Discovery of N-(5,6-diarylpyridin-2-yl)amide derivatives as potent and selective A2B adenosine receptor antagonists

Article abstract of DOI:10.1016/j.bmcl.2010.01.045

The synthesis and SAR of a series of N-(5,6-diarylpyridin-2-yl)amide derivatives as potent A_2B adenosine receptor antagonists is described. Several compounds showed good selectivity versus other adenosine receptors. The potent and selective analogue 9 was shown to have good oral bioavailability in the rat.

Full text of DOI:10.1016/j.bmcl.2010.01.045

Bioorganic & Medicinal Chemistry Letters 20 (2010) 1697–1700
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Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Discovery of N-(5,6-diarylpyridin-2-yl)amide derivatives as potent and
selective A2B adenosine receptor antagonists
*
Paul Eastwood , Jacob Gonzalez, Sergio Paredes, Arsenio Nueda, Teresa Domenech,
Joan Alberti, Bernat Vidal
Almirall Research Center, Almirall S.A., Ctra. Laureà Miró 408, St. Feliu de Llobregat, E-08980 Barcelona, Spain
a r t i c l e i n f o
a b s t r a c t
Article history:
The synthesis and SAR of a series of N-(5,6-diarylpyridin-2-yl)amide derivatives as potent A2B adenosine
receptor antagonists is described. Several compounds showed good selectivity versus other adenosine
receptors. The potent and selective analogue 9 was shown to have good oral bioavailability in the rat.
Ó 2010 Elsevier Ltd. All rights reserved.
Received 22 December 2009
Revised 8 January 2010
Accepted 10 January 2010
Available online 20 January 2010
Keywords:
Adenosine
A2B
Adenosine receptor antagonists
Asthma
The mediator adenosine has been linked to the pathophysiology
of human asthma based on the observation that it triggers bron-
choconstriction in asthmatics and the presence of high levels of
N
N
O
N
N
N
N
H
this substance in the bronchoalveolar lavage fluid of asthmat-
N
A
1–4
ics.
A
receptors are responsible for the adenosine-mediated re-
2B
O
A
1
: LAS38096
O
lease of several inflammatory cytokines from mast cells, airway
and bronchial epithelial cells, fibroblasts, smooth muscle cells,
intestinal epithelial cells, monocytes and dendritic cells.4–7 These
observations have led to the hypothesis that the A2B receptor could
be playing a major role as mediator of the effect of adenosine in
human asthma.3 Therefore, A2B adenosine receptor antagonists
have the potential to become a new pharmacological drug class
for the treatment of this inflammatory condition.8
N
N
H
R
N
O
S
N
3: A = CH, N
O
N
H
O
O
2
Figure 1. N-(5,6-Diarylpyridin-2-yl)amide derivatives.
The likely similarity (Fig. 1), with respect to the pharmacophoric
elements, of structures 1 (LAS38096), which pertains to a series of
potent and selective A2B adenosine receptor antagonists recently
disclosed by our group,9 and 2, an orally active and selective A3
receptor antagonist,10 was considered. Both 1 and 2 possess a cen-
tral heteroaromatic ring containing a hydrogen bond acceptor, two
aromatic rings attached to the central core in an ortho arrange-
ment, one of which is weakly basic in nature, and a hydrogen bond
donating NH group. This led to the hypothesis that amides of type
3 would lead to novel series of antagonists. Herein is disclosed the
synthesis and SAR of compounds of type 3 as potential A2B adeno-
sine receptor antagonists.
Compound 5, the acetamide analogue of 1, was synthesized as
shown in Scheme 1 by acetylation of the previously described
intermediate 4.9 It was found in earlier studies that the 4-furyl-
5-pyrimidinyl substitution pattern in compounds of type 1 led to
a good balance of potency/selectivity with regard to A2B versus
other adenosine receptors. Thus, it was gratifying to find that 5
was a reasonably potent A2B adenosine receptor antagonist that re-
tained selectivity versus the other adenosine receptors (Table
1).11,12
Synthetic methods to access derivatives 6–14, in which a pyri-
dine nucleus is present as the central scaffold, are shown in
Schemes 2–4 and biological results are given in Table 1.
Compound 6, the pyridine equivalent of 5, was found to have
improved potency whilst retaining good selectivity. All other
* Corresponding author. Tel.: +34 933128610; fax: +34 933128635.
E-mail addresses: paulroberteastwood@yahoo.co.uk, paul.eastwood@almirall.
com (P. Eastwood).
0960-894X/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2010.01.045

1698
P. Eastwood et al. / Bioorg. Med. Chem. Lett. 20 (2010) 1697–1700
N
N
N
N
N
N
O
(i-ii)
N
(iii)
CN (ii-iii)
O
N
N
CN
(i)
N
N
N
N
CO2Et
O
N
N
N
O
N
H
N
NH2
O
O
O
O
N
(iv-v)
(vi)
N
(iv)
6,9
O
N
N
N
NH2
N
NH2
N
N
O
O
H
O
4
5
Scheme 2. Reagents and conditions: (i) 2-cyanoacetamide, NaOMe, DMF, 80 °C,
91%; (ii) POCl3, 110 °C, 88%; (iii) satd NH3 in EtOH, 80 °C, 76%; (iv) NaOH, EtOH,
reflux, 99%; (v) Cu, quinoline, 205–215 °C, 58%; (vi) RCOCl, pyridine, 70 °C, 65–70%.
Scheme 1. Reagents and conditions: (i) LiHMDS, THF, 0 °C to rt, 94%; (ii) DMF–
DMA, 100 °C, 87%; (iii) guanidine carbonate, K2CO3, DMF, 70 °C, 61%; (iv) CH3COCl,
pyridine, rt, 68%.
Br
Br
Br
O
(i)
(ii-iii)
NH2
compounds described in this Letter possess the pyridyl moiety as
the central scaffold. Analogues 7 and 8 show that by incorporation
of a 4-pyridyl moiety at C-5 one arrives at very potent A2B adeno-
sine receptor antagonists, albeit with a certain loss of selectivity
with respect to other adenosine receptors. Parallel studies utilizing
a different central core ring system (unpublished results) showed
that the optimal substituents for the amide moiety were acetyl
and cyclopropyl and as such no further amide derivatives were
prepared in this series. Incorporation of other non-basic substitu-
ents at C-5 (compounds 10 and 11) gave potent but pan-adenosine
receptor antagonists. Placement of an acidic tetrazole moiety at C-
5 (compound 12) abolished all potency. Derivative 14, in which a
fluorine atom was introduced in the meta position (with respect
to the ring nitrogen) of the C-5 4-pyridyl moiety, had excellent po-
tency and displayed an improved selectivity profile with respect to
compound 8. In general, it was found that placement of either a
pyrimidin-4-yl (compound 9) or a 3-fluoropyridin-4-yl radical
(compound 14) at C-5 of the pyridine core ring resulted in com-
pounds with the best balance of potency and selectivity.
Attention was now turned to modifications at position C-6 with
a focus on replacement of the furan moiety, a potential metabolic
liability and toxicophore.13 Synthetic methods are shown in
Scheme 4 (compounds 15–33) and the results are presented in
Table 2.
As expected from previous studies, the replacement of the furan
moiety with non-aromatic substituents led to compounds which
showed weaker antagonism at the A2B receptor (compounds 15–
17). Placement of a methyl group on C-5 of the furan ring of 8,
which could potentially attenuate the formation of toxic metabo-
lites derived from an unsubstituted furan ring, led to compound
18, a potent A2B adenosine receptor antagonist; however, the selec-
tivity of this compound versus other adenosine receptors was
N
N
H
R
Br
N
NH2
N
O
10
(iv)
7,8,13,14
Scheme 3. Reagents and conditions: (i) NBS, DMF, rt, 86%; (ii) furan-2-ylboronic
acid, Pd(PPh3)4, 2 M Na2CO3 (aq), toluene, MeOH, reflux, 32%; (iii) RCOCl, pyridine,
70 °C, 70–84%; (iv) ArB(pin), PdCl2dppfꢀDCM, 2 M Cs2CO3 (aq), 1,4-dioxane, 85 °C,
40–65%.
unacceptable. Several other five-membered heterocyclic deriva-
tives were prepared (compounds 19–25). The oxazole derivative
21, although not as potent as 8, showed a similar selectivity profile.
Other derivatives could not match the potency/selectivity profile of
the furan derivative 8. Regarding the placement of six-membered
aromatic ring systems at C-6 it was discovered that the ortho-flu-
oro phenyl derivative 26 had a similar potency/selectivity profile
to that of 8. Once again all other derivatives synthesized could
not match the potency/selectivity profile of furan 8.
Selected compounds were profiled in an in vitro metabolism as-
say using hepatic microsomes (Table 3). Percentage turnover of the
compounds was found to vary widely in both rat and human
microsomes. Additionally, it was noted that in several instances
non-oxidative metabolism was found to be occurring when assays
were performed in the absence of the oxidative co-factor NAPDH.
For example, in the case of compound 14, a 99% turnover was
noted upon incubation with rat microsomes both in the presence
and absence of NADPH. Examination of the mass-spectral data
from both studies revealed that the major metabolite was the cor-
responding 2-aminopyridine, the compound produced by the
hydrolysis of the amide bond of 14.
Table 1
Amide derivatives and modifications at C-5
R1 5
A
R2
Ki (nM) or % inhibition of radioligand binding at a compound concentration of 1 l
M)12
N
N
H
O
Compound
A
R1
R2
hA2B
17
380 175
47 19
7
1
4
28
41
23%
5
hA2A
hA1
hA3
1043 147
1
5
6
7
8
N
N
Pyrimidin-4-yl
Pyrimidin-4-yl
Pyrimidin-4-yl
Pyridin-4-yl
Pyridin-4-yl
Pyrimidin-4-yl
Br
C„N
Tetrazol-5-yl
3-Chloropyridin-4-yl
3-Fluoropyridin-4-yl
Pyridin-3-yl
C(@O)Me
C(@O)Me
C(@O)Me
C(@O)cyc-propyl
C(@O)cyc-propyl
C(@O)cyc-propyl
C(@O)cyc-propyl
C(@O)cyc-propyl
C(@O)cyc-propyl
C(@O)cyc-propyl
4
40%
10%
20%
209 45
30
239 46
35 14
12
5
2
4
2821 228
2%
7%
358 17
82 19
931 121
285 79
289 114
1
2
2%
28%
1
2
CH
CH
CH
CH
CH
CH
CH
CH
CH
0
0
1
2
8
4
2
0
333 50
1337 383
3754 866
6
9
10
11
12
13
14
617
326
8%
9
7
7
2
1638 296
147 18
150 29
1%
250 42
374 22
1
1866 454
11%
1
9

P. Eastwood et al. / Bioorg. Med. Chem. Lett. 20 (2010) 1697–1700
1699
NC
O
I
O
(i)
(ii-iv)
(v)
12
Cl
N
NH2
N
N
H
Cl
N
NH2
11
(iii), (vi)
N
N
N
(vii)
(x)
(xi)
O
O
O
19,21
Cl
N
N
H
N
N
H
N
N
H
O
N
O
16
17
(iv)
(ix)
(vi)
(xiii)
(xii)
20, 30 (+15)
25
(viii)
33
24
18,22,23 26-29,31,32
Scheme 4. Reagents and conditions: (i) NIS, DMF, rt, 86%; (ii) Zn(CN)2, Pd2dba3, dppf, DMF, 120 °C, 80%; (iii) cyclopropylcarbonyl chloride, pyridine, 70 °C, 60–75%; (iv)
ArSnBu3, Pd(PPh3)4, xylenes, reflux, 53–86%; (v) NaN3, NH4Cl, DMF, 110 °C, 20%; (vi) ArB(pin) or ArB(OH)2, PdCl2dppfꢀDCM, Cs2CO3 (aq), 1,4-dioxane, 80–100 °C, 22–67%; (vii)
ArZnBr, Pd(PPh3)4, THF, reflux, 20–25%; (viii) ArH (oxazole or 2-methylfuran), Pd(PPh3)4, KOAc, DMA, 150 °C; (ix) pyrazole, Cs2CO3, DMF, 120 °C, 15%; (x) (1-
ethoxyvinyl)tributylstannane, Pd(PPh3)4, xylenes, reflux then 2 M HCl (aq), rt, 90%; (xi) DMF–DMA, 100 °C, 99%; (xii) NH2NH2ꢀH2O, EtOH, reflux, 67%; (xiii) formamidine
acetate, EtOH, toluene 115 °C, 42%.
Table 2
Modifications at C-6
N
O
Ki (nM) or % inhibition of radioligand binding at a compound concentration of 1 l
M)12
R1
N
N
H
R2
6
Compound
R1
R2
hA2B
hA2A
hA1
82 19
hA3
1337 383
8
Furan-2-yl
H
Cl
C(@O)Me
5-Methylfuran-2-yl
Thiazol-2-yl
Thiazol-5-yl
Oxazol-2-yl
Cyclopropyl
Cyclopropyl
Cyclopropyl
Cyclopropyl
Cyclopropyl
Cyclopropyl
Cyclopropyl
Cyclopropyl
Cyclopropyl
Cyclopropyl
Cyclopropyl
Cyclopropyl
Cyclopropyl
Cyclopropyl
Me
1
29%
380 133
3668 882
5
42
78
32
30
134 34
202 15
72 19
0
9
30
2%
7%
2%
11
6
1
6
1
3
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
8%
5%
6%
6
3
4
7%
14%
2%
5
1
1
1
4
6
7
9
25 10
914 304
320 51
702 245
635 158
189 23
11%
4851 1522
302 25
813 138
1359 112
635 158
1373 397
9
22%
5%
12%
1%
7
3
5
0
1
Oxazol-5-yl
Oxazol-4-yl
1%
3%
22%
1
2
9
1H-Pyrazol-3-yl
1H-Pyrazol-1-yl
2-Fluorophenyl
3-Fluorophenyl
3-Fluorophenyl
4-Fluorophenyl
Pyridin-2-yl
Pyridin-3-yl
Pyridin-4-yl
Pyrimidin-4-yl
4%
1
1440 232
61 19
57
286 121
39 13
862 103
1465 568
163 56
2%
2
2
1
0
123 41
817 92
715 124
471 18
5
14
58
35
3
4
3
30 11
4
47 24
33
14
Cyclopropyl
Cyclopropyl
Cyclopropyl
Cyclopropyl
Cyclopropyl
1
27%
2%
10%
6%
4
1
4
4
1
940 182
3
6
21%
338
3%
4
3
0
208 29
9%
1
3%
The iv pharmacokinetic profiles in the rat of the compounds
with the lowest in vitro metabolism (9, 21 and 30) are presented
in Table 4. Half lives in rat were short for all compounds tested
as a result of moderate-to-high plasma clearance and moderate
volumes of distribution.
An oral pharmacokinetic study conducted with 9 (10 mg/kg, rat,
0.1% tween 80 + 0.5% methylcellulose) showed that the compound
was rapidly absorbed (Tmax = 0.3 h) and had good bioavailability
(F = 39%).
Table 3
In vitro metabolism (hepatic microsomes)
Compound
% Turnovera
Rat
Human
9
27b
99b
27
Not tested
14
21
26
30
77b
14
86b
0
100b
12b
In summary, a new series of potent and selective A2B adenosine
receptor antagonists has been disclosed and preliminary data show
that the compounds demonstrate oral bioavailability. In subse-
quent disclosures it will be shown how the further development
of this series led ultimately to the selection of a clinical candidate.
a
% Turnover after a 30 min incubation period at 37 °C of a 5
lM solution of test
compound with hepatic microsomes (1 mg/mL).
b
Non-NADPH dependent metabolism observed.
Table 4
Pharmacokinetic profiles of derivatives 9, 21 and 30 in rat (1 mg/kg iv)
Compound
t
terminal (h)
Cmax
(ng/mL)
Cl
AUC0ꢁ1
(ng h/mL)
Vss
(L/kg)
½
Acknowledgements
(L/h/kg)
9
21
30
0.5
0.9
0.5
538
761
822
3.8
1.9
2.1
267
533
485
1.6
1.6
1.0
We thank Maria Isabel Loza and Maria Isabel Cadavid from the
Universidad de Santiago de Compostela for performing the radioli-
gand binding assays mentioned in this work.

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P. Eastwood et al. / Bioorg. Med. Chem. Lett. 20 (2010) 1697–1700
8. For recent reviews, see: (a) Caruso, M.; Varani, K.; Tringali, G.; Polosa, R. Curr.
References and notes
Med. Chem. 2009, 16, 3875; (b) Haskó, G.; Csóka, B.; Németh, Z. H.; Vizi, E. S.;
Pacher, P. Trends Immunol. 2009, 30, 263; (c) Haskó, G.; Linden, J.; Cronstein, B.;
Pacher, P. Nat. Rev. Drug Disc. 2008, 7, 759; (d) Ham, J.; Rees, D. Endocr. Metab.
Immune Disord. Drug Targets 2008, 8, 244; (e) Beukers, M.; Meurs, I.; Ijzerman,
A. Med. Res. Rev. 2006, 26, 667; (f) Zablocki, J.; Elzein, E.; Kalla, R. Expert Opin.
Ther. Pat. 2006, 16, 1347; (g) Cacciari, B.; Pastorin, G.; Bolcato, C.; Spalluto, G.;
Bacilieri, M.; Moro, S. Mini-Rev. Med. Chem. 2005, 5, 1053; (h) Jacobson, K.; Gao,
Z.-G. Nat. Rev. Drug Disc. 2006, 247.
1. Linden, J. J. Mol. Pharmacol. 2005, 67, 1385.
2. Forsythe, P.; Ennis, M. Inflamm. Res. 1999, 48, 301.
3. Fozard, J. Curr. Opin. Pharmacol. 2003, 3, 264.
4. Holgate, S. Br. J. Pharmacol. 2005, 145, 1009.
5. Feoktistov, I.; Biaggioni, I. J. Clin. Invest. 1995, 96, 1979.
6. Linden, J. J. Clin. Invest. 2006, 116, 1835.
7. (a) Feoktistov, I.; Goldstein, A.; Ryzhov, S.; Zeng, D.; Belardinelli, L.; Voyno-
Yasenetskaya, T.; Biaggioni, I. Circ. Res. 2002, 90, 531; (b) Feoktistov, I.;
Ryzhov, S.; Goldstein, A.; Biaggioni, I. Circ. Res. 2003, 91, 485; (c) Feoktistov,
I.; Ryzhov, S.; Zhong, H.; Goldstein, A.; Matafonov, A.; Zeng, D.; Biaggioni, I.
Hypertension 2004, 44, 649; (d) Rees, D.; Lewis, B.; Lewis, M.; Francis, K.;
Scanlon, M. F.; Ham, J. Br. J. Pharmacol. 2003, 140, 764; (e) Zhong, H.; Wu, Y.;
Belardinelli, L.; Zeng, D. Am. J. Respir. Cell Mol. Biol. 2006, 35, 587; (f)
Novitskiy, S.; Ryzhov, S.; Zaynagetdinov, R.; Goldstein, A.; Huang, Y.;
Tikhomirov, O.; Blackburn, M.; Biaggioni, I.; Carbone, D.; Feoktistov, I.;
Dikov, M. Blood 2008, 112, 1822; (g) Ryzhov, S.; Zaynagetdinov, R.;
Goldstein, A.; Novitskiy, S.; Dikov, M.; Blackburn, M.; Biaggioni, I.;
Feoktistov, I. J. Immunol. 2008, 180, 7212; (h) Ryzhov, S.; Zaynagetdinov,
R.; Goldstein, A.; Novitskiy, S.; Blackburn, M.; Biaggioni, I.; Feoktistov, I. J.
Pharmacol. Exp. Ther. 2008, 324, 694; (i) Ryzhov, S.; Zaynagetdinov, R.;
Goldstein, A.; Novitskiy, S.; Dikov, M.; Blackburn, M.; Biaggioni, I.; Feoktistov,
I. J. Immunol. 2008, 180, 7212.
9. Vidal, B.; Nueda, A.; Esteve, C.; Domenech, T.; Benito, S.; Reinoso, R.; Pont, M.;
Calbet, M.; López, R.; Cadavid, M.; Loza, M.; Cárdenas, A.; Godessart, N.; Beleta,
J.; Warrellow, G.; Ryder, H. J. Med. Chem. 2007, 50, 2732.
10. Press, N. J.; Fozard, J. R.; Beer, D.; Haberthuer, S.; Heng, R.; Jones, K.; Schoeffter,
P.; Tranter, P.; Keller, T. H. Curr. Top. Med. Chem. 2004, 4, 863.
11. Results obtained with compounds 1 (previously reported—see Ref. 9), 5–7, 10,
28 and other related compounds in functional assays measuring cAMP levels in
both human HEK293 cells (expressing the human A2B receptor) and CHO cells
(transfected with the mouse A2B receptor) indicated that these compounds are
acting as antagonists. Further details can be found in Ref. 9.
12. Details of the procedures used to perform the binding assays in this work can
be found in Ref. 9.
13. Kalgutkar, A. S.; Gardner, I.; Obach, R. S.; Shaffer, C. L.; Christopher, L.; Callegari,
E.; Henne, K. R.; Mutlib, A. E.; Dalvie, D. K.; Lee, J. S.; Nakai, Y.; O’Donnell, J. P.;
Boer, J.; Harriman, S. P. Curr. Drug. Metab. 2005, 6, 161.