Unprecedented Alkaloid Skeleton From the Mediterranean Sponge Reniera-sarai - X-ray Structure of An Acetate Derivative of Sarain-A

The Mediterranean sponge Reniera sarai is a rich source of new alkaloids. Until now the study has been limited to the less polar compounds. In this paper we report the first studies on the more polar UV absorbing alkaloid fraction, which resulted a mixture of three homologs, sarains A-C. A resolutive X-ray study on an acetate derivative of sarain-A has descovered an unprecedented alkaloid skeleton exhibiting a central cage structure, characterized by a charged pseudobase moiety, in the middle of two cyclic alkyl chains.