Synthesis of a bistetrahydrofuran C17-C32 fragment of the polyether antibiotic ionomycin.

A Zn-initiated triepoxide cascade cyclization reaction was employed for the synthesis of the bistetrahydrofuran core segment of the polyether ionophore antibiotic ionomycin.

Leptostatin: a synthetic hybrid of the cytotoxic polyketides callystatin A and leptomycin B.

Four stereoisomeric hybrids of the polyketide natural products callystatin A and leptomycin B have been prepared by parallel synthetic routes involving chiral allenylstannane methodology. Like their natural counterparts, these hybrids exhibit nanomolar levels of cytotoxicity toward HCT-116 human colon cancer cells.