Synthesis of DNA-Intercalating 6H-Benzo[c]chromen-6-one Derivatives through a Strategic Combination of Garratt-Braverman and Minisci Acyloxylation Reactions

Fluoroquinolone antibiotics show genotoxic effect through DNA-binding and oxidative damage

The fluoroquinolones (FQs) are one the most successful class of synthetic antibiotics that primarily target the type II topoisomerases. With a pursuit to evaluate their genotoxicity, the present work established moderate to good DNA-damaging properties of some of the well-known and clinically prescribed fluoroquinolone antibiotics (2^nd and 3^rd generation). Hypochromic shift in UV-Vis absorption titration, fluorescence quenching in competitive ethidium bromide displacement assay (with calf-thymus DNA) and in-silico studies established DNA-intercalation with binding constants of the order 10⁴. A basic Structure Activity Relationship (SAR) has been derived from the docking results. MTT assay has been also done to evaluate the effect of these antibiotics on cell viability. The expression level of specific DNA-glycosylase enzymes responsible for repairing the oxidized DNA bases are quantified through western blot analysis. The studies revealed that fluoroquinolone antibiotics initiate the genotoxic effect at a concentration of above 50 μg/mL. Recruitment of APE1 and NEIL1 was found to be significantly increased to remove the oxidized nucleobases.

Oxidant-free, three-component synthesis of 7-amino-6H-benzo[c]chromen-6-ones under green conditions

An oxidant-free three-component synthesis of biologically significant 7-amino-6H-benzo[c]chromen-6-ones was established involving a Sc(OTf)3 catalyzed three-component reaction between primary amines, β-ketoesters and 2-hydroxychalcones under green conditions. In this strategy, both the B and C rings of 6H-benzo[c]chromen-6-ones were constructed simultaneously starting from acyclic precursors by generating four new bonds including two C-C, one C-N and one C-O in a single synthetic operation. The mechanism of this sequential cascade process involves the initial formation of a β-enaminone intermediate followed by Michael addition with 2-hydroxychalcone, intramolecular cyclization, dehydration, lactonization and aromatization steps. Unlike the related literature approaches, this reaction delivered the products without the addition of any external oxidants to achieve the key aromatization step.

Amine-Triggered Highly Facile Oxidative Benzannulation Reaction for the Synthesis of Anthranilates under Solvent-Free Calcium(II) Catalysis

An amine-triggered facile synthetic approach of anthranilates has been described through benzannulation of readily available chemicals under one-pot solvent-free conditions using Ca(OTf)₂ as the sustainable catalyst. In this regioselective approach, we described a reasonably longer cascade, which proceeds through β-enamino ester formation/Michael addition/intramolecular aldol reaction/elimination/aromatization/oxidative debenzylation/lactonization with a broad substrate scope and high yields. The isolation of intermediates authenticated the mechanism, and the synthetic utility of the products was also demonstrated.