Flavonoids from the Aerial Parts of Astilbe rubra

Abstract

Astilbe rubra Hook. f. & Thomson (syn. A. chinensis), belonging to the family Saxifragaceae, is a perennial herb found in Korea, mainland China, Japan, and eastern Russia. As an herbal remedy, the rhizomes of A. rubra have long been used for the treatment of arthralgia, chronic bronchitis, headache, and stomachalgia [1]. Extracts of A. rubra rhizomes have been reported to exhibit a broad range of pharmacological activities such as anti-inflammatory, antitumor, and antiplatelet activities [2–9]. Previous phytochemical studies of the rhizomes of A. rubra led to the isolation of steroids, triterpenes, and other phenolic compounds [5–11]. Some of these chemical constituents have exhibited significant biological properties, such as immunomodulatory and anti-tumor [5–9]. However, to date, no study has been carried out to investigate the secondary metabolites from the aerial parts of A. rubra. In continuation of our studies on chemical constituents from the aerial parts of A. rubra, nine compounds were isolated and elucidated as quercetin 3-O-(5′′-Omalonyl)-α-L-arabinofuranoside (1), avicularoside (2), quercetin (3), quercitrin (4), rutin (5), (+)-catechin (6), (–)-catechin (7), (–)-epicatechin (8), and (+)-epicatechin (9). The structures of the isolated compounds were identified on the basis of their spectroscopic and MS data and comparison with literature data. To the best our knowledge, compounds 1, 2, 4, 8, and 9 were obtained from the genus Astilbe for the first time. General. Optical rotations were measured using a JASCO P-2000 polarimeter (Tokyo, Japan). NMR spectra were acquired on a Bruker Ascend III 700 spectrometer (Rheinstetten, Germany) using DMSO-d6 or CD3OD as solvent. HR-ESI-MS was performed on a Triple TOF 5600+ mass spectrometer (AB SCIX, USA). Open column chromatography was performed using ODS-A (12 nm S-7 μm, YMC GEL, Japan). Thin-layer chromatography (TLC) was performed using precoated silica gel 60 F254 (0.25 mm, Merck) plates, and spots were detected using a 10% aqueous vanillin-H2SO4 spray reagent. MPLC (Combi Flash RF, Teledyne ISCO, USA) separations were performed using a RediSep® Rf silica-gel column. Preparative HPLC was performed on a Shimadzu chromatograph (LC-8A pump and SPD-20A UV/VIS detector) using a YMC-Pack ODS A column (250 × 20 mm I.D.), with a mixed MeCN–H2O solvent system at a flow rate of 10 mL/min. All other chemicals and reagents were of analytical grade. Plant Material. The aerial parts of Astilbe rubra were collected in Yanggu-gun, Gangwon-do, Korea, in July 2016 and identified by one of the authors (Dr. S. S. Hong). A voucher specimen (G68) was deposited in the Herbarium of the Bio-Center, Gyeonggido Business & Science Accelerator (GBSA), Suwon, Korea.