Synthesis, transformations and biological evaluation of 5‑chloro-8-hydroxyquinoline hybrids

Taking in consideration of previous studies in the field of biological relevance and the chelating properties of derivatives bearing the hydroxyquinoline skeleton, establishing cationic centre by direct amidation as well as preparation compound with amino acid character was proposed. In order to test anticancer activity of the synthesised compounds, the applying of preliminary biological screening systems was planned. This concept is demonstrated in the context of the synthesis and transformation of a bifunctional glycine-type precursor substituted with 5‑chloro-8-hydroxyquinoline to hybrids with amino acid and amine feature. Stabilization of the precursor and formed amide composed of N,N-dimethylethylamine via partially aromatic ortho-quinone methide intermediate was tested with different cyclic imines in [4 + 2] cycloaddition. In these [4 + 2] cycloaddition reactions, ¹H NMR analysis of the crude reaction mixture proved the formation of a single product in all cases. The relative configuration of the two newly formed stereogenic centres was determined by 2D-NMR technique. Compared to the precursor, all new derivatives exhibited less potent anticancer activity. Based on biological evaluations, out of the synthesized compounds the derivative with amino acid feature and some amidated derivatives showed toxic activity against the Colo 205 cell line.