The synthesis of Zinquin ester and Zinquin acid, zinc(II)-specific fluorescing agents for use in the study of biological zinc(II)

The syntheses of Zinquin ester [ethyl [2-methyl-8-(p-tolylsulfonylamino)-6-quinolyloxy]acetate] and the corresponding acid, both of which are zinc(II)-specific fluorophores, are described. 6-Methoxy-2-methyl-8-(p-tolylsulfonylamino)quinoline (2) can be demethylated, with boron tribromide, to form either the expected phenol or a mixture of the phenol and the corresponding 5-bromo derivative depending upon the reaction conditions. These compounds react with ethyl bromoacetate to give the corresponding esters, as well as the S-ethoxycarbonyl derivative formed by electrophilic substitution. Halogenation of the sulfonamide (2) occurs readily at the 5-position. The 5-iodo product undergoes a Heck coupling with ethyl acrylate. The crystal structures of ethyl [5-ethoxycarbonylmethyl-2-methyl-8-(p-tolylsulfonylamino)-6-quinolyloxy]acetate and [5-carboxymethyl-2-methyl-8-(p-tolylsulfonylamino)-6-quinolyloxy]acetic acid are described.