Two New Flavonol Glycosides from Sarcopyramis bodinieri var. delicate

Detailed chemical investigation of the herb Sarcopyramis bodinieri var. delicate resulted in the isolation of two new flavonol glycosides, namely, isorhamnetin-3-O-(6′′-O-E-feruloyl)-β-D-glucopyranoside (1) and isorhamnetin-3-O-(6′′-O-E-feruloyl)-β-D-galactopyranoside (2). In addition, four known compounds, quercetin-3-O-(6′′-acetyl)-β-D-glucopyranoside (3), isorhamnetin-3-O-(6′′-acetyl)-β-D-glucopyranoside (4), quercetin-3-O-(6′′-O-E-p-coumaroyl)-β-D-glucopyranoside (5), and isorhamnetin-3-O-(6′′-O-E-p-coumaroyl)-β-D-glucopyranoside (6) were obtained. The structures of the new isolates were determined by extensive spectroscopic analysis.


Introduction
Members of the Melastomataceae family are widespread in many regions of the world and particularly in tropical and subtropical regions, mainly in South America and South China. Many species of this family are known by their different use in folk medicine as antioxidant [1],
As a rare species, Sarcopyramis bodinieri var. delicate was widely used as hepatoprotective drug in Fujian province, China. The water extract of this dried herb could reduce aminotransferase and cure choloplania and hepatoma. Detailed fractionation led to the isolation of two new flavonol glycosides, (2), along with four known compounds. The structures of the new isolates were determined by extensive spectroscopic analysis.

Results and Discussion
The known compounds 3-6 corresponded to quercetin- [12], and isorhamnetin-3-O-(6′′-O-E-p-coumaroyl)-β-Dglucopyranoside (6) [13,14]. The structures of these known flavonol glycosides were identified on the basis of extensive spectroscopic data analysis and by comparison of their spectral data with those reported in the literature.  , combined with the 13 C-NMR and DEPT spectra. The IR spectrum of compound 1 revealed the aliphatic and aromatic hydroxyl signals at 3200-3550 cm -1 . A conjugated carbonyl group (1656 cm -1 ) and an additional α,β-unsaturated carbonyl ester group (1724 cm -1 ) were observed in the same region. The absorptions at 3310 and 1057 cm -1 indicated the presence of a glycosidic moiety [15].
The 1 H-NMR spectrum confirmed many of the above features and revealed a set of isorhamnetin signals, a feruloyl group and a glucopyranose moiety. The presence of isorhamnetin was suggested by the following signals: two doublets at δ H 6.14 (d, J = 1. 2) suggested glucopyranose as the sugar moiety. A downfield shift of C-6′′ was from δ C 61.8 to 64.2, and an upfield shift of C-5′′ was from δ C 76.8 to 76.0, which were in accordance with the acylation of C-6′′ of the glucose moiety [17]. Moreover, the downfield shift of H 2 -6′′ to 4.11 (dd, J = 6.8, 11.5 Hz) and 4.19 (dd, J = 2.1, 11.5 Hz) further confirmed the presence of a C-6′′ feruloyl in compound 1 [18]. Consequently, the structure of compound 1 was established as isorhamnetin-3-O-(6′′-O-E-feruloyl)-β-D-glucopyranoside.
Compound 2, a yellow powder, shared the same molecular formula C 32 H 30 O 15 with 1, according to the [M+Na] + peak at m/z 677 and [M+K] + peak at m/z 693. Moreover, its NMR data is very similar to those of 1. Detailed comparison of the 13 C-NMR and HMQC spectra between the two compounds indicated that the major difference was in the glycoside moiety. The carbon signals at δ C 103.4 (C-1′′), 71.2 (C-2′′), 74.6 (C-3′′), 69.5 (C-4′′), 74.3 (C-5′′), and 62.9 (C-6′′) revealed a galactopyranoside moiety [16]. The structure of compound 2 was therefore assigned as isorhamnetin-3-O-(6′′-O-Eferuloyl)-β-D-galactopyranoside. The UV spectra of the different flavonol glycosides showed an interesting phenomenon (see Table  2) according to our experiments. The substituted fraction on the glycosidic moiety could be characterized by the absorption over 300 nm. For example, the absorption maxima at 315 nm means a p-substituted aromatic ring in R 2 , while the absorption at 330-336 nm indicates a tri-substituted aromatic ring in the same position.

General
The IR spectra were determined on a Thermo Nicolet Nexus 470 FT-IR spectrometer. Optical rotations were measured with a Perkin-Elmer 243 B polarimeter using a 1 dm microcell. The 1 H-NMR and 13 C-NMR spectra were recorded on a Bruker Avance-600 FT NMR spectrometer. ESI-MS were recorded on a PE Q-STAR ESI-TOF-MS/MS spectrometer. Column chromatography was carried with silica gel (200-300 mesh), and HF 254 silica gel for TLC was obtained from Qingdao Marine Chemistry Co. Ltd., Qingdao, People′s Republic of China. ODS and Sephadex LH-20 (18-110 μm) were obtained from Pharmacia Co.