Four new ent-kaurene diterpene glucosides from Mikania micrantha

Phytochemical study on the aerial parts of Mikania micrantha led to the isolation of four new ent-kaurene diterpene glucosides, β-D-glucopyranosyl-15α-(3-hydroxy-3-methylbutanoyloxy)-9β-hydroxy-ent-16-kauren-19-oate (1), β-D-glucopyranosyl-15α-(3-methylbutanoyloxy)-9β-hydroxy-ent-16-kauren-19-oate (2), β-D-glucopyranosyl-15α-(2-methylbutanoyloxy)-9β-hydroxy-ent-16-kauren-19-oate (3), β-D-glucopyranosyl-15α-(3-methyl-2-butenoyloxy)-9β-hydroxy-ent-16-kauren-19-oate (4), along with a known one, β-D-glucopyranosyl-15α-(3-hydroxy-3-methylbutanoyloxy)-ent-16-kauren-19-oate (5). Their structures were elucidated on the basis of extensive spectroscopic analysis. Compounds 1–4 are a group of C-9 hydroxylated ent-kaurene diterpene glucosides which is relatively rare in nature. These compounds selectively showed in vitro antibacterial activity against four assayed Gram-(+) and three Gram-(-) bacteria. In addition, the in vitro growth inhibitory activity of these compounds against human cancer cell lines Hela, A549, HepG-2 and MCF-7, were also tested.