*Article* **New Isomalabaricane-Derived Metabolites from a** *Stelletta* **sp. Marine Sponge**

**Sophia A. Kolesnikova 1,\*, Ekaterina G. Lyakhova 1, Anastasia B. Kozhushnaya 2, Anatoly I. Kalinovsky 1, Dmitrii V. Berdyshev 1, Roman S. Popov <sup>1</sup> and Valentin A. Stonik 1,2**


**Abstract:** In continuation of our studies on a Vietnamese collection of a *Stelletta* sp., sponge we have isolated two new isomalabaricane triterpenoids, stellettins Q and R (**1** and **2**), and four new isomalabaricane-derived *nor*-terpenoids, stellettins S-V **3**–**6**, along with previously known globostelletin N. Among them, compound **3** contains an acetylenic fragment, unprecedented in the isomalabaricane family and extremely rare in other marine sponge terpenoids. The structures and absolute configurations of all new compounds were established by extensive NMR, MS, and ECD analyses together with quantum-chemical modeling. Additionally, according to obtained new data we report the correction in stereochemistry of two asymmetric centers in the structures of two known isomalabaricanes, 15*R*,23*S* for globostelletin M and 15*S*,23*R* for globostelletin N.

**Keywords:** isomalabaricanes; *Stelletta* sp.; marine sponge; terpenoid; structure elucidation
