Grayanane Diterpenoids from the Fruits of Pieris formosa

Many species of the family Ericaceae, such as the plants belonging to the genera Pieris, Rhododendron, Lyonia, Kalmia, and Leucothoe, are usually rich in grayanane-type diterpenoids with a 5/7/6/5 ring system, which is responsible for the toxicity of these species [1, 2]. Recently, a series of novel highly acylated diterpenoids with specific 3,4-secograyanane skeleton have been reported from Rhododendron molle and Pieris formosa by Jian-Gong Shi and coworkers, Sheng-HongLi and coworkers and our group [3 – 6]. In searching for new natural compounds with more new skeletons, we had investigated the leaves and stems of Lyonia ovalifolia, and obtained a novel polyesterified diterpenoid with a unique 9,10-seco grayanane skeleton, named lyonin A [7]. This finding made us interested in the biosynthetic pathway of seco-grayanane diterpenoids, and we further investigated the chemical constituents, especially diterpenoids, of the fruits of