(75)Selenonorcholesterol 19-Norcholest-5(10)-en-3-ol, 6-((methylseleno-(75)Se)methyl) (3beta,6beta) 6-Methyl-(75)selenomethyl-19-norcholest-5(10)-en-3beta-ol 63795-61-9 Scintadren selenonorcholesterol