Antineoplastic agents. 278. Isolation and Structure of Axinastatins 2 and 3 from a Western Caroline Island Marine Sponge

The Republic of Palau marine sponge Axinella sp. was found to be an exceptionally productive source of cell growth inhibitory substances. The strongly antineoplastic polyether macrocyclic lactones halichondrin B (1) and homohalichondrin B (2) were isolated in 1.2 × 10⁻⁶% and 5.4 × 10⁻⁷% yields, respectively. In addition to axinastatin 1 (3), two new and cytostatic (GI₅₀ values of 0.35 to 0.0072 µg/mL against six human cancer cell lines) cycloheptapeptides designated axinastatins 2 (4) and 3 (5) were discovered in 1.4 × 10⁻⁶% and 1.25 × 10⁻⁶% yields. Structures were elucidated by high-resolution FABMS and tandem MS/MS techniques augmented by high-field (400 and 500 MHz) 2D-NMR spectral analyses. The absolute configurations were established by a combination of hydrolysis, derivatization, and chiral gas chromatographic methods.