Antimicrobial Acylphloroglucinol Meroterpenoids and Acylphloroglucinols from Dryopteris crassirhizoma

Ten novel meroterpenoids, dryoptins/11″-epi-dryoptins A~E (1: ~10: ) with an unprecedented skeleton consisting of dimeric or trimeric acylphloroglucinols and dehydrotheonelline, two undescribed acylphloroglucinol-nerolidol meroterpenoids (11: ~12: ), and ten known acylphloroglucinol derivatives (13: ~22: ), were isolated from D. crassirhizoma. The novel structures including absolute configurations were established by comprehensive spectroscopic analyses and quantum chemical electronic circular dichroism (ECD) calculations. A biosynthetic pathway of 1: ~10: was assumed. The trimeric acylphloroglucinol meroterpenoids 7: /8: showed significant antifungal activity against standard Candida albicans with a MIC₅₀ value of 1.61 µg/mL [fluconazole (FLC): 3.41 µg/mL], and when combined with FLC, the principal components 20: and 21: exhibited strong antifungal activities against FLC-resistant C. albicans with MIC₅₀ values of 8.39 and 7.16 µg/mL (FLC: > 100 µg/mL), respectively. Moreover, compounds 2, 5: /6, 18, 19: , and 21: exhibited inhibitory effects against several pathogenic fungi and bacteria, with MIC₅₀ values of 6.25 ~ 50 µg/mL.