Clerodane diterpenoids with anti-inflammatory and synergistic antibacterial activities from Tinospora crispa

Ten new and four known clerodane diterpenoids were isolated from the vine and leaves of Tinospora crispa . The chemical structures and absolute stereochemical configurations of all the compounds were established by spectroscopic methods and single-crystal X-ray diffraction analysis combined with electronic circular dichroism (ECD) analysis. All these compounds possess a lactone ring system except compound 10 which has a rare bridge ring between C-2 and C-20. The lactone ring in these compounds is diversely constructed between C-1 and C-18, C-6 and C-18, C-6 and C-17, C-12 and C-17, or C-15 and C-16 in the clerodane diterpenoid skeleton. All the compounds were assayed for their anti-inflammatory activities on lipopolysaccharide (LPS)-activated microglial BV-2 cells. Compounds 5 and 7 exhibited nitric oxide (NO) release inhibitory activities with IC 50 values of 7.5 and 10.6 μM respectively. In particular, compound 7 exhibited better inhibitory activity and less cytotoxicity than the positive control minocycline. Moreover, compounds 9 and 14 were found to synergize with oxacillin (OXA) against methicillin-resistant Staphylococcus aureus (MRSA). This synergy was further confirmed by checkerboard and time-killing assays. Compounds 9 and 14 at the sub-MIC level significantly decreased the MIC of OXA from 32.0 to 1.0 μg mL −1 and 0.5 μg mL −1 , respectively.