Fluorescent properties of some butyrophenones

Abstract

A spectrofluorimetric investigation of therapeutically used butyrophenones (neuroleptic drugs) is described. These substances, under certain conditions, emit fluorescent light on exposure to ultraviolet radiation.

The first part deals with the fluorescence of the butyrophenones in solution; the qualitative and quantitative aspects of the phenomenon depend on the solvent. Benperidol, droperidol, azaperone and fluanisone exhibit a distinct signal, caused by the heterocyclic substitution of the 4-aminobutyric acid chain. Qualitative tests as well as quantitative determinations were carried out, the latter requiring preliminary removal of interfering substances that absorb ultraviolet radiation. Haloperidol, bromoperidol, trifluperidol and pipamperone exhibit a weak signal.

The influence of acidity and nature of the solvent on the fluorescence was examined and the optimum pH range and the appropriate wavelengths of excitation and emission were established for the determination of each species; limits of detection are reported. Adjuvants that absorb ultraviolet radiation within the range of excitation or emission spectra need to be extracted.

The action of strong acids on the fluorescence of trifluperidol and pipamperone is discussed. Azaperone fluoresces intensely in acidic medium; direct and sensitive determinations can be performed with a limit of detection of 10^–2µg ml^–1. The drug can be made visible on chromatographic plates by its fluorescence in acidic medium.