Synthesis of a radioiodine‐labeled 2,4‐dinitrophenyl‐hapten and its use for binding assays

A monovalent DNP‐hapten, α, N‐(4‐hydroxyphenacetyl)‐ϵ, N‐DNP‐L‐lysine (6), was synthesized. The 4‐hydroxyphenacetyl residue of this compound can be radioiodinated yielding a labeled hapten of high specific activity, which proves to be a useful reagent for assaying anti‐DNP sera by measuring their capacity to bind the hapten in a salt precipitation test based on the Farr assay. This method appears to be more generally applicable to other haptenic groups which can be bound to the ϵ‐amino group of lysine.