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.