Straightforward synthesis and biological evaluation as topoisomerase I inhibitors and antiproliferative agents of hybrid Chromeno[4,3-b][1,5]Naphthyridines and Chromeno[4,3-b][1,5]Naphthyridin-6-ones.

This work describes the synthesis of hybrid tetrahydro-1,5-naphthyridine and 1,5-naphthyridine derivatives fused with heterocycles such as chromenes and chromen-2-ones or coumarins, which were synthesized in good to high general yields. The synthetic route involves an intramolecular [4 + 2]-cycloaddition reaction of functionalized aldimines obtained by the condensation of 3-aminopyridine and aldehydes containing a double or triple carbon-carbon bond in orto position and allows the selective generation of three stereogenic centers in a short, efficient and reliable synthesis. The subsequent dehydrogenation of the fused tetrahydrochromeno[4,3-b][1,5]naphthyridines and/or tetrahydrochromeno[4,3-b][1,5]naphthyridin-6-ones leads to the formation of the corresponding tetracyclic chromeno[4,3-b][1,5]naphthyridine derivatives and/or chromeno[4,3-b][1,5]naphthyridin-6-ones in quantitative yields. Some of the prepared products showed activity as inhibitors of Topoisomerase I (TopI). Additionally, the cytotoxic behavior of these compounds has been studied in cell lines derived from human lung adenocarcinoma (A549) and human ovarian carcinoma (SKOV03), and on non-cancerous lung fibroblasts cell line (MRC5) where, on the last ones, the absence of cytotoxicity was observed. 7-Phenyl-6H-6a,7,12,12a-tetrahydrochromeno[4,3-b][1,5]naphthyridine 5a showed excellent cytotoxic activity with a IC value of 1.03 ± 0.30 μM against the A549 cell line and a IC value of 1.75 ± 0.20 μM against the SKOV03 cell line. The obtained results point to these compounds as good antiproliferative candidates.