A new antibacterial clerodane diterpenoid from the resinous exudate of Haplopappus uncinatus

The antibacterial activity of Haplopappus uncinatus is attributed to a new clerodane diterpenoid, 18-acetoxy-cis-cleroda-3-en-15-oic acid (10βH, 16ξ 19β, 17β, 20α form) (1), isolated as a major component from the resinous exudates of its twigs and leaves, together with the inactive 3,5-dihydroxy-6,7,3′,4′-tetramethoxyflavone, n-alkanes and a few sesquiterpenoids.