The synthesis and fluorescent properties of analogues of the zinc(II) specific fluorophore zinquin ester

The synthesis and fluorescent properties in the absence and presence of zin c(II) of a range of a-substituted derivatives of N-(6-methoxy-2-methyl-8-qu inolyl)-4-methylbenzenesulfonamide are described. These analogues formed co mplexes with zinc(II) as indicated by a bathochromic shift in their UV/vis spectra. Analogues with isobutenyl and isobutyl side chains at the 2-positi on formed fluorescent complexes whose fluorescence was stronger than that o f the 2-methyl-containing parent. These derivatives were converted, via con version to the phenol with boron tribromide and reaction with ethyl bromoac etate, to systems with ester-containing side chains analogous to zinquin es ter, a specific cellular fluorophore for zinc(ll). All of these ester deriv atives formed complexes with zinc(II) resulting in a bathochomic shift in t heir UV/vis spectra. Compounds with isobutyl, isobutenyl, and styryl. side chains exhibited increased fluorescence compared to that of zinquin ester i n the presence of zinc(II). The compound with the 2-isobutyl side chain was more selective in its fluorescence for zinc(II) over cadmium(II) compared to zinquin ester.