A potent, reversible proteasome inhibitor with Ki of 21 nM for 20S proteasome and 35 nM for 26S proteasome. The inhibition of proteasome was through specific inhibition of chymotrypsin-like activity of the proteasome. Also shown to induce apoptosis in Rat-1 and PC12 cells via a p3-independent pathway. MW: 461.59. Purity ≥95% by HPLC