Fragment-Based Online OzESI-MS, NMR, and Computational DP4+/DFT Approaches to the Characterization of the Putative Biosynthetic Lipid Precursor of Atkamine from Alaskan <i>Latrunculia</i> Sponges

The extraction of <i>Latrunculia</i> sponges collected along the coast of the Aleutian Islands of Alaska yielded a lipid fraction, in which a natural long-chain monounsaturated aldehyde, (<i>Z</i>)-docos-15-enal (<b>1</b>), was isolated for the first time from this genus of sponge. Experimental, DP4+/DFT structure-probability calculations, and <i>ab initio</i> NMR chemical shift (CS) computational data comparing (<i>Z</i>)-docos-15-enal isolated from a natural sponge source with the previously reported synthetic material, confirmed the <i>cis</i> (<i>Z</i>) configuration of the double bond. Online ozonolysis LC-ESI-MS (OzESI) data validated the assignment of the C-15/C-16 olefin along the lipid chain. Aldehyde-based metabolites may serve as biosynthetic precursors for complex lipid alkaloids such as the atkamine pyrroloiminoquinone (PIQ).