Hypophyllins A–D, Labdane-Type Diterpenoids with Vasorelaxant Activity from Hypoestes phyllostachya “Rosea”

Three rearranged labdane-type diterpenoids, hypophyllins A–C (1–3), and a caged labdane diterpenoid possessing a 8,9-dioxatricyclic­[4.2.1.13,7]­decane moiety, hypophyllin D (4), as well as two new biogenetically related diterpernoids, hypophyllins E (5) and F (6), were isolated from the aerial parts of Hypoestes phyllostachya “Rosea”. The absolute configurations of 1–4 were determined by X-ray diffraction analysis. The plausible biogenetic pathway for 1–4 was also proposed. Compounds 4 and 5 showed potent vasorelaxant activity on endothelium-intact thoracic aorta rings precontracted with KCl.