Optical rotations were measured on
a Rudolph Autopol IV polarimeter (Hackettstown). Ultraviolet (UV)
spectra were obtained using a double beam spectrophotometer (UH5300,
Hitachi High-Technologies, Tokyo, Japan). Infrared (IR) spectra were
obtained on a Shimadzu Fourier transform infrared spectrometer using
KBr pellets. High-resolution electrospray ionization mass spectra
(HRESIMS) were measured on an Exactive Orbitrap mass spectrometer
with a HESI ion source (ThermoFisher Scientific, Bremen, Germany).
Nuclear magnetic resonance (NMR) spectra were recorded with a Bruker
Avance III 600 MHz spectrometer (Bruker, Karlsruhe, Germany) with
tetramethylsilane (TMS) as an internal standard. Circular dichroism
(CD) spectra were measured with an Applied Photophysics spectrometer
(Chirascan, New Haven). Silica gel (200–300 mesh), Sephadex
LH-20 (GE Healthcare), and reverse phase (RP)-18 gel (20–45
μm, FuJi) were used for column chromatography. Preparative or
semipreparative high-performance liquid chromatography (HPLC) was
performed on an Agilent 1260 liquid chromatography system equipped
with Zorbax SB-C18 columns (5 μm, 9.4 mm × 150 mm or 21.2
mm × 150 mm). Chiral separation was carried out on a Chiralpak
AD-H chiral column (5 μm, 250 × 4.6 mm, Daicel).
a Rudolph Autopol IV polarimeter (Hackettstown). Ultraviolet (UV)
spectra were obtained using a double beam spectrophotometer (UH5300,
Hitachi High-Technologies, Tokyo, Japan). Infrared (IR) spectra were
obtained on a Shimadzu Fourier transform infrared spectrometer using
KBr pellets. High-resolution electrospray ionization mass spectra
(HRESIMS) were measured on an Exactive Orbitrap mass spectrometer
with a HESI ion source (ThermoFisher Scientific, Bremen, Germany).
Nuclear magnetic resonance (NMR) spectra were recorded with a Bruker
Avance III 600 MHz spectrometer (Bruker, Karlsruhe, Germany) with
tetramethylsilane (TMS) as an internal standard. Circular dichroism
(CD) spectra were measured with an Applied Photophysics spectrometer
(Chirascan, New Haven). Silica gel (200–300 mesh), Sephadex
LH-20 (GE Healthcare), and reverse phase (RP)-18 gel (20–45
μm, FuJi) were used for column chromatography. Preparative or
semipreparative high-performance liquid chromatography (HPLC) was
performed on an Agilent 1260 liquid chromatography system equipped
with Zorbax SB-C18 columns (5 μm, 9.4 mm × 150 mm or 21.2
mm × 150 mm). Chiral separation was carried out on a Chiralpak
AD-H chiral column (5 μm, 250 × 4.6 mm, Daicel).