Diaminopyrimidine and diaminopyridine 5-HT7 ligands

Article abstract of DOI:10.1016/j.bmcl.2004.06.007

The present studies have identified a series of diaminopyrimidines and diaminopyridines as novel 5-HT₇ receptor ligands. Three regiosiomeric classes of pyrimidines and four regioisomeric classes of pyridines were synthesized and analyzed for binding to the 5-HT₇ receptor. The 5-HT₇ binding affinities of different regioisomers show clearly the structure-activity relationship with position of ring nitrogens.

Full text of DOI:10.1016/j.bmcl.2004.06.007

Bioorganic & Medicinal Chemistry Letters 14 (2004) 4249–4252
Diaminopyrimidine and diaminopyridine 5-HT7 ligands
Derek J. Denhart,* Ashok V. Purandare,* John D. Catt, H. Dalton King, Aiming Gao,
Jeffrey A. Deskus, Michael A. Poss, Arlene D. Stark, John R. Torrente,
Graham Johnson and Ronald J. Mattson
Bristol-Myers Squibb Pharmaceutical Research Institute, Wallingford, CT 06492-7660, USA
Received 29 March 2004; accepted 3 June 2004
Available online 26 June 2004
Abstract—The present studies have identified a series of diaminopyrimidines and diaminopyridines as novel 5-HT7 receptor ligands.
Three regiosiomeric classes of pyrimidines and four regioisomeric classes of pyridines were synthesized and analyzed for binding to
the 5-HT7 receptor. The 5-HT7 binding affinities of different regioisomers show clearly the structure–activity relationship with
position of ring nitrogens.
ꢀ 2004 Elsevier Ltd. All rights reserved.
The 5-HT7 receptor has been implicated in a variety of
therapeutic targets: cognition,1 depression,2 sleep dis-
orders,3 migraine,4 and schizophrenia.5 In a previous
paper6 we outlined the discovery of a novel class of 5-
HT7 ligands, the aminotriazines 1. To explore the limits
of the pharmacophore, ring nitrogens were replaced by
CH groups to arrive at the diaminopyrimidines 2–4 and
the diaminopyridines 5–8. Several analogs from each
series were synthesized and tested for binding to the 5-
HT7 receptor, and the results demonstrate the impor-
tance of the ring nitrogens in the positions denoted by W
and Y in 2–8.
The diaminopyrimidines, iii, were prepared by the
sequential displacement of the halogens on the appro-
priate dichloropyrimidine i (Scheme 1). The choice of
amines was guided by previous experience from the
triazine class, which indicated that one of the amines
was preferably a branched amine ((S)-a-methylbenzyl-
amine preferred). The branched amine sidechain was
introduced by refluxing the dichloropyrimidine with a-
methylbenzylamine and diisopropylethylamine in ace-
tonitrile to give ii. In the case of 2,4-dichloropyrimidine,
this reaction gave a mixture of 2- and 4-amino products,
which were separated by flash chromatography and
carried on to the desired products separately. A neat
mixture of the appropriate primary amine and the
intermediate ii was heated at 140 ꢁC to give the diami-
nopyrimidine products, iii.7
R
X
W
Y
N
N
R'HN
Z
NHR''
R'HN
N
NHR''
2 (W,Y = N; X,Z = CH) 5 (W = N; X,Y,Z = CH)
3 (W,Z = N; X,Y = CH) 6 (X = N; W,Y,Z = CH)
4 (Y,Z = N; W,X = CH) 7 (Y = N; W,X,Z = CH)
8 (Z = N; W,X,Y = CH)
1
X
X
Z
a
W
b
Y
CH3
W
Y
Cl
Z
i
Cl
N
H
Cl
ii
X
Z
CH3
W
Y
R'
N
H
N
H
* Corresponding authors. Tel.: +1-203-677-7117 (D.J.D.); tel.: +1-609-
252-4320 (A.V.P.); e-mail addresses: derek.denhart@bms.com;
ashok.purandare@bms.com
iii
Scheme 1. Reagents and conditions: (a) RNH2, NEt(iPr)2, THF; (b)
R0NH2, heat.
Present address: Rib-X Pharmaceuticals, 300 George Street, Suite
301, New Haven, CT 06511, USA.
0960-894X/$ - see front matter ꢀ 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2004.06.007

4250
D. J. Denhart et al. / Bioorg. Med. Chem. Lett. 14 (2004) 4249–4252
Table 1. 5-HT7 binding9 of 9–17
X
CH3
W
Y
R'
N
H
Z
N
H
9-17
#
*
W
X
Y
Z
R0
5-HT7 Ki (nM)
9
S
S
S
N
CH
CH
CH
CH
CH
CH
CH
CH
CH
N
CH
CH
CH
N
–(CH2)2–Ph
33
5
10
11
12
13
14
15
16
17
N
N
–(CH2)2–(4-F–Ph)
–(CH2)2–O–(4-F–Ph)
–(CH2)2–Ph
N
N
5
N
CH
CH
N
6
N
N
–(CH2)2–O–(4-F–Ph)
–(CH2)2–Ph
1
S
CH
CH
CH
CH
N
0.6
6
N
N
–(CH2)2–(4-F–Ph)
–(CH2)2–O–Ph
–(CH2)2–O–(4-F–Ph)
S
S
N
N
2
0.3
N
N
8
The influence of amines on the 5-HT7 binding SAR of
pyrimidines followed trends similar to those observed
for the triazines.6 One amine was fixed as a-methyl-
benzylamine (either the S enantiomer or the racemate),
and the other amine was preferentially phenethylamine,
phenoxyethylamine, or their 4-fluoro derivatives. The
results of this SAR for the pyrimidines are shown in
Table 1.
products, which were separated by flash chromatogra-
phy and carried on to the desired products separately.
The appropriate primary amine was reacted with the
intermediate v, using palladium catalysis to give the
diaminopyridine products, vi. The second amine addi-
tion was routinely done in parallel reactions using pre-
mixed stock solutions of catalyst and ligand.11
As can be seen from Table 2, changes in the location of
ring nitrogens in the pyridine series caused significant
effects on 5-HT7 binding. 2,6-Disubstituted pyridines
30–31 (Z ¼ nitrogen) showed a loss of activity, whereas
the 3,5-disubstituted pyridines 22–25 (X ¼ nitrogen)
provided moderate activity. The 2,4-disubstituted pyr-
idines 18–21 (W ¼ nitrogen) and 26–29 (Y ¼ nitrogen)
both demonstrated high affinity for the 5-HT7 receptor,
with 26–29 being slightly more potent. Compound 29
demonstrated the highest affinity binding of the pyridine
class with an Ki of 0.2 nM. Compounds 32 and 33 are
included to show that at least one nitrogen does appear
to be necessary for activity.
The 4,6-disubstituted pyrimidines, 9–11 (nitrogen in
positions W and Y), showed moderate binding affinity
to the 5-HT7 receptor. The 2,4-disubstituted pyrim-
idines, 12–13 (nitrogen in positions W and Z) demon-
strated slightly improved affinity, while the third class of
2,4-disubstituted pyrimidines, 14–17 (nitrogen in posi-
tions Y and Z), appear to possess the highest affinity
5-HT7 binding. The most potent pyrimidine from this
series was 17, with a binding affinity of 0.3 nM.
Replacement of another ring nitrogen by a CH group
led to diaminopyridines, which were synthesized as
shown in Scheme 2. The diaminopyridines, vi, were
prepared by the sequential displacement of the halogens
on the appropriate dibromopyridine iv. The branched
amine sidechain was introduced by reacting the di-
bromopyridine with a-methylbenzylamine (using heat
for 2,6-dibromopyridine and palladium catalysis10 for
other dibromopyridines). In the case of 2,4-dibromo-
pyridine, this reaction gave a mixture of 2- and 4-amino
Several compounds were also assayed against other
receptors to determine selectivity for 5-HT7 (Table 3).
Good to moderate affinity for the a1 adrenergic receptor
was shown by pyrimidines 13 and 17 and by pyridines 21
and 29, while pyridine 25 showed poor binding. Good to
moderate affinity binding to the 5-HT2c receptor was
shown by pyrimidine 13 and pyridines 21 and 29, and
again pyridine 25 showed poor binding (no value ob-
tained for pyrimidine 17). Only pyridine 29 showed some
binding to the 5-HT6 receptor. None of the compounds
X
Z
X
CH3
W
Y
W
c
Y
in Tables
1 and 2 exhibited significant affinity
a (Z = N)
(Ki > 1000 nM) for the 5-HT1a receptor, the D2L receptor
(excepting the potent pyridine 29), or the serotonin
transporter. One can note that the selectivity ratios for
binding to 5-HT7 versus binding to a1 and 5-HT2c are
similar for the compounds in Table 3, even though each
has different nitrogen positions. Thus, for the com-
pounds represented in Table 3, the SAR for binding to a1
and D2L roughly parallels the SAR for binding to 5-HT7.
N
H
Br
Br
Z
Br
b (W,X, or Y = N)
v
iv
X
CH3
W
Y
R'
N
H
Z
N
H
vi
In conclusion, the present studies have identified 5-HT7
receptor ligands of two new structural types, the dia-
mino-pyrimidines and -pyridines, and a clear SAR
Scheme 2. Reagents and conditions: (a) RNH2, K2CO3, DMF, heat;
(b) RNH2, NaOBut, Pd2dba3, BINAP, toluene, 70 ꢁC; (c) R0NH2,
NaOBut, Pd2dba3, BINAP, toluene, 90 ꢁC.

D. J. Denhart et al. / Bioorg. Med. Chem. Lett. 14 (2004) 4249–4252
4251
Table 2. 5-HT7 binding9 of 18–33
X
CH3
W
Y
R'
N
H
Z
N
H
18-33
#
W
X
Y
Z
R0
5-HT7 Ki (nM)
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
N
CH
CH
CH
CH
N
CH
CH
CH
CH
CH
CH
CH
CH
N
CH
CH
CH
CH
CH
CH
CH
CH
CH
CH
CH
CH
N
–(CH2)2–Ph
3
4
N
–(CH2)2–(4-F–Ph)
–(CH2)2–O–Ph
–(CH2)2–O–(4-F–Ph)
–(CH2)2–Ph
N
0.4
0.4
N
CH
CH
CH
CH
CH
CH
CH
CH
CH
CH
CH
CH
13
16
N
–(CH2)2–(4-F–Ph)
–(CH2)2–O–Ph
–(CH2)2–O–(4-F–Ph)
–(CH2)2–Ph
N
4
N
4
0.3
CH
CH
CH
CH
CH
CH
CH
CH
N
–(CH2)2–(4-F–Ph)
–(CH2)2–O–Ph
–(CH2)2–O–(4-F–Ph)
–(CH2)2–Ph
0.4
0.4
N
N
0.2
CH
CH
CH
CH
>1000
>1000
>1000
>1000
N
–(CH2)2–O–Ph
–(CH2)2–Ph
–(CH2)2–O–Ph
CH
CH
Table 3. 5-HT6, 5-HT2C, and a1 binding9 (rat) of 13, 17, 21, 25, 29
Compd
5-HT7 Binding Ki (nM)
D2L Binding Ki (nM)
a1 Binding Ki (nM)
5-HT2C Binding Ki (nM)
13
17
21
25
29
1
>1000
>1000
>1000
>1000
370
57
14
27
379
8
40
––
0.3
0.4
4
13
476
15
0.2
Johnson, G. Bioorg. Med. Chem. Lett. 2004, 14, in press.
doi:10.1016/j.bmcl.2004.06.008.
emerged from the regiochemistry of the ring hetero-
atoms. The most active compounds were pyridines with
one nitrogen in positions denoted W or Y in the general
structure. The addition of a second nitrogen produced
pyrimidines with similar or slightly diminished activity
compared to the pyridines. The most active pyrimidines
were those with a nitrogen in either position W or Y and
another nitrogen in the Z position. These studies have
helped to further define the SAR of the amino-triazine
5-HT7 antagonists and have produced ligands which
may be useful in elucidating the role of the 5-HT7
receptor as a therapeutic target.
7. Procedure for synthesis of 11: A mixture of 4,6-dichloro-
pyrimidine (14.9 g, 0.10 mol), (S)-())-a-methylbenzyl-
amine (13.3 g, 0.11 mol), and diisopropylethylamine
(15.5 g, 0.12 mol) in acetonitrile (100 mL) were heated to
reflux for 4 h. The reaction was cooled, then partitioned
between ether (500 mL) and water (250 mL). The organic
layer was separated, dried over sodium sulfate, and
concentrated in vacuo. Purification by flash chromato-
graphy on silica gel with hexane/ethyl acetate (3:1) yielded
pure (S)-6-chloro-N-(1-phenylethyl)pyrimidin-4-amine
(18.6 g, 80%).
The above intermediate (1.40 g, 6.0 mmol) and 4-fluoro-
phenoxyethylamine (2.14 g, 13.8 mmol) were heated neat
in a sealed tube at 150 ꢁC for 3 h. After cooling, the
solidified mass was dissolved in dichloromethane (150 mL)
and extracted with saturated aqueous sodium carbonate
and water. The organic layer was dried over sodium
sulfate, partially concentrated, and precipitated with
hexane. The solid brown product was filtered and washed
with dichloromethane/hexane (2:1) to give compound 11
(1.30 g). Conversion to the HCl salt was accomplished by
dissolving this material in dichloromethane (40 mL) and
treating with a solution of 1 N HCl in ether (20 mL).
Concentration yielded an oil, which was co-evaporated
from acetonitrile to yield the HCl salt as a foam (1.33 g,
63%).
References and notes
1. Meneses, A.; Terron, J. A. Behav. Brain Res. 2001, 21, 21–
28.
2. Middlemiss, D. N.; Price, G. W.; Watson, J. M. Curr.
Opin. Pharm. 2002, 2, 18–22.
3. Mullins, U. L.; Gianutsos, G.; Eison, A. S. Neuropsycho-
pharmacology 1999, 21, 352–367.
4. Terron, J. A.; Falcon-Neri, A. Brit. J. Pharmacol. 1999,
127, 609–616.
5. Pouzet, B.; Didriksen, M.; Arnt, J. Pharm. Biochem.
Behav. 2002, 71, 655–665.
6. Mattson, R. J.; Denhart, D. J.; Catt, J. D.; Dee, M. F.;
Deskus, J. A.; Ditta, J. L.; Epperson, J.; King, H. D.; Gao,
A.; Poss, M. A.; Purandare, A.; Tortolani, D.; Zhao, Y.;
Yang, H.; Yeola, S.; Palmer, J.; Torrente, J.; Stark, A.;
8. 5-HT7 binding assay: Membranes are prepared for binding
using the human 5-HT7 receptor expressed in CHO cells.
Cells are collected and ruptured using
a dounce

4252
D. J. Denhart et al. / Bioorg. Med. Chem. Lett. 14 (2004) 4249–4252
homogenizer. The cells are spun at 18,000g for 10 min and
dried with MgSO4, and evaporated to dryness. The
products were easily separated by flash chromatography
on a silica gel column, eluting with 15:85 ethyl acetate/
hexanes to obtain v(W ¼ N) (128 mg, 24%) and with 25:75
ethyl acetate/hexanes to obtain v(Y ¼ N) (102 mg; 19%).
The regioisomers were identified by NOE studies of their
1H NMR spectra.
the pellet is resuspended in assay buffer, frozen in liquid
nitrogen and kept at )80 ꢁC until the day of the assay. The
assay is carried out in 96-deep-well plates with a total of 30
ug protein used per well in an assay buffer of 50 mM
HEPES. The membrane preparation is incubated at 25 ꢁC
for 60 min with 0.1–1000 nM test compound and 1 nM 3H-
5-carboxamidotryptamine. 10 lM serotonin is used as
blocking agent to determine nonspecific binding. The
reaction is terminated by the addition of 1 mL of ice cold
50 mM HEPES buffer and rapid filtration through a
Brandel Cell Harvester using Whatman GF/B filters. The
filter pads are counted in an LKB Trilux liquid scintilla-
tion counter. Ki values are determined using nonlinear
regression by Exel-fit.
Compound v(W ¼ N) (20 mg; 0.072 mmol), phenoxyethyl-
amine (16 mg; 0.11 mmol), and sodium t-butoxide (8 mg;
0.08 mmol) were added to toluene (1 mL) in a 1 dram glass
vial. A catalyst stock solution was prepared by adding
Pd2dba3 (12 mg; 0.013 mmol) and (+) BINAP (18 mg;
0.029 mmol) to toluene (6 mL) and heating gently until
most solids dissolved. A portion of this stock solution
(1 mL) was added to the vial of amine and bromide
prepared earlier. The vial was sealed with a teflon-backed
lid and heated at 90 ꢁC for 2 h. The solvent was removed
in vacuo and the residue was dissolved in methanol and
filtered before being purified by preparative reverse phase
HPLC with conditions: column ¼ YMC ODS-A
20 ·100 mm S5; solvent A ¼ 10:90:0.1 methanol/H2O/
TFA; solvent B ¼ 90:10:0.1 methanol/H2O/TFA; elution
gradient from 30% B to 100% B; gradient time ¼ 10 min;
flow rate ¼ 20 mL/min. Obtained product 28 as a TFA salt
9. IC50 values are the mean of 1–4 determinations run at five
different concentrations with the radioligand at the Kd
concentration. Each experiment was carried out in dupli-
cate. Standard errors were typically 20% of the mean
value.
10. Wagaw, S.; Buchwald, S. L. J. Org. Chem. 1996, 61, 7240–
7241.
11. Procedure for synthesis of 28: To a solution of 2,4-
dibromopyridine (0.45 g; 1.9 mmol) and (S)-a-methylbenz-
ylamine (0.23 g; 1.9 mmol) in toluene (10 mL) was added
sodium t-butoxide (0.22 g; 2.3 mmol), tris(dibenzylideneac-
etone)palladium(0) (35 mg; 0.038 mmol), and (+) BINAP
(47 mg; 0.076 mmol; either enantiomer would work). The
reaction was heated at 70 ꢁC for 2 h and then diluted with
H2O (20 mL), extracted with ethyl acetate (2 · 10 mL),
1
in a yield of 11 mg (25%). H NMR (CDCl3) d 8.80 (m,
1H), 7.46 (m, 1H), 7.17–7.38 (m, 6H), 6.98 (m, 2H), 6.79
(d, J ¼ 7:8 Hz, 2H), 6.63 (d, J ¼ 7:6 Hz, 1H), 5.98 (d,
J ¼ 5:8 Hz, 1H), 5.50 (d, J ¼ 5:5 Hz, 2H), 4.51 (m, 1H),
3.96 (m, 2H), 3.44 (m, 2H), 1.59 (d, J ¼ 6:6 Hz, 3H); MS
(ESIþ) (M+H)þ 334.0 obs.