Antibacterial Prenylated Acylphloroglucinols from Psorothamnus fremontii.

Psorothatins A–C (1–3), three antibacterial prenylated acylphloroglucinol derivatives, were isolated from the native American plant Psorothamnus fremontii. 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 (3) was the most active compound against methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus faecium, with IC50 values in the range 1.4–8.8 μg/mL. The first total synthesis of 3 described herein permits future access to structural analogues with potentially improved antibacterial activities.