Spiroquinazolinones as novel, potent, and selective PDE7 inhibitors. Part 1

Article abstract of DOI:10.1016/j.bmcl.2004.07.011

The synthesis and SAR studies of spiroquinazolinones as novel PDE7 inhibitors are discussed. The best compounds from the series displayed nanomolar inhibitory affinity and were selective versus other PDE isoenzymes.

Full text of DOI:10.1016/j.bmcl.2004.07.011

Bioorganic & Medicinal Chemistry Letters 14 (2004) 4623–4626
Spiroquinazolinones as novel, potent, and selective PDE7
inhibitors. Part 1
a
a
a
Edwige Lorthiois,a, Patrick Bernardelli, Fabrice Vergne, Chrystelle Oliveira,
*
Abdel-Kader Mafroud,a Emmanuelle Proust,a Lamia Heuze,a Franc¸ois Moreau,a
Moulay Idrissi,a Anita Tertre,a Bernadette Bertin,a Magali Coupe,a Roger Wrigglesworth,a
Arnaud Descours,a Patricia Soulardb and Patrick Bernaa
aPfizer Global Research and Development, 3–9 rue de la Loge 94265Fresnes, France
bPfizer Discovery Technology Center, 620 Memorial Drive, Cambridge, MA 02139, USA
Received 23 January 2004; revised 17 June 2004; accepted 2 July 2004
Available online 27 July 2004
Abstract—The synthesis and SAR studies of spiroquinazolinones as novel PDE7 inhibitors are discussed. The best compounds from
the series displayed nanomolar inhibitory affinity and were selective versus other PDE isoenzymes.
Ó 2004 Elsevier Ltd. All rights reserved.
1. Introduction
Phosphodiesterase enzymes (PDEs) play an important
role in various biological processes by hydrolyzing the
key secondary messengers adenosine and guanosine
30,50-cyclic monophosphates (cAMP and cGMP) into
their corresponding 50-monophosphate nucleotides,
Figure 1. Structure of the hit 1.
thereby decreasing concentrations of cAMP and cGMP,
respectively.1 At least eleven isoenzymes of mammalian
cyclic nucleotide phosphodiesterase have been identified
on the basis of primary structure, substrate specificity,
or sensitivity to cofactors or inhibitory drugs.2 Among
these, PDE7 is a high-affinity cAMP-specific PDE
(Km = 0.2lM) and its mRNA is expressed in various cell
types and tissues known to be important in the patho-
genesis of several diseases such as T-cell related dis-
eases,3 autoimmune diseases,3 airway diseases,4
leukemia,5 CNS disorders,6 and fertility disorders.7 In
addition, a functional role of PDE7 in T-cell activation
has been reported.3
trations.8 Selectivity for PDE7 over other members of
the phosphodiesterase family is also important to poten-
tially avoid secondary effects such as emesis or cardio-
toxicity. In this context, compound 1 was identified by
high throughput screening of the compound collection
as a PDE7 inhibitor with an IC50 of 0.17lM (Fig. 1).
This communication describes our preliminary efforts
toward the identification of novel potent and selective
PDE7 inhibitors by exploring the SAR around this
new spiroquinazolinone hit.
The increasing interest in the therapeutic potential of
PDE7 inhibitors is driving current medicinal chemistry
efforts to identify compounds active at very low concen-
2. Chemistry
The quinazolinone derivatives 1–21 were prepared by
condensation of the readily available ureas with the
desired ketones in polyphosphoric acid (PPA) at 80–
100°C (Scheme 1).9 To the best of our knowledge, this
type of intermolecular reaction between an urea and a
Keywords: PDE7; Phosphodiesterase.
*
Corresponding author at present address: Novartis Pharma AG,
Novartis Institutes for BioMedical Research, WKL-122-3-27, CH-
4002 Basel, Switzerland. Tel.: +41-61-6961955; fax: +41-61-
6961163; e-mail: edwige.lorthiois@pharma.novartis.com
0960-894X/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2004.07.011

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E. Lorthiois et al. / Bioorg. Med. Chem. Lett. 14 (2004) 4623–4626
Scheme 1. Reagents and conditions: (a) R1R2C@O, PPA, 80–100 °C; (b) N-chlorosuccinimide, DMF, 60°C; (c) N-iodosuccinimide, TFA, H2SO4,
55°C; (d) Pd(PPh3)4, 2-pyridylZnBr in THF or RB(OH)2, K2CO3 in DMF, reflux (where R = p- or m-C6H4–CO2H, 3- or 4-pyridyl or o-C6H4CO–N-
methylpiperazine); (e) SOCl2, toluene, reflux; (f) R3R4NH, toluene (where R3R4NH = H2N–(CH2)2–NMe2, H2N–(CH2)3–NMe2, or 1-
methylpiperazine).
ketone has not been previously reported in the literature.
The cyclization reaction performed using 2-substituted
or 4-monosubstituted ureas led to a single compound
as depicted in Scheme 1 (Eqs. 1 and 3). Yet when 3-
chloro or 3,4-dichloro-phenylurea and cyclohexanone
were used as starting materials, a mixture of regioiso-
mers (5- and 7-chloro or 5,6- and 6,7-dichloroquinazol-
inones, respectively), was obtained and was separated by
flash chromatography on silica gel (Eq. 2). The 6,8-di-
substituted derivatives 22–25 were synthesized from
the corresponding 6-monosubstituted intermediates by
chlorination with N-chlorosuccinimide in DMF at
60°C (Eq. 3). The 6-aryl substituted quinazolinone ana-
logs 27–32 were obtained from 1 (Eq. 4). Iodination of 1
under acidic conditions10 afforded iodo-intermediate 26,
which was further converted to the biaryl-derivatives via
Negishi (compound 27) or Suzuki palladium-catalyzed
cross-coupling reaction (compounds 28–32). Finally
compounds 33–39 were derived from the corresponding
carboxylic acids after conversion to the intermediate
acid chloride and condensation with the appropriate
amine.
Table 1. PDE7A1 inhibitory activity for compounds 1–25
Compd
R1–R2
R
PDE7A1
IC50, lMa
1
2
–Spirocyclohexyl–
–Spirocyclohexyl–
–Spirocyclohexyl–
–Spirocyclohexyl–
–Spirocyclohexyl–
–Spirocyclohexyl–
–Spirocyclohexyl–
–Spirocycloheptyl–
–Spirocyclobutyl–
–4-Methyl-
8-Cl
8-H
0.17
6.60
0.39
0.066
6.85
0.79
2.96
0.068
1.40
0.21
3
8-F
4
8-Br
8-I
5
6
8-CH3
8-CF3
8-Br
8-Br
8-Br
7
8
9
10
spirocyclohexyl–
Propyl–propyl
Ethyl–ethyl
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
8-Br
8-Br
2.66
6.54
2.7
–Spirocyclohexyl–
–Spirocyclohexyl–
–Spirocyclohexyl–
–Spirocyclohexyl–
–Spirocyclohexyl–
–Spirocyclohexyl–
–Spirocyclohexyl–
–Spirocyclohexyl–
–Spirocyclohexyl–
–Spirocyclohexyl–
–Spirocyclohexyl–
–Spirocyclohexyl–
–Spirocyclohexyl–
7-Cl
7-OMe
6-Cl
9.5
4.8
3. Biological results and discussion
6-OMe
6-Ph
5-Cl
3.2
0.98
0.84
3.7
The compounds described in this paper were assessed
against both PDE7A and PDE7B subtypes. Since no
selectivity was observed, only the PDE7A inhibitory
activities will be presented herein.
6,7-DiCl
5,6-DiCl
5,8-DiCl
6,8-DiCl
6-Ph,8-Cl
6-Me, 8-Cl
6-OMe, 8-Cl
0.6
0.014
0.12
0.016
0.16
0.16
Initial results for the inhibition of PDE7 using our spiro-
quinazolinone analogs showed that the nature of the
substituent in position 8 has an impact on activity
(Table 1, compounds 1–7). The following order of
a Measured against the human full length enzyme produced in bacu-

E. Lorthiois et al. / Bioorg. Med. Chem. Lett. 14 (2004) 4623–4626
4625
potency 8-Br > 8-Cl > 8-F > 8-CH3 > 8-CF3 > 8-H, 8-I
cannot be easily explained considering physical parame-
ters such as +p-effect, +r-effect11 or molecular volume
but indicated that a size limited halogen or a methyl
group were preferred.
The recognition of this effect led us to the biphenyl sub-
series. In this study, the 8-chloro substituent was pre-
ferred to the 8-bromo because of reduced lipophilicity
and better pharmaceutical suitability. The reference
compound 23 exhibited good selectivity versus PDE1,
3A, 4D, 5 with selectivity ratios greater than 85 (Table
2).
We next explored the SAR around the cyclohexyl ring
while retaining the 8-bromo substituent, which is opti-
mal for activity. From the results of compounds 8–12
(Table 1), several phamacophoric features can be high-
lighted: preference for a cyclic ring (4, 8, 9, 10) over
two alkyl substituents (11, 12) and for a six or seven
membered ring (4, 8) compared to the four membered
ring (9). In addition the nonsubstituted cyclohexyl deriv-
ative 4 was 3-fold more potent than its analog with a
methyl group on the cyclohexyl ring (10).
Replacement of the phenyl group in position 6 by other
heterocycles showed that the unsubstituted 2-, 3-, or 4-
pyridyl derivatives (27–29) were slightly less potent than
the reference compound 23. In order to improve drug-
like characteristics, especially solubility, we further
explored the substitution of the aromatic ring by intro-
ducing ionizable functions. Introduction of a carboxy
group in para (30) or meta (31) position led to almost
equipotent compounds but with lower selectivity versus
the others tested PDEs. Similar results were obtained
when an amide group was introduced in para-position
as illustrated by compound 33. Interestingly, substitut-
ing the amide function in 33 with an alkylamine group
(34–37) resulted in compounds with good selectivity
and greater solubility at pH7.4 (30–70lg/mL in pH7.4
buffer solution12). It is worth noting that introduction
on the phenyl ring of functionalities with different
physicochemical properties (from carboxylic acid to ba-
sic amines) led only to little variation in PDE7 inhibitory
activity.
Further modifications were designed to study the influ-
ence of other substituents on the aromatic ring while
keeping the spirocyclohexyl group as R1–R2. As illus-
trated by compounds 13–16, the substitution of the 6-
or 7-position with a chloro or a methoxy group did
not lead to a significant increase in potency. However,
interestingly, the 6-phenyl substituted analog 17 gave
promising results with an IC50 of 0.98lM. Substitution
at C5 (see compound 18) was also favorable resulting in
a 7-fold increase in potency compared to the reference
compound 2. Except for 19, a similar tendency was ob-
served among the disubstituted derivatives synthesized
(20–25). Indeed, a synergistic effect was demonstrated
when combining a 5-chloro or 6-phenyl substituent with
the 8-chloro substituent, leading to the most potent
PDE7 inhibitors, respectively, compounds 21 and 23.
Further studies around the N-substitution of the amide
showed that the length of the linker could be extended
from 2 to 3 carbon atoms and that both meta- or
para-substitutions were tolerated as demonstrated by
Table 2. In vitro data for biphenyl-compounds 23 and 27–39
Compd
R
PDE7A1
PDE1
PDE3A3
PDE4D3
PDE5
IC50, lMa
IC50, lMb
IC50, lMa
IC50, lMa
IC50, lMc
23
27
28
29
30
31
33
34
35
36
37
38
39
32
–Phenyl
–2-Pyridyl
0.016
0.033
0.051
0.031
0.013
0.025
0.020
0.021
0.026
0.024
0.019
0.014
0.044
1.52
3.26
8.30
2.86
3.01
0.89
0.71
1.28
6.29
11.6
6.47
5.16
7.01
6.39
20.1
>101
45.1
14.8
11.2
21.3
16.7
0.28
42.2
>79.9
44.5
78.1
29.3
31.6
>92
1.42
1.8
69.8
68.4
–3-Pyridyl
–4-Pyridyl
1.55
1.01
0.47
0.74
0.69
1.63
1.59
1.50
1.46
1.70
1.31
15.7
19.3
9.47
8.50
–p-C6H4–CO2H
–m-C6H4–CO2H
–p-C6H4–CONH2
12.6
11.6
–p-C6H4–CONH–(CH2)2–NMe2
–m-C6H4–CONH–(CH2)2–NMe2
–p-C6H4–CONH–(CH2)3–NMe2
–m-C6H4–CONH–(CH2)3–NMe2
–p-C6H4–CO–N-Methylpiperazine
–m-C6H4–CO–N-Methylpiperazine
–o-C6H4–CO-N-Methylpiperazine
>67.3
>101
>50.7
>84.9
29.3
52.4
>101
a Measured against the human full length enzyme produced in baculovirus infected sf9 cells. Values are means of three experiments.
b Measured against the human full length enzyme partially purified from THP-1 cell pellets. Values are means of three experiments.

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compounds 34–37. Conformational restriction of the
basic side chain via incorporation into a piperazine
(compounds 38 and 39) maintained a similar activity
level however the solubility decreased (<5lg/mL in
pH7.4 buffer solution12), which most likely results from
a lower pKa. The point of attachment for the piperazine
carboxy side chain was also examined and a significative
reduction in potency was observed as the point of
attachment was moved from para or meta to ortho (see
compounds 38, 39, and 32).
The most active, selective, and soluble compounds 34–
37 were considered for further in vitro and in vivo
evaluation.
4. Conclusion
The spiroquinazolinone derivatives represent a new class
of PDE7 inhibitors. Preliminary SAR around this series
led to the discovery of a promising biphenyl subseries. In
the course of this study, introduction of ionizable func-
tions onto the aromatic ring, aimed at improving solu-
bility in this series, resulted in the identification of
soluble and highly potent PDE7 inhibitors. The best
compounds tested 34–37 also showed good selectivity
versus PDE1, 3A, 4D, and 5.
Acknowledgements
The authors are grateful to PGRD Fresnes Analytical
Support for their help in compound characterization.
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