P-menthane-based meroterpenoids with neuroprotective effects from the bark of Magnolia officinalis var. biloba

Seven undescribed meroterpenoids with different substituted types of p-menthane, named maglignans D–J (1–7), were obtained from the bark of Magnolia officinalis var. biloba. Maglignan D (1) was an unusual meroterpenoid, featuring two p-menthane units with different substitution types were connected to two C6C3 fragments, respectively. Maglignans E–G (2–4) were characterized by a 6/5/6 or 6/6/6 tricyclic skeleton. The p-menthane in others connected to the magnolol through the ether or carbon-carbon single bonds directly. Spectroscopic techniques, NMR calculations with DP4+ analysis, and ECD calculations were used for the structure elucidation of these compounds. Moreover, maglignan E (2) showed significant neuroprotective effects on glutamic acid-induced cellular damage in cortical and hippocampal neurons. [Display omitted] •Seven undescribed p-menthane-based meroterpenoids were isolated from the bark of Magnolia officinalis var. biloba.•Maglignan D (1) was an unusual meroterpenoids possessing two different types of p-menthane.•The structures were determined by spectroscopic techniques and theoretical calculations.•Maglignan E (2) showed neuroprotective effect on glutamic acid-induced cellular damage in cortical and hippocampal neurons.