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S. T. Murphy et al. / Bioorg. Med. Chem. Lett. 17 (2007) 2150–2155
Table 2. Rat PK on selected nitrile-containing fluoroquinolonesa
Compound
AUC, iv (lg h/mL)
CL, iv (mL/min/kg)
Vd, iv (L/kg)
t1/2, iv (h)
Cmax, po (lg/mL)
%F, po
19
22
27
34
37
3.5
4.4
5.2
2.5
6.5
24
19
16
33
13
2.5
1.8
0.5
2.5
1.0
2.7
2.4
1.8
1.3
1.4
1.2
1.4
1.4
0.3
2.6
70
53
22
18
92
a Rats were dosed at 5 mg/kg orally (po) or 1 mg/kg intravenously (iv). All values are an average of at least n = 3.
in the C-substituted series (pKa = 9.5 vs 6.7 for 21 vs 22),
in the N-substituted pyrrolidine series (pKa = 9.9 vs 6.9
for 18 vs 19), and in the N-substituted azetidine series
(pKa = 8.6 vs 6.5 for 34 vs 35).
By modifying the fluoroquinolone core and the side
chain nitrogen substituents, we were able to attenuate
the genotoxicity and discover several compounds which
had both potency and good safety profiles in our in vitro
assays. Further work on the activity of these compounds
in an expanded panel of organisms and in vivo efficacy
models will be reported in due course.
Clonogenicity has been shown to be a useful predictor of
human genotoxicity in the fluoroquinolone class.21 Suto
et al.8 have shown that the clonogenicity in the fluoroqu-
inolone class is affected by the nature of the core as well
as the substituent R0 on the amine (see Table 1). We
sought to control the clonogenicity using similar chang-
es to obtain a compound with an IC50 of >100 lg/mL.
Acknowledgments
We thank Ziqiang Wang for the preparative chiral
HPLC separation of the nitrile side chains.
Compared to the R8 = OMe core, the R8 = Me core ana-
logs were more genotoxic in the clonogenicity assay (19
vs 29), as was observed in the previous study.8 In
contrast, changing to the R6 = H (des-F) core or the
R8–R1 = (S)-OCH2CHMe (Levofloxacin) core generally
improved the clonogenicity (e.g., 20 vs 27 and 32), and
in many cases the target criterion of >100 lg/mL was
satisfied.
References and notes
1. Talbot, G. H.; Bradley, J.; Edwards, J. E., Jr.; Gilbert, D.;
Scheld, M.; Bartlett, J. G. Clin. Infect. Dis. 2006, 42, 657.
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7. Domagala, J. M.; Hagen, S. E.; Joannides, T.; Keily, J. S.;
Laborde, E.; Schroeder, M. C.; Seanie, J. A.; Shapiro, M.
A.; Suto, M. J.; Vanderroest, S. J. Med. Chem. 1993, 36,
871.
8. Suto, M. J.; Domagala, J. M.; Roland, G. E.; Mailloux,
G. B.; Cohen, M. A. J. Med. Chem. 1992, 35, 4745.
9. Jones, M. E.; Critchley, I. A.; Karlowsky, J. A.; Blosser-
Middleton, R. S.; Schmitz, F.-J.; Thornsberry, C.; Sahm,
D. F. Antimicrob. Agents Chemother. 2002, 46, 1651.
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Chem. Pharm. Bull. 1985, 33, 2762.
Substitution on the nitrogen of the side chain also brought
about improvements in the clonogenicity. N-Methylation
showed a dramatic increase in clonogenicity IC50 from
24 lg/mL up to 139 lg/ml in 20 vs 22, respectively,
although the antibacterial activity did show a modest de-
crease. In the azetidine series, the N-substitution of the
ethylcyano group showed a pronounced increase in clo-
nogenicity IC50 (e.g., 34 vs 35 and 36 vs 37), although little
or no effect was seen by the same substitution in the pyr-
rolidine series (e.g., 23 vs 24 and 28 vs 29).
Selected compounds which met the criteria for antibac-
terial activity, dofetilide, and/or clonogenicity were test-
ed in vivo in rats to assess their pharmacokinetic
performance, and the results are shown in Table 2.
The nitrile-containing fluoroquinolones showed good
overall pharmacokinetics. In the C-substituted series,
the pyrrolidine analog 22 (designated PF-00951966)
showed both good bioavailability and AUC. The azeti-
dine analog 37 (designated PF-02298732) showed excel-
lent bioavailability and a good AUC. On the other
hand, the R6 des-fluoro analog (27) showed a sub-opti-
mal volume of distribution and low bioavailability. The
non-nitrile-containing fluoroquinolone, 34, shown for
comparison, showed higher clearance and lower bio-
availability compared to the other compounds tested.
11. S. pneumo.R MICs for stereoisomers of 22: diastereomer A
(faster eluting) = 8 lg/mL, diastereomer B (slower elut-
ing) = 1 lg/mL, and enantiomer B1 (faster eluting) = 8 lg/
mL, enantiomer B2 (slower eluting, desired) = 0.5 lg/mL.
Diastereomers were separated on silica gel eluted with
hexanes/ethyl acetate. Enantiomers were separated by
chiral HPLC on a ChiralPak AD column eluted with
methanol/ethanol.
12. Baldwin, J. E.; Adlington, R. M.; Gollins, D. W.
Tetrahedron 1995, 51, 5169.
13. Frigola, J.; Pares, J.; Corbera, J.; Vano, D.; Merce, R.;
Torrens, A.; Mas, J.; Valenti, E. J. Med. Chem. 1993, 36,
801.
14. Denmark, S. E.; Forbes, D. C.; Hays, D. S.; DePue, J. S.;
Wilde, R. G. J. Org. Chem. 1995, 60, 1391.
15. Unfortunately, these compounds are not very active
against the Enterobacteriaceae. Other than the fastidious
Gram-negatives (H. influenzae and M. catarrhalis) these
compounds have no real efficacy against Gram-negative
In summary, we have synthesized a set of nitrile-con-
taining fluoroquinolones with activity against resistant
strains of S. aureus and S. pneuomoniae and low dis-
placement of dofetilide in the dofetilide binding assay.