2152
N. Chauret et al. / Bioorg. Med. Chem. Lett. 12 (2002) 2149–2152
[40-fold more potent on the human whole blood assay14
(222 nM for the O-cyclobutyl vs 8211 nM for the
O-cyclopentyl analogue)]. Therefore, the metabolism
profile of the promisinganalogues 5 and 6 in rat hepa-
tocytes was compared to 4. From the HPLC analysis of
the incubates (Fig. 1), 5 and 6 were found to be meta-
bolically more stable than 4 (10% metabolism as com-
pared to 30%). HPLC/MS analysis indicated that two
minor peaks in the incubates of 5 originated from the
dealkylation of the cyclobutyloxy moiety. The other
metabolites were related to the hydroxylation on the
cyclobutyl, the glucuronidation of the carbinol moiety
and oxidation of the pyridine, analogous to what was
observed for 4. Regarding compound 6, the O-glucu-
ronide of the carbinol and N-oxidation of the pyridine
were observed but no metabolites derived from the
catechol moiety were found. The N-oxide metabolite
was identified as L-791,943.14 Compounds 5, 6, and
L-791943 were tritiated at the pyridine moiety and
incubated in rat microsomes to address covalent binding
to proteins. As indicated in Table 1, the levels of cova-
lent bindingdue to metabolism were singificantly
reduced with 19 while there was none observed with 20
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3
or H L-791943. These results support the hypothesis
that metabolic stability of the alkoxy substituents of the
catechol prevents the formation of reactive quinone
intermediates responsible for covalent binding.
10. Dybing, E.; Nelson, S. D.; Mitchell, J. R.; Sasame, H. A.;
Gillette, J. R. Mol. Pharmacol. 1976, 12, 911.
In conclusion, formation of reactive metabolites that
can covalently bind to microsomal protein were identi-
fied with the p-hexafluorocarbinol analogue of CDP-
840. Metabolic liability of the alkoxy substituents
makes the catechol moiety susceptible for further oxi-
dation and thus potential source of reactive inter-
mediates. Stable catechol moieties were introduced and
these significantly reduced or eliminated the covalent
binding. In addition, these new analogues exhibited
excellent PDE4 potency and improved pharmaco-
kinetics.14 These findings had a significant impact on the
synthetic efforts as many PDE4 inhibitors synthesized in
our laboratory now bear the stable difluoromethoxy
moiety.
11. He, K.; Woolf, T. F.; Kindt, E. K.; Fielder, A. E.; Talaat,
R. E. Biochem. Pharmacol. 2001, 62, 191.
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356, 1587.
14. Guay, D.; Hamel, P.; Blouin, M.; Brideau, C.; ChangC.
C.; Chauret, N.; Ducharme Y; Frenette, R.; Friesen R. W.;
Huang, Z.; Girard, M.; Jones, T.; Laliberte, F.; Li, C.; Mas-
son, P.; MacAuliffe, M.; Piechuta, H.; Young, R.; Girard, Y.
Biooorg. Med. Chem. Lett. 2002, 12, 1457.
15. Alexander, R. P.; Warrellow, G. J.; Graham, J.; Head,
J. C.; Boyd, E. C.; Porter, J. R. WO Patent 9517386; Chem.
Abstr. 1995, 124, 29604.
16. Krause, W.; Kuehne, G. Xenobiotica 1993, 23, 1277.
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References and Notes
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