Naturally occurring seco- and nor-polycyclic polyprenylated acylphloroglucinols: distribution, structural diversity, andbiological activity

Polycyclic polyprenylated acylphloroglucinols (PPAPs) represent a distinct subclass of specialized metabolites predominantly found in the plant kingdom, particularly within the Guttiferae (Clusiaceae) family. These compounds exhibit remarkable structural diversity and a wide range of biological activities. Seco- and nor-PPAPs, two unique variants of PPAPs with diverse skeletal structures, have been extensively investigated. As of June 2023, 200 compounds have been isolated from four genera, with Hypericum being the primary source. Notably, 115 of these compounds were identified in the past four years, indicating a significant increase in research activity. Seco- and nor-PPAPs can be categorized into six main subgroups based on the original PPAP scaffolds. Biological studies have revealed their potential in various therapeutic applications, including anti-cancer, anti-inflammatory, hepatoprotective, anti-Alzheimer's disease (anti-AD), multidrug resistance (MDR) reversal, anti-depressant, neuroprotective, and immunosuppressive effects. This review provides a comprehensive overview of the occurrence, structures, and bioactivities of natural seco- and nor-PPAPs, offering valuable insights for the further development of PPAPs.