Proteasome selectivity towards Michael acceptor containing oligopeptide-based inhibitors.

The synthesis and biological evaluation of ten Michael acceptors containing potential proteasome inhibitors are described. Cellular targets of azide containing inhibitors and were assessed in HEK293T and RAW264.7 cells by a two step labeling strategy, followed by biotin-pulldown, affinity purification, on-bead tryptic digestion and LC-MS(2) identification. This strategy appears to be an attractive alternative to gel-based competition assays.