utilizing this newmethod. The synthesis is based on the two-step transformation of the readily available flavonolignans from milk thistle (Silybum marianum), accessible by isolation from the commercial extract silymarin. The first step relies on the regioselective formylation of the C-3 hydroxy group of the dihydroflavonol-type precursor using the Vilsmeier–Haack reagent, followed by formic acid elimination
Synthesis and Structures of Regioisomeric Hydnocarpin-Type Flavonolignans
作者:Nathan R. Guz、Frank R. Stermitz
DOI:10.1021/np000166d
日期:2000.8.1
Flavonolignans represent natural compounds whose biosynthesis presumes a radical coupling of a ring B catecholic flavonoid with a molecule of coniferyl alcohol or an analogue. Many natural flavonolignans can exist as regioisomers, depending on how the coupled coniferyl alcohol moiety orients to the flavonoid. These regioisomers are often difficult to separate and have virtually identical NMR spectra. Structural assignments for some have changed with time or have been given without proof. We here report syntheses of both regioisomers of the flavonolignan hydnocarpin and one isomer of a plant isolate previously known as 5'-methoxyhydnocarpin. This isomer, here renamed 5'-methoxyhydnocarpin-D, was recently shown to be a potent inhibitor of a Staphylococcus aureus multidrug resistant efflux pump.
Unconventional application of the Mitsunobu reaction: Selective flavonolignan dehydration yielding hydnocarpins
Various Mitsunobu conditions were investigated for a series of flavonolignans (silybin A, silybin B, isosilybin A, and silychristin A) to achieve either selective esterification in position C-23 or dehydration in a one-pot reaction yielding the biologically important enantiomers of hydnocarpin D, hydnocarpin and isohydnocarpin, respectively. This represents the only one-pot semi-synthetic method to