Antimicrobial Benzyltetrahydroisoquinoline-Derived Alkaloids from the Leaves of <i>Doryphora aromatica</i>.
Liu M, Han J, Feng Y, Guymer G, Forster PI, Quinn RJ.
Four new alkaloids, (<i>R</i>)-nomimantharine trifluoroacetate (<b>2</b>), 12-demethylphaeantharine trifluoroacetate (<b>3</b>), nominanthranal trifluoroacetate (<b>4</b>), and the enolic form of 1-hydroxy-6,7-dimethoxy-2-methylisoquinoline trifluoroacetate (<b>5</b>), together with the known dimeric alkaloid phaeantharine trifluoroacetate (<b>1</b>), have been isolated from the extract of the leaves of the rainforest tree <i>Doryphora aromatica</i> (Monimiaceae). The structures of these compounds were elucidated by HRMS and 1D and 2D NMR data. (<i>R</i>)-Nomimantharine trifluoroacetate (<b>2</b>) contains an ether linkage connecting a benzylisoquinoline unit with a tetrahydroisoquinoline, a novel class of dimeric alkaloid. The absolute configuration of (<i>R</i>)-nomimantharine trifluoroacetate (<b>2</b>) was established via electronic circular dichroism data. The compounds isolated were subjected to in vitro antimicrobial assays against a panel of pathogenic microorganisms, including <i>Mycobacterium smegmatis</i>, <i>M. tuberculosis</i>, <i>Escherichia coli</i>, <i>Staphylococcus aureus</i> (SA), and five clinical isolates of oxacillin/methicillin-resistant <i>S. aureus</i> (MRSA). Phaeantharine trifluoroacetate (<b>1</b>) and (<i>R</i>)-nomimantharine trifluoroacetate (<b>2</b>) showed moderate inhibitory activities against <i>Mycobacteria</i> and MRSA strains.