Naturally occurring seco- and nor-polycyclic polyprenylated acylphloroglucinols: Distribution, structural diversity, and biological activity

Polycyclic polyprenylated acylphloroglucinols (PPAPs) are a subclass of specialized metabolites from the plant kingdom, especially from the family Guttiferae (Clusiaceae), displaying a high structural diversity and extensive biological activities. Seco- and nor-PPAPs, two special types of PPAPs possessing diverse skeletons, are widely studied. 200 compounds have been isolated from four genera, primarily Hypericum, up to June 2023. 115 compounds have been identified during the last 4 years with a dramatic increase. Seco- and nor-PPAPs can be correspondingly classified into six main subgroups based on the original scaffolds of PPAPs. Their biological studies revealed anticancer, anti-inflammatory, hepatoprotective, anti-Alzheimer’s, multidrug resistance reversal, antidepressant, neuroprotective, and immunosuppressive effects. This review summarizes the occurrence, structures, and bioactivities of natural seco- and nor-PPAPs to provide a comprehensive and in-depth insight into the further development of PPAPs.