Isolation and structural elucidation of β-tocopherol derivatives from Dryopteris crassirhizoma

Abstract

Dryopteris crassirhizoma Nakai (Dryopteridaceae), a thick-stemmed wood fern, is a semi-evergreen plant mainly distributed in North and Northeast China. It is of great value in horticultural and medicinal applications. In this study, five β-tocopherol derivatives, drycrasspherols A–E (1–5), with three kinds of skeletons, were isolated from the rhizomes of Dryopteris crassirhizoma. Compounds 1–2 represent the basic architecture featuring a phenol motif fused with the phytyl-type diterpene via a pyran ring, compounds 3–4 possess an unprecedented tetracyclic system in which a 4-methylcyclohexanone is incorporated into the base unit of 1. Interestingly, compound 5 is a novel dimer constructed from two monomers via a pyran ring to form a pentacyclic system. These structures were elucidated by comprehensive spectroscopic data and quantum chemical electronic circular dichroism (ECD) calculations. Importantly, compound 1 exhibited the comparable anti-respiratory syncytial virus activity with an IC50 value of 6.50 ± 1.25 μM to the positive control ribavirin. This study suggested the rhizomes of D. crassirhizoma as well as the β-tocopherol derivatives had new potential applications in pharmaceutical industry.