A new class of potent proteasome inhibitors is described, of which the members contain an amino acid inspired sulfonyl fluoride as the electrophilic trap. In total 24 peptido sulfonyl fluoride inhibitors have been designed and synthesized, which were inspired by the backbone sequences of the proteasome inhibitors Bortezomib, epoxomicin and Cbz-Leu3-aldehyde. Nine of them were very potent proteasome inhibitors, of which the best one had an IC50 of 7 nM. A number of the peptido sulfonyl fluoride inhibitors was found to be highly selective for the β5 proteasome subunit.