Abstract
Six γ-oxa-ε-lactones, 4-phenyl-3,4-dihydro-2H-1,5-benzodioxepin-2-one (5a) and its five derivatives with methoxy groups in different positions of A and B rings (5b–f), were synthesized from corresponding flavanones. Three of the obtained lactones (5b,c,f) have not been previously described in the literature. Structures of all synthesized compounds were confirmed by complete spectroscopic analysis with the assignments of signals on 1H and 13C-NMR spectra to the corresponding atoms. In most cases, lactones 5a–f exerted an inhibitory effect on the growth of selected pathogenic bacteria (Escherichia coli, Bacillus subtilis, and Staphylococcus aureus), filamentous fungi (Fusarium graminearum, Aspergillus niger, and Alternaria sp.), and yeast (Candida albicans). The broadest spectrum of activity was observed for unsubstituted lactone 5a, which was particularly active against filamentous fungi and yeast. Lactones with methoxy groups in the 3′ (5c) and 4′ (5d) position of B ring were more active towards bacteria whereas lactone substituted in the 7 position of the A ring (5e) exhibited higher antifungal activity. In most cases, the introduction of lactone function increased the activity of the compound compared to its flavonoid precursors, chalcones 3a–e, and flavanones 4a–f.
Highlights
Antibiotic resistance is a serious problem on a global scale, becoming the biggest challenge for global health, food security, and development today
The γ-oxa-ε-lactones were obtained in a three-step synthesis (Scheme 1)
It was shown that γ-oxa-ε-lactones 5a–f containing methoxy groups with different substitution patterns in the A and B ring inhibited the growth of selected bacteria, filamentous fungi, and yeast
Summary
Antibiotic resistance is a serious problem on a global scale, becoming the biggest challenge for global health, food security, and development today. Statistics show that 70% of two million bacterial infections in United States hospitals are caused by the strains resistant to at least one drug [1]. 50% of Staphylococcus aureus strains are resistant to methicillin. A growing number of diseases, such as tuberculosis, pneumonia, or salmonellosis, are becoming difficult to treat as antibiotics become less effective, which leads to longer hospital stays, increasing medical costs and mortality. Another serious problem are fungal diseases, which affect over a billion people. 3,000,000 cases of Molecules 2019, 24, 4151; doi:10.3390/molecules24224151 www.mdpi.com/journal/molecules
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