Abstract Short and efficient total syntheses of (4S,5S,11R)- and (4S,5S,11S)-iso-cladospolide B were achieved in five steps each without using any protecting groups. The key steps were an alkyne-zipper reaction, a Suzuki cross coupling, and a Sharpless asymmetric dihydroxylation. The biological activities of both natural products toward various cancer cell lines were tested for the first time. Short and