Synthesis, characterization, and antimicrobial activity of ruthenium(II) polypyridyl complexes of flavones and aurones derived from dihydroflavonols rearrangement

Six heteroleptic ruthenium(II) polypyridyl complexes containing flavones (kaempferol and 4′,7-dimethoxykaempferol), and dihydroauronols derived from 4′,7-di-O-methylaronzadendrine and 2 R,3R-(+)-3-acetoxy-4′,5,7-trihydroxyflavanone as co-ligands were synthetized. The complexes were characterized by spectroscopic and spectrometric techniques which showed that the ruthenium center was octahedrally coordinated by two molecules of the ancillary ligand (1,10-phenanthroline or 2,2′-bipyridine) and one flavonoid unit. The flavones were linked to the metal center via the 4,5-chelating oxygen donor set while the dihydroauronol derivatives obtained during the thermal rearangement of the starting dihydroflavonols were linked through the 3,4 site. Luminescence studies showed a chelation enhanced fluorescence for the dihydroauronols complexes. Preliminary in vitro antimicrobial assessment revealed improved antimicrobial potential upon complexation with a MIC value of 10 µM against Micrococcus luteus ATCC 381, Fusarium graminearum DSM 21727, and Pseudomonas aeruginosa ATCC15442. Both complexes and ligands exhibited an overall weak activity against Botrytis cinerea DSM 0877, and Aneurinibacillus migulanus ATCC 9999. Molecular docking study of the synthetized complexes to detect their potential interaction with some microbial enzymes showed that the Ru(II) complex of 4′,7-dimethoxykaempferol bearing 2,2′-bipyridine co-ligand has the best binding score (−6.9 kcal/mol) against the receptor 6KQ9 of Micrococcus luteus ATCC 381. Furthermore, this is the first report of Ru(II)-based dihydroauronol complexes.