Methylenedioxy bridge-forming cytochrome P450 involved in the biosynthesis of isoquinoline alkaloids. Converts (S)-scoulerine into (S)-cheilanthifoline, a precursor of sanguinarine. Catalyzes an oxidative reaction that does not incorporate oxygen into the product. (S)-scoulerine + O2 + reduced [NADPH--hemoprotein reductase] = (S)-cheilanthifoline + H(+) + 2 H2O + oxidized [NADPH--hemoprotein reductase] kcat is 3.3 min(-1) for (S)-scoulerine. Optimum pH is 7.5. Optimum temperature is between 30-35 degrees Celsius. Expressed in roots and at lower levels in stems, leaves and plantlets. Belongs to the cytochrome P450 family.