Antimicrobial Acylphloroglucinol Meroterpenoids and Acylphloroglucinols from Dryopteris crassirhizoma.

ABSTRACT

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.