Antibacterial Prenylated Acylphloroglucinols from <i>Psorothamnus
fremontii</i>
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Abstract
Psorothatins A–C (<b>1</b>–<b>3</b>),
three antibacterial prenylated acylphloroglucinol derivatives, were
isolated from the native American plant <i>Psorothamnus fremontii</i>. They feature an unusual α,β-epoxyketone functionality
and a β-hydroxy-α,β-unsaturated ketone structural
moiety. The latter forms a pseudo-six-membered heterocyclic ring due
to strong intramolecular hydrogen bonding, as indicated by the long-range
proton–carbon correlations in the NMR experiments. Psorothatin
C (<b>3</b>) was the most active compound against methicillin-resistant <i>Staphylococcus aureus</i> and vancomycin-resistant <i>Enterococcus
faecium</i>, with IC<sub>50</sub> values in the range 1.4–8.8
μg/mL. The first total synthesis of <b>3</b> described
herein permits future access to structural analogues with potentially
improved antibacterial activities