A practical approach to asymmetric synthesis of dolastatin 10.

Dolastatin 10, an antineoplastic agent for cancer chemotherapy, is a linear peptide possessing N,N-dimethyl Val-OH, l-valine, (3R,4S,5S)-dolaisoleucine, (2R,3R,4S)-dolaproine and (S)-dolaphenine. Our efficient synthesis includes the following three key features: (1) SmI-induced cross-coupling was employed to couple aldehyde 11 with (S)-N-tert-butanesulfinyl imine 12 to generate the required stereocenters of Dap (7); (2) asymmetric addition of chiral N-sulfinyl imine 10 provided a straightforward approach to the synthesis of the protected Doe ((S,S)-8); (3) a practical method to the key subunit Val-Dil (24a) has been established as an alternative synthetic route for the synthesis of this challenging chemical structure.