2242 Journal of Medicinal Chemistry, 2005, Vol. 48, No. 6
Brief Articles
Figure 4. Development of potent low molecular weight HIV-1 PR dimerization inhibitors.
were also well supported; the nature of the alkyl side
chain geometry at position 3 was found to be significant
with the efficacy trend sec-butyl (Ile) > sec-propyl (Val)
> isobutyl (Leu). Modifications at position 3 with
aromatic side chains with an electron-withdrawing
group (36-38) demonstrated significant increases in
potency (Table 1), whereas electron-donating groups on
the aromatic ring decreased potency.
Acknowledgment. This work was supported by the
National Institutes of Health (Grant GM52379).
Supporting Information Available: Synthesis of key
intermediates and their NMR values, inhibition constants with
error bars, amino acid analysis results, reverse-phase HPLC
conditions, and mass spectrometry results. This material is
Although only a small number of modifications were
attempted in this study at position 4 of 6 because of
synthetic difficulties, in general no large changes were
observed in potency when extending the aromatic
moiety. Similarly, the use of more bulky cycloalkyl side
chains also displayed little difference in potency. The
one exception, however, was the Phe4Tyr mutation that
resulted in significant loss of inhibitory activity (15%
inhibition at 1 µM).
References
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Conclusions
In conclusion, this study demonstrated that minor
modifications in HIV-1 PR dimerization inhibitors im-
proved inhibitory activity significantly. A number of
agents demonstrated better inhibitory efficacy than the
full length, cross-linked interfacial peptides (1) with
about the half of the molecular weight (Figure 4).
Previous studies in our group demonstrated that mul-
tiple modifications based on the best individual changes
in dimerization inhibitors led to a significant increase
in potency against HIV-1 PR.11 It will be worthwhile to
design an extensive library containing multiple muta-
tions for the development of low molecular weight,
extremely potent HIV-1 protease dimerization inhibitors
based on this series of compounds.
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Experimental Section
Enzyme Assay. For standard inhibition determination, 50
µL of HIV-1 protease (50 nM in aqueous buffer A; 20 mM
phosphate (KH2PO4), 10% glycerol, 0.1% CHAPS, 1 mM EDTA,
1 mM DTT, pH 5.52 (adjusted using Na2PO4))10 was incubated
with 10 µL of the inhibitor solution in DMSO for 1 h. The
solution was added to 40 µL of the substrate13 solution (buffer
A with 10% DMSO) to yield a final substrate concentration of
60 µM. The final concentration of DMSO was kept constant
at 14%. The change in fluorescence at 430 nm (λex ) 360 nm)
was monitored at 30 °C. For the determination of Ki values,
all parameters were identical with the following exceptions:
enzyme concentrations ranged from 5 to 160 nM and the final
substrate concentration was kept constant at 25 µM. All
experiments were performed in triplicate.
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