Four New Diterpenoids from Ballota limbata

Six diterpenoids (1–6) belonging to the clerodane and tetracyclic diterpene types were isolated from the CHCl3 extract of Ballota limbata. The structures of the new compounds 1 and 4–6 (named ballatenolide A and limbatenolides A–C, resp.) were established by their spectral data, and their relative configuration was determined by 2D NMR. Compounds 2 and 3 were identified as known clerodanes. Compound 1 had a unique feature, i.e., an α,β‐unsaturated γ‐lactone moiety at C(4)/C(6), whereas limbatenolides A–C (4–6) belonged to the rare class of tetracyclic diterpenoids, which are known to occur only in the genus Ballota. All of the isolated compounds showed inhibitory potential in a cholinesterase‐inhibition assay.