New tocopherol and acylphloroglucinol derivatives from Dryopteris crassirhizoma and their antimicrobial activities

Nine previously undescribed compounds including six tocopherol derivatives (1-6) and three acylphloroglucinol derivatives (7-9) were isolated and characterized from the plants of Dryopteris crassirhizoma. Their structures with absolute configurations were determined by extensive spectroscopic analyses, including IR, HRESIMS, NMR, and calculated electronic circular dichroism (ECD). Compounds 1 and 2 are the first tocopheroid derivatives possessing unique 2,5-dimethylcyclopent-4-ene-1,3-dione carbon skeleton, and compounds 3-6 were new 5a-norcyclopentenones having a spirofused bicyclic carbon skeleton. The biosynthetic pathway of compounds 1-6 was postulated. When combined with fluconazole (FLC), compound 3 showed significant antifungal activity against standard Candida albicans with MIC₅₀ value of 1.19 μg/mL (FLC: 3.41 μg/mL). Furthermore, the anti-plant pathogenic fungi and bacterial activities have been evaluated in vitro, compounds 5 and 8 showed anti-Verticillium dahlia and Sclerotinia sclerotiorum with MIC value of 50 μg/mL, respectively. Compounds 1 and 5 exhibited moderate antibacterial activities against Micrococcus luteus with MIC value of 50 μg/mL, respectively.