Nalmefene Impurity B Catalogue N211332 CAS 42971-33-5 M.W 285.34 M.F C17H19NO3 Specifications FAQs (4R,4aS,7aS,12bS)-7-methylene-1,2,3,4,5,6,7,7a-octahydro-4aH-4,12-methanobenzofuro[3,2-e]isoquinoline-4a,9-diol