The phosphinic acid isosteres of di-, tetra- and hexapeptides containing a hydrophobic amino acid side chains at the P1-P'1 positions are powerful inhibitors of Human Immunodeficiency Virus protease. Ki's ranged from 0.4 nM to 26 microM at pH 6.5 and were lower at pH 4.5. The compounds showed no activity against trypsin, weak activity against renin at pH 6.5, moderate activity against pepsin at pH 2.0 (Ki values in the microM range) and substantial activity against cathepsin D at pH 3.5 (Ki values from 9 to 300 nM).
