Psiguajadials A-K: Unusual Psidium Meroterpenoids as Phosphodiesterase-4 Inhibitors from the Leaves of Psidium guajava

Bioassay-guided fractionation of the ethanolic extract of the leaves of Psidium guajava led to the isolation of 11 new Psidium meroterpenoids, psiguajadials A-K (1-11), along with 17 known ones (12-28). Their structures and absolute configurations were elucidated by spectroscopic methods and comparison of experimental and calculated ECD. Compounds 1 and 2 represent two unprecedented skeletons of 3,5-diformyl-benzyl phloroglucinol-coupled sesquiterpenoid, while 3 is the first example of Psidium meroterpenoids coupling via an oxepane ring. Putative biosynthetic pathways towards 1 and 2 are proposed. Compounds 1-13 and 16-26 exhibited moderate inhibitory activities against phosphodiesterase-4 (PDE4), a drug target for asthma and chronic obstructive pulmonary disease, with IC50 values in the range of 1.34-7.26 mu M.