Helikaurolides A–D with a Diterpene-Sesquiterpene Skeleton from Supercritical Fluid Extracts of Helianthus annuus L. var. Arianna

Four novel compounds (1–4) with an unprecedented skeleton that combines a sesquiterpene lactone and a kaurane diterpene acid were isolated from Helianthus annuus L. var. Arianna extract, which was obtained under supercritical conditions. The structures of 1–4 were elucidated by NMR and MS analyses. The biosynthetic routes involve sesquiterpene lactones and kauranic acid, both of which were previously isolated from this species.