A photometric screening method for dimeric naphthylisoquinoline alkaloids and complete on-line structural elucidation of a dimer in crude plant extracts, by the LC-MS/LC-NMR/LC-CD triad

An efficient evaluation procedure for the chemical screening and on-line st ructural elucidation of dimeric naphthylisoquinoline alkaloids has been dev eloped. The method is based on the lead tetraacetate oxidation of the centr al binaphthalene core of the alkaloids, W spectra of the extracts after add ition of the oxidant show, in the presence of naphthylisoquinoline dimers, the appearance of a characteristic long-wavelength absorption indicative of dinaphthoquinones. The efficiency and relevance of the method has been dem onstrated in the discovery of a constitutionally and configurationally new dimeric naphthylisoquinoline alkaloid, named ancistrogriffithine A (4), fro m the previously uninvestigated Asian liana Ancistrocladus griffithii. Afte r verification of this screening result by LC-ESI-MS/MS, the constitution a nd the relative configuration of the compound were elucidated on line, by L C-NMR and LC-CD on the extract. Using an LC-NMR-WET-ROESY experiment, it wa s possible for the first time to determine the relative axial configuration of a natural biaryl compound on line, by observing long-range ROE interact ions. Finally, an oxidative degradation right on the extract delivered the absolute configuration of 4, without isolation of the alkaloid, Ancistrogri ffithine A is the as yet only dimeric naphthylisoquinoline from an Asian An cistrocladaceae plant.