Abstract: &agr;-ketoamide compounds useful for treating disorders mediated by 20S proteasome in mammals having the following formula: wherein X2 is Ar or Ar—X3 wherein X3 is is —C═O, or —CH2CO—, and wherein Ar is phenyl, substituted phenyl, indole, substituted indoles, and any other heteroaryls; R1, and R2 are each individually selected from the side chains of the known natural &agr;-amino acids and unnatural amino acids, hydrogen, 1-10 carbon linear and branched alkyl, 1-10 carbon linear and branched substituted alkyl, aryl, substituted aryl, 1-10 carbon linear, branched substituted aryl, alkoxyaryl, 3-8 carbon cycloalkyl, heterocycle substituted heterocycle, heteroaryl and substituted heteroaryl; X1 is selected from hydroxide, monoalkylamino, dialkylamino, alkoxide, arylkoxide and wherein X4 is hydroxide, arylamino, monoalkylamino, dialkylamino, alkoxide, or arylalkoxide; and R3 is selected from the known natural &agr;-amino acids, unnatural amino acids