Optical rotations were measured on a JASCO P-1020 polarimeter.
UV spectra were detected on an SHMADZU UV-2401PC spectrometer.
IR spectra were determined on a Bruker FT-IR Tensor-27 infrared
spectrophotometer with KBr disks. 1D and 2D NMR spectra
were recorded on Bruker AVANCE III-600, DRX-500, and AM-
400 MHz spectrometers using TMS as an internal standard. ECD
spectra were recorded with an Applied Photophysics Chirascan
spectrometer. Unless otherwise specified, chemical shifts (d) were
expressed in parts per million (ppm) with reference to the solvent
signals. ESIMS and HREIMS analysis were carried out on Waters
Xevo TQS, Bruker HTC/Esquire and Waters AutoSpec Premier P776
mass spectrometers, respectively. Column chromatography (CC)
was performed on silica gel (200e300 mesh, Qingdao Marine