Camaldulensals A-C, the First Meroterpenoids Possessing Two Spatially Separated Formyl Phloroglucinols Conjugated to a Terpene Core from the Leaves of Eucalyptus camaldulensis Dehnh.

Three new bis-formyl phloroglucinol-meroterpenoids ( 1 - 3 ), three new euglobal type formyl phloroglucinol-meroterpenoids ( 4 - 6 ), and one new dimeric formyl phloroglucinol ( 7 ) were isolated from the leaves of Eucalyptus camaldulensis . Camaldulensal A ( 1 ) is the first bis-isovaleryl-formyl-phloroglucinol-sesquiterpenoid. It features a novel 6/6/10/3/6/6 fused ring system and contains six stereogenic centers. Camaldulensals B ( 2 ) and C ( 3 ) are the first bis-isovaleryl-formyl-phloroglucinols, each conjugated to a monoterpene. Formyl phloroglucinol compounds (FPCs) containing two spatially separated formyl phloroglucinols conjugated to a terpene core such as 1 - 3 have not been reported previously. The structures of these compounds were elucidated by spectroscopic methods and computational analysis. Camaldulensals B ( 2 ) and C ( 3 ) exhibited significant antibacterial activity against methicillin-susceptible and methicillin-resistant Staphylococcus aureus . Structure activity relationships are discussed in relation to previously reported antibacterial activities of other molecules from the FPC structure class.