The boron containing TSAI of proteasomes need higher lipophilicity (clogP 0.81.3) to effectively bind in the active site of the proteasome. Bortezomib is a potent boronic acid inhibitor of the chymotryptic-like site of the 20S proteasome (Ki 0.62 nM) and establishes a slowly reversible (half-life B20 min) tetrahedral intermediate with the active site
N-terminal threonine residue.