A new Cycloamphilectene metabolite from the Vanuatu sponge Axinella sp.

A new diterpene, N-formyl-7-amino-11-cycloamphilectene was isolated from the apolar extract of the Vanuatu sponge Axinella sp. The structure was suggested through spectroscopic data and totally clarified by single crystal X-ray analysis, including the relative stereochemistry: 1S,3S,4R,7S,8R,13R. This diterpenoid presents a tetracyclic carbon skeleton characterized by an uncommon cis-junction along the C8 and C13 bond and a double bond between the 11,12-positions. The equatorial N-formyl substitution at C7 is strictly planar, with C21 trans to the C6 ring carbon and the carbonyl group eclipsed to the N-C bond. In the crystal, screw-related molecules are joined by means of hydrogen bonds involving the N-formyl groups. This class of substances with hydrocarbon skeletons cycloamphilectene type is usually found in sponges of the Halichondrida order and recently also in taxonomically different sponges. Many of these substances show significant biological activities, such as antimalarial, cytotoxic or antimicrobial, stricly correlated with type and stereochemistry of the functional groups.