Discovery of a new family of heterocyclic amine linked plastoquinone analogs for antimicrobial evaluation.

A series of aminobenzoquinones, denoted as PQ analogs (PQ1-13), were synthesized by employing a green methodology approach using water as solvent developed by Tandon et al. Subsequently, in vitro antimicrobial potential of all PQ analogs was evaluated in a panel of seven bacterial strains (three gram positive and four gram negative bacteria) and three fungi. The antifungal profile of all PQ analogs indicated that four analogs (while PQ2, PQ9, and PQ10 were effective against Candida tropicalis, PQ11 is effective against Candida albicans) have potent antifungal activity. The results revealed that PQ9 showed similar antibacterial activity against Staphylococcus epidermidis compared clinically prevalent antibacterial drugs cefuroxime. PQ11 exhibited the highest antibacterial activity against S. epidermidis, which was about fourfold better than that of cefuroxime. Owing to their outstanding activities, PQ9 and PQ11 were chosen for a further investigation for biofilm and cytotoxicity evaluation. Based on the tests performed, there was a significant positive correlation between inhibition of the biofilm attachment and time. In addition, PQ9 and PQ11 showed cytotoxic effects at high concentrations on Balb/3T3, HaCaT, HUVEC, and NRK-52E cells (>24 and >18 μg/mL, respectively). Thus, two analogs (PQ9 and PQ11) were identified as the hits with the strong antibacterial efficiency against the S. epidermidis with low MIC values.