Anthranilic sulfonamide CCK1/CCK2 dual receptor antagonists I: Discovery of CCKR1 selectivity in a previously CCKR2-selective lead series

Article abstract of DOI:10.1016/j.bmcl.2009.09.064

A series of CCK2R-selective anthranilic amides is shown to derive CCK1R affinity via selective substitution of the amide side chain. Thus, extending the length of the original benzamide side chain by a single methylene unit imparts CCK1R affinity to the s

Full text of DOI:10.1016/j.bmcl.2009.09.064

Bioorganic & Medicinal Chemistry Letters 19 (2009) 6373–6375
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Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Anthranilic sulfonamide CCK1/CCK2 dual receptor antagonists I: Discovery
of CCKR1 selectivity in a previously CCKR2-selective lead series
Marna Pippel, Brett D. Allison, Victor K. Phuong, Lina Li, Magda F. Morton, Clodagh Prendergast,
*
Xiaodong Wu, Nigel P. Shankley, Michael H. Rabinowitz
Johnson & Johnson Pharmaceutical Research and Development, L.L.C., 3210 Merryfield Row, San Diego, CA 92121, United States
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of CCK2R-selective anthranilic amides is shown to derive CCK1R affinity via selective substitution
of the amide side chain. Thus, extending the length of the original benzamide side chain by a single meth-
ylene unit imparts CCK1R affinity to the series, and further fine tuning of the affinity results in CCK1R
selectivity of greater than 100-fold.
Received 5 August 2009
Revised 16 September 2009
Accepted 17 September 2009
Available online 23 September 2009
Ó 2009 Published by Elsevier Ltd.
Keyword:
CCK receptor antagonist
Small molecule cholecystokinin type 1 receptor (CCK1R) antag-
onists have been known in the literature since the discovery and
biological profiling of the natural product asperlicin.1 Since then,
high affinity ligands selective for CCK1R over the related cholecys-
tokinin type 2 receptor (CCK2R) have been described.2–4 In prac-
tice, high receptor subtype selectivity has been readily realized
via optimization of affinity for just one receptor (i.e., pharmaco-
phore determinants for the two receptor subtypes are typically
distinct such that improvement in the affinity of a small molecule
series for just one of the subtypes typically results in no improve-
ment of affinity for the other). However, important examples in
which subtype selectivity has been reversed through SAR studies
have been reported, notably in benzodiazepine5 and glutamic acid
based series.4,6,7
We discovered that by simply extending the amide side chain
by a single methylene unit to give phenethyl amides such as 2a,
high CCK1R affinity and selectivity was achieved (CCK1R pKi 6.8,
CCK2R pKi 5.2, Fig. 1, Table 1). Further extension of this side chain
(e.g., 3) resulted in a significant loss of CCK1R affinity (CCK1R pKi
5.7). Interestingly, the high CCK1R affinity and selectivity of the
phenethylamides could be reversed by the simple N-methylation
of compound 2 (i.e., 4, CCK1R pKi 5.4, CCK2R pKi 6.5).
O
O
N
H
N
H
We have previously reported the discovery and initial optimiza-
tion of a novel series of anthranilic amides as high affinity CCK2R
selective antagonists.8 Few compounds in this series were found
HN
S O
Cl
HN
S O
Cl
O
O
to have measurable CCK1R affinities below 10 lM IC50, in contrast
N
S
N
S
2a
to that demonstrated in a related indole amide series.9 The best
compounds in the series were shown to have favorable pharmaco-
kinetic profiles in the rat and dog and have high potency for the
reversal of gastrin stimulated gastric acid secretion upon oral dos-
ing. Researchers from our labs have also reported the discovery of
novel, highly selective CCK1R antagonists in the pyrazole carbox-
ylic acid class.10,11 Selectivity for the respective receptor subtypes
was always found to be extremely high, with early compounds in
our benzamide series showing little to no affinity for the CCK1
receptor (e.g., 1; CCK1R pKi = 5.6).
N
1
N
O
O
N
H
HN
N
Cl
HN
Cl
S O
O
S O
O
N
N
3
4
N
S
N
S
* Corresponding author.
E-mail address: mrabinow@its.jnj.com (M.H. Rabinowitz).
Figure 1. Selected early compounds.
0960-894X/$ - see front matter Ó 2009 Published by Elsevier Ltd.
doi:10.1016/j.bmcl.2009.09.064

6374
M. Pippel et al. / Bioorg. Med. Chem. Lett. 19 (2009) 6373–6375
with side chain amine groups R3NH2 to provide, after reduction,
anthranilic amides 6. Sulfonylation with 4-chlorosulfonyl-2,1,3-
benzothiadiazole afforded final compounds 2 or 10. Alternately,
anthranilic amides 6 were prepared directly from the correspond-
ing isatoic anhydrides 7 via direct condensation with R3NH2. In a
second route, methyl anthranilates 8 were sulfonylated to afford
intermediates 9, which were then saponified and coupled as
described above.
Table 1
Selectivity and affinity analysis of selected early compounds and Phe-derived amides
3'
R2
4'
O
R1
N
H
HN
S O
Cl
Compound affinity was evaluated in CCK1R and CCK2R radioli-
gand binding assays that have been previously described.13–15
Table 1 shows selected initial compounds aimed at improving both
CCK1R affinity and selectivity in the series. Starting with the
unsubstituted phenethyl amide 2a (CCK1 pKi 6.8; CCK2R pKi 5.2),
CCK1R affinity was significantly reduced by the addition of a chlo-
rine atom at the aryl C40 position of the phenethyl side chain (2b).
Interestingly, good CCK1R affinity returned by the addition of a
second chlorine atom at the aryl C30 position (2c, pKi 7.1).
In order to help increase the aqueous solubility of this series,
and recognizing that a common motif in known CCK receptor
ligands is the carboxylic acid (or equivalent), we examined amides
of phenylalanine (Phe) and their halogenated derivatives (2d–j,
Table 1). The addition of an (S)-COOH group to 2a (2d, derived from
O
N
2a-j
N
S
Compds
R1
R2
CCK1R pKia
CCK2R pKia
Log ratiob
1
—
H
—
H
H
H
<5
5.6
5.2
<5
<ꢁ0.6
1.6
>1
2a
2b
2c
2d
2e
2f
2g
2h
2i
2j
3
6.8
6.0
7.1
5.4
5.5
5.7
6.5
6.6
7.1
6.7
5.7
5.4
40-Cl
30,40-Cl2
H
5.1
7.1
6.8
7.2
6.2
7.8
6.3
7.4
6.0
6.5
2.0
(S)-COOH
(R)-COOH
(S)-COOH
(R)-COOH
(S)-COOH
(R)-COOH
(S)-COOH
—
ꢁ1.7
ꢁ1.3
ꢁ1.5
0.3
H
40-Cl
40-Cl
30,40-Cl2
30,40-Cl2
30-Br, 40-Cl
—
ꢁ1.2
0.8
ꢁ0.7
ꢁ0.3
ꢁ0.9
L-Phe) resulted in a reversal of affinity with an unexpectedly high
4
—
—
CCK2R affinity of pKi 7.1 and selectivity over CCK1R (pKi 5.4). This
result is in contrast to that observed in literature reports in which
addition of a COOH group in a related, racemic series resulted in
poor CCK2R affinity, with high selectivity for CCK1R.9 This demon-
strates an important pharmacophoric difference between the pres-
ent benzothiadiazole sulfonamides and the literature indole amide
somewhat reduced CCK2R affinity but still 20ꢀDselectivity over
anthranilates. The enantiomer (2e, derived from -Phe) showed a
CCK1R.
As we observed for the phenethyl-derived amides 2a–c, the
receptor affinity of the Phe-derived amides also showed a pro-
nounced sensitivity to the pattern of halogenation of the aryl ring.
Simple mono-chlorination of the aryl C40 position in the (S) enan-
tiomer showed little change in receptor affinity or selectivity.
Chlorination at the same position in the (R) series resulted in a
substantial improvement of CCK1R affinity (ca. 10ꢀ) and a con-
comitant reduction in CCK2R affinity to provide a compound (2g)
a
Negative logarithm of the antagonist equilibrium dissociation constant calcu-
lated from the concentration required to displace 50% 125I-CCK-8S (pIC50) by the
method of Cheng and Prussoff.16 All values are 0.3 log units unless otherwise
stated.
b
pKiCCK1R–pKiCCK2R
.
In this Letter we report our efforts at capitalizing on this discov-
ery and identifying compounds exhibiting high CCK1R selectivity
within the anthranilic amide series. In the accompanying Letter,12
we describe the tuning of CCK1R and CCK2R affinities in this series
to produce dual receptor antagonists for the potential treatment of
gastroesophageal reflux disease (GERD).
The preparation of test compounds is depicted in Scheme 1.
Appropriately halogenated 2-nitrobenzoic acids 5 were coupled
with near equal receptor affinities of about 0.5 lM (Ki). Further
O
R3
ring chlorination in the (S) series (2h) resulted in a 4–10ꢀ
improvement in affinity at both receptors with respect to the
mono-chlorinated analog, while maintaining CCK2R selectivity. In
contrast, applying the same analysis to the (R) series (i.e.,
2e?2g?2i) we see a complete reversal in receptor subtype selec-
tivity. Finally, this series could be refined for high CCK2R affinity
through further manipulation of the halogenation pattern of the
aryl ring (2j). We found that substitution of this ring by polar or
highly electron-donating substituents resulted in a marked reduc-
tion in affinity for both receptors (data not shown).
O
N
H
R3
HOOC
O2N
a, b
or
c, b
d
N
H
HN
S O
O
R
R
H2N
R
5
2a-k
10a-l
6
N
S
N
f
O
O
e, a
In a second line of investigation, we examined the effect of in-
creased hydrophobicity and conformational restriction on the alkyl
portion of the phenethyl side chain. Placing a methyl group at the
C2 alkyl position (R3, Table 2) of 2b resulted in racemate 10a that re-
tained CCK1 selectivity while increasing affinity with respect to 2b.
Quarternization of this center results in gem-dimethyl analog 10b
that shows a further improvement in CCK1R affinity (pKi 7.3) and
160ꢀ (log ratio 2.2) selectivity over CCK2R. An investigation into
the effect of the absolute stereochemistry in the methylated series
on receptoraffinity was performed in thebromo anthranilicacidser-
ies (10c–f). Compared with the racemic material (10d), the single
enantiomers (10e and 10f) fail to reveal a eutomeric/distomeric pair
at CCK1R, but the (S) enantiomer (10e) appears to have a small pref-
erence for CCK2R binding with the result that the (R) enantiomer
(10f) shows greater overall receptor selectivity (log ratio 1.3 vs 0.9).
O
N
H
R
7
MeOOC
HN
SO2Cl
R
MeOOC
H2N
S O
O
N
d
S
R
N
N
S
8
N
9
R = Cl, Br
Scheme 1. Reagents and conditions: (a) R3NH2, HATU, pyr, DMF, 1 h (DIPEA added
when the HCl salt of R3NH2, was used); (b) SnCl2ꢂ2H2O, EtOAc, DCM; (c) (i) SOCl2;
(ii) R3NH2, DMF; (d) 4-chlorosulfonyl-2,1,3-benzothiadiazole, pyr, DCM, 16 h; (e)
LiOHꢂH2O, THF, water, 3–16 h; (f) R3NH2, DMAP, DMF, 50 °C, 12 h.

M. Pippel et al. / Bioorg. Med. Chem. Lett. 19 (2009) 6373–6375
6375
Table 2
Selectivity and affinity analysis of selected alkyl- and aryl-substituted phenethyl amides
3'
R2
4'
O
R1
2
N
H
1
R3
R4
HN
S O
O
N
S
10a-l
N
Compound
R1
R2
R3
R4
CCK1R pKia
CCK2R pKia
Log ratiob
10a
10b
10c
10d
10e
10f
10g
10h
10i
4-Cl
4-Cl
H
H
H
H
H
H
H
H
H
H
H
(R/S)-Me
Me2
H
Cl
Cl
Br
Br
Br
Br
Cl
Cl
Cl
Cl
Cl
Cl
Cl
7.0
7.3
6.4
7.1
7.2
7.1
7.5
7.9
6.3
6.7
5.4
<5
6.4
5.1
6.2
6.2
6.3
5.8
<5
6.3
6.8
5.8
6.0
5.9
5.9
0.6
2.2
0.2
0.9
0.9
1.3
>2.5
1.6
(R/S)-Me
(S)-Me
(R)-Me
4-Cl-Ph
(R/S)-Me
(R)-Me
(R)-Me
Me2
H
4-Cl
3,4-Cl2
3,4-Cl2
3,4-Cl2
4-Cl
4-Cl
3-Br
(S)-COOH
(R)-COOH
(S)-COOH
(S)-COOH
(R)-Me
ꢁ0.5
10j
10k
10l
0.9
ꢁ0.6
<ꢁ0.9
1.7
4-Cl-Ph
(S)-OH
10m
7.6
a
Negative logarithm of the antagonist equilibrium dissociation constant calculated from the concentration required to displace 50% 125I-CCK-8S (pIC50) by the method of
Cheng and Prussoff.16 All values are 0.3 log units unless otherwise stated.
b
pKiCCK1R–pKiCCK2R
.
Substitution was added to the alkyl C2 position without chiral-
ity by the addition of a 4-chlorophenyl group to 2b. The resulting
analog, 10g, showed very good affinity for the CCK1 receptor with
no measurable affinity for CCK2R, making this the most selective
compound we have discovered to date in the anthranilic sulfon-
amide series.
of the phenethyl ring as well as by alkylation at the C2 position of
the side chain. Armed with the knowledge of how to adjust both
CCK1R and CCK2R affinities within this series, we were then able
to design CCK1/CCK2 dual receptor antagonists with affinities
modulated toward inhibiting both receptors in the periphery with
the aim of providing treatment for GERD. The preliminary in vivo
work in support of this effort is described in the following article
in this series.
As with previous compounds, the presence of aryl 3,4-dihalo-
genation in the C2-methylated series produced an increase in
CCK1R affinity with little change in CCK2R affinity (cf. 10h and
10a). Unfortunately for the sake of improving aqueous solubility,
the combination of C2 substitution and C1 carboxylation did not
result in compounds with useful affinities for either receptor sub-
type (10i–l). The combination of (S)-COOH at C1 and (R)-methyl
group at C2 resulted in a compound, 10i, showing significant loss
of CCK1R affinity coupled with only a modest improvement in
CCK2R affinity (at least with respect to the non-carboxylated ana-
log 10h). The addition of an (R)-COOH in the same manner pro-
vided stereoisomer 10j, which, unlike the trend observed for the
compounds in Table 1, failed to provide improved affinity for
CCK1R. The addition of an (S)-COOH group to gem-dimethyl analog
10b gave 10k a compound exhibiting poor CCK1R affinity with
only modest improvement in CCK2R affinity. Likewise, addition
of an (S)-COOH group to benzhydryl analog 10g produced a
compound, 10l, with no measurable CCK1R affinity and little
improvement in CCK2R affinity.
We also evaluated a series of ephedrine-based derivatives. The
result is that compounds bearing the (1R,2S) stereochemistry were
the only ones of the three stereoisomers investigated (the (1R,2R)
analog was not prepared) showing affinity of <100 nM for either
receptor. A representative example is given in Table 2 (10m,
CCK1 pKi 7.6).
In conclusion, we have discovered for the first time that within
a very narrow structural subclass of anthranilic sulfonamide CCK
receptor antagonists (phenethyl amides), one can observe CCK1R
selectivity. The level of the CCK1R affinity as well as selectivity
over CCK2R was found to be enhanced by appropriate halogenation
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