Sofosbuvir Impurity 33

Isopropyl ((S) - (((2R,3R,4R,5R) -5- (2,4-dioxo-3,4-dihydropyrimidin-1 (2H) -yl) -4-fluoro-2- ((((S) - (((S) -1-isopropoxy-1-oxopropan-2-yl) amino) (phenoxy) phosphoryl) oxy) methyl) -4-methyltetrahydrofuran-3-yl) oxy) (phenoxy) phosphoryl) -L-alaninate