Synthesis and characterization of 4-ethoxymethylene-2-[1]-naphthyl-5(4H)-oxazolone and its fluorescent amino acid derivatives

4-Ethoxymethylene-2- [1]-naphthyl-5 (4H)-oxazolone Ib was synthesized from 1-naphthoyl-glycine and triethyl orthoformate as a fluorescent analogue of the hapten 4-ethoxymethylene-2-phenyl-5(4H)-oxazolone A simple and general method has been devised to prepare conjugates of type 6 between Ib and amin es and amino acids by direct reaction. Compounds 6 are stable in solid form and in aqueous solution at 20 degreesC, but are a mixture of two isomers. H-1- and C-13-NMR experiments on model compounds have identified the more s table isomer. Comparative analysis of fluorescence properties of Ib and of amino acid derivatives has identified the spectral properties of two chromo phores. An intense and ptr-sensitive emission band centered at lambda =460 nm (lambda (ex)=360 nm) in aqueous solution has been discovered. This featu re might be useful for monitoring cellular compartments of different pH. (C ) 2001 Elsevier Science Ltd. All rights reserved.