Shishijimicins A−C, Novel Enediyne Antitumor Antibiotics from the Ascidian Didemnum proliferum

Three new compounds of the enediyne antibiotics, shishijimicins A−C (1−3), have been isolated from the ascidian Didemnum proliferum. They encompass a novel sugar component, which is a conjugation product of a hexose and a β-carboline, attached to the calicheamicinone aglycone. Their structures have been determined by interpretation of spectral data. Shishijimicins showed extremely potent cytotoxicity against HeLa cells with IC₅₀ values of 1.8−6.9 pM.