Isosativene and sativene sesquiterpene derivatives from Dendrobium nobile

Two unusual isosativene sesquiterpene derivatives, named dendronobilol A (1) and dendronobilside A (2), and two unusual sativene sesquiterpene derivatives, named dendronobilsides B (3) and C (4), had been isolated from the stems of Dendrobium nobile. The structures of all the compounds were established using spectroscopic methods and by comparison with literature data, and their absolute configurations were confirmed via single-crystal X-ray diffraction data and electronic circular dichroism (ECD) calculations. Dendronobilol A (1) and dendronobilside A (2) possessed a unique tricyclo[4.3.0.1^{2, 8}]decan ring system, while dendronobilsides B (3) and C (4) presented a unique tricyclo[4.4.0.0^{2, 8}]decan core carbon skeleton. The above two types of sesquiterpene derivatives had been isolated and purified from plants for the first time. Compounds 1 and 2 exhibited significant effects on glucose consumption with doses of 20 and 40 μmol/L in insulin-resistant HepG2 cells, and thus improve insulin resistance.