Bioactive neolignans from Piper rivinoides Kunth (Piperaceae)

The genus Piper is known for the biosynthesis of a wide variety of special metabolites. Piper rivinoides Kunth (C.DC.) is a species of Piperaceae that has never been investigated on the chemical point of view. In this study bioguided fractionation of the hexane leaf fraction from P. rivinoides was performed to investigate the potential antimicrobial activity of sub-fractions and the pure isolated compounds. The crude extract, the hexane fraction and pure isolated compounds were evaluated against two strains of Candida albicans as well as two species of the genus Leishmania, L. amazonensis and L. chagasi. The hydroalcoholic extract (19 g) was suspended in water-methanol (7:3) and successively partitioned with hexane, dichloromethane, ethyl acetate and butanol. From the bioactive hexane fraction (8.0 g) it was purified six benzofuranneolignans characterized as eupomatenoid-3 (5 mg), 7'-(4'-methoxyphenyl)-3'-methyl-1-(E)-propenylbenzofuran (7.5 mg), eupomatenoid-5 (72 mg), (7'R,8'R)-7',8'-dihydro-7'-(4'-hidroxy-3'-methoxyphenyl)-8'-methyl-1-(E)-propenylbenzofuran (31.1 mg), eupomatenoid-6 (32 mg) and (+)-conocarpan (1.7 g). Among all tested isolated neolignans conocarpan was shown as the most bioactive one with IC₅₀ of (34.6 ± 4.2) and (73.7 ± 8.6)µM for C. albicans PRI and C. albicans ATCC 10231, and IC₅₀ of (40.6 ± 0.2) and (92.1 ± 0.1)µM for L. amazonensis and L. chagasi, respectively. The cytotoxicity by 50% cytotoxic concentration (CC₅₀) of the compounds were assayed on lines of fibroblasts (L929), macrophages (RAW) and epithelial (VERO) cells. The conocarpan neolignan was found as the safer compound tested with Selective Index (SI) of 4.2, while the eupomatenoid-6 was the most toxic compounds with SI of 0.93 on fibroblasts (L929) cells. Our findings showed that P. rivinoides is a remarkable natural source of a variety of neolignans with biological properties.

Keywords: Piper, Piper rivinoides, neolignans, leishmania, candida, natural products