A New Monoterpene from Callicarpa nudiflora and Its Anti-MRSA Activity Evaluation
Methicillin-resistant Staphylococcus aureus (MRSA) accounts for over 30% of clinical S. aureus isolates globally, with bacteremia mortality reaching 27.3%—approximately threefold that of methicillin-sensitive infections. Existing antibiotics face cross-resistance across β-lactams, macrolides, quinolones, and sulfonamides. This study isolated five compounds from the ethyl acetate fraction of Callicarpa nudiflora dried leaf ethanol extract via silica gel, Sephadex LH-20, and ODS column chromatography. Structures were elucidated by IR, HR-ESI-MS, 1H-NMR, 13C-NMR, HSQC, HMBC, and COSY. Compound 1, a new monoterpene named callinuene A, is (Z)-2-methyl-6-methyleneocta-2,7-dien-1-yl (E)-3-(4-hydroxyphenyl)acrylate. Compounds 2–5 were identified as monasuslunin, (1S,5R,9R)-10,10-dimethyl-2,6-dimethylenebicyclo[7.2.0]undecan-5-ol, 7-epi-eudesm-4(15)-ene-1β,6β-diol, and sclareolide, respectively; compounds 3–5 are first isolates within this species. Minimum inhibitory concentrations (MICs) were determined by nutrient broth dilution. Compound 1 exhibited MICs of 8 μg/mL against S. aureus ATCC29213 and MRSA T144, while MICs against E. coli ATCC25922 and multidrug-resistant E. coli B2 exceeded 128 μg/mL. Compounds 2–5 showed no meaningful activity (MIC ≥ 64 μg/mL). Oxacillin MICs were <0.25, 16, 32, and 32 μg/mL for the same strains; meropenem MICs were <0.25, 2, <0.25, and <0.25 μg/mL. Compound 1 demonstrates selective anti-staphylococcal activity, warranting further development as a lead scaffold against MRSA.