Total synthesis of syringolin A.

A convergent, efficient synthesis of syringolin A has been accomplished in 13 steps from commercially available materials, Garner's aldehyde and L-valine. The unnatural 3,4-dehydrolysine fragment was prepared using successive Johnson-Claisen/Curtius rearrangement reactions. The macrolactamization and late-stage introduction of the side chain will provide convenient access to analogues of this promising proteasome inhibitor.