Gf254

Tetrandrine (purity ≥98%) was purchased from Nanjing Jingzhu Biotechnology Co., Ltd. (Nanjing, China). All reagents and solvents were sourced from commercial companies, Adamas (Shanghai, China) and Energy & Chemical (Shanghai, China), and used without additional purification unless otherwise stated. Anhydrous dichloromethane (DCM) was dried over calcium hydride prior to distillation under an argon atmosphere. Column chromatograph was filled with 300–400 mesh silica gel (Qingdao Marine Chemical Co., Ltd, Qingdao, China) and eluted using a mixture of dichloromethane, methanol, and diethylamine. Thin layer chromatography (TLC; 0.25 mm; GF254; Qingdao Marine Chemical Co., Ltd, Qingdao, China) was used to monitor the reactions, and UV light (254 nm) or 10% phosphomolybdic acid/ethanol was used for visualization. Bruker AVANCE III 600 MHz spectrometers (Bruker Biospin, Billerica, United States) were used to collect the nuclear magnetic resonance (NMR) spectra (¹H, ¹³C, and ¹⁹F). High-resolution mass spectra were obtained using Thermo Scientific Q Exactive Focus (Thermo Scientific Q Exactive Focus). Melting points were determined using a WRX-4 micro melting point instrument (Tansoole, Shanghai, China).

1D and 2D NMR spectra were recorded on Bruker DRX-500 spectrometers using TMS as an internal standard. Chemical shifts (δ) were expressed in ppm with reference to the solvent signals. Optical rotations were measured on a JASCO P-1020 polarimeter. IR spectra were determined on a Bruker FT-IR Tensor-27 infrared spectrophotometer with KBr disks. UV spectra were detected on a SHMADZU UV-2401PC spectrometer. MS and HRMS analysis were carried out on Waters Xevo TQS and Waters AutoSpec Premier P776 mass spectrometers, respectively. Semipreparative HPLC was performed on a Waters 600 with a COSMOSIL C18 (10 × 250 mm) column. Silica gel (100–200 and 200–300 mesh, Qingdao Marine Chemical Co., Ltd., People’s Republic of China), and MCI gel (75–150 μm, Mitsubishi Chemical Corporation, Tokyo, Japan) were used for column chromatography. Fractions were monitored by thin-layer chromatography (TLC) (GF254, Qingdao Marine Chemical Co., Ltd.), and spots were visualized by 10% sulfuric acid ethanol solution.

The UV spectrum was recorded on a Shimadzu UV-2600 PC spectrometer (Shimadzu, Beijing, China). The IR spectrum was obtained using an IR Affinity-1 spectrometer (Shimadzu). Optical rotations were determined with an Anton Paar MPC 500 polarimeter. HRESIMS spectra were recorded with a Bruker maXis Q-TOF mass spectrometer. The NMR spectra were recorded on a Bruker Avance-500 spectrometer (Bruker BioSpin International AG, Fällanden, Switzerland), and chemical shifts were recorded as δ-values. Semipreparative high-performance liquid chromatography (HPLC) was performed on the Hitachi Primaide with a DAD detector, using an ODS column (YMC-pack ODS-A, 10 × 250 mm, 5 μm). Thin-layer chromatography analysis (TLC) and column chromatography (CC) were carried out on plates precoated with silica gel GF254 (10–40 μm) and over silica gel (200–300 mesh) (Qingdao Marine Chemical Factory, Qingdao, China) and Sephadex LH-20 (Amersham Biosciences, Uppsala, Sweden), respectively. Spots were detected on TLC (Qingdao Marine Chemical Factory) under 254 nm UV light. All solvents employed were of analytical grade (Tianjin Fuyu Chemical and Industry Factory, Tianjin, China).

UV spectra were measured on a Shimadzu UV-2600 PC spectrophotometer (Shimadzu, Kyoto, Japan). Optical rotations were recorded on a PerkinElmer MPC 500 (Waltham, MA, USA) polarimeter. For ECD spectra, Chirascan circular dichroism spectrometer (Applied Photophysics, Leatherhead Surrey, UK) was used. NMR spectra were acquired by a Bruker Avance spectrometer (Bruker, Billerica, MA, USA) at 700 MHz for ¹H and 175 MHz for ¹³C. HRESIMS spectra were recorded on a Bruker miXis TOF-QII mass spectrometer (Bruker, Billerica, MA, USA). X-ray diffraction intensity data were measured on an Agilent Xcalibur Nova single-crystal diffractometer (Santa Clara, CA, USA) using Cu Kα radiation. TLC and column chromatography were performed on plates precoated with silica gel GF₂₅₄ (10–40 μm) and over silica gel (200–300 mesh) (Qingdao Marine Chemical Factory, Qingdao, China), respectively. Spots were detected on TLC (Qingdao Marine Chemical Factory, Qingdao, China) under 254 nm UV light. Semi-preparative HPLC was performed using an ODS column (YMC-pack ODS-A, YMC Co., Ltd., Kyoto, Japan, 10 mm × 250 mm, 5 μm).

One-dimensional and two-dimensional NMR spectra of fladins B and D were recorded on a JEOL JNM-ECS400 (400 MHz) spectrometer (JEOL, Tokyo, Japan), and those of fladin C were recorded on a JEOL ECX 500M (500 MHz) spectrometer (JEOL, Tokyo, Japan). Chemical shifts (δ) were expressed in ppm, and coupling constants (J) were reported in Hz. All NMR experiments were obtained by using standard pulse sequences supplied by the vendor. Optical rotation was measured with a Perkin-Elmer model 241 polarimeter (Perkin Elmer, Waltham, MA, USA). IR spectra were recorded on a Bruker VECTOR22 spectrophotometer (Bruker, Rheinstetten, Germany) with KBr pellets. High-resolution electrospray ionization mass spectroscopy (HR-ESI-MS) was recorded on a VG Autospec-3000 spectrometer (VG, Manchester, England). Column chromatography was performed with silica gel (200–300 mesh; Qingdao Marine Chemical, Inc., Qingdao, China). Thin-layer chromatography (TLC) was performed on glass plates coated with silica gel GF₂₅₄ (Qingdao Marine Chemical Inc.). All solvents, including petroleum ether (60–90 °C), were distilled prior to use. X-ray crystallographic data were obtained on a Bruker APEX-II CCD instrument (Bruker, Rheinstetten, Germany) using Cu Kα radiation.

IR spectra were measured on a Bruker FT-IR Tensor-27 infrared spectrophotometer with KBr disks. Optical rotations were recorded on a JASCO P-1020 polarimeter. UV spectra were obtained with a Shimadzu UV-2401PC spectrometer. 1D and 2D NMR spectra were performed on a Bruker DRX-600 spectrometer using TMS as an internal standard. The chemical shifts (δ) were expressed in ppm with reference to the solvent signals. HREIMS and HRESIMS analysis were obtained from Waters Xevo TQS and Agilent G6230 TOF mass spectrometers, respectively. Single-crystal X-ray diffraction data were exhibited on a Bruker D8 QUEST diffractometer. Semi-preparative HPLC was performed on a Waters 1525 HPLC with a ZORBAX SB-C₁₈ (9.4 × 250 mm) column. Silica gel (100–200 and 200–300 mesh, Qingdao Marine Chemical Co., Ltd., People’s Republic of China), and MCI gel (75–150 μm, Mitsubishi Chemical Corporation, Tokyo, Japan) were used for column chromatography. Fractions were monitored by TLC (GF 254, Qingdao Marine Chemical Co., Ltd.), and spots were visualized by heating Silica gel plates immersed in 10% H₂SO₄ in ethanol. Methanol (HPLC grade) and acetonitrile (HPLC grade) was purchased from CINC High Purity Solvents Co., Ltd (Shanghai, China). 4-Nitrophenyl-α-d-glucopyranoside (PNPG), α-glucosidase, PTP1B assay kit, quercetin, and acarbose were purchased from Sigma Chemical (Merck KGaA, Darmstadt, Germany).