3540
M. E. Fraley et al. / Bioorg. Med. Chem. Lett. 12 (2002) 3537–3541
that had been shown to greatly enhance physical prop-
erties in a related benzimidazole class of KDR kinase
inhibitors. The chemistry in the 3-phenyl series involved
oxidation of the corresponding 4-pyridyl ring followed
by rearrangement of the resulting pyridine n-oxide
under standard conditions (Scheme 2). Selective alkyl-
ation of the 4-pyridinonyl nitrogen provided com-
pounds 5a and 5b in modest yield (Table 2).
Introduction of the 6-(4-pyridinonyl) group in the more
potent 3-(3-thienyl) series required an alternative synth-
esis due to the oxidatively sensitive 3-thiophene ring
(Scheme 3). Key steps in the synthesis of 5c included the
Suzuki cross-coupling reaction of 6-bromo-3-(3-thio-
phenyl)pyrazolo[1,5-a]pyrimidine19 with the 4-pinacol-
boronic ester of 2-methoxypyridine,20 hydrolysis of the
2-methoxypyridine intermediate,21 and the selective
N-alkylation of the penultimate pyridinone under the
optimized conditions shown.
In conclusion, we have identified a number of modifi-
cations to the pyrazolo[1,5-a]pyrimidine class of KDR
kinase inhibitors that have improved the physical prop-
erties of these compounds over those of the initial leads.
Modifications such as the addition of a basic side-chain
to the 6-aryl ring, introduction of 3-pyridyl groups, and
incorporation of a 4-pyridinonyl substituent at the
6-position of the nucleus afforded enhanced cellular
potency and more favorable pharmacokinetics in rats.
Acknowledgements
We thank Dr. Art Coddington, Dr. Chuck Ross, and
Dr. Harri Ramjit for mass spectral analyses, Matt
Zrada, Ken Anderson, and Patrice Ciecko for logP
determinations, and Dr. George Hartman and Elaine
Walker for editing and assistance in the preparation of
this manuscript.
Biochemical, cellular, and partition coefficient data are
summarized for compounds 5a–c in Table 2. A sig-
nificant increase in polarity and aqueous solubility was
observed with the incorporation of the 4-pyridinonyl
group within 5a (logP=2.4) as compared to the highly
lipophilic and relatively insoluble homologue 4e (logP
>4.0). Physical properties and potency were further
optimized in this series with addition of the 4-methyl-
piperazinyl and 3-thienyl appendages found in 5c.
References and Notes
1. Adamis, A. P.; Shima, D. T.; Yeo, K. T.; Yeo, T. K.;
Brown, L. F.; Berse, B.; D’Amore, P. A.; Folkman, J. Bio-
chem. Biophys. Res. Commun. 1993, 193, 631.
2. Giatromanolaki, A.; Sivridis, E.; Athanassou, N.; Zois, E.;
Thorpe, P. E.; Brekken, R. A.; Gatter, K. C.; Harris, A. L.;
Koukourakis, I. M.; Koukourakis, M. I. J. Path. 2001, 194,
101.
The KDR kinase selectivity profiles for compounds 4e–g
and 5c against a panel of kinases are expressed as bio-
chemical IC50 (nM) ratios to KDR in Table 3.22 In
general, these inhibitors showed modest selectivity for
KDR kinase versus the highly homologous kinases
PDGFRb, Flt-1, and Flt-4 and moderate to high selec-
tivity versus FGFR-1, FGFR-2, and SRC kinases.
Of note, the branched side-chain within 4f offered
enhancement in KDR selectivity versus the FGF recep-
tor kinases and SRC kinase.
3. Detmar, M. Dermatol. Sci. 2000, 24, S78.
4. (a) For reviews, see: Carmeliet, P.; Jain, R. K. Nature 2000,
407, 249. (b) Folkman, J. Nature Med. 1995, 1, 27.
5. (a) Hanahan, D.; Folkman, J. Cell 1996, 86, 353. (b)
Holmgen, L.; O’Reilly, M. S.; Folkman, J. Nature Med. 1995,
1, 149.
6. (a) Veikkola, T.; Karkkainen, M.; Claesson-Welsh, L.;
Alitalo, K. Cancer Res. 2000, 60, 203. (b) Thomas, K. A. J.
Biol. Chem. 1996, 271, 603.
7. Kim, K. J.; Li, B.; Winer, J.; Armanini, M.; Gillett, N.;
Phillips, H. S.; Ferrara, N. Nature 1993, 362, 841.
8. Witte, L.; Hicklin, D. J.; Zhu, Z.; Pytowski, B.; Kotanides,
H.; Rockwell, P.; Bohlen, P. Cancer Metastasis Rev. 1998, 17,
155.
9. (a) Fong, T. A. T.; Shawyer, L. K.; Sun, L.; Tang, C.;
App, H.; Powell, T. J.; Kim, Y. H.; Schreck, R.; Wang, X.;
Risau, W.; Ullrich, A.; Hirth, K. P.; McMahaon, G. Can-
cer Res. 1999, 59, 99. (b) Drevs, J.; Hofmann, I.; Hugen-
schmidt, H.; Wittig, C.; Madjar, H.; Muller, M.; Wood, J.;
Martiny-Baron, G.; Unger, C.; Marme, D. Cancer Res. 2000,
60, 4819.
The pharmacokinetic parameters of compounds 4e, 4g,
and 5c in rats are summarized in Table 4. The data
show reductions in clearance and volume of distribution
as well as improvements in bioavailability with the more
polar analogues 4g and 5c compared to the highly lipo-
philic, less soluble derivative 4e.
Table 3. KDR kinase selectivity (fold) of compounds 4e–g and 5c
Compound PDGFRb FLT-1 FLT-4 FGFR-1 FGFR-2 SRC
10. For a current review, see Bilodeau, M. T.; Fraley,
M. E.; Hartman, G. D. Expert Opin. Investig. Drugs
2002, 11, 737.
11. Fraley, M. E.; Hoffman, W. F.; Rubino, R. S.; Hungate,
R. W.; Tebben, A. J.; Rutledge, R. Z.; McFall, R. C.; Huckle,
W. R.; Kendall, R. L.; Coll, K. E.; Thomas, K. A. Bioorg.
Med. Chem. Lett. 2002, 12, 2767.
4e
4f
4g
5c
2.0
2.2
5.3
4.6
7.7
3.9
9.5
8.5
12.9
3.3
5.0
7.3
103
>1000
51
—
370
26
52
>1000
80
242
86
358
12. The KDR IC50 value, reported as the mean of at least two
determinations, represents biochemical inhibition of phos-
phorylation of a poly-Glu/Tyr (4:1) peptide substrate by iso-
lated KDR kinase (cloned and expressed as a GST-fusion
protein) in the presence of 2.5 mM ATP: see: Kendall, R. L.;
Rutledge, R. Z.; Mao, X.; Tebben, A. J.; Hungate, R. W.;
Thomas, K. A. J. Biol. Chem. 1999, 274, 6453.
Table 4. Rat pharmacokinetic parameters of 4e, 4g, and 5c23
Compound
CI (mL/min/kg)
t1/2 (h)
Vdss (L/kg)
%F
4e
4g
5c
80
23
28
5.1
3.3
3.4
16
6.0
7.9
18
42
56
13. Partition coefficients were determined by HPLC analysis
in octanol/water.