Secoiridoids and lignans from the leaves of Diospyros kaki Thunb. with antioxidant and neuroprotective activities

• First report secoiridoids obtained from persimmon leaves.
• Antioxidant mechanism of secoiridoids and lignans from persimmon leaves was elucidated by three different methods.
• Neuroprotective evaluation of all isolates using human SH-SY5Y cells.
• The direct quantitation of twelve identified compounds was established from persimmon leaves and fruits by HPLC-QQQ-MS/MS.

The leaves of persimmon (LP) have been used for centuries in China, Korea and Japan as a delicate, pleasant beverage and an effective herbal remedy. Phytochemical investigations of LP have resulted in the discovery of two new secoiridoid glucosides, named persimmonoid A and B (1–2), together with ten known ones. Antioxidant and neuroprotective assays of all compounds were carried out, and compounds (+)-medioresinol (5), (+)-pinoresinol (7), (+)-pinoresinol-β-D-glucoside (10) and (−)-(7′S,8S,8′R)-4,4′-dihydroxy-3,3′,5,5′-tetramethoxy-7′,9-epoxylignan-9′-ol-7-one (12) were found to exhibit significant activity in the ABTS radical scavenging assay, while compounds (+)-syringaresinol (6), (+)-pinoresinol (7) and (+)-isolariciresinol (11) displayed stronger activity than the positive control in the FRAP assay. In addition, some of these compounds showed statistically significant neuroprotective activities. The HPLC-QQQ-MS/MS method was successfully applied to quantify twelve compounds from LP and fruits of persimmon (FP). The bioactive studies supported LP potential for development as a new antioxidant and neuroprotective functional food.

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