Synthesis and Antibactericidal Activities of Amines and Imines Containing (Aza, Thio)Xanthene Rings

Xanthene Derivatives Targeting Bacterial Efflux Pumps, Quorum-Sensing, and Biofilm Formation

“…1 H and 13 C nuclear magnetic resonance (NMR) spectra were taken in deuterated chloroform or dimethyl sulfoxide (DMSO), purchased from Deutero GmbH (Kastellaun, Germany), on a Bruker Avance 300 instrument (300.13 or 500. 16 MHz for 1 H and 75.47 or 125.77 MHz for 13 C, Bruker Biosciences Corporation, Billerica, MA, USA) or Bruker AVANCE III (400.14 MHz for 1 H and 100.62 MHz for 13 C), all at room temperature. Tetramethylsilane (TMS) was used as an internal reference, in relation to which all the chemical shifts are expressed.…”

“…Xanthenes (1, Figure 1) are a class of oxygen-incorporating tricyclic compounds, explored for different biological applications, where the presence of different substituents in position 9 impacts their chemical properties and bioactivity [11]. The synthesis of xanthenes through the modification of the carbonyl in position 9 of xanthones represents the most straightforward procedure to easily obtain a variety of xanthenes [11] Several studies have shown their potential as antibacterial agents, where xanthenes revealed moderate to good inhibition in Gram-positive and Gram-negative bacteria [12][13][14][15][16][17]. Additionally, the tricyclic nucleus of xanthenes possesses electronic and geometrical similarities to phenothiazines, thioxanthones and thioxanthenes, classes of compounds known for their activity in inhibiting biological processes responsible for antimicrobial resistance, namely QS [18,19] and efflux pump activity [19][20][21][22][23].…”