New nor-ent-Halimane and nor-Clerodane Diterpenes from Callicarpa integerrima with Anti-MRSA Activity

Two new nor-ent-halimane diterpenes and three unreported nor-clerodane diterpenes, namely callicaintides A-E (1-5), including (1-2) with unique 5/6-ring system and (3-5) with 18, 17, and 16 carbons, along with four known compounds (6-9) were isolated from Callicarpa integerrima. Their structures were elucidated with the help of advanced spectroscopic methods such as NMR, HR-ESI-MS, UV, IR, ORD, DP4 + analysis and ECD supported by quantum chemical calculations. Compounds (1-9) were tested for their anti-MRSA potential. Compound 6 exhibited substantial anti-MRSA activity, with a minimum inhibitory concentration (MIC) of 16 µg/mL.