Fluorescence Reagents for Labelling of Biomolecules. Part I. Synthesis and Spectral Characterization of 2- and 4-Substituted 9-Isothiocyanatoacridines

Abstract

9-Isothiocyanatoacridines VIII - XIV were prepared from the corresponding 9-chloroacridines I - VII. The IR, 1H NMR, 13C NMR and fluorescence spectra of the products are given. The 13C NMR chemical shifts of the C-9 ipso carbon atom exhibit a trend that is in accord with the Hammett constants of substituents bonded to the C-2 carbon. Effect of these substituents on the chemical shift of C-NCS was only small. The dependence of hydrolysis of isothiocyanates VIII - XIV on pH of the medium was studied. It was found that 9-isothiocyanatoacridines do not undergo hydrolysis at pH 7 - 10. The relative fluorescence intensities (F/F0) of compounds VIII - XIV at pH 7.4 have been determined in comparison with that of 9-aminoacridine. No direct dependence between the fluorescence intensity and the polar character of substituents has been found.