 significantly attenuated inhibition.
Encouraged by the CGRP potency of 19 and 20, coupling with
their diminished CYP3A4 affinities, we continued to explore
NH
O
NH
hCGRP Ki (nM)
0.23
N
CYP3A4-BFC IC50 (µM) > 40
CYP3A4-BZR IC50 (µM) 4.0
N
HN
O
23
N
N
O
NH
O
NH
F
hCGRP Ki (nM)
CYP3A4-BFC IC50 (µM) 26
CYP3A4-BZR IC50 (µM) 6.7
0.013
N
N
heteroaromatic D-tyrosine mimetics while also replacing the piper-
idyl-imidazolone GPCR recognition motif with the piperidyl-qui-
nazolinone, which generally resulted in improved CGRP binding
affinities (Table 2). Indeed, sub-nanomolar affinity was achieved
with all new examples save 24, the S-enantiomer of indazole 23
and the 2-methylbenzimidazole 28. The latter was interesting in
that it may be another example of a limited steric tolerance for
non-aromatic lipophilicity in this part of the receptor binding pock-
Me
BMS-694153
Figure 1.
N
HN
and amide 13 are much less active, possibly due to a lack of toler-
ance for hydrogen bond acceptors in that part of the receptor bind-
Table 1
CGRP receptor binding and CYP3A4 inhibition of ureidoamides 3–21
O
NH
N
O
H
N
N
N
O
N
Compounds
AA Moiety (Stereochemistry)
Ki (nM)
CYP3A4 (IC50BZR,
lM)
Compounds
AA Moiety (Stereochemistry)
Ki (nM)
CYP3A4 (IC50BZR, lM)
(R)
3
2400
16
13
1900
—
NH
O
(R)
4
5
300
—
—
14
15
7.2
0.03
0.03
(R)
(R)
(R)
>1000
230
(R)
(R)
6
>1000
—
16
250
1.3
(R)

X. Han et al. / Bioorg. Med. Chem. Lett. 22 (2012) 4723–4727
4725
M)
Table 1 (continued)
Compounds
AA Moiety (Stereochemistry)
Ki (nM)
CYP3A4 (IC50BZR,
>40
lM)
Compounds
AA Moiety (Stereochemistry)
Ki (nM)
CYP3A4 (IC50BZR,
>40
l
7
8
2.5
17
84
NH
(R)
OH
(R)
OH
2100
1400
—
—
18
19
16
32
0.10
2.5
(R)
N
(R)
9
N
O
( )
H
(R)
Br
N
N
10
0.65
2.4
20
68
17
OH
H
( )
Br
(R)
O
Br
OH
(R)
11
12
>1000
750
—
—
21
22
>1000
>1000
—
—
OH
Br
(S)
O
NH2 (R)
NH2
(R)
Table 2
CGRP receptor binding and CYP3A4 inhibition of ureidoamides 23–28
H
N
O
N
O
H
N
N
N
O
N
Compounds
AA Moiety (Stereochemistry)
Ki (nM)
CYP3A$ (IC50, lM) BZR
23
0.23
4.0
N
N
N
H
(R)
24
25
26
250
0.27
0.65
7.3
30
11
N
H
(S)
O
O
N
H
(R)
O
N
H
(R)
(continued on next page)

4726
X. Han et al. / Bioorg. Med. Chem. Lett. 22 (2012) 4723–4727
Table 2 (continued)
Compounds
AA Moiety (Stereochemistry)
Ki (nM)
CYP3A$ (IC50, lM) BZR
N
27
28
0.55
23
N
N
H
(R)
N
28
—
N
H
(R)
100
80
Sumatriptan, Emax = 47.6 5.0 %, EC50 = 120nM, n = 5
Zolmitriptan, Emax = 39.1 6.0 % , EC50 = 40nM, n = 4
Compound 20
0
Compound 23
25
60
50
75
*
*
*
*
40
100
20
CGRP VEH 0.01 0.03 0.1
0.3
1
1
(mg/kg, SC)
Compd 23
Compd 24
0
Figure 3. Effects of compounds 23 and 24 on CGRP-induced marmoset facial blood
flow.
10-9
10-8
10-7
10-6
10-5
Log [Drug] M
Figure 2. Effect of sumatriptan, zolmitriptan and compounds 20 and 23 on ex vivo
human coronary arteries.
We used a marmoset facial blood flow model to assess the
in vivo efficacy of our CGRP receptor antagonists.10 In this model,
marmosets were anesthetized, and facial blood flow was increased
by intravenous (iv) administration of haCGRP (10 lg/kg) at 45 min
et as was previously seen with 9 and 13. On the other hand, the fact
that benzoxazolinone 25 and indolone 26 were equipotent with 23
might imply some tolerance in the hydrogen bond donor-acceptor
interaction. All of these compounds maintained favorable CYP3A4
BZR inhibition profiles (Table 2).
We chose compound 23 for further ex vivo and in vivo studies.
To confirm that compound 23 did not have the vasoconstriction lia-
bility of 5-HT1B/1D agonists (triptans), we measured basal artery
tension upon cumulative addition of 23 to ex vivo human coronary
intervals (ꢀ30, 15, 60, and 105 min). The effect of antagonist, deliv-
ered at 0 min, on CGRP-induced changes in facial blood flow were
measured by laser Doppler flowmetry. In this study (Fig. 3), com-
pound 23 (0.3–1 mg/kg) showed a dose-dependent inhibition of
CGRP-induced increase in marmoset facial blood flow upon subcu-
taneous (sc) dosing. In the same study, compound 24, the S-enan-
tiomer of 23 was inactive.
The synthesis of compound 23 is shown in Scheme 1. The
coupling of amino ester 29 and quinazolinone 30 afforded urea
31. Saponification of the methyl ester of 31 with LiOH gave the
carboxylic acid, which was coupled with 1,40-bipiperidine to
afford compound 23. The other compounds in this paper were pre-
pared in the same way using amino esters that were either com-
mercially available or whose synthesis has been reported by us
previously.14
In summary, we have found that ureidoamides derived from
novel amino acids containing hydrogen-bond donors in the
alpha substituent, namely 1H-indazol-5-yl (23), 2-oxo-2,3-dihy-
drobenzo[d]oxazol-6-yl (25), 2-oxoindolin-5-yl (26), and 1H-
benzo[d][1,2,3]triazol-5-yl (27) substituted alanines, were potent
CGRP receptor antagonists with relatively weak CYP3A4 inhibition.
Unlike the triptans, compound 23 did not cause active constriction
of ex vivo human cerebral arteries. At doses of 0.3–1 mg/kg, (sc), 23
showed robust inhibition of CGRP-induced increases in marmoset
facial blood flow, a validated migraine model.10 Efforts to further
arteries. As a positive control, serotonin (10 lM) was added to each
tissue bath at the end of a test session to provide a control measure
of maximal contractility in each vessel. Compounds 23 and 20 did
not produce measurable contraction in ex vivo human arteries up
to 10
produced concentration-dependent vessel contraction up to
approximately 48% of the serotonin derived maximum (EC50
lM (Fig. 2). In contrast, both sumatriptan and zolmitriptan
=
120 nM) and 39% of maximum (EC50 = 40 nM), respectively. The
absence of active constriction using 23 indicated the different
mechanism of action for CGRP receptor antagonists, which is an
antidilatory effect—returning dilated vessels to normal. This adds
to the body of evidence that CGRP antagonists should be free from
mechanism-based cardiovascular liabilities associated with the
triptans; and these results are in good agreement with Merck’s
work on telcagepant (MK-0974).13
.

X. Han et al. / Bioorg. Med. Chem. Lett. 22 (2012) 4723–4727
4727
CO2Me
NH2
CDI/THF, then
References and notes
N
O
N
N
H
1. Goadsby, P. J.; Lipton, R. B.; Ferrari, M. D. N. Eng. J. Med. 2002, 346, 257.
2. Lipton, R. B.; Stewart, W. F.; Diamond, S.; Diamond, M. L., Reed, M. Headache,
2001, 41, 646.
NH
29
HN
3. Silberstein, S. D. Lancet 2004, 363, 381.
30
4. (a) Goadsby, P. J. Drugs 2005, 65, 2557; (b) Edvinsson, L. Cephalalgia 2004, 24,
611; (c) Williamson, D. J.; Hargreaves, R. J. Microsc. Res. Tech. 2001, 53, 167.
5. Tepper, S. J.; Rapoport, A. M. CNS Drugs 1999, 12, 403.
O
O
N
MeO
N
HN
6. Lassen, L. H.; Haderslev, P. A.; Jacobson, V. B.; Iversen, H. K.; Sperling, B.; Olesen,
J. Cephalalgia 2002, 22, 54.
NH
NH
N
7. Olesen, J.; Diener, H. C.; Husstedt, I. W.; Goadsby, P. J.; Hall, D.; Meier, U.;
Pollentier, S.; Lesko, L. M. N. Engl. J. Med. 2004, 350, 1104.
O
31
8. Oral CGRP receptor antagonist medicinal chemistry efforts have been reported
in: (a) For MK-0974 Paone, D. V.; Shaw, A. W.; Nguyen, D. N.; Burgey, C. S.;
Deng, J. Z.; Kane, S. A.; Koblan, K. S.; Salvatore, C. A.; Mosser, S. D.; Johnston, V.
K.; Wong, B. K.; Miller-Stein, C. M.; Hershey, J. C.; graham, S. L.; Vacca, J. P.;
Williams, T. M. J. Med. Chem. 2007, 50, 5564; (b) For MK-3207 Bell, I. M.;
Gallicchio, S. N.; Wood, M. R.; Quigley, A. G.; Stump, C. A.; Zartman, C. B.; Fay, J.
F.; Li, C.; Lynch, J. J.; Moore, E. L.; Mosser, S. D.; Prueksaritanont, T.; Regan, C. P.;
Roller, S.; Salvatore, C. A.; Kane, S. A.; Vacca, J. P.; Selnick, H. G. ACS Med. Chem.
Lett. 2010, 1, 24.
9. (a) IDDB, Thomson Scientific reports that the development of BIBN4096BS has
been discontinued.; (b) Merck & Co., Inc. announced discontinuation of the
clinical development program for MK-3207 on Sept. 10, 2009.
10. Degnan, A. P.; Chaturvedula, P. V.; Conway, C. M.; Cook, D. A.; Davis, C. D.;
Denton, R.; Han, X.; Macci, R.; Mathias, N. R.; Moench, P.; Pin, S. S.; Ren, S. X.;
Schartman, R.; Signor, L. J.; Thalody, G.; Widmann, K. A.; Xu, C.; Macor, J. E.;
Dubowchik, G. M. J. Med. Chem. 2008, 51, 4858.
1. LiOH/THF/MeOH/H2O
2. PyBOP/DIEA/DMF
23
HN
N
1, 4'-bipiperidine
Scheme 1. Synthesis of compound 23.
optimize the potency and pharmacokinetics properties of com-
pound 23 will be reported in due course.
11. Chaturvedula, P. V.; Pin, S.; Tholady, G.; Conway, C. M.; Macor, J. E.; Dubowchik,
G. M. Bioorg. Med. Chem. Lett. preceeding paper in this journal, BMCL-D-12-
00760.
12. For experimental procedures used to measure
[
125I]CGRP binding, CYP
Acknowledgments
inhibition, in vivo efficacy in marmoset facial blood flow, and
pharmacokinetics properties, see the supplementary data in Ref. 10.
13. Lynch, J. L.; Regan, C. P.; Edvinsson, L.; Hargreaves, R. J.; Kane, S. A. J. Cardiovasc.
Pharmacol. 2010, 55, 518.
14. Han, X.; Civiello, R. L.; Fang, H.; Wu, D.; Gao, Q.; Chaturvedula, P. V.; Macor, J.
E.; Dubowchik, G. M. J. Org. Chem. 2008, 73, 8502.
We thank the members of Discovery Analytic Sciences in MSCO
for their help in the purification and characterization of com-
pounds contained herein.