SYNTHESIS AND CHARACTERIZATION OF POLYSUBSTITUTED 5-QUINOLINECARBALDEHYDE DERIVATIVES

A new quinolinecarbaldehyde, 7-(carboxymethoxy)-6-hydroxy-3-sulfoquinoline-5-carbaldehyde (1), was synthesized from eugenol, a natural phenol, by four successive reaction steps. The condensation of 1 with various amino compounds afforded 12 Schiff-bases (2 – 13) and 3 hydrazones (14 – 16). The structures of the aldehyde, its Schiff-bases and the hydrazone derivatives were determined by analyzing their IR, 1D NMR, 2D NMR and MS spectra. 1H NMR and NOESY data show that the imine -CH=Ngroup in the reported Schiff-bases and hydrazones exists in E-configuration. The quinoline scaffold is an important class of heterocyclic compounds that possesses diverse chemotherapeutic activities. Several quinoline compounds isolated from natural resources or prepared synthetically are significant with respect to medicinal chemistry and biomedical use.1-5 Many quinolinecarbaldehyde derivatives exhibit high antituberculosis,6 antibacterial,7,8 and anticancer9,10 activities. The quinolinecarbaldehyde derivatives, in particular Schiff-base, are also reported as corrosion inhibitors,11,12 as organic ligands for synthesis of various interesting complexes,13-15 and as intermediates for synthesis of new heterocycles.16 Many hydrazones containing quinoline ring exhibit significant antitubercular properties17,18 and high antimalarial activity.19,20 Recently, we have reported on an efficient and simple method for the synthesis of 7-(carboxymethoxy)6-hydroxy-3-sulfoquinoline starting with eugenol,21 the main constituent of Ocimum sanctum L. oil (a cheap natural source for commercial extraction of eugenol22). This quinoline derivative could act as a key compound in order to prepare useful poly-functionalized quinolines. In this study, we present the synthesis and the structure of a new polysubstituted quinolinecarbaldehyde, 7-(carboxymethoxy)6-hydroxy3-sulfoquinoline-5-carbaldehyde, its Schiff-bases and hydrazones. HETEROCYCLES, Vol. 91, No. 9, 2015 1797