(S)-4-Methyl-N-((R)-1-(((S)-4-Methyl-1-((R)-2-Methyloxiran-2-yl)-1-oxopentan-2-yl)aMino)-1-oxo-3-phenylpropan-2-yl)-2-((R)-2-(2-MorpholinoacetaMido)-4-phenylbutanaMido)pentanaMide

(S)-4-Methyl-N-((R)-1-(((S)-4-methyl-1-((R)-2-methyloxiran-2-yl)-1-oxopentan-2-yl)amino)-1-oxo-3-phenylpropan-2-yl)-2-((R)-2-(2-morpholinoacetamido)-4-phenylbutanamido)pentanamide is an impurity of Carfilzomib (C183460), which is a second-generation proteasome inhibitor that is used as a treatment in relapsed and refractory multiple myeloma.