Synthesis of chalcones for analysis as anti-microbial agents

Chalcones are diphenyl α-β-unsaturated compounds that are present in a wide variety of plants. Naturally occurring chalcones as well as synthetic chalcones have demonstrated an assortment of biological activity, including anti-inflammatory, antiviral and antimicrobial activity. The need for new antimicrobially active agents is becoming more imperative as antimicrobial resistance continues to present a large threat. In this project, a series of chalcones were synthesised via a Claisen-Schmidt condensation reaction. The compounds were analysed using NMR spectroscopy and Gas-Chromatography Mass Spectrometry. An attempt was made to convert four of the chalcones to thiochalcones using Lawesson’s Reagent. The compounds were tested against E. coli, P. aeruginosa and S. epidermidis. None of the synthesised chalcones displayed any antimicrobial activity but the thiochalcones showed activity against all bacterial strains. Upon further analysis, the thiochalcones appeared to have decomposed in situ, with the major product being the oxa-thiophosphorane compound. This compound could have been the cause behind the activity seen in compound 11 against S. epidermidis and compound 14 against all bacterial strains studied. Compound 11 produced a zone of inhibition of 10mm against S. epidermidis whilst compound 14 produced zones of inhibition against S. epidermidis, P. aeruginosa and E. coli of 16mm, 10.3mm and 15.3mm respectively. The MICs and MBCs of the compounds were not greater than Ciprofloxacin, the antibiotic used in this project as the positive control, as shown by the results