Acylphloroglucinols-based meroterpenoid enantiomers with antiviral activities from Dryopteris crassirhizoma

The rhizome of Dryopteris crassirhizoma Nakai is an important traditional Chinese medicine listed in Chinese Pharmacopoeia for the treatment of parasitic infestation and viral diseases. In this work, ten enantiomeric pairs of new acylphloroglucinol meroterpenoids, ( +/- )-dryocrassoids A - J [( +/- )-1 - 101, along with six known acylphloroglucinols (11-16) were isolated from the rhizomes of D. crassirhizoma. Notably, these new enantiomers were the first examples of meroterpenoids constructed by acylphloroglucinols and nerolidol-type sesquiterpenes, while ( +/- )-1a/1b, ( +/- )-2a/2b, ( +/- )-4a/4b were obtained as the inseparable interconverting mixtures of keto and enol tautomers. The new structures and absolute configurations were identified by the interpretation of high resolution electron spray ionization mass spectrum (HRESIMS), nuclear magnetic resonance (NMR) spectroscopic data, and quantum chemical electronic circular dichroism (ECD) calculations. In addition, these compounds were assayed for the in vitro antiviral activities against herpes simplex virus type 1 (HSV-1), herpes simplex virus type 2 (HSV-2), and respiratory syncytial virus (RSV). The results indicated that most of the compounds showed anti-HSV-1 and anti-RSV effects to different extent under the concentration of 100 mu M. This study provided evidences for further study and utilization of D. crassirhizoma in medicinal products.