Synthesis and structures of regioisomeric hydnocarpin-type flavonolignans

Flavonolignans represent natural compounds whose biosynthesis presumes a ra dical coupling of a ring B catecholic flavonoid with a molecule of conifery l alcohol or an analogue. Many natural flavonolignans can exist as regioiso mers, depending on how the coupled coniferyl alcohol moiety orients to the flavonoid. These regioisomers are often difficult to separate and have virt ually identical NMR spectra. Structural assignments for some have changed w ith time or have been given without proof. We here report syntheses of both regioisomers of the flavonolignan hydnocarpin and one isomer of a plant is olate previously known as 5'-methoxyhydnocarpin. This isomer, here renamed 5'-methoxyhydnocarpin-D, was recently shown to be a potent inhibitor of a S taphylococcus aureus multidrug resistant efflux pump.