A New Stereoisomeric Acetogenic Glycoside from the Flower Buds of Buddleja officinalis

Experimental Section

General Experimental Procedures. NMR spectra were recorded on a Bruker Avance III 700 MHz NMR spectrometer using CD3OD as solvent, and TMS was used as an internal standard. Chemical shifts are presented in ppm. Optical rotation was evaluated on JASCO P-2000. TLC analysis was performed on a precoated silica gel 60 F254 (0.24 mm, Merck). Open column chromatography was performed using a silica gel (Kieselgel 60, 70-230 mesh, Merck), RP18 (Part NO. 5982-5752, Agilent), MCI CHP20P gel (75-150 μM, Mitsubishi), and Sephadex LH-20 (GE Healthcare). Semi-preparative HPLC was performed on a Shimadzu Prominence UFLC with UV detector. HRTOFMS and ESI-MS spectra were obtained using a Waters UPLC-QTOF micro, and a LCQ Fleet (Thermo Scientific), respectively. GC-MS spectra were acquired using an Agilent 6890/5973i.

Plant Materials. The flower buds of B. officianlis were purchased from a commercial market (Samhong medicinal herb market, Seoul, South Korea) in 2013. One of the authors (S.-Y. Park) performed botanical identification, and a voucher specimen has been deposited at the College of Pharmacy, Dankook University, South Korea.

Extraction and Isolation. The air-dried flower buds of B. officinalis (3 kg) were pulverized and then extracted with 100% methanol (24 L, three times) at room temperature. The methanolic filtrate was evaporated in vacuo to generate the methanolic extract (301 g), and the extract was partitioned with n-hexane, methylene chloride, ethyl acetate, n-butanol, and water, progressively. Among them, some of n-butanol extract (10 g) was loaded onto MCI gel to yield 4 subfractions (BOD1-BOD4) with a step gradient composed of methanol and water (40, 60, 80, 100% methanol). The subfraction BOD1 was further chromatographed on Sephadex LH-20 to give two portions (BOD1A-BOD1B), and BOD1A was then re-chromatographed on silica gel to generate 9 subfractions (BOD1A1-BOD1A9) with a step gradient solvent system composed of chloroform, methanol, and water (8:3:1 to 3:3:1). The subfractions BOD1A1, BOD1A6, and BOD1A7 was further purified by semi-preparative RP-HPLC (Ace, C18, 21.2 × 250 mm, flow rate 7 mL/min) to furnish 1 (4.5 mg), 2 (3.0 mg), 3 (5.0 mg), 4 (4.0 mg), 5 (3.0 mg), 6 (3.5 mg), 7 (7.4 mg), 8 (12 mg), and 9 (2.0 mg).

Compound 1: White powder; −17.0 (c 0.15, MeOH); HRESIMS m/z 423.1860 (calcd for C18H31O11, 423.1866); 1H and 13C NMR in Table 1.

Acid Hydrolysis of Compound 1 and Determination of Sugar Component. Compound 1 (1.0 mg) was dissolved in 1.0 N HCl (1 mL), followed by heating at 120 ℃ in a water bath for 3 h. The solvent was evaporated in vacuo, and mixture was extracted with chloroform three times over. The hydrolyzate containing sugar portion in a vial dissolved in dry pyridine (100 μL), and then L-cystein methyl ester hydrochloride in dry pyridine (0.06 M, 100 μL) was added. After heating the mixture at 60 ℃ for 2 h, NaBH4 (2.0 mg) was added into vial, and the reaction mixture was stirred for 1 h at room temperature. Trimethylsilylimidazole solution (100 μL) was added and the reaction mixture was then heated at 60 ℃ for 2 h. The reaction mixture was evaporated in vacuo, and the dried product was then partitioned with nhexane and water. The n-hexane layer was analyzed by GCMS: the standard sugar generated peak at tR 18.95 for D-glucose.