Application of spin labeling to drug assays. I. Synthesis of 2,2,6,6‐tetramethylpiperidin‐4‐one‐1‐oxyl‐¹⁵N‐d₁₆

Spin labeled drugs can be utilized for immunoassays and determining the fraction of free drug in serum. To improve the sensitivity we have synthesized triacetonamine‐¹⁵N‐d₁₇ by cyclization of phorone‐d₁₄ with ¹⁵ND₃. Phorone‐d₁₄ was obtained by condensation of acetone‐d₆. Triacetonamine‐¹⁵N‐d₁₇ gave Tempone‐¹⁵N‐d₁₆, a nitroxide with just two absorption peaks on the ESR spectrum, whereas Tempone gives 3 peaks. The contribution to line width of methylene and methy1 hydrogens of Tempone is evaluated by appropriate substitution of protium with deuterium.