4,4'-{Methylenebis[(diphenylphosphoranylylidene)nitrilo]}bis(1,3,5,7-tetramethyl-2,6-dithia-1,3,5,7-tetraaza-4lambda~5~-phosphaspiro[3.3]heptane) 2,2,2',2',6,6,6',6'-octaoxide AIDS-013396 AIDS013396 NSC645930