Triamino pyrimidines and pyridines as histamine H4 receptor modulators

Article abstract of DOI:10.1016/j.bmcl.2011.03.017

Two series of triamino pyrimidines and a series of triamino pyridines have been synthesized and their structure-activity relationships evaluated for activity at the H₄ receptor in competitive binding and functional assays. Small structural changes in these three hetereoaromatic cores influenced the functional activity of these compounds.

Full text of DOI:10.1016/j.bmcl.2011.03.017

Bioorganic & Medicinal Chemistry Letters 21 (2011) 3113–3116
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Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Triamino pyrimidines and pyridines as histamine H4 receptor modulators
⇑
Steven P. Meduna , Brad M. Savall, Hui Cai, James P. Edwards, Robin L. Thurmond, Patricia M. McGovern
Johnson & Johnson Pharmaceutical Research & 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:
Two series of triamino pyrimidines and a series of triamino pyridines have been synthesized and their
structure–activity relationships evaluated for activity at the H4 receptor in competitive binding and func-
tional assays. Small structural changes in these three hetereoaromatic cores influenced the functional
activity of these compounds.
Received 19 January 2011
Revised 3 March 2011
Accepted 4 March 2011
Available online 10 March 2011
Ó 2011 Elsevier Ltd. All rights reserved.
Keywords:
Pyrimidine
Pyridine
Histamine
Histamine H4
Antagonist
The histamine H4 receptor is a 390 amino acid G-protein
coupled receptor that is implicated in the treatment of inflamma-
tory diseases such as asthma and allergic rhinitis based on the
expression of the H4 receptor on eosinophils, mast cells, dendritic
cells and other leukocytes.1,2 Previous reports from these laborato-
ries have described a series of H4 receptor selective antagonists
that include JNJ 7777120 (1) and JNJ 10191584 (2).3,4 Both ligands
possess a basic amine linked to a heterocycle, a motif prevalent in
known histamine ligands.5 In an effort to find other heteroaromatic
replacements for (1) and (2), we began investigating triamino
pyrimidines6 (3) with diamine sidechains. After surveying a series
of diamines, the more active piperazine and aminopyrrolidine dia-
mines became the focus of additional SAR. Small structural
changes led to divergent functional activity within a series. Fur-
thermore, other triamino pyrimidine regioisomers6 and triamino
pyridines were explored to evaluate the placement and role of
the ring nitrogen (Fig. 1).
H
N
N
H
N
O
O
N
N
Cl
N
Cl
N
Me
Me
hH4 Ki = 4 nM
2
1
hH4 Ki = 26 nM
NH2
NH2
NH2
N
N
N
N
R1
R1
R1
N
DA
N
N
DA
N
DA
R2
R2
R2
3 a-r
6 a-n
8 a-n
Figure 1. H4 receptor selective antagonists. R1R2N and DA are defined by Tables 1–4.
Scheme 1 describes the synthetic route used to make the
triamino 1,3 pyrimidine core. Commercially available 2-amino-
4,6-dichloropyrimidine (4) was used as the starting material. Sym-
metry allowed for either the desired primary or secondary amine
or a diamine (N-methylpiperazine or (R)-3-methylaminopyrroli-
dine) to be incorporated first. In practice, adding 1 equiv of the pri-
mary or secondary amine, followed by the diamine was the
preferred sequence, as the primary amines were difficult to add
to the deactivated diamino substituted chloropyrimidine.
NH2
N
NH2
N
a, b
N
N
R1
Cl
Cl
N
DA
R2
4
3 a-r
N
N
Scheme 2 outlines the syntheses of the triamino 1,5 pyrimidine
and triamino pyridine cores. In the case of 4-amino-2,6-dichloro-
or
DA =
NH
Me
N
Me
Scheme 1. Reagents and conditions: (a) R1R2NH, DIEA, IPA, 100–160 °C, 1–2 h
microwave W); (b) diamine, DIEA, IPA, 100–160 °C, 1–2 h W), 10–74%
combined a and b steps.
⇑
Corresponding author.
E-mail address: smeduna@its.jnj.com (S.P. Meduna).
(
l
(l
0960-894X/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2011.03.017

3114
S. P. Meduna et al. / Bioorg. Med. Chem. Lett. 21 (2011) 3113–3116
Table 2
NH2
NH2
Triamino 1,3 pyrimidine series
a, b
c, d
N
N
N
R1
NH2
N
NH2
N
Cl
Cl
N
Cl
N
N
DA
1
3
1
3
R2
N
N
R1
R1
H
N
5
6 a-n
N
N
N
N
R2
N
R2
Me
Me
NH2
NH2
3b, 3g-3l
3d, 3m-3r
N
R1
b
a
R1R2N
#
hH4 Kia (nM)
#
hH4 Ki (nM)
Cl
N
DA
8 a-n
R2
7
N
H
3g
3h
3
3m
3n
3
N
N
or
DA =
NH
Me
N
Me
N
Me
24
51
Scheme 2. Reagents and conditions: (a) R1R2NH, DIEA, IPA, 180 °C, 1 h (
diamine, IPA, 100–180 °C, 1 h (
W), 13–50% combined a and b steps; (c) R1R2NH
(neat), 160 °C, 8–15 h ( W); (d) diamine, Yb(OTf)2, IPA, 160 °C, 2 h ( W), 3–30%
combined c and d steps.
lW); (b)
N
H
3i
2
6
3o
3d
4
l
l
l
N
3b
36
N
H
3j
1
3p
9
pyrimidine (5), initial substitution occurred predominately in the 2
position, so the primary or secondary amine was driven in first, fol-
lowed by the diamine. Substitution of 2-amino-4,6-dichloropyri-
dine (7) with primary amines required microwave heating in the
neat amine for several hours. The diamine addition to the disubsti-
tuted chloropyridine required Lewis acid activation by adding
1.3 equiv of ytterbium triflate to obtain better yields.
The structure–activity relationship of the triamino 1,3 pyrimi-
dine series is shown in Tables 1 and 2. A number of diamines were
screened in the triamino 1,3 pyrimidine series, but the focus of this
disclosure will be on molecules derived from the N-methylpipera-
zine and (R)-3-methylaminopyrrolidine.The initial compound
made in this series contained a pyrrolidine ring and the N-methyl-
piperazine moiety (previously determined as a potent amine ter-
N
H
3k
3l
20
25
3q
3r
58
44
HO
N
H
Displacement of [3H]histamine from the recombinant human histamine H4
a
receptor. Ki values are the geometric mean of three or more independent deter-
minations and calculated according to Cheng and Prusoff.8
b
All compounds were at least 95% pure with the majority being greater than 98%
pure.
minus in the indole and benzimidazole series)1,2 on the
pyrimidine core (3b, Ki = 6 nM). Further analogs indicated that
switching from a tertiary amine to a secondary amine resulted in
increased activity (3g vs 3h). In this series, the N-methylpiperazine
diamine displayed up to 9 fold better H4 binding over the 3-meth-
ylaminopyrrolidine diamine, regardless of the 6-positon
substitution.
Investigations of an alternate triamino pyrimidine regioisomer
(herein referred to as the triamino 1,5 pyrimidines) led to a differ-
entiated series (Table 3). Unlike the triamino 1,3 pyrimidine series,
the triamino 1,5 pyrimidine series favored the 3-methylamino-
pyrrolidine diamine over the N-methylpiperazine diamine in H4
binding affinity. The trend of more favorable activity of the substi-
tuted secondary amines over tertiary amines continued in this ser-
ies (6a vs 6b), though generally this series was less active. Such
divergent SAR in closely related series suggests that the two series
may have different binding modes.7
The role of the pyrimidine nitrogen was further explored by
making a series of substituted triamino pyridines (Table 4). Rela-
tive to the triamino pyrimidines, the H4 binding affinity of the tria-
mino pyridines was comparable or better. The other pyridine
regioisomer, displaying a ring nitrogen in the two position in refer-
ence to the diamine, resulted in an inactive compound (data not
shown). Again, as in the triamino 1,5 pyrimidine series, the 3-
methylaminopyrrolidine diamine was favored over the N-methyl-
piperazine diamine. As in both triamino pyrimidine series, substi-
tuted secondary amines displayed higher receptor affinity over
tertiary amines.
The differences between the three series were not only evident
in the H4 binding affinities; they were also present in the func-
tional activity of these compounds. Tables 5 and 6 show a compar-
ison of functional activity of several triamino 1,3 pyrimidines,
triamino 1,5 pyrimidines and triamino pyridine compounds as
measured by the EC50 and pA2 data. All compounds containing
the 3-methylaminopyrrolidine diamine tested in each of the three
series behaved as functional antagonists against the H4 receptor
Table 1
Diamine scan on triamino 1,3 pyrimidine core
NH2
N
N
N
DA
b
Compd #f
DA
hH4 Kia,e (nM)
EC50 nM (
>10,000
>10,000
a
)
pA2b,c,d
N/D
N
NH
3a
3b
8
6
N
N
N Me
8.7
R
3c
3d
3e
64
36
83
N/D
N/D
8.1
NH2
N
N
R
>10,000
N/D
NHMe
S
N/D
NHMe
N
3f
40
N/D
N/D
N
H
a
Displacement of [3H]histamine from the recombinant histamine H4 receptor. Ki
values are the geometric mean of three or more independent determinations and
calculated according to Cheng and Prusoff.8
b
Compounds with Ki >100 nM not tested in functional assays.
c
Compounds with
a
> 0.40 were not tested in the pA2 assay.
d
Antagonism of histamine inhibition of forskolin-stimulated cAMP-mediated
reporter gene activity in SK-N-MC cells expressing the human histamine H4
receptor.
e
Unless noted chiral compounds were tested as racemates. Detailed experi-
mental for EC50 and pA2 determinations included in Ref. 9. N/D = not determined.
f
All compounds were at least 95% pure with the majority being greater than 98%
pure.

S. P. Meduna et al. / Bioorg. Med. Chem. Lett. 21 (2011) 3113–3116
3115
Table 5
Table 3
Functional activity of the 3-methylaminopyrrolidine compounds
Triamino 1,5 pyrimidine series
NH2
X
NH2
NH2
1
1
N
N
N
R1
R1
R1
H
N
Me
NH
N
Y
N
N
N
N
N
N
N
R2
R2
N
R2
5
5
Me
Me
e
b
6a-6g
6h-6n
#
R1R2N
X
Y
Kia (nM)
EC50 (nM)
ac
pA2d
b
R1R2N
#
hH4 Kia (nM)
#
hH4 Kia (nM)
N
H
8h
3m
6h
8l
CH
CH
3
>10,000
>10,000
>10,000
>10,000
>10,000
>10,000
––
8.8
8.0
N
H
6a
6b
162
6h
6i
6
N
H
N
CH
N
3
––
––
––
––
––
N
Me
853
140
N
H
CH
CH
N
6
7.9
N
6c
15
6j
1
H
*
N
H
CH
CH
N
0.9
9
N
6d
132
6k
127
N
H
6e
10
6l
6
3p
6l
N
H
9.4
7.9
N
H
6f
1076
1155
6m
6n
69
N
H
CH
6
HO
N
H
6g
255
N
H
8j
CH
N
CH
CH
N
0.2
4
>10,000
>10,000
>10,000
––
––
––
8.8
9.3
8.8
Displacement of [3H]histamine from the recombinant human histamine H4
a
N
H
3o
6j
receptor. Ki values are the geometric mean of three or more independent deter-
minations and calculated according to Cheng and Prusoff.8
b
N
H
All compounds were at least 95% pure with the majority being greater than 98%
CH
1
pure.
N
N
8k
3d
CH
N
CH
CH
77
36
>10,000
>10,000
––
––
7.8
8.1
Table 4
Triamino pyridine series
a
Displacement of [3H]histamine from the recombinant human histamine H4
NH2
NH2
receptor. Ki values are the geometric mean of three or more independent deter-
minations and calculated according to Cheng and Prusoff.8
N
N
R1
R1
H
N
b
Compounds with Ki >100 nM not tested in functional assays.
values determined relative to histamine as a control with histamine assigned
N
N
N
N
c
R2
N
R2
Me
Me
a
= 1.0. Compounds with
a
>0.40 were not tested in the pA2 assay.
8a-g
8h-n
d
Antagonism of histamine inhibition of forskolin-stimulated cAMP-mediated
b
R1R2N
#
hH4 Kia (nM)
#
hH4 Kia (nM)
reporter gene activity in SK-N-MC cells expressing the human histamine H4
receptor. Detailed experimental for EC50 and pA2 determinations included in Ref. 9.
e
All compounds were at least 95% pure with the majority being greater than 98%
N
H
8a
8b
28
8h
8i
3
pure.
*
Displays possible insurmountable antagonism.
N
Me
189
29
N
H
8c
2
8j
0.2
77
Table 6
Functional activity of the N-methylpiperazine compounds
N
8d
100
8k
NH2
N
X
R1
N
H
8e
3
8l
0.9
N
Y
N
R2
N
Me
N
H
8f
148
0.3
8m
8n
50
e
b
#
R1R2N
X
Y
Kia (nM)
EC50 (nM)
ac
pA2d
––
N
H
8g
0.04
N
H
8a
3g
6a
8e
3j
CH
CH
28
533
0.6
Displacement of [3H]histamine from the recombinant human histamine H4
a
receptor. Ki values are the geometric mean of three or more independent deter-
minations and calculated according to Cheng and Prusoff.8
N
H
N
CH
N
3
12
0.57
––
––
––
––
––
b
All compounds were at least 95% pure with the majority being greater than 98%
pure.
N
H
CH
CH
N
162
3
––
(Table 5). The N-methylpiperazine substituted diamines, however,
did display variable functional activity (Table 6). All of the second-
ary amine substituted triamino 1,5 pyrimidines (e.g., 6c and 6e)
and triamino pyridines (e.g., 8a, 8e, and 8c) displayed partial ago-
nist activity. The only triamino pyridine with N-methylpiperazine
substitution that behaves as a full antagonist was the tertiary
N
H
CH
CH
11
0.73
0.46
N
H
1
101
(continued on next page)

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S. P. Meduna et al. / Bioorg. Med. Chem. Lett. 21 (2011) 3113–3116
N-methyl piperazine the pyridines and triamino 1,5 pyrimidines
Table 6 (continued)
behaved as partial agonists while the triamino 1,3 pyrimidines
showed a mix of partial agonists and antagonists.
e
b
#
R1R2N
X
Y
Kia (nM)
EC50 (nM)
ac
pA2d
––
6e
N
H
CH
N
10
16
0.63
Supplementary data
N
H
8c
3i
CH
N
CH
CH
N
2
50
0.51
––
––
8.9
––
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.bmcl.2011.03.017.
N
H
2
>10,000
86
N
H
6c
CH
15
0.71
References and notes
N
N
8d
3b
CH
N
CH
CH
100
6
>10,000
>10,000
––
––
7.7
––
1. de Esch, I. J. P.; Thurmond, R. L.; Ling, P.; Karlsson, L. Trends Pharmacol. Sci. 2005,
26, 462.
2. Fung-Leung, W.-P.; Thurmond, R. L.; Ling, P.; Karlsson, L. Curr. Opin. Invest. Drugs
2004, 5, 1174.
3. Jablonowski, J. A.; Grice, C. A.; Chai, W.; Dvorak, C. A.; Venable, J. D.; Kwok, A. K.;
Ly, K. S.; Wei, J.; Baker, S. M.; Desai, P. J.; Jiang, W.; Wilson, S. J.; Thurmond, R. L.;
Karlsson, L.; Edwards, J. P.; Lovenberg, T. W.; Carruthers, N. I. J. Med. Chem. 2003,
46, 3957.
4. Venable, J. D.; Cai, H.; Chai, W.; Dvorak, C. A.; Grice, C. A.; Jablonowski, J. A.;
Shah, C. R.; Kwok, A. K.; Ly, K. S.; Pio, B.; Wei, J.; Desai, P. J.; Jiang, W.; Nguyen, S.;
Ling, P.; Wilson, S. J.; Dunford, P. J.; Thurmond, R. L.; Lovenberg, T. W.; Karlsson,
L.; Carruthers, N. I.; Edwards, J. P. J. Med. Chem. 2005, 48, 8289.
5. Venable, J. D.; Thurmond, R. L. Anti-Inflammatory Anti-Allergy Agents Med. Chem.
2006, 5, 307.
6. For simplicity between the pyrimidine regioisomers, compounds where the NH2
group is between the ring nitrogens are referred to as triamino 1,3 pyrimidines
while analogues of the other regioisomer are referred to as triamino 1,5
pyrimidines.
7. (a) Jojart, B.; Kiss, R.; Viskolcz, B.; Keseru, G. M. J. Chem. Inf. Model. 2008, 48,
1199–1210; (b) Igel, P.; Geyer, R.; Strasser, A.; Dove, S.; Seifert, R.; Buschauer, A.
J. Med. Chem. 2009, 52, 6297.
3h
N
CH
24
>10,000
––
––
N
Me
Displacement of [3H]histamine from the recombinant human histamine H4
a
receptor. Ki values are the geometric mean of three or more independent deter-
minations and calculated according to Cheng and Prusoff.8
b
Compounds with Ki >100 nM not tested in functional assays.
c
a
values determined relative to histamine as a control with histamine assigned
>0.40 were not tested in the pA2 assay.
Antagonism of histamine inhibition of forskolin-stimulated cAMP-mediated
a
= 1.0. Compounds with a
d
reporter gene activity in SK-N-MC cells expressing the human histamine H4
receptor. Detailed experimental for EC50 and pA2 determinations included in Ref. 9.
All compounds were at least 95% pure with the majority being greater than 98%
pure.
e
8. Cheng, Y.-C.; Prusoff, W. H. Biochem. Pharmacol. 1973, 22.
9. Details for EC50 and pA2 assays: Mouse and human H4 were cloned into the
pCINeo mammalian expression vector and transfected into the human
neuroblastoma SK-N-MC cell line. The construct contains the reporter gene B
galactosidase under the control of cyclic AMP responsive element. In the EC50
assay, the compounds are added to the media and allowed to incubate for
amine (8d). The triamino 1,3 pyrimidines, on the other hand, dis-
played either antagonism (e.g., 3b, 3h, and 3i) or partial agonism
(e.g., 3g and 3j) again setting this series apart from the other two.
Comparison of the three heteroaromatic cores demonstrated a
rank order potency (triamino pyridines > triamino 1,3 pyrimi-
dines > triamino 1,5 pyrimidines) among the three cores. Addition-
ally the relative potency of 3-methylaminopyrrolidine versus N-
methylpiperazine was dependant on the core, where N-methylpi-
perazine was favored for the triamino 1,3 pyrimidines and N-meth-
ylpyrrolidine was favored for the triamino 1,5 pyrimidine and the
triamino pyridine cores. However, the functional activity against
the H4 receptor was dependant on both the nature of the diamine
and the heteroaromatic core. The use of 3-methylamino pyrroli-
dine resulted in antagonists across all three cores. Finally, with
10 min at room temperature before the addition of forskolin (5 lM final
concentration). In the pA2 assay, the cells are preincubated with compound for
10 min, then incubated with agonist for 10 min before the addition of forskolin.
After a 6 h incubation (for both assays) at 37 °C, the media is aspirated and the
plates are stored at À40 °C overnight. Cells are lysed with 25
buffer (10 mM Na phosphate, pH 8, 0.2 mM MgSO4, 0.01 mM MnCl2) and
incubated at room temperature for 10 min. Cells are then incubated with 100
of 1Â assay buffer including 0.5% Triton X-100 and 40 mM B mercaptoethanol
for 10 min. 25 of substrate solution (1 mg/mL chlorophenolred B–D
galactopyranoside) was added and the color was quantitated at an absorbance
of 570 nm. values are calculated using the full agonist (positive control) as the
standard of 1.
lL of 0.1Â assay
lL
lL
a