Enantioselective construction of the oxidized tryptophan fragment of proteasome inhibitors TMC-95A and TMC-95B

The oxidized tryptophan analogue 5, a proposed intermediate for a synthesis of the proteasome inhibitors TMC-95A and TMC-95B, is prepared using the condensation of oxindole 7 with the (R)-Garner aldehyde and stereoselective dihydroxylation of olefin 6 as key steps.