Secondary Metabolites from Nelumbo nucifera cv. Rosa-plena

Abstract

Nelumbo nucifera Gaertn. cv. Rosa-plena is a perennial aquatic crop grown and consumed throughout Asia. All parts of N. nucifera have been used for various medicinal purposes in oriental medicine. In particular, the leaves are known for diuretic and astringent properties and are used to treat fever, sweating, and strangury, and as a styptic [1]. To further understand the chemotaxonomy of the Nelumbo species [1, 2], Nelumbo nucifera Gaertn. cv. Rosa-plena was chosen for phytochemical investigation. There is only one paper describing the constituents of this plant [3]. Previously, we have isolated seven aporphines, two oxoaporphines, one dioxoaporphine, one dehydroaporphine, two steroids, and two chlorophylls from this plant [3]. As part of our continuing investigation of the phytochemical and bioactive compounds of Nelumbo plants, seven flavonoids, quercetin [4], quercetin 3-O-D-glucopyranoside [5], quercetin 3-O-D-galactopyranoside [6], quercetin 3-O-Dglucopyranosyl-(1 6)-D-glucopyranoside [7], isorhamnetin [8], isorhamnetin 3-O-D-glucopyranoside [8], and isorhamnetin 3-O-D-galactopyranoside [8] were obtained by systematic extraction and isolation from the leaves of Nelumbo nucifera Gaertn. cv. Rosa-plena. All of these compounds were isolated for the first time from this source. The leaves of Nelumbo nucifera Gaertn. cv. Rosa-plena were collected from Tainan County, Taiwan, November 2008. Plant material was identified by Prof. Fu-Yuan Lu (Department of Forestry and Natural Resources College of Agriculture, National Chiayi University). A voucher specimen (Nelumbo nucifera Gaertn. cv. Rosa-plena) was deposited in the Department of Medical Laboratory Science and Biotechnology, School of Medical and Health Sciences, Fooyin University, Kaohsiung, Taiwan. The air-dried leaves of Nelumbo nucifera Gaertn. cv. Rosa-plena (1.5 kg) were extracted with MeOH (5 L 5) at room temperature, and a MeOH extract (108.7 g) was obtained upon concentration under reduced pressure. The MeOH extract, suspended in H2O (1 L), was partitioned with CHCl3 (3 L 4) to give fractions soluble in CHCl3 (57.23 g) and H2O (43.62 g). The CHCl3-soluble fraction was chromatographed over silica gel (1700 g, 70–230 mesh) using n-hexane–EtOAc– MeOH mixtures as eluents to produce six fractions. Part of fraction 5 (5.34 g) was subjected to silica gel chromatography by eluting with CH2Cl2–MeOH (40:1) and enriched with MeOH to furnish two fractions (5-1–5-2). Fraction 5-2 (1.67 g) was eluted with n-hexane–EtOAc mixtures to obtain isorhamnetin (2 mg). Part of fraction 6 (4.21 g) was subjected to silica gel chromatography by eluting with EtOAc–MeOH (20:1) and enriched with MeOH to furnish five further fractions (6-1–6-5). Fraction 6-1 (1.46 g) was subjected to silica gel chromatography by eluting with n-hexane–EtOAc (1:9) and enriched gradually with EtOAc to produce quercetin (5 mg). Fraction 6-2 (0.76 g) was subjected to silica gel chromatography by eluting with EtOAc–MeOH (30:1) and enriched gradually with MeOH to produce isorhamnetin 3-O-D-glucopyranoside (5 mg) and isorhamnetin 3-O-D-galactopyranoside (7 mg). Fraction 6-3 (1.51 g) was further purified on a silica gel column using EtOAc–MeOH mixtures to obtain quercetin 3-O-D-glucopyranoside (5 mg) and quercetin 3-O-D-galactopyranoside (4 mg). Fraction 6-4 (0.76 g) was eluted with EtOAc–MeOH (9:1) and repeatedly subjected to silica gel CC to give quercetin 3-O-D-glucopyranosyl-(1 6)-D-glucopyranoside (6 mg).