Toona sinensis, popularly known as Chinese toon or Chinese mahogany, is a perennial deciduous arbor belonging to the genus Toona in the Meliaceae family, which is widely distributed and cultivated in eastern and southeastern Asia. Its fresh young leaves and buds have been consumed as a very popular nutritious vegetable in China and confirmed to display a wide variety of biological activities. To investigate the chemical constituents and their potential health benefits from the fresh young leaves and buds of T. sinensis, a
phytochemical study on its fresh young leaves and buds was therefore undertaken. In our current investigation, 16
limonoids (1-16), including four new
limonoids, toonasinenoids A-D (1-4), and a new naturally occurring
limonoid, toonasinenoid E (5), were isolated and characterized from the fresh young leaves and buds of T. sinensis. The chemical structures and absolute configurations of
limonoids 1-5 were elucidated by comprehensive spectroscopic data analyses. All known
limonoids (6-16) were identified via comparing their experimental spectral data containing mass spectrometry data, 1H and 13C nuclear magnetic resonance data, and optical rotation values to the data reported in the literature. All known
limonoids (6-16) were isolated from T. sinensis for the first time. Furthermore, the
neuroprotective effects of all isolated
limonoids 1-16 against 6-hydroxydopamine-induced cell death in human
neuroblastoma SH-SY5Y cells were assessed in vitro.
Limonoids 1-16 exhibited notable neuroprotective activities, with EC50 values in the range from 0.27 ± 0.03 to 17.28 ± 0.16 μM. These results suggest that regular consumption of the fresh young leaves and buds of T. sinensis might prevent the occurrence and development of
Parkinson's disease (PD). Moreover, the isolation and characterization of these
limonoids that exhibit notable neuroprotective activities from the fresh young leaves and buds of T. sinensis could be very significant for researching and developing new
neuroprotective drugs used for the prevention and treatment of PD.