3.4.9. Rhabdastins

The first members of this family, Rhabdastins A-G, were first isolated in 2010 by Iwagawa from the sponge *Rhabdastrella globostellata* [88]. They belong to the group ofisomalabaricane triterpenes. In 2021, the tetrahydrofuran-containing rhabdastins H (**94**) and I (**95**) (Figure 23) were isolated from the sponge *Rhabdastrella* sp. [89]. They are the first marine isomalabaricanes that present a tetrahydrofuran unit in their structure. Both compounds show antiproliferative effect against K562 (IC50 11.7 and 9.8 μM, respectively) and Molt4 (IC50 16.5 and 11.0 μM) leukemic cells.

**Figure 23.** Structure of rhabdastins H (**94**) and I (**95**).
