Preparation and spectroscopic behavior of acetylderivatives of sulphonamides

Acetylderivatives of five sulpha drugs (N1-phenylsulphamilamide, sulphapyridine, sulphapyrimidine, sulphamerazine, sulphamethazine) and of three reference compounds, devoid of the para amino group, are synthetized. The trends of the U.V. spectra and of the symmetric stretching frequency of the SO2 group of the prepared compounds are described and discussed in a systematic way, by means of a simple conjugation model. Our data show that, on the basis of the values of the indices of electronic structure [upsilons(SO2), lambdap], the N1-acetylderivatives would appear to have a lower bacteriostatic activity than that of the non-acetylated compounds, which is in disagreement with the literature. The question therefore arises as to whether the N1-acetylderivatives are to be considered an exception to the structure-activity correlations previously put forward, or whether, owing to phenomena of hydrolysis, the degree of activity can no longer be attributed to the form characterized by the indices measured.