Syntheses of (+)-costic acid and structurally related eudesmane sesquiterpenoids and their biological evaluations as acaricidal agents against .

Synthesis of (+)-costic acid, isolated from (L.) W. Greuter as a natural acaricidal sesquiterpenoid, was achieved in 16 steps from ()-carvone with an overall yield of 4.8%, involving the radical cyclization of selenoester to construct a decalone framework as the key step. Other structurally related natural products, (+)-costal, (+)-costol, and (+)-β-selinene, were also synthesized. The acaricidal activities of these four natural products and some synthetic intermediates were also evaluated against . Among them, (+)-costal especially exhibited potent acaricidal activity.