Optimization and immunological characterization of a photochemically coupled lysergic acid diethylamide (LSD) immunogen

A photoreactive heterobifunctional linker was used to prepare an immunogen in which lysergic acid diethylamide was indirectly coupled to keyhole limpet hemocyanin at multiple sites on the drug. It was possible to attach approximately 35 drug molecules to each protein using approximately equal amounts of both species during the reaction. The presence of buffer components or water severely compromised reaction efficiency, as estimated from the molar substitution ratio. Factors such as excess linker, pH, irradiation of dry matrix in the absence of buffer, and the drug/protein ratio used during photolysis were shown to have pronounced effects on reaction efficiency. Structural insights regarding immunogen coupling were obtained by determining the specificities of antibodies which were raised against the immunogen. Cross-reactivity data indicated that haptenation of protein likely occurred at positions N1 and N6 of lysergic acid diethylamide, which is plausible given the electrophilicity of the photogenerated aryl nitrene.