Anti-methicillin-resistant Staphylococcus aureus (Anti-MRSA) flavonoids from Iraqi Citrus sinensis (L.) Osbeck

Citrus sinensis (L.) Osbeck (Rutaceae) was investigated as a potential source of anti-MRSA compounds. A bioassay-guided isolation approach afforded fourteen compounds from the peel and leaf extracts of C. sinensis , including a new flavanone glycoside, sinensidin ( 10 ). Structural elucidation was based on spectroscopic analyses, including 1D and 2D NMR and HRMS data. Among the isolated compounds, 3-methoxynobiletin ( 4 ), sinensetin ( 7 ), and rutin 3′-methyl ether ( 12 ) exhibited moderate anti-MRSA activity (MIC = 128–256 µg/mL). The crude extract showed higher apparent activity than the individual compounds, suggesting possible contributions from additional constituents and/or synergistic interactions. This study expands the phytochemical profile of C. sinensis and suggests that its polymethoxylated flavonoids and flavonoid glycosides may contribute to anti-MRSA activity.