SL 0101-1 (SL0101), a kaempferol glycoside, isolated from the tropical plant F. refracta, is a cell-permeable, selective, reversible, ATP-competitive p90 Ribosomal S6 Kinase (RSK) inhibitor, with an IC50 of 89 nM[1]. SL 0101-1 (SL0101) is a selective RSK1/2 inhibitor, with a Ki of 1 μM[2].