Ionostatin

Ionostatin (Figure 21) [96], extracted from an actinomycite of *Streptomycetaceae* family, is the most recently discovered polyether ionophore [97–99]. Its structure and absolute stereochemistry were determined by NMR experiments, X-ray diffraction (calcium salt) and bioinformatic approach. The compound, a close analog to ionomycin (Figure 22) [100], contains 15 chiral centers and two tetrahydrofuran rings.

**Figure 21.** Structure of ionostatin.

**Figure 22.** Structure of ionomycin.

Polyether ionophores are chemotherapeutic agents for the treatment of cancer [101]. Initial bioactivity essays of ionostatin revealed inhibition (LD50 = 7.4 μg/mL) against two important cancer cell lines such as U87 glioblastama and SKOV3 ovarian carcinoma.
