Clerodane furanoditerpenoids from the stems of Tinospora sinensis

One new clerodane-type furanoditerpenoid tinosinoid A ( 1 ) and nine new nor-clerodane analogs tinosinoids B–J ( 2 − 10 ) have been isolated from the stems of Tinospora sinensis . The structures of the new compounds with absolute configurations have been elucidated by spectroscopic means, including MS, NMR and ECD techniques, as well as chemical correlation. Compound 1 is a rare sulfur-containing clerodane diterpenoid incorporating a 2-mercaptoethanol unit via a thioether bond, while compounds 4 / 5 and 9 represent two pairs of unusual equilibrium regioisomers through an interesting intramolecular transesterification. Our bioassays established that 1 and 8 displayed moderate antiproliferative effects against two human tumor cell lines, and 9 and 10 showed significant α -glucosidase inhibitory activities. A kinetics study revealed that compound 10 was a noncompetitive α -glucosidase inhibitor, and its possible binding mode to the enzyme was further probed by molecular docking experiments.