Poecillastrosides, Steroidal Saponins from the Mediterranean Deep-Sea Sponge Poecillastra compressa (Bowerbank, 1866)

Abstract

The first chemical investigation of the Mediterranean deep-sea sponge <i>Poecillastra compressa</i> (Bowerbank, 1866) led to the identification of seven new steroidal saponins named poecillastrosides A-G (<b>1</b>-<b>7</b>). All saponins feature an oxidized methyl at C-18 into a primary alcohol or a carboxylic acid. While poecillastrosides A-D (<b>1</b>-<b>4</b>) all contain an <i>exo</i> double bond at C-24 of the side-chain and two osidic residues connected at O-2', poecillastrosides E-G (<b>5</b>-<b>7</b>) are characterized by a cyclopropane on the side-chain and a connection at O-3' between both sugar units. The chemical structures were elucidated through extensive spectroscopic analysis (High-Resolution Mass Spectrometry (HRESIMS), 1D and 2D NMR) and the absolute configurations of the sugar residues were assigned after acidic hydrolysis and cysteine derivatization followed by LC-HRMS analyses. Poecillastrosides D and E, bearing a carboxylic acid at C-18, were shown to exhibit antifungal activity against <i>Aspergillus fumigatus</i>.