Guajamers A—I, Rearranged Polycyclic Phloroglucinol Meroterpenoids from <i>Psidium guajava</i> Leaves and Their Antibacterial Activity

Abstract

Main observation and conclusion Eight new polycyclic phloroglucinol meroterpenoids guajamers A—H ( 1 — 8 ), a methylated benzoylphloroglucinol meroterpenoid guajamer I ( 9 ) representing a new skeleton, and two known analogues ( 10 and 11 ) were isolated from the leaves of Psidium guajava . The structures of new molecules were elucidated by detailed analysis of spectroscopic data, and those of 1 , 2 , 8 , and 9 were unambiguously confirmed by single‐crystal X‐ray diffraction study. Structurally, compounds 1 — 8 were sesquiterpene and monoterpene‐ based meroterpenoids with rearranged skeletons, while compound 9 was the first case of 3‐alkyl‐5‐formyl‐benzoylphloroglucinol‐ coupled sesquiterpene containing an unusual C‐1‐spiro‐fused 6/6/9/4 polycyclic skeleton. In addition, all the isolated compounds were evaluated for their antibacterial activity against three bacterial strains, and most of them (compounds 2 — 7 , 10 , and 11 ) showed antibacterial activity against Staphylococcus aureus and Staphylococcus epidermidis with MIC values of 8—32 μmol/L. These findings suggested that meroterpenoids isolated from Psidium guajava can be considered as potential antibacterial leading compounds for pharmaceutical industry.