Catalyzes the conversion of protopine and allocryptopine to dihydrosanguinarine and dihydrochelerythrine, respectively, in the biosynthesis of isoquinoline alkaloid sanguinarine. O2 + protopine + reduced [NADPH--hemoprotein reductase] = 6-hydroxyprotopine + H(+) + H2O + oxidized [NADPH--hemoprotein reductase] Alkaloid biosynthesis. Belongs to the cytochrome P450 family.