Two new ent-kaurane diterpenoids from Wedelia trilobata (L.) Hitchc

Two new ent-kaurane diterpenoids, 16α,17,19-trihydroxy-18-nor-ent-kauran-4β-ol (1) and 17-chloro-16β-hydroxy-ent-kauran-19-oic acid (2) were isolated from the whole plant of Wedelia trilobata, together with five known ones (3–7). Their structures were elucidated on the basis of extensive spectroscopic analyses, including NMR and MS techniques. Compound 1 is an 18-nor-ent-kaurane type diterpenoid which is rare in nature, and compound 2 is the first chlorine-containing ent-kaurane diterpenoid so far isolated from plant family of Asteraceae. Known compound 4 was obtained from the genus Wedelia for the first time. Compounds 4–6 selectively showed in vitro antibacterial activity against three assayed Gram-(+) bacteria, especially 5 and 6 which showed the antibacterial activity against Staphylococcus aureus with MIC values (3.125–6.25 μg/mL) comparable to reference compound Kanamycin (MIC 3.125 μg/mL). Compounds 4–6 further displayed significant antibacterial activity against Gram-(?) bacterium Shigella dysenteriae with MIC value 3.125–12.5 μg/mL.