Catalyzes the C23-alpha-hydroxylation step in brassinosteroid biosynthesis (By similarity). Converts 6-deoxocathasterone (6-deoxoCT) to 6-deoxoteasterone (6-deoxoTE) in the late C6-oxidation pathway and cathasterone (CT) to teasterone (TE) in the early C6-oxidation pathway of brassinolide (BL) biosynthesis (By similarity). Plant hormone biosynthesis; brassinosteroid biosynthesis. Belongs to the cytochrome P450 family.