Total Synthesis of Echinomycin and Its Analogues.

The first total synthesis of echinomycin (1) was accomplished by featuring the late-stage construction of the thioacetal moiety via Pummerer rearrangement and simultaneous cyclization, as well as two-directional elongation of the peptide chains to construct a C2-symmetrical bicyclic octadecadepsipeptide bridged with a sulfide linkage. This strategy can be applicable to a variety of echinomycin analogues.