Stereospecific total syntheses of proteasome inhibitors omuralide and lactacystin

Omuralide, a transformation product of the microbial metabolite lactacystin, was the first molecule discovered as a specific inhibitor of the proteasome and is unique in that it specifically inhibits the proteolytic activity of the 20S subunit of the proteasome without inhibiting any other protease activities of the cell. The total syntheses of omuralide and (+)-lactacystin are reported. An important key intermediate is synthesized at an early stage, which allows analogues of these two natural products to be made readily.