Rearranged clerodanes from the stems of Tinospora baenzigeri

The genus Tinospora (Family Menispermacae) comprises approximately 30 species, widely distributed throughout Asia, Africa, Australia, and the Pacific. T. crispa and T. baenzigeri are well known in Thailand and used as herbal remedy, particularly T. crispa. By contrast, T. baenzigeri has not been extensively studied. Previous investigations of the plant resulted in the isolation and characterization of a number of rearranged clerodane furanoditerpenoids and their glucosides. Their claimed antimalarial activity against Plasmodium falciparum could not be confirmed, and other biological activities have not been examined yet. In order to discover natural compounds with diverse structure and biological activity from Thai medicinal plants and to extend the study on T. baenzigeri, the plant specimens were examined for their phytochemical constituents. Four new rearranged clerodane-type diterpenoids (1‒4), a new glucoside (5), and six known compounds (6‒11) were obtained from the EtOAc crude extract of T. baenzigeri stem. The structures of the new compounds were elucidated by interpreting their spectroscopic data, particularly 1D and 2D NMR. Single-crystal X-ray diffraction analysis was subsequently performed to confirm the structures and relative configurations of compounds 1‒4. These compounds are rare examples of rearranged clerodanes, particularly compound 4 possessing a fully oxidized tetrahydrofuranyl ring. The isolated compounds were assayed for their protective effect against N-acetyl-p-aminophenol (APAP)-induced HepG2 cell damage. Compounds 8, 9, and 11 showed hepatoprotective activity at 10 M with 17.0, 19.2 and 39.0% inhibition, respectively, whereas rearranged clerodanes (1-3 and 5) were weakly active.

Fig. 1

• References

• 1 Tuntiwachwuttikul P, Boonrasri N, Bremner JB, Taylor WC. Rearranged clerodane diterpenes from Tinospora baenzigeri . Phytochemistry 1999; 52: 1335-1340
• 2 Tuntiwachwuttikul P, Taylor WC. New rearranged clerodane diterpenes from Tinospora baenzigeri. Chem Pharm Bull 2001; 49: 854-857