High-value flavonoids with potential anti-inflammatory benefits from Platanus × acerifolia Willd leaves: Turning waste into treasure

The London plane tree (Platanus × acerifolia Willd, PaW) is a deciduous urban ornamental tree extensively found in major cities in Southern China. It produces a significant volume of waste leaves, which hold the potential to serve as an abundant and valuable alternative source of bioactive flavonoids and other bioproducts. The seasonal variations of predominant flavonoids in leaves collected from the same individual PaW trees growing in Shanghai (China) during the life cycle [spring (May 2017), autumn (October 2017), and winter (January 2018)] were estimated according to their HPLC-PDA profiles, which revealed higher content in the samples of May (green pruning waste leaves) and January (brown fallen leaves). A total of 29 flavonoids (1–29) were subsequently isolated from an EtOAc fraction of the 90 % MeOH extract from the May leaves. Their structures were determined by spectroscopic methods, especially 1D- and 2D-NMR techniques. Platanosides 1–3 have been previously described as a unique chemical class of flavonoid glycosides, while isoprenylated flavonols 4 and 5 are reported for the first time in nature. The in-silico molecular docking and in vitro nitric oxide inhibitory studies provided compelling computational and experimental evidence supporting the anti-inflammatory potential of the isolated platanosides. These results demonstrate the significant potential of the waste PaW leaves as a sustainable raw material for large-scale production of flavonoids (especially platanosides), which are highly valued compounds with growing pharmaceutical interest.