New natural sulfoxides from a Mediterranean Aplidium sp : absolute configuration assignment through combination of spectroscopic and computational methods

Ascidians belonging to the genus Aplidium of the Polyclinidae family are renowned for the variability of their metabolic content. A great chemiodiversity is devised from non-nitrogenous metabolites, mainly prenyl quinones or hydroquinones, to a vast array of nitrogenous metabolites. Within a research project directed to the study of the chemistry of marine ascidians from the Mediterranean sea we have investigated an Aplidium sp. collected in the Bay of Naples. It revealed a very unusual metabolic content, since it was completely lacking in meroterpenes, whilst the major component of its methanol extract was shown to be a group of unique alkyl sulfoxides. The structures of the novel metabolites have been elucidated through extensive spectroscopic analysis and their stereochemical analysis has been carried out in a three stages-approach, relying on the combination of NMR spectroscopy, CD studies, and computational methods