Design, synthesis of some novel coumarins and their nanoformulations into lipid-chitosan nanocapsule as unique antimicrobial agents

Developing and creating novel antibiotics is one of the most important targets in treating infectious diseases. Novel coumarins were synthesized and characterized using different spectroscopic techniques such as Fourier Transform Infrared (FTIR), Nuclear magnetic resonance¹H and ¹³C and mass spectroscopy (MS). All of the synthesized compounds have been tested for activity and sensitivity against the microbial strains of B. subtilis, S. aureus, E. coli, P. aeruginosa, S. typhi, and C. albicans. All compounds showed substantial results against the tested microbes except S. typhi, which was not affected in any way by these coumarins. Exceptional results were shown by compounds 4, 6d, and 8b, which made them the best candidates for loading to the vicinity of nanostructure lipid carrier and coated by chitosan nanocapsule (NLC-Cs). Transmission electron microscope (TEM) confirmed spherical morphology with particles size less than 500 nm. Also, dynamic light scattering (DLS) were utilized to measure the average particle size (between 100 and 200 nm) and the stability assessed by zeta potential were found to be more positive confirming the chitosan encapsulation. Antimicrobial activity assessments were performed for both synthetic compounds and their NLCs analogues. The nanoformulation of 4-NLC-Cs, 6d-NLC-Cs, and 8b-NLC-Cs manifested unique biological results, especially 8b-NLC-Cs, which revealed powerful effects over all the tested organisms including S. typhi. The increasing biological effect of the drugs in their nanoscale form is reflected in the increasing value of inhibition zone diameter and suppressing the value of MIC to reach record levels like 8b-NLC-Cs disclosed MIC = 0.48 and 0.24 µg/ml against S. aureus and C. albicans, respectively, by the mean 8b-NLC-Cs nanoformulation suppressed the MIC by 65 folds of its initial value before nano. In continuation, it was proven that the compounds 4, 6d and 8b were found to make noticeable changes on the DNA-Gyrase levels with reduced IC₅₀ values particularly 8b showed excellent inhibitory effect with IC₅₀ = 4.56 µM. TEM was used to pursue the morphological changes that occur in bacterial cells of P. aeruginosa. The weakness of the cell wall in most bacterial cells treated with nanomaterials, 8b-NLC-Cs, has reached the point of the cell wall rupture and the cell components spilling out of the cells causing necrotic cell death.