Letters
J ournal of Medicinal Chemistry, 2004, Vol. 47, No. 10 2413
used for compounds 2a -c. After amidoalkylation in
AcOH, the phthalimide moiety was removed with hy-
drazine. This deprotection unfortunately gave low yields
due to the instability of the diphenyl phosphonate group.
Aldehyde 3b can also be prepared through acid hydroly-
sis of the N-phthalimido-protected 4-aminobutyralde-
hyde diethylacetal.
The diphenyl phosphonate tripeptides 1a -g were
evaluated for their ability to inhibit various trypsin-like
serine proteases.15 The IC50 values were calculated for
uPA and four other trypsin-like serine proteases in-
volved in the blood coagulation cascade (tPA, thrombin,
plasmin, FXa). Potent and selective irreversible inhibi-
tors of uPA were discovered. Compounds 1b and 1f were
the most potent inhibitors for uPA with IC50 values
around 60 nM. The results are summarized in Table 1.
Amiloride was used as the standard uPA inhibitor.
Compound 1b containing the substratelike arginine
side chain showed poor selectivity toward thrombin.
Compound 1f with a guanylated benzyl side chain
showed a selectivity ratio (IC50 enzyme/IC50 uPA) of
more than 200 for all enzymes tested.
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After diluting the inhibited enzyme with substrate
solutions, no rise in activity of uPA was observed, and
it was concluded that these inhibitors were irreversible
inhibitors of uPA. The kapp values for uPA were calcu-
lated from the progress curves. Further optimization of
Z-D-Ser-Ala-amino-(4-guanylphenyl)ethanephospho-
nate diphenyl ester (1f) as an uPA inhibitor is in
progress.
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Ack n ow led gm en t. This work received support from
The Fund for Scientific Research-Flanders (Belgium)
(FWO). J . J oossens and P. Van der Veken are fellows
of the Institute of Promotion of Innovation in Science
and Technology of Flanders (IWT). The excellent techni-
cal assistance of W. Bollaert is greatly appreciated.
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Su p p or tin g In for m a tion Ava ila ble: Experimental, bio-
chemical, and analytical data. This material is available free
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