HIV-protease assay kits (Bachem Feinchemikalien AG, Bubendorf,
Switzerland) were used. Twenty five microliter of HIV-protease
assay buffer (50 mM NaOAc, pH 4.9) containing 2.5 lg of the
substrate [His-Lys-Ala-Arg-Val-Leu-(pNO2-Phe)-Glu-Ala-Nle-Ser-
NH2] was mixed with 2 ll of a compound solution (using DMSO
as a solvent), then 8 ll of recHIV-protease (0.01 mg/ml) was added.
The reaction mixture was incubated for 30 min at 37 C and then
terminated by addition of 3.0 ll of 10% trifluoroacetic acid (TFA).