Syntheses and evaluation of pyrido[2,3-d]pyrimidine-2,4-diones as PDE 4 inhibitors

Article abstract of DOI:10.1016/S0960-894X(00)00681-8

The syntheses and in vitro evaluation of a new series of pyrido[2,3-d]pyrimidine-2,4-diones bearing substituents at C-3 and/or C-4 positions on the pyridine ring are described. Some of these compounds, especially 5l and 6f, were found to be potent phosphodiesterase 4 (PDE 4) inhibitors exhibiting improved ratio of PDE 4 inhibitory activity:rolipram binding assay (RBA).

Full text of DOI:10.1016/S0960-894X(00)00681-8

Bioorganic & Medicinal Chemistry Letters 11 (2001) 611±614
Syntheses and Evaluation of Pyrido[2,3-d]pyrimidine-2,4-diones
as PDE 4 Inhibitors
Ghilsoo Nam,a Cheol Min Yoon,b Euikyung Kim,c Chung K. Rhee,c Joong Hyup Kim,a
Jung Hyu Shind and Sung Hoon Kima,*
aBiochemicals Research Center, Korea Institute of Science and Technology, PO Box 131, Cheongryang, Seoul 130-650,
South Korea
bDepartment of Chemistry, College of Science and Technology, Korea University, Jochiwon, Choong-nam, 339-700,
South Korea
cCheiljedang Corp., 522-1, Dokpyong-ri, Majang-myon, Ichon-si, Kyonggi-do, 467-810, South Korea
dSchool of Chemistry and Molecular Engineering, Seoul National University, Seoul 151-742, South Korea
Received 29 September 2000; accepted 10 November 2000
AbstractÐThe syntheses and in vitro evaluation of a new series of pyrido[2,3-d]pyrimidine-2,4-diones bearing substituents at C-3
and/or C-4 positions on the pyridine ring are described. Some of these compounds, especially 5l and 6f, were found to be potent
phosphodiesterase 4 (PDE 4) inhibitors exhibiting improved ratio of PDE 4 inhibitory activity:rolipram binding assay (RBA).
# 2001 Elsevier Science Ltd. All rights reserved.
The phosphodiesterase (PDE) family1 is particularly
abundant in immunocompetent cells, where an increase
of cAMP leads to the inhibition of the synthesis and the
release of pro-in¯ammatory mediators.2 Due to their
crucial role in regulation of cell function, PDEs have
become good clinical targets for the treatment of
in¯ammation,3 asthma,4 erectile dysfuncion,5 etc. Per-
sistent e€orts and desire to elucidate the active site of
PDEs make possible to solve the three-dimensional
structure of the catalytic domain of phosphodiesterase 4
(PDE 4).6 Since the discovery of rolipram,7 the ®rst
PDE 4 inhibitor, a number of compounds such as SB-
207499 have been synthesized to increase the activity
and to reduce side e€ects such as vomiting, nausea,
etc.8,9 Despite much progress in the development of
PDE 4 inhibitors, the search for new sca€olds to reduce
side e€ects is worth continuing as well.
It has recently been reported that a number of com-
pounds such as RS-2534410 and CP-7705911 bearing the
pyridopyrimidine moiety exhibited excellent PDE 4
inhibitory activity (Fig. 1). However, there has been no
report on the evaluation of pyridopyrimidine analogues
having substitutents on the pyridine ring for PDE 4
Figure 1.
*Corresponding author. Fax: +82-2-958-5189; e-mail: kimsh@kist.re.kr
0960-894X/01/$ - see front matter # 2001 Elsevier Science Ltd. All rights reserved.
PII: S0960-894X(00)00681-8

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G. Nam et al. / Bioorg. Med. Chem. Lett. 11 (2001) 611±614
inhibitors so far. In this paper, we wish to report the
syntheses of new pyridopyrimidine derivatives repre-
sented by compound A and the evaluation for PDE 4
inhibitory activity and rolipram binding anity.
DMA, followed by N-benzylation of the resultant pro-
duct 2 with benzylchloride a€ording 3 and vinyl iodina-
tion of 3 with N-iodosuccinimide in MeOH (Scheme 1).
Heck coupling of 4 with appropriate vinyl substrates,
followed by ring cyclization formed the regio-isomeric
mixture of pyridopyrimidine compounds 5 and 6. It has
been found that the ratio of 5 and 6 is dependent on the
substituents R. In the case of the reaction with n-butyl-
vinyl ether was obtained only 6a. However, the reac-
tions with acrylonitrile, ethyl acrylate, 2-tri¯uorostyrene
and 3-nitrostyrene a€orded only the C-3 substituted
isomers 5b, 5c, 5i and 5j, respectively. All other
Chemistry
The compounds A were synthesized using palladium
catalyzed Heck coupling reaction of 4, followed by ring
cyclization according to our reported procedure.12 The
key intermediate 4 was easily prepared by the reaction
of commercially available aminouracil 1 with DMF±
Scheme 1. (i) DMF±DMA, MeOH, re¯ux, 88%; (ii) benzylchloride, K2CO3, DMF, re¯ux, 70%; (iii) NIS, MeOH, re¯ux, 93%.
Scheme 2. (i) CH2ˆCH-R, Pd(OAc)2 (5 mol%), K2CO3 (2 equiv), PPh3 (0.1 equiv), DMF, 120 ꢀC.
Scheme 3. (i) Pd(OAc)2 (5 mol%), K2CO3 (2 equiv), PPh3 (0.1 equiv), DMF, 110 ꢀC.

G. Nam et al. / Bioorg. Med. Chem. Lett. 11 (2001) 611±614
613
Table 1. PDE 4 inhibitory activity of pyridopyrimidine derivatives 5±8
PDE 4 inhibition (mM) (A)a,13
RBAb, IC5014 (mM) (B)
B/A
Compounds
10 mM
3 mM
1 mM
0.3 mM
0.1 mM
IC50 (mM)
5b
5c
5d
5e
5f
5g
5h
5i
5j
5k
5l
6a
6d
6f
6g
6h
6k
6l
7a
7b
7c
8a
8c
44.6
48.3
40.4
49.0
55.1
32.6
48.0
65.4
36.0
42.4
72.9
35.9
83.7
83.9
38.6
89.7
62.3
59.5
58.7
53.4
63.5
58.0
51.3
ND
67.8
29.9
43
31.3
47.8
44
21.9
30.3
17.4
35.5
41.4
31.5
40.7
38.1
17.4
31.7
60.3
25.6
59.8
63.6
19.3
66.8
50.2
49.3
38.2
39.4
42.1
41.7
41.5
69.1
43.8
NDc
ND
ND
ND
ND
ND
ND
ND
ND
ND
54.7
22.6
45.7
57.6
ND
53.2
52.3
ND
ND
ND
ND
ND
ND
54
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
45.8
29.7
>10
>10
>10
>10
5.75
>10
>10
2.31
>10
>10
0.11
>10
0.43
0.07
>10
0.24
0.95
3.34
4.48
6.11
3.05
5.15
4.75
0.11
1.8
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
23.4
ND
1.01
0.755
ND
0.491
0.95
ND
ND
ND
ND
ND
ND
0.18
0.002
30.2
46.4
53.7
23.5
37.6
68.2
28.2
67.6
72.1
35.1
69.7
54.3
57.1
46.7
45.1
49.8
43.5
49.2
72.2
ND
212.73
2.35
10.79
2.05
1.00
SB-207499
Rolipram
1.64
0.001
35
aIsolated from rat liver.
bRolipram binding assay (isolated from rat brain).
cND=not determined.
substrates a€orded a mixture of 5 and 615 (Scheme 2).
The pyridopyrimidines 7 and 815 were also prepared by
the reactions of 4 with allyl ethers (Scheme 3).
References and Notes
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Biological Properties
Table 1 shows the PDE 4 inhibitory activity and roli-
pram binding anity of the compounds 5±8. It has been
found that all of the C-4 substituted pyridopyrimidine
derivatives 6 except the benzyl substituted compound 6l
exhibited more potent inhibitory activity than the cor-
responding C-3 substituted compounds 5. The com-
pound 5l having a benzyl group at the C-3 position
exhibited 33 times more potent activity than the C-4
substituted compound 6l. The compounds 7 and 8
showed also moderate PDE 4 inhibitory activities. For
evaluation in high rolipram binding site, we selected ®ve
compounds (5l, 6d, 6f, 6h and 6k), of which the activity
for PDE 4 was submicromolar. Biological data of 6f for
PDE 4 inhibitory activity and rolipram binding anity
is superior to those of SB-207499.9b The inhibitory value
of 6f for PDE 4 is more potent than that of 5l. Never-
theless, the compound 5l showed more promising rolipram
binding assay data and B/A value. This compound 5l is
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and inhibitory activity for TNF-a production.
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This work was ®nancially supported by Cheiljedang
corp, Brain Korea 21 program and MOST (2N20120).

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15. Representative procedure for the synthesis of 5±8: The
compound 4 (150 mg, 0.36 mmol) was reacted with acryloni-
trile (47.3 mL, 0.72 mmol), K2CO3 (99.3 mg, 0.72 mmol) and
Pd(OAc)2 (4.0 mg, 0.018 mmol) in DMF (4 mL) at 120 ꢀC for
5 h in a sealed tube. The resulting mixture was ®ltered through
Celite and extracted with methylene chloride (30 mLÂ3),
washed with water and dried over Na2SO4. The solution was
concentrated under reduced pressure and the residue was pur-
i®ed by column chromatography on silica gel (EtOAc:n-hex-
ane=1:3) to give 5b (76.3 mg, 73%) as a white solid; mp 146±
147 ꢀC; 1H NMR (CDCl3, 300 MHz) d 3.72 (s, 3H), 5.22 (s,
2H), 7.27 (m, 3H), 7.48 (d, J=7.45 Hz, 2H), 8.71 (d,
J=2.13 Hz, 1H), 8.89 (d, J=2.13 Hz, 1H); 13C NMR (CDCl3,
75 MHz) d 30.26, 45.68, 104.78, 110.98, 116.09, 127.94, 128.34,
129.37, 136.17, 141.76, 151.03, 152.92, 156.90, 159.96, 163.41;
IR (KBr pellet, cmÀ1) 3455, 3106, 2947, 2368, 2249, 1720,
1671, 1616, 1491, 1461, 1391, 1347, 1277, 1112, 948, 788, 704,
614.