Three acetylated flavonol glycosides from Forsteronia refracta that specifically inhibit p90 RSK

A survey of plant extracts for the presence of p90 ribosomal S6 kinase (RSK) inhibitors resulted in the isolation of three acetylated flavonol glycosides. Kaempferol 3-O-(2″,4″-O-diacetyl-α-l-rhamnopyranoside) (1), kaempferol 3-O-(3″,4″-O-diacetyl-α-l-rhamnopyranoside) (2), and kaempferol-3-O-(4″-O-acetyl-α-l-rhamnopyranoside) (3) were isolated from Forsteronia refracta as the first RSK inhibitors. Of these, compound 2 was found to be the best inhibitor with an IC50 value of 89 nM.

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