(S)-3-Hydroxy Midostaurin(IC50 range of 200-400 nM) against the ITD and D835Y mutants and low micromolar activity against the wild-type enzyme. The epimeric mixture of metabolites ((R)-3-Hydroxy Midostaurin + (S)-3-Hydroxy Midostaurin) substantially inhibits the proliferation of only the Tel-PDGFRβ with GI50 of 63 nM, KIT D816V (GI50=320 nM), and FLT3-ITD (GI50=650 nM) BaF3 cell lines, while the wild-type cells are relatively insensitive.